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

RE: Adaptation field use in ULE / MPG2-TS specification



Hi Marie-Jose,
    I understand your point here about extension headers. But actually Adaptation field specified here is part of MPEG2-TS header and not ULE, in that case even ULE is a payload for MPEG2-TS. If adaption field control is 10 or 11 in bits, MPEG2-TS contains private adaption field, and incase of "10" we need not care about anything, but still ULE draft says anything other than " 01" in AFC, receiver MUST discard.
    Thanks for your comment Tor Brekke, but i wonder why we have such limitation in ULE, even though we are not worried in ULE about the MPEG2-TS private section of Adaption field, if we are not going to take any action based on the adaption field and control field we can just ignore. I see this as an implementation issue and should not be limited in specification/draft.
 
transport_packet(){
        sync_byte                                                                                                 8 bslbf
        transport_error_indicator                                                                            1 bslbf
        payload_unit_start_indicator                                                                       1 bslbf
        transport_priority                                                                                       1 bslbf
        PID                                                                                                          13 uimsbf
        transport_scrambling_control                                                                      2 bslbf
        adaptation_field_control                                                                              2 bslbf
        continuity_counter                                                                                     4 uimsbf
        if(adaptation_field_control=='10' || adaptation_field_control=='11'){
              adaptation_field()
        }
        if(adaptation_field_control=='01' || adaptation_field_control=='11') {
             for (i=0;i<N;i++){
                 data_byte                                                                                        8 bslbf
            }
       }
}
 
here N data_byte's is SNDU as specified by ULE.
 
Also ULE cannot limit anything on exisiting underlying protocol as such MPEG2-TS. But definitly it can limit or provide more services to above layers.
 
 
Best Regards,
William StanisLaus
CalSoft, Nortel Networks Division
 
-----Original Message-----
From: owner-ip-dvb@erg.abdn.ac.uk [mailto:owner-ip-dvb@erg.abdn.ac.uk]On Behalf Of Marie-Jose Montpetit
Sent: Tuesday, April 13, 2004 4:00 PM
To: ip-dvb@erg.abdn.ac.uk
Subject: Re: Adaptation field use in ULE / MPG2-TS specification

Thanks for you input. If you follow recent discussions there is a proposal to use extension headers in ULE to support system specific signalling (and other). It would be interesting to know more about how you process the information but I think our philosophy would be to use the headers in the same way as you describe: transparent to system who do not know what to do with them, processed by the ones who do. This is consistent with IPv6 extension headers and also with other implementations of extension headers (cable for example).
 
So I do believe we could use ULE in RCS. Actually in a recent study sponsored by ESA we showed that for traffic with a lot of ACK bursts (http: for example) ULE was very efficient because of it's packing capability.
 
Again thanks for your input.
 
Marie-Jose
 
 
 
----- Original Message -----
From: Tor Brekke
Sent: Tuesday, April 13, 2004 3:02 AM
Subject: Adaptation field use in ULE / MPG2-TS specification


Hello,

I am jumping into this discussion at a fairly late stage. Having just read the ULE draft I have to make a comment about the use of the adaptation field though. In the draft it says that "TS Packets from a ULE Encapsulator MUST be sent with an AFC value of '01'", i.e. without adaptation field. Now the adaptation field contains a private field which according to the MPG2-TS specification (ISO/IEC 13818-1) can be used to transmit system dependent data.  
Now to the question: Why is this limitation imposed on ULE?  

I have two main reasons to ask this.
1) Firstly there is ongoing work to use the private adaptation field for network internal signalling in the DVB-RCS standard. This means that ULE will not work over DVB-RCS systems employing the adaptation field signalling.
2) As far as I have been able to determine all other encapsulation forms over MPG2-TS are transparent to the adaptation field, i.e. the adaptation field and payload are handled independently (even though there may be an implicit connection between them). It seems strange to break this logicinf the MPG2- TS mechanism for a new encapsulation type.

Best Regards
Tor Brekke
Nera Broadband Satellite AS.