[Tsvwg] comments on draft-dawkins-trigtran-linkup-01
Aaron Falk <falk@isi.edu> Wed, 05 November 2003 01:42 UTC
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Date: Tue, 04 Nov 2003 17:41:40 -0800
From: Aaron Falk <falk@isi.edu>
To: spencer@mcsr-labs.org, carlw@mcsr-labs.org
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Subject: [Tsvwg] comments on draft-dawkins-trigtran-linkup-01
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Spencer, Carl- I just read through draft-dawkins-trigtran-linkup-01.txt and have a couple of comments. I'm not sure if this document is on the agenda for tsvwg this IETF so I'm sending my comments now. Hope this is helpful, --aaron -------------- In section 2.3, you say: Hosts supporting TCP-based applications over subnetwork interfaces subject to multi-second outages MAY perform the actions described in Section 3. These actions are more attractive for TCP implementations used with "human-in-the-loop" applications, but are safe for any TCP-based implementation. Just to be clear: this proposal is only for end-systems, right? Not for routers? The text here is clearly talking about hosts but later in section 3 you talk about subnetworks. The proposal seems a little vague on this. I feel like you are saying that he retransmitted packet may come from a router along the path (as suggested in draft-ietf-pilc-link-design) but the language seems to imply that it is _hosts_ saving and retransmitting the packets. A block diagram would help. :) Because, if it is the sender saving and retransmitting the packets and the sender directly connected to the wireless interface, the question comes up: why not just kick the RTO timer when the interface comes back up, as Phil Karn suggested? ---------------- Section 3.1 "Layering Violation Tradeoffs" This section is quite confusing. I don't know what is meant by a "subnetwork implementation". At a minimum it's mis-titled. It doesn't say why one should be concerned about layering violations, nor what the tradeoffs are. ---------------- In section 3. "When a Local Interface Returns to UP", you say: When the subnetwork implementation detects that a local interface has returned to "UP" status, the subnetwork implementation MAY retransmit the last packet stored for each TCP connection. (Again: the subnetwork vs. end-host issue.) My concern here is that the proposal in this draft is for links that are down for long enough that recovering from an RTO is onerous. Links that are down for only a few RTTs should be allowed to recover using the existing algorithm. So, I think you should say something about how long a link is down before engaging in this behavior. For example, you might say 'the local interface has returned to "UP" and the/one/all connection(s) are in RETRANSMISSION-WAIT.' Of course, this means makes implementation a bit harder since you a) need to be on the end-system and b) need to correlate packets you are saving to resend with the state of the connection. A simple approach would be to have the implementor fix a lower bound in seconds. -------------- Finally in Section 3. you need to say something about aging old buffered packets. I have this vision of hosts with lots of idle or even closed connections, a link going down and up triggering a storm of saved packets from hours/days previous trying to restart connections that are idle. The hosts and connections will probably survive but it seems an un-neighborly thing to do to the network. So, I'd propose a setting maximum time that packets can be held, say 1 MSL (2 minutes, I believe), by any entity doing this algorithm. -------------- _______________________________________________ tsvwg mailing list tsvwg@ietf.org https://www1.ietf.org/mailman/listinfo/tsvwg