SIMPLE USER DATAGRAM PROTOCOL
PROTOCOL SPECIFICATION
ZXDSTD: 3
author: tntxxd@ztx6d
last-update: 2025/01/31


1.  INTRODUCTION

  This Simple User Datagram Protocol (SUDP) is defined to make available a datagram  mode of packet-switched  computer  communication in the environment of an interconnected set of computer networks.  This protocol assumes that the Zxdnet Protocol (ZP) is used as the underlying protocol.

  This protocol provides a procedure for application programs to send messages to other programs with a minimum of protocol mechanism. The protocol is transaction oriented, and delivery and duplicate protection are not guaranteed.

2.  FORMAT

                  0               7 8              15
                 +--------+--------+--------+--------+
                 |   Source Port   | Destination Port|
                 +--------+--------+--------+--------+
                 |              Checksum             |
                 +--------+--------+--------+--------+
                 |            data octets ...
                 +---------------- ...
                   Simple User Datagram Header Format



3.  FIELDS

  Source Port indicates the port of the sending process, and may be assumed to be the port to which a reply should be addressed in the absence of any other information.

  Destination Port has a meaning within the context of a particular Zxdnet destination address.

  Checksum is the 16-bit one's complement of the one's complement sum of the SUDP header and the data, padded with zero octets at the end (if necessary) to make a multiple of two octets. During computation, the checksum field itself is treated as zero. If the computed checksum is zero, it is transmitted as all ones. If the checksum field is zero, the receiver must skip the verification process.

4.  USER INTERFACE

  A user interface should allow the creation of new receive ports, receive operations on the receive ports that return the data octets and an indication of source port and source address, and an operation that allows a datagram to be sent, specifying the data, source and destination ports and addresses to be sent.

5.  ZP INTERFACE

  The SUDP module must be able to determine the source and destination Zxdnet addresses and the protocol field from the Zxdnet header. One possible SUDP/ZP interface would return the whole Zxdnet datagram including all of the Zxdnet header in response to a receive operation. Such an interface would also allow the SUDP to pass a full Zxdnet datagram complete with header to the ZP to send. The ZP would verify certain fields for consistency and compute the Zxdnet header checksum.


6.  PROTOCOL NUMBER

  This is protocol 2 when used in the Zxdnet Protocol.