Pseudowire Emulation Edge to Edge
Pseudowire Emulation Edge to Edge WG
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Network transport service providers and their users are
seeking to rationalize their networks by migrating their
existing services and platforms onto IP or MPLS enabled
IP packet switched networks (PSN). This migration requires
communications services that can emulate the essential
properties of traditional communications links over a PSN.
Some service providers wish to use MPLS technology to
replace existing transport network infrastructure, relying
upon pseudowire technology is an integral component of
these network convergence architectures.
Pseudowire Emulation Edge to Edge (PWE3) will specify the
encapsulation, transport, control, management, interworking
and security of services emulated over IETF-specified PSNs.
A pseudowire emulates a point-to-point or point-to-multipoint
link, and provides a single service which is perceived by
its user as an unshared link or circuit of the chosen
service. It is not intended that an emulated service will
be indistinguishable from the service that is being emulated.
The emulation need only be sufficient for the satisfactory
operation of the service. Emulation necessarily involves a
degree of cost-performance trade-off. In some cases it may
be necessary to design more than one emulation mechanism in
order to resolve these design conflicts. All emulated service
definitions must include an applicability statement describing
the faithfulness of the emulation.
Switching, multiplexing, modification or other operation on
the traditional service, unless required as part of the
emulation, is out of the scope of the PWE3 WG.
PWE3 will make use of existing IETF-specified mechanisms
unless there are technical reasons why the existing mechanisms
are insufficient or unnecessary.
PWE3 operates "edge to edge" and will not exert control on
the underlying PSN, other than to use any existing QoS or
path control mechanism to provide the required connectivity
between the endpoints of the PW.
PWE3 will co-ordinate this with the AVT and TICTOC WGs.
Where AVT or TICTOC require extensions to PWs to support
time or frequency transfer this work will be undertaken by
the PWE3 WG in co-ordination with the these WGs.
A PW operating over a shared PSN does not necessarily have
the same intrinsic security as a dedicated, purpose built,
network. In some cases this is satisfactory, while in other
cases it will be necessary to enhance the security of the PW
to emulate the intrinsic security of the emulated service.
PW specifications MUST include a description of how they
are to be operated over a shared PSN with adequate security.
PWE3 will work with the MPLS, L2VPN and other relevant WGs
for definitions of common solutions for the secure operation
Whilst a service provider may traffic engineer their network
in such a way that PW traffic will not cause significant
congestion, a PW deployed by an end-user may cause
congestion of the underlying PSN. Suitable congestion
avoidance mechanisms are therefore needed to protect the
Internet from the unconstrained deployment of PWs. Congestion
avoidance may be more difficult with P2MP pseudowires than
P2P pseudowires. The WG will consider both cases.
PWE3 will work closely with the L2VPN WG to ensure a clear
demarcation is defined for where PWE3 stops and L2VPN starts,
in particular in defining point-multipoint (P2MP) PWs.
PWE3 will work with MPLS and L2VPN to enhance the OAM suite
for transport applications. PWE3 will coordinate very closely
with any WG that is responsible for protocols which PWE3
intends to extend (e.g., the MPLS WG for LDP), as well as
foster interaction with WGs that intend to extend PWE3
The IETF PWE3 WG is the design authority for pseudo-wire
over IP/MPLS PSN technology. An entity or individual that
wishes to propose extensions or changes to this technology
must bring the corresponding proposals to the PWE3 WG that
would treat them via a process similar to one described in
RFC 4929 for the MPLS/GMPLS change process.
Specify the following PW types:
Most of the initial specific PW types have been specified
(e.g., Frame Realy, Ethernet, ATM). Investigation into
and specification of a "generic PW" type and/or MPLS PW
should be undertaken.
PWE3 will specify a PW type for the special case where the
access service payloads at both ends are known to consist
entirely of IP packets. PWE3 will not specify mechanisms
by which a PW connects two different access services
unless the Network Layer protocol is IP or MPLS.
Specify the control and management functions of chartered PW
types, to include PW setup, configuration, maintenance and
tear-down. The PWE3 WG will do this in its entirety for
MPLS PSNs, and the L2TPEXT WG will develop the L2TP specifics
for L2TPv3-based PWs.
Specify Operations and Management (OAM) mechanisms for all
PW types, suitable for operation over both IP/L2TPv3 and
MPLS PSNs, and capable of providing the necessary
interworking with the OAM mechanisms of the emulated
Define requirements for and mechanisms to provide
interconnection of PWs (to include inter-domain PWs).
Define requirements for and mechanisms to provide
protection and restoration of PWs.
Publish document outlining PW-specific congestion avoidance
and response guidelines.
Publish document outlining PW-specific security
Specify requirements and mechanisms for P2MP functionality
for PWs. This work will be coordinated with the L2VPN and
MPLS working groups.
Publish requirements and specification for PW to take
advantage of multiple PSN paths that exist between PEs.
Publish requirements and specification for enhanced OAM.
Include extensions to the PWE3 protocols and RFCs
necessary to create an MPLS Transport Profile (MPLS-TP).
The work on the MPLS TP needs to be coordinated between
three primary working groups (MPLS, PWE3, L2VPN and CCAMP) that
are chartered to do MPLS TP work.