On 04/07/2010 09:02 PM, Pasi Sarolahti wrote:
On Apr 7, 2010, at 7:26 AM, Phelan, Tom wrote:
Have the benefits vs. disadvantages of defining a different DCCP
header for UDP encapsulation been discussed earlier? The current
method saves some redundant header space, but may add to
implementation complexity in the DCCP side. I can't say if this is a
significant concern, but I wonder if it is a problem that DCCP-UDP
supports different set of features than native DCCP, such as not
supporting the short sequence numbers?
[Tom P.] The purpose of short sequence numbers in DCCP-STD is to reduce
header length. Supporting short sequence numbers in DCCP-UDP doesn't
reduce the header size. The purpose of long sequence numbers in
DCCP-STD is to reduce the probability of a blind attacker correctly
guessing the sequence numbers in use.
So in my view short sequence numbers are more of a bug than a feature,
and not supporting them in DCCP-UDP is the better solution.
Ok, this is fair reasoning. But still, as a matter of design principle,
I think it is a little unusual that when receiving a packet for a
protocol, the receiver would need to consider what was the previous
header in order to parse the current protocol header. Ideally one might
want to use the same DCCP implementation regardless of whether the
packets go inside IP or UDP. But I'd be interested to hear what others
think.
[JM]: I personally don't like to idea that the DCCP header is changed
when it goes through UDP encapsulation. Otherwise we are not talking
anymore about just simply UDP encapsulation but rather about a whole new
protocol. So the WG should either consider
a) straight UDP encapsulation of DCCP (DCCP specific or generic? that is
the question), or
b) a new UDP-based DCCP-like protocol, as this draft proposes.
But you shouldn't say that this draft is point a, which it is not.
Regards,
Jukka
