Subject: [rohc] Question about ROHC Type 1 packet in UO mode

From: Haipeng Jin <[email-masked]>
Date: Wed, 29 Oct 2003 14:55:09 -0800

Hi,

I am reading the RFC3095, and encountered the following problem:

In 5.7.3, the packet format for UO-1-TS is shown as

      0   1   2   3   4   5   6   7
    +---+---+---+---+---+---+---+---+
    | 1   0 |T=1|        TS         |
    +===+===+===+===+===+===+===+===+
    | M |      SN       |    CRC    |
    +---+---+---+---+---+---+---+---+

However, comparing with UO-1-ID, it seems that the M bit here should be X, 
is this a typo? If no, why is it different from the UO-1-ID packet?
This also makes me think about the packet format for UO-1, which is shown as:

      0   1   2   3   4   5   6   7
    +---+---+---+---+---+---+---+---+
    | 1   0 |          TS           |
    +===+===+===+===+===+===+===+===+
    | M |      SN       |    CRC    |
    +---+---+---+---+---+---+---+---+

Again, does M here really mean M or does it mean X?

Could anyone please clarify the above problems?

BTW, I have seen the mention of 3095bis on this mailing list several times, 
is this an existing document? If yes, could you please tell me where to get 
it? I can not find it on IETF website.

Thanks.

Haipeng

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---

From: Vicknesan Ayadurai <[email-masked]>
Date: Thu, 30 Oct 2003 00:28:06 +0100 (CET)

Hi Haipeng,

No, there is no typo with the M/X-bits you mentioned.

UO-1 packets carrying RTP timestamp bits are meant to be used during
talkspurts/jumps in the RTP timestamp. These timestamp jumps also
usually affect the RTP Marker-bit, and hence, these ROHC packets also
carry the Marker-bit info.

UO-1 ID does not carry timestamp bits in the base header and hence, no
Marker-bit either. Instead, extensions are made possible as indicated
by the presence of an X-bit in place of the Marker-bit.

As to your final question, I have no knowledge of a 3095bis document.

Regards,
vick