RE: [rohc] Problem about list compression
"Lars-Erik Jonsson \(LU/EAB\)" <lars-erik.jonsson@ericsson.com> Wed, 05 April 2006 14:10 UTC
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Subject: RE: [rohc] Problem about list compression
Date: Wed, 05 Apr 2006 16:10:47 +0200
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Thread-Topic: [rohc] Problem about list compression
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From: "Lars-Erik Jonsson (LU/EAB)" <lars-erik.jonsson@ericsson.com>
To: tangzhenghua <tangzhenghua@huawei.com>, rohc@ietf.org
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Hi Zhenghua, I get a little confused by your question since it seems to be addressing how to do things according to RFC 3095, but at the same time you refer to draft-ietf-rohc-rfc3095bis-improvements-01. Anyway, I will try to clarify both the actual functionality of RFC 3095 and the envisioned functionality for "ROHC v2" or "ROHC bis", whatever we prefer to call the envisioned outcome which draft-ietf-rohc-rfc3095bis-improvements-01 aims at. First, what do draft-ietf-rohc-rfc3095bis-improvements-01 aim at? It is correct that "ROHC v2" is planned to only use the generic scheme. Further, v2 is supposed to use a unified mode approach as ROHC TCP, which means a U/O-like scheme. However, "ROHC v2" will clearly be a second generation ROHC variant defining new profile, while current profiles will still stay as defined by RFC 3095. So, what about your question regarding list compression in RFC 3095? You have correctly noticed that gen_id is only needed in U/O-mode. R mode has a sliding window of references, and the compressor must keep in its sliding window all possible references the decompressor can potentially use for decompression. When compressing, the compressed header must be made decompressible with any of these references. The decompressor on the other hand keeps only one single reference, which is acked. There are no sliding windows at the decompressor. This is how it works for several fields in R-mode, and thus also for list compression. Hope this helps! /L-E ----Original Message---- From: tangzhenghua [mailto:tangzhenghua@huawei.com] Sent: den 29 mars 2006 08:33 To: rohc@ietf.org Subject: [rohc] Problem about list compression > Hi,Rohcer's > > I have a problem about list compression > > Section 5.8.6.1 of RFC3095 define the compressed list format > of generic scheme.there is a field of gen_id to express the reference > list But this field just exist at u/0 mode,if compressor and > decompressor work at R mode,How decompressor find the correct > reference list from the compressed list format. > 5.8.6.1. Encoding Type 0 (generic scheme) > > 0 1 2 3 4 5 6 7 > +---+---+---+---+---+---+---+---+ > | ET=0 |GP |PS | CC = m | > +---+---+---+---+---+---+---+---+ > : gen_id : 1 octet, if GP = 1 > +---+---+---+---+---+---+---+---+ > | XI 1, ..., XI m | m octets, or m * 4 bits > / --- --- --- ---/ > | : Padding : if PS = 0 and m is odd > +---+---+---+---+---+---+---+---+ > | | > / item 1, ..., item n / variable > | | > +---+---+---+---+---+---+---+---+ > > For example, > (1)In IR state and R mode,compressor send 5 IR packet to > decompressor,decompressor put this 5 reference list into > sliding window and send ACK to compressor one by one. > (2)Compressor receive the ACK of NO.1 packet after send No.5 > IR packet,So the list of No.1 can be used as reference list. > (3)Compressor receive a new packet marked with No.6.It can be > compressed according to above format . > (4)decompressor receive a compressed list,Because there is no > gen_id in this format and there are 5 reference list in the > sliding window,So how can decompressor choose the reference > list to restore the origin list. > > > Because draft-ietf-rohc-rfc3095bis-improvements-01 > demonstrate that the List compression should only use the > generic scheme.So i am confusing with this problem. > > Can someone give me some suggestion > > Thanks > > Regards > > Zhenghua _______________________________________________ Rohc mailing list Rohc@ietf.org https://www1.ietf.org/mailman/listinfo/rohc
- [rohc] Problem about list compression tangzhenghua
- RE: [rohc] Problem about list compression Lars-Erik Jonsson (LU/EAB)
- Re: [rohc] Problem about list compression tangzhenghua