Dear Stewart, This liaison is a follow-up to our previous requests for codepoints from the Attachment Individual Identifier (AII) Type Registry in the Pseudo Wire Name Spaces, as defined in "IANA Allocations for Pseudo Wire Edge to Edge Emulation (PWE3)". Thank you for allocating the two AII type codepoints that we requested in our last liaison ("ATM/FR Control Channel" and "ATM/FR Signalling Call Reference").  This will allow us to finalize the "ATM and Frame Relay to MPLS Control Plane Interworking: Client-Server" and "ATM-MPLS Control Plane Network Interworking" specifications. As mentioned in our last liaison, we owe you further clarification regarding the other two AII type codepoints that we requested, for SPVC interworking. This was discussed at the MFA Forum Technical Committee meeting during the last week of June.  The results of this discussion are: - The Technical Committee reaffirmed the intent to define two new AII formats for SPVC interworking between MPLS pseudowires and ATM: one for the case where the connection identifier part of the AII format takes on ATM syntax and semantics (i.e. VPCI or VPCI/VCI); the other for the case where the connection identifier part of the AII format takes on Frame Relay syntax and semantics (i.e. DLCI). - Whether the ATM or FR AII format is used, it is possible for the opposite pseudowire type to be used.  One example is when FR endpoints are connected across ATM and MPLS networks, with the FRF.8 interworking functionality located at the destination LER.  For this case, AAL5 SDU mode could be used.  Another example is when the AII uses the ATM syntax and semantics, but the attachment circuit (and possibly the pseudowire type) is Frame Relay.  Many vendors implemented solutions for SPVCs across ATM networks to FR endpoints using ATM connection identifiers in the Called party SPVC information element.  This is largely due to the multi-year lag between definition of the Called party SPVC information element format using VPCIs/VCIs and the definition of the Called party SPVC information element format using DLCIs. - The Technical Committee prefers that two AII type codepoints be allocated for these two formats.  In order to reduce this to one AII type codepoint, a "connection identifier type" field would have to be added to the format in order to distinguish between ATM and FR connection identifiers.  Such a "connection identifier type" field is not otherwise required.  Use of two separate AII type codepoints simplifies these AII formats. - The Technical Committee does not currently foresee any need to request more AII type codepoints for ATM and FR to MPLS control plane interworking.  We expect that a resolution of this latest request would allow us to complete our work on this subject. - The length of these AIIs can be narrowed down to "variable: 2 to 30".  This range should be sufficient to provide the flexibility required to progress the SPVC interworking specification. In summary, the MFA Forum Technical Committee requests allocation of the following two AII type codepoints in the Pseudo Wire Name Spaces, from the range 2 through 64 (expert review): AII Length Description Reference Type TBD Variable: 2 to 30 Frame Relay Port and [SPVC IW] Connection Identifier TBD Variable: 2 to 30 ATM Port and Connection [SPVC IW] Identifier Thank you again for your consideration of this matter. Cordially, Rao Cherukuri Chairman, MFA Forum Technical Committee References: [Client-Server]   ATM and Frame Relay to MPLS Control Plane Interworking: Client-Server, MFA Forum 10.0.0, work in progress. [NIW]             ATM-MPLS Control Plane Network Interworking, ATM Forum: af-aic-0206.000, work in progress. [SPVC IW]         Soft Permanent Virtual Circuit Interworking between MPLS Pseudowires and ATM, MFA Forum, work in progress (this specification is at the baseline text stage).