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Interface for Virtual Devices in Network Nodes

IP.com Disclosure Number: IPCOM000089427D
Original Publication Date: 1977-Oct-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 7 page(s) / 149K

Publishing Venue

IBM

Related People

Hayward, RC: AUTHOR [+2]

Abstract

Normally in network nodes, functions are provided and dialogs defined to provide communications with real terminals. It may be useful to define virtual devices which reside within the network node itself and use existing functions and dialogs. Such a virtual device would be useful to provide programmed terminal applications, service functions for the node, networking functions, service/application functions for real terminals or combinations of these.

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Interface for Virtual Devices in Network Nodes

Normally in network nodes, functions are provided and dialogs defined to provide communications with real terminals. It may be useful to define virtual devices which reside within the network node itself and use existing functions and dialogs. Such a virtual device would be useful to provide programmed terminal applications, service functions for the node, networking functions, service/application functions for real terminals or combinations of these.

This article describes an interface for the development of a virtual device and its associated function. As an example, this interface will be described in relation to the IBM 3705 Network Control Program (NCP), a network node in an IBM System Network Architecture (SNA) network. Therefore, the reader should be familiar with the following IBM documents: (a) System Network Architecture Formats and Protocols Reference Manual (a) System Network Architecture Formats and Protocols Reference Manual SC30-3112, (b) IBM 3704 and 3705 Communications Controllers Network Control Program, Program Logic Manual SY30-3013.

For the purpose of compatibility with SNA, the definition of each virtual device to be defined must include logical attachment to a virtual link and include within the virtual device a virtual physical unit and, at least, one virtual logical unit. If we define more than one virtual device, all may be logically attached to the same virtual link. All the virtual resources must be defined to the host access method system services control point (SSCP).

Because the attachment of these virtual devices to the network node is via virtual links, there appears to be no necessity for a boundary node function. Additionally, we can logically move all adjacent node physical services into the virtual device. Therefore, we have chosen to interface the virtual device to the network node at the intermediate node interface to boundary node services and NCP physical unit services. The pIU (Path Information Unit) types which flow through this interface are format identifiers FIDO and FID1. Defining Virtual Resources to the NCP.

Each virtual link, station and LU (Logic Unit) require a unique element address in the NCP subarea. Entries must be added to the NCP's Resource Vector Table (RVT) for each at the offset appropriate to that element address. The full word entry for each must contain the appropriate designation (type resource) in byte 0. Byte 1 is specified as X'3X', where bit 2 means SNA resource, bit 3 means virtual device, and bits 6 and 7 are the high order bits of the address of an associated control block. Bytes 2 and 3 provide the rest of the address. (See Fig. 2.) Control Blocks (Fig. 2). Virtual Link Block (VLB).

One VLB must be defined for each virtual link defined. The VLB contains information similar to that currently kept in the LKB (Link Control Block). The VLB is used to maintain the status of the virtual link. Information which may be k...