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

From: marc1.bailly at rd.francetelecom.com (zze-BAILLY Marc RD-CORE-LAN)
Date: Fri Sep 2 09:45:50 2005

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

---

From: bryan at ethernot.org (David A. Bryan)
Date: Fri Sep 2 10:37:17 2005

I definitely agree this is important. I think there is even a slightly
more fundamental issue touched on here that needs to be discussed,
which is interconnection of groups (realms?) of P2P SIP users. One way
(and one I think is a good one) is to interconnect them in a P2P way,
but we should also discuss other approaches, such as nodes that
participate in each realm and serve as "gateways" between them, or
even techniques using the PSTN to bridge (ugh), etc.

Also related to this, this list has touched on at least 3 different
applications but using similar routing technology -- connecting nodes,
interconnecting groups of nodes, and using P2P to load balance
servers. I think it would be interesting to see if, at all possible,
we can use the same protocol for all applications (maybe not, but it
would nice!)

--David

On 9/2/05, zze-BAILLY Marc RD-CORE-LAN
<[email-masked]> wrote:
> _______________________________________________
> p2p-sip mailing list
> [email-masked]
> http://lists.cs.columbia.edu/mailman/listinfo/p2p-sip
>

---

From: slavitch at gmail.com (Michael Slavitch)
Date: Fri Sep 2 10:44:44 2005

The value of P2P-SIP rises immensely when realms can be both interconnected 
and realm members, or services, (like, dare I say, E911) identified. Some 
realms will be ad-hoc where someone is just someone and other realms may 
have an identification scheme with some form of authentication. Additionally 
it is important to consider how existing non-P2P SIP UA's can join the 
realms either directly or through a proxy and be advertised on it.

Think of the telephone directory, both for identifying individuals (white 
pages) and organizations (yellow pages). P2P works fine for both joining and 
identifying scalar entities like individuals (with a level of trust that may 
be dependant on what realm it is on) but if the effort is made to allow 
organizations with structure to publish their own heirarchy in one or more 
realms (or be a P2P realm of its own that publishes to all other realms) 
then it becomes a very powerful communications medium indeed.

Regards

Michael

On 02/09/05, David A. Bryan <[email-masked]> wrote:
> > ID and register their domain on KeyID = HASH(domain.com<http://domain.com>
> ).
> > HASH(domain.com <http://domain.com>).
> >

-- 
Michael Slavitch
Ottawa, Ontario Canada
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