Fec Element For T-Ldp Signaling; Figure 77: Generalized Pseudowire-Id Fec Element - Alcatel-Lucent 7750 SR Manual

FEC Element for T-LDP Signaling

Two LDP FEC elements are defined in RFC 4447, PW Setup & Maintenance Using LDP. The
original pseudowire-ID FEC element 128 (0x80) employs a 32-bit field to identify the virtual
circuit ID and it was used extensively in the initial VPWS and VPLS deployments. The simple
format is easy to understand but it does not provide the required information model for BGP auto-
discovery function. In order to support BGP AD and other new applications a new Layer 2 FEC
element, the generalized FEC (0x81) is required.
The generalized pseudowire-ID FEC element has been designed for auto discovery applications. It
provides a field, the address group identifier (AGI), that is used to signal the membership
information from the VPLS-ID. Separate address fields are provided for the source and target
address associated with the VPLS endpoints called the Source Attachment Individual Identifier
(SAII) and respectively, Target Attachment Individual Identifier (TAII). These fields carry the VSI
ID values for the two instances that are to be connected through the signaled pseudowire.
The detailed format for FEC 129 is depicted in
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Gen PWid (0x81)|C|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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0
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
AGI Type |
AII Type |
AII Type |

Figure 77: Generalized Pseudowire-ID FEC Element

Figure
1
PW Type
Length | Value
AGI Value (contd.)
Length | Value
SAII Value (contd.)
Length | Value
TAII Value (contd.)
77.
2
|PW info Length |
7750 SR OS Services Guide
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