Re: [p2pi] ALTO and caching (Was: Re: Charter and problem statement)

[Stanislav Shalunov <shalunov at shlang.com>]

On Jul 16, 2008, at 8:13 AM, Vijay K. Gurbani wrote:
> Who do you see doing cache discovery?  The ALTO server or the
> individual peers?

Peers mainly.  The ALTO server might use these same means as a  
convenience, but one can think of it as being configured with this  
information.

> If we take the view that a cache is a selfless peer who wants
> nothing in return, then its discovery is no different than
> discovering other peers.  Then this is best relegated as a
> normal peer-discovery algorithm/process implemented in any
> given P2P overlay.

Unfortunately, this won't work too well.  Consider a large BitTorrent  
swarm.  You're only going to ever unchoke a very small fraction of the  
swarm, and the cache, most probably, is not going to be in it.   
Further, the cache would need to be cued by something like DPI then to  
even know it needs to be in the swarm.  If you actively come to it  
knowing it's a very special peer, it solves both problems.

> Now, let's tackle the ALTO server doing cache discovery.  If the
> ALTO server can use a standard means to discover a cache, why
> can't the peer use the same means?

It should.

> I believe that if cache discovery is moved to the realm of
> the ALTO server, it becomes more of cache "dissemination" problem
> than of cache "discovery."  In other words, the ALTO server
> will be pre-configured by the ISP  -- or if it is not operated by
> the ISP, will use other means -- to maintain a set of known caches.
> It has been suggested that caches "register" to the ALTO server.
> I think that this is probably not a good idea for a variety of
> reasons.

I don't see why we need to standardize how ALTO servers are configured  
in this regard.  The ISP buys something that somehow makes it work.   
Maybe it uses automated discovery so you don't configured it twice.   
Maybe it's bundled with the DNS server so you don't configure it twice  
(probably not, but a theoretic possibility).  Maybe it's manually  
configured.

> Then, peers will query the ALTO server using a protocol yet to
> be defined (let's refer to this as the TBD protocol.)  This
> TBD protocol will have an extension that the peer can use to
> provide the ALTO server with some hints (overlay protocol, i.e.,
> BitTorrent, eDonkey; hash of the content, etc.)  The TBD
> protocol will arrange it such that in a response, the querying
> peer is told to contact the cache first.

It might or might not work, depending on what an ALTO server is.  If,  
for example, an ALTO server is a URL that contains BGP dump with all  
the communities, it'll work for traffic optimization, but won't help  
you find the cache.

On the other hand, if you find the cache in the same way you find  
whatever is the ALTO server, it will definitely work, and it's easier  
to do.

> With some additional work, this extension to the TBD protocol
> could be used to also find other resources like VoIP relays,
> and it can also be applicable for non-P2P uses like CDN.


Yes.

--
Stanislav Shalunov
http://shlang.com

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