RE: [rohc] [Fwd: I-DACTION:draft-svanbro-rohc-lower-layer-guideli nes-00.txt]

[wnk@fub.it (Roberto Winkler)]

Anders,

thanks for the clarification, I had not thought about this possibility.

ps I'm on the list, you don't need to Cc messages.

Best regards

Roberto

>Ciao Roberto,
>
>It is true that the error detection indication offered
>by the physical layer (L1) is valid for a whole transport
>channel, but from that fact one can not draw the conclusion
>that the support requested by Krister's document is not
>offered by the 3GPP specs of today.
>The solution is to define seperate transport channels
>for the different parts of a "frame".
>
>This is supported already in the Rī99 where it is used
>to get efficient radio transport of the CS speech service.
>A speech frame can be divided in 3 groups of bits. One of
>these groups (including the Class A, or 1a, bits) should be
>covered by a CRC. This can be done by spearating these bits
>into a transport channel of its own, where the CRC is enabled.
>
>The exact same method could be configured to offer an error
>detection indication for the compressed header bits only.
>If this is the right way to do it or not, is still an open
>issue though, but the support is already there if needed.
>
>
>Tanti Saluti,
>
>Anders Liljekvist
>WCDMA Systems Management
>
>Ericsson Radio Systems AB
>Torshamnsgatan 33                Tel.  +46 8 58530974
>SE-164 80 STOCKHOLM              Fax.  +46 8 50877300
>Sweden                           Cell. +46 70 6760862
>
>
>-----Original Message-----
>From: wnk@fub.it [mailto:wnk@fub.it]
>Sent: den 17 mars 2000 08:56
>To: rohc@cdt.luth.se
>Subject: Re: [rohc] [Fwd:
>I-DACTION:draft-svanbro-rohc-lower-layer-guidelines-00.txt]
>
>
>Krister and all other HC-ers,
>
>It's true what the sentence in latest Krister's mail says
>
>>RLC and PDCP are layer 2 protocols in 3GPP and they don't provide with
>>this kind of error detection. The error detection is instead done at the
>>physical layer - layer 1.
>
>but, please, consider that this indication is provided for an entire
>Transport Block, which may contain the entire (compressed or not
>compressed) header but also bits from the payload of the PDCP PDU
>(depending on the data rate on the radio interface, the PDCP header length
>and L2/L1 configuration). In this case the CRC status indication provided
>by L1 to L2 is of no help in determining whether the header is ok or not,
>as the possible errored bits in a Transport Block may pertain to the header
>as well as to the payload of the PDCP PDU. The consequence is that L2 has
>no means to provide the required service to header
>compression/decompression (unless data rates are constrained to values that
>ensure a 'perfect' mapping between the boundaries of the (compressed)
>header and those of one or more radio frames (e.g. 10 ms worth of
>information).
>
>To summarize, I don't think that current 3GPP specs support our needs and
>I'm not sure that we can go on by simply saying we in ROHC focus on
>development of an efficient scheme and how to use it in UMTS it's a matter
>of 3GPP. While pushing 3GPP to improve their specs, we should also take the
>current status into account and work towards good solutions that fit the
>best possible to the state of the art.
>
>I understand these issues are not in the scope of this IETF group, but I
>bet that many of us have UMTS and other 3G systems when dealing with header
>compression strategies so please have patience....
>
>I wish I could attend this IETF meeting.....
>
>BR
>
>Roberto
>
>
>
>>Roberto,
>>
>>The purpose of producing a draft in the ROHC wg with lower layer
>>guidelines is to push these kind of discussion and work to the
>>standardisation bodies were they belong. This allows us in ROHC to focus
>>on development of an efficient scheme. E.g., the discussion of how to
>>enable error detection in for example 3GPP type of links should thus be
>>solved in related groups in 3GPP. It is however  important that we in
>>the ROHC wg makes sure that the scheme is possible to use in relevant
>>systems such as those standardized by 3GPP. However, I think that this
>>specific question is an issue for 3GPP rather then the ROHC wg.
>>
>>To give an short answer:
>>RLC and PDCP are layer 2 protocols in 3GPP and they don't provide with
>>this kind of error detection. The error detection is instead done at the
>>physical layer - layer 1. If you look at the attributes of an UMTS
>>bearer (in 3GPP 23.107 for example) you'll se that there are parameters
>>for residual bit error rate, etc. It is possible to choose a certain
>>value for residual BER, which results in that a CRC of for example 8 or
>>16 bits is used for error detection. Moreover, in release 99 of 3GPP is
>>already now RFC2507 supported and 2507 requires also error detection on
>>headers.
>>
>>Hence, I am confident that 3GPP type system can provide with the
>>required error detection but we must put requirements on this error
>>detection.
>>
>>/ Krister
>>
>
>Roberto Winkler
>Senior Researcher
>Fondazione Ugo Bordoni
>Via B. Castiglione, 59
>00142 Rome Italy
>
>tel +39 0654803411
>fax. +39 0654804404
>e-mail wnk@fub.it
>
>
>
>---
>Mailing list for Robust Header Compression WG
>Archive: http://www.cdt.luth.se/rohc/


Roberto Winkler
Senior Researcher
Fondazione Ugo Bordoni
Via B. Castiglione, 59
00142 Rome Italy

tel +39 0654803411
fax. +39 0654804404
e-mail wnk@fub.it