One document matched: draft-shah-pwe3-pw-qos-signaling-01.txt
Differences from draft-shah-pwe3-pw-qos-signaling-00.txt
Himanshu Shah
Ciena Corp
Ping Pan
HammerHead Systems
PWE3 Working Group
Internet Draft Hamid Ould-Brahim
Nortel Networks
February 2005 Chris Metz
Expires: August 2005 Cisco Systems
Qos Signaling for PW
draft-shah-pwe3-pw-qos-signaling-01.txt
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Abstract
This document discusses how a tail-end PE can signal the Quality of
Service parameters of the local Attachment Circuit to the head-end
PE for appropriate Pseudowire generation from head to tail end PE.
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The Pseudowires traditionally provide connectivity between two
Attachment Circuits that are on the edges of a service providerÆs
network. A service provider assigns specific QOS parameters (i.e.
via manual configuration or dynamic signaling) to these Attachment
Circuits based on the service sold to the customer. In order to
interconnect and maintain the same level of service parameters
across the service provider network, it is prudent that the Provider
Edge devices that are endpoints of the Pseudowires, select or create
a suitable transport path that meets the PseudowireÆs quality of
service requirements. It is also possible that a PE may use
appropriate policing for traffic entering Pseudowire that match
remote Attachment CircuitÆs capabilities as well as perform an
admission control check to ensure that the PE can indeed support the
desired QOS.
In order to accomplish an integrated service delivery it becomes
necessary that each PE understand the QOS requirements of the remote
Attachment Circuit.
This draft proposes an extension to the PWE3 control signaling to
enable a PE to exchange QOS parameters of the local Attachment
Circuit at the time of the PW establishment.
With advent of recent interest in multi-segmented Pseudowire
signaling the Pseudowire specific QOS requirements through multiple
PSN domains has become an important step in procuring the right
resources through intermediate PEs that perform Pseudowire
stitching.
In this revision we have added some more parameters that address
some of the requirements placed by Multi-hop Pseudowire Signaling.
1.0 Specification of Requirements
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 RFC 2119.
2.0 Introduction
The [PWE3-CONTROL] draft describes how two PEs signal PW-FEC to each
other in order to establish a pseudowire. The PW-FEC is exchanged
over the targeted LDP session and contains Pseudowire signaling
information that includes interface parameters of the local
Attachment Circuit.
This draft describes a mechanism whereby additional information,
such as QOS parameters of the local Attachment Circuit can be
dispatched with the VC-FEC in a backward compatible fashion.
This document specifies QOS TLV that can be included in the initial
Label Mapping Message and subsequently in LDP notification message
for conveying up-to-date information about the Pseudowire.
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This proposal is orthogonal to the type of PW-FEC used. Both PWid
FEC (value 128) and Generalized ID FEC (value 129) can make use of
the new additions. In the case of PWid FEC the signaled QOS
information can be related to the GROUP_ID value when this field is
used in signaling. The term VC-FEC and PW-FEC is used
interchangeably in this document and refers to both the FEC Ids.
It is expected that capability of exchanging QOS information
dynamically would facilitate various applications to optimize the
use of core resources effectively. For example, a PE may use this
signaling for backpressure when æforward congestionÆ is detected on
its local AC.
3.0 Capability Learning for QOS exchange
For the purpose of learning remote end capabilities and for the
purpose of signaling to the remote end the local capabilities, this
draft suggests that the QOS TLV be included initially in the Label
Mapping message and particularly in the Optional Parameter field of
Label Mapping Message. When subsequent updates are required (after
the PW is established), the sender PE will use the LDP notification
message to convey an update of the new information.
Note that the mechanism described in this draft allows a given PE
that does not support the QOS TLV to be able to establish a
Pseudowire using normal operations. Indeed, the PEs that are
upgraded with such new functionality, examine the optional
parameters and note QOS TLV to learn the capability of the sending
peer. The sender must include the QOS TLV that it intends to use
later as an update, in the Label Mapping message that is used to
setup the FIB. Typically, such Label Mapping message is either the
first Label Mapping message or the one right after the Label
Withdraw/Release message and is referred to in this document as a
ôLearning Label Mappingö message.
The absence of a given TLV in the Learning Label Mapping message
indicates to the receiver that the sending PE is either not capable
of processing such TLV or does not wish to engage in dynamic update
exchange for that TLV. The absence of QOS TLV indicates to the
receiving PE that normal PW signaling procedures should be used to
establish the PW (i.e., no inclusion of the optional TLVs in the
reverse label mapping). Similarly, the receiving PE that has not
been upgraded with the new TLVs and receives a label mapping with
the new TLVs will just ignore these TLVs during label mapping
processing phase.
The capability learning aspect of the PW QOS is only applicable for
the use of QOS TLV for dynamic update notifications. It does not
change the need to send the initial QOS TLV, irrespective of whether
remote PE is capable of processing the optional TLV or not.
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It is also possible that the receiving PE is capable of processing
QOS TLV and uses unacceptable QOS requirement as a criterion to
release the VC-FEC. In such event, a status TLV is defined to be
included in the optional parameter field of the label release
message that informs the remote PE about the reasons for the
rejection.
4.0 Pseudowire QOS TLV
The pseudowire QOS TLV is used to notify the remote PE about Quality
of Service requirements of the local Attachment Circuit.
As stated earlier, this information can also be passed as an update.
It is possible that receiver may either adjust QOS parameters of the
existing tunnel or may respond to the update by first withdrawing
the advertised PW label and re-advertise new PW label with same VC-
FEC.
It is possible to send more than one QOS TLVs. The Flag field in the
QOS TLV provides the context for each TLV.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1|0| PW QOS TLV (TBD) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Committed Information Rate (CIR) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Peak Information Rate (PIR) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Committed Burst Size (CBS) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Peak Burst Size (PBS) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags |R|D| Number of Sub-TLVs |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-TLVs (1-n) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Traffic Engineering Parameters
Each TE parameter is encoded as a 32-bit IEEE single precision
floating-point number. The CIR and PIR are in units of bytes per
second while CBS and PBS are in units of bytes.
Flags
This field contains set of flag. There are two flags bits are
defined currently. They are,
D û Direction flag. The value zero in Direction Flag means Forward
direction. The forward direction typically represents the
direction from the advertiser to the receiver. The value 1 in
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Direction flag means Reverse direction. The reverse direction
typically represents the return path to the advertiser.
R û Request/Available flag. The value zero in Request/Available
flag means Requested QOS by the advertiser. The value one means
what is available. In multi-segment PW signaling intermediate PEs
can adjust the available QOS when propagating the signal towards
the destination PE.
The rest of the bits in the Flag field are reserved. They should
be set to zero on send and ignored on receive.
Number of Sub-TLVs
This field identifies the number of Sub-TLVs that follow. In
absence of any Sub-TLVs, this field should be set to zero. This
field is mandatory.
Sub-TLVs (1-n)
The n number of Type-Length-Value fields where ænÆ is equal to
æNumber of Sub-TLVsÆ field. The presence of field facilitates
future/proprietary extensions
5.0 New LDP Status Codes
The PW Status TLV described in this document is the status code
point that may be used by the receiving PE to inform the sender the
specific reasons for not accepting the Label Mapping message. The
status TLV should be included in the æoptional parameterÆ field of
the Label Release message.
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The format of the PW Status TLV is:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1|0| PW Status (0x096A) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Status Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where the status code is a 4 octet bit field is specified in the PW
IANA Allocations document [13].
According to Section 4.4 in RFC3036, we can define new status codes
in the range of 0x20000000-0x3effffff. Here are the new status
codes:
- 0x20000003 "TC is OK"
- 0x20000004 "Cannot accept the TC parameters"
- 0x20000005 "Preempted due to TC processing"
6.0 General Procedures
The PW QOS TLV is included in the Optional Parameter Field of the
Label Mapping Message and the LDP Notification Message. In case of
Label Mapping Message, Optional Parameter Field follows the Label
TLV object. In LDP Notification Message, Optional Parameter Field
must include PW-FEC TLV before QOS-TLV. As described above, exchange
of QOS TLV in Notification Message is determined by the capability
learning during the initial Label Mapping exchange.
The PW QOS TLV conveys Quality of Service parameters that
advertising PE would like remote PE to consider when
selecting/creating appropriate transport tunnel to carry the
Pseudowire from remote PE to the advertising PE. The Quality of
Service parameters can also be used by the receiving PE to select
appropriate policer for his Attached Circuit or perform an admission
control check.
The QOS TLV is optional. The received PE uses this information as a
suggestion.
Note that use of PW QOS exchange helps utilize core resources
effectively in the following manner.
. Head end PE selects a transport tunnel that best suits remote
Attachment CircuitÆs QOS requirement
. More PWs can be multiplexed over a transport tunnel
. Transport tunnel can be right-sized with various upsize and
downsize thresholds
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. Eliminates the wastage of packet forwarding resources in the
core when received traffic exceeds the Attachment Circuit QOS
criteria at the tail end.
7.0 The role of PW QOS in multi-hop PW signaling
In a multi-segmented Pseudo-wire, each intermediate PE stitches two
pseudo-wire segments in order to create a pseudo-wire from source PE
to destination PE through multiple PSN domains. In this topology it
becomes necessary that each PE hop æknowsÆ what the QOS requirements
are for this multi-segmented pseudo-wire so that it can procure the
correct network resources in each direction.
It is expected that source PE may include a set of QOS TLVs, one for
each direction, requested and available QOS parameters in the
initial Label Mapping message. Each intermediate PE then uses this
QOS information to acquire network resources and if unsuccessful, to
reject the multi-hop Pseudo-wire generation through that PE hop. The
Available QOS TLV could be adjusted at each PE hop in order for the
destination PE to determine the suitability of the end-to-end
Pseudo-wire path.
The details for signaling PW QOS and itÆs processing at each hops as
well as at the source and destination PE would be discussed in the
future revision of this document.
8.0 Security Considerations
The security aspects of this solution will be discussed at a later
time.
9.0 References
[PWE3-CONTROL] Martini et. Al., ôTransport of Layer 2 Frames Over
MPLSö, draft-ietf-pwe3-control-protocol-14.txt, December 2004 (work
in progress)
Acknowledgement
Author's Address
Himanshu Shah
Ciena Corp
35 Nagog Park
Acton, MA 01720
Email: hshah@ciena.com
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Ping Pan
HammerHead Systems
Email : pingpan@cs.columbia.edu
Hamid Ould-Brahim
Nortel Networks
P O Box 3511 Station C
Ottawa, ON K1Y 4H7, Canada
Email: hbrahim@nortelnetworks.com
Chris Metz
Cisco Systems, Inc.
3700 Cisco Way
San Jose, Ca. 95134
Email: chmetz@cisco.com
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