Hi, H.225.0 section 6.2.2 mandate the size of video packet not to exceed the MTU size unless the macro block is larger then the MTU. It also say that the frame have to be broken on a GOB or macroblock boundary. The reason is for robustness of information. If a packet is lost then you are losing part of the frame and can still synchronize on the rest of information or replace the missing part. Roni Even

-----Original Message----- From: Rosen, Brian [mailto:Brian.Rosen@MARCONI.COM] Sent: Thursday, October 26, 2000 4:09 AM To: ITU-SG16@MAILBAG.INTEL.COM Subject: Re: Sanity check on Packet Sizes....

There is the "real" answer, and the practical answer.

The real answer is that depending on what kind of network you are on, you could see, in theory, packets of up to 64K bytes. 4K bytes can actually be seen in some Gig-E systems. Whether you will find a video codec using such large packets sizes or not is uncertain; I've never seen one.

It used to be that we thought 1510-odd bytes was the biggest practical packet you see on a LAN, but that's no longer the case. There is a lot of code around that fails above that 1500 ish number.

Brian

-----Original Message----- From: Chris Farmer [mailto:cfarmer@smithmicro.com] Sent: Wednesday, October 25, 2000 9:05 PM To: ITU-SG16@mailbag.cps.intel.com Subject: Sanity check on Packet Sizes....

Okay,

I was researching an arcane fact on the theoretical and practical sizes for RTP packet sizes for video conferencing.

What I have come up with is: There is specific RFC's about implimenting H.263, H.261, G.723, but I'm looking for just an overall practical size to check input buffer sizes.

RFC 1889 RTP packet structure referes to 768, RFC 791 RFC 768 UDP refers to obsolete RFC 760. RFC 791 states in the Glossory, ARPANET messages max size is about 1012 octets (8096)bits. ARPANET packet max size is about 126 octets (1008) bits.

As a client side EP, should I be concerned about the ARPANET message size or the ARPANET packet size?

RFC 760 states: 65,536 octets theoretically, put not practical Page 22, every destination should be able to receive a datagram of 576 octets in one piece or as fragments to be reassembled

so my guess here is 4608 bits max? Or is this too low level and there is another RFC that I should reference?

Any help in this direction?

Thanks,

Christopher B. Farmer Software Engineer Smith Micro Software, Inc. (503) 641-1221 ext 28 ====================================================================== Daily C\C++ Tidbits at www.EngageUs.com\c "Challenges in life are inevitable. Failure is optional" - Roger Crawford ======================================================================

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