Subject: [AVT] Question about AMR

From: Xin Chen <[email-masked]>
Date: Mon, 17 Jun 2002 14:27:42 +0100

Hi,
Some questions about the draft-ietf-avt-rtp-amr-13.txt.
Under section 3.9, it says when an IP terminals talks with a GW, it should
not set the CMR. The question is how the IP terminal knows that it talks to
a GW? 
Is it assumed in this draft that the IP terminals mentioned in this draft
are wired terminal? Is this draft also applicable for wireless IP terminal,
etc 3GPP IMS terminal?
What happen in the case that a session is between two wireless IP terminals.
One is in a very good transmission condition, and another is in a very bad
transimission condition. The one in good transmission condition will set the
CMR to the maximum bit rate, and when the other one which is in a very bad
radio connection receives this CMR, will it change its codec to the maximum
bit rate even if it is in a bad connection?
Thanks
Xin Chen

---

From: Magnus Westerlund <[email-masked]>
Date: Mon, 17 Jun 2002 15:58:30 +0200

Hi,

See my answers below:

Xin Chen wrote:

> Hi,
> Some questions about the draft-ietf-avt-rtp-amr-13.txt .
> Under section 3.9, it says when an IP terminals talks with a GW, it 
> should not set the CMR. The question is how the IP terminal knows that 
> it talks to a GW?
>
The IP terminal does not need to know that it talks to a GW or not. If 
the application is communicating over IP and has no knowledge of link 
layer performance it should not set the CMR to request a certain mode. 
The IP terminal shall chose the mode and packetization that it sends 
based on other information, including congestion control.

> Is it assumed in this draft that the IP terminals mentioned in this 
> draft are wired terminal? Is this draft also applicable for wireless 
> IP terminal, etc 3GPP IMS terminal?
>
Yes it is applicable also for wireless IP terminals. A terminal having 
information about the link layer carrying the IP traffic is recommended 
to use if it can result in a better working application.

> What happen in the case that a session is between two wireless IP 
> terminals. One is in a very good transmission condition, and another 
> is in a very bad transmission condition. The one in good transmission 
> condition will set the CMR to the maximum bit rate, and when the other 
> one which is in a very bad radio connection receives this CMR, will it 
> change its codec to the maximum bit rate even if it is in a bad 
> connection?
>
As the draft states the sending terminal must take all into account, in 
this case both the requested mode and the local link layer conditions.

Regards

Magnus Westerlund 

Multimedia Technologies, Ericsson Research ERA/TVA/A
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