Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!seismo!rutgers!ames!ucbcad!ucbvax!MONK.PROTEON.COM!jas From: jas@MONK.PROTEON.COM (John A. Shriver) Newsgroups: comp.protocols.tcp-ip Subject: Ethernet Suffering Message-ID: <8705111625.AA15357@monk.proteon.com> Date: Mon, 11-May-87 12:25:26 EDT Article-I.D.: monk.8705111625.AA15357 Posted: Mon May 11 12:25:26 1987 Date-Received: Wed, 13-May-87 07:12:30 EDT References: <6603@mimsy.UUCP> Sender: daemon@ucbvax.BERKELEY.EDU Distribution: world Organization: The ARPA Internet Lines: 37 We are looking at several effects here. One is server saturation proper-how fast its disks and protocols can run. The next is saturation of the server interface. The third is saturation of the LAN itself. All three are sensitive to the LAN technology. Server protocol performance can be effected relatively easily by LAN packet size. If you've got big packets (4K instead of 1.5K), you'll take less interrupts and context switches. Saturation of the server interface is to a great degree a matter of good design. Having enough buffering, a clean programming interface, and an ability to pipeline can definitely help receive/transmit more data. However, having any level of data link flow or congestion control can really help. Most CSMA networks have no way to know if a packet was really received at the server, or was dropped for lack of a buffer. Some CSMA networks (DEC's CI) do this, and it helps a lot. (Ethernet does not.) All of the Token-Ring networks (IBM's, our ProNET, ANSI's FDDI standard) have this, in the "frame copied" bit that comes back around from the recipient. This makes the possibility of lost packets due to server congestion dramatically lower, which really speeds things up. The data link can implement flow control & retransmission much faster than the transport code. The LAN itself can have dramatically different total capacity, which matters when you want 3 servers on one LAN, not just one. On 10 megabit networks, you can get more total data through, with less delay, on a Token-Ring than a CSMA/CD network. While vendors will disagree on where CSMA/CD congests terminally (somewhere between 4 and 7 megabits/second), it is true that Token-Ring can really deliver all 10 megabits/second. Moreover, at speeds beyond 10 megabits/second, CSMA/CD does not scale, and you almost have to go Token-Ring. (You can go CSMA/CA, but it can degenerate into a Token-Bus.) The FDDI standard is a Token-Ring, as is the ProNET-80 product.