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
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 -----
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.