Subject: [Sip] RE: EPIC

From: "Price, Richard" <[email-masked]>
Date: Thu, 2 Aug 2001 13:05:02 +0100

Hi Aniruddha,

We can implement "learning" EPIC in 3 ways:

Offline version: Train the scheme offline for, say, SIP compression and
put the resulting profile into an Internet Draft.

Profiling version: Whilst performing SIP compression, dynamically update
the profile at the compressor only. Periodically download the updated
profile to the decompressor, and switch to the new profile when the download
is complete.

Dynamic version: Update the profile simultaneously at the compressor and
decompressor. Note that as both the compressor and decompressor must
see exactly the same packets, this only works over a reliable link.

My own preference for SIP compression is just to use the offline version.
If the profile becomes out-of-date then we suffer a slight drop in compression
efficiency, but this is outweighed by the very low working memory requirements
(as the SIP profile can be fixed in ROM).

Richard P

-----Original Message-----
From: Aniruddha Kulkarni [mailto:[email-masked]]
Sent: Thursday, August 02, 2001 12:03 PM
To: Price, Richard
Cc: SIP mailing-list; RoHC mailing-list
Subject: EPIC

Hi Price

    I read about "learning" EPIC but I don't understand how a decompressor will know what a "learning" compressor has "learned" so far? 
    I understand that both compressor and decompressor negotiate the profile and by that they know how other side will behave. But the compressor is "learning".. if I have understood it correct then "learning" would mean that the compressor will learn about new fields in the packets and add them to existing profile and other part is choosing compression scheme depending on probability of occurance of the field.. how does decompressor synchronize with that? How will this be handled in packet loss conditions?

---Aniruddha