[chord] Chord and SIP

[Emil Sit]

On Wed, 26 January 2005 at 01:47 (+0000), Johnston, Alan wrote:
> I'm interested in finding out about the Chord protocol "on the wire"
> between peers over the Internet.  The documentation I've read so far
> says that it uses sends RPCs over UDP using ephemeral ports.  

We use sun rpc packets.  The packet formats are specified using
XDR and are available at 
    http://amsterdam.lcs.mit.edu/cgi-bin/cvsweb.cgi/sfsnet/svc/
You can also refer to RFC 1832 and 1831.

> Are there any plans to use TLS as a transport? 

I think TLS would be too heavy-weight for the kind of communication
patterns that we currently see in Chord/DHash.  Our storage layer
(DHash) stripes data out over many nodes for resilience and to balance
storage load across participating nodes evenly.  As a result, DHash
exchanges traffic with many of the nodes in the overlay in the course of
storing and retrieving data.  There is no guarantee that once your local
node talks to a remote node once, it will need to talk to that same
remote node again in the near future.  

Even in our small deployments, implementations using persistent
connections (e.g. TCP) have caused the local node to rapidly use up
available socket buffers in the local node's kernel.

> Use of certificates for peer authentication?

Certificates would need to be signed by some sort of central
authority.  Some lines of peer-to-peer thinking are not in
favor of such authorities.  Some previous work in security
has suggested certificate authorities for admission control
(e.g. http://www.cs.rice.edu/~druschel/publications/security.pdf),
but how to securely route packets in structured overlays (such
as Chord) is still an open research question.  


> Transporting Chord over SIP would allow the use of some of SIP's
> security and authentication mechanisms (such as TLS, S/MIME, etc.) but
> I'm still not sure that it is a good justification.

I'm unsure about tunneling/running Chord over SIP as well.  I wouldn't
want to make SIP the next HTTP.

-- 
Emil Sit / MIT CSAIL PDOS / http://pdos.lcs.mit.edu/chord/