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
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