[ell-i-developers] Re: Initial plans for a truly minimal UDP/IP for CoAP
- From: Jose Granados Vergara <jose.granados@xxxxxx>
- To: "<ell-i-developers@xxxxxxxxxxxxx>" <ell-i-developers@xxxxxxxxxxxxx>
- Date: Mon, 24 Feb 2014 21:46:38 +0000
I was trying to setup this freertos + UDP project but even though I followed
the instructions and fixed compilation errors I don't get any response, so I
was planning to do a basic UDP stack too starting with dhcp.
Your plan looks good to me, I would only add dhcp.
> El 24/02/2014, a las 21:11, "Pekka Nikander" <pekka.nikander@xxxxxx> escribió:
>
> I've now started the work on a minimal UDP/IP stack for CoAP. Here are my
> current plans; please make questions and comments.
>
> Basic principle: Be liberal in what you accept, conservative in what you
> send. However, due to space limitations the plan is to drop (almost) all
> optional features and support only the bare minimum.
>
> IP
> ==
> No ability to generate packets on its own, only able to reply incoming
> packets.
>
> - IPv4 only, header length always the default 20 bytes
> - Type of Service: ignored when received, copied to a reply
> - ID: ignored when received, copied to a reply
> - Framentation: not supported; dropped if received, never sent.
> - Options: not supported; dropped if received, never sent.
> - Local address: Only one unicast address supported, no multicast support.
> - Remote address: Copied to a reply.
>
> How about the following?
> - TTL: ignored when received, copied to replies.
> - checksum ignored when received, sent as such when replying
> - simply swapping src and dst does not change the checksum, right?
> - if we do anything more but copy to ID and/or TTL, we must implement
> checksum updates...
> - but updating the checksum is easier than verifying/computing it
> - no gateway nor netmask, always send back to the sender ethernet address
>
> ICMP
> ====
> Only supports ping (ICMP echo) as a compile-time option. ICMP errors never
> sent, received errors silently ignored.
>
> ARP
> ===
> - replies to ARP queries pertaining to its own IP address
> - reply Ethernet destination address copied from the received packet
> - does not cache ARP data, as only replies
> - never sends ARP queries itself or keeps state
>
> UDP
> ===
> Again, no ability to generate packets on its own, only able to reply incoming
> packets.
>
> - packets received on non-bound ports silently ignored
> - checksum ignored when received, always zero when sent
>
> Once this is up and running, we can consider adding more functionality, but
> AFAIK this should be enough to allow the host to answer to CoAP packets.
>
> Comments?
>
> --Pekka
>
>
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