Re: [alto] Mandatory and optional in alto protocol

On Wed, Aug 24, 2011 at 5:34 AM, Robert Varga <robert.varga@pantheon.sk> wrote:
> Hi,
>
> On 08/03/11 18:13, manbhard wrote:
>>
>> I agree with the opinion in the meeting that all services should be
>> optional. A client should use an ALTO server that advertises the service
>> it
>> needs via the directory service. As mentioned below, downloading full
>> network and cost maps (and maintaining them) might be a disincentive for
>> certain clients. Similarly it might be a disincentive to servers run by
>> SPs
>> who do not want to export their prefix list, and if forced to will do
>> quite
>> a lot of aggregation which undermines the effectiveness of ALTO.
>>
>> An approach that would satisfy the client and server constraints above
>> would
>> be all the services that only provide information (properties, costs) for
>> that client only.
>
> I second this opinion. In the pre-08 revisions of the draft, when services
> resided on fixed URIs, the notion of mandatory and optional services made
> sense, in that the client could make a blind query as soon as it (somehow)
> got a server address.
>
> With the latest draft, though, the client needs to find a service which is
> able to execute its query. Since current ALTO discovery deals only with
> servers, I think it is safe to assume the result of the discovery will be an
> URI pointing to a server IRD. From the IRD the client needs to select the
> appropriate service, and that service may reside on a completely different
> host than the one which hosts the IRD.
>
> This has the interesting consequence that a 'server' as resolved from the
> discovery service may actually be a set of logical servers, tied together by
> the IRD. Each of them is an ALTO server in the sense they speak the
> protocol, but in my mind that does not mean that each of them has to provide
> a Network Map service -- or anything beyond the service advertised by the
> IRD.
>
> To sum this up: I think an 'RFC-compliant ALTO server' should be required to
> provide the IRD service. All other services should be purely optional. That
> way each deployment site is free to combine multiple ALTO server
> implementations to provide a mix of services which are most appropriate for
> that particular site, but at the same time implementations are not limited
> in what services they can provide.

When it comes to mandatory vs. optional, the draft intended to refer
to a logical ALTO Server (which may be made up by multiple physical
servers as in your example).  That is, each physical server need not
implement the Network Map service.  Only one of them does.  Does that
affect your opinion?

(Let us know if you think this should be made more clear in the draft.)

Thanks,
Rich

>
> Bye,
> Robert
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