TCP-IP@BRL (09/15/82)
TCP/IP Digest Tuesday, 14 Sept 1982 Volume 1 : Issue 22 Today's Topics: SAMNET TCP/IP Implementation Observations Pointer to Gateway Article in Data Communications Magazine Query about "Standard Gateway" Code TCP/IP - VDH: Queries and Answers for VAX UNIX TCP/IP for PWB/UNIX Query && Cray for TCP/IP -- Request for Help TCP/IP for Intel MDS (8086)? TCP/IP for Honeywell Level 6? How about IBM MVS? TCP/IP on a PDP-11/40 with 80Kbytes? ---------------------------------------------------------------------- LIMITED DISTRIBUTION For Research Use Only --- Not for Public Distribution ---------------------------------------------------------------------- Date: 27 Jul 1982 0708-EDT From: GEORGE at Afsc-Hq To: tcp-ip at BRL Subject: Testing SAMNET TCP/IP implementation In testing the SAMNET (PDP-11, RSX11-M) TCP/IP implementation against its first service host, the ISI TOPS-20 system, some peculiar aspects of retransmission are becoming evident. These may be of interest to other implementors. First, a few notes about the SAMNET implementation - The TCP/IP/1822 layers are implemented in a multiprocess task with internal scheduling on a prioritized basis; lower layers have higher priority than higher layers, receive side has higher priority than send side . All told there are about 10 processes with a timer process which gets a chance to execute once-a-second. As soon as a process gives up control the highest priority process with a need to execute gets control. Of course, all this is executing under the RSX11-M operating system but the TCP/IP/1822 task is generally at a higher priority than the various user tasks (TELNET and FTP). At the TCP layer, SEND requests from higher level protocols (TELNET, FTP) are processed by (1) moving the data to a TCP buffer, (2) freeing the requestor to issue additional SENDs, and (3) forming TCP segments to pass to the IP layer. Send-flow is blocked for a connection when the send-side of the connection owns too many TCP buffer resources for unacknowledged data octets and segments. Retransmission timeout is set using the technique illustrated in RFC793, p41, with ALPHA=15/16, BETA=2, UBOUND=255, and LBOUND=2. Only the oldest segment will be retransmitted. The ACK strategy is to delay an ACK until the next second-boundary unless data is flowing in the direction of the ACK. Issuing immediate ACKs or timing more frequently places an excessive burden on processing and seemed impractical. The IP layer has no significance to the discussion at hand. At the local net (ARPANET) layer, messages are queued to a host table if another message is in transit to the destination host. (Note: the use of "message-ID" field for link number seems to prevent having more than one message outstanding to a host if one wants to handle the 1822 IMP-host error messages). Since the higher layers can produce messages faster than the local net layer can dispatch them, a queue of messages quickly builds waiting for the one active output to get a RFNM. Now for the retransmission pecularities - (1) When the TCP level decides to retransmit a segment, the IP and local net layers have no way to be aware that the segment from TCP should be put at the front of the host table queue, so it goes to the end of the queue to wait its turn. A retransmitted segment usually is being passed through the IP and local net layers when an ACK arrives for the original segment. The TCP layer discards an ACKed entry from the connection retransmission queue and uncovers the next entry which perhaps has a retransmission timeout equivalent to the one just ACKed due to a bursty mode of segment generation. Frequently, this next segment on the connection retransmission queue also will get retransmitted just before its ACK arrives at the TCP layer (this is particularly true when the receiving host send ACKs for each message arriving). This situation seems to propagate into an interleaving of retransmitted segments and new segments as both the TCP segment generator and the retransmitter do their jobs. The result is that the IP and local net layers process retransmitted segments even after an ACK has been processed for the original segment. A temporary resolution to this problem has been to not put so much reverence in the calculated response time (especially when it gets down to the range of 1-2 seconds). When the retransmission timeout is delayed to twice the calculated response time, the retransmissions disappeared. (2) For incoming messages to the SAMNET system, the ACK delay to the next second-boundary is causing the remote host to retransmit, sometimes 3-4 times. Of course the outgoing ACK is somewhat impeded because it's generated by a lower priority process (high layer, send side) and must contend with the queue which might exist at the local net host table (in this situation there's been little contention at the queue because the data flow was principally incoming). In both cases the retransmissions have been kicked off by a too-strict adherence to the retransmission timeout when it is in the range of 1-2 seconds. The highly modularized, layered approach taken by the SAMNET implementation is producing results that are not entirely satisfactory. Some more sophisticated cross-talk between the TCP layer and the IP/local net layer and between the segment generator and the retransmission processor are being investigated in search for a more satisfactory performance. Implementors need to be aware of other implementation internal techniques. Some dissemination of strategies along the lines of Dave Clark's recent RFCs will be of use, but we've a ways to go yet. Chuck Norris (george@afsc-hq) ------------------------------ Date: 17 Aug 1982 12:37:42 EDT (Tuesday) From: Jack Haverty <haverty@Bbn-Unix> To: iccb at Bbn-Unix Subject: Gateway article in Data Communications Redistributed-by: Bob Hinden <hinden@Bbn-Unix> Redistributed-to: gateway-info at BBN-UNIX The August 1982 issue [of Data Communications] contains an article about the gateway system. It made it through the editorial pass largely unscathed (at least they didn't put TCP on top of X.25 or some similar 'clarification'...). Jack ------------------------------ Date: 8-Sep-82 10:00PM-EDT (Wed) From: Nathaniel Mishkin <Mishkin@Yale> Subject: Standard Gateway Code To: Tcp-Ip at BRL I have a question with what must be an obvious answer: what is the "Standard Gateway Code available from BBN" that I've seen referred to on several occasions? I get the impression it runs on -11s. Is this true? What does it gateway between (among)? -- Nat [ The MACRO-11 Gateway is implemented in MACRO-11 for the smaller PDP-11s, and supports a variety of "standard" network peripherals, such as the ACC LH/DH-11. ] ------------------------------ Date: 23-Aug-82 9:36AM-EDT (Mon) From: Nathaniel Mishkin <Mishkin@Yale> Subject: TCP/IP - VDH Query To: Tcp-Ip at BRL I have heard that there exists or someone is working on a VDH driver for either the BBN 4.1 Unix/IP or the Berkeley 4.2 Unix/IP. Can anyone supply a pointer? -- Nat ------------------------------ Date: 4 Sep 82 12:03:29-EDT (Sat) From: Mark Weiser <mark.umcp-cs@Udel-Relay> To: unix-wizards at Sri-Csl cc: tcp-ip at Mit-Ai Subject: Very Distant Host support under 4.1bsd Unix. Our 50 kbit line to the Arpanet arrives next month, I thought I was all prepared by obtaining the IP/TCP kernel from BBN (although I haven't looked at installing it yet), but now I hear a rumor... We want to run Very Distant Host protocol directly on our Vax-11/780 running Berkeley 4.1 Unix. Is this possible? Friends at the University of Rochester tell me they have tried and it doesn't work, only local host support is any good. Help! Do I really need a C30? [ For now, you either need ECUs, or a C/30. -Mike ] ------------------------------ Date: 8 Sep 82 4:44:12-EDT (Wed) From: Doug Kingston <dpk@BRL> To: Mark Weiser <mark.umcp-cs@Udel-Relay> cc: unix-wizards at Sri-Csl, tcp-ip at Mit-Ai Subject: Re: Very Distant Host support under 4.1bsd Unix. I can't speak to the condition of the VDH (or HDH) code in 4.1, but even if it worked, you would not want to use it, the system load of doing all the VDH (HDH) protocol on top of TCP/IP is prohibitively expensive. A better solution to your problem of being distant from the IMP, is to buy a pair of ECU's (error correction units) which are manufactured by the same people who bring you the LH/DH-11 ArpaNet Interface (ACC, Associated Computer Consultants). These wonderful boxes are designed to be placed between the IMP host port and your CPU interface. The ECU at the IMP end looks like a host, and the ECU at the HOST end looks like an IMP. In the you hook up the best phone line you can get (the one you would be running VDH on) and the ECU do the error correction in hardware to provide an error free link from HOST to IMP. The ECU can look like a DISTANT or LOCAL host on either end, and the ECU is good for all the bandwidth you can give it. Its also a lot cheaper than getting another IMP. Don't let VDH get you down, -Doug- ------------------------------ Date: 8 Sep 1982 09:43:45-PDT From: mo at Lbl-Unix (Mike O'Dell [system]) To: mark.umcp-cs at Udel-Relay cc: tcp-ip at Mit-Ai Subject: Re: Very Distant Host support under 4.1bsd Unix. With all due respect for the people that did the VDH back in the Dark Ages, the VDH is famous for not working very well. They have been the cause of premature retirement for more than one good ARPAnet software support person. There are persistant rumors that Greg Noel down at NOSC may be working on a VDH driver for 4.1a, but if he gives up, noone would blame him. The best thing to do, if your IMP must be remote from you, is to get a pair of ECU-II's from ACC. The Error Control Units connect to modems between the pair, and to the host, it looks like a local IMP interface, and to the IMP, it looks like a local host interface. ECU's are not perfect, and if you have a really rotten phone line between them, you will have grief, but not nearly as much as with a VDH. The other alternative would be to do an HDH driver, which would actually be doing the world a large service. But I am somewhat curious about your comment about "do I really need a C30?" If you don't have one, who does?? I have been assuming from your questions that you will be remote from some other IMP. Somewhere the must be an IMP HOST PORT to which your machine is attached. -Mike ------------------------------ Date: Wednesday, 8 Sep 1982 10:29-PDT From: obrien at Rand-Unix To: Mark Weiser <mark.umcp-cs@Udel-Relay> Cc: unix-wizards at Sri-Csl, tcp-ip at Mit-Ai Subject: Re: Very Distant Host support under 4.1bsd Unix. I have never actually attempted to run VDH, but everyone I've ever talked to has been very negative about the experience. It is apparently extremely difficult to get the software exactly right for checksumming, etc. the packets from the IMP, and the link is very, very slow. If your phone Co. is good you might try running a local host interface using ACC ECU boxes, which shove 1822 over a phone line using SDLC. These let you run a local/distant host interface over miles and miles of phone line, if your IMP actually has room in it for a local/distant interface. Our own experience in this department has not been sterling, because we have General Telephone here. The link to Rand-Relay is an ECU link over a leased line to an IMP four or five miles away. This link worked just fine until the Rixon-Sangamo T209 modem on the other end blew up, and it hasn't been right since. Our new C-30 eliminates our need for this link. It seems to be a little-known fact that on a Honeywell TIP, the TIP hardware takes up so much rack space that the fourth hookup to the IMP MUST be a VDH. On C-30's this restriction has been removed. That was our situation and is the reason we chose to run with ECU's to an IMP miles away, rather than attempting to run VDH for 50 feet. After Gen. Tel. I'm not sure which alternative was worse. ------------------------------ Date: 10 Sep 1982 01:32:33-PDT From: CCVAX.ron at Nosc-Cc To: mark.umcp-cs at Udel-Relay, mo at Lbl-Unix Subject: Re: Very Distant Host support under 4.1bsd Unix. Cc: tcp-ip at Mit-Ai, unix-wizards at Sri-Csl The "persistent rumors that Greg Noel down at NOSC may be working on a VDH driver for 4.1a" are no longer valid. Greg quit NPRDC a few weeks ago and the VDH project is now dead. The day after he quit his management scrambled for the $$$ to buy an LHDH and a pair of ECUs. --Ron ------------------------------ Date: 10 Sep 1982 1207-PDT From: DEDWARDS at Usc-Isi Subject: Re: Very Distant Host support under 4.1bsd Unix. To: mark.umcp-cs at Udel-Relay, unix-wizards at Sri-Csl cc: tcp-ip at Mit-Ai Don't know about the VDH support, but you do NOT need a c/30. You can use a pair of ECU's to go the long haul and they allow you to look like a local host (ECU's are built by ACC). Howard Weiss ------------------------------ Date: 23 Aug 1982 at 1020 Pacific Daylight Time From: wss at Lll-Unix (Walter Scott - Consultant/SC) Subject: Berkeley TCP/IP on 2.8bsd at SRI? To: tcp-ip at BRL Cc: gp kawin at lll-unix A few months ago, I remember reading on this mailing list that some folks at SRI were attempting to port the Berkeley TCP/IP code to 2.8 bsd on an 11/70. What's the story now? Was it successful? Is it available? Has anybody else tried to do something similar? I guess what I really want to know is whether anybody has TCP/IP working under 2.8bsd. Thanks, Walter Scott [ The SRI project to integrate the 4.1a code into 2.8 is well underway. I'm sure we will be hearing a status report soon. -Mike ] ------------------------------ Date: 17 Jun 1982 1242-PDT From: PADLIPSKY at Usc-Isi Subject: A Possibly Old Question To: tcp-ip at BRL It's probably come up before, but I haven't been saving back Digests, so with apologies for redundancy can anybody tell me what the state of availability of TCP/IP (and even process-level protocols) is for PWB UNIXtm (Version 6, I think). Thanks and cheers, map ------------------------------ Date: 22 Jul 1982 1722-PDT From: Johnson at Sumex-Aim Subject: Cray TCP/IP To: tcp-ip at BRL cc: samuelson at Sandia TCP/IP implementation is not available for Cray. CRI (Cray Research Inc.) has been gathering data on what protocols they will need to support in the future. I suggested that since the government is a large customer of theirs, they should consider TCP/IP support. They were not familiar with the protocol. They are, however, interested in Cray user response, so I suggest you contact: Derek Robb CRI 1440 N. Land Road Mendota Heights, MN 55120 800-328-0248 (In fact, if anything will move them toward support, demand from current, or prospective, Cray owners will do it.) --Suzanne Johnson ------------------------------ Date: 24 Jul 82 23:47:21-EDT (Sat) From: J. C. Pistritto <jcp@brl-bmd> To: tcp-ip at Brl-Bmd Subject: TCP-IP for Intel MDS? Does anyone know of a TCP-IP implementation being done for any of the Intel MDS-240 series processors? These are the 8086 development systems that Intel markets. An implementation using either the 3Com or Interlan Ethernet boards would be of interest. On the subject of which, does anyone have experience/comments on using these on a PDP-11 series processor, (not VAX)? -JCP- ------------------------------ Date: 5 Aug 82 19:19:08-EDT (Thu) From: Doug Kingston <dpk@BRL> To: tcp-ip at BRL Subject: TCP/IP for hard cases This is an inquiry for a third party... TCP/IP for the following machines or close enough to consider porting: Honeywell Level 6 running GECOS IBM 30xx (3033?) running MVS Sigh. -Doug- ------------------------------ Date: 7 Sep 1982 1202-PDT (Tuesday) From: yale at Nosc-Sdl (Bob Yale) Subject: Re: tcp mailing list To: tcp-ip at BRL Mike, I think I am going to have a problem getting the TCP/IP protocols up and running. The problem is that I have a PDP 11/40 running V6 with only 80kb of memory. Do you know of anyone who has brought a V7 system up on an 11/40? Also what is the size of the TCP/IP code? I might able to make it fit but if not we will have to get a new CPU. That will be a real nightmare getting the paper work through for new ADP equipment. Basically, my question is: How much memory will I need to bring a V7 Unix with a TCP/IP kernel? And does Bell Labs distribute a V7 for 11/40's? Thanks Bob Yale\@nosc-sdl [ Unless you use an ENABLE/34 from Able to add more memory to your 11/40, it will be *very* *painful* to fit UNIX plus TCP/IP in an 11/40. You might consider running the 11/40 as a Mills FUZZBALL. -Mike ] END OF TCP-IP DIGEST ********************