-*-Mode:Text-*-  File: NETWRK Node: Top Up: (DIR) This file attempts to describe various computer networks of two types -- those to which ITS systems are directly connected, and those which are of interest to the ITS user community because they link up personal computers or research institutions that are not accessible by the first kind of network. There are two networks to which ITS machines are connected: the ARPANet and the Chaosnet. These networks support file transfer, mail, remote login, and other services -- they may appear to be quite similar to the user, but have differing implementations. All the other networks documented herein are mostly for mail and file transfer. * Menu: * ARPANet: (Internet) The Arpanet * Chaosnet: (CHAOS) The Chaosnet * User programs for either of the above * Internet: (Internet) The Internet * CSNET: (CSNET) The NSF CSnet. * PCNET: (MC:PCNET;PCNET INFO) Personal Computer Network Internet The Internet is a very large computer network that connects various educational, military, and commericial establishments, all involved in some way in computer science research. It is actually a ``catenet'' of many computer networks that run a protocol, the Internet Protocol, to allow packets to be sent from one host to another, possibly through several other networks. An accompanying protocol called TCP provides a reliable byte stream that programs can use, thus ignoring data errors and all the other nitty-gritty details involved in getting a packet from here to there. The ARPANet is perhaps the most famous of the Internet networks. It stretches from Massachusetts to Stanford. Before the days of Internet, it ran a protocol called NCP, which, unfortunately, was beginning to show its age. (The ARPANet is at least ten years old.) Because the net had ceased to become a research project, turning into a heavily-used resource, it was decided that it would be interesting, now that a long-haul network was shown feasible, to try to connect various networks together. Then the hosts on these networks, all differing in one characteristic or another, could talk to each other without having to contact special hosts that would translate one high-level protocol into another. IP came out of this desire. (In a false start, all the internetwork issues were going to be resolved in the TCP layer, but the details were wisely factored out.) So the ARPANet become ``just another'' network in the Internet, although it still carries most of the long-distance traffic. When the switch from ARPAnet to Internet in software was made, it was a cataclysm underneath, but the user could not notice much. Most of the high-level protocols used in the NCP days were simply carried over: Telnet, SUPDUP (where it was implemented), FTP, and SMTP. Some ITS user programs contain commands to switch from TCP to NCP mode, though this is not usually required. At MIT, Internet appears in a variety of ways. First, there is the ARPANet. The second type of network to embrace IP was the LCS/Pronet Ring net. The main users of these networks are the LCS VAXes and many of the Athena machines. Thirdly, there are Ethernets at Tech Square who run IP, usually along with Chaosnet. The users of this mode include some VAXes at the AI Lab, and some LCS machines. And last, but not least, the Chaosnet can also support Internet (after much heated discussion). A few Unix machines have taken this option. As for the ITS machines, they all connect to the Internet through their ARPANet IMPs. The Internet host tables can be found in SYSENG; HSTNIC > ITS implements both server and user programs for FTP, TELNET, and SUPDUP. The MLDEV is also supported. There is also an SMTP (mail) server. Sources for various TCP-related programs can be found in the TCP; directory on MC. For programmers, there is a quick rundown of the ITS TCP interface (and documentation that applies to network system calls in general) in TCP;TCPDOC > The network status can be checked with the PEEK program. CHAOS The Chaosnet was developed at the MIT AI lab as a local network to allows Lisp Machines (CADRs, specifically) to access files on AI and MC. Its success caused it to become the most widely used local network at MIT. The following operation systems have support Chaosnet: LispM, ITS, Twenex, Tenex, Unix, Multics, VMS, Seconds, MINITS, and MOS. The last three are used mainly in terminal concentrators and bridges. Chaosnet has also been used at Yale, TI, and many other Lisp Machine installations. The definitive Chaosnet documentation can be found in AI Memo 628, ``Chaosnet,'' by David Moon. Chaosnet started out being supported by special Chaosnet hardware, but is now mostly used with Ethernet II hardware. Leased serial lines and microwave links have also been used to run Chaosnet. It is stressed that Chaosnet is local network, but it has been used with some success transcontinentally. On ITS, most programs (except FINGER) will automatically chose to use the Chaosnet. Here is a list of current user and server programs: Service Protocol User Server -------------------------------------------------------------- Remote Login TELNET :TELNET yes SUPDUP :SUPDUP yes File Access FILE :CFTP yes Mail MAIL (COMSAT) yes SMTP (COMSAT) yes TTY send SEND :SEND yes CONVERSE There are also the usual servers for HOSTAB, TIME, UPTIME, and STATUS. All ITS machines offer a TCP server as well -- it allows Chaosnet hosts to contact Internet hosts at a specified port number. There is also a GMSGS server and a LIMERICK server. For contacting a host at an arbitary contact name, use :MOON;CHARFC host contact The K PEEK mode will show that status of the Chaosnet.