One document matched: draft-lior-radius-prepaid-extensions-07.txt
Differences from draft-lior-radius-prepaid-extensions-06.txt
Network Working Group A. Lior
INTERNET-DRAFT Bridgewater Systems
Category: Informational P. Yegani
draft-lior-radius-prepaid-extensions-07.txt Cisco
Expires: 20 July, 2005 K. Chowdhury
Starent Networks
Y. Li
Bridgewater Systems
C. Guenther
Siemens
February 20, 2005
PrePaid Extensions to Remote Authentication Dial-In User Service
(RADIUS)
Status of this Memo
By submitting this Internet-Draft, I certify that any applicable
patent or other IPR claims of which I am aware have been disclosed,
and any of which I become aware will be disclosed, in accordance
with RFC 3668.
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This Internet-Draft will expire on July 20, 2005
Copyright Notice
Copyright (C) The Internet Society (2005). All Rights Reserved.
Lior, et al. [Page 1]
RADIUS Extensions for PrePaid July 2005
Abstract
This draft presents an extension to the Remote Authentication Dial-
In User Service (RADIUS) protocol to support charging for prepaid
services. The charging models supported are namely: volume-based
charging, duration-based charging and one-time-based charging.
Table of Contents
1. Introduction...................................................4
1.1 Terminology................................................6
1.2 Requirements language......................................6
2. Overview.......................................................6
2.1 PrePaid Charging Model.....................................7
2.2 Architectural Model........................................7
2.3 Why not existing RADIUS attributes?.......................13
3. Use-cases.....................................................15
3.1 Simple pre-paid access use-case...........................15
3.2 Support for Multi-Services................................17
3.3 Resource Pools............................................18
3.4 Support for Complex Rating Functions......................20
3.5 One-Time-based Prepaid Charging...........................21
3.6 Support for Tariff Switching..............................22
3.7 Support for Roaming.......................................24
3.8 PrePaid termination.......................................24
3.9 Querying and Rebalancing Prepaid Resources................25
4. Operations....................................................25
4.1 General Requirements......................................25
4.1.1 Broker AAA Requirements..............................25
4.2 Authentication and Authorization for Prepaid Enabled SADs.26
4.3 Session Start Operation...................................28
4.4 Mid-Session Operation.....................................29
4.5 Dynamic Operations........................................31
4.5.1 Unsolicited Session Termination Operation............31
4.5.2 Unsolicited Change of Authorization Operation........32
4.6 Termination Operation.....................................32
4.7 Mobile IP Operations......................................33
4.8 Operation consideration for Multi-Services................34
4.8.1 Initial Quota Request................................34
4.8.2 Quota Update.........................................35
4.8.3 Termination..........................................35
4.8.4 Dynamic Operations...................................36
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RADIUS Extensions for PrePaid July 2005
4.8.5 Support for Resource Pools...........................36
4.8.6 One-Time-Charging....................................36
4.8.7 Error Handling.......................................37
4.9 Accounting Considerations.................................38
4.10 SAD Operation............................................38
4.11 Interoperability with Diameter Credit Control Application38
5. Attributes....................................................38
5.1 PPAC Attribute............................................39
5.2 Session Termination Capability............................40
5.3 PPAQ Attribute............................................40
5.4 Prepaid Tariff Switching (PTS)............................46
5.5 Table of Attributes.......................................49
6. Security Considerations.......................................49
6.1 Authentication and Authorization..........................49
6.2 Replenishing Procedure....................................50
7. IANA Considerations...........................................50
8. Normative References..........................................51
9. Informative References........................................51
10. Call Flows...................................................52
10.1 Simple Concurrent Services...............................53
10.2 One-time Charging........................................55
Contributor......................................................56
Acknowledgments..................................................56
Author's Addresses...............................................56
Intellectual Property Statement..................................57
Disclaimer of Validity...........................................57
Copyright Statement..............................................57
Expiration Date..................................................58
Lior, et al. Informational [Page 3]
RADIUS Extensions for PrePaid July 2005
1.
Introduction
This draft describes RADIUS protocol extensions supporting charging
for PrePaid Data Services.
PrePaid data services are cropping up in many wireless and wireline
based networks. A PrePaid Data Service subscriber is one that
purchases a contract to receive a data service for either a period
of time, or a quantity of data. Before providing a prepaid data
service, the service provider checks that the prepaid subscriber has
sufficient funds to cover the particular service request. Only after
confirmation that funds are available is the service provided to the
user.
The subscriber purchases the Data Service using various means such
as buying a PrePaid Card, or online. How the subscriber purchases
their PrePaid Data Service depends on the deployment and is not in
scope for this document.
In some deployments, the PrePaid data service will be combined with
other Prepaid services such as PrePaid circuit voice service. This
is not an issue for this document other than the fact that the
PrePaid Data Services described in this paper should work with other
PrePaid data and or circuit voice services.
The fundamental business driver for a carrier to provide PrePaid
data services is to increase participation (subscriber base) and
thus to increase revenues. Therefore, it makes sense that PrePaid
services meet the following goals:
- Leverage existing infrastructure, hence reducing capital
expenditures typically required when rolling out a new service;
- Ability to rate service requests in real-time;
- Ability to check that the end userÆs account for coverage for the
requested service charge prior to execution of that service;
- Protect against revenue loss, i.e., prevent an end user from
generating chargeable events when the credit of that account is
exhausted or expired;
- Protect against fraud;
- Be as widely deployable over Dialup, Wireless and WLAN networks.
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RADIUS Extensions for PrePaid July 2005
The protocol described in this document maximizes existing
infrastructure as much as possible û hence the use of the RADIUS
protocol. The protocol is used in ways to protect against revenue
loss or revenue leakage. This is achieved by defining procedures
for the real-time delivery of service information to a pre-paid
enabled AAA server, to minimize the financial risk, for the pre-paid
enabled AAA server to be able to allocate small quotas to each data
session and having the ability to update the quotas from a central
quota server dynamically during the lifetime of the PrePaid data
session. As well, mechanisms have been designed to be able to
recover from errors that occur from time to time.
Protection against fraud is provided by recording of accounting
records, and by providing mechanisms to thwart replay attacks. As
well, mechanisms have been provided to terminate data sessions when
fraud is detected.
PrePaid Systems will become more prevalent and sophisticated as the
various networks such as Dialup, Wireless and WLAN converge. This
protocol extension is designed to meet the challenges of converged
networks. The draft mainly addresses how to use the RADIUS protocol
to achieve a PrePaid Data Service. The prepaid architecture assumes
that rating of chargeable events does not occur in the element
providing the service. This rating could be performed in the prepaid
enabled AAA server or may exist in an entity behind this AAA server.
Business logic and service rules may define that tariffing of events
vary in time, e.g., the particular price per megabyte download may
be defined to switch at 8pm from a high tariff to a low tariff. The
RADIUS extensions for prepaid support scenarios enable scalable
implementation of tariff switched prepaid systems.
Furthermore, the prepaid architecture assumes that a quota server is
available which, through co-ordination with the rating entity and
centralized balance manager is able to provide a quota response in
response for prepaid data service. This quota server functionality
could be performed in the prepaid enabled AAA server or may exist in
an entity behind this AAA server. Finally, the details of the
PrePaid System, such as its persistent store, how it maintains its
accounts are not covered at all. However, in order to define the
RADIUS protocol extensions it is necessary to discuss the functional
behavior of the PrePaid System.
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1.1
Terminology
Service Access Device
PrePaid Client(PPC) The Prepaid Client (PPC) is the entity which
triggers the RADIUS message exchange
including prepaid extensions defined in this
document. Typically the Prepaid Client
Resides in the NAS.
PrePaid Server(PPS) The Prepaid Server is the entity that
interacts with the Prepaid Client using the
RADIUS prepaid extensions defined in this
document.
Home network The network which contains the user profile
and the userÆs prepaid account.
WLAN Wireless Local Area Network
Service Event
Access Service The service that is provided to the user
when the user is authenticated and
authorized. In this document the term is
used to differentiate between authorization
of services that are explicitly identified
by a Service Identifier. Example of Access
Service would be the Main Service instance
of 3GPP2.
Furthermore, we use the following Mobile IP and AAA terminology:
Home agent (HA), Home network, Home AAA (HAAA), Broker AAA (BAAA),
Visited AAA (VAAA) and Foreign Agent (FA)
1.2
Requirements language
In this document, several words are used to signify the requirements
of the specification. These words are often capitalized. The key
words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
this document are to be interpreted as described in [RFC2119].
2.
Overview
This section gives a concise overview of the Prepaid Charging models
that is supported by this document, and the Architectural model
relevant to this draft.
Lior, et al. Informational [Page 6]
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2.1
PrePaid Charging Model
There are several PrePaid Charging models of how to charge customers
for availing data services:
. Volume-based charging (VBC): (e.g., 2 Cents/KiloByte);
. Duration-based charging (DBC): (e.g., 3 Cents/minute);
. Subscription-based charging (SBC): (e.g.,
Dollars/month+service);),
. Event-based charging (EBC): (e.g., 7 Cents/URL or email).
Charging models can be further divided into those with debiting of
prepaid user accounts and those with debiting of non-prepaid
accounts (such as current accounts at banks). From the perspective
of this document all userÆs as treated as userÆs having a prepaid
accounts.
2.2
Architectural Model
The architectural model supports prepaid clients on a service access
device. A SAD (e.g. a NAS) typically provides a access to data
service to end-users. A SAD is a network entity on the data path
that includes a RADIUS client and a PrePaid Client.
When prepaid service is used the SAD collects service event
information and reports it while and/or after services are provided
to the prepaid user. This event information is sent to a prepaid
server by using the prepaid RADIUS extensions.
If real-time credit control is required, the SAD (prepaid client)
contacts the prepaid server with service event information included
before the service is provided. The prepaid server, depending on the
service event information, performs credit check and allocates a
portion of available credit to the service event. The rating entity
converts this credit value into a time and/or volume amount, which
is then returned to the requesting SAD. The rating entity may
determine that during the allocated quota, a tariff switch will
occur in which case the rating entity will include details of the
quota allocated prior to the tariff switch, details of the quota
allocated after the tariff switch together with details of when the
tariff switch will occur.
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The requesting SAD then monitors service execution according to the
instructions returned by the prepaid server. After service
completion or on a subsequent request for service, the prepaid
server deducts the reserved allocation of credit from the prepaid
userÆs account.
Similarly, when a user terminates an on-going prepaid service, the
prepaid client signals the prepaid server with the a value
corresponding to the unused portion of the allocated quota. The
prepaid server is then able to refund unused allocated funds into a
userÆs prepaid account.
There MAY be multiple prepaid servers in the system for reasons of
redundancy and load balancing. The system MAY also contain separate
rating server(s) and accounts MAY be located in a centralized
database. System internal interfaces can exist to relay messages
between servers and an account manager. However the detailed
architecture of prepaid system and its interfaces are implementation
specific and are out of scope of this specification.
accounting
+------------+ +-----------+ protocol +--------------+
| Subscriber |<----->| Service | | |
| | | Access |<------------>| Accounting |
| Device | | Device |<-----+ | Server |
+------------+ +-----------+ | +--------------+
|
|
| +--------------+
+------>| PrePaid |
prepaid | Server |
protocol +--------------+
Figure 1 Basic Prepaid Architecture
The prepaid server and accounting server in this architecture model
are logical entities. The real configuration MAY combine them into a
single host.
There MAY exist protocol transparent RADIUS Proxies between prepaid
client and prepaid server. These proxies transparently support the
prepaid RADIUS extensions.
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In order to generalize the solution, in this paper we generalize the
SADs, which in reality may be a NAS in Dialup deployments, PDSN
(Packet Data Serving Node) or HA (Home Agent) in CDMA2000
deployments, an 802.11 WLAN Access Points or GGSN (Gateway GPRS
Serving Node) in GPRS/UMTS deployments. To actively participate in
Prepaid procedures outlined here, the SAD MUST have the Prepaid
Client capabilities. Prepaid Client Capabilities include the
ability to meter the usage for a prepaid data session; this usage
includes time or volume (e.g. number of bytes) usage.
In the case of roaming scenarios using mobile IP (in a wireless or
wireline network), the prepaid client functionality may be delegated
to the Home Agent. It may also be possible to deliver limited
prepaid services using RADIUS capabilities specified in RFC2865 and
RFC2866.
Furthermore, the device including the prepaid client functionality
may also have Dynamic Session Capabilities that include the ability
to terminate a data session and/or change the filters associated
with a specific data session by processing Disconnect Messages and
Change of Authorization messages as per [RFC3576].
In this document RADIUS is used as the AAA server. There are three
kinds or categories of AAA servers. The AAA server in the home
network, the HAAA, is responsible for authentication of the
subscriber and also authorization of the service. In addition, the
HAAA communicates with the Prepaid servers using the RADIUS protocol
to authorize prepaid subscribers. In AAA based roaming deployments
the AAA server in the visited network, the VAAA, is responsible for
forwarding the RADIUS messages to the HAAA. The VAAA may also
modify the messages. In roaming deployments, the visited network
may be separated from the home network by one or more broker
networks. The AAA servers in the broker networks, BAAA are
responsible to route the RADIUS packets transparently and hence
donÆt play an active roll in the Prepaid Data Service delivery.
In this document the Prepaid Server is described in functional terms
related to their interface with the HAAA. The Prepaid Server
interfaces to entities which:
i) Keep the accounting state of the prepaid subscribers (balance
manager);
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ii) Allow access service requests to be rated in real-time (Rating
Engine); and
iii) Allow quota to be managed for a particular pre-paid service
(Quota Server).
The various deployments for Prepaid are presented in the remainder
of this section. The first deployment is the basic Prepaid data
service and is depicted in figure 2. The SAD, which supports the
prepaid client functionality, the HAAA and the Prepaid Server are
collocated in the same provider network.
The Subscriber Device establishes a connection with one of several
Access Devices in the network. The SAD communicates with one or
more HAAA servers in the network. To provide redundancy more than
one HAAA may be available to use by a SAD.
The network will have one or more Prepaid Servers. Multiple Prepaid
Servers may be used to provide redundancy and load sharing. The
interface between the HAAA and the PPS is implemented using the
RADIUS protocol in this specification. However, in cases where the
PPS does not implement the RADIUS protocol, the implementation would
have to map the requirements defined in this document to whatever
protocol is used between the HAAA and the PPS.
+------+ +-----+
| | | |
+--------+ +--------+ +--| HAAA |--+--| PPS |
| | | | | | | | | |
| Sub | | Service| | +------+ | +-----+
| |---| Access |--+ |
| Device | | Device | | +------+ | +-----+
| | | | | | | | | |
+--------+ +--------+ +--| HAAA |--+--| PPS |
| | | |
+------+ +-----+
Figure 2 Basic Prepaid Access Architecture
Figure 3 shows a static roaming prepaid architecture that is typical
of a wholesale scenario for Dial-Up users or a broker scenario used
in Dial-Up or WLAN roaming scenarios.
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+----+ +----+ +----+ +-----+
| | | | | | | |
+------+ +-------+ +-|VAAA|-+-|BAAA|-+-|HAAA|-+-| PPS |
| | | | | | | | | | | | | | | |
|Sub | |Service| | +----+ | +----+ | +----+ | +-----+
| |--|Access |-+ | | |
|Device| |Device | | +----+ | +----+ | +----+ | +-----+
| | | | | | | | | | | | | | | |
+------+ +-------+ +-|VAAA|-+-|BAAA|-+-|HAAA|-+-| PPS |
| | | | | | | |
+----+ +----+ +----+ +-----+
| Visited | |Broker | | Home |
| Network | |Network| | Network |
Figure 3 Static Roaming Prepaid Architecture
As in the basic prepaid architecture the subscriberÆs device
establishes a connection with the SAD (NAS, WLAN Access Point).
The SAD communicates with the Visiting AAA server (VAAA) using the
RADIUS protocol. Again for redundancy there maybe more then one
VAAA. The VAAA communicate using the RADIUS protocol with AAA
servers in the broker network (BAAA). There maybe more then one
Broker Network between the Visited Network and the Home Network.
The Home Network is the same as in the simple architecture.
To support dynamic roaming the network will utilize Mobile-Ip as
illustrated in Figure 4. Note that typically the mobile device
would be moving between networks that use the same technology such
as Wireless or WLAN. Increasingly, device will be able to roam
between networks that use different technology such as between WLAN
and Wireless and Broadband. Fortunately, Mobile-Ip can address this
type of roaming and therefore we need not be concerned with the
underlying network technology.
Lior, et al. Informational [Page 11]
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+------+ +-------+ +----+ +----+ +----+ +-----+
| | |Service| | | | | | | | |
|Sub | |Access +-----|VAAA|--|BAAA|--|HAAA|--| PPS |
| |--|Device | | | | | | | | |
|Device| | (FA) +--+ +----+ +-+--+ +----+ +-----+
| | | | | |
+------+ +------ + | |
| | | +----+
| | | | |
|ROAMS +------------------+ HA |
| | | |
V +----+ | +----+
+------+ +-------+ | | | |
| | |Service| +-|VAAA+------+ |
|Sub | |Access | | | | |
| |--|Device +-+ +----+ |
|Device| | (FA) | |
| | | +------------------------+
+------+ +-------+
Figure 4 Roaming using Mobile-IP and pre-paid enabled SADs
In figure 4, the Subscriber device establishes a prepaid session
between the SAD in the foreign network, which has prepaid
capabilities. The subscriberÆs home address will be anchored at the
Home Agent (HA) in the home network. The setup for this access
service is identical to the cases covered above. Notice that the
SAD may be collocated with the Foreign Agent (FA) in case of Mobile-
IPv4. As the subscriber device moves it establishes a connection
with another SAD in the same foreign network or in another foreign
network. The prepaid data service should continue to be available.
When a device associates to another SAD it MUST re-authenticate at
the new SAD and de-associate or logoff from the old SAD.
Furthermore, any unused quota at the old SAD MUST be promptly
credited back to the subscribers account. The reason we say
promptly, is because if the subscriber is very low on resources to
start with, the subscriber may not have enough resources to log on
to the new SAD. The speed at which resources can be returned depend
on the type of handoff procedure that is used. Some of the example
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RADIUS Extensions for PrePaid July 2005
of handoffs in wireless networks are dormant handoff, active handoff
and fast handoff.
As well, notice that if the SADs could communicate with each other
then there could be a way to accelerate a faster handoff procedure.
In particular, it could accelerate the return of the unused portion
of the quotas from the old Access Device.
Unfortunately, standards with regards to handoff are evolving with
each network technology creating their own scheme to make the
handoff procedures more efficient.
2.3
Why not existing RADIUS attributes?
It has been asked ôWhy not use existing RADIUS attributes to build a
prepaid solution? This will allow us to have a solution with
existing devices without code modification.ö
It is possible to build a prepaid solution using existing RADIUS
attributes. The RADIUS server can simply send an Access-Accept
message containing Session-Timeout(27) and set Termination-
Action(29) to RADIUS-request. Upon receiving the Access-Accept
message, the NAS will meter the duration of the session and upon
termination of the session the NAS generate an Access-Request
message again. The RADIUS server would re-authenticate the session
and reply with an Access-Accept message with additional time in
Session-Timeout(27) or an Access-Reject message if there were no
more resources in the userÆs account.
If the user terminates the session before the time expressed in
Session-Timeout(27). The NAS will recover any unused time from the
accounting stream.
There are several problems with such a solution:
-It only allows for time-based prepaid. The solution presented in
this document allows for both time and volume based prepaid. As
well as extensibility for other features such as tarified based
solutions.
-Using accounting messages to recoup unused time may be problematic
because RADIUS accounting messages are not real-time. A RADIUS
server may store-and-forward accounting messages in batches. The
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solution presented in this paper does not rely on Accounting Packets
at all. It uses Access-Request, messages which do flow through any
network in real-time. Delaying accounting messages may cause
revenue leakage.
-Session-Timeout(27) is not a mandatory attribute. If a prepaid
subscriber is being serviced by a NAS that does not adhere to
Session-Timeout then that subscriber will obtain unlimited service.
-Termination-Action(29) presents its own issues. First the
behaviour of Termination-Action(29) is not mandatory. Second,
according to RFC2865 Termination-Action fires when the Service is
complete. But we should not be terminating the service while
negotiating additional quota. The refreshing of the time quota
should be transparent to the user. Because Termination-Action
occurs when the Service is complete it is unclear whether or not the
user experience would be transparent. For example, will the RADIUS
server allocate the subscriber a new IP address? Furthermore, the
RADIUS server has no way of telling why the Access-Request message
was generated. The RADIUS server will have to wait for the
corresponding accounting packet to determine the reason for this
Access-Request message. Lastly re-authenticating the subscriber may
take far too long. The solution presented in this document allows
quota replenishing to occur in an undisruptive manner from the
perspective of the user. No re-authentication is required and
quotas can be negotiated prior to the quotas running out.
-Prepaid ambiguity. Implementing prepaid using existing RADIUS
attributes presents another problem. Due to the fact that the
standard RADIUS attributes are not mandatory, then the correct
prepaid operation is really an act of faith on the part of the
RADIUS server. If Session-Timeout(27) and/or Termination-Action(29)
are not supported, the prepaid subscriber will get free access. The
solution described in this document, requires that a prepaid capable
SAD inform the RADIUS server whether or not it supports prepaid
capabilities. The RADIUS server can now determine whether service
should be granted or not. For example, if a prepaid subscriber is
connected to a NAS that does not support prepaid, the RADIUS server
can either instruct the NAS to tunnel the traffic to another entity
in the home network that does support prepaid client function (e.g.
Home Agent) or it may allow the subscriber to get access but
restrict the traffic.
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The prepaid solution we present is a robust carrier grade prepaid
solution. It only requires the support of 2 mandatory attributes
and one optional attribute. Furthermore, it does not really
require much code support at the NAS. NASes already support
measurement of time and volume. This solution requires that they
advertise their prepaid capabilities in an Access-Request; that they
generate an Access-Request Authorize-Only packet to obtain more
quota at or before the quota is used up. It also requires that the
NAS send an Access-Request with Authorize-Only when the session
terminates to return any unused quota to the prepaid system.
Lastly the solution provided in this document is extensible. This
document defines the basic exchanges between a prepaid capable NAS
and a RADIUS server. The protocol can easily be extended to support
tariff switching and other prepaid business models.
3.
Use-cases
In this section we present a set of use cases that help establish
the requirements needed to deliver PrePaid data services. These
use-cases donÆt address how the PrePaid account is established or
maintained. It is assumed that the PrePaid subscriber has obtained
a valid account from a service provider such as a wireless operator
or a WLAN operator.
To make the document as general as possible, the use cases cover the
experience from the SAD and not from the UserÆs Device. The
connection between the UserÆs Device, which typically involves
setting up a layer 2 session, e.g., PPP session or GPRS PDP Context,
is specific to a given network technology and the details are not
required to deliver a PrePaid service.
3.1
Simple pre-paid access use-case
A PrePaid subscriber connects to his home network. As usual, the
Access Device that is servicing the subscriber will use the AAA
infrastructure to authenticate and authorize the subscriber.
The SAD sends a RADIUS Access-Request to the AAA system to
authenticate the subscriber, and identify and authorize the service.
The Access-Request includes the subscriberÆs credentials and may
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include the PrePaid capabilities of the SAD. PrePaid capabilities
MUST be included if the SAD supports PrePaid functionality.
The AAA System proceeds with the authentication procedure. This may
involve several transactions such as in EAP [RFC2284]. Once the
subscriber has been authenticated, the AAA system determines that
the subscriber is a PrePaid subscriber and requests that the PrePaid
System authorize the PrePaid subscriber. The request MUST include
the PrePaid Capabilities of the serving SAD.
The PrePaid System will validate that the subscriber has a PrePaid
Account; it will validate that the account is active; and will
validate that the SAD has the appropriate PrePaid capabilities. If
all is in order, the PrePaid System will authorize the subscriber to
use the network. Otherwise it will reject the request. The
response is sent back to the AAA System. The response includes
attributes to indicate the allocation of a portion of the
subscriberÆs account called the initial quota (in units of time or
volume) and optionally a threshold value.
The reason we allocate a portion of the userÆs account is that the
user may be engaged in other Services that may draw on the same
Prepaid account. For example the user may be engaged in a data
session and a voice session. Although, these two services would
draw from the same account the involved separate parts of the
system. If the entire quota was allocated to the data session then
the user would have no more funds for a voice session.
The AAA system incorporates the PrePaid attributes received from the
PrePaid System into an Access-Accept message that it sends back to
the SAD. Note the AAA System is responsible for authorizing the
service whereas the PrePaid System is responsible for PrePaid
authorization.
Upon receiving the Access-Response, the SAD allows the PrePaid data
session to start and it starts to meter the session based on time or
volume, as indicated in the returned Quota
Once the usage for the session approaches the allotted quota (as
expressed by the threshold), the SAD will request an additional
quota. The re-authorization for additional quota flows through the
AAA system to the PrePaid System. The PrePaid System revalidates
the subscriberÆs account; it will subtract the previous quota
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allocation from the userÆs account balance and if there is a balance
remaining it will reauthorize the request with an additional quota
allotment. Otherwise, the PrePaid System will reject the request.
Note the replenishing of the quotas is a re-authorization procedure
and does not involve re-authentication of the subscriber.
It is important to note that the PrePaid System is maintaining
session state for the subscriber. This state includes how much
account balance was allocated during the last quota allocation for a
particular session and how much is left in the account. Therefore,
it is required that all subsequent messages about the PrePaid
session reach the correct PrePaid System.
Upon receiving a re-allotment of the quota, the SAD will, continue
the data service session until the new threshold is reached. If the
request for additional quota cannot be fulfilled then the SAD will
let the subscriber use up the remaining quota and terminate the
session.
Alternatively, instead of terminating the session, the SAD may
restrict the data session such that the subscriber can only reach a
particular web server. This web server maybe used to allow the
subscriber to replenish their account. This restriction can also be
used to allow new subscribers to purchase their initial PrePaid
Service.
Should the subscriber terminate the session before the quota is used
up, the remaining balance allotted to the session must be credited
back to the subscriberÆs account.
As well, while the Access Device is waiting for the initial quota,
the subscriber may have dropped the session. The initial quota must
be credited back to the subscribers account.
3.2
Support for Multi-Services
Up to now we were looking at session that consisted of a single
service, ôAccess Serviceö. An ôAccess Serviceö is the basic service
that is provided to the user by the SAD after successful
authentication and authorization. When we donÆt differentiate
between different types of services the ôAccess Serviceö aggregates
all the services that the user my be engaged in on a particular SAD.
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For example, the user may be browsing the web, and participating in
a VoIP conversation, watching streaming video and downloading a
file.
Some operators may want to distinguish between these services. Some
services are billed at different rates and services maybe metered
differently. Therefore, the prepaid solution needs to be able to
distinguish services, and allocate quotas to the services using
different units (e.g. time, volume) and allow for those quotas to be
utilized at different rates.
+---------+
| Session |
+---------+
|
V N
+--------------+ +-------+
| Service |------>| Quota |
| (service-Id) | +-------+
+--------------+
As shown in the above diagram, a Session can have N Services. Each
service is identified by a Service-Id. The format of the Service-Id
is not in the scope of this document but the Service-Id could be
expressed as an IP flow using the stand 5-tuple (Source-IP and Port,
the Destination-IP and Port, and the protocol type). Each service
is allocated an appropriate quota.
3.3
Resource Pools
When working with multiple services that results in multiple quota
allocation another problem arises. Even though quotas are portioned
out in fractional parts of the userÆs prepaid account, there could
be a situation where one Service utilizes its quota faster then
another Service. When the userÆs account is used up, there could be
a situation where one Service is unable to obtain additional quota
while another Service has plenty of quota remaining. Unless the
quotas can be rebalanced, the SAD would then have to terminate that
Service. As well, even before that happens, the existence of
several Services could generate an excessive amount of traffic as
the services update their quotas.
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One method to solve these problems is to utilize resource pools.
Resource pools allow us to allocate resources to several services of
a session by allocating resources to a pool and have services draw
their quota from the pool at a rate appropriate to that service.
When the quota allocated to the pool runs out, we replenish the
pool.
+-----------+
| Service-A |-----+ +--------+
+-----------+ | Ma | |
+-------->| |
| Pool |
+-------->| (1) |
+-----------+ | Mb | |
| Service-B |-----+ +--------+
+-----------+
As the figure above shows, Service-A and Service-B are bound to
Pool(1). Ma and Mb are the pool multipliers (that are associated
with Service-A and Service-B respectively) that determines the rate
at which Service-A and Service-B draw from the pool.
The pool is initialized by taking the quota allocated to each
service and multiplying it by Mn. Therefore, the amount of
resources allocated to a pool is given by:
Poolr = Ma*Qa + Mb*Qb + . . .
A Pool is empty if:
Poolr <= Ca*Ma + Cb*Mb + . . .
where:
Ca,Cb are the consumed resources of Service-A and Service-B
respectively.
Note that the resources assigned to the pool are unit less. That
is, Service-A can be rated at $1 per Mbyte and Service-B can rated
at $0.10 per Minute. In this case if we allocate $5 worth of
resources on behalf of service-A to the pool we would set Ma = 10
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and place 50 units into the pool. If we allocate $5 on behalf of
Service-B to the Pool, then M=1 and place 50 units into the Pool.
The pool would have a total sum of 100 units to be shared between
the two services. Each Mbyte used by Service-A will draw 10 units
from the pool and each minute used by Service-B will draw 1 unit
from the pool.
3.4
Support for Complex Rating Functions
The rate of use of a resource by a service can be very complex.
Some services use resources (e.g. time, volume) linearly. For
example, a service maybe consuming resources at a rate of $1 per
Mbyte.
In some cases an operator may wish to apply a much more complex
rating function. For example, a service provider may wish to rate a
service such that the first N Mbytes are free, then the next M
Mbytes are rated at $1 per Mbyte and volume above M bytes be rated
at $0.50 per Mbyte. This rating function could be achieved by
repeated message exchanges with the Prepaid System.
To avert the need to exchange many messages and to support even more
complex rating functions we support Rating Groups. A Rating Group
is provisioned at the SAD. As illustrated in the figure below, a
Rating Group is associated with one or more Services and defines the
rate that the services associated with the Rating Group consume the
quota.
+-----------+
| Service-A |------+
+-----------+ | +--------------+ +-------+
+---->| | | Quota |
| Rating Group |------>| or |
+-----------+ +---->| | | Pool |
| Service-B |------+ +--------------+ +-------+
+-----------+
During authorization of the of a service, if the service is
associated with a Rating Group, the Prepaid Client sends the Rating
Group to the Prepaid Server. The prepaid service authorizes the
Rating Group by assigning it a Quota and optionally assigning it to
a Resource Pool.
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When service that belongs to an authorized Rating Group is
instantiated, then the Prepaid Client does not need to authorize
that service. This could greatly reduce the amount of traffic
between the Prepaid Client and the Prepaid Server.
3.5
One-Time-based Prepaid Charging
One-Time-based Prepaid Charging is used for charging of Service
Events where there is no session. That is, the Service Event does
not have a start or an end. An example of a one-time service event
is the purchase of a ring-tone. The one-time event in this case is
the userÆs purchasing the right to use a ring-tone. The actual
downloading of the tone is a separate service event totally distinct
from the right to use the ring tone. For example, the user may have
already downloaded the tone and then after being totally satisfied
with the quality, decides to purchase the right to use the tone.
Subscription based services can also be modeled as a One-Time event.
In this case the one-time service event is the purchase of a
subscription to use a service for a month. While the user uses the
service his usage maybe metered especially if there are limits
associated with the service.
For a given user, One-time-based charging may occur in conjunction
with the other charging models. For example, the prepaid user maybe
accessing a website which is being metered based time or volume
while they purchase the right to use a ring tone (a one-time-based
event). Note: it is up to the service providers to decide whether
or not the user will be charged for the download of the tone and
also be charged for the time and volume required to download the
ring-tone. The facilities provided by this document gives the
service provider the capability to achieve their service charging
business goals. For example, should the service provider choose not
to charge for the download volume or time, then they can treat the
download IP flow as a separate service that is exempt from charging.
One-time-based charging occurs when the SAD sends an indication to
the PPS identifying the service, and the units that need to be
debited from the account. The units to be debited from the account
and how those units are rated (if they donÆt represent money) is not
in scope of this specification.
One-time-based charging may occur under two conditions: the SAD may
not have a authenticated context (or access to an authenticated
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context for the subscriber); the SAD has access to authenticated
context for the subscriber. In the former case the SAD will have to
authenticate the subscriber. For example, the prepaid user maybe
authenticated by the SAD providing access service. However when the
user accesses the subscription server to purchase a subscription,
the subscription server may not have access to the authentication
context of the subscriber and thus will have to authenticate the
subscriber. Authentication of the subscriber and the generation of
the one-time charging event will happen at the same time.
Note that one-time-based charging can be used to credit the prepaid
userÆs account. For example, the SAD can return resources back to
the prepaid subscriber by making a one-time charge request that
includes the amount of resource to be credited back to the user.
3.6
Support for Tariff Switching
The PPC and the PPS may support tariff switching for volume based
prepaid packet service. Tariff switching allows the PPS to signal
the PPC when a change of rating or tariff switch is to occur. For
example as shown in the figure below, traffic before 18:00 hours is
rated at ær1Æ or business rates and traffic after 18:00 hours is
rated at ær2Æ or non-business rates. The PPC will then be able to
report usage before the tariff switch point and usage after the
tariff switch point. Since time is measured in seconds, tariff
switching only makes sense for volume based prepaid service where
the volume is billed at different rates: one rate before the tariff
switch period and another rate after the tariff switch period.
18:00
------------------+-----------------
r1 | r2
------------------+-----------------
^ ^
|<----TSI---> |
| |
Access-Accept Access-Request
When tariff switching is supported by the PPC it indicates support
for tariff switching by setting the appropriate bit in the PPAC. If
the PPS requires to signal a tariff switch time it will send a PTS
attribute which will indicate when the tariff switch period is to
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occur as a number of seconds from the current time
(TarrifSwitchInterval TSI).
Sometime after the tariff switch period the PPC will send another
online Access-Request. Either the user has logged off or the volume
threshold has been reached. The PPC will report how much volume was
used using the PPAQ and how much volume was used after the tariff
switch using the PTSÆs VUATS subtype.
If the PPC will send and event before the tariff switch time, say
the Volume threshold has been reached, the PPS will respond with
another PTS with the TSI indicating how many seconds until the
tariff switch time.
In situations where there is going to be another tariff switch
period, as shown below, the PPS MUST specify the length of the
tariff switch period using the TimeIntervalAfterTariffSwitchUpdate
(TITSU) in the PTS attribute.
18:00 23:30
------------------+---------------------+--------------
r1 | r2 | r3
------------------+---------------------+--------------
^ ^ ^
|<----TSI---><-----------|-------->|TITSU
| |
Access-Accept Access-Request
When TITSU is specified in the PTS, the PPC MUST generate an online
Access-Request within the time after TSI and before TITSU expires.
Normally the PPC will be triggered by the Volume Threshold, but
there is no guarantee that the user session will generate any volume
during the period between 18:00 and 23:30 hours. If TITSU was not
specified in this case, then if there was some volume generated
during r2 but not enough to trigger a prepaid update before the next
tariff switch at 23:30. Then the PPC will not be able to report how
much volume was generated during r1, r2, and r3.
When prepaid for multiple flows is supported, then each flow could
have it own tariff switch period. For example, best effort flow may
not have a tariff switch associated with it, yet a voice over IP
call may have a tariff switch period. The Voice over IP call may
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bill at one rate for the first 5 minutes and another rate for the
rest of the call.
[EDITORÆS NOTE: Need to consider tariff switching with pools. Is it
worthwhile?]
3.7
Support for Roaming
For some networks it is essential that PrePaid Data Services be
offered to roaming subscribers. Support for static and dynamic
roaming models are needed. Static roaming is where the subscriber
logs onto a foreign network. The foreign network has a roaming
agreement directly with the home network or through a broker network
or networks. The subscriber remains logged into the network until
the subscriber changes location. When changing location a new
connection and a new login procedure is required.
Dynamic roaming allows to subscriber to move between networks while
maintaining a connection with the home network seamlessly. As the
subscriber moves between networks, the data session is handed off
between the networks.
In both roaming scenarios, the subscriber always authenticates with
the home network. PrePaid authorization and quota replenishing for
the session need to be received at the home network and more
specifically at the PrePaid System where state is being maintained.
Dynamic roaming is particularly challenging. A subscriber that
established a PrePaid Data Session may roam to another Access Device
that doesnÆt not support PrePaid functionality. The system should
be capable to continue the PrePaid session.
3.8
PrePaid termination
When fraud is detected by the PrePaid System, or when an error is
detected, it may be beneficial for the PrePaid system to terminate a
specific session for the subscriber or all the sessions of a
subscriber.
Some errors can occur such that the PrePaid System is in a state
where it is not sure whether the session is in progress or not.
Under conditions such as this, the PrePaid system may wish to
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terminate the PrePaid data session to make sure that resources are
not being utilized for which it canÆt charge for reliably.
Some handoff procedure used during dynamic roaming may require that
the PrePaid system explicitly terminate the subscribers PrePaid data
session at an SAD. For example, if time based PrePaid service is
being used and the mobile subscriber performs a dormant handoff, the
PrePaid System needs to explicitly terminate the PrePaid session at
the old SAD.
3.9
Querying and Rebalancing Prepaid Resources
It should be possible to allow the Prepaid Server to Query the
current uses state of a prepaid balance at a SAD and adjust the
prepaid resources.
For example, a request to the PPS is made (e.g., a one-time charging
event) but the userÆs account is depleted but resources have been
allocated to the SAD. The PPS should have a the capability to query
the SAD and if it has the spare resources to reassign the quotas to
the SAD and to the pending request. Note that the PPS doesnÆt know
resource usage until the SAD request for more resources. This can
be a long time.
In the absence of this capability the PPS can minimize the
occurrence of this scenario by allocated smaller quotas. But the
result will be many more transactions. The ability to query and to
rebalance resources provides a good trade-off.
4.
Operations
4.1
General Requirements
4.1.1
Broker AAA Requirements
Broker AAA servers MUST support the Message-Authenticator(80)
attribute as defined in [RFC2869]. If BAAA servers are used, the
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BAAA servers function is to forward the RADIUS packets as usual to
the appropriate RADIUS servers.
Accounting messages are not needed to deliver a PrePaid service.
However, accounting messages can be used to keep the PrePaid Server
current as to what is happening with the PrePaid data session.
Therefore, BAAA SHOULD deliver RADIUS Accounting messages using the
pass through mode described in [RFC2866].
4.2
Authentication and Authorization for Prepaid Enabled SADs
The SAD initiates the authentication and authorization procedure by
sending a RADIUS Access-Request to the HAAA.
If the SAD has PrePaid Client capabilities, it MUST include the
PPAC(TBD) attribute in the RADIUS Access-Request. The PPAC(TBD)
attribute indicates to the PrePaid server the PrePaid capabilities
possessed by the SAD. These are required in order to complete the
PrePaid authorization procedures.
If the SAD supports the Disconnect-Message or the Change-of-
Authorization capabilities, then it SHOULD include the Dynamic-
Capabilities attribute.
In certain deployments, there may be other ways in which to
terminate a data session, or change authorization of an active
session. For example, some SADs provide a session termination
service via Telnet or SNMP. In these cases, the AAA server MAY add
the Dynamic-Capabilities message to the Access-Request. Upon
receiving the Change-of-Authorization message, the AAA server would
then be responsible for terminating the session using whatever means
that are supported by the device.
If the authentication procedure involves multiple Access-Requests
(as in EAP), the SAD MUST include the PPAC(TBD) attribute and the
Dynamic-Capabilities attribute (if used) in at least the last
Access-Request of the authentication procedure.
The Access-Request will be sent as usual to the HAAA. The packet
may be proxied through zero or more BAAA.
Once the Access-Request arrives at the HAAA, the HAAA will
authenticate the subscriber. If the subscriber is cannot be
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authenticated, the HAAA will send an Access-Reject message back to
the client. If the subscriber is authenticated, the HAAA will
determine whether or not the subscriber is a PrePaid subscriber.
The techniques used to determine whether or not a subscriber is a
PrePaid subscriber is beyond the scope of this document. If the
subscriber is not a PrePaid subscriber, then the HAAA will respond
as usual with an Access-Accept or Access-Reject message. If the
subscriber is a PrePaid Subscriber the HAAA SHALL forward the
Access-Request to a PrePaid server for further authorization.
The Access-Request will contain the PPAC(TBD) attribute, the
Dynamic-Capabilities attribute if one was included; the User-Name(1)
attribute MAY be set to a value that would represent the
SubscriberÆs PrePaid Identity. This attribute is used by the
PrePaid server to locate the PrePaid SubscriberÆs account. For
added security, the HAAA MAY also set the User-Password(2) attribute
to the password used between the HAAA and the PrePaid server.
The PrePaid server lookups the subscriberÆs PrePaid account and will
authorize the subscriber taking into consideration the SAD PrePaid
Client Capabilities.
Upon successful authorization, the PrePaid server will generate an
Access-Accept containing the PPAC(TBD) attribute and the PPAQ(TBD)
attribute.
The PPAC attribute returned to the client indicates the type of
prepaid service to be provided for the session. The PPAQ(TBD)
attribute includes:
- The QUOTA-Id, which is set by the PrePaid server to a unique
value that is used to correlate subsequent quota requests;
- Volume and/or Time quotas, which are set to a value representing a
portion of the subscribers account;
- MAY contain a Time or Volume Threshold that controls when the SAD
requests additional quota;
- The IP address of the Serving PrePaid Server and one or more
alternative PrePaid Servers. This is used by the HAAA to route
subsequent quota replenishing messages to the appropriate PrePaid
server(s).
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Note: Idle-Timeout(28) can be used to trigger the premature
termination of a pre-paid service following subscriber inactivity.
Depending on site policies, upon unsuccessful authorization, the
PrePaid server will generate an Access-Reject to terminate the
session immediately. Alternatively, the PrePaid server may generate
an Access-Accept blocking some or all of the traffic and/or redirect
some or all of the traffic to a location where the subscriber can
replenish their account for a period of time. Blocking of traffic
is achieved by either Filter-Id(11) or NAS-Filter-Rule(see Redirect
I-d). Redirection is achieved by sending Redirect-Id or Redirect-
Rule, HTTP Redirection defined in the Redirect I-d. The period of
time before the blocked/redirected session last can be specified by
Session-Timeout(27) attribute.
Upon receiving the Access-Accept from the PrePaid Server, the HAAA
will append the usual service attributes and forward the packet to
the SAD. The HAAA SHOULD NOT overwrite any attributes already set
by the PrePaid server. If the HAAA, receives an Access-Reject
message, it will simply forward the packet to its client. Depending
on site policies, if the HAAA fails to receive an Access-Accept or
Access-Reject message from the PrePaid server it MAY do nothing or
send an Access-Reject or an Access-Accept message back to its
client.
4.3
Session Start Operation
The real start of the session is indicated by the arrival of
Accounting-Request(Start) packet. The Accounting-Request (Start)
MAY be routed to the PrePaid Server so that it can confirm the
initial quota allocation.
Note that the PrePaid Server role is not to record accounting
messages and therefore it SHOULD not respond with an Accounting
Response packet.
If the Prepaid server does not receive the Accounting-Request(start)
message it will only know that the session has started upon the
first reception of a quota replenishment operation.
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If the Prepaid server does not receive indication directly (via
Accounting-Request(start)) or indirectly, it SHOULD after some
configurable time, deduce that the Session has not started. If the
SAD supports termination capabilities, the PPS SHOULD send a
Disconnect Message to the SAD to ensure that the session is indeed
dead.
4.4
Mid-Session Operation
During the lifetime of a PrePaid data session the SAD will request
to replenish the quotas using Authorize-Only Access-Request
messages.
Once the allocated quota has been reached or the threshold has been
reached, the SAD MUST send an Access-Request with Service-Type(6)
set to a value of ôAuthorize Onlyö and the PPAQ(TBD) attribute.
The SAD MUST also include NAS identifiers, and Session identifier
attributes in the Authorize Only Access-Request. The Session
Identifier should be the same as those used during the Access-
Request. For example, if the User-Name(1) attribute was used in the
Access-Request it MUST be included in the Authorize Only Access-
Request especially if the User-Name(1) attribute is used to route
the Access-Request to the Home AAA server.
The Authorize Only Access-Request MUST not include either User
Password or Chap Password. In order to authenticate the message,
the SAD MUST include the Message-Authenticator(80) attribute. The
SAD will compute the value for the Message-Authenticator based on
[RFC2869].
When the HAAA receives the Authorize-Only Access-Request that
contains a PPAQ(TBD), it SHALL validate the message using the
Message-Authenticator(80) as per [RFC2869]. If the HAAA receives an
Authorize Only Access-Request that contains a PPAQ(TBD) but not a
Message-Authenticator(80) it SHALL silently discard the message. An
Authorize Only Access-Request message that does not contain a
PPAQ(TBD) is either in error or belongs to another application (for
example, a Change of Authorization message [RFC3576]). In this case
the Authorize Only Access-Request will either be silently discarded
or handled by another application (not in scope of this document).
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Once the Authorize Only Access-Request message is validated, the
HAAA SHALL forward the Authorize Only Access-Request to the
appropriate PrePaid Server. The HAAA MUST forward the Authorize
Only Access-Request to the PrePaid server specified in the
PPAQ(TBD). The HAAA MUST sign the message using the Message-
Authenticator(80) and the procedures in [RFC2869]. As with the
Access-Request message, the HAAA MAY modify the User-Name(1)
attribute to a value that represents the userÆs internal PrePaid
account in the PrePaid server. Note the PrePaid server could use
the Quota-ID sub-attribute contained within the PPAQ(TBD) to locate
the user account.
Upon receiving the Authorize Only Access-Request containing a
PPAQ(TBD) attribute, the PrePaid server MUST validate the Message-
Authenticator(80) as prescribed in [RFC2869]. If the message is
invalid, the PrePaid server MUST silently discard the message. If
it received an Authorize Only Access-Request message that does not
contain a PPAQ(TBD) it MUST silently discard the message.
The PrePaid server will lookup the PrePaid session by using the
PrePaid Quota Id contained within the PPAQ(TBD). The PrePaid Server
would, take the last allocated quota and subtract that from the
UserÆs balance. If there is remaining balance, the PrePaid server
re-authorizes the PrePaid session by allocate an additional quota.
The PrePaid server may want to calculate a different threshold
values as well.
Upon successful re-authorization, the PrePaid server will generate
an Access-Accept containing the PPAQ(TBD) attribute. The Access-
Accept message MAY contain Service-Type(6) set to Authorize-Only and
MAY contain the Message-Authenticator(80).
Depending on site policies, upon unsuccessful authorization, the
PrePaid server will generate an Access-Reject or an Access-Accept
with Filter-Id(11) or Ascend-Data-Filter (if supported) attribute
and the Session-Timeout(27) attribute such that the PrePaid
subscriber could get access to a restricted set of locations for a
short duration to allow them to replenish their account, or create
an account; or to browse free content.
Upon receiving the Access-Accept from the PrePaid server, the HAAA
SHALL return the packet to its client. If the HAAA, receives an
Access-Reject message, it will forward the packet. Depending on
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site policies, if the HAAA fails to receive an Access-Accept or an
Access-Reject message from the PrePaid server it MAY do nothing or
it MAY send an Access-Reject message back to its client.
Upon receiving an Access-Accept, the SAD SHALL update its quotas and
threshold parameters with the values contained in the PPAQ(TBD)
attribute. Note that the PrePaid server MAY update the
PrePaidServer attribute(s) and these may have to be saved as well.
Upon receiving an Access-Accept message containing either Filter-
Id(11) or Ascend-Data-Filter attributes, and or Session Timeout(27).
The SAD SHALL restrict the subscriber session accordingly.
4.5
Dynamic Operations
The PrePaid server may want to take advantage of the dynamic
capabilities that are supported by the SAD as advertised in the
Dynamic-Capabilities attribute during the initial Access-Request.
There are two types of actions that the PrePaid server can perform:
it can request that the session be terminated; or it can request
that attributes associated with the session be modified. More
specifically, it can modify previously sent PPAQ(TBD)
Both of these actions require that the session be uniquely
identified at the SAD. As a minimum the PrePaid server:
-MUST provide either the NAS-IP-Address(4) or NAS-Identifier(32)
-MUST provide at least one session identifier such as User-Name(1),
Framed-IP-Address(), the Accounting-Session-Id(44).
Other attributes could be used to uniquely identify a PrePaid data
session.
For a discussion on Dynamic Operations as they related Mutli-Service
operations see further on.
4.5.1
Unsolicited Session Termination Operation
At anytime during a session the Prepaid Server may send a Disconnect
Message to terminate a session. This capability is described in
detail in [RFC3576]. The PrePaid server sends a Disconnect Message
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that MUST contain identifiers that uniquely identify the
subscriberÆs data session and the SAD servicing that session.
If the SAD receives a Disconnect-Message, it will respond with
either a Disconnect-ACK packet if it was able to terminate the
session or else it will respond with a Disconnect-NAK packet.
Upon successful termination of a session the SAD MUST return any
unused quota to the Prepaid Server by issuing an Authorize Only
Access-Request containing the PPAQ which contains any unused Quota
and the Update-Reason set to ôRemote Forced Disconnectö.
4.5.2
Unsolicited Change of Authorization Operation
At anytime during the prepaid session the Prepaid Client may receive
a Change of Authorization (CoA) message. A Prepaid Server may send
a new Quota to either add additional quota or to remove quota
already allocated for the service.
If the Change of Authorization contains a PPAQ then that PPAQ will
override a previously received PPAQ. The PPAQ may contain more
allocated Quota or less allocated quota. The PPS MUST NOT change
the units used in the PPAQ.
If the newly received PPAQ reduces the amount of allocated quota
beyond what is currently used then the SAD will accept the new PPAQ
and act as it normally would when the quota is used up. For
example, if the threshold is reached then is request a quota update;
if the quota received is less then the currently used level then the
SAD would follow the normal procedures followed when a quota is used
up.
4.6
Termination Operation
The termination phase is initiated when either: the Subscriber logs
off; the quotas have been consumed, or when the SAD receives a
Disconnect Message.
In the case where the user logged off, or the SAD receives a
Disconnect Message, the SAD will send an Authorize-Only Access-
Request message with a PPAQ(TBD) and Update-Reason attribute set to
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either ôClient Service terminationö or ôRemote Forced disconnectö
and the currently used quota.
In the case where the quota has been reached, if the PPAQ(TBD)
contained Termination-Action field, the SAD will follow the
specified action which would be to immediately terminate the
service, to request more quota, or to Redirect/Filter the service.
4.7
Mobile IP Operations
In roaming scenarios using Mobile-IP, as the mobile subscriber roams
between networks, or between different types of networks such as
between WLAN and CDMA2000 networks, the PrePaid data session should
be maintained transparently if the HA is acting as the SAD.
As the subscriber device associates with the new SAD (AP or PDSN
that supports prepaid client capability), the SAD sends a RADIUS
Access-Request and the subscriber is re-authenticated and
reauthorized. The SAD MUST include the PPAC(TBD) attribute in the
RADIUS Access-Request. In this manner the procedure follows the
Authentication and Authorization procedure described earlier.
If the HA was acting as the SAD before handoff, the userÆs prepaid
session does not undergo any change after the handoff because the
Mobile IP session is anchored at the HA and the userÆs Home IP
address remains the same.
In the case of AP or PDSN acting as the SAD it is likely that the
userÆs IP address will change (Care of Address). Therefore, the
ongoing prepaid session will have some impact. In the case the SAD
shall send an Access-Request.
The Access-Request message is routed to the home network and MUST
reach the PrePaid System that is serving the PrePaid session. The
PrePaid system will then correlate the new authorization request
with the existing active session and will assign a quota to the new
request. Any outstanding quota at the old SAD MUST be returned to
the PrePaid system. If the Mobile-IP nodes (HA and FA) supports
registration revocation (Mobile IPv4 only). Specifically, the quota
SHOULD be returned when the SAD sends the Authorize Only Access-
Request with PPAQ(TBD) Update-Reason set to either ôRemote Forced
disconnectö or ôClient Service terminationö. In order to trigger
the sending of this last Authorize Only Access-Request, the PrePaid
system may issue a Disconnect Message [3576] to the SAD.
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If the subscriber has roamed to an SAD that does not have any
PrePaid Capabilities, PrePaid data service may still be possible by
requesting the Home Agent (providing it has PrePaid Capabilities) to
assume responsibilities for metering the service. The procedure for
this scenario will be given in the next release of this draft.
4.8
Operation consideration for Multi-Services
This section describes the operation for supporting Prepaid for
multi-services on the same SAD. The operations for multi-services
are very similar to operations for single service. Message flows
illustrating the various interactions are presented at the end of
this document.
A SAD that supports prepaid operations for multi-services SHOULD set
the ôMulti-Services Supportedö bit in the PPAC.
When working with multi-services, we need to differentiate between
the services. A Service-Id attribute is used in the PPAQ(TBD) to
uniquely differentiate between the services. The exact definition
of the Service-Id attribute is out of scope for this document.
A PPAQ that contains a Service-Id is associated with that Service.
A PPAQ that contains a Rating-Group-Id is associated with that
Rating-Group. A PPAQ MUST not contain both a Rating-Group-Id and a
Service-Id. A PPAQ that contains neither a Rating-Group-Id or a
Service-Id applies to the ôAccess Serviceö.
4.8.1
Initial Quota Request
When operations with multi-services is desired, the SAD will request
the initial quota for the Service by sending a PPAQ containing the
Service-Id for that Service in an Authorize-Only Access-Request
packet. Similarly, if the SAD supports Rating-Groups then it may
request a prepaid quota for the Rating-Group by sending a PPAQ
containing the Rating-Group-Id. In both cases the Update-Reason
will be set to ôInitial-Requestö.
The Authorize-Only Access-Request packet may contain more than one
PPAQ. The Authorize-Only Access-Request MUST include one or more
attributes that serve to identify the session so that it can be
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linked to the original authentication. Which Session Identifier(s)
is included is up to specific deployments. The Authorize-Only
message must contain the Message-Authenticator(80) attribute for
integrity protection of the Authorize-Only Access-Request message.
Upon receiving an Authorize-Only Access-Accept message containing
one or more PPAQs the Prepaid System will allocate resources to each
PPAQ. The resources, can be in units of time, volume as before.
Each PPAQ will be assigned a unique QID that MUST appear in a
subsequent PPAQ update for that service or rating-group. As well,
the PPAQ MUST contain the Service-ID; or Group-ID; or neither, if
the PPAQ applies to the ôAccess Serviceö.
4.8.2
Quota Update
Once the services start to utilize their allotted quota they will
eventually need to replenish their quotas (either the threshold is
reached or no more quota remains). To replenish the quota the
Prepaid Client will send an Authorize-Only Access-Request message
containing one or more PPAQs. Each PPAQ MUST contain the
appropriate QID, Service-ID or Group-ID (or neither the Service-ID
or Group-Id if the quota replenishment is for the ôAccess Serviceö).
The Update-Reason filed will indicate either ôThreshold reachedö(3),
or ôQuota reachedö(4). The Authorize-Only message must contain
identifiers to identify the session.
Upon receiving an Authorize-Only Access-Request packet with one or
more PPAQs the Prepaid Server will respond with a new PPAQ for that
service. The PPAQ will contain a new QID, the Service-Id or Rating-
Group-Id, a new Quota. If the Prepaid Server does not want to grant
additional quota to the Service it MUST include the Termination-
Action subfield in the PPAQ that will instruct the SAD what to do
with the service.
4.8.3
Termination
When an allotted quota for the service is used up the SAD shall act
in accordance to the Termination-Action field set in the Quota. If
the Termination-Action field is absent then the Service MUST be
terminated.
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If the Service is to be terminated then the SAD shall send a PPAQ
with the appropriate QID, the Service-Id, the used quota, and
Update-Reason set to ôClient Service Terminationö.
If the ôAccess Serviceö has terminated, then all other services must
be terminated as well. In this case the SAD must report on all
issued quotas for the various services. The Update-Reason field
should be set to ôAccess Service Terminatedö.
Note when sending more then on PPAQ it may be required to send
multiple Authorize Only Access-Requests.
4.8.4
Dynamic Operations
Dynamic operations for multi-services are similar to dynamic
operations described for single service operations. The prepaid
system may send a COA message containing a PPAQ for an existing
service instance. The SAD will match the PPAQ to the service using
the Service-ID attribute. The new quota could be higher then the
last allocated value or it could be lower. The SAD must react to
the new quota accordingly.
A Disconnect message may not be send for a specific service. A
disconnect message terminates the ôAccess Serviceö. As such the SAD
must report back all unused quotas by sending an Authorize Only
Access Request message containing a PPAQ for each active service.
The Update-Reason shall indicate that the reason for the update
reason.
4.8.5
Support for Resource Pools
If the Prepaid Client supports pools as indicated by setting the
ôPools supportedö bit in the PPAC(TBD) then the Prepaid Server may
associate a Quota with a Pool by including the Pool-Id and the Pool-
Multiplier in the PPAQ(TBD).
When Resource Pools are used, the PPAQ must not use the threshold
field.
4.8.6
One-Time-Charging
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To initiate a One-Time charge the PPC include the PPAQ attribute in
an Access-Request packet. The Access Request packet MUST include
the Message-Authenticator(80) and Event-Timestamp(55) attributes.
The Service Id field of the PPAQ identifies the Service that is be
charged for. The amount of to be charged is specified using the
Resource Quota and Resource Quota overflow subtypes. If the value
specified is negative then the resources will be credited to the
userÆs account.
The QID field MUST be set to a unique value and will be used by the
PPS to detect duplicates should the packet be retransmitted.
The Update Reason field MUST be set to One-Time Charging.
Upon receiving a PPAQ configured as a One-Time charge, the RADIUS
server authenticates the user and if authenticated, pass the PPAQ to
the PPS. The PPS shall locate the subscriber account and debit or
credit the account accordingly. The PPS MUST repond to the PPS with
an Access-Accept message upon success. Or an Access-Reject message
if it cant locate the userÆs account or if there is no balance
remaining in the account.
The RADIUS server shall respond back to the SAD with an Access
Accept message. Since this is a one-time event charge the SAD must
not allow the session to continue. Therefore, the RADIUS server
should include in the Access-Accept a Session-Timeout set to 0. The
Upon receiving an Access-Accept response the SAD shall generate an
Accounting Stop message.
A PPAQ used for One-Time charging may appear in an Authorize-Only
Access Request. This is the case where a session already exists for
the user. The PPS shall respond back with an Access-Accept to
indicate that the userÆs account has been debited or an Access-
Reject indicating that the account could not be debited.
4.8.7
Error Handling
If the Prepaid Server receives a PPAQ with an invalid QID it MUST
ignore that PPAQ.
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If the Prepaid Server receives a PPAQ containing a Service-Id, or a
Rating-Group-Id that it does not recognize, then it MUST ignore that
PPAQ.
If the Prepaid Client receives a PPAQ containing a Service-Id, or a
Rating-Group-Id that it does not recognize, then it must ignore that
PPAQ.
If the Prepaid Client receives a PPAQ that contains a Pool-Id
without a Pool-Multiplier; or a Pool-Multiplier without a Pool-Id it
must ignore that PPAQ.
4.9
Accounting Considerations
Accounting messages are not required to deliver PrePaid Data
Service. Accounting message will typically be generated for PrePaid
Data Service. This because accounting message are used for auditing
purposes as well as for bill generation.
Accounting messages associated with PrePaid Data Sessions should
include the PPAQ(TBD) attribute.
4.10
SAD Operation
To be completed
4.11
Interoperability with Diameter Credit Control Application
RADIUS PrePaid solutions need to interoperate with Diameter
protocol. Two possibilities exist: The AAA infrastructure is
Diameter based and the SAD are RADIUS based; or the SAD is Diameter
based and the AAA infrastructure is RADIUS based.
The Diameter Credit Control Application [DIAMETERCC] describes how
to implement a PrePaid using an all Diameter based infrastructure.
<This section to be completed.>
5.
Attributes
This draft is using the RADIUS [RFC2865] namespace.
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5.1
PPAC Attribute
The PrepaidAccountingCapability (PPAC) attribute is sent in the
Access-Request message by a Prepaid Capable NAS and is used to
describe the PrePaid capabilities of the NAS. The PPAC is available
to be sent in an Access-Accept message by the Prepaid server to
indicate the type of prepaid metering that is to be applied to this
session.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TYPE | LENGTH | SUB-TYPE 1 | LENGTH |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AvailableInClient (AiC) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
TYPE : value of PPAC
LENGTH: 8
VALUE : String
The value MUST be encoded as follows:
Sub-Type (=1) : Sub-Type for AvailableInClient attribute
Length : Length of AvailableInClient attribute
(= 6 octets)
AvailableInClient (AiC):
The optional AvailableInClient Sub-Type, generated by the PrePaid
client, indicates the PrePaid Accounting capabilities of the NAS and
shall be bitmap encoded. The possible values are:
0x00000001 Volume metering supported.
0x00000002 Duration metering supported.
0x00000004 Resource metering supported.
0x00000008 Pools supported
0x00000010 Rating groups supported
0x00000020 Multi-Services supported.
0x00000040 Tariff Switch supported.
Others Reserved
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5.2
Session Termination Capability
The value shall be bitmap encoded rather than a raw integer. This
attribute shall be included RADIUS Access-Request message to the
RADIUS server and indicates whether or not the NAS supports Dynamic
Authorization.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TYPE | LENGTH | String |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type : value of Session Termination Capability
Length: = 4
String encoded as follows:
0x00000001 Dynamic Authorization Extensions (rfc3576) is
supported.
5.3
PPAQ Attribute
One or more PPAQ(TBD) attributes are available to be sent in an
Access Request, Authorize Only Access-Request and Access-Accept
messages. In an Access Request message, it is used to One-Time
charging transactions; in Authorize Only Access-Request messages it
is used to for One-Time charging, report usage and request further
quota or request prepaid quota for a new service instance; in an
Access-Accept message it is used to allocate the quotas (initial
quota and subsequent quotas).
When concurrent service are supported a PPAQ is associated with a
specific service as indicated by the presence of Service-Id; or a
Rating Group, as indicated by the presence of a Rating-Group-Id; or
the ôAccess Serviceö as indicated by the absence of a Service-Id or
a Rating-Group-Id.
The attribute consists of a number of subtypes. Subtypes not used
are omitted in the message.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TYPE | LENGTH | SUB-TYPE 1 | LENGTH |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| QuotaIdentifier (QID) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SUB-TYPE 2 | LENGTH | Volume Quota |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Volume Quota | SUB-TYPE 3 | LENGTH |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| VolumeQuotaOverflow (VQO) | SUB-TYPE 4 | LENGTH |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| VolumeThreshold (VT) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SUB-TYPE 5 | LENGTH | VolumeThresholdOverflow (VTO) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SUB-TYPE 6 | LENGTH | DurationQuota (DQ) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DurationQuota (DQ) | SUB-TYPE 7 | LENGTH |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DurationThreshold (DT) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SUB-TYPE 8 | LENGTH | Update-Reason attribute (UR) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SUB-TYPE 9 | LENGTH | PrePaidServer |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PrePaidServer |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type : Value of PPAQ
Length: variable, greater than 8
String: The String value MUST be encoded as follows:
Sub-Type (=1): Sub-Type for QuotaIDentifier attribute
Length : Length of QuotaIDentifier attribute (= 6 octets)
QuotaIDentifier (QID):
The QuotaIDentifier Sub-Type is generated by the PrePaid server
at allocation of a Volume and/or Duration Quota. The on-line
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quota update RADIUS Access-Request message sent from the SAD to
the PPS shall include a previously received QuotaIDentifier.
Sub-Type (=2): Sub-Type for VolumeQuota attribute
Length : length of VolumeQuota attribute (= 6 octets)
VolumeQuota (VQ):
The optional VolumeQuota Sub-Type is only present if Volume Based
charging is used. In RADIUS Access-Accept message (PPS to SAD
direction), it indicates the Volume (in octets) allocated for the
session by the PrePaid server. In RADIUS Authorize Only Access-
Request message (SAD to PPS direction), it indicates the total
used volume (in octets) for both forward and reverse traffic
applicable to PrePaid accounting.
Sub-Type (=3): Sub-Type for VolumeQuotaOverflow
Length : length of VolumeQuotaOverflow attribute (= 4 octets)
VolumeQuotaOverflow (VQO):
The optional VolumeQuotaOverflow Sub-Type is used to indicate how
many times the VolumeQuota counter has wrapped around 2^32 over
the course of the service being provided.
Sub-Type (=4): Sub-Type for VolumeThreshold attribute
Length : length of VolumeThreshold attribute (= 6 octets)
VolumeThreshold (VT):
The VolumeThreshold Sub-Type shall always be present if
VolumeQuota is present in a RADIUS Access-Accept message (PPS to
SAD direction). It is generated by the PrePaid server and
indicates the volume (in octets) that shall be used before
requesting quota update. This threshold should not be larger than
the VolumeQuota.
Sub-Type (=5): Sub-Type for VolumeThresholdOverflow
Length : Length of VolumeThresholdOverflow attribute
(= 4 octets)
VolumeThresholdOverflow (VTO):
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The optional VolumeThresholdOverflow Sub-Type is used to indicate
how many times the VolumeThreshold counter has wrapped around
2^32 over the course of the service being provided.
Sub-Type (=6): Sub-Type for DurationQuota attribute
Length : length of DurationQuota attribute (= 6 octets)
DurationQuota (DQ):
The optional DurationQuota Sub-Type is only present if Duration
Based charging is used. In RADIUS Access-Accept message (PPS to
SAD direction), it indicates the Duration (in seconds) allocated
for the session by the PrePaid server. In on-line RADIUS Access-
Accept message (PPC to PPS direction), it indicates the total
Duration (in seconds) since the start of the accounting session
related to the QuotaID.
Sub-Type (=7): Sub-Type for DurationThreshold attribute
Length : length of DurationThreshold attribute (= 6 octets)
DurationThreshold (DT):
The DurationThreshold Sub-Type shall always be present if
DurationQuota is present in a RADIUS Access-Accept message (PPS
to SAD direction). It represents the duration (in seconds) that
shall be used by the session before requesting quota update. This
threshold should not be larger than the DurationQuota and shall
always be sent with the DurationQuota.
Sub-Type (=8): Sub-Type for Update-Reason attribute
Length : length of Update-Reason attribute (= 4 octets)
Update-Reason attribute (UR):
The Update-Reason Sub-Type shall be present in the on-line RADIUS
Access-Request message (SAD to PPS direction). It indicates the
reason for initiating the on-line quota update operation. Update
reasons 4, 5, 6, 7 and 8 indicate that the associated resources
are released at the client side, and therefore the PPS shall not
allocate a new quota in the RADIUS Access_Accept message.
1. Pre-initialization
2. Initial Request
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3. Threshold Reached
4. Quota Reached
5. Remote Forced Disconnect
6. Client Service Termination
7. ôAccess Serviceö Terminated
8. Service not established
9. One-Time Charging
Sub-Type (=9) : Sub-Type for PrePaidServer attribute
Length : Length of PrePaidServer
(IPv4 = 6 octets, IPv6= 18 octets
PrePaidServer:
The optional, multi-value PrePaidServer indicates the address of
the serving PrePaid System. If present, the Home RADIUS server
uses this address to route the message to the serving PrePaid
Server. The attribute may be sent by the Home RADIUS server. If
present in the incoming RADIUS Access-Accept message, the PDSN
shall send this attribute back without modifying it in the
subsequent RADIUS Access-Request message, except for the first
one. If multiple values are present, the PDSN shall not change
the order of the attributes.
Sub-Type (=10) : Sub-Type for Service ID
Length : Length of Service ID
Service-Id:
Opaque string that uniquely describes a service instance for which
we want to apply prepaid metering to. A Service-Id could be an IP
5-tuple (source address, source port, destination address,
destination port, protocol). If Service-ID is present in the PPAQ
the PPAQ applies to that Service. If a PPAQ does not contain a
Service-Id then the PPAQ applies to the Access Service.
Sub-Type (=11) : Sub-Type for Rating-Group-Id
Length : 6
Rating-Group-Id
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Identifies that this PPAQ is associated with resources allocated
to a Rating Group with the corresponding ID.
Sub-Type (=12) : Sub-Type for Termination-Action
Length : 6
This field is an enumeration of the action to take when the prepaid
server does not grant additional quota. Valid actions are as
follows:
0 Reserved
1 Terminate
2 Request More Quota
3 Redirect/Filter
Sub-Type (=13) : Pool-Id
Length : 6
Identifies the Pool that this quota is to be associated with.
Sub-Type (=14) : Pool-Multiplier
Length : 6
The pool-multiplier determines the weight that resources are
inserted into the pool and the rate at which resources are taken out
of the pool by this Service, or Rating-Group.
Sub-Type (=13) : Sub-Type for Resource Quota
Length : 6
The optional ResourceQuota Sub-Type is only present if Resource
Based charging is used or when One-Time charging is being used.
In RADIUS Access-Accept message (PPS to SAD direction), it
indicates the Resources allocated for the session by the PrePaid
server. In RADIUS Authorize Only Access-Request message (SAD to
PPS direction), it indicates the total used resource for both
forward and reverse traffic applicable to PrePaid accounting. In
one-time charging scenarios, the subtype represents the number of
units to charge the user or to credit the user (negative values).
Sub-Type (=14) : Sub-Type for Resource Quota Overflow
Length : 6
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Sub-Type (=15) : Sub-Type for ResourceThreshold
Length : 6
NOTES:
Either Volume-Quota, Time-Quota, or Resource-Quota MUST appear in
the attribute.
Volume Threshold may only appear if Volume Quota appears
A PPAQ MUST NOT CONTAIN both a Service-Id and a Rating-Group-Id.
A PPAQ that does not contain a Service-ID or a Rating-Group-Id
applies to the ôAccess Serviceö.
When the PPAQ contains a Pool-Id it MUST also contain the Pool-
Multiplier.
5.4
Prepaid Tariff Switching (PTS)
This specification defines the PTS attribute to allow for
changeovers from one service charge to another during service
execution.
Support for tariff switching is OPTIONAL for both PPC and PPS. PPCs
use the flag "Tariff Switching supported" of the AvailableInClient
subtype of the PPAC attribute to indicate support for tariff
switching; PPSs employ the PTS attribute to announce their support
for tariff switching. Details of this issue are specified later on,
when the format of the PTS attribute has been defined.
If a RADIUS message contains a PTS attribute, it MUST also contain
at least one PPAQ attribute. This requirement is related to the
identification of the service to which tariff switching applies. If
a RADIUS Access-Request message contains a PTS attribute or if it
contains a "Tariff Switching supported" flag, it MUST also contain
an Event-Timestamp RADIUS attribute (see [RFC2869]). This
requirement is related to the TariffSwitchInterval subtype of the
PTS attribute (see below).
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TYPE | LENGTH | SUB-TYPE 1 | LENGTH |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| QuotaIDentifier (QID) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SUB-TYPE 2 | LENGTH | VolumeUsedAfter- |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TariffSwitch (VUATS) | SUB-TYPE 3 | LENGTH |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| VUATSOverflow (VUATSO) | SUB-TYPE 4 | LENGTH |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TariffSwitchInterval (TSI) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SUB-TYPE 5 | LENGTH | TimeIntervalAfter- |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TariffSwitchUpdate (TITSU) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type : Value of PTS
Length: variable, greater than 8
Subtype (=1): QuotaIDentifier (QID)
Length : Length of QuotaIDentifier Subtype (= 6 octets)
The QID subtype MUST be present in each PTS attribute. In an
online RADIUS Access-Request message sent from the PPC to the
PPS, its value MUST be a quota identifier received previously
from the PPS and MUST be the same as a quota identifier of one of
the PPAQ attributes included the same RADIUS message.
A PPAQ attribute that is transported along with a PTS attribute
and has the same quota identifier value as the PTS attribute in
its own QID subfield shall be referred to as "accompanying PPAQ
attribute". If a PPS receives an Access-Request message from a
PPC, it associates a unique quota identifier to this service
access request. Thus, a quota identifier also identifies a
particular service.
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Subtype (=2): VolumeUsedAfterTariffSwitch (VUATS)
Length : Length of VolumeUsedAfterTariffSwitch Subtype
(= 6 octets)
The VolumeUsedAfterTariffSwitch subtype SHALL be used in online
RADIUS Access-Request messages (PPC to PPS direction). It
indicates the volume (in octets) used during a session after the
last tariff switch for the service specified via the QID subfield
and the accompanying PPAQ attribute (see the remarks under
"Subtype 1: QID").
Subtype (=3): VUATSOverflow (VUATSO)
Length : Length of VUATSOverflow Subtype (= 4 octets)
If an online RADIUS Access-Request message contains a VUATS
subfield and if the VolumeUsedAfterTariffSwitch has wrapped
around 2^32 over the course of provisioning the service
identified via the QID subfield, then the VUATSO subfield MUST be
present in the PTS attribute. In this case, it indicates how
many times the VolumeUsedAfterTariffSwitch has wrapped around
2^32. In all other cases, the VUATSO subfield MUST NOT be
present in the PTS attribute.
Subtype (=4): TariffSwitchInterval (TSI)
Length : Length of TSI Subtype (= 6 octets)
The TSI subtype MUST be present in each PTS attribute that is
part of a RADIUS Access-Accept message (PPS to PPC direction).
It indicates the interval (in seconds) between the value of
Event-Timestamp RADIUS attribute (see [RFC2869]) of the
corresponding RADIUS Access-Request message and the next tariff
switch condition.
Subtype (=5): TimeIntervalafterTariffSwitchUpdate (TITSU)
Length : Length of TITSU Subtype
(= 6 octets)
The PPS MUST include the TITSU subtype if there is another tarrif
switch period after this period. TITSU represents the length of
the tariff switch period in seconds. If this attribute is
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omitted or is zero, the tariff period that commences in TSI
seconds will last indefinitely or until a new PTS is received
with new information. If TITSU is specified, the prepaid client
must send a quota update before the end of the tariff switch
period as specified by TITSU.
If a RADIUS message contains a PTS attribute, it MUST also contain
at least one PPAQ attribute. The PTS will be associated to the PPAQ
by the QID. If multiple services are supported and if the PPAQ is
associated with a service as indicated by the Service-Id sub-
atrribute of the PPAQ, then the PTS will specify the tarrif switch
for that service. If the PPAQ does not have a Service-Id, then the
PTS will be the tarrif switch of the Access-Service.
If a PPC supports tariff switching then it MUST set the 0x00000040
(Tariff switching supported) flag of the AvailableInClient subtype
of the PPAC attribute that is contained in the Access-Request packet
starting the prepaid session.
5.5
Table of Attributes
TO BE COMPLETED.
Request Accept Reject Challenge # Attribute
Authorize_Only Request Accept Reject
6.
Security Considerations
The protocol exchanges described are susceptible to the same
vulnerabilities as RADIUS and it is recommended that IPsec be
employed to afford better security.
If IPsec is not available the protocol in this draft improves the
security of RADIUS. The various security enhancements are explained
in the following sections.
6.1
Authentication and Authorization
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RADIUS is susceptible to replay attacks during the Authentication
and Authorization procedures. A successful replay of the initial
Access-Request could result in an allocation of an initial quota.
To thwart such an attack...
6.2
Replenishing Procedure
A successful replay attacks of the Authorize Only Access-Request
could deplete the subscribers prepaid account.
To be completed.
7.
IANA Considerations
This document requires the assignment of new Radius attributes type
numbers for the following attributes:
1) Prepaid-Accounting-Capability (PPAC)
with subtype:
AvailableInClient
2) Prepaid-Accounting-Operation (PPAQ)
with subtypes:
QuotaID (QID)
VolumeQuota (VQ)
VolumeQuotaOverflow (VQO)
VolumeTreshold (VT)
VolumeTresholdOverflow (VTO)
DurationQuota (DQ)
DurationTreshold (DT)
UpdateReason (UR)
PrePaidServer (PPS)
ServiceID (SID)
RatingGroupId (RGID)
TerminationAction (TA)
PoolID (PID)
PoolMultiplier (PM)
Cost (COST)
TariffChangeTime (TCT)
3) Prepaid-Tariff-Switch (PTS)
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4) Session-Termination-Capability (STC)
5) International-Mobile-Subscriber-Identity (IMSI)
8.
Normative References
[RFC2026] Bradner, S., "The Internet Standards Process --
Revision 3", RFC 2026, October 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, March 1997.
[RFC2865] Rigney, C., Rubens, A., Simpson, W. and S. Willens,
"Remote Authentication Dial In User Server
(RADIUS)", RFC 2865, June 2000.
[RFC2866] Rigney, C., "RADIUS Accounting", RFC 2866, June
2000.
[RFC2869] Rigney, C., Willats, W., Calhoun, P., "RADIUS
Extensions", RFC 2869, June 2000.
[RFC2868] Zorn, G., Leifer, D., Rubens, A., Shriver, J.,
Holdrege, M., Goyret, I., "RADIUS Attributes for
Tunnel Protocol Support" , RFC 2868, June 2000.
[RFC3576] Chiba, M., Dommety, G., Eklund, M., Mitton, D.,
Aboba, B., "Dynamic Authorization Extensions to
Remote Authentication Dial-In User Service
(RADIUS)", RFC 3576, February 2003.
[RFC3748] Aboba, B., et al., "Extensible Authentication
Protocol", RFC 3748, June 2004.
9.
Informative References
[DIAMETERCC] Hakkala, H., et al., "Diamter Credit-Control
Application", Internet Draft, AAA WG, April 2004,
Work in Progress.
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[REDIRECT] "RADIUS Redirection", Internet Draft, Work in
progress.
10.
Call Flows
This section includes call flows illustrating various scenarios
enabled by this specification.
The following are used in the call flows:
RADIUS packets:
AR Access Request
ARA Access Accept
AC Accounting Requests
A Authorize-Only Access-Request
AA Access-Accept for Authorize-
Only Access-Request
RADIUS Attributes:
PPAQ PPAQ as defined in this
specification
SID One or more attributes
representing the Session that
the RADIUS packets is correlated
to.
PPAC PPAC as defined in this
specification
ASID Acct-Session-Id as defined by
RADIUS
MSID Acct-Multi-Session-Id as define
by RADIUS
PPAQ fields:
SRVID Service-Id
Reason Update-Reason
QID Quota-Id
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10.1
Simple Concurrent Services
In this scenario the Prepaid Client authenticates and authorizes the
user. The Prepaid Server responds back with Prepaid Quota for the
ôAccess Serviceö instance. The NAS then request quota for Service-
A.
Accounting is turned on.
NAS/ RADIUS/
PPC PPS
=== ===
| |
| AR{SID,PPAC} |
A |-------------------------------------------------->|
| |
| ARA{SID,PPAQ(QID=1,Q=100)} |
B |<--------------------------------------------------|
| |
| AC(start){ASID=25,MSID=13} |
C |-------------------------------------------------->|
| |
| A{SID,PPAQ(SRVID=SA, Reason=Initial} |
D |-------------------------------------------------->|
| |
| AA{SID,PPAQ(QID=200,SRVID=SA, Q=50)} |
E |<--------------------------------------------------|
| |
| AC(start){ASID=30,MSID=13, PPAQ } |
F |-------------------------------------------------->|
| |
| A{SID, PPAQ(QID=200 SRVID=SA, Q=50 Reason=Quota)}|
G |-------------------------------------------------->|
| |
| AA{SID,PPAQ(QID=300,SRVID=SA, Q=100)} |
H |<--------------------------------------------------|
| |
| A{SID, |
| PPAQ(QID=1, Q=100 Reason=Quota), |
| PPAQ(QID=300, SRVID=SA Q=100 Reason=Quota)} |
I |-------------------------------------------------->|
| |
| AA{SID,
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| PPAQ(QID=3, Q=200), |
| PPAQ(QID=303, SRVID=SA Q=150)} |
J |<--------------------------------------------------|
A This is the initial Access-Request that indicates the Prepaid
Capabilities of the NAS. In this scenario it will indicate
that Concurrent Session are supported. Access-Request also
includes SID (Session Id) which is the Session Identifier
assigned by this NAS to session. Session Identifier is out of
scope in this document. It can be a single attribute such as
3GPP2 Correlation ID or it could be a set of attributes that
define a session.
B RADIUS authenticates the user and determines that the user is
prepaid. RADIUS responds with a PPAQ for the ôAccess Serviceö
(PPAQ does not contain a Service-ID or Rating-Group-ID). The
PPAQ has a QID=1 assigned by the Prepaid System and Quota of
Q=100. The quota could be time or volume and may or may not
have a threshold associated with it.
C NAS starts the Access Service and generates an Accounting-
Request (Start) message as normal. It will include the Acct-
Session-Id and may include the Acct-Multi-Session-Id.
D The NAS wants to start a new Service, call it Service-A. It
sends an Authorize-Only access request to RADIUS. The SID
links this Authorize-Only access request to the initial
Authentication & Authorization (Step-A and Step-B).The
Authorize-Only message contains a PPAQ requesting quota for
Service-A, Update-Reason = Initial-Request.
E PPS checks the resources available to the user and assigns 50
units (time/volume etc) to this service. RADIUS sends an
Access Accept message contain a PPAQ assigning quota Q=50 for
Service-A. The PPAQ contains a QID = 200.
F NAS starts Service-A and sends an Accounting-Request (Start)
message for that service. Acct-Multi-Session-Id can be used
to tie all of the sessions in the accounting streams together.
G Quota for Service-A requires refreshing, the quota was
completely used). An Authorize-Only message is sent
containing a PPAQ with QID = 200 which corresponds to the
prior QID received for this service. Note QID is sufficient
for the PPS server to link this request to the previous
request and hence to the original authentication steps.
Therefore SID is not really required. The PPAQ will report the
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used part of the quota (50 units).
H RADIUS deducts the used quota from the users accounts and
reserves 50 more additional units for a total quota of 100
(Q=100) for Service-A. It sends back a PPAQ with QID=300.
I NAS needs to refresh both the ôAccess Serviceö and Service-A.
It sends an Authorize Only message contain two PPAQs, one for
the Main Service with QID=1 and one for Service-A with
QID=300. Each PPAQ reports the used resources so far and the
reason why the update is being sent.
J RADIUS responds back with two PPAQs. The PPAQ without the
Service-Id grants an additional 100 units for a total of 200
units to the ôAccess Serviceö û QID=3; the other PPAQ,
containing SRVID=SA grants an additional 50 units for a total
quota to service-a of 150 units û QID=303.
This step illustrates why SRVID needs to be specified in the
PPAQ. If it were not, then the NAS would not be able to
differentiate between the PPAQs. QIDs are not sufficient to
correlate the PPAQ to a service since they are changed (and
not necessarily sequentially) by the PPS at every transaction.
In this scenario, notice how each PPAQ attribute represents a
sequential conversation about a service between the Prepaid Client
and the Prepaid Server. The links between the messages are the QIDs
and the Service-Ids.
As well, notice how a SID is needed to tie the Authorize-Only
messages to the Authentication steps. This SID is only really
needed the first time a PPAQ is sent û since the PPAQ does not have
a QID.
Accounting messages have an Accounting-Session-ID. But that is not
enough to allow the back end system to associate that accounting
message with a particular Service. We therefore need the PPAQ in
the accounting message.
10.2
One-time Charging
In this One-time charging scenario, the Prepaid Client (PPC)
authenticates and authorizes the user and requests charging for a
service event requested by the user. The PPC already knows the
price to charge for the service event identified by SRVID=SA.
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Contributor
We would like to thank Hannes Tschofenig for his contributions to
this draft.
Acknowledgments
The authors would like to thank Mark Grayson (Cisco), Nagi Jonnala
and Tseno Tsenov for their contribution to this draft.
Author's Addresses
Avi Lior Parviz Yegani, Ph.D.
Bridgewater Systems Mobile Wireless Group
303 Terry Fox Drive Cisco Systems
Suite 100 3625 Cisco Way
Ottawa Ontario San Jose, CA 95134
Canada USA
avi@bridgewatersystems.com pyegani@cisco.com
Kuntal Chowdhury Yong Li
Starent Networks Bridgewater Systems
30 International Place, 3rd Flr 303 Terry Fox Drive
Tewksbury, MA 01876 Suite 100
kchowdhury@starentnetworks.com Ottawa Ontario
Canada
Yong.li@bridgewatersystems.com
Christian Guenther
Siemens
Otto-Hahn-Ring 6
81739 Munich
Germany
christian.guenther@siemens.com
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07.txt, and will expire 20 July, 2005.
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