ICS 54
Klefstad

Networking and Communications

Networking and Interprocess Communication (IPC)
    . local area networks (LAN)
        . small distance between hosts (one organization)
        . high speed transfer lines (3-10 mbytes/sec)
        . eg Ethernet
    . wide area networks (WAN) remote networks
        . large physical distances between hosts
        . medium speed transfer lines (less than 100 kbytes/sec)
        . eg ARPANet, CSNet
    . `protocols` are standard rules for:
        . initiating and terminating logical connections
        . address and data format
        . manner of transmission
        . remote and local services

Unix IPC Model: Sockets
    . sockets are I/O descriptors that may span machines
    . provide two-way interprocess/intermachine communication
    . some operations on sockets <sys/socket.h>
        . socket - creates (open) a socket descriptor
        . connect - joins two or more sockets for I/O
        . send/write - sends a message to a socket
        . select - query status of a socket
        . recv/read - gets a message from a socket
        . close - close a socket

A Standard Protocol
    . tcp/ip allow for data transmission/reception over networks
    . ip - Internet Protocol
        . low-level network protocol
        . initiated with
            s = socket(AF_INET, SOCK_RAW, 0);
    . tcp - Internet Transmission Control Protocol
        . high-level sequenced, two-way byte-stream protocol
        . initiated with
            s = socket(AF_INET, SOCK_STREAM, 0);

Mail Transfer
    . uucp source_file dest_file
        . copies files between machines along an explicit network path
        . remote files are specified as system!file
        . uusend can deliver across a network path
    . uux command
        . gathers files from various systems, then executes a command
        . eg
            uux "!diff bonnie!~/foo blanche!~/bar > ics!~/diff"
    . uucico transfers files queued by uucp or uux

Remote login
    . rlogin allows login on another Unix machine
    . behaves like a direct login and sets TERM variable
    . % rlogin host [-l remote_userid]
    . ~ escapes
        . ~. - same as logout
        . ~^Z - suspends rlogin
    . telnet and tip are like rlogin, but useful for non-Unix machines

Remote shell
    . rsh executes a specified command on a specified host
    . % rsh host [-l userid] [-n] [command]
    . remote stdin, stdout, and stderr are connected to those
        of the local machine
    . if command is omited, it does rlogin
    . remote file-name meta-characters must be quoted

Remote copy
    . rcp allows limited file copying across Unix machines
    . % rcp from_file to_file
    . % rcp [-r] files... directory
    . files are of the form:
        . user@host:file_path
        . eg rcp klefstad@bonnie:bin/"*" .
        . `user` defaults to you
        . `host` defaults to local machine
        . relative file path is relative to user's home
    . remote file-name meta-characters must be quoted

Equivalent hosts
    . passwords are required for rlogin, but are waved for
        equivalent hosts
    . ~userid/.rhosts
        . contains list of trusted hosts that may login as userid
        . allows rcp and rlogin without password
        . eg on bonnie, my .rhost file
            clipperton.ics.uci.edu klefstad
            blanche.ics.uci.edu klefstad
    . /etc/hosts.equiv
        . master list of trusted hosts

ARPANet File Transfer Program
    . ftp allows standard file copy interface across networks
    . user logs in to both machines, so is more general than rcp
    . % ftp [host]
        . cd, ls, mkdir - Unix commands on remote machine
        . lcd - cd on local machine
        . !cmd - Unix command on local machine
        . prompt - turn off confirmation prompting
        . mget *.dvi - copy remote *.dvi to local
        . mput *.tex - copy local *.tex to remote
        . quit - leave ftp command processor
        . ? [command] - help for command

Network Databases and Address Mapping
    . /etc/hosts
        . list of internet and local hosts accessible from local machine
        . eg
             # Subnet 3: Machines behind london in cs 308
             # Address Full name            Aliases
             128.195.3.1 londongw.ics.uci.edu london londongw clgw labgw
             128.195.3.5 bloomsbury.ics.uci.edu lab4 bloomsbury cl3
             128.195.3.8 whitechapel.ics.uci.edu whitechapel lab7 cl6
    . /etc/networks
        . list of DARPA networks
        . eg
             # Net name      Net number      Alias
             uciics-net      128.195
             uciics-main     128.195.1       localnet
             uciicslab       128.195.3       ucilabnet uci-labnet
             uciicsrsh       128.195.4       ucirshnet uci-rshnet

    . /etc/services
        . list of available network services
        . eg
             # Service name  Port/Protocol   Alias
             uucp            540/tcp         uucpd
             chforw          701/tcp         chforwd
             exec            512/tcp         execserver
             login           513/tcp         loginserver
    . /etc/protocols
        . information about known protocols
        . eg
             # Internet (ip) protocols
             # name  Number  Alias   # Comment
             ip      0       ip      # internet protocol, pseudo protocol number
             icmp    1       icmp    # internet control message protocol
             ggp     3       ggp     # gateway-gateway protocol
             tcp     6       tcp     # transmission control protocol
             pup     12      pup     # parc universal packet protocol
             udp     17      udp     # user datagram protocol