LDP Extensions to Support Private Line Emulation (PLE)

Introduction and Motivation has already specified extensions to the Label Distribution Protocol (LDP) for the setup of structure-agnostic TDM pseudowires specified in , structure-aware pseudowires specified in and SONET/SDH Circuit Emulation over Packet (CEP) pseudowires in . Private Line Emulation pseudowires are specified in . This document focuses on the LDP definitions and extensions required for the setup of PLE pseudowires taking and as a starting point.

Requirements Notation The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP14 when, and only when, they appear in all capitals, as shown here.

Terminology

PW FEC for Setup of PLE Pseudowires does define two types of PW Forwarding Equivalent Classes (FECs)

PWId FEC (FEC 128)
Generalized PW FEC (FEC 129)

The Group ID and the Interface Parameters are contained in separate TLVs, called the PW Grouping TLV and the Interface Parameters TLV. Either of these types of PW FEC MAY be used for the setup of PLE PWs with the PW type TBD1 and appropriate interface parameters. The two endpoints MUST agree on the PW type, as both directions of the PW are required to be of the same type. The Control bit MUST be set as PLE PW encapsulation uses a control word.

Interface Parameters for PLE Pseudowires

Overview The interface parameters that are relevant for the setup of PLE pseudowires are listed in Relevant Interface Parameters

Interface Parameter	Sub-TLV	Length
PLE/CEP/TDM Payload Bytes	0x04	4
PLE/CEP/TDM Bit-Rate	0x07	6
PLE/CEP Options	0x05	4
Endpoint-ID	TBD2	0-80

PLE/CEP/TDM Payload Bytes The payload byte sub-TLV already defined in does also apply to PLE and MAY be included if a non-default payload size is to be used. If this TLV is omitted then the default payload size defined in MUST be assumed. The format of the PLE/CEP/TDM Payload Bytes sub-TLV is shown in .

PLE/CEP/TDM Payload Bytes sub-TLV Type : 4 Length : 4

The total length in octets of the value portion of the TLV.

PLE/CEP/TDM Payload Bytes :

A two byte field denoting the desired payload size to be used.

PLE/CEP/TDM Bit-Rate The bit-rate sub-TLV already defined in is MANDATORY for PLE pseudowires in order to unambiguously indicate the attachment circuit type. The format of the PLE/CEP/TDM Bit-Rate sub-TLV is shown in .

PLE/CEP/TDM Bit-Rate sub-TLV Type : 7 Length : 6

The total length in octets of the value portion of the TLV.

PLE/CEP/TDM Bit-rate :

A four byte field denoting the data rate in units of 1-kbps

PLE/CEP Options The options sub-TLV already defined in MUST be present when signaling PLE pseudowires. The format of the PLE/CEP options sub-TLV is shown in .

PLE/CEP Options sub-TLV Type : 5 Length : 4

The total length in octets of the value portion of the TLV.

PLE/CEP Options :

A two byte field with the format as shown in

PLE/CEP Options AIS, UNE, RTP, EBM :

These bits MUST be set to zero and ignored by the receiver.

Reserved :

7-bit field for future use. MUST be set to ZERO and ignored by receiver.

CEP/PLE Type :

Indicates the connection type for CEP and PLE. CEP connection types are defined in . Two new values for PLE are defined in this document:

- 0x3 - Basic PLE payload

- 0x4 - Byte aligned PLE payload

Async :

These bits MUST be set to zero and ignored by the receiver.

Endpoint-ID The Endpoint-ID sub-TLV MAY be included to allow for misconnection detection. The format of the Endpoint-ID sub-TLV format is shown in .

Endpoint-ID sub-TLV Type : TBD2 Length : 2-82

The total length in octets of the value portion of the TLV.

Endpoint Identifier :

Arbitrary string of variable length from 0 to 80 octets used to describe the attachment circuit to the remote PE node.

LDP Status Codes Per in case of incompatible bit-rate the LDP status code 0x00000026 (incompatible bit-rate) and in case of incompatible PLE options the LDP status code 0x00000027 (CEP-TDM mis-configuration) has to be used to indicate the reason of failure to establish the pseudowire. Setting of the Control bit to zero MUST result in an LDP status of 0x00000024 (Illegal C-Bit).

Using the PW Status TLV The PLE PW control word carries status indications for both attachment circuits (L bit) and the PSN (R bit) indication (see ). Similar functionality is available via use of the PW Status TLV (see ). If the latter mechanism is employed, the signaling PE sends its peer a PW Status TLV for this PW, setting the appropriate bits (see ):

Pseudowire Not Forwarding
Local Attachment Circuit (ingress) Receive Fault
Local Attachment Circuit (egress) Transmit Fault
Local PSN-facing PW (ingress) Receive Fault
Local PSN-facing PW (egress) Transmit Fault

As long as the TDM PW interworking function is operational, usage of the Status TLV is NOT RECOMMENDED in order to avoid contention between status indications reported by the data and control plane. However, if the TDM PW interworking function (IWF) itself fails while the PWE3 control plane remains operational, a Status TLV with all of the above bits set SHOULD be sent.

Security Considerations This document does not have any additional impact on the security of PWs above that of basic LDP-based setup of PWs specified in .

IANA Considerations As already indicated in section 10 of , IANA is requested to assign a PW type value TBD1 for PLE pseudowires from the "MPLS Pseudowire Types" registry.

Acknowledgements to be added