Subject: [core] coap #103 (new): Message sizes

From: "core issue tracker" <[email-masked]>
Date: Mon, 07 Feb 2011 17:46:11 -0000

#103: Message sizes

 This ticket is to incorporate the results of the (yet to happen)
 discussion on message sizes into the draft.

 Issues:

   1. Implementations need to allocate a buffer for incoming messages.

   2. Messages larger than a fragment result in undesired packet
 fragmentation.

 On the first issue, the draft could add information about implementation
 strategies with limied buffer sizes, such as the following:

 Implementations are usually able to determine if the trailing portion of a
 datagram was discarded and to retrieve the initial portion. So, if not all
 of the payload, at least the CoAP header and options are likely to fit
 within the buffer. A server can thus fully interpret a request and return
 a 4.13 (Request Entity Too Large) response if the payload was truncated. A
 client receiving a response larger than the buffer can repeat a safe
 request with a suitable Block Option.

 The second issue cannot be solved without referring to the IP layer and
 link layer sizes. In addition to IPv6, also IPv4 should be addressed.

 With IPv4, it is harder to ensure that there is no L3 fragmentation.
 Implementations may want to limit themselves to usual IPv4 datagram sizes
 such as 576 bytes (note that, however, the minimum value of the maximum
 transmission unit for IPv4 is 68). Implementations might also set the DF
 bit and perform some form of path MTU discovery.

-- 
----------------------------+-----------------------------------------------
 Reporter:  hartke@…        |       Owner:  cabo@…      
     Type:  enhancement     |      Status:  new         
 Priority:  minor           |   Milestone:              
Component:  coap            |     Version:              
 Severity:  -               |    Keywords:              
----------------------------+-----------------------------------------------

Ticket URL: <http://trac.tools.ietf.org/wg/core/trac/ticket/103>
core <http://tools.ietf.org/core/>