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 Introduction

 Point-To-Point Communication

     The CA-Clipper Tools contain functions that allow direct communication
     between workstations in Novell or NetBIOS compatible networks by
     bypassing the file server.  This type of communication is called Point-
     To-Point communication.

     The data exchange between two workstations is interrupt controlled.
     Incoming data is copied in the background to a receiving buffer and can
     then be read with CA-Clipper Tools functions.  As soon as the receiving
     buffer is full, incoming data is discarded.  Outgoing data is copied to
     a sending buffer.  While the CA-Clipper application continues, data is
     sent in the background from the sending buffer to the target address.
     Interrupt controlled sending of data is necessary to avoid a long wait
     when you send large datasets.  When you use IPX/SPX communication or one
     of two possible NetBIOS communication variants, the data is broken up
     into packets internally.  The packet size depends on the protocol used
     (IPX: 546 bytes, SPX: 534 bytes, NetBIOS: 512 bytes).  The packets are
     sent sequentially.

     Normally, the packet structure of the transmitted data is transparent
     and does not affect the handling of the data.  The receiving buffer of
     the target workstation receives the data in the same way that the data
     has been written to the sending buffer.  When you use IPX/SPX protocols
     in addition to the data, a header that is included in each IPX or SPX
     packet can be transmitted to the receiving buffer.   This header makes a
     number of packet specific functions possible.  The tables 31.1 and 31.2
     describe the structure of the IPX and SPX header.  The header positions
     start with 1, corresponding to string functions.

     The NetBIOS communication variants have no similar mechanism available.

     Table 31.1:  IPX Packet Header
     ------------------------------------------------------------------------
     Position     Length    Description
     ------------------------------------------------------------------------
     1            2         Checksum
     3            2         Packet length in bytes
     5            1         Transmission control
     6            1         Packet type (4=IPX)
     7            4         Network number of target station
     11           6         Station ID of target station
     17           2         Target socket (High, Low format)
     19           4         Network number of source station
     23           6         Station ID of source station
     29           2         Source socket (High,  Low format)
     ------------------------------------------------------------------------

     Table 31.2:  SPX Packet Header
     ------------------------------------------------------------------------
     Position  Length  Description
     ------------------------------------------------------------------------
     1         2       Check sum
     3         2       Packet length in bytes
     5         1       Transmission control
     6         1       Packet type (5=SPX)
     7         4       Network number of target station
     11        6       Station ID of target station
     17        2       Target socket (High, Low format)
     19        4       Network number of source station
     23        6       Stations ID of source station
     29        2       Source socket (High, Low format)
     31        1       Connection control
     32        1       Datastream type
     33        2       Connection number on source station (High, Low format)
     35        2       Connection number on target station (High, Low format)
     37        2       Sequence number (High, Low format)
     39        2       Acknowledge number (High, Low format)
     41        2       Allocation number (High, Low format)
     ------------------------------------------------------------------------

     When you install a communication buffer (a communication buffer can
     contain a sending and a receiving buffer), you receive a communication
     handle as a return value.  You should store this handle in a variable as
     it is absolutely necessary for further operations with the communication
     buffer.

     The functions for Point-To-Point communication fall into two groups:
     protocol specific functions and functions that can be used for any kind
     of communication buffer.  Protocol specific functions are functions for
     a connection setup: (IPXOPEN(), SPXESTBCON(), SPXLISTCON(), NBDOPEN(),
     NBSCALL(), and NBSLISTCON()).  The name of a protocol specific function
     always starts with three characters that describe the respective
     protocol  (IPX, SPX, NBD: NetBIOS Datagram, NBS: NetBIOS Session).

     Functions that write or read a buffer, or query the buffer status, are
     not protocol specific and can be used for any kind of communication
     buffer.  The names of these functions start with PPC (Point-To-Point
     Communication).  For example, the function PPCWRITE() is used to write
     data to a communication buffer.  The protocol specific process of the
     data is regulated internally.

 IPX/SPX Communication

     Novell Netware (including Netware Lite) allows the direct use of the IPX
     and SPX communication functions.  By loading the Novell NetBIOS emulator
     (NETBIOS.EXE), you can also use NetBIOS communication functions in
     Novell networks.  However, the use of the emulator compared to IPX/SPX
     reduces the performance and the available memory.  Therefore, you should
     use the IPX/SPX communication functions for applications running only in
     Novell networks.

     IPX (Internetwork Packet Exchange Protocol) is a rudimentary protocol
     whose main advantage is that data can be sent to all waiting
     workstations in an internal network with only one call.  However, IPX
     has no suitable handshake mechanism available that guarantees a
     successful delivery and a correct process of the sent data on the
     destination workstation.  (Related mechanisms can be implemented with
     the IPX functions of CA-Clipper Tools.  However, these mechanisms are
     application specific and have no general validity.)

     The SPX protocol (Sequenced Packet Exchange Protocol) only allows
     communication between two workstations within an internal network.  SPX
     has mechanisms available that guarantee the successful delivery of sent
     data.

     Unlike SPX, which can be seen as real Point-To-Point communication
     protocol, the IPX communication is implemented as a pseudo Point-To-
     Point communication.  When you use IPX, data for a specific workstation
     can be received by any workstation.  However,  a destination address is
     defined for interrupt controlled sending.  (This address can specify all
     workstations within an internal network.)  The destination address is
     not defined by the protocol, so it is not necessary to specify the
     destination address each time you access the send buffer.  When you use
     the SPX protocol, a connection between two workstations is established.

     The IPX/SPX communication between two workstations is based on two
     sockets on each side of the connection that can be opened and closed,
     similar to files.  Sockets are represented by numeric values between 1
     and 65535.  Some socket numbers are reserved either by the Netware
     operating system or by Novell for third party vendors. The sockets
     between 16384 and 20480 (4000h - 5000h) are the dynamic sockets, meaning
     there are no reserved sockets in this range.  A collision with socket
     numbers reserved by Netware can be avoided by using sockets out of that
     range.

 NetBIOS Communication

     The NetBIOS communication functions can be used in all networks that are
     based on NetBIOS specifications.  In CA-Clipper Tools, two kinds of
     NetBIOS communication have been implemented: NetBIOS datagram and
     NetBIOS session communication. The NetBIOS datagram communication can be
     compared to the IPX communication; a successful delivery of sent data on
     the destination workstation is not guaranteed by the protocol.  Like
     IPX, the datagram connection can also be implemented as pseudo Point-To-
     Point communication between two workstations.  Additionally, a
     workstation can communicate with a group of workstations or with all
     workstations in a network.

     Like an SPX connection, a session connection is a fixed connection
     between two workstations.  The dataflow between two workstations is
     supervised internally by a protocol that guarantees the delivery of sent
     data on the destination workstation.

     For the communication with other workstations in a NetBIOS network,
     NetBIOS names are used.  A NetBIOS name can be up to 15 characters long
     and is case sensitive.  NetBIOS differentiates between two kinds of
     names: station names that specify a workstation and are unique in a
     network, and group names that can be assigned to any number of stations.
     Each workstation contains a local name table with up to 20 NetBIOS
     names.  A workstation can be addressed with each name in the name table.
     Once you have defined single or group names, messages can be sent easily
     to a station or a group of stations.

     Because of the importance of NetBIOS names for the Point-To-Point
     communication, CA-Clipper Tools not only includes functions for the
     sending and receiving of data, but also functions for creating and
     deleting NetBIOS names.