Multiplex communications – Wide area network – Packet switching
Patent
1994-01-14
1995-08-22
Marcelo, Melvin
Multiplex communications
Wide area network
Packet switching
370 79, 370 8513, H04J 316, H04L 1246
Patent
active
054447038
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention is directed generally to Integrated Services Digital Networks (ISDN), and more particularly to apparatus for enabling access to an ISDN line by a personal computer, or local area network.
BACKGROUND ART
ISDN is a relatively newly developed and emerging field of telecommunications which integrates computer and communications technologies to provide, worldwide, a common, all-digital network. This is based, in part, on standardizing the structure of digital protocols developed by the Internacional Telegraph and Telephone Consultative Committee (CCITT). Despite the implementation of multiple networks within national boundaries, from a user's point of view there is a single, uniformly accessible, worldwide network capable of handling a broad range of telephone, data and other conventional and enhanced services.
A complete description of the architecture of ISDN is beyond the scope of this specification. For details, and for an extensive bibliography of references on ISDN, see Stallings, ISDN, An Introduction, MacMillan Publishing Company, 1989.
An ISDN is structured by architecture closely following the OSI Seven Layer Reference Model. Within the framework of ISDN, the network provides services and the user accesses the services through the user-network interface. A "channel" represents a specified portion of the information carrying capacity of an interface. Channels are classified by two types, Basic Rate ISDN (BRI) and Primary Rate ISDN (PRI). BRI delivers two B-channels, each having a capacity of 64 Kbps, capable of transmitting voice and data simultaneously. A 16 Kbps D-channel transmits call control messages and user packet data. PRI provides twenty three B-channels of 64 Kbps capacity each for carrying voice, circuit switched data or packet data. The D-channel is a 64 Kbps signaling channel. The B and D channels are logically multiplexed together at Layer 1 of the OSI Reference Model.
FIG. 1 depicts the conventional ISDN interfaces. At the customer premises, an "intelligent" device, such as a digital PBX terminal controller or Local Area Network (LAN), can be connected to an ISDN terminal TE, such as a voice or data terminal, which is connected to a Network Termination (NT1). Non-ISDN terminals TE may be connected to a Network Termination (NT2) and a Terminal Adapter TA. The NT2 in turn is connected over an "S/T-Interface", which is a four-wire bus, to a termination NT1 that performs functions such as signal conversion and maintenance of the electrical characteristics of the loop.
At the local loop, a two-wire bus, termed the "U-Interface", or "Loop", interconnects NT1 and a Loop Termination (LT) at the central office. Finally, the "U-Interface" is a bus between the local loop at the carrier end and exchange switching equipment. Details of this architecture are provided in ISDN: An Overview, Data Pro Research, Concepts & Technologies, MT 20-365; pp 101-110, published by McGraw Hill, Incorporated (December 1988).
For connecting a personal computer to a conventional telephone line, a modem is required to convert outgoing digital signals generated by the computer into analog signals to be carried by the line, and to convert incoming analog signals to digital signals. Because an ISDN line is a digital network, however, no modem is required to interface a computer with the line; a computer is able to be connected to the ISDN line directly.
On the other hand, any interface between a computer and the ISDN must carry out conversion between the protocol stack implemented by the computer and ISDN protocol. The present invention provides gateway functions between personal computers and ISDN lines in a manner supporting existing communication protocols.
An interface may operate at any of several layers of the OSI model. A "repeater" is an interface operating at the physical link layer. A "bridge" interconnects networks at the data-link layer, and a "router" functions at the network layer. "Gateways" handle higher-level internetwork protocols. This terminology is not universal; for e
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Cummings Paul
Gagliardi Ugo O.
Hsu Meichun
Mattin Stephen A.
Jung Min
Marcelo Melvin
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