One document matched: draft-lior-radius-prepaid-extensions-05.txt
Differences from draft-lior-radius-prepaid-extensions-04.txt
Network Working Group A. Lior
INTERNET-DRAFT Bridgewater Systems
Category: Informational P. Yegani
draft-lior-radius-prepaid-extensions-05.txt Cisco
Expires: 17 January, 2005 K. Chowdhury
Nortel
Y. Li
Bridgewater Systems
July 19, 2004
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 January 17, 2005
Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
Lior, et al. [Page 1]
RADIUS Extensions for PrePaid February 2004
Abstract
The draft presents an extension to the Remote Authentication Dial-In
User Service (RADIUS) protocol to support PrePaid data services for
a wide range of deployments such as Dial, Wireless, WLAN.
Consideration for roaming using mobile-ip is also given.
Table of Contents
1. Introduction...................................................4
1.1 Terminology................................................6
1.2 Requirements language......................................6
2. Architectural Model............................................6
2.1 Why not existing RADIUS attributes?.......................12
3. Use-cases.....................................................14
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......................19
3.5 Support for Roaming.......................................20
3.6 PrePaid termination.......................................21
4. Operations....................................................21
4.1 General Requirements......................................21
4.1.1 Broker AAA Requirements..............................21
4.2 Authentication and Authorization for Prepaid Enabled Service
Access Devices................................................22
4.3 Session Start Operation...................................24
4.4 Mid-Session Operation.....................................25
4.5 Dynamic Operations........................................27
4.5.1 Unsolicited Session Termination Operation............27
4.5.2 Unsolicited Change of Authorization Operation........28
4.6 Termination Operation.....................................28
4.7 Mobile IP Operations......................................29
4.8 Operation consideration for Multi-Services................30
4.8.1 Initial Quota Request................................31
4.8.2 Quota Update.........................................31
4.8.3 Termination..........................................32
4.8.4 Dynamic Operations...................................32
4.8.5 Support for Resource Pools...........................32
4.8.6 Error Handling.......................................33
4.9 Accounting Considerations.................................33
4.10 Service Access Device Operation..........................33
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RADIUS Extensions for PrePaid February 2004
4.11 Interoperability with Diameter Credit Control Application33
5. Attributes....................................................34
5.1 PPAC Attribute............................................34
5.2 Session Termination Capability............................35
5.3 PPAQ Attribute............................................35
5.4 Table of Attributes.......................................41
6. Security Considerations.......................................41
6.1 Authentication and Authorization..........................41
6.2 Replenishing Procedure....................................41
7. IANA Considerations...........................................42
8. Normative References..........................................42
9. Call Flows....................................................42
9.1 Simple Concurrent Services................................43
Acknowledgments..................................................46
Author's Addresses...............................................46
Intellectual Property Statement..................................47
Disclaimer of Validity...........................................47
Copyright Statement..............................................48
Expiration Date..................................................48
Lior, et al. Informational [Page 3]
RADIUS Extensions for PrePaid February 2004
1. Introduction
This draft describes RADIUS protocol extensions supporting 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 February 2004
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, by providing mechanisms to thwart replay attacks. As well,
mechanisms have been provided to terminate data sessions when fraud
is detected.
PrePaid System 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)
PrePaid Server(PPS)
Home agent (HA)
Home network
Home AAA (HAAA)
Broker AAA (BAAA)
Visited AAA (VAAA)
Foreign Agent (FA)
WLAN
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 Id. Example of Access Service
would be the Main Service instance of 3GPP2.
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. Architectural Model
The architectural model supports prepaid clients on a service access
device. A service access device (e.g. a NAS) typically provides a
access to data service to end-users. A service access device in an
entity on the data path that includes a RADIUS client.
When pre-paid service is used the service access device 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 service access device
(prepaid client) contacts the prepaid server with service event
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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
service access device. 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.
The requesting service access device 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.
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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.
In order to generalize the solution, in this paper we generalize the
Service Access Devices, 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 Service Access Device 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
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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);
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. Here the Service Access Device
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 Service Access Device
communicates with one or more HAAA servers in the network. To
provide redundancy more than one HAAA may be available to use by a
Service Access Device.
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
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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.
+----+ +----+ +----+ +-----+
| | | | | | | |
+------+ +-------+ +-|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 Service Access Device (NAS, WLAN
Access Point). The Service Access Device communicates with the
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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.
+------+ +-------+ +----+ +----+ +----+ +-----+
| | |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 Service
Access Devices
In figure 4, the Subscriber device establishes a prepaid session
between the Service Access Device in the foreign network, which has
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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 Service Access Device may be collocated with the Foreign
Agent (FA) in case of Mobile-IPv4. As the subscriber device moves
it establishes a connection with another Service Access Device 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 Service Access Device it MUST re-authenticate
at the new Service Access Device and de-associate or logoff from the
old Service Access Device. Furthermore, any unused quota at the old
Service Access Device 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 Service Access
Device. The speed at which resources can be returned depend on the
type of handoff procedure that is used. Some of the example of
handoffs in wireless networks are dormant handoff, active handoff
and fast handoff.
As well, notice that if the Service Access Devices 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.
2.1 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
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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
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
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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
Service Access Device 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.
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 will 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.
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To make the document as general as possible, the use cases cover the
experience from the Service Access Device 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 Service Access Device 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 include the PrePaid capabilities of the Service
Access Device. PrePaid capabilities MUST be included if the Service
Access Device 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 Service Access Device.
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 Service Access Device 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
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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 Service Access Device. 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 Service Access Device 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 Service Access Device 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 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 Service Access
Device will, continue the data service session until the new
threshold is reached. If the request for additional quota cannot be
fulfilled then the Service Access Device will let the subscriber use
up the remaining quota and terminate the session.
Alternatively, instead of terminating the session, the Service
Access Device 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
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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 Service Access Device 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 Service Access Device. 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 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) | +-------+
+--------------+
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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 IP 5-tuple (Source-IP and Port,
the Destination-IP and Port, and the protocol). Each Service is
allocated a Quota appropriate to the service.
3.3 Resource Pools
When working with multiple services which results in multiple quota
allocation another problem arises. Even though quotas are portioned
out in fractional parts of the users 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 Service Access Device 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.
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 above figure shows, Service-A and Service-B is 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.
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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
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
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is provisioned at the Service Access Device. 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.
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 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.
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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.
3.6 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
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 Service Access Device. 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 Service Access Device.
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
BAAA servers function is to forward the RADIUS packets as usual to
the appropriate RADIUS servers.
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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 Service Access
Devices
The Service Access Device initiates the authentication and
authorization procedure by sending a RADIUS Access-Request to the
HAAA.
If the Service Access Device 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 Service Access Device. These are
required in order to complete the PrePaid authorization procedures.
If the Service Access Device 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 Service Access Devices 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 Service Access Device 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
authenticated, the HAAA will send an Access-Reject message back to
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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 Service
Access Device 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
Service Access Device 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 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 Service Access Device. 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.
If the Prepaid server does not receive indication directly (via
Accounting-Request(start)) or indirectly, it SHOULD after some
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configurable time, deduce that the Session has not started. If the
Service Access Device supports termination capabilities, the PPS
SHOULD send a Disconnect Message to the Service Access Device to
ensure that the session is indeed dead.
4.4 Mid-Session Operation
During the lifetime of a PrePaid data session the Service Access
Device 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 Service Access Device MUST send an Access-Request with
Service-Type(6) set to a value of ôAuthorize Onlyö and the PPAQ(TBD)
attribute.
The Service Access Device 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 Service Access Device MUST include the Message-Authenticator(80)
attribute. The Service Access Device 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).
Once the Authorize Only Access-Request message is validated, the
HAAA SHALL forward the Authorize Only Access-Request to the
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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
site policies, if the HAAA fails to receive an Access-Accept or an
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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 Service Access Device 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 Service Access Device 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 Service Access Device 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 Service Access Device. 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
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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
that MUST contain identifiers that uniquely identify the
subscriberÆs data session and the Service Access Device servicing
that session.
If the Service Access Device 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 Service Access Device
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 Service Access Device 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 Service Access Device would follow the normal
procedures followed when a quota is used up.
4.6 Termination Operation
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The termination phase is initiated when either: the Subscriber logs
off; the quotas have been consumed, or when the Service Access
Device receives a Disconnect Message.
In the case where the user logged off, or the Service Access Device
receives a Disconnect Message, the Service Access Device will send
an Authorize-Only Access-Request message with a PPAQ(TBD) and
Update-Reason attribute set to 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 Service Access Device 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 Service
Access Device.
As the subscriber device associates with the new Service Access
Device (AP or PDSN that supports prepaid client capability), the
Service Access Device sends a RADIUS Access-Request and the
subscriber is re-authenticated and reauthorized. The Service Access
Device 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 Service Access Device 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 Service Access Device 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 Service Access Device 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
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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 Service Access Device
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 Service Access
Device 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 Service Access Device.
If the subscriber has roamed to an Service Access Device 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 Service Access Device. 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 Service Access Device 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.
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4.8.1 Initial Quota Request
When operations with multi-services is desired, the Service Access
Device 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 Service Access Device
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
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
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additional quota to the Service it MUST include the Termination-
Action subfield in the PPAQ that will instruct the Service Access
Device what to do with the service.
4.8.3 Termination
When an allotted quota for the service is used up the Service Access
Device 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.
If the Service is to be terminated then the Service Access Device
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 Service Access Device 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 Service Access Device 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
Service Access Device 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
Service Access Device 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
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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 Error Handling
If the Prepaid Server receives a PPAQ with an invalid QID it MUST
ignore that PPAQ.
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 Service Access Device 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
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Diameter based and the Service Access Device are RADIUS based; or
the Service Access Device 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.
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):
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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.
Others Reserved
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
Authorize Only Access-Request and Access-Accept messages. In
Authorize Only Access-Request messages it is used to report usage
and request further quota or request prepaid quota for a new service
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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.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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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
quota update RADIUS Access-Request message sent from the Service
Access Device 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 Service
Access Device direction), it indicates the Volume (in octets)
allocated for the session by the PrePaid server. In RADIUS
Authorize Only Access-Request message (Service Access Device 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):
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The VolumeThreshold Sub-Type shall always be present if
VolumeQuota is present in a RADIUS Access-Accept message (PPS to
Service Access Device 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):
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
Service Access Device 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 Service Access Device 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.
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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 (Service Access Device 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
3. Threshold Reached
4. Quota Reached
5. Remote Forced Disconnect
6. Client Service Termination
7. ôAccess Serviceö Terminated
8. Service not established
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:
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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
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.
NOTES:
Either Volume-Quota or Time-Quota MUST appear in the attribute.
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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 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
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.
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7. IANA Considerations
To be completed.
This draft does create RADIUS attributes. However, the authors
recognize that it may not be possible to obtain such attributes.
Therefore, in subsequent drafts it will be proposed to use a Vendor
space as an Application Space.
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.
[DIAMETERCC] Work in Progress.
[REDIRECT] RADIUS Redirection Internet Draft. Work in progress.
RFC 2284 EAP
9. Call Flows
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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
9.1 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.
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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,
| 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
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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
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
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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.
Acknowledgments
The authors would like to thank Mark Grayson (Cisco) and Nagi
Jonnala 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
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RADIUS Extensions for PrePaid February 2004
Ottawa Ontario San Jose, CA 95134
Canada USA
avi@bridgewatersystems.com pyegani@cisco.com
Kuntal Chowdhury Yong Li
Nortel Networks Bridgewater Systems
2221, Lakeside Blvd, 303 Terry Fox Drive
Richardson, TX-75082 Suite 100
chowdury@nortelnetworks.com Ottawa Ontario
Canada
Yong.li@bridgewatersystems.com
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RADIUS Extensions for PrePaid February 2004
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Lior, et al. Informational [Page 48]
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