Browse Prior Art Database

Communication Protocol on Virtual Link

IP.com Disclosure Number: IPCOM000059626D
Original Publication Date: 1986-Jan-01
Included in the Prior Art Database: 2005-Mar-08
Document File: 3 page(s) / 48K

Publishing Venue

IBM

Related People

Gergaud, CJ: AUTHOR [+3]

Abstract

Meshed communication networks are widely used for interconnecting communication units. Such networks reduce the number of links, but require transit nodes that are connected to peripheral nodes. The existing X25 transit nodes combine in one product the network access functions with the network transit functions. The control programs are generally complex and the path lengths are such that the performances are low (100 to 1000 frames per second). This article describes a technique which allows one to simplify the transit nodes by removing the error recovery and protocol management therefrom, transit nodes becoming transparent to the communication protocol.

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Communication Protocol on Virtual Link

Meshed communication networks are widely used for interconnecting communication units. Such networks reduce the number of links, but require transit nodes that are connected to peripheral nodes. The existing X25 transit nodes combine in one product the network access functions with the network transit functions. The control programs are generally complex and the path lengths are such that the performances are low (100 to 1000 frames per second). This article describes a technique which allows one to simplify the transit nodes by removing the error recovery and protocol management therefrom, transit nodes becoming transparent to the communication protocol. In the proposed technique, communication protocol, error recovery, and pacing are performed on each virtual link in the peripheral nodes rather on each physical link, thus providing a very high performance transit node. The figure illustrates a network embodying the proposed technique. The Transit Node (TN) is a data packet switching unit which is connected to high speed communication lines, and which routes packets from one line to another in a very fast way. A TN can be connected through communication lines to either another TN to form a meshed net work, or to peripheral nodes which are the source and the destination of the data packets, or to both. In the example shown in the figure, each data packet consists of an HDLC (High-Level Data Link Control) frame. HDLC frames transiting trough TNs have a standard format but comprise a routing tag inserted by the source peripheral node before the control part of the HDLC header, and which is used by the TNs to route the frame to the destination peripheral node. A TN mainly includes Communication Processors (CPs) which can send and receive frames and Service Processors (SPs) including a cyclic redundancy check (CRC) and a bus access arbiter to control the access of the CPs and SPs to a common bus. An HDLC frame received from one communication line is handled by the CP serving that line, and that CP carries out the following tasks...