Hi Jonathan, I am ok with 2 or 3. Regarding compression of both ports simultaneously, I do not know if it useful, but as we must support at least 3 scenarios (src only compressed, dst only, or none), we need two bits. Hence I would say we can reserve the 4th value for the case where both ports are compressed.
Regards, Julien -----Original Message----- From: Jonathan Hui [mailto:[EMAIL PROTECTED] Sent: mercredi 8 octobre 2008 16:45 To: Julien Abeille (jabeille) Cc: [email protected] Subject: Re: Hc-01 LOWPAN_UDP encoding Hi Julien, Fixing UDP compression was definitely on the list of TODOs. So there are a few options: 1) Expand the compressed range to 256 ports (the encoding lengths for the ports are then 2, 3, or 4 bytes). 2) When compressing only one port, add a 4-bit pad as you suggest. However, I would rather add the 4-bit pad to be with the 4-bit compressed port and keep the 16-bit uncompressed port byte-aligned (the encoding options would be 1, 3, or 4 bytes). 3) A hybrid of the two: When only one port is compressed, the compressed form is 8 bits (don't waste the 4 bits on padding). But when both ports are compressed, both only 4 bits. 00 - Neither source nor dest are compressed 01 - Source port uncompressed, dest port 8 bits. 10 - Source port 8 bits, dest port uncompressed 11 - Source port 4 bits, dest port 4 bits. Basic question to ask the group is if compressing both source and dest ports to 4 bits simultaneously useful? -- Jonathan Hui On Oct 8, 2008, at 2:22 AM, Julien Abeille (jabeille) wrote: > Hi Jonathan, all, > > one comment regarding hc-01 LOWPAN_UDP encoding for now source and > destination ports compression are splitted. It means if only one of > them is compressed, the UDP compressed fields will be 36 bits long > (4bits port + 16 bits port + checksum). We lose byte alignment this > way. > > to avoid this, you could either not split the compression of ports, or > when only one is compressed, pad to 3bytes (4 bits port + 16 bits port > + 4bits padding) What do you think? > > Cheers, > Julien > > _______________________________________________ 6lowpan mailing list [email protected] https://www.ietf.org/mailman/listinfo/6lowpan
