[AVT] Fw: some questions regarding 3GPP UP over RTP

[Haining.Liu at mindspeed.com]

Firstly, thanks Dr. Thomas's comments.
 May I get some more opinions?

Best,

haining


----- Forwarded by Haining
Liu/USA/Mindspeed on 09/28/2005 09:53 AM -----

Haining Liu/USA/Mindspeed wrote on 09/27/2005 11:27:05
PM:

> Hello,
>  
> When we implement 3GPP UP over RTP in our products,
we've fould some
> confusions regarding how to stack UP and RTP together correctly.  
> Some of our customers have different opinions regarding these 
> issues. We consulted 3GPP standards, and the answers are simply not
> there. Can you guys throw some opinions? Can we somehow standardize
> this within IETF? I can certainly contribute on this if necessary...
>  
> Let me first give a brief overview of the problem.
>  
>  
> Iu/NbUP is a user plane protocol which is designed
to convey GSM AMR
> traffic or G711 traffic between base stations and the core networks.
> Similar to RTP, it has sequence number, payload type indication, 
> though defined in a different way. Apart from attaching these 
> information to each encoded frame, it also has specified some other
> control functionalities, such as the delivery of requests such as
> error indication, time alignment and rate control. The frames 
> deliever this type of information are categorized as control frames.
> Since IP-based infrastructure is gradually replacing the traditional
> PSTN or ATM networks, different venders  
> and ISPs are calling for IuUP/NbUP over RTP/UDP/IP. 3GPP has two 
> separate standards that specify how to do this, but there are plenty
> of grey zones left which are basically left for the vendors or ISPs
> to interpret.
> Here are some specific issues. As in past practice,
UP layer is 
> directly stacked over RTP layer. As a result, control frames and 
> data frames are indeed multiplexed into a single RTP packet flow at
> the sender. The how should the sequence number be generated if data
> frames and control frames are interleaved together? What about time
> stamp, RTP statistics, and RTCP stats? 
>  
> Some think that as long as there is only one
RTP packet flow, time 
> stamp value and sequence number value should reference a single 
> space because all packets use a single SSRC value (e.g., if we have
> data packets at 0ms and 20ms, and a control packet at 15ms, we have
> the following event sequence: data-->control-->data). This certainly
> will create some confusion at the receiver, since there might be 
> some sequence number gaps between neighbouring data packets. Arguing
> this, others think control frames should not share the sequence 
> number space with data frames. But the down side of this approach
is
> that some RTP implementation will drop the out-of-the-sequence 
> packets without investigating what is actually inside the payload.
>  
> Basically the confusion here is about how RTP
layer should package 
> heterogenous upper layer content. How should the time stamp value
> and the sequence number value be defined here? 
>  
> Any comments or pointers are welcome!
>  
> Haining Liu
> Mindspeed Technologies Inc.
> Newport Beach, CA, USA
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