Date: Sat, 30 Sep 1995 12:54:27 +0100 (MET) From: Luigi Rizzo <luigi@labinfo.iet.unipi.it> To: hackers@freebsd.org Cc: luigi@labinfo.iet.unipi.it (Luigi Rizzo) Subject: Unreliable networks... Message-ID: <199509301154.MAA20709@labinfo.iet.unipi.it>
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Hi, the growth of the internet in the last year, possibly together with some management problems somewhere, has caused the quality of the connection between Europe and the US (at least as seen from our site) to decay dramatically. In the last few months, it is common to see a packet loss in the range 10..50% when pinging a host overseas (things go much better for hosts in France or UK). This means that the connection is there, it's simply overloaded (or misconfigured: at times we regularly loose every second or third packet!) Such a large loss rate almost completely defeats the algorithms used by TCP to determine the RTT, to the point that ftp-ing a file larger than 100K takes a huge amount of time if it succeeds at all. While it is clear that this behaviour lies in the configuration or management of routers, there is not much I can do to improve the situation. So I start to feel the need for countermeasures which allow a connection to stay up and perform reasonably even in presence of large packet losses. One idea might be to tunnel the TCP connection using a couple of processes in the sender and the receiver. The processes could negotiate the expected bandwidth, transfer length and have an idea of the packet loss, and send packets using UDP. On the receiving side, incoming packets are buffered (possibly using a large enough buffer), requests are sent for missing packets, and the collected data are sent up to the receiving process via TCP. This is probably something that must be tailored to the specific application (e.g. FTP), but would have, IMHO, some advantages for the servers because it would avoid many many failed connections. Any ideas on such an approach, or on something that already exist to solve this problem ? 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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