RFC4045 - Extensions to Support Efficient Carrying of Multicast Traffic in Layer-2 Tunneling Protocol (L2TP)

The following AVPs MUST be present in an MSEN message:

Message Type
Result Code
Assigned Session ID

The associated Message Type AVP is encoded with the following values:

Vendor ID = 0
Attribute Type = 0
Attribute Value = 27 (16 bits)

The M-bit MUST be set to 0, and the H-bit MUST be set to 0.

7.3. Result Codes

The following values are the defined result codes for MSEN control
messages:

1 (16 bits) - No multicast traffic for the group
2 (16 bits) - Session terminated for the reason indicated in
the error code
3 (16 bits) - No more receivers
4 (16 bits) - No more receivers (filter-mode change)

o The code 1 MAY be used when the LAC detects that no traffic is
coming down the multicast session, or when the LNS doesn't
receive multicast traffic to be conveyed over the L2TP
multicast session during a certain period of time.

o The code 2 refers to General Error Codes maintained by the IANA
for L2TP.

o The code 3 MAY be used by the LAC or the LNS when the OSL is
empty.

o The code 4 MAY be used by the LNS when a multicast session is
torn down because of a filter-mode change. This result code
SHOULD also be used when the OSL becomes empty after a filter-
mode change (passive termination when filter-mode changes from
INCLUDE to EXCLUDE; see Section 4.3).

8. Traffic Merging

Both unicast and multicast traffics have to be merged by the LAC in
order to forward properly framed data to the end-user. Multicast
packets are framed by the LAC and transmitted toward the proper end-
user. Methods used to achieve this function are not described here,
since it is an implementation-specific issue.

All frames conveyed from the LAC to the end-users have to follow the
framing scheme applied for the considered peer to which the traffic
is destined (e.g., the LAC is always aware of the PPP [RFC1661] link
parameters, as described in [RFC2661], Section 6.14). Note that
using L2TP Multicast Extension features is not appropriate for end-
users who have negotiated a sequenced layer-2 connection with the
LNS. While inserting PPP-encapsulated multicast packets in a
session, the LAC cannot modify PPP sequencing performed by the LNS
for each PPP session.

9. IANA Considerations

This document defines:

- 5 new Message Type (Attribute Type 0) Values:
o Multicast-Session-Request (MSRQ) : 23

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