Subject: [rohc] Timer based TS encoding

From: "Sarkar, Rajib" <[email-masked]>
Date: Tue, 5 Nov 2002 08:49:02 -0800

Hi,
	As I have understood that Timer Based TS encoding is optional, that
means that we can implement either W-LSB encoding of scaled TS or Timer
based encoding of Scaled TS. Is my understanding correct? I have gone
through the chapter 4, but still it is not clear to me why do we need Timer
based TS encoding?
Thanks
Rajib
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From: "Lars-Erik Jonsson (EAB)" <[email-masked]>
Date: Tue, 5 Nov 2002 23:40:21 +0100

Rajib,
 
> Hi,
> 	As I have understood that Timer Based TS encoding is 
> optional, that means that we can implement either W-LSB encoding
> of scaled TS or Timer based encoding of Scaled TS.
> Is my understanding correct? 

You will have to implement regular encoding, i.e. W-LSB of scaled
TS, while timer-based is an optional enhancement.

> I have gone through the chapter 4, but still it is not clear to
> me why do we need Timer based TS encoding?

You do not *need* it, but it provides an optimization to reduce
TS bits to a fixed number of bits.

BR
/L-E

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From: "Sarkar, Rajib" <[email-masked]>
Date: Tue, 5 Nov 2002 15:12:46 -0800

Hi,
	Still the things are a little bit unclear to me about how Timer
based TS encoding reduces the the number of bits?
Rajib

-----Original Message-----
From: Lars-Erik Jonsson (EAB) [mailto:[email-masked]]
Sent: Tuesday, November 05, 2002 2:40 PM
To: [email-masked]
Subject: RE: [rohc] Timer based TS encoding

Rajib,

BR
/L-E

---

From: "Lars-Erik Jonsson (EAB)" <[email-masked]>
Date: Wed, 6 Nov 2002 00:22:00 +0100

> based TS encoding reduces the the number of bits?

OK, let me give you a simple example:

Assume that the RTP stream carries speech data, i.e. packets are
sent regularly and TS normally increases with a fixed value for
each packet. However, if no packets are sent during silent periods,
the TS value will have to be included in compressed headers when
packets start to appear again after silence suppression. The number
of bits needed to convey the TS value in such cases depends on the
length of the silent period, if regular W-LSB encoding is used. 

With timer-based compression, the number of bits needed for TS
can be kept constant, since the local timer is used to get the
TS MSB's right at the decompressor. Long periods of silence will
therefore not result in larger compressed headers than short
periods of silence.

Cheers,
/L-E