On Sun, 24 Jan 1999, SOM Bandyopadhyay wrote:

> Thanks Magnus for ur quick reply.
> 
> Is there a tcp based implementation planned in the near future? 
> What are the reasons of selecting udp as the preferred transport in afs or coda?

First of all Coda inherits RPC2 from AFS.  When the AFS project started,
TCP was thought not to be very scalable and there were many subtle
platform dependent issues.  So UDP turned out to work a lot better.

Given that at present the entire world revolves around TCP, this may no
longer be true.  In defense of UDP, it is true that handling very many TCP
connections is quite hard, even for large systems, and particularly on
Windows maybe.

It's working reasonably well, and at present we don't have plans to change
it.  We have contemplated and experimented a bit with replacing the side
effect with a TCP based one, but I don't see that come in as a usable
option unless someone is going to throw a lot of time at it.

- Peter -




> 
> thanks, som.
> 
> >>> Magnus Ahltorp <map_at_stacken.kth.se> 01/24 5:15 PM >>>
> > I have this question for CODA ...
> 
> I really only know (disconnected) AFS, but I hope I'm correct in this.
> 
> > 1. Is there a callback mechanism from CODA server to client?
> 
> Yes, when files are updated, the client gets a message from the
> server.
> 
> > 2. If so, does it happen when clients are not connected to servers?
> > In that case, do CODA servers initiate TCP connections to CODA
> > clients?
> 
> The communication is UDP based. This means that there are no TCP
> connections between the client and the server. "Disconnected" is a
> state when the network between the client and the server is not able
> to forward packets (as in a offline laptop).
> 
> For obvious reasons, the server cannot contact the client when it is
> offline. Coda solves this through reintegration when the client is
> back on the network.
> 
> /Magnus
> map_at_stacken.kth.se 
> 
>