Subject: [rohc] Incorrect ROHC mode received when D_TRANS is (D)ONE

From: "Szymanski, Pawel" <[email-masked]>
Date: Wed, 5 Apr 2006 18:33:51 +0100

HI All,

RFC3095 describes scenarios of mode transitions. However, there is no
statement defining what the decompressor must/should do when the value
passed in the Mode field located in the ROHC format packet differs from
the current mode. Let assume the following scenario:

- the current mode is Bidirectional Optimistic, and 

- the RTP/UDP/IP profile is associated with the context, and

- transition is done, and

- the decompressor is receiveing the UOR-2* packet with Extension 3
where the rtp bit-field is set, and

- the RTP header in this extension contains the value 1 (Unidirectional
compression mode) in the Mode field.

Questions:

1. Should the decompressor discard such a packet?

2. Should the decompressor initiate the transition procedure from the
O-mode to the U-mode?

Could anybody help me with the above questions

Thanks in advance

Pawel

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From: "Lars-Erik Jonsson" <[email-masked]>
Date: Wed, 5 Apr 2006 21:24:21 +0200

If the decompressor has switched to O-mode but receives packets 
indicating the compressor is still operating in U-mode (which simply 
means it sends periodic "updates"), the decompressor should just (if it 
wants to) send new feedback packets to tell the compressor to switch to 
O-mode. Since U- and O-mode works similarly (same packet formats) the 
scenario you describe is in no way troublesome and decompression would 
never fail due to this, which is why U->O transition is defined as a 
lightweight procedure.

Note: U->O transition does not even include setting D_TRANS, as there 
are no handshakes.

/L-E

----- Original Message ----- 
From: "Szymanski, Pawel" <[email-masked]>
To: <[email-masked]>
Sent: Wednesday, April 05, 2006 7:33 PM
Subject: [rohc] Incorrect ROHC mode received when D_TRANS is (D)ONE

HI All,

Questions:

Thanks in advance

Pawel

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