Subject: Re: [rohc] Queries from a beginner

From: Robert Stangarone <[email-masked]>
Date: Mon, 27 Jul 2009 08:44:59 -0700

Nikhil, you should respond to the [email-masked] address, which includes 
myself, so that other members of the list can follow the discussion.

The compressor will use the Optimistic Approach when determining which 
packet to send. See section 5.1.1 of RFC 5225. See also section 5.1.3 of 
  RFC 5225 on how the compressor chooses which packet to send to the 
decompressor. Examining the decompressor state machine found in 5.2.1 of 
RFC 5225 may also provide insight into the compressor's choice of packets.

The packet sizes will be the sum of the ROHC header used and the result 
of the encoding method used. The packet size has many influences. In the 
unidirectional mode, the pattern of change observed for each of the 
fields in the packet headers which are being compressed is the primary 
influence, with the timeout period also determining when an IR will be sent.

If you are doing just IP headers, you should review the field 
classifications found in Appendix A of RFC 5225.

I would suggest you throughly read each of the related RFCs, as many of 
your questions are addressed in each of those documents.

Good luck,

Bob

Hello Bob,
          Thanks for responding to my previous email with regard to the ROHC
queries. After going through your reply I went back to the ietf working
group and had a look at the rfc5225 (previously I was looking at rfc3095).
All my queries are with regard to only IP header compression (i.e. profile
0x0104 or 0x0004) and for uni-directional mode. I am trying to do a
numerical analysis of ROHC(/v2). Following are my questions:

In RFC 3095, it is mentioned that for each of the modes(i.e.uni-directional,
bidirectional,etc) there will be 3 states (IR, FO, SO). In terms of what
sort of packet is going to be sent during each of these states in the
unidirectional mode, can you give me a packet to state guide please,i.e. IR
= normal uncompressed packet, FO = IR packet with static and dynamic, SO =
IR packet with only dynamic.

In RFC 5225, the 3 states for each mode is not mentioned. I assume that mode
of thinking has been completely removed and now it is just a IR state and a
CO state?
IF that is the case then what is the packet sizes for IR, IR-Dyn and CO
state packets. I understand that it will vary if there are inner headers,
etc but what will be the case for just the single IP header present,
irrespective of inner headers (UDP,TCP, UDP-lite, RTP , etc).

Any feedback would be much appreciated.
Cheers
Nikhil
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