Samita, Please see the comments in line. > -----Original Message----- > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf > Of Samita Chakrabarti > Sent: Friday, October 14, 2005 9:32 AM > To: [EMAIL PROTECTED] > Cc: [email protected] > Subject: [6lowpan] MultiHop Format document issues > > > Hi Gabe, > > I have some questions regarding the M bit in lowpan. > > The draft says in pg 5: > The LoWPAN payload (e.g., an > IPv6 packet) follows this encapsulation header. Alternatively, if > the 'M' bit is on, before this actual payload, a "Final Destination" > field will be present (Section 9). > > On pg 6 > M: This bit is used to signal whether there is a "Final Destination" > field as used for ad hoc or mesh routing. If set to 1, a "Final > Destination" field precedes the IPv6 packet (Section 9). > > Q1: What is meant by 'used for adhoc or mesh routing' ? I assume that > it > means M bit is used for both control and data path for multihop routing > - > is it correct? > > If it's used for data routing in mesh-network, then I see why the draft > wanted to keep original MAC source address field unchanged. But I > beleive > the MAC implementation sets its own MAC address anyway when it transmits > a packet. ( I don't know of all implementations though). > > It seems if we can come up with a IEEE address format for lowpan, then > it can be compressed easily over a LowPAN network to include both > originator address and final address. > > ---------------------------------------- > 9. Packet Delivery in a Link-Layer Mesh > > A device that wishes > to send a packet may, in such cases, use other intermediate devices > as forwarders towards the final destination. In order to achieve > such packet delivery using unicast, it is necessary to include the > final destination in addition to the hop-by-hop destination. This > final destination may be expressed either as a layer 2 or as an IP > (layer 3) address. > > In the latter case, there is no need to provide any additional header > support in this document (i.e., at the sub-IP layer). The link-layer > destination address points to the next hop destination address while > the IP destination address points to the final destination (IP) > address (that may be multiple hops away from the source). Thus, > while forwarding data, the single-hop destination address changes > hop-by-hop pointing to the "best" next hop, while the destination IP > address remains unchanged. > ---------------------------------------------- > Does the above paragraph mean we could have M bit set and final > destination > address could be a 16 byte IPv6 address? > I wonder why do we need IPv6 address > in M bit case? Shouldn't the final IP destination be extracted from the > IPv6 header in the payload? Not sure, what it means by 'any additional > header support'.
The final IP destination can be extracted from the payload if it contains the IPv6 header). But, if the IP packet is fragmented in the payload, all the fragments except the first one do not contain the destination address. This means that the adaptation layer should provide its own final destination field without relying on the payload. I hope I got the right point of the question. > > I wonder what is the need for supporting a L3 address in final > destination > field (when it talks about packet delivery in the link-layer)? > > Thanks, > -Samita > > > _______________________________________________ > 6lowpan mailing list > [email protected] > https://www1.ietf.org/mailman/listinfo/6lowpan _______________________________________________ 6lowpan mailing list [email protected] https://www1.ietf.org/mailman/listinfo/6lowpan
