[openbeosnetteam] Re: Information about routes and interfaces for protocols

> -----Original Message-----
> From: openbeosnetteam-bounce@xxxxxxxxxxxxx 
> [mailto:openbeosnetteam-bounce@xxxxxxxxxxxxx] On Behalf Of 
> Oliver Tappe
> Sent: dimanche, 30. juillet 2006 19:51
> To: openbeosnetteam@xxxxxxxxxxxxx
> Subject: [openbeosnetteam] Information about routes and 
> interfaces for protocols
> 
> Hi there,
> 
> now that a first version of UDP is at least basically 
> working, I'd like to continue with filling in some holes in the stack:
> 
> UDP needs to know the IP of the outgoing interface when sending data. 
> Normally, only IP would determine this (as a result of the 
> routing decision), but since UDP requires it, too, I have 
> implemented a workaround that grabs the domain (via 
> get_domain()) and then fetches the route for the given 
> destination address. Now that UDP knows the route, it can 
> copy over the source address from the route. 

Maybe having the UDP checksum calculated afterwards is possible ?

We pass the UDP payload to Ip layer without having calculated UDP checksum
and we tag somewhere that we want a callback as soon as a routing decision
is taken.
Is this possible that a route changes between UDP try to guess it and IP
layer makes its own decision afterwards ?

A way to "tag" the buffer and let the IP layer call back UDP CRC calculation
after IP routing decision is taken by IP layer.

I've also seen that there are also incrementals CRC algos.
Meaning we can calculate the UDP checksum without the pseudo header at
first, and let the IP layer finish the calculation using that kind of algo
for the remaining bytes (no duplicate effort nor callbacks)... 
See http://www.faqs.org/rfcs/rfc1624.html or
http://www.inf.uni-konstanz.de/disy/publications/waldvogel/braun01fast.pdf
or http://www.haifa.il.ibm.com/satran/ips/crc_23feb2003.pdf

Is there another reason than CRC calculation for what IP source and
destination has to be known to UDP layer ?

   Regards,

      Emmanuel

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