Re: [alto] Cost Maps, Endpoint Cost Maps and Coarse Grained Searches

["Y. Richard Yang" <[e-mail]>]

Wendy, Lyle,

On Tue, Sep 15, 2015 at 10:08 AM, Wendy Roome <[e-mail]>
wrote:

> Lyle,
>
> Here is my opinion on Endpoint Cost Service (ECS) vs. Network Maps & Cost
> Maps (NM/CM): They are two different ways to present the same data. They
> are different viewports into the same data, if you will, with different
> levels of detail, and different performance and ease-of-use.
>
> To start, I believe most clients will prefer ECS.


 I agree that most (simple) clients prefer ECS. One may consider NM/CM as a
batch/summary query for a set of ECS queries.

Clients really care
> about costs between endpoints; PIDs and Network Maps are irrelevant. For
> example, consider a Bittorrent peer which gets 50 new peers every 15
> minutes or so. That ALTO client would prefer to send an ECS request to the
> ALTO server to rank those peers, rather than fetching full maps,
> converting endpoints to PIDs and looking up the costs between PIDs.
>
> For a client, ECS is simple & easy to use: the client does not have to
> maintain any maps, and the client gets the latest cost data.
>
> Now consider a busy Bittorrent tracker. It gets 10+ requests/second, and
> for each request, it must select 50 out of (say) 5,000 peers. If the
> tracker used ECS, it would have to send 10 ECS requests a second, each
> with 5,000 endpoints. That would add too much latency to the tracker
> response, and would overload the ALTO server.
>
> So a tracker client would prefer to download the full NM/CM and evaluate
> costs locally, without involving the ALTO server each time. That requires
> more programming effort, but is more efficient.
>
> Here is another piece of historical motivation that is not clear in the
> RFC: we expect ALTO Servers will be offered by network service providers.
> Some providers will be (understandably!) reluctant to publish a detailed
> breakdown of their internal network. The NM/CM model allows a service
> provider to control the level of detail it wants to make available to the
> outside world.
>
> Incidentally, the RFC says an ALTO Server MUST provide an NM/CM, while ECS
> is optional. Personally, I think that is a mistake. I think NM/CM should
> be optional, and ECS should be required.
>
>
There have been very strong supporters on ECS from the very beginning. In
retrospect, it will indeed help if we make ECS required.

Richard


> So if you are writing a server, I recommend you build an internal cost
> map, with as high a level of detail as practical. Offer an ECS that uses
> that underlying detailed map. Then to satisfy the RFC, use some form of
> cluster analysis to partition the endpoints in the underlying map into
> (say) 100 to 200 PIDs, and offer a Network Map & Cost Map based on that
> partitioning.
>
> I hope that helps.
>
>         - Wendy Roome
>
>
> >Date: Tue, 8 Sep 2015 20:53:37 -0500
> >From: Lyle Bertz <[e-mail]>
> >To: [e-mail]
> >Subject: [alto] Cost Maps, Endpoint Cost Maps and Coarse Grained
> >       Searches
> >Message-ID:
> >       <CAC5bAiYH5N2tQpr3CEZn+eO8C9kYgWttyqNrwKKe=
> [e-mail]>
> >Content-Type: text/plain; charset="utf-8"
> >
> >All,
> >
> >I am implementing an Erlang based ALTO server and had a couple of
> >questions
> >based upon an observation of 7285.
> >
> >The Cost Map is assumed to be coarse grained and one cannot make a
> >determination about whether an endpoint cost measure is fine or coarse per
> >the RFC.
> >
> >If i am to search for a cost between two endpoints (1 source and 1
> >destination) and 'miss' on the first endpoint map I am looking at the
> >other
> >endpoint costs responses I may have available for an answer.  In such a
> >case I can just look for the two endpoints and, if present, I have a hit
> >and I am good to go.
> >
> >However, if I am looking to Cost Maps the map dependency assumes that both
> >endpoints are members of the same map.   This implies that only endpoint
> >cost maps can contain metrics between two endpoints that are not in the
> >same map.   I find this interesting in that as a designer if you want all
> >data in Network Cost Maps you have to model the entire internet or you can
> >just rely on endpoint cost maps.
> >
> >What was the intent in this relationship?  I like the open ended option
> >the
> >endpoint cost maps provide but I am a bit reluctant to begin coding
> >something that may have not been an intentional feature in ALTO.
> >
> >Thanks.
> >
> >Lyle
> >
> >PS - Code for Erlang ALTO server (very Alpha) can be found at
> >
> https://urldefense.proofpoint.com/v2/url?u=https-3A__github.com_lylebe_e-5F-5Falto&d=AwICAg&c=-dg2m7zWuuDZ0MUcV7Sdqw&r=4G36iiEVb2m_v-0RnP2gx9KZJjYQgfvrOCE3789JGIA&m=bsmcTVcdu8qOJFBpCCyYNy8FyoE7j1RI0_OP-y3fGDg&s=R5Ss1SQJ0WXr0U5o1CYjG-Uq4QVHmG2HLXUq1hpRawQ&e=
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