|
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.
|