Date: Fri, 20 Sep 1996 09:49:54 +0200 (MET DST) From: Luigi Rizzo <luigi@labinfo.iet.unipi.it> To: hackers@freebsd.org Cc: luigi@labinfo.iet.unipi.it (Luigi Rizzo) Subject: IP queues -- how to limit them ? Message-ID: <199609200749.JAA23058@labinfo.iet.unipi.it>
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Hi, (with reference to BSD implementations of TCP, but I'd be curious to know how routers approach this problem): is there any way to limit the amount of packets queued for delivery on a given interface ? I am asking because I notice an annoying problem when using PPP over a 14.4 line (easily reproducible when using a WWW browser). When one or more connections are transferring data, queues tend to pile up segments, up to the maximum window size for each connection (16K default). Since the bandwidth is so low, the queues are not very long (10-12 segments per connection) but take a long time to flush (4..12 sec per 16k, depending on the effectiveness of compression). The connections end up with an RTT constantly growing, up to unacceptable values (10s or more), and the RTT is totally dominated by the queueing delay. All this is totally pointless (as it delays other data, causes reduced control over the line, etc.) but since TCP as it is now does not stop expanding windows until a drop occurs, the only solution would be to avoid that a queue on an interface contains more than X seconds of data (related to its speed). So, any idea on how to set this limitation ? Thanks Luigi ==================================================================== Luigi Rizzo Dip. di Ingegneria dell'Informazione email: luigi@iet.unipi.it Universita' di Pisa tel: +39-50-568533 via Diotisalvi 2, 56126 PISA (Italy) fax: +39-50-568522 http://www.iet.unipi.it/~luigi/ ====================================================================
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