Re: [lp-wan] Fw: re-order header field request

["Carles Gomez Montenegro" <[e-mail]>]

Hi,

> Hi Arun and all,
>
> After reading through the draft-ietf-lpwan-ipv6-static-context-hc-04,
> one point needs to be exiplicit described: how many Rule IDs are used to
> fragment one large IPv6 packet?

What we currently have in the document is:

   "The Rule ID in a fragment is set to a value that indicates that the data
   unit being carried is a fragment."

So currently we do not explicitly indicate how many Rule IDs are needed
for fragments of a large IPv6 packet. The most efficient solution is to
just use one Rule ID to signal "this is a fragment". However, it is
probably safe to keep this open in the SCHC document, so that future
technology-specific SCHC over foo documents have freedom to specify
whatever better suits their needs.

> By my understanding, whne one IPv6 packet is fragmented, it adopts only
> one Rule ID.
> Each fragment contains the same rule ID and Dtag.
> Anything wrong?

DTag (if present) has to be the same in all fragments carrying the same
IPv6 packet.

One Rule ID to signal 'this is a fragment' is fine.

> Such a way to deliver the repeated Rule ID can be suppressed.
> It may be available to have the first fragement only include the Rule ID
> while containing the Dtag.
> And the following successive fragments have the Dtage without the Rule ID.
> The receiver can get the correct Rule ID from the first fragment referred
> as the same Dtag.
>
> The Rule ID is suppressed in fragments from the second to the last.

I think there are problems with this proposal. If the Rule ID of
successive fragments is suppressed, how does a receiver know whether those
successive data units are actual fragments or not, or how the data unit
has to be processed?

Thanks,

Carles