GB2279538A

GB2279538A - Binary data communication switch

Info

Publication number: GB2279538A
Application number: GB9313031A
Authority: GB
Inventors: Kim Philip Lyon
Original assignee: Individual
Current assignee: Individual
Priority date: 1993-06-24
Filing date: 1993-06-24
Publication date: 1995-01-04
Also published as: GB9313031D0

Abstract

The Binary Data Communication Switch combines the advantages of the high speed routing of virtual circuits with the advantages of the low passive overhead of packet switching. The data communication switch consists of 3 ports A, B, C and requires only 1 bit in the data streams at port A to specify which port B or C the packet is going out of. The Binary Data Communication Switch also localises all data transfer and error handling operations. The Binary Data Communication Switch is designed primarily for high speed fibre optic networks. Binary Data Communication Switches can be connected together in a tree topology to form large networks. <IMAGE>

Description

Binary Data Communication Switch Binary Data Communication Switch The Binary Data Communication Switch has been designed to solve the problem of routing delays within current networks The Binary Data Communication Switch combines the advantages of virtual circuits and packet switching networks . The Binary Data Communication Switch is also designed to be a simple connectable building block which when connected together forms large networks of tree topology or variants thereof The Binary Data Communication Switch consists of 3 ports Each port passes data onto 1 of the 2 other ports .A single bit in the data stream is used to specify which port the data is to go out of Binary Data Communication Switch Showing the 3 ports - A , B and C

I c A A B Figure 1 Conventions The Following conventions are used :1) The most significant bit ( the left most bit ) shown is shifted out first Binary Data Communication Switch 2 A Simplified Protocol Given a frame generated protocol using a known line state and a fixed packet length where the communication line consists of spaces ( O's ) in the rest state and where the frame start bit consequently consists of a 1 and the stop bit consists of a 0 and where the communication is specified to travel from port A to port C and where the address for port B relative to port A is 0 and the address for port C relative to port A is 1 the following bit stream illustrates the minimum information required:

- frame start bit ≈ - frame stop bit 1 1 message 0 I I I - header , data and error check syndrome - binary switch address As can be seen the message can be switched with the first 2 bits of the packet being received .This means that although the address size is longer the routing time is considerably shorter than in data communication systems that use more than 1 bit in the address specification Linking Up the Binary Data Communication Switches

BDCS1 1 C 1 I A OB I I I BDCS2 I BDCS3 I C I l C 1 1 1 I loll A OB I I A B I I I Figure 2 Binary Data Communication Switch 3 Addresses are shown for the communication of the message from port A of the Binary Data Communication Switch 2 to port B of the Binary Data Communication Switch 3 A Subsequent Simplified Protocol

- frame start bit I - frame stop bit 1 1 0 1 message 0 III I I I I - header , data and error check syndrome I I - binary switch address BDCS3 I - binary switch address BDCS1 - binary switch address BDCS2 Practical Considerations Within a practical data communication system the following practical considerations must be taken into account ::1) i) The unpredictability of a totally free path combined with ii) the low chance of a multi Binary Data Communication Switch path being totally free at any one time combined with iii) the considerably higher chance of individual Binary Data Communication Switch links being free at any one time combined with iv) the requirement for as quick as possible transfer time from initial source to final destination requires that i) the Binary Data Communication Switch has store and forward facilities Binary Data Communication Switch and ii) the Binary Data Communication Switch has hold off transmission \ resume transmission protocol commands 2) The ability to be able to determine the paths to other units in the network this requires the pressence of network control stations 3) The derivation of the reverse path so that the final destination unit can determine the path to be taken to communicate with the initial source unit 4) The localising of responses to error conditions so that the available time on the network is maximised A Resulting Protocol Messages for Units Message to Unit ( up and down tree ) Message for All Units in Network ( down tree Message for Network Control Station ( up tree Messages for Binary Data Communication Switches Hold Off Transmission - Buffer Full Continue \ Resume Transmission - Buffer Space Available Retransmit Message - message was received in error Sychronisation Sequence Link O Down Link 1 Down Link O Restored Link 1 Restored Initial Sychronisation Sychronisation Sequence - > repeated until a Line State Reset response received Inactive Time < - Continue \ Resume Transmission Binary Data Communication Switch Continue \ Resume - > Transmission Error Handling First Message - > Inactivity < - Retransmit Message Line State Reset Inactive Time Sychronisation Sequence - > < - Resume Transmission First Message Repeated - > or First Message - > Second Message - > < - Retransmit Message Line State Reset Inactive Time Sychronisation Sequence - > < - Resume Transmission First Message Repeated - > Second Message Repeated - > Bit Patterns Message types

- frame start bit I 1 0 Unit Message 1 1 Command Message Unit Message

- frame start bit - frame stop bit 1 0 0 path message 0 Unit 1 0 1 0 blank path message 0 All Units ( from Network Control Station 1 0 1 1 blank path message 0 Network Control Station Binary Data Communication Switch The reverse path for the All Units and Network Control Station messages is inserted directly prior to the message as per the path format listed below as the message passes through the Binary Data Communication Switches Command Message

- frame start bit I - extra bit to ensure uniqueness of bit pattern I l - frame stop bit I I 1 1 0 0 0 0 0 Hold Off Transmission 1 1 0 0 1 0 0 Continue \ Resume Transmission 1 1 0 1 0 0 0 Retransmit Message 1 1 0 1 1 0 0 Sychronisation Sequence 1 1 1 0 0 1 blank path 0 Link O Down 1 1 1 0 1 1 blank path 0 Link 1 Down 1 1 1 1 0 1 blank path 0 Link O Restored 1 1 1 1 1 1 blank path 0 Link 1 Restored The Link Down and Link Restored messages are passed on to the next Network Control Station . The reverse path is inserted directly prior to the frame stop bit as per the path format listed below as the message passes through the Binary Data Communication Switches Paths For purposes of practicality :i) All paths must be specified in multiples of 8 bits and ii) Networks of varying sizes must be accomadated As such to accomadate the varying bit lengths of the messages the first byte will consist of the operation that follows the frame start bit combined with the path start . A second path byte follows with 7 bits of path information and an extension absent \ present bit at the 8 th. bit .Extensions are 16 bits in length with an extension bit in the 16 th. bit Binary Data Communication Switch Path Handling and Reverse Path Generation As the packet passes from one port to another the path bits are shifted up 1 bit so that the next switch address is at the first path position . The address of the port that the packet came from relative to the port that the packet is going to is placed at the last path position Data Messages A frame generated system with a fixed packet length has limitations as far as effective usage of the network time is concerned .This can be combatted by one of three ways :i) Placing a message length ( eg. byte \ word ) at the start of the data message - retains the low overhead of the frame generated system ii) Placing a message extension bit at the end of each block of the data message - retains the low overhead of the frame generated system for full block usage messages iii) Placing a unique character ( flag ) at the start of the message , at the end of the message ( flag \ poll and retaining the uniqueness of those messages by inserting and subsequently extracting bits into and out of the data messages - removes the low overhead of the frame generated system The maximum message length in practice could be set to 512 bytes . As such a 9 bit message length of type i) would be the most practical .The path being of such a length to ensure that the total packet length exclusive of the frame start and stop bits is a multiple of 8 bits Binary Data Communication Switch Providing a maximum path length of 87 bits and 6 extensions and a maximum message length of 512 bytes thus providing a total maximum packet length of 4,202 bits including the frame start and stop bits and the packet type bits provides a known maximum line inactive time required to achieve time out before sychronisation can be ensured Unit Message

10 0 P P P P P P P P P P P P E m.l. message 0 II I I I I - message length I I I ( 9 bits ) ------------------------ - 0 not extended 1 1 extended - path All Unit Message 10 1 0 0 0 0 0 0 0 0 0 0 0 0 0 E m.l. message 0 II I I I I - message length I I / ( 9 bits ) ------------------------ - 0 not extended 1 1 extended - path Message to Network Control Station 10 1 1 1 1 1 1 1 1 1 1 1 1 1 1 E m.l. message 0 II I I I I - message length I I I ( 9 bits ) ------------------------ - 0 not extended 1 1 extended - path Hold Off Transmission 1 1000 0 0 Continue \ Resume Transmission 1 1001 0 0 Binary Data Communication Switch Retransmit Message 1 1 0 1 0 0 0 Sychronisation Sequence 1 1 0 1 1 0 0 Link 0 Down

1 1 1 0 0 1 1 1 1 1 1 1 1 1 1 1 E 0 l l --------------------- - 0 not extended 1 1 extended - path Link 1 Down

1 1101 1111 1111 111E0 II --------------------- - 0 not extended 1 1 extended - path Link 0 Restored

1 11101111 1111 111ego II --------------------- - 0 not extended 1 1 extended - path Link 1 Restored

1 1111 1111 1 1 1 1 111E0 II --------------------- - 0 not extended 1 1 extended - path Binary Data Communication Switch

Claims

Claims 1) A Data Communications Switch that :

i) consists of 3 ports and

ii) passes messages from one port to one of the two other ports and

iii) uses a single bit in the data stream to determine which port the packet is going to go out of 2) A Data Communications Switch as defined in claim 1 that uses message storing and forwarding 3) A Data Communications Switch as defined in claim 1 that handles error detection , resychronisation and retransmission 4) A Data Communications Switch as defined in claim 1 that detects and reports the loss and regaining of communication into each port