Subject: [p2p-sip] [P2P SIP] Hierarchical P2P architecture

From: kumarb at research.panasonic.com (Brijesh Kumar)
Date: Fri Sep 2 10:50:57 2005

Marc:

We actually have fully evolved designed of P2P SIP based on hierarchical
DHT - the work builds upon the work of Bryan, Cullen and others that you
mentioned.

My colleague Mahfuz and I created this design quite some time ago and hope
to publish this very soon in this forum and/or in IETF as soon as we are
done with the draft. The document already exists in the non-IETF draft form
and we are right now converting that to an IETF draft.  Our target was for
IETF 63, but we just got tied with few other things. We have looked the
issues of reliability and load balancing, security and others and have
defined various procedures for node registration and maintaining peer
hierarchy.

We hope to get that out very soon ...

cheers,

--brijesh
----- Original Message ----- 
From: "zze-BAILLY Marc RD-CORE-LAN" <[email-masked]>
To: <[email-masked]>
Sent: Friday, September 02, 2005 9:45 AM
Subject: [p2p-sip] [P2P SIP] Hierarchical P2P architecture

The current work has shown 2 main approaches to add P2P to SIP
architecture

- P2P SIP: use SIP as the protocol of the P2P layer (Bryan, Jennings,
Schulzrinne approach) and with of course SIP as the above layer for call
control
- SIP P2P: use SIP only at the call control layer and let P2P layer use
its own protocol, the two (SIP and P2P layer being glued by an interface
typically the location service interface (Johnston approach)
Lots of rationales seem to oppose these two approaches.

But using a 2 level hierarchical P2P model, it seems that we could
combine these 2 views.

This idea of hierarchical P2P was already proposed in section 6.4.1 of
Singh and Schulzrinne's paper.
(http://www1.cs.columbia.edu/~kns10/publication/sip-p2p-design.pdf).

On this topic about hierarchical P2P systems, there is an interesting
paper called "Hierarchical P2P systems"
(http://www.eurecom.fr/~btroup/P2P/papers/Hp2p.pdf). One section
presents some adaptations to Chord algorithm which could be done to
implement a top level DHT :
[Section 4.2] "In the top-level overlay network, each "node" is actually
a group of peers. This implies that the top-level lookup system must
manage an overlay of groups, each of which is represented by a set of
superpeers that may fail independently from the group they belong to.
Chord requires some adaptations for being used in the top-level overlay
network and managing groups instead of nodes."

Our idea would be to use P2P SIP (with these adaptations) at the top
level for interconnection routing but let domains use their own SIP P2P
or even not a P2P approach.
Regarding this top level DHT used for inter domains routing, there are
two approaches:
- The set of nodes responsible for a domain joins this DHT with a random
ID and register their domain on KeyID = HASH(domain.com).
- The set of nodes responsible for a domain joins this DHT with the ID =
HASH(domain.com).

We would privilege the second approach because it better takes
heterogeneity in sub networks size into account: If a set of peers from
a very small network in the top level DHT is responsible for storing the
association between AOR and contact SIP for a domain with a large amount
of users, this set of peers risks to be overloaded (maybe this problem
could be avoided thanks to caching mechanism).

This architecture seems to tailor the benefits of the 2 approach (P2P
SIP and SIP P2P):
- offer standardized interconnection to isolated islands (which is, I
guess, one of the goals of the P2P Sip WG) in a P2P way
- does not preclude the use of P2P SIP in a domain
- does not preclude the use of optimized P2P layer protocol (in a
specific environment for example mobile or wifi network)
- does not preclude to connect centralized, by nature, PSTN GW

This would mean that we must continue the on-going work of P2P SIP for
him to be applied in a SIP P2P world but extend it with a top level
overlay view for interconnection.

What do you think of this vision?

Best regards.
Marc Bailly

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