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+Network Working Group                                           G. Clark
+Request for Comments: 2217                           Cisco Systems, Inc.
+Category: Experimental                                      October 1997
+
+
+                     Telnet Com Port Control Option
+
+
+Status of this Memo
+
+   This memo defines an Experimental Protocol for the Internet
+   community.  This memo does not specify an Internet standard of any
+   kind.  Discussion and suggestions for improvement are requested.
+   Distribution of this memo is unlimited.
+
+Introduction
+
+   This memo proposes a protocol to allow greater use of modems attached
+   to a network for outbound dialing purposes.
+
+Table of Contents
+       1. Negotiation of the Com Port
+          Control Option Protocol          ..................   5
+       2. Com Port Configuration Commands  ..................   6
+            Version
+            Baud Rate
+            Data Bit Size
+            Parity
+            Stop Bit size
+       3. Special Com Port Control Commands .................   8
+            XON/XOFF Flow Control
+            HARDWARE Flow Control
+            BREAK Signal
+            DTR Signal
+            RTS Signal
+     4. Notification of Com Port and     ..................    12
+        Modem Line Changes
+     5. Flow Control                     ..................    13
+     6. Security Considerations          ..................    13
+     7. Author's Address                 ..................    14
+     8. Reference Section                ..................    14
+
+Discussion
+
+   The Telnet protocol defines an interactive, character-oriented
+   communications session.  It was originally designed to establish a
+   session between a client and a remote login service running on a host
+   [5].
+
+
+
+Clark                         Experimental                      [Page 1]
+
+RFC 2217          Telnet Com Port Control Option            October 1997
+
+
+   Many new business functions require a person to connect to remote
+   services to retrieve or deposit information.  By in large, these
+   remote services are accessed via an async dial up connection.  This
+   new class of functions include:
+
+     -  dial up connections to the Internet
+     -  connecting to bulletin boards
+     -  connecting to internal and external databases
+     -  sending and receiving faxes.
+
+   The general nature of this new class of function requires an
+   interactive, character-oriented communications session via an async
+   modem.  This is typically known as outbound modem dialing.
+
+   To help defer the cost of installing and maintaining additional phone
+   lines which may be used very little per person, many equipment
+   manufacturers have added the ability to establish a Telnet session
+   directly to the outbound ports on many of the most popular access
+   servers and routers, here after referred to as access servers.
+
+   However, the current Telnet protocol definitions are not sufficient
+   to fully support this new use.  There are three new areas of
+   functionality which need to be added to the Telnet protocol to
+   successfully support the needs of outbound modem dialing.  These are:
+
+      -  The ability for the client to send com port configuration
+         information to the access server which is connected to the
+         outbound modem.  This is needed to ensure the data being
+         transmitted and received by the modem is formatted correctly
+         at the byte level.
+
+      -  The ability for the access server to inform the client of any
+         modem line or signal changes such as RLSD changes (carrier
+         detect).  This information is vital, since many client software
+         packages use this information to determine if a session with the
+         remote service has been established.  RLSD changes are also
+         used for signaling in Class I faxing [6].
+
+      -  The ability to manage flow control between the client and
+         the access server which does not interfere with the flow
+         control mechanisms used by the session between the client and
+         the remote service.  Unfortunately RFC 1372 "Telnet Remote
+         Flow Control Option" [2] can not be used for this purpose
+         because it relies on sending XON/XOFF style characters which
+         maybe transmitted or received as a normal course of the
+         client / remote service session.
+
+
+
+
+
+Clark                         Experimental                      [Page 2]
+
+RFC 2217          Telnet Com Port Control Option            October 1997
+
+
+   Though this discussion has focused on outbound modem dialing as the
+   primary use of this protocol, the protocol can also be used for any
+   serial device attached to an access server.  Such devices could be:
+
+     -  serial printers
+     -  plotters
+     -  monitoring devices such as pipe line monitors or medical
+        monitors
+     -  general office equipment such as photo-copiers and cash
+        registers
+
+Definition of Terms
+
+   Access Server - Any network device which accepts Telnet sessions
+                   and passes the data received to a com port, and
+                   passes data received from the com port to the client
+                   via the Telnet session.
+
+   Baud Rate  -  For the purposes of this document, baud rate will
+                 mean the communications of data in bits per second.
+
+   Client - Any network device which initiates a Telnet session
+            to an access server.
+
+   Outbound - Transmission of data from the modem attached to the
+              access server to a remote service.
+
+   Inbound - Transmission of data from the remote service to the
+             modem attached to the access server.
+
+   Remove Service - Any service which accepts dial-up connections,
+                    including fax machines.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Clark                         Experimental                      [Page 3]
+
+RFC 2217          Telnet Com Port Control Option            October 1997
+
+
+Illustration
+
+  =====================
+  |                   |
+  |      CLIENT       |\
+  |                   | \ < ---- Local Area /
+  =====================  \       Enterprise Network
+                          \
+                           \
+                         =============================
+                         |      Telnet Interface     |
+                         |                  |        |
+                         |                  |        |
+                         |  ACCESS SERVER   |        |
+                         |                  |        |
+                         |                  |        |
+                         |     Com Port Interface    |
+                         =============================
+                                      |
+                                      |
+                              ==================
+                              |                |
+                              |      MODEM     |
+                              |                |
+                              ==================
+                                      |
+  Access to Remote Service            |
+  most commonly Public Switched ----->|
+  Network                             |
+                                      |
+                                      |
+                            ======================
+  Could be Internet Service |                    |
+  Provider, Bulletin Board  |                    |
+  or FAX machine            |    REMOTE SERVICE  |
+                            |                    |
+                            |                    |
+                            ======================
+
+
+  Command Names and Codes:
+       COM-PORT-OPTION       44
+
+
+
+
+
+
+
+
+
+Clark                         Experimental                      [Page 4]
+
+RFC 2217          Telnet Com Port Control Option            October 1997
+
+
+                   Client to Access Server   Access Server to Client
+       SIGNATURE            text                      text
+       SET-BAUDRATE            1                      101
+       SET-DATASIZE            2                      102
+       SET-PARITY              3                      103
+       SET-STOPSIZE            4                      104
+       SET-CONTROL             5                      105
+       NOTIFY-LINESTATE        6                      106
+       NOTIFY-MODEMSTATE       7                      107
+       FLOWCONTROL-SUSPEND     8                      108
+       FLOWCONTROL-RESUME      9                      109
+       SET-LINESTATE-MASK     10                      110
+       SET-MODEMSTATE-MASK    11                      111
+       PURGE-DATA             12                      112
+
+   Discussion: As initially proposed, com port configuration
+               commands are only sent from the client to the access
+               server.  There is no current vision that the access
+               server would initiate the use of a com port configuration
+               command, only the notify commands. However, to allow for
+               access server initiated com port configurations different
+               command values have been established.
+
+1. Negotiation of the Com Port Control Option Protocol
+
+   The negotiation of the com port control option protocol uses the
+   standard Telnet negotiation protocol mechanism:
+
+     IAC WILL COM-PORT-OPTION
+       The sender of this command is willing to send com port
+       control option commands.
+     IAC WONT COM-PORT-OPTION
+       The sender of this command refuses to send com port
+       control option commands.
+     IAC DO COM-PORT-OPTION
+       The sender of this command is willing to accept com port
+       control option commands.
+     IAC DONT COM-PORT-OPTION
+       The sender of this command refuses to accept com port control
+       options commands.
+
+    Typically a client will use WILL and WONT, while an access server
+    will use DO and DONT.
+
+
+
+
+
+
+
+
+Clark                         Experimental                      [Page 5]
+
+RFC 2217          Telnet Com Port Control Option            October 1997
+
+
+2. Com Port Configuration Commands
+
+   Once DO and WILL have been negotiated, the client may send any of the
+   following commands. The client can send these commands at any time
+   and multiple times throughout the Telnet session. Each command
+   transmitted from the client to the access server must be acknowledged
+   once the command has been processed by the access server.  This
+   confirmation informs the client of the value set at the access server
+   after the processing of the command. This acknowledgment is not used
+   to acknowledge the receipt of the command, which is handled at the
+   TCP protocol layer.  Its purpose is to inform the client of the value
+   in use, which may be different than the value requested in the
+   client's command.  For example, the client may request a baud rate
+   higher than the access service can provide.  If an acknowledgment is
+   not received by the client within a reasonable time (such as twice
+   the delay acknowledgment timer), the client may wish to resend the
+   command or terminate the session.
+
+   Though the commands may be sent from the client to the access server
+   in any sequence, there are sequences which may result in invalid
+   configurations for the com port (for example: EVEN parity is only
+   valid if the data size is set to less than 8 bits). Thus it is
+   recommended that commands be issued in the following sequence:
+
+      1. SET-BAUDRATE
+      2. SET-DATASIZE
+      3. SET-PARITY
+      4. SET-STOPSIZE
+
+     IAC SB COM-PORT-OPTION SIGNATURE <text> IAC SE
+       This command may be sent by either the client or the access
+       server to exchange signature information.  If the command is
+       sent without <text> it is a request from the sender to receive
+       the signature text of the receiver.  The text may be a
+       combination of any characters.  There is no structure to the
+       <text> field.  It may contain manufacturer information, version
+       number information, or any other information desired.  If an
+       IAC character appears in the text it must be translated to
+       IAC-IAC to avoid conflict with the IAC which terminates
+       the command.
+
+     IAC SB COM-PORT-OPTION SET-BAUD <value(4)> IAC SE
+       This command is sent by the client to the access server to set
+       the baud rate of the com port. The value is four octets (4 bytes).
+       The value is represented in network standard format.  The value
+       is the baud rate being requested.  A special case is the value 0.
+       If the value is zero the client is requesting the current baud
+       rate of the com port on the access server.
+
+
+
+Clark                         Experimental                      [Page 6]
+
+RFC 2217          Telnet Com Port Control Option            October 1997
+
+
+       Discussion: Though baud rates used today form a very sparse space,
+                   and the initial version of the option used an index
+                   based baud rate table, after much discussion with a
+                   number of groups it has been determined that the
+                   actual baud rate should be used.  There are two main
+                   reasons. 1) It limits the number of updates to the
+                   option as faster baud rates come into use,
+                   2) It provides the greatest amount of flexibility
+                   in the selection of the baud rates.
+
+     IAC SB COM-PORT-OPTION SET-DATASIZE <value> IAC SE
+       This command is sent by the client to the access server to set
+       the data bit size. The command can also be sent to query the
+       current data bit size. The value is one octet (byte). The value
+       is an index into the following value table:
+
+           Value       Data Bit Size
+             0           Request Current Data Bit Size
+             1           Available for Future Use
+             2           Available for Future Use
+             3           Available for Future Use
+             4           Available for Future Use
+             5           5
+             6           6
+             7           7
+             8           8
+             9-127       Available for Future Use
+
+       Discussion: There are only eight possible values for the data bit
+                   size, only four have ever been used historically and
+                   only two are commonly used today. The use of the
+                   command-value format is recommended to preserve
+                   consistency with other commands. It also reduces the
+                   number of commands defined in the protocol, and
+                   allows for future expansion.
+
+     IAC SB COM-PORT-OPTION SET-PARITY <value> IAC SE
+       This command is sent by the client to the access server to set
+       the parity.  The command can also be sent to query the current
+       parity. The value is one octet (byte). The value is an index into
+       the following value table:
+
+            Value      Parity [1]
+              0           Request Current Data Size
+              1           NONE
+              2           ODD
+              3           EVEN
+              4           MARK
+
+
+
+Clark                         Experimental                      [Page 7]
+
+RFC 2217          Telnet Com Port Control Option            October 1997
+
+
+              5           SPACE
+              6-127       Available for Future Use
+
+       Discussion: There are only five possible values for parity
+                   commonly used today. The use of the command-value
+                   format is recommended to preserve consistency with
+                   other commands.
+
+     IAC SB COM-PORT-OPTION SET-STOPSIZE <value> IAC SE
+       This command is sent by the client to the access server to set
+       the number of stop bits. The command can also be sent to query
+       the current stop bit size. The value is one octet (byte). The
+       value is an index into the following value table:
+
+           Value      Stop Bit Size
+             0           Request Current Data Size
+             1           1
+             2           2
+             3           1.5
+             4-127       Available for Future Use
+
+       Discussion: Stop bit 1.5 is supported by most com port hardware
+                   only if data size is set to 5 bits. It is not
+                   commonly used.
+
+3. Special Com Port Control Commands
+
+   The client can send this command to the access server at any time
+   and multiple times throughout the Telnet session. Each command
+   transmitted from the client to the access server is acknowledged
+   with a confirmation of the command and the actual value set. The
+   client should expect a response within a reasonable time (such as
+   twice the delay acknowledgment timer). The client may wish to
+   resend any command which is not acknowledged or terminate the
+   session.
+
+     IAC SB COM-PORT-OPTION SET-CONTROL <value> IAC SE
+       This command is sent by the client to the access server to set
+       special com port options. The command can also be sent to query
+       the current option value. The value is one octet (byte). The
+       value is an index into the following value table:
+
+           Value      Control Commands
+             0           Request Com Port Flow Control Setting
+                           (outbound/both)
+             1           Use No Flow Control (outbound/both)
+             2           Use XON/XOFF Flow Control (outbound/both)
+             3           Use HARDWARE Flow Control (outbound/both)
+
+
+
+Clark                         Experimental                      [Page 8]
+
+RFC 2217          Telnet Com Port Control Option            October 1997
+
+
+             4           Request BREAK State
+             5           Set BREAK State ON
+             6           Set BREAK State OFF
+             7           Request DTR Signal State
+             8           Set DTR Signal State ON
+             9           Set DTR Signal State OFF
+            10           Request RTS Signal State
+            11           Set RTS Signal State ON
+            12           Set RTS Signal State OFF
+            13           Request Com Port Flow Control Setting (inbound)
+            14           Use No Flow Control (inbound)
+            15           Use XON/XOFF Flow Control (inbound)
+            16           Use HARDWARE Flow Control (inbound)
+            17           Use DCD Flow Control (outbound/both)
+            18           Use DTR Flow Control (inbound)
+            19           Use DSR Flow Control (outbound/both)
+            20-127       Available for Future Use
+
+       Discussion: Flow control options were divided into inbound and
+                   outbound to take full advantage of existing
+                   programming interfaces and access server
+                   capabilities.
+
+       Discussion: The outbound values should set flow control for both
+                   outbound and inbound.  If inbound is to be, or can
+                   be, set separately it should be done after the
+                   setting of the outbound value.
+
+       Discussion: If the access server is not able to set inbound flow
+                   control differently from the outbound flow control,
+                   it should ignore the inbound flow control commands
+                   and set the flow control option based on the outbound
+                   flow control commands only.
+
+     IAC SB COM-PORT-OPTION SET-LINESTATE-MASK <value> IAC SE
+       This command is sent by the client to the access server to set a
+       bit mask for the sending of the NOTIFY-LINESTATE option (see
+       section 4).  When the LINESTATE changes on the access server, the
+       access server will "AND" the new LINESTATE with the LINESTATE-
+       MASK.  If the result is not zero, the access server will send the
+       result of the "AND" as the value in a NOTIFY-LINESTATE com port
+       option. If more than one bit satisfies the LINESTATE-MASK, only
+       one NOTIFY-LINESTATE, with all the satisfying bits, will be sent
+       to the client.  The SET-LINESTATE-MASK may be any combination of
+       bits as listed below.  These are the same bit values used in the
+       NOTIFY-LINESTATE option.  The SET-LINESTATE-MASK values are based
+       on the most popular UART (com port control chip) in use [1].
+
+
+
+
+Clark                         Experimental                      [Page 9]
+
+RFC 2217          Telnet Com Port Control Option            October 1997
+
+
+           Bit Position     Value     Meaning
+              7              128         Time-out Error
+              6               64         Transfer Shift Register Empty
+              5               32         Transfer Holding Register Empty
+              4               16         Break-detect Error
+              3                8         Framing Error
+              2                4         Parity Error
+              1                2         Overrun Error
+              0                1         Data Ready
+
+       Discussion: The SET-LINESTATE-MASK value of 0 will prevent the
+                   access server from sending NOTIFY-LINESTATE options
+                   to the client.
+
+       Discussion: The SET-LINESTATE-MASK value of 255 will allow the
+                   access server to send a NOTIFY-LINESTATE option to
+                   the client each time the LINESTATE changes on the
+                   access server.
+
+       Discussion: The initial LINESTATE-MASK at the access server is 0.
+
+       Discussion: The client does not have to send a new
+                   SET-LINESTATE-MASK after receiving a NOTIFY-
+                   LINESTATE.  The LINESTATE-MASK on the access server
+                   is retained until set by the client or reset at the
+                   start of a new Telnet session.
+
+     IAC SB COM-PORT-OPTION SET-MODEMSTATE-MASK <value> IAC SE
+       This command is sent by the client to the access server to set a
+       bit mask for the sending of the NOTIFY-MODEMSTATE option (see
+       section 4).  When the MODEMSTATE changes on the access server,
+       the access server will "AND" the new MODEMSTATE with the
+       MODEMSTATE-MASK.  If the result is not zero, the access server
+       will send the result of the "AND" as the value in a NOTIFY-
+       MODEMSTATE com port option. If more than one bit satisfies the
+       MODEMSTATE-MASK, only one NOTIFY-MODEMSTATE, with all the
+       satisfying bits, will be sent to the client.  The SET-
+       MODEMSTATE-MASK may be any combination of bits as listed below.
+       These are the same bit values used in the NOTIFY-MODEMSTATE
+       option.  The SET-MODEMSTATE-MASK values are based on the most
+       popular UART (com port control chip) in use [1].
+
+
+
+
+
+
+
+
+
+
+Clark                         Experimental                     [Page 10]
+
+RFC 2217          Telnet Com Port Control Option            October 1997
+
+
+           Bit Position     Value     Meaning
+              7              128        Receive Line Signal Detect
+                                        (also known as Carrier Detect)
+              6               64        Ring Indicator
+              5               32        Data-Set-Ready Signal State
+              4               16        Clear-To-Send Signal State
+              3                8        Delta Receive Line Signal Detect
+              2                4        Trailing-edge Ring Detector
+              1                2        Delta Data-Set-Ready
+              0                1        Delta Clear-To-Send
+
+       Discussion: The SET-MODEMSTATE-MASK value of 0 will prevent the
+                   access server from sending NOTIFY-MODEMSTATE options
+                   to the client.
+
+       Discussion: The SET-MODEMSTATE-MASK value of 255 will allow the
+                   access server to send a NOTIFY-MODEMSTATE option to
+                   the client each time the MODEMSTATE changes on the
+                   access server.
+
+       Discussion: The initial MODEMSTATE-MASK at the access server
+                   is 255.
+
+       Discussion: The client does not have to send a new
+                   SET-MODEMSTATE-MASK after receiving a NOTIFY-
+                   MODEMSTATE.  The MODEMSTATE-MASK on the access server
+                   is retained until set by the client or reset at the
+                   start of a new Telnet session.
+
+     IAC SB COM-PORT-OPTION PURGE-DATA <value> IAC SE
+       This command is sent by the client to the access server to
+       instruct the access server to immediately clear all data from the
+       buffer or buffers referenced by the value.  The value is one
+       octet (byte).  The value is an index into the following value
+       table:
+
+           Value      Purge Data Buffer
+             0           Available for Future Use
+             1           Purge access server receive data buffer
+             2           Purge access server transmit data buffer
+             3           Purge both the access server receive data
+                         buffer and the access server transmit data
+                         buffer
+             4-127       Available for Future Use
+
+
+
+
+
+
+
+Clark                         Experimental                     [Page 11]
+
+RFC 2217          Telnet Com Port Control Option            October 1997
+
+
+4. Notification of Com port and Modem Line Changes
+
+   The access server can send these commands to the client any time
+   and multiple times throughout the Telnet session. The access
+   server should send the appropriate command to the client as soon
+   as the com port or modem line changes occurs.  The client does
+   not issue a response to these commands.
+
+     IAC SB COM-PORT-OPTION NOTIFY-LINESTATE <value> IAC SE
+       The value is one octet (byte). The value is a bit level
+       composition made up from the value table below. Multiple bit
+       values may be set in a single transmission. The values are based
+       on the most popular UART (com port control chip) in use [1].
+
+           Bit Position     Value     Meaning
+              7              128         Time-out Error
+              6               64         Transfer Shift Register Empty
+              5               32         Transfer Holding Register Empty
+              4               16         Break-detect Error
+              3                8         Framing Error
+              2                4         Parity Error
+              1                2         Overrun Error
+              0                1         Data Ready
+
+
+       Discussion: The LINESTATE is the line state of the UART on
+                   the access server.
+
+     IAC SB COM-PORT-OPTION NOTIFY-MODEMSTATE <value> IAC SE
+       The value is one octet (byte). The value is a bit level
+       composition made up from the value table below. Multiple bit
+       values may be set in a single transmission. The values are based
+       on the most popular UART (com port control chip) in use [1].
+
+           Bit Position     Value     Meaning
+              7              128        Receive Line Signal Detect
+                                        (also known as Carrier Detect)
+              6               64        Ring Indicator
+              5               32        Data-Set-Ready Signal State
+              4               16        Clear-To-Send Signal State
+              3                8        Delta Receive Line Signal Detect
+              2                4        Trailing-edge Ring Detector
+              1                2        Delta Data-Set-Ready
+              0                1        Delta Clear-To-Send
+
+
+
+
+
+
+
+Clark                         Experimental                     [Page 12]
+
+RFC 2217          Telnet Com Port Control Option            October 1997
+
+
+5. Flow Control
+
+   The client and/or access server can send these commands any time and
+   multiple times throughout the Telnet session.
+
+     IAC SB COM-PORT-OPTION FLOWCONTROL-SUSPEND IAC SE
+       The sender of this command is requesting that the receiver
+       suspend transmission of both data and commands until the
+       FLOWCONTROL-RESUME is transmitted by the sender.
+
+     IAC SB COM-PORT-OPTION FLOWCONTROL-RESUME IAC SE
+       The sender of this command is requesting that the receiver resume
+       transmission of both data and commands.
+
+       Discussion: Established Telnet sessions are initially in a
+                   resume state between the client and the access server
+                   and the access server and the client.  There is no
+                   need to send the resume command during session
+                   initialization.
+
+       Discussion: Multiple concurrent suspend commands may be sent.
+                   Secondary suspend commands can be ignored.
+                   Transmission will resume with the sending of a single
+                   resume command.
+
+       Discussion: The flow control option is designed to handle client
+                   to access server flow control for the Telnet session.
+                   This option has been added in deference to RFC 1372:
+                   Telnet Remote Flow Control Option [2].  RFC 1372 uses
+                   a simple character XON/XOFF technology to implement
+                   flow control.  This can lead to two problems.  First,
+                   the flow control characters may be valid data values.
+                   Second, the flow control characters may be used for
+                   end to end flow control (client application to remote
+                   dial up service).
+
+6. Security Considerations
+
+   There are two security issues to discuss; authentication and
+   resetting resources.
+
+   Authentication can follow either the Kerberos authentication protocol
+   established in RFC 1411 [3] or the SPX authentication protocol
+   established in RFC 1412 [4].
+
+   Once the Telnet session between the client and the access server has
+   been terminated, the access server should ensure the connection to
+   the remote service is disconnected and the com port geometry (baud
+
+
+
+Clark                         Experimental                     [Page 13]
+
+RFC 2217          Telnet Com Port Control Option            October 1997
+
+
+   rate, data size, stop bits, parity, and flow control) is reset to a
+   factory or administrator defined configuration.  This ensures the com
+   port is in a known state and ready to receive the next client
+   session.  This will make operations more predicable and avoid
+   problems which might occur from starting a new session with random
+   com port configurations.
+
+7. Author's Address
+
+  Glen Clark, Software Architect
+  Cisco Systems, Inc.
+  170 West Tasman Drive
+  San Jose, CA  96134
+  USA
+
+  EMail:      glenc@cisco.com
+  WEB:        www.cisco.com
+
+8. Reference Section
+
+   [1]  Joe Campbell. C Programmer's Guide to Serial Communications,
+        Second Edition. Indianapolis: SAMS Publishing, 1993. 213-224.
+
+   [2]  Hedrick, C., and D. Borman, "Telnet Remote Flow Control Option",
+        RFC 1372, Cray Research, Inc., October 1992.
+
+   [3]  Borman, D., "Telnet Authentication: Kerberos Version 4",
+        RFC 1411, Cray Research, Inc., January 1993.
+
+   [4]  Alagappan, K., "Telnet Authentication: SPX",
+        RFC 1412, Digital Equipment Corporation, January 1993.
+
+   [5]  D. E. Comer and David Stevens.  Internetworking with TCP/IP,
+        Volume III.  Prentice Hall, 1993.
+
+   [6]  Andrew Margolis. The FAX Modem Sourcebook.  John Wiley & Sons.
+        1995.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Clark                         Experimental                     [Page 14]
+