WATM11 — Issue/Telecom Wireless CORBA: Closing UTP Communication Session

There is no way in the current specification to gracefully close a communication session. This is not a problem, but may complicate recovery from communication failures.

Resolution: Add CloseRequest, CloseReply and CloseIndication chunks. CloseRequest/CloseReply pair of chunks allows negotiated closing of the UTP communication session. CloseIndition chunk allows a bridge to inform its peer bridge that it is going to close the UTP communication session.

Revised text:
Add the following three descriptions of UTP chunks at the end of subsection 7.4.1 'UDP Tunneling Protocol':
7. CloseRequest: sent by the Terminal or Access Bridge. No Flags, Lenght, and Value field.
8. CloseReply: sent by the Terminal or Access Bridge. No Flags, Lenght, and Value field.
9. CloseIndication: sent by the Terminal or Access Bridge. No Flags, Lenght, and Value field.

Add the following three subsections at the end of section 7.4 'UDP Tunneling':

Close Request

The chunk Type is 0x07. The chunk does not have any other fields.

The chunk can be sent either by the Terminal Bridge or by the Access Bridge.

The bridge sends this chunk when it wants to close the communication session. After sending this chunk the bridge mwaits for the UTP message cointaining the CloseReply chunk. The bridge sending the CloseRequest chunk MUST process and acknowledge all UTP messages until receiving the CloseReply chunk.

When a bridge receives the CloseRequest chunk, it SHOULD immediately retransmit all unacknowledged UTP messages as well as all remaining GTP messages before sending the CloseReply chunk.

CloseReply

The chunk Type is 0x08. The chunk does not have any other fields.

The chunk can be sent either by the Terminal Bridge or by the Access Bridge in response to the CloseRequest chunk.

The bridge receiving the CloseRequest chunk SHOULD NOT send the CloseReply chunk before all other UTP messages have been acknowledgeged. After sending the CloseReply chunk, the bridge SHOULD wait for the acknowledgement before releasing all data structures associated with the UTP communication session.

The bridge receiving the CloseReply chunk SHOULD acknowledge the UTP message containing the CloseReply chunk by a UTP message having sequence number 0x0000. After sending this reply the bridge can release all data structures associated to the UTP communication session.

If a bridge receives CloseReply chunk, but it has not send the CloseRequest chunk, the bridge SHOULD send the CloseIndication chunk. See section 7.4.n 'CloseIndication'.

CloseIndication

The chunk Type is 0x09. The chunk does not have any other fields.

The chunk can be sent either by the Terminal Bridge or by the Access Bridge.

The bridge send this chunk to inform the peer bridge that it will close the communication session. The bridge MAY wait for the acknowledgement of the UTP message containing the CloseIndication chunk. In this case the bridge SHOULD discard all arriving UTP messages and response by retransmitting the UTP message containing the CloseIndication chunk. However, the bridge does not need to wait for the acknowledgement of the UTP message containing the CloseIndication chunk. It can immediately, after sending the CloseIndication chunk, release all data structures related to this communication session and stop accepting messages to the UDP port.

When the peer bridge receives the CloseIndication chunk, it SHOULD immediately acknowledge that UTP message and stop using the UDP end-point of the peer bridge. After sending the acknowledgement, the bridge SHOULD release all data structures related to the UTP communication session.

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