Subject: [rohc] Ambiguity in usage of UO-1 Packet (RTP- Profile)

From: "Rajani A" <[email-masked]>
Date: Thu, 27 Dec 2007 10:37:34 +0530

Hi All,

UO-1 packet is used when we have RND = 1, i.e, when we find IP-ID field is
randomly assigned.
RFC clearly states that when ever we have IP-ID randomly assigned we need to
send it in uncompressed IP-ID value.
So general way is we send the other fields (SN/TS) in compressed mode and
send the IP-ID in uncompressed mode.
For this we should have IP-ID field in the packet type that we send or for
that packet we should be able to use extension so at least the packet should
have extension bit.
But for UO-1 neither there is IP-ID field and nor the Extension bit, So how
do we send IP-ID with this packet, which is used when RND=1.

Regards,
Rajani

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---

From: Biplab Sarkar <[email-masked]>
Date: Thu, 27 Dec 2007 12:44:47 +0530

Hi Rajani,

The uncompressed IP-ID will be sent as a part of the packet outside the
compressed UO-1 packet. 
Since the IP-ID field is not compressed there is no need to have it in
the compressed packet format.

-----------------RFC4815--------------------
2.  IP-ID

   According to RFC 3095-Section 5.7, IP-ID means the compressed value
   of the IPv4 header's 'Identification' field.  Compressed packets
   contain this compressed value (IP-ID), while IR packets with dynamic
   chain and IR-DYN packets transmit the original, uncompressed
   Identification field value.  The IP-ID field always represents the
   Identification value of the innermost IPv4 header whose corresponding
   RND flag is not 1.

   If RND or RND2 is set to 1, the corresponding IP-ID(s) is (are) sent
   as 16-bit uncompressed Identification value(s) at the end of the
   compressed base header, according to the IP-ID description (see the
   beginning of RFC 3095-Section 5.7).  When there is no compressed IP-
   ID, i.e., for IPv6 or when all IP Identification information is sent
   as is (as indicated by RND/RND2 being set to 1), the decompressor
   ignores IP-ID bits sent within compressed base headers.
-----------------------------
The order of the uncompressed data is given by the "general format" in RFC3095[5.7]. 
The supporting context will decide what attribute is expected in the packet.

Hope this helps.

-- 
Thanks & Regards,
Biplab Sarkar

On Thu, 2007-12-27 at 10:37 +0530, Rajani A wrote:
> Hi All,
>  
> UO-1 packet is used when we have RND = 1, i.e, when we find IP-ID
> field is randomly assigned. 
> RFC clearly states that when ever we have IP-ID randomly assigned we
> need to send it in uncompressed IP-ID value.
> So general way is we send the other fields (SN/TS) in compressed mode
> and send the IP-ID in uncompressed mode.
> For this we should have IP-ID field in the packet type that we send or
> for that packet we should be able to use extension so at least the
> packet should
> have extension bit.
> The information contained in this electronic message and any
> attachments to this message are intended for the exclusive use of the
> addressee(s) and may contain proprietary, confidential or privileged
> information. If you are not the intended recipient, you should not
> disseminate, distribute or copy this e-mail. Please notify the sender
> immediately and destroy all copies of this message and any attachments
> contained in it. Contact your Administrator for further information.
> 
>

---

From: PRASAD D <[email-masked]>
Date: Thu, 27 Dec 2007 00:20:08 -0800 (PST)

raj_tutor wrote:
> The information contained in this electronic message and any attachments
> to this message are intended for the exclusive use of the addressee(s) and
> may contain proprietary, confidential or privileged information. If you
> are not the intended recipient, you should not disseminate, distribute or
> copy this e-mail. Please notify the sender immediately and destroy all
> copies of this message and any attachments contained in it.
> 
Hi Rajani,

If RND bit is set then uncompressed IPID has to be appended to any
compressed packet.So there is no need for extension bit in UO-1 packet for
this purpose.

Regards
PRASAD.D 
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