Subject: [6lowpan] comments about the header compression of ipv6 in format-02

From: "郜帅" <[email-masked]>
Date: Mon, 22 May 2006 10:26:07 +0800

Hi all:

  In Format-02,it is suggested that the hoplimit in ipv6 header should be treated as non-compressed field. I think this byte,that is to say,the hoplimit can also be compressed.

  The reason is as follows:

  In Format-02, adaptation layer is used to find route and send packet.In the mesh delievery frame, there is a "hops left" field which is decreased by one when the packet passes one router. Hence,we can use the "hops left" in mesh delievery frame instead of the hoplimit in the ipv6 header. 
  And if we compress the hoplimit, how can it be obtained at the destination node? we can use the idea of tunnel for reference.  Before sending a ipv6 compressed packet,we can get the hoplimit out, and put its value to the "hops left"  in mesh delivery field, then,we needn't transfer the hoplimit any longer when the packet is routed. And at the destination node ,when we want to use the hoplimit, we can get the "hops left" value in mesh delivery field out,and put its value to the hoplimit.In this way,we can compress the hoplimit.     
  Therefore,the ipv6 header can be compressed to only one octet.
  
  It's noted that the length of hoplimit in ipv6 header is 8bits, the length of hop left  in mesh delivery field is 6bits. Here we can assume that 6 bits hoplimit is enough in 6lowpan.  

              copy hoplimit to hopsleft                   copy hopsleft to hoplimit
origin packet--------------------------->compressed packet-------------------------->origin packet

   Any comments is welcome. 
	
 Thanks. 

Regards,
　　　　　　　　Gao Shuai
				
				[email-masked]
　　　　　　　　　　2006-05-22
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