Network Working Group T. Li
Request for Comments: 2430 Juniper Networks
Category: Informational Y. Rekhter
Cisco Systems
October 1998
A Provider Architecture for
Differentiated Services and Traffic Engineering
(PASTE)
Status of this Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (1998). All Rights Reserved.
1.0 Abstract
This document describes the Provider Architecture for Differentiated
Services and Traffic Engineering (PASTE) for Internet Service
Providers (ISPs). Providing differentiated services in ISPs is a
challenge because the scaling problems presented by the sheer number
of flows present in large ISPs makes the cost of maintaining per-flow
state unacceptable. Coupled with this, large ISPs need the ability
to perform traffic engineering by directing aggregated flows of
traffic along specific paths.
PASTE addresses these issues by using Multiprotocol Label Switching
(MPLS) [1] and the Resource Reservation Protocol (RSVP) [2] to create
a scalable traffic management architecture that supports
differentiated services. This document assumes that the reader has
at least some familiarity with both of these technologies.
2.0 Terminology
In common usage, a packet flow, or a flow, refers to a unidirectional
stream of packets, distributed over time. Typically a flow has very
fine granularity and reflects a single interchange between hosts,
such as a TCP connection. An aggregated flow is a number of flows
that share forwarding state and a single resource reservation along a
sequence of routers.
Li & Rekhter Informational [Page 1]
RFC 2430 PASTE October 1998
One mechanism for supporting aggregated flows is Multiprotocol Label
Switching (MPLS). In MPLS, packets are tunneled by wrapping them in
a minimal header [3]. Each such header contains a label, that
carries both forwarding and resource reservation semantics. MPLS
defines mechanisms to install label-based forwarding information
along a series of Label Switching Routers (LSRs) to construct a Label
Switched Path (LSP). LSPs can also be associated with resource
reservation information.
One protocol for constructing such LSPs is the Resource Reservation
Protocol (RSVP) [4]. When used with the Explicit Route Object (ERO)
[5], RSVP can be used to construct an LSP along an explicit route
[6].
To support differentiated services, packets are divided into separate
traffic classes. For conceptual purposes, we will discuss three
different traffic classes: Best Effort, Priority, and Network
Control. The exact number of subdivisions within each class is to be
defined.
Network Control traffic primarily consists of routing protocols and
network management traffic. If Network Control traffic is dropped,
routing protocols can fail or flap, resulting in network instability.
Thus, Network Control must have very low drop preference. However,
Network Control traffic is generally insensitive to moderate delays
and requires a relatively small amount of bandwidth. A small
bandwidth guarantee is sufficient to insure that Network Control
traffic operates correctly.
Priority traffic is likely to come in many flavors, depending on the
application. Particular flows may require bandwidth guarantees,
jitter guarantees, or upper bounds on delay. For the purposes of
this memo, we will not distinguish the subdivisions of priority
traffic. All priority traffic is assumed to have an explicit
resource reservation.
Currently, the vast majority of traffic in ISPs is Best Effort
traffic. This traffic is, for the most part, delay insensitive and
reasonably adaptive to congestion.
When flows are aggregated according to their traffic class and then
the aggregated flow is placed inside a LSP, we call the result a
traffic trunk, or simply a trunk. The traffic class of a packet is
orthogonal to the LSP that it is on, so many different trunks, each
with its own traffic class, may share an LSP if they have different
traffic classes.
Li & Rekhter Informational [Page 2]
RFC 2430 PASTE October 1998
3.0 Introduction
The next generation of the Internet presents special challenges that
must be addressed by a single, coordinated architecture. While this
architecture allows for distinction between ISPs, it also defines a
framework within which ISPs may provide end-to-end differentiated
services in a coordinated and reliable fashion. With such an
architecture, an ISP would be able to craft common agreements for the
handling of differentiated services in a consistent fashion,
facilitating end-to-end differentiated services via a composition of
these agreements. Thus, the goal of this document is to describe an
architecture for providing differentiated services within the ISPs of
the Internet, while including support for other forthcoming needs
such as traffic engineering. While this document addresses the needs
of the ISPs, its applicability is not limited to the ISPs. The same
architecture could be used in any large, multiprovider catenet
needing differentiated services.
This document only discusses unicast services. Extensions to the
architecture to support multicast are a subject for future research.
One of the primary considerations in any ISP architecture is
scalability. Solutions that have state growth proportional to the
size of the Internet result in growth rates exceeding Moore's law,
making such solutions intractable in the long term. Thus, solutions
that use mechanisms with very limited growth rates are strongly
preferred.
Discussions of differentiated services to date have frequently
resulted in solutions that require per-flow state or per-flow
queuing. As the number of flows in an ISP within the "default-free
zone of the Internet" scales with the size of the Internet, the
growth rate is difficult to support and argues strongly for a
solution with lower state requirements. Simultaneously, supporting
differentiated services is a significant benefit to most ISPs. Such
support would allow providers to offer special services such as
priority for bandwidth for mission critical services for users
willing to pay a service premium. Customers would contract with ISPs
for these services under Service Level Agreements (SLAs). Such an
agreement may specify the traffic volume, how the traffic is handled,
either in an absolute or relative manner, and the compensation that
the ISP receives.
Differentiated services are likely to be deployed across a single ISP
to support applications such as a single enterprise's Virtual Private
Network (VPN). However, this is only the first wave of service
implementation. Closely following this will be the need for
differentiated services to support extranets, enterprise VPNs that
Li & Rekhter Informational [Page 3]
RFC 2430 PASTE October 1998
span ISPs, or industry interconnection networks such as the ANX [7].
Because such applications span enterprises and thus span ISPs, there
is a clear need for inter-domain SLAs. This document discusses the
technical architecture that would allow the creation of such inter-
domain SLAs.
Another important consideration in this architecture is the advent of
traffic engineering within ISPs. Traffic engineering is the ability
to move trunks away from the path selected by the ISP's IGP and onto
a different path. This allows an ISP to route traffic around known
points of congestion in its network, thereby making more efficient
use of the available bandwidth. In turn, this makes the ISP more
competitive within its market by allowing the ISP to pass lower costs
and better service on to its customers.
Finally, the need to provide end-to-end differentiated services
implies that the architecture must support consistent inter-provider
differentiated services. Most flows in the Internet today traverse
multiple ISPs, making a consistent description and treatment of
priority flows across ISPs a necessity.
4.0 Components of the Architecture
The Differentiated Services Backbone architecture is the integration
of several different mechanisms that, when used in a coordinated way,
achieve the goals outlined above. This section describes each of the
mechanisms used in some detail. Subsequent sections will then detail
the interoperation of these mechanisms.
4.1 Traffic classes
As described above, packets may fall into a variety of different
traffic classes. For ISP operations, it is essential that packets be
accurately classified before entering the ISP and that it is very
easy for an ISP device to determine the traffic class for a
particular packet.
The traffic class of MPLS packets can be encoded in the three bits
reserved for CoS within the MPLS label header. In addition, traffic
classes for IPv4 packets can be classified via the IPv4 ToS byte,
possibly within the three precedence bits within that byte. Note
that the consistent interpretation of the traffic class, regardless
of the bits used to indicate this class, is an important feature of
PASTE.
Li & Rekhter Informational [Page 4]
RFC 2430 PASTE October 1998
In this architecture it is not overly important to control which
packets entering the ISP have a particular traffic class. From the
ISP's perspective, each Priority packet should involve some economic
premium for delivery. As a result the ISP need not pass judgment as
to the appropriateness of the traffic class for the application.
It is important that any Network Control traffic entering an ISP be
handled carefully. The contents of such traffic must also be
carefully authenticated. Currently, there is no need for traffic
generated external to a domain to transit a border router of the ISP.
4.2 Trunks
As described above, traffic of a single traffic class that is
aggregated into a single LSP is called a traffic trunk, or simply a
trunk. Trunks are essential to the architecture because they allow
the overhead in the infrastructure to be decoupled from the size of
the network and the amount of traffic in the network. Instead, as
the traffic scales up, the amount of traffic in the trunks increases;
not the number of trunks.
The number of trunks within a given topology has a worst case of one
trunk per traffic class from each entry router to each exit router.
If there are N routers in the topology and C classes of service, this
would be (N * (N-1) * C) trunks. Fortunately, instantiating this
many trunks is not always necessary.
Trunks with a single exit point which share a common internal path
can be merged to form a single sink tree. The computation necessary
to determine if two trunks can be merged is straightforward. If,
when a trunk is being established, it intersects an existing trunk
with the same traffic class and the same remaining explicit route,
the new trunk can be spliced into the existing trunk at the point of
intersection. The splice itself is straightforward: both incoming
trunks will perform a standard label switching operation, but will
result in the same outbound label. Since each sink tree created this
way touches each router at most once and there is one sink tree per
exit router, the result is N * C sink trees.
The number of trunks or sink trees can also be reduced if multiple
trunks or sink trees for different classes follow the same path.
This works because the traffic class of a trunk or sink tree is
orthogonal to the path defined by its LSP. Thus, two trunks with
different traffic classes can share a label for any part of the
topology that is shared and ends in the exit router. Thus, the
entire topology can be overlaid with N trunks.
Li & Rekhter Informational [Page 5]
RFC 2430 PASTE October 1998
Further, if Best Effort trunks and individual Best Effort flows are
treated identically, there is no need to instantiate any Best Effort
trunk that would follow the IGP computed path. This is because the
packets can be directly forwarded without an LSP. However, traffic
engineering may require Best Effort trunks to be treated differently
from the individual Best Effort flows, thus requiring the
instantiation of LSPs for Best Effort trunks. Note that Priority
trunks must be instantiated because end-to-end RSVP packets to
support the aggregated Priority flows must be tunneled.
Trunks can also be aggregated with other trunks by adding a new label
to the stack of labels for each trunk, effectively bundling the
trunks into a single tunnel. For the purposes of this document, this
is also considered a trunk, or if we need to be specific, this will
be called an aggregated trunk. Two trunks can be aggregated if they
share a portion of their path. There is no requirement on the exact
length of the common portion of the path, and thus the exact
requirements for forming an aggregated trunk are beyond the scope of
this document. Note that traffic class (i.e., QoS indication) is
propagated when an additional label is added to a trunk, so trunks of
different classes may be aggregated.
Trunks can be terminated at any point, resulting in a deaggregation
of traffic. The obvious consequence is that there needs to be
sufficient switching capacity at the point of deaggregation to deal
with the resultant traffic.
High reliability for a trunk can be provided through the use of one
or more backup trunks. Backup trunks can be initiated either by the
same router that would initiate the primary trunk or by another
backup router. The status of the primary trunk can be ascertained by
the router that initiated the backup trunk (note that this may be
either the same or a different router as the router that initiated
the primary trunk) through out of band information, such as the IGP.
If a backup trunk is established and the primary trunk returns to
service, the backup trunk can be deactivated and the primary trunk
used instead.
4.3 RSVP
Originally RSVP was designed as a protocol to install state
associated with resource reservations for individual flows
originated/destined to hosts, where path was determined by
destination-based routing. Quoting directly from the RSVP
specifications, "The RSVP protocol is used by a host, on behalf of an
application data stream, to request a specific quality of service
(QoS) from the network for particular data streams or flows"
[RFC2205].
Li & Rekhter Informational [Page 6]
RFC 2430 PASTE October 1998
The usage of RSVP in PASTE is quite different from the usage of RSVP
as it was originally envisioned by its designers. The first
difference is that RSVP is used in PASTE to install state that
applies to a collection of flows that all share a common path and
common pool of reserved resources. The second difference is that
RSVP is used in PASTE to install state related to forwarding,
including label switching information, in addition to resource
reservations. The third difference is that the path that this state
is installed along is no longer constrained by the destination-based
routing.
The key factor that makes RSVP suitable for PASTE is the set of
mechanisms provided by RSVP. Quoting from the RSVP specifications,
"RSVP protocol mechanisms provide a general facility for creating and
maintaining distributed reservation state across a mesh of multicast
or unicast delivery paths." Moreover, RSVP provides a straightforward
extensibility mechanism by allowing for the creation of new RSVP
Objects. This flexibility allows us to also use the mechanisms
provided by RSVP to create and maintain distributed state for
information other than pure resource reservation, as well as allowing
the creation of forwarding state in conjunction with resource
reservation state.
The original RSVP design, in which "RSVP itself transfers and
manipulates QoS control parameters as opaque data, passing them to
the appropriate traffic control modules for interpretation" can thus
be extended to include explicit route parameters and label binding
parameters. Just as with QoS parameters, RSVP can transfer and
manipulate explicit route parameters and label binding parameters as
opaque data, passing explicit route parameters to the appropriate
forwarding module, and label parameters to the appropriate MPLS
module.
Moreover, an RSVP session in PASTE is not constrained to be only
between a pair of hosts, but is also used between pairs of routers
that act as the originator and the terminator of a traffic trunk.
Using RSVP in PASTE helps consolidate procedures for several tasks:
(a) procedures for establishing forwarding along an explicit route,
(b) procedures for establishing a label switched path, and (c) RSVP's
existing procedures for resource reservation. In addition, these
functions can be cleanly combined in any manner. The main advantage
of this consolidation comes from an observation that the above three
tasks are not independent, but inter-related. Any alternative that
accomplished each of these functions via independent sets of
procedures, would require additional coordination between functions,
adding more complexity to the system.
Li & Rekhter Informational [Page 7]
RFC 2430 PASTE October 1998
4.4 Traffic Engineering
The purpose of traffic engineering is to give the ISP precise control
over the flow of traffic within its network. Traffic engineering is
necessary because standard IGPs compute the shortest path across the
ISP's network based solely on the metric that has been
administratively assigned to each link. This computation does not
take into account the loading of each link. If the ISP's network is
not a full mesh of physical links, the result is that there may not
be an obvious way to assign metrics to the existing links such that
no congestion will occur given known traffic patterns. Traffic
engineering can be viewed as assistance to the routing infrastructure
that provides additional information in routing traffic along
specific paths, with the end goal of more efficient utilization of
networking resources.
Traffic engineering is performed by directing trunks along explicit
paths within the ISP's topology. This diverts the traffic away from
the shortest path computed by the IGP and presumably onto uncongested
links, eventually arriving at the same destination. Specification of
the explicit route is done by enumerating an explicit list of the
routers in the path. Given this list, traffic engineering trunks can
be constructed in a variety of ways. For example, a trunk could be
manually configured along the explicit path. This would involve
configuring each router along the path with state information for
forwarding the particular label. Such techniques are currently used
for traffic engineering in some ISPs today.
Alternately, a protocol such as RSVP can be used with an Explicit
Route Object (ERO) so that the first router in the path can establish
the trunk. The computation of the explicit route is beyond the scope
of this document but may include considerations of policy, static and
dynamic bandwidth allocation, congestion in the topology and manually
configured alternatives.
4.5 Resource reservation
Priority traffic has certain requirements on capacity and traffic
handling. To provide differentiated services, the ISP's
infrastructure must know of, and support these requirements. The
mechanism used to communicate these requirements dynamically is RSVP.
The flow specification within RSVP can describe many characteristics
of the flow or trunk. An LSR receiving RSVP information about a flow
or trunk has the ability to look at this information and either
accept or reject the reservation based on its local policy. This
policy is likely to include constraints about the traffic handling
functions that can be supported by the network and the aggregate
capacity that the network is willing to provide for Priority traffic.
Li & Rekhter Informational [Page 8]
RFC 2430 PASTE October 1998
4.6 Inter-Provider SLAs (IPSs)
Trunks that span multiple ISPs are likely to be based on legal
agreements and some other external considerations. As a result, one
of the common functions that we would expect to see in this type of
architecture is a bilateral agreement between ISPs to support
differentiated services. In addition to the obvious compensation,
this agreement is likely to spell out the acceptable traffic handling
policies and capacities to be used by both parties.
Documents similar to this exist today on behalf of Best Effort
traffic and are known as peering agreements. Extending a peering
agreement to support differentiated services would effectively create
an Inter-Provider SLA (IPS). Such agreements may include the types
of differentiated services that one ISP provides to the other ISP, as
well as the upper bound on the amount of traffic associated with each
such service that the ISP would be willing to accept and carry from
the other ISP. Further, an IPS may limit the types of differentiated
services and an upper bound on the amount of traffic that may
originate from a third party ISP and be passed from one signer of the
IPS to the other.
If the expected costs associated with the IPS are not symmetric, the
parties may agree that one ISP will provide the other ISP with
appropriate compensation. Such costs may be due to inequality of
traffic exchange, costs in delivering the exchanged traffic, or the
overhead involved in supporting the protocols exchanged between the
two ISPs.
Note that the PASTE architecture provides a technical basis to
establish IPSs, while the procedures necessary to create such IPSs
are outside the scope of PASTE.
4.7 Traffic shaping and policing
To help support IPSs, special facilities must be available at the
interconnect between ISPs. These mechanisms are necessary to insure
that the network transmitting a trunk of Priority traffic does so
within the agreed traffic characterization and capacity. A
simplistic example of such a mechanism might be a token bucket
system, implemented on a per-trunk basis. Similarly, there need to
be mechanisms to insure, on a per trunk basis, that an ISP receiving
a trunk receives only the traffic that is in compliance with the
agreement between ISPs.
Li & Rekhter Informational [Page 9]
RFC 2430 PASTE October 1998
4.8 Multilateral IPSs
Trunks may span multiple ISPs. As a result, establishing a
particular trunk may require more than two ISPs. The result would be
a multilateral IPS. This type of agreement is unusual with respect
to existing Internet business practices in that it requires multiple
participating parties for a useful result. This is also challenging
because without a commonly accepted service level definition, there
will need to be a multilateral definition, and this definition may
not be compatible used in IPSs between the same parties.
Because this new type of agreement may be a difficulty, it may in
some cases be simpler for certain ISPs to establish aggregated trunks
through other ISPs and then contract with customers to aggregate
their trunks. In this way, trunks can span multiple ISPs without
requiring multilateral IPSs.
Either or both of these two alternatives are possible and acceptable
within this architecture, and the choice is left for the the
participants to make on a case-by-case basis.
5.0 The Provider Architecture for differentiated Services and Traffic
Engineering (PASTE)
The Provider Architecture for differentiated Services and Traffic
Engineering (PASTE) is based on the usage of MPLS and RSVP as
mechanisms to establish differentiated service connections across
ISPs. This is done in a scalable way by aggregating differentiated
flows into traffic class specific MPLS tunnels, also known as traffic
trunks.
Such trunks can be given an explicit route by an ISP to define the
placement of the trunk within the ISP's infrastructure, allowing the
ISP to traffic engineer its own network. Trunks can also be
aggregated and merged, which helps the scalability of the
architecture by minimizing the number of individual trunks that
intermediate systems must support.
Special traffic handling operations, such as specific queuing
algorithms or drop computations, can be supported by a network on a
per-trunk basis, allowing these services to scale with the number of
trunks in the network.
Agreements for handling of trunks between ISPs require both legal
documentation and conformance mechanisms on both sides of the
agreement. As a trunk is unidirectional, it is sufficient for the
transmitter to monitor and shape outbound traffic, while the receiver
polices the traffic profile.
Li & Rekhter Informational [Page 10]
RFC 2430 PASTE October 1998
Trunks can either be aggregated across other ISPs or can be the
subject of a multilateral agreement for the carriage of the trunk.
RSVP information about individual flows is tunneled in the trunk to
provide an end-to-end reservation. To insure that the return RSVP
traffic is handled properly, each trunk must also have another tunnel
running in the opposite direction. Note that the reverse tunnel may
be a different trunk or it may be an independent tunnel terminating
at the same routers as the trunk. Routing symmetry between a trunk
and its return is not assumed.
RSVP already contains the ability to do local path repair. In the
event of a trunk failure, this capability, along with the ability to
specify abstractions in the ERO, allows RSVP to re-establish the
trunk in many failure scenarios.
6.0 Traffic flow in the PASTE architecture
As an example of the operation of this architecture, we consider an
example of a single differentiated flow. Suppose that a user wishes
to make a telephone call using a Voice over IP service. While this
call is full duplex, we can consider the data flow in each direction
in a half duplex fashion because the architecture operates
symmetrically.
Suppose that the data packets for this voice call are created at a
node S and need to traverse to node D. Because this is a voice call,
the data packets are encoded as Priority packets. If there is more
granularity within the traffic classes, these packets might be
encoded as wanting low jitter and having low drop preference.
Initially this is encoded into the precedence bits of the IPv4 ToS
byte.
6.1 Propagation of RSVP messages
To establish the flow to node D, node S first generates an RSVP PATH
message which describes the flow in more detail. For example, the
flow might require 3kbps of bandwidth, be insensitive to jitter of
less than 50ms, and require a delay of less than 200ms. This message
is passed through node S's local network and eventually appears in
node S's ISP. Suppose that this is ISP F.
ISP F has considerable latitude in its options at this point. The
requirement on F is to place the flow into a trunk before it exits
F's infrastructure. One thing that F might do is to perform the
admission control function at the first hop router. At this point, F
would determine if it had the capacity and capability of carrying the
flow across its own infrastructure to an exit router E. If the
admission control decision is negative, the first hop router can
Li & Rekhter Informational [Page 11]
RFC 2430 PASTE October 1998
inform node S using RSVP. Alternately, it can propagate the RSVP
PATH message along the path to exit router E. This is simply normal
operation of RSVP on a differentiated flow.
At exit router E, there is a trunk that ISP F maintains that transits
ISP X, Y, and Z and terminates in ISP L. Based on BGP path
information or on out of band information, Node D is known to be a
customer of ISP L. Exit router E matches the flow requirements in
the RSVP PATH message to the characteristics (e.g., remaining
capacity) of the trunk to ISP L. Assuming that the requirements are
compatible, it then notes that the flow should be aggregated into the
trunk.
To insure that the flow reservation happens end to end, the RSVP PATH
message is then encapsulated into the trunk itself, where it is
transmitted to ISP L. It eventually reaches the end of the trunk,
where it is decapsulated by router U. PATH messages are then
propagated all the way to the ultimate destination D.
Note that the end-to-end RSVP RESV messages must be carefully handled
by router U. The RESV messages from router U to E must return via a
tunnel back to router E.
RSVP is also used by exit router E to initialize and maintain the
trunk to ISP L. The RSVP messages for this trunk are not placed
within the trunk itself but the end-to-end RSVP messages are. The
existence of multiple overlapping RSVP sessions in PASTE is
straightforward, but requires explicit enumeration when discussing
particular RSVP sessions.
6.2 Propagation of user data
Data packets created by S flow through ISP F's network following the
flow reservation and eventually make it to router E. At that point,
they are given an MPLS label and placed in the trunk. Normal MPLS
switching will propagate this packet across ISP X's network. Note
that the same traffic class still applies because the class encoding
is propagated from the precedence bits of the IPv4 header to the CoS
bits in the MPLS label. As the packet exits ISP X's network, it can
be aggregated into another trunk for the express purpose of
tranisiting ISP Y.
Again, label switching is used to bring the packet across ISP Y's
network and then the aggregated trunk terminates at a router in ISP
Z's network. This router deaggregates the trunk, and forwards the
resulting trunk towards ISP L. This trunk transits ISP Z and
terminates in ISP L at router U. At this point, the data packets are
removed from the trunk and forwarded along the path computed by RSVP.
Li & Rekhter Informational [Page 12]
RFC 2430 PASTE October 1998
6.3 Trunk establishment and maintenance
In this example, there are two trunks in use. One trunk runs from
ISP F, through ISPs X, Y and Z, and then terminates in ISP L. The
other aggregated trunk begins in ISP X, transits ISP Y and terminates
in ISP Z.
The first trunk may be established based on a multilateral agreement
between ISPs F, X, Z and L. Note that ISP Y is not part of this
multilateral agreement, and ISP X is contractually responsible for
providing carriage of the trunk into ISP Z. Also per this agreement,
the tunnel is maintained by ISP F and is initialized and maintained
through the use of RSVP and an explicit route object that lists ISP's
X, Z, and L. Within this explicit route, ISP X and ISP L are given
as strict hops, thus constraining the path so that there may not be
other ISPs intervening between the pair of ISPs F and X and the pair
Z and L. However, no constraint is placed on the path between ISPs X
and Z. Further, there is no constraint placed on which router
terminates the trunk within L's infrastructure.
Normally this trunk is maintained by one of ISP F's routers adjacent
to ISP X. For robustness, ISP F has a second router adjacent to ISP
X, and that provides a backup trunk.
The second trunk may be established by a bilateral agreement between
ISP X and Y. ISP Z is not involved. The second trunk is constrained
so that it terminates on the last hop router within Y's
infrastructure. This tunnel is initialized and maintained through
the use of RSVP and an explicit route that lists the last hop router
within ISP Y's infrastructure. In order to provide redundancy in the
case of the failure of the last hop router, there are multiple
explicit routes configured into ISP X's routers. These routers can
select one working explicit route from their configured list.
Further, in order to provide redundancy against the failure of X's
primary router, X provides a backup router with a backup trunk.
6.4 Robustness
Note that in this example, there are no single points of failure once
the traffic is within ISP F's network. Each trunk has a backup trunk
to protect against the failure of the primary trunk. To protect
against the failure of any particular router, each trunk can be
configured with multiple explicit route objects that terminate at one
of several acceptable routers.
Li & Rekhter Informational [Page 13]
RFC 2430 PASTE October 1998
7.0 Security Considerations
Because Priority traffic intrinsically has more 'value' than Best
Effort traffic, the ability to inject Priority traffic into a network
must be carefully controlled. Further, signaling concerning Priority
traffic has to be authenticated because it is likely that the
signaling information will result in specific accounting and
eventually billing for the Priority services. ISPs are cautioned to
insure that the Priority traffic that they accept is in fact from a
known previous hop. Note that this is a simple requirement to
fulfill at private peerings, but it is much more difficult at public
interconnects. For this reason, exchanging Priority traffic at
public interconnects should be done with great care.
RSVP traffic needs to be authenticated. This can possibly be done
through the use of the Integrity Object.
8.0 Conclusion
The Provider Architecture for differentiated Services and Traffic
Engineering (PASTE) provides a robust, scalable means of deploying
differentiated services in the Internet. It provides scalability by
aggregating flows into class specific MPLS tunnels. These tunnels,
also called trunks, can in turn be aggregated, thus leading to a
hierarchical aggregation of traffic.
Trunk establishment and maintenance is done with RSVP, taking
advantage of existing work in differentiated services. Explicit
routes within the RSVP signaling structure allow providers to perform
traffic engineering by placing trunks on particular links in their
network.
The result is an architecture that is sufficient to scale to meet ISP
needs and can provide differentiated services in the large, support
traffic engineering, and continue to grow with the Internet.
8.1 Acknowledgments
Inspiration and comments about this document came from Noel Chiappa,
Der-Hwa Gan, Robert Elz, Lisa Bourgeault, and Paul Ferguson.
Li & Rekhter Informational [Page 14]
RFC 2430 PASTE October 1998
9.0 References
[1] Rosen, E., Viswanathan, A., and R. Callon, "A Proposed
Architecture for MPLS", Work in Progress.
[2] Braden, R., Zhang, L., Berson, S., Herzog, S., and S. Jamin,
"Resource ReSerVation Protocol (RSVP) -- Version 1 Functional
Specification", RFC 2205, September 1997.
[3] Rosen, E., Rekhter, Y., Tappan, D., Farinacci, D., Fedorkow,, G.,
Li, T., and A. Conta, "MPLS Label Stack Encoding", Work in
Progress.
[4] Davie, B., Rekhter, Y., Rosen, E., Viswanathan, A., and V.
Srinivasan, "Use of Label Switching With RSVP", Work in Progress.
[5] Gan, D.-H., Guerin, R., Kamat, S., Li, T., and E. Rosen, "Setting
up Reservations on Explicit Paths using RSVP", Work in Progress.
[6] Davie, B., Li, T., Rosen, E., and Y. Rekhter, "Explicit Route
Support in MPLS", Work in Progress.
[7]
http://www.anxo.com/
10.0 Authors' Addresses
Tony Li
Juniper Networks, Inc.
385 Ravendale Dr.
Mountain View, CA 94043
Phone: +1 650 526 8006
Fax: +1 650 526 8001
EMail:
[email protected]
Yakov Rekhter
cisco Systems, Inc.
170 W. Tasman Dr.
San Jose, CA 95134
EMail:
[email protected]
Li & Rekhter Informational [Page 15]
RFC 2430 PASTE October 1998
11. Full Copyright Statement
Copyright (C) The Internet Society (1998). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Li & Rekhter Informational [Page 16]
