Network Working Group X. Fu
Internet-Draft ZTE
Intended status: Standards Track V. Manral
Expires: April 10, 2012 Hewlett-Packard Corp.
D. McDysan
A. Malis
Verizon
S. Giacalone
Thomson Reuters
M. Betts
Q. Wang
ZTE
J. Drake
Juniper Networks
October 8, 2011
Traffic Engineering architecture for services aware MPLS
draft-fuxh-mpls-delay-loss-te-framework-02
Abstract
With more and more enterprises using cloud based services, the
distances between the user and the applications are growing. A lot
of the current applications are designed to work across LAN's and
have various inherent assumptions. For multiple applications such as
High Performance Computing and Electronic Financial markets, the
response times are critical as is packet loss, while other
applications require more throughput.
[RFC3031] describes the architecture of MPLS based networks. This
draft extends the MPLS architecture to allow for latency, loss and
jitter as properties. It describes requirements and control plane
implication for latency and packet loss as a traffic engineering
performance metric in today's network which is consisting of
potentially multiple layers of packet transport network and optical
transport network in order to make a accurate end-to-end latency and
loss prediction before a path is established.
Note MPLS architecture for Multicast will be taken up in a future
version of the draft.
Requirements Language
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].
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Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on April 10, 2012.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Architecture requirements overview . . . . . . . . . . . . . . 4
2.1. Communicate Latency and Loss as TE Metric . . . . . . . . 4
2.2. Requirement for Composite Link . . . . . . . . . . . . . . 5
2.3. Requirement for Hierarchy LSP . . . . . . . . . . . . . . 5
2.4. Latency Accumulation and Verification . . . . . . . . . . 5
2.5. Restoration, Protection and Rerouting . . . . . . . . . . 6
3. End-to-End Latency . . . . . . . . . . . . . . . . . . . . . . 6
4. End-to-End Jitter . . . . . . . . . . . . . . . . . . . . . . 7
5. End-to-End Loss . . . . . . . . . . . . . . . . . . . . . . . 8
6. Protocol Considerations . . . . . . . . . . . . . . . . . . . 8
7. Control Plane Implication . . . . . . . . . . . . . . . . . . 9
7.1. Implications for Routing . . . . . . . . . . . . . . . . . 9
7.2. Implications for Signaling . . . . . . . . . . . . . . . . 10
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
9. Security Considerations . . . . . . . . . . . . . . . . . . . 12
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
11.1. Normative References . . . . . . . . . . . . . . . . . . . 12
11.2. Informative References . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13
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1. Introduction
In High Frequency trading for Electronic Financial markets, computers
make decisions based on the Electronic Data received, without human
intervention. These trades now account for a majority of the trading
volumes and rely exclusively on ultra-low-latency direct market
access.
Extremely low latency measurements for MPLS LSP tunnels are defined
in [draft-ietf-mpls-loss-delay]. They allow a mechanism to measure
and monitor performance metrics for packet loss, and one-way and two-
way delay, as well as related metrics like delay variation and
channel throughput.
The measurements are however effective only after the LSP is created
and cannot be used by MPLS Path computation engine to define paths
that have the latest latency. This draft defines the architecture
used, so that end-to-end tunnels can be set up based on latency, loss
or jitter characteristics.
End-to-end service optimization based on latency and packet loss is a
key requirement for service provider. This type of function will be
adopted by their "premium" service customers. They would like to pay
for this "premium" service. Latency and loss on a route level will
help carriers' customers to make his provider selection decision.
2. Architecture requirements overview
2.1. Communicate Latency and Loss as TE Metric
The solution MUST provide a means to communicate latency, latency
variation and packet loss of links and nodes as a traffic engineering
performance metric into IGP.
Latency, latency variation and packet loss may be unstable, for
example, if queueing latency were included, then IGP could become
unstable. The solution MUST provide a means to control latency and
loss IGP message advertisement and avoid unstable when the latency,
latency variation and packet loss value changes.
Path computation entity MUST have the capability to compute one end-
to-end path with latency and packet loss constraint. For example, it
has the capability to compute a route with X amount of bandwidth with
less than Y ms of latency and Z% packet loss limit based on the
latency and packet loss traffic engineering database. It MUST also
support the path computation with routing constraints combination
with pre-defined priorities, e.g., SRLG diversity, latency, loss and
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cost.
2.2. Requirement for Composite Link
One end-to-end LSP may traverses some Composite Links [CL-REQ]. Even
if the transport technology (e.g., OTN) component links are
identical, the latency and packet loss characteristics of the
component links may differ.
The solution MUST provide a means to indicate that a traffic flow
should select a component link with minimum latency and/or packet
loss, maximum acceptable latency and/or packet loss value and maximum
acceptable delay variation value as specified by protocol. The
endpoints of Composite Link will take these parameters into account
for component link selection or creation. The exact details for
component links will be taken up seperately and are not part of this
document.
2.3. Requirement for Hierarchy LSP
One end-to-end LSP may traverse a server layer. There will be some
latency and packet loss constraint requirement for the segment route
in server layer.
The solution MUST provide a means to indicate FA selection or FA-LSP
creation with minimum latency and/or packet loss, maximum acceptable
latency and/or packet loss value and maximum acceptable delay
variation value. The boundary nodes of FA-LSP will take these
parameters into account for FA selection or FA-LSP creation.
2.4. Latency Accumulation and Verification
The solution SHOULD provide a means to accumulate (e.g., sum) of
latency information of links and nodes along one LSP across multi-
domain (e.g., Inter-AS, Inter-Area or Multi-Layer) so that an latency
validation decision can be made at the source node. One-way and
round-trip latency collection along the LSP by signaling protocol and
latency verification at the end of LSP should be supported.
The accumulation of the delay is "simple" for the static component
i.e. its a linear addition, the dynamic/network loading component is
more interesting and would involve some estimate of the "worst case".
However, method of deriving this worst case appears to be more in the
scope of Network Operator policy than standards i.e. the operator
needs to decide, based on the SLAs offered, the required confidence
level.
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2.5. Restoration, Protection and Rerouting
Some customers may insist on having the ability to re-route if the
latency and loss SLA is not being met. If a "provisioned" end-to-end
LSP latency and/or loss could not meet the latency and loss agreement
between operator and his user, the solution SHOULD support pre-
defined or dynamic re-routing to handle this case based on the local
policy.
If a "provisioned" end-to-end LSP latency and/or loss performance is
improved (i.e., beyond a configurable minimum value) because of some
segment performance promotion, the solution SHOULD support the re-
routing to optimize latency and/or loss end-to-end cost.
The latency performance of pre-defined protection or dynamic re-
routing LSP MUST meet the latency SLA parameter. The difference of
latency value between primary and protection/restoration path SHOULD
be zero.
As a result of the change of latency and loss in the LSP, current LSP
may be frequently switched to a new LSP with a appropriate latency
and packet loss value. In order to avoid this, the solution SHOULD
indicate the switchover of the LSP according to maximum acceptable
change latency and packet loss value.
3. End-to-End Latency
Procedures to measure latency and loss has been provided in ITU-T
[Y.1731], [G.709] and [ietf-mpls-loss-delay]. The control plane can
be independent of the mechanism used and different mechanisms can be
used for measurement based on different standards.
Latency on a path has two sources: Node latency which is caused by
the node as a result of process time in each node and: Link latency
as a result of packet/frame transit time between two neighbouring
nodes or a FA-LSP/ Composite Link [CL-REQ].
Latency or one-way delay is the time it takes for a packet within a
stream going from measurement point 1 to measurement point 2.
The architecture uses assumption that the sum of the latencies of the
individual components approximately adds up to the average latency of
an LSP. Though using the sum may not be perfect, it however gives a
good approximation that can be used for Traffic Engineering (TE)
purposes.
The total latency of an LSP consists of the sum of the latency of the
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LSP hop, as well as the average latency of switching on a device,
which may vary based on queuing and buffering.
Hop latency can be measured by getting the latency measurement
between the egress of one MPLS LSR to the ingress of the nexthop LSR.
This value may be constant for most part, unless there is protection
switching, or other similar changes at a lower layer.
The switching latency on a device, can be measured internally, and
multiple mechanisms and data structures to do the same have been
defined. Add references to papers by Verghese, Kompella, Duffield.
Though the mechanisms define how to do flow based measurements, the
amount of information gathered in such a case, may become too
cumbersome for the Path Computation element to effectively use.
An approximation of Flow based measurement is the per DSCP value,
measurement from the ingress of one port to the egress of every other
port in the device.
Another approximation that can be used is per interface DSCP based
measurement, which can be an agrregate of the average measurements
per interface. The average can itself be calculated in ways, so as
to provide closer approximation.
For the purpose of this draft it is assumed that the node latency is
a small factor of the total latency in the networks where this
solution is deployed. The node latency is hence ignored for the
benefit of simplicity.
The average link delay over a configurable interval should be
reported by data plane in micro-seconds.
4. End-to-End Jitter
Jitter or Packet Delay Variation of a packet within a stream of
packets is defined for a selected pair of packets in the stream going
from measurement point 1 to measurement point 2.
The architecture uses assumption that the sum of the jitter of the
individual components approximately adds up to the average jitter of
an LSP. Though using the sum may not be perfect, it however gives a
good approximation that can be used for Traffic Engineering (TE)
purposes.
There may be very less jitter on a link-hop basis.
The buffering and queuing within a device will lead to the jitter.
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Just like latency measurements, jitter measurements can be
appproximated as either per DSCP per port pair (Ingresss and Egress)
or as per DSCP per egress port.
For the purpose of this draft it is assumed that the node latency is
a small factor of the total latency in the networks where this
solution is deployed. The node latency is hence ignored for the
benefit of simplicity.
The jitter is measured in terms of 10's of nano-seconds.
5. End-to-End Loss
Loss or Packet Drop probability of a packet within a stream of
packets is defined as the number of packets dropped within a given
interval.
The architecture uses assumption that the sum of the loss of the
individual components approximately adds up to the average loss of an
LSP. Though using the sum may not be perfect, it however gives a
good approximation that can be used for Traffic Engineering (TE)
purposes.
There may be very less loss on a link-hop basis, except in case of
physical link issues.
The buffering and queuing mechanisms within a device will decide
which packet is to be dropped. Just like latency and jitter
measurements, the loss can best be appproximated as either per DSCP
per port pair (Ingresss and Egress) or as per DSCP per egress port.
The loss is measured in terms of the number of packets per million
packets.
6. Protocol Considerations
The protocol metrics above can be sent in IGP protocol packets RFC
3630. They can then be used by the Path Computation engine to decide
paths with the desired path properties.
As Link-state IGP information is flooded throughout an area, frequent
changes can cause a lot of control traffic. To prevent such
flooding, data should only be flooded when it crosses a certain
configured maximum.
A seperate measurement should be done for an LSP when it is UP. Also
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LSP's path should only be recalculated when the end-to-end metrics
changes in a way it becomes more than desired.
7. Control Plane Implication
7.1. Implications for Routing
The latency and packet loss performance metric MUST be advertised
into path computation entity by IGP (etc., OSPF-TE or IS-IS-TE) to
perform route computation and network planning based on latency and
packet loss SLA target.
Latency, latecny variation and packet loss value MUST be reported as
a average value which is calculated by data plane.
Latency and packet loss characteristics of these links and nodes may
change dynamically. In order to control IGP messaging and avoid
being unstable when the latency, latency variation and packet loss
value changes, a threshold and a limit on rate of change MUST be
configured to control plane.
If any latency and packet loss values change and over than the
threshold and a limit on rate of change, then the latency and loss
change of link MUST be notified to the IGP again. The receiving node
detrimines whether the link affects any of these LSPs for which it is
ingress. If there are, it must determine whether those LSPs still
meet end-to-end performance objectives.
A minimum value MUST be configured to control plane. If the link
performance improves beyond a configurable minimum value, it must be
re-advertised. The receiving node detrimines whether a "provisioned"
end-to-end LSP latency and/or loss performance is improved because of
some segment performance promotion.
It is sometimes important for paths that desire low latency is to
avoid nodes that have a significant contribution to latency. Control
plane should report two components of the delay, "static" and
"dynamic". The dynamic component is always caused by traffic loading
and queuing. The "dynamic" portion SHOULD be reported as an
approximate value. It should be a fixed latency through the node
without any queuing. Link latency attribute should also take into
account the latency of node, i.e., the latency between the incoming
port and the outgoing port of a network element. Half of the fixed
node latency can be added to each link.
When the Composite Links [CL-REQ] is advertised into IGP, there are
following considerations.
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o One option is that the latency and packet loss of composite link
may be the range (e.g., at least minimum and maximum) latency
value of all component links. It may also be the maximum latency
value of all component links. In both cases, only partial
information is transmited in the IGP. So the path computation
entity has insufficient information to determine whether a
particular path can support its latency and packet loss
requirements. This leads to signaling crankback.
o Another option is that latency and packet loss of each component
link within one Composite Link could be advertised but having only
one IGP adjacency.
One end-to-end LSP (e.g., in IP/MPLS or MPLS-TP network) may traverse
a FA-LSP of server layer (e.g., OTN rings). The boundary nodes of
the FA-LSP SHOULD be aware of the latency and packet loss information
of this FA-LSP.
If the FA-LSP is able to form a routing adjacency and/or as a TE link
in the client network, the total latency and packet loss value of the
FA-LSP can be as an input to a transformation that results in a FA
traffic engineering metric and advertised into the client layer
routing instances. Note that this metric will include the latency
and packet loss of the links and nodes that the trail traverses.
If total latency and packet loss information of the FA-LSP changes
(e.g., due to a maintenance action or failure in OTN rings), the
boundary node of the FA-LSP will receive the TE link information
advertisement including the latency and packet value which is already
changed and if it is over than the threshold and a limit on rate of
change, then it will compute the total latency and packet value of
the FA-LSP again. If the total latency and packet loss value of FA-
LSP changes, the client layer MUST also be notified about the latest
value of FA. The client layer can then decide if it will accept the
increased latency and packet loss or request a new path that meets
the latency and packet loss requirement.
7.2. Implications for Signaling
In order to assign the LSP to one of component links with different
latency and loss characteristics, RSVP-TE message needs to carry a
indication of request minimum latency and/or packet loss, maximum
acceptable latency and/or packet loss value and maximum acceptable
delay variation value for the component link selection or creation.
The composite link will take these parameters into account when
assigning traffic of LSP to a component link.
One end-to-end LSP (e.g., in IP/MPLS or MPLS-TP network) may traverse
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a FA-LSP of server layer (e.g., OTN rings). There will be some
latency and packet loss constraint requirement for the segment route
in server layer. So RSVP-TE message needs to carry a indication of
request minimum latency and/or packet loss, maximum acceptable
latency and/or packet loss value and maximum acceptable delay
variation value. The boundary nodes of FA-LSP will take these
parameters into account for FA selection or FA-LSP creation.
RSVP-TE needs to be extended to accumulate (e.g., sum) latency
information of links and nodes along one LSP across multi-domain
(e.g., Inter-AS, Inter-Area or Multi-Layer) so that an latency
verification can be made at end points. One-way and round-trip
latency collection along the LSP by signaling protocol can be
supported. So the end points of this LSP can verify whether the
total amount of latency could meet the latency agreement between
operator and his user. When RSVP-TE signaling is used, the source
can determine if the latency requirement is met much more rapidly
than performing the actual end-to-end latency measurement.
Restoration, protection and equipment variations can impact
"provisioned" latency and packet loss (e.g., latency and packet loss
increase). For example, restoration/provisioning action in transport
network that increases latency seen by packet network observable by
customers, possibly violating SLAs. The change of one end-to-end LSP
latency and packet loss performance MUST be known by source and/or
sink node. So it can inform the higher layer network of a latency
and packet loss change. The latency or packet loss change of links
and nodes will affect one end-to-end LSPs total amount of latency or
packet loss. Applications can fail beyond an application-specific
threshold. Some remedy mechanism could be used.
Pre-defined protection or dynamic re-routing could be triggered to
handle this case. In the case of predefined protection, large
amounts of redundant capacity may have a significant negative impact
on the overall network cost. Service provider may have many layers
of pre-defined restoration for this transfer, but they have to
duplicate restoration resources at significant cost. Solution should
provides some mechanisms to avoid the duplicate restoration and
reduce the network cost. Dynamic re-routing also has to face the
risk of resource limitation. So the choice of mechanism MUST be
based on SLA or policy. In the case where the latency SLA can not be
met after a re-route is attempted, control plane should report an
alarm to management plane. It could also try restoration for several
times which could be configured.
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8. IANA Considerations
No new IANA consideration are raised by this document.
9. Security Considerations
This document raises no new security issues.
10. Acknowledgements
TBD.
11. References
11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, December 2001.
[RFC3473] Berger, L., "Generalized Multi-Protocol Label Switching
(GMPLS) Signaling Resource ReserVation Protocol-Traffic
Engineering (RSVP-TE) Extensions", RFC 3473, January 2003.
[RFC3477] Kompella, K. and Y. Rekhter, "Signalling Unnumbered Links
in Resource ReSerVation Protocol - Traffic Engineering
(RSVP-TE)", RFC 3477, January 2003.
[RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
(TE) Extensions to OSPF Version 2", RFC 3630,
September 2003.
[RFC4203] Kompella, K. and Y. Rekhter, "OSPF Extensions in Support
of Generalized Multi-Protocol Label Switching (GMPLS)",
RFC 4203, October 2005.
11.2. Informative References
[CL-REQ] C. Villamizar, "Requirements for MPLS Over a Composite
Link", draft-ietf-rtgwg-cl-requirement-04 .
[EXPRESS-PATH]
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S. Giacalone, "OSPF Traffic Engineering (TE) Express
Path", draft-giacalone-ospf-te-express-path-01 .
[G.709] ITU-T Recommendation G.709, "Interfaces for the Optical
Transport Network (OTN)", December 2009.
[Y.1731] ITU-T Recommendation Y.1731, "OAM functions and mechanisms
for Ethernet based networks", Feb 2008.
[ietf-mpls-loss-delay]
D. Frost, "Packet Loss and Delay Measurement for MPLS
Networks", draft-ietf-mpls-loss-delay-03 .
Authors' Addresses
Xihua Fu
ZTE
Email: fu.xihua@zte.com.cn
Vishwas Manral
Hewlett-Packard Corp.
191111 Pruneridge Ave.
Cupertino, CA 95014
US
Phone: 408-447-1497
Email: vishwas.manral@hp.com
URI:
Dave McDysan
Verizon
Email: dave.mcdysan@verizon.com
Andrew Malis
Verizon
Email: andrew.g.malis@verizon.com
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Spencer Giacalone
Thomson Reuters
195 Broadway
New York, NY 10007
US
Phone: 646-822-3000
Email: spencer.giacalone@thomsonreuters.com
URI:
Malcolm Betts
ZTE
Email: malcolm.betts@zte.com.cn
Qilei Wang
ZTE
Email: wang.qilei@zte.com.cn
John Drake
Juniper Networks
Email: jdrake@juniper.net
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