Re: The requiremnts and proposalsforM2PA/M3UA/SCTPExtension from China Mobile

Dear 鲁帽,

Dear Michael Tuexen,

1. What does "unionize of the primary paths between nodes" mean?

It means拢卢for one multi-homed SCTP endpoint,the primary path拢篓source IP address=IP1---destination IP=IP2拢漏 shall be the same as the remote endpoint's ( source IP address=IP2---destination IP=IP1 )

You can easily do your "unionize" by using ASCONF to set the primary
destination at both endpoints. In other words, this extension is
already provided by draft-ietf-tsvwg-addip-sctp-22.txt (which is in RFC
editor's queue).

Many venders implement Multi-homing in the following way:

one multi-homed SCTP endpoint has two local IP addresses(IP1/IP2) and two remote IP address(IP3/IP4) within an association.
There's two paths within an association:IP1-IP3,and IP2-IP4.not 4 paths.

For example, endpoint1 has two local IP addresses(IP1/IP2)拢卢 and endpoint2 has two local IP addresses(IP3/IP4).

if two endpoints' primary path isn't the same,that is endpoint1 use IP1-IP3 as the primary path, use IP2-IP4 as the second path; endpoint2 use IP3-IP2 as the primary path, use IP4-IP1 as the second path.

These two endpoints can't send data to each other successfully.

2. Not sure about the SACK issue: You are currently allowed to
send the SACK back to an addresses different from the source
address of the corresponding DATA chunk. As far as I know
it is only a SHOULD describing that you send the SACK back
to the source address of the DATA chunk.

You are right,it is only a SHOULD describing that you send the SACK back
to the source address of the DATA chunk in RFC2960.
That's why we get in trouble in multi-homing situation.
If the path to the source address of the DATA chunk is unreachable拢卢the sack can't send to the remote endpoint for ever although the other path is available.Soon the other path will be failure.

The "SHOULD" is meant to say that when possible (meaning your path is
healthy), you always send the SACK back to the source address of the
DATA chunk. When the path to the source address of the DATA chunk is
unreachable, you are of cause allowed to send the SACK back to other
address(es). In other words, what you want to do is already perfectly
allowed in SCTP.

regards,

-Qiaobing

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