Subject: [rohc] open issues on ROHC-TCP

From: "Qian Zhang" <[email-masked]>
Date: Tue, 19 Mar 2002 15:30:45 +0800

Dear ROHCers,

I would like to summarize some open issues need to be further discussed
for ROHC-TCP.

1. MSN (master sequence number) and feedback related issues

a. Whether ROHC-TCP should support feedback in U-mode?

Considering the definition for U-mode and the cost for MSN in feedback,
in this version, we do not assume that there would be any feedback in
U-mode case.

b. Another issue related to feedback is its format. 

Since ROHC had reserved a prefix code for feedback, it seems that it is
not necessary to use EPIC-LITE to generate the feedback format. We plan
to define the format for TCP feedback similar to the format for RTP.

2. Issues related to context replication for short-lived TCP transfers.

a. How to make sure the correctness of the context that to be
replicated, especially in U-mode?

A simple solution: the compressor sends the IR packet when jump back to
IR state

b. Should we support possible encoding methods in context updating
(IR-UPDATE) packet?

Possible solution: apply lsb (refers to w-lsb) for IP-ID and Timestamp,
apply delta (compared with the value in the original context) encoding
for port

3. Issues related to compressed format generator (EPIC-LITE)

a. Simplify stack control mechanism to make sure the consistent of
profile 

b. List encoding for TCP options

Call for more efficient representation for order

c. A default set of compressed format sets should be explicitly provided
for Format (As offline discussed with Mark, FORMAT encoding method can
support this functionality, which may need to explicitly point out)

Considering the cost for change the FORMAT, the other compressed format
sets are selected only for the long-term traffic, and should be regarded
as the enhancement in the compressor

d. Should separate the control of state machine with the format
generator

For example, the decision of Format selection should be taken only in IR
state

BR,

Qian