Re: [Anima-bootstrap] bootstrap over CoAP

[Brian E Carpenter <[e-mail]>]

On 10/07/2016 07:40, Carsten Bormann wrote:
>>> I'm not sure I understood that part of the draft*), but generally CoAP
>>> is designed so you can avoid fragmentation 
>>
>> That isn't what the draft seems to say, though. However, it's clearly talking
>> about application-layer fragmentation to avoid IP fragmentation.
> 
> (that's segmentation...  I know.)
> 
>>> (and use the segmentation
>>> provided by draft-ietf-core-block instead); the latter has per-segment
>>> reliability (acknowledgements and retransmits).   DTLS may require
>>> fragmentation during its handshake; this is mitigated if you can use a
>>> PSK (symmetric) or, if you need asymmetric, ECC-based ciphersuite, which
>>> allows the packets to stay well below 1280 bytes.
>>
>> Right. So the app layer chops the message into <1280 byte pieces, and one
>> of them is lost...?
> 
> Each of those segments ("blocks") is (actually, can be, but you do want
> to do this with the block-wise protocol) transmitted reliably, so it
> doesn't get lost.

OK, so I think that a couple of sentences in draft-pritikin-coap-bootstrap
could clarify all that.

Thanks
    Brian

> Grüße, Carsten
>