This list has been quiet for a while, so I thought I'd shake it up.
While an IRD does define an ALTO server's resources, it leaves a lot of
questions unanswered. For example, before retrieving a cost map, a client
might like to know whether the map has 200 costs or 2,000,000 costs. Or
whether a network map has 50 PIDs and 200 CIDRs, or 2,000 PIDs and 200,000
CIDRs.
So what do you think of adding an "advice" field to IRD entries? Like
"capabilities", it would be a JSON object with attributes specific to the
resource type. The values would be approximate guidelines, not exact
values. For example, sizes should be ranges, with the implication that no
matter how much the map changes, it SHOULD stay within that range. E.g.,
rather than saying that a network map has exactly 78 PIDs and 363 PIDs,
the advice might be that the map has between 50 and 100 PIDs, and 250 to
500 CIDRs.
For network maps, another advisory would be the set of endpoint addresses
for which this map is authoritative (for want of a better word). While it
would be wonderful if an ALTO server had detailed PIDs for every endpoint
in the network, and had costs to and from every PID, it is very unlikely
that will happen. Instead, most ALTO servers will be run by ISPs. The
server will have detailed PIDs for the ISP's customers, and will have
source and destination costs between its customer's PIDs and the rest of
the network. But as you get farther from the ISP's coverage area, the PIDs
get less detailed, and the cost maps will be unlikely to have costs
between those PIDs.
If a P2P tracker knows about (say) a dozen different different ALTO
servers, the tracker can use their "authoritative sets" to select the
appropriate ALTO server. E.g., if a peer at address X asks for a set of
peers, the tracker would use the ALTO server whose set covers X to
evaluate the costs from the other peers to X. Similarly, if an ALTO server
offers several network maps, a client could use this to distinguish
between those maps.
Before I develop this as a formal proposal, I have two questions for y'all:
1. Do you think this extension is useful?
2. How would this fit into the update charter? My take is that it could
come under the heading of "server discovery." True, it doesn't allow a
client discover a server from scratch. But it does allow a client to
select the appropriate server from a set of twisty little ALTO servers,
all alike.
- Wendy Roome
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