IP over T1.6ca
"k1io@FN42jk 08-Oct-1990 1136" <goldstein@carafe.enet.dec.com> Mon, 08 October 1990 15:58 UTC
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Date: Mon, 08 Oct 1990 08:53:37 -0700
From: "k1io@FN42jk 08-Oct-1990 1136" <goldstein@carafe.enet.dec.com>
To: frame-relay@NRI.Reston.VA.US
Subject: IP over T1.6ca
Status: OR
I belong to T1S1 and worked on ANSI T1.6ca, the pending ANS for the Frame Relay "Core Aspects" protocol. We did discuss TCP/IP, in particular with regard to congestion control. Perhaps this will be of use. Here are a few thoughts about how to converge IP over FR. You can use the FR network two ways. One is to run an edge-to-edge connection-mode data link (actually subnetwork, to be an OSIRM purist) protocol across the FR. In that case, flow and congestion across the FR are determined by that protocol; the gateway device (IP router) manages its own queues as it sees fit, discarding what it must. The congestion avoidance options in T1.6ca can be used in this edge protocol. Note taht this is a lot like X.25; it just moves some of the effort out of the network and into the users' edge nodes. The alternative is to run UI-like frames across the FR, with end-to-end (TCP) recovery of loss. In that case the Jacobson dynamic window takes care of congestion recovery. Note though that IP has no congestion avoidance (explicit) mechanism, though T1.6ca and for that matter ISO-IP (IS8473) do. Whether that helps or hinders the TCP/IP user depends upon the way the network protects itself. A network that has full-bore congestion avoidance, with leaky-bucket enforcement, may discard "excess" frames (the ones sent by users who don't take the hint from explicit congestion avoidance signaling) a bit more rapidly than one that doesn't. So a user who doesn't slow down when told is more likely to lose a packet and hit the "cliff", which will cause a much more severe slowdown. But if the FR network doesn't enforce congestion avoidance (by selective discard) and just puts what it can't handle into the bit-bucket, then the TCP users (with no explicit congestion avoidance slowdowns) will tend to "win", by hogging the network during periods of mild congestion. If the FR network is public, it'll probably have a time component to its cost, as well as a per-frame component. Tariffs aren't filed yet but FR tends to have more bandwidth reservation than X.25, which will lead telcos to charge for VCs. So you may end up with a demand for time-cutting, too, not unlike ISDN circuit mode. fred
- IP over T1.6ca k1io@FN42jk 08-Oct-1990 1136