Re: [rohc] TCP/IP EPIC profile

["West, Mark (ITN)" <[e-mail]>]

>>>[Mark]
>>>Ok, see my discussion above for one way to support such a flag.
>>>
>>>Also, consider the following fragment of EPIC-speak...
>>>
>>>A_and_B = AB_1(50%) | AB_2(50%)
>>>
>>>AB_1 = XXXX
>>>        YYYY
>>>
>>>AB_2 = PPPP
>>>        QQQQ
>>>
>>>which says that if A is encoded as XXXX then B is encoded as
>>>YYYY (and
>>>this happens 50% of the time), but if A is encoded as PPPP then B is
>>>encoded as QQQQ (and this happens 50% of the time).
>>>
>>>
>>[Hongbin]
>>Great idea! Such a simple format is really what we need! However, you
>>
> need
> 
>>'otherwise' to simply the enumeration of all possible, however,
>>
> ignorable
> 
>>(from the point of overall performance) combinations of encodings of
>>
> these
> 
>>fields (there may exist {A:XXXX B:QQQQ} or {A:PPPP B:YYYY}).
>>
>>
> 
> Yes, the extension for supporting correlation can really enhance the
> expression ability of EPIC-LITE. For ROHC-TCP case, we can combine
> bulk-data-co, bulk-ack-co, interactive-co to a more intuitionistic
> representation.


No, the above approach cannot usefully encode the flow behaviour in this 
way.

There are different types of correlation, where the probability 
distribution is:
- random, but known
- stable, but unknown

Something like the 'marker bit + timestamp' of the RTP profile fall into 
the former category -- you can think about putting a rough probability 
on the marker bit being set.
This is notated as the 'A_and_B' example above.

However, the TCP flow behaviour is a higher level dependency which 
should remain stable for the duration of the flow (or for significant 
proportions of the flow).
This uses the FORMAT construction.

> 
> Since this group wants to use EPIC-LITE as a "generic compressed format
> generator" for use in ROHC profile standardization, it would be better
> that EPIC-LITE can provide more convenience and intuitionistic way for
> developers to write the profile.


-- 
Mark A. West, Consultant Engineer
Roke Manor Research Ltd., Romsey, Hants.  SO51 0ZN
Phone [phone]   Fax  [phone]

(Yes, I do know that my disclaimer is in an attachment.  And, no, I 
didn't ask for it to be that way)