
PC/custom, version 2.0

A command to customize the PC/IP environment, allowing setting of
parameters that describe the network environment and preferred
option settings.


Usage:

     custom netdev [model]

begins customization of the device description found in the file
named "netdev.sys".  When finished customizing, custom rewrites
the file netdev.sys with the new parameters in place.  The
customizer is menu-driven and self-explanatory.  If a second
argument is given, custom reads the values of the customization
parameters of the command found in the file "model.sys" and uses
them as initial values.  It then enters the usual starting menu
so that the user can review the result.

For simplicity and uniformity, the one device driver contains the
customization parameters for all network levels and all commands.
For example, one can set serial line parameters even though the
PC/IP commands to be used contain an Ethernet driver.  It is not
necessary to specify values for customization parameters that
will not be used.  For example, if the command PC/setclock will
not be used, one need not specify the internet addresses of time
servers. 

Note that customizing the file netdev.sys will have no effect
until the next time DOS is bootloaded.  See the writeup entitled
"software installation" for more details.


Standard customization parameters:

There are several customization parameters that are applicable to
all or several different PCIP commands.  Customization parameters
that apply to just one command are described in the writeup of
that command.

Site customization to match network hardware options, switch
settings, and parameters:

     1) Serial line speed.  Can be set to any baud rate from 110 
        to 19,200.  (Needs to be set only for serial line use.)   

     2) Interrupt vector for network interface.  Should be set
        to correspond to the interrupt vector number that the
        hardware interface will use.  If not set, the PC/IP 
        Ethernet and Pronet drivers will use interrupt vector 
        number five as a default, and the PC/IP serial line driver 
        will use interrupt vector number four as a default.

     3) DMA channel for network interface.  Should be set to 
        correspond to the DMA channel that the hardware interface
        will use.  If not set, the PC/IP network drivers will use
        DMA channel one as a default.  (Need not be set for 
        serial line use.)  [Note:  the current version of PC/custom
        has no provision for changing this parameter.]

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     4) Network interface I/O address.  Should be set to match the
        I/O base address used by the network hardware.  Default is 
        0300 (Hex).

     5) Ethernet address.  One can customize the Ethernet 
        in one of three ways:

        a) to the Ethernet address found on the network interface 
           card,
        b) to an Ethernet address derived from the internet address 
           by concatenating 16 leading zero bits,
        c) to an arbitrary Ethernet address specified to the 
           customizer.  

        One should normally use the first option; the others are 
        available to deal with non-standard Ethernet environments.

     6) Number of network interfaces.  This parameter is currently 
        not used; it is provided for future implementation of 
        multi-network attachment.


Site customization of network level parameters:

     1) Internet address of this computer.  (Needs to be set for
        Ethernet only.)

     2) Internet address of default IP gateway.  (Needs to be set
        for Ethernet only.)

     3) Internet addresses of up to five IP name servers.

     4) Internet addresses of up to five time servers.  The
        servers are polled at two second intervals in the order
        they were set by the customizer, so one may place 
        preferred services nearer the head of the list.  (Needed 
        only by IP/setclock.)

     5) Internet address of a print server.  (Needed only by 
        PC/iprint.)

     6) Internet address of an IP log server.  If this address
        is non-zero, some PC/IP commands send error-logging or
        statistics-gathering packets to this address.  For 
        privacy, the address may be set to 0,0,0,0, in which 
        case all logging is suppressed.

     7) Up to three initial values for Ethernet-to-Internet
        address cache.  (Needs to be set only for Ethernet use
        and when the environment does not provide the proper
        protocol.)  IP addresses are entered in standard octal
        or decimal form.  Ethernet addresses are entered as 6
        octal byte values (each between 0 and 377) separated by
        commas.


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     8) TCP window size and low window level.  These two parameters
        affect the performance and smoothness of flow of data in 
        commands such as Telnet.  The window size is the count, 
        in bytes, of the maximum amount of data that another host 
        should send to the PC without waiting for authorization to 
        send more.  If not customized, its default value is 1000 
        bytes.  One might make this value smaller if there is a 
        gateway with limited buffering ability in the pathway
        between the PC and a commonly-used host.  The low window 
        level is the trigger point at which the PC sends 
        authorization to send more data to the other host.  If not 
        customized, its default value is 200 bytes.  If there is a 
        long round-trip delay to a commonly-used host, one might 
        adjust this value so as to just fill up the pipeline from
        that host.  The low window level must be less than the 
        window size, and the window size must be less than 2000 
        bytes.

     9) Telnet transmission trigger.  Can be set to send every
        character as it is typed (necessary if using a 
        character-based remote echo system) or to send a batch
        of typed characters only when a newline character is typed 
        (less demanding on the remote system.)

    10) First RVD drive.  This parameter is provided for a future 
        feature.

    11) Number of subnet bits.  This parameter determines how many
        bits, following the network part of an IP address, are used
        to identify the attached subnetwork.  PC/custom displays on
        octal "subnet mask" that is derived from the IP address
        and the number of subnet bits.  This feature is used in a
        simple way, as follows:  when an IP packet is to be sent
        from the PC, its IP destination address is masked with the
        subnet mask.  The part of the destination address that is
        revealed by the subnet mask is then compared with the
        corresponding part of the PC's own IP address.  If the
        revealed section of the two addresses are different, the
        destination is assumed to be on another subnetwork, and the
        routing layer sends the packet to the default gateway.  If
        the revealed sections are the same, the destination is assumed
        to be on the same local area network as the PC itself, and
        the concealed portion of the destination address is used by
        the network layer to construct the proper physical address 
        (perhaps using an Address Resolution Protocol).  If 
        subnetwork routing is not in use, an extent of zero is
        appropriate.  At M.I.T. the subnetwork routing scheme uses
        8 bits for subnetwork identification.


Personal customization of terminal emulation options:

     1) Action on lines too long to fit on screen.  Discard
        mode places all excess characters in column 80.
        Wraparound mode places excess characters on next line.

     2) Swap interpretation of backspace with control-backspace.
        (See telnet description of emulation conventions for
        further information.)

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Other parameters:

     1) User's name, office number, and telephone number.
        Character strings that are included in error logging 
        messages and are placed in headers of files sent to a 
        print server.  May be set to (or left) blank.

     2) Debug options.  There are several options that turn on
        various degrees of progress reports, tracing, and
        otherwise suppressed error messages.  These options are
        of interest primarily to system programmers.  One
        normally sets them to "all off".

     3) Local standard time offset, in minutes before GMT.  West
        of GMT the value is positive, east of GMT the value is
        negative.  For EST the value is +300.  For SET the value
        is -60 in the winter.  

     4) Local standard time designation string.  Three letters,
        such as EST, EDT, or SET.


On-the-fly error correction:

Errors in typing names and addresses can be corrected with the
following common editing conventions:  The backspace key discards
the last character typed, while Control-U discards the entire
name or address typed so far, allowing one to start over.


Temporary customization:

The command

     custom netcust

will recustomize the currently active device driver, which is 
named "netcust:".  Customization of netcust takes effect 
immediately, rather than at next bootload, and is lost when the 
next bootload takes place.  Temporary customization of the 
active device driver is sometimes useful in debugging, for
example to turn on a tracing option for a while.  Note that for 
temporary customization to work there must be an already-present 
active device driver, previously loaded by DOS.



26 December 1984.  This document is in file custom.txt
