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Data Loop Architecture Using Transmit Receive Message Pairs

IP.com Disclosure Number: IPCOM000085845D
Original Publication Date: 1976-Jun-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 6 page(s) / 149K

Publishing Venue

IBM

Related People

Abraham, R: AUTHOR [+8]

Abstract

The loop communication method shown has the advantages that: synchronous as well as asynchronous messages can be transmitted. An inbound message from a station i can be carried in the same frame that was used to carry an outbound message to station j (where i is greater than j), and simple error recovery is possible by counting originate messages whether the message contains data or a data request.

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Data Loop Architecture Using Transmit Receive Message Pairs

The loop communication method shown has the advantages that: synchronous as well as asynchronous messages can be transmitted. An inbound message from a station i can be carried in the same frame that was used to carry an outbound message to station j (where i is greater than j), and simple error recovery is possible by counting originate messages whether the message contains data or a data request.

The loop communication method uses fixed-length frames for communicating between a master loop controller or station and a plurality of remote stations 1, 2, -- n. Each frame has a nonunique synchronizing frame byte F including a station bit position for indicating that the frame contains a message to or from a station, and an available/unavailable bit position for indicating that the frame is available for communication from a station to the master controller.

The frame format may be the same as the synchronous data link control (SDLC) format, for example, including 7 bytes of 8 bits each.

The 7 bytes in order of their transmission on the loop are frame byte F, address byte A, control byte C, two information bytes I1 and I2, and two cyclic redundancy check (CRC) bytes K1 and K2. The last check byte is followed by the framing byte of the next frame. Thus, each frame begins and ends with a frame byte even though the second frame byte is considered to be part of the next frame.

The first few bits of the frame byte contain a synchronizing pattern such as a 0 and five 1's. Synchronism is recognized by the frame sync logic in each station and the controller when the synchronizing pattern repeats in every eighth byte received from the loop.

Each station on the loop has a separate address. The address byte A contains either the address of the station that is to receive the frame from the loop controller or the address of the station that is sending the frame to the loop controller. An all 1's address applies to all stations.

The control byte contains information used in the control of the loop operation. Bits 6 and 7 are used to define the frame type. They are 0,0 for a sequenced information transfer frame; 1,0 for a sequenced supervisor frame; and 1,1 for a nonsequenced frame. In the two sequenced frames, bit 2 is the sequence count bit (N). For all frames bit 3 is the originate/response bit (R). 0 indicates an originate frame, 1 indicates a response frame. Any frame that is not part of an originate/response pair also gives this bit a value of 0.

The loop controller starts a loop sequence by transmitting an unavailable frame having an optional response poll (ORP) in the control byte. This is a nonsequenced frame with an all stations address.

Each remote station having an originate message to send must do so in the first contiguous available frames that it receives after the optional response poll (ORP). If a station has no message to send, it resets its option circuits in its control...