Subject: [6lowpan] Compressing the extension header

From: Daniel Gavelle <[email-masked]>
Date: Tue, 26 Jan 2010 17:29:27 +0000

When ROLL sends a packet from the DAG root to a node over a 6LowPAN 
network, there are two choices:-

(1) Source routing is used, where the DAG root (edge router) is the only 
node that knows the route state.  The root node would then use the 
"Routing Header" specified in RFC 2460 to specify the route.

(2) Each routing node has a full routing table that knows the route to 
all its descendants (grand children, great grand children etc) as well 
as its immediate children and parent.

Option (1) has several advantages, including reduced memory requirements 
for normal router nodes and avoiding the need to poison routes as the 
DAG changes.

However, using source routing requires the full IPv6 address of each 
segment to be carried in the extension header. This will reduce the 
effectiveness of the very good work that has been done in 
draft-ietf-6lowpan-hc-06 to reduce the size of the IPv6 header.

Adding context based compression of the addresses in a routing header 
would result in a much smaller header.  All the addresses will have at 
least the same /64 prefix and if short addresses were used, only 16 bits 
would need to be stored for each address.

Daniel.

-- 
__________________________________________________
Daniel Gavelle, Software Engineer
Tel: +44 114 281 2655
Fax: +44 114 281 2951
Jennic Ltd, Furnival Street, Sheffield, S1 4QT, UK
Comp Reg No: 3191371  Registered In England
http://www.jennic.com
__________________________________________________

---

From: "Anders Brandt" <[email-masked]>
Date: Wed, 27 Jan 2010 13:25:39 +0100

Daniel,

I agree.

This sounds like an obvious extension to the IPHC draft.

It is a fair requirement that all intermediate nodes are
in the same (local) subnet and may thus be compressed to short
addresses.
For sure the Internet or any backbone (?) will not use source routing
anyway.

Cheers,
  Anders

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On
Behalf Of Daniel Gavelle
Sent: Tuesday, January 26, 2010 18:29
To: [email-masked]
Subject: [6lowpan] Compressing the extension header

Daniel.

--
__________________________________________________
Daniel Gavelle, Software Engineer
Tel: +44 114 281 2655
Fax: +44 114 281 2951
Jennic Ltd, Furnival Street, Sheffield, S1 4QT, UK Comp Reg No: 3191371
Registered In England http://www.jennic.com
__________________________________________________
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