[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

[AVT] Comments on draft-koren-avt-ecrtp-reorder-00.txt

Hi,

Here are some comments on this ID. It seems that remembering the last RTP SN where delta IPID has changed may not be enough.

For example, for a sequence of RTP packet with sequence number from 1 to 100. Suppose delta IPID changed on packet(1) to 1 and stays the same all the time, however, IPID jumped on packet(50) by 10, on packet(75) by 10, as a result, packet(100) has IPID 120 (assume IPID is 1 for packet(1)).

Now let's look at packet 101 ~ 104:
101: IPID = 121, compressed_RTP,
102: IPID = 130, CUDP, IPID = 130
103: IPID = 131, CUDP, IPID = 131
104: IPID = 132, CUDP, IPID = 132

Now if packet(103) is received before packet(101), the decompressor context will have IPID = 131, delta IPID = 1, RTP SN = 103, last RTP SN with delta IPID change = 1. When the decompressor receives packet(101),
1) it cannot decompress IPID based on (SN =103, IPID = 131) because IPID has jumped and the difference in RTP SN tells nothing.
2) it cannot decompress IPID based on the knowledge that last RTP SN with delta IPID change = 1, because there have been multiple IPID jumps between packet(1) and packet(100) even though delta IPID doesn't change.
To solve the above problem, the decompressor actually needs to remember the last RTP SN where IPID changed irregularly.

Another  example is
101: IPID = 121, CRTP
102: IPID =  131, CUDP, IPID = 131, delta IPID = 10
103: IPID = 141, CUDP, IPID = 141, delta IPID = 10
104: IPID = 151, CUDP, IPID = 151, delta IPID = 10

If packet(103) is received before packet(101), the decompressor context will have IPID = 141, delta IPID = 10, RTP SN = 103, last RTP SN with delta IPID change = 103. Again, the decompressor will have trouble decoding the late packet(101). One way to solve this problem is for the decompressor to remember both the last and the next to last RTP SNs where IPID changed irregularly.


To summarize, the decompressor needs to remember the following info for the last and the next to last packets where IPID changed irregularly: RTP SN, delta IPID, and IPID.

Regards,
Haipeng

At 12:59 PM 2/16/2005, Colin Perkins wrote:
Begin forwarded message: 
From: Internet-Drafts at ietf.org
Date: 16 February 2005 15:14:15 GMT
To: i-d-announce at ietf.org
Subject: I-D ACTION:draft-koren-avt-ecrtp-reorder-00.txt
Reply-To: internet-drafts at ietf.org

A New Internet-Draft is available from the on-line Internet-Drafts
directories.


        Title           : Packet reordering in Extended CRTP (ECRTP)
        Author(s)       : T. Koren, P. Ruddy
        Filename        : draft-koren-avt-ecrtp-reorder-00.txt
        Pages           : 0
        Date            : 2005-2-15

Extended RTP Header Compression (ECRTP) is tolerant to packet
   misordering. This document describes how ECRTP validates packets
   that arrive out of order.

A URL for this Internet-Draft is:
http://www.ietf.org/internet-drafts/draft-koren-avt-ecrtp-reorder -00.txt



_______________________________________________
Audio/Video Transport Working Group
avt at ietf.org
https://www1.ietf.org/mailman/listinfo/avt



_______________________________________________
Audio/Video Transport Working Group
avt at ietf.org
https://www1.ietf.org/mailman/listinfo/avt