Communications Processors Rise to Challenge of Larger, Faster Networks

As data networks grow in size, speed and complexity, communications processors are taking on increasingly important roles. Communications processors have become critical elements of computer vendor architectures, such as IBM's SNA and Digital Equipment's DECnet. At the same time, other vendors have begun using communications processors as gateways between their own systems and SNA networks, or for accessing X.25-based public data networks or a variety of local-area networks.

Value-added carriers such as GTE Telenet, as well as independent firms like Amnet, also supply communications processors for use as nodes in private packet-switched networks. In a more general sense, communications processors remain the keystone of most network plans, allowing users to readily adapt to changes in network traffic and equipment, and providing such advanced capabilities as adaptive routing, statistical multiplexing and network management.

Perhaps the best-know communications processor is IBM's 3705 controller, which was the workhorse of the early SNA networks. The backbone of any SNA network is the host-based Advanced Communications Function/Virtual Telecommunications Access Method (VTAM) and the ACF/Network Control Program (NCP), which runs on the communications controller. Together, VTAM and NCP control and direct the flow of data traffic between any terminal and any computer application on the network, while ensuring data security and integrity. As multiple-node networks grew, the 3705 became stretched by increasing demand for more storage and processing power, as well as added functions.

IBM's response was to design a new controller, the 3725, using the latest circuit technologies, modular subsystems and microcode to make it flexible enough to accommodate current requirements and expandable enough for future growth. The 3725 has more high-speed lines, more memory and can handle twice the message traffic of the 3705. In addition, it can control larger, more sophisticated networks more reliably yet its size is one-half that of its predecessor.

Microcode Simplifies Change

One of the most innovative changes was to replace the hardware scanners of the 3705 with up to 14 microprocessors, controlled by microcode, to search input lines for data. Microcode is easier and less expensive to change than hardware, and makes future enhancements possible without major redesign. In addition, distributing intelligence through microcode into several microprocessors, each driving a group of lines, allows smooth recovery procedures to be implemented without bringing down the entire controller. The use of microcode has also made it possible to reduce the number of features, simplifying ordering and maintenance--but complicating the development of plug-compatible models by competitors. In addition, diagnostic microcode is provided on a diskette for user checkout and problem determination online.

further, the 3725 takes account of the increased emphasis on reliability and problem determination due to the growing size and importance of data networks. A new console display acts as window into the system and provides two-way interactive communications. A separate, dedicated service subsystem, with its own microprocessor, can "take a picture" of the entire system and surrounding network to help the user and maintenance personnel diagnose problems.

The 3725 comprises five key components:

* A control subsystem, including a central control unit with main storage available in 256K-byte increments from 512K to 2048K-byte sizes. It attaches to host processor byte or block multiplexer or selected channels through one to six channel adapters. With the two-processor switch feature, the 3725 can be attached to a maximum of eight channels, six of s which can operate concurrently. It can also be used as a remote unit.

* A Maintenance and Operator Subsystem that includes a separate processor, diskette drive and console attachment. It provides diagnostic and operational functions to improve 3725 availability.

* A 3727 operator console that is attached to the 3725 controller. An alternate 3727 can be attached in addition to the primary one. A console switching unit allows them to be used with any one of several 3725 controllers.

* A transmission subsystem, using a single type of microprocessor-based communications scanner and only five different types of line interface couplers. The couplers enable attachment of the 3725 to as many as 256 full or half-duplex lines. IPt provides asynchronous terminal support at rates to 19.2 kb/s; it also supports a wide range of line interfaces with speeds to 256 kb/s. An attachment takes the speed to 1.5 Mb/s.

* The Model 1 base frame can house up to 96 full or half-duplex lines, two channel adapters and two two-processor switches, enabling connection of as many as four host computers. With the addition of the 3726 Expansion Unit, you can connect up to 256 lines and eight channels. The Model 2 can have up to 80 full or half-duplex lines and four channel adapters. It provides 2048K-bytes of storage and is field-upgradable to the 3725 Model 1. With its high-speed line attachment capability and full ACF/NCP networking support, the Model 2 is well-suited for use as a remote concentrator.

Any combination of 3725s and 3705s using ACF/NCP can coexist in the same network. Non-SNA devices and programs can be supported via the Emulation Program or the Network Terminal Option. The 3725 also supports X.21 and X.25 protocols.

Last September, IBM extended its controller line further with the introduction of the 3710, whose role is to integrate non-SNA devices into SNA networks by "protocol enveloping" and to extend SNA network management capability to the devices. The 3710 can be remotely or directly attached to a host computer via any IBM 3725 or 3705 controller using a point-to-point or multipoint SDLC link or through an X.25 packet-switched network.

A variety of start-stop, bisync or SDL devices may be attached on the downstream side of the IBM 3710, which all appear to the SNA controller as Physical Unit Type 2 devices. The 3710 can concentrate data from up to 32 separate lines at rates to 64 kb/s for transmission to one or more processors over single or multiple SDLC or X.25 lines. Scheduled to be available during the second quarter, the base model costs $20,300 and is about the size of a single file drawer.

Digital Closes on Goal

Of all vendor architectures, SNA has been the most widely accepted by users. In marking the architecture's 10th anniversary last September, IBM claimed the SNA base stood at more than 20,000 host computers. The only other vendor that comes close is Digital Equipment, whose Digital Network Architecture was announced in 1975. Like SNA, the Digital Network Architecture is a system of layered protocols that establish links and govern data transmission between computer systems. DEGnet products embody the architecture and facilitate construction of distributed processing networks with Digital computers.

Digital's stated goal with DECnet was to permit generalized interconnection of different host computers in point-to-point, multipoint or switched networks so that all users could share programs, data files and remote I/O devices systemwide. With its latest DECnet offering, known as Phase IV, Digital comes close to its goal.

DECnet's first three phases provided adaptive routing, task-to-task communications, file access and transfer through non-adjacent nodes, and support of X.25 packet-switched network protocols. Another feature of Phase III is the network command terminal software, which provides users on one node with direct access to program and devices on other network nodes using the same operating system. To the user, the terminal operates as if it were local to the remote system. Other software provides network management functions for evaluating overall network efficiency and initiating diagnostic tests to isolate network faults. These management functions can be either centralized or fully distributed across all nodes. They permit mointoring of communications loads, error rates, line conditions and node status at all points in the network.

One of the more innovative features of Phase III is the adaptive path-routing capability, which allows a DECnet network node to send messages to another node through as many as five intermediate nodes. When more than one path exists between the source and destination nodes, the network automatically selects the "least-cost" path, based on line values assigned by the network manager. The values for each line are primarily determined by its bandwidth, or data rate capability; the higher the data rate, the lower the "cost" assigned to the line.

Routing Tables

These line values are included in routing tables that are generated automatically when the software comes on-line. Each node maintains a routing table for the entire network. By using these tables, a node is able to select the optimum path for each ongoing message. There are two types of nodes: routing nodes, which can send, receive and forward messages; and end nodes, which only send and receive.

To provide the "adaptive" capability, the routing tables are updated whenever changes in line or system status occur. For instance, if service is interrupted on a particular circuit, its line value goes to infinity, which automatically causes messages to be re-routed across the next leastcost path. This process is completely transparent to the user. However, the network manager can adjust the line values at any time, either to control data flow or to perform line or system testing without disrupting the rest of the network.

Phase IV DECnet has all the features of Phase III, but expands the maximum number of supported nodes from 255 to 1000. It also incorporates support for Ethernet and SNA. The DECnet/SNA gateway comprises a Digital mini running a variety of optional software modules. Included is a network management package that allows any DECnet node to operate and maintain the SNA link, momtor and control the DECnet and SNA components and their configuration, do event logging and loopback testing and run applications packages. These packages provide a remote-job-entry capability and interactive 3270 facility.

Last October, Digital announced software products running on the full range of VAX computer systems that provide more extensive links between DECnet and SNA networks. The new products include DDXF, a DISOSS document exchange facility; DHFC, a distributed host command facility; PrE, a printer emulator; Micro VMS operating system versions of the 3270 terminal emulator and gateway management; and a new version of the VAX/VMS operating system 2780/3780 protocol emulator.

Working through Digital's DECnet/SNA gateway, the products provide VAX users with the centralized resources of IBM SNA networks. Additionally, the distributed host command facility enables SNA users to access VAX resources, providing two-way operations over the gateway. Digital claims that DDXF was the first implementation of a direct interface to DISOSS by a computer manufacturer. It enables users on a DECnet network to access both final form document distribution and library services of an IBM System 370 host computer supported by DISOSS/370.

Users of non-Digital computers and terminals will soon be able to communicate with Digital host computers within DECnet environments, thanks to a product developed by Stuart Wecker and his colleagues at Technology Concepts. Before founding the Sudbury, Massachusetts firm, Wecker worked at Digital, where he was one of the architects of DECnet. He believes his new product, called Portable DECnet, is the only implementation of the architecture outside of Digital. Once Portable DECnet has been ported to an operating system, that system is then capable of performing as a DECnet node, with all the phase IV functions such as task-to-task communications, file transfer, file access and virtual terminal support, as well as a rich subset of the network management capabilities.

Portable DECnet has already been ported to two operating systems: VRTX, a small, real-time operating system that runs on 8086 and 68000-based processors, designed and marketed by Hunter and Ready of Palo Alto, California; and PSOS, a 68000-based, real-time operating system designed and marketed by Software Component Group of Santa Clara, California, for multi-tasking applications. Wecker claims the product, which is written in the "C" programming language, can be easily ported to most of the popular micro and minicomputer operating system environments, including Unix and MS-DOS. He reports that he is holding "active negotiations" with a number of large vendors to port the software to their systems. Many of these vendors are "heavily into Unix," he adds. Several special-purpose system vendors are also interested in the product as a means for interfacing with Digital systems.

What makes the product so portable is its Communications Executive, a software interface program that creates an environment for the firm's communications components. The Executive uses the support services of the host operating system, including timer support, buffer management and process control. The back end of the Communications Executive presents a universal interface that mates the Executive to the Portable DECnet; the front end is modified to mate with the host operating system.

Because all host-specific routines are confined to the Executive, the universal interface need not be re-written when the product is ported to different environments. Thus, the DECnet code is identical for all ported versions. Wecker believes this is a tremendous advantage for users because, as bugs are found or new versions are implemented, the same changes can be made for all users regardless of what operating system they use.

Wecker sees enormous potential for Portable DECnet. He estimates there are already some 18,000 DECnet nodes in operation, and he expects this figure to grow substantially with the popularity of MicroVAX and the Professional 380. While there are other ways to communicate with these nodes, Wecker believes DECnet is the best since it uses Digital's own architecture.

"The best way to communicate with a vendor is on his own terms," he says. "For IBM, it's through SNA, for Digital it's through DECnet." In addition, DECnet offers automatic routing as well as sophisticated network management services not always offered with the other communications alternatives.

Ultimately, Wecker envisions Portable DECnet serving as a generic vehicle for interconnecting, say, dispersed Unix workstations. "Our objective in creating the Communications Executive is to provide a 'Technology Concepts Environment,' whereby several major communications architectures will be implemented in addition to DNA across many operating environments, such as Unix and MS-DOS," he explains. Technology Concepts is currently discussing certification of the product with Digital. Wecker reports that the next two follow-on products will be SNA and X.25 gateways, available before year-end.

Mainframers Eye OSI

Other computer vendors, including Honeywell, Sperry, Burroughs and NCR, have developed proprietary network architectures, but with substantially less user acceptance. They all have one eye on the effor tunderway within the International Standards Organization to establish a "universal architecture" for Open Systems Interconnection (OSI). With the rapid progress being made in this standards work, the vendors can be expected to follow a two-pronged strategy: provide an SNA gateway to assure interconnection of their systems with IBM networks; and migrate their network offerings to be compatible with the evolving universal architecture standards.

Honeywell's Distributed Systems Architecture conforms to the seven-layer OSI reference model, and the firm has comitted itself to support new protocols and other standards as they are established. In addition, Honeywell was the first non-IBM vendor to offer an SNA file and transmission facility. Its SNA Release 1.1 allows the transmission of data bases, word processing documents and print files from an IBM host to Honeywell DPS 6 satellites. The enhancements also include simplification of Honeywell's existing SNA Interactive and SNA Remote Job Entry facilities.

Within DSA networks, the Datanet 8 Newtowrk Processor can serve as a front-end, switch or remote concentrator, supporting primary and secondary network connections. In can handle up to 16 lines, and 64 or 128 lines with performance and comfurability enhancements. A maximum of eight processors can be supported on one DPS 8 system, and up to 16 on a DPS 88 system.

Honeywell recently became the first to earn the Department of Defense's highest security rating for a communications processor, when its Secure Communications Processor (Scomp) won an A-1 security rating under the DOD Trusted Computer System Criteria. Scomp, which was developed by Honeywell in cooperation with the US Navy, provides eight levels of security and 32 mutually independent security categories. It is based on a standard Honeywell DPS 6 16-bit minicomputer with the addition of a Security Protection Module and the replacement of the conventional processor with an enhanced version.

Software support is provided by the Scomp Trusted Operating Porgram, a multi-user operating system founded on the Trusted Computing Base (TCB). TCB controls access to data in accordance with its embedded security policy. The Security Protection Module provides a demand paging virtual memory environment, four Multics-like links of protection and a fast-access descriptor store. The module enforces the complete mediation and isolation properties of the Scomp system.

Sperry unveiled its Distributed Communications Architecture in late 1976, heralding it as the firm's most significant communications development in 15 years. DCA's initial implementation, known as Telcon, made use of network software and the Distributed Communications Processor (DCP), which serves as a front-end processor, remote concentrator or network node processor for the firm's host computers. Multiple DCPs may be combined to form a node of high throughput and processing capability. DCA network software is resident in every node, and users can choose to centralize control in a single node or distribute it among several nodes. Networks can be completely reconfigured, with terminals and processors added or replaced, without disrupting the operation of other elements in the system.

NCR Comten's Next Generation

NCR's Communications Network Architecture supports NCR or IBM hosts with SNA, bisync or start/stop terminals. It also permits interconnection with X.21 and X.25 public networks. CNA products include NCR Comten communications processors, a wide range of network software and NCR host communications access methods.

In February, NCR Comten introduced additional networking products to better support users of NCR host computers and SNA networks. NCR/Advanced Communications System (NCR/ACS) extends the communications capabilities of the Comten 3600 processor to NCR VRX hosts. With NCR/ACS, users of the Comten processor can share IBM and/or NCR host applications between terminals, reducing communications line costs and eliminating terminal duplication. When Comten Multiple Access Facility with Remote-Host Option is used in conjunction with NCR/ACS, users can expand their network connectivity to include access to non-NCR and non-IBM hosts. As a result, users can access established application programs on those hosts from their NCR or IBM networks.

Another communication processor-resident network connectivity product, the Comten Network Gateway (CNG), can interconnect up to eight independent SNA networks, allowing SNA users to share information and access data and application programs between multiple SNA networks. SNA users can connect an indefinite number of networks by installing multiple Comten CNGs. With Comten CNG, users can divide one large SNA network into several smaller ones and then interconnect them. The result is a larger number of available network addresses and a simplified network regeneration process.

NCR Comten was the first to locate the communications access method in a front-end processor in SNA networks. The Comten Communications Access Method (CAM) allows users to write their own communications applications programs and run them in the Comten 3600 communications processor independent of the host computer. The St. Paul firm claims this approach provides a level of reliability, availability, responsiveness and security not economically feasible when all communications applications reside in the host computer. Also, CAM allows users to move network operations to the NCR Comten console, effectively isolating the network from the host so that changes in network configuration will have little or no impact on host software or operations. CAM communicates with non-IBM machines in addition to SNA and pre-SNA IBM hosts, and supports most of the popular start/stop, bisync and SNA-type terminals.

Unique Storage Capability

Other recent enhancements to the Comten 3600 include the Integrated Protocol Converter, which gives network users access to the full range of 3270 host application programs from asynchronous terminals and personal computers, and a 29M-byte disk for the Comten 3690 processor, which provides an industry-unique capability to store system load module and memory dumps in a communications processor. In addition, the firm recently unveiled the first of its new generation of cummunications processors, the Comten 5620, which features modular components and VLSI technology for high network reliability, low power consumption and a small footprint. Comprehensive, built-in self-test programs isolate faults to a specific board so that repairs usually involve replacing only one board.

The Comten 5620 does not require computer center conditions and can operate in a standard office environment. It extends full-scale communications processor capabilities, such as application switching, routing, polling, automatic dialing, error recovery and data concentration, to small or remote network sites. Compared with sophisticated statistical multiplexers, the Comten 5620 provides more-extensive application switching and routing functions, polling to save line overhead, a greater degree of programmability for improved error and recovery, and an unrestricted choice of communications facilities, including support for X.25 networks and satellite links. When used as a nodal processor in SNA networks, the Comten 5620 functions as an SNA PU Type 4 via standard SNA trunk protocols. For mixed SNA and non-SNA environments, the unit attaches to the network through NCR Comten's Proprietary Communications Networking System procedures.

The Comten 5620 supports any combination of IBM or NCR hosts and asynchronous, bisync and SDLC line protocols. It can handle up to 32 lines at speeds up to 64 kb/s, with automatic baud-rate detection capability to 19.2 kb/s. Prices begin at $22,000, and the processor will be available starting in the fourth quarter.

DG And HP Push Coexistence

for Data General, Hewlett-Packard and other minicomputer suppliers, the byword in networking is coexistence, whether it is with SNA or X.25 networks, the OSI architecture or local-area networks. Data General was one of the first to support the IEEE 802.3 standard for local-area networks, allowing the firm's products to communicate over industrystandard local-area networks as well as SNA and X.2k networks.

In January, the Westboro, Massachusetts, firm announced its support of two new industry-standard communications protocols, the Transmission Control Protocol/Internet Protocol (TCP/IP) and the Xerox Network System (XNS) internet transport protocol under Data General's AOS/VS proprietary opeerating system. It also made a commitment to support the General Motors Manufacturing Automation Protocol (GM MAP) for factory automation. Data General also announced four new communications products: a multi-communications processor for all 32-bit Eclipse MV/Family superminicomputers; an intelligent local-area network controller for Eclipse MV/Family systems; and IEEE 802.3 segment repeater; and the Net/One broadband LAN manufactured by, and available through, Ungermann-Bass.

In announcing the new developments, Robert Miller, senior vice president at Data General, said that the firm believed it must not only provide complete application solutions and compatibility within its product line, but must also adhere to standards, both formal and de facto, in order to offer its customers complete solutions to their specific business needs. "In conjunction with our X.25, SNA and IEEE 802.3 products," he stated, "these new offerings provide users with the most comprehensive line of communications tools for business and industrial automation."

In offering TCP/IP, Data General believes it is the first vendor to support the industry-standard network protocol for a native Unix (DG/UX) and a proprietary operating system (AOS/VS). The protocol enables the company's 32-bit Eclipse MV superminicomputers and distributed system workstations running AOS/VS or DG/UX to coexist in LANs which support the Berkeley 4.2 version of TCP/IP, a popular technical environment protocol.

The XNS protocol will provide users with three levels of communications capabilities over the Ethernet network: virtual circuit, and acknowledged and unacknowledged datagrams. Data General's support of the GM MAP will ensure its participation in vendor-independent local-area networks connecting computers and other intelligent devices via MAP in factory environments.

Hewlett-Packard also maintain an open-systems strategy, using the sevenlayer OSI reference model as the basis for its AdvanceNet products. AdvanceNet supports local and remote communications at the personal, departmental and corporate levels across and within HP product lines, with links to other vendors' equipment, including Digital Equipment and IBM. It also supports automatic conversion between Wang and HP word processing files, as well as industry standards such as X.25 and the IEEE 802.3.

Last month, the Palo Alto, California, firm introduced the first local-area network product for its HP 3000 family of computers based on the IEEE 802.3 networking standard. It also unveiled new HP 3000 network-services software and augmented the family of HP-to-IBM communications with an interactive SNA-compatible IBM 3270 emulation product for the HP 3000.

The HP LAN/3000 Link product is a full implementation of the IEEE 802.3 standard and contains all the hardware and software needed to connect an HP 3000 computer system to the network. Up to 100 HP 3000 computers may be connected to a single HP LAN/3000 Link. to ensure easy installation, the product includes node-management software, a screen-driven system of utilities that allow users to easily add new network nodes while the rest of the network is operating. The new HP Network Services/3000, available with HP LAN/3000 Link, provides network services required to allow programmatic and interactive access to the power and flexibility of the network. Capabilities include network file transfer, virtual terminal and remote command execution, remote file and peripheral access, network-interprocess communications, remote process management and remote data base access.

HP says it plans to implement an IEEE 802.3 LAN Link and network-services software on the HP 1000 and HP 9000 families of computers to allow factory, commercial and laboratory applications to communicate over a LAN. It already provides a local-area network, manufactured by 3Com, to allow HP and IBM personal computer users to send each other electronic mail. The firm has announced that the Microsoft Networks 1.0 software package will also become part of its personal computer networking strategy. Microsoft Networks allow personal computers to share resources and run applications programs independent of networking hardware. It will run in conjunction with HP's standard networking protocol, allowing communications among all HP computer families, including the HP 3000.

With the new HP SNA Interactive Mainframe Facility network-services software, HP 3000 users may now access applications written for IBM 3270 devices using SNA protocols. The interactive SNA product joins HP SNA Network Remote Job Entry network-services software for batch SNA communications, and HP SNA Link to complete the family of SNA products for the HP 3000.

HP SNA Link provides the physical connection via leased or dial-up line to an IBM host. It can support both batch and interactive communications over the same line. HP has also said it will enhance compatibility with SNA by supporting additional IBM network architectures, such as the Document Content Architecture and the Document Interchange Architecture. HP adds that it plans to offer products based on the IEEE 802.4 token-bus local-area network standard, as defined by General Motors' Manufacturing Automation Protocol, and the National Bureau of Standards' transport level Number 4, to make it even easier for HP systems to communicate with other vendors' hardware and software.

Prime Computer was one of the first to employ token passing in its local-area network, Ringnet, for communications among Prime 50 series systems. Last year, the Natick, Massachusetts, firm introduced a Ringnet repeater which doubles the maximum distance between nodes on a ring to 1500 feet, or 3,280 feet (one kilometer) using fiber-optic cable. Prime also increased the maximum number of nodes in a ring to 128 and added new utilities that provide a dynamic display of network activity for each node and help locate physical breaks in Ringnet.

At the same time, the firm enhanced its Primenet architecture to increase network performance and connectivity and impove network management. The result for Primenet users is access to a larger number of systems and users, along with a more reliable, more available network for distributed processing.

Primenet software offers three distinct sets of services. The Inter-Program Communications Facility (IPCF) lets programs running under the Primos operating system establish virtual circuits to programs in the same or another Prime system, or in other vendors' systems that support the X.25 standard. The Interactive Terminal Support (ITS) facility permits terminals attached to either a packet-switching network or another Prime system to log into a Prime system and function as though physically attached to the remote system. The Remote File Access (RFA) method allows terminal users or programs running under Primos to use files physically stored on other Prime systems in a network.

In addition to supporting X-25 networks, Primenet provides communications with SNA networks through the Prime/SNA product family. The Prime/SNA interactive subsystem allows Prime terminal users to access applications on IBM mainframes using SNA 3270 emulation; while the Prime/SNA RJE subsystem allows files to be transferred between Prime systems and IBM mainframes using 3770 RJE emulation support. Prime also plans to develop a local-area network based on Ethernet technology and international standards. Based on a layered architecture, the new network will follow the IEEE 802.3 standard for lower-level protocols, and will adopt compatible draft specifications for the higher transport layer based on the work of the ISO and NBS. In the meantime, Ringnet will continue to be enhanced and will be able to coexist with the new LAN

Private Packet Networks

Besides supplying X.25-based network services, carriers such as GTE Telenet also offer communications processors for users wanting to implement private packet-switched networks. Peter Thornton, director of marketing for Amnet, believes the market for such networks will grow at a compound annual rate of more than 30 percent over the next five years. His firm recently unveiled its third-generation packet-switching processor, the Nucleus 6000, which is built from a simple set of microprocessor-based components. The processor comes in three models: the N6000/XAS X.25 Access Switch supports up to 300 packets per second throughput; the N6000/XTS X.25 Transport Switch handles up to 500 packets per second; while the N6000/XPS Extended Performance Switch supports up to 1,000 packets per second.

With different models using the same hardware and software components, Nucleus 6000 configurations are readily expandable from the smallest to the largest, according to Thornton. Packet-processing modules increase the packet throughput, while front-end processors can be added to increase the number of lines supported. The Nucleus 6000 uses dedicated processors for packet routing , data-link protocol support and packet I/O queue management. A typical node can include 20 microporcessors. Each micro executes its own program from local random-access memory, but they all manipulate common tables and data packets.

The control sectionf eatures up to 10 packet processors, common memory for packet routing and other tables, and an intelligent node buffe riwth its own microprocessor for queue, DMA and buffer management. The port section employs a proprietary high-speed bus that supports the DMA transfers of data packets to and from the front-end processors. Used for access by subscriber computers, terminals, PADs and personal computers, or to access lower-speed trunks between nodes, the lower-speed front-end processor supports four RS 232/V.24 ports at an aggregate of 19.2 kb/s; the high-speed front-end processor supports up to 64 kb/s.

Options such as load-sharing power supplies, redundant data-base storage, dual control sections and live on-line maintenance of the front-end processors enhance the network availability, and firmware and on-line diagnostic programs support hardware problem detection. Prices range from $30,000 for a small access switch to $200,000 for a dualchassis extended performance switch.

Case Rixon recently added a series of new tools for its powerful DCX Data Concentrating Exchanges. One adds the benefit of X.25 packet operation to the terminal-concentration and statistical-multi-plexing capabilities of the DCX series by providing a DCX asynchronous-to-X.25-PAD facility called Xgate. Any authorized terminal on the DXC system with Xgate can access the X.25 network.

Xgate is a single card occupying one card slot in the master frame of a DCX840 or DCX850, allowing up to 64 DCX network users access to X.25 networks and host services. Xgate is configured through a password-protected, soft manager port with no hardware stops or switches. The configuration is stored in a battery-protected RAM.

IBM bisync systems are now accessible to asynchronous ASCII terminals on the DCX network, thanks to a new option called Bluegate, which emulates an IBM 3271/3274 (model 2) cluster controller making asynchronous ASCII terminals look like IBM 3277/3278 (model 2) terminals.

As an integral protocol converter, Bluegate is installed in a single card slot in a DCX840 and DCX850 frame. Each card supports up to 32 network users, concentrating them onto a single link at speeds up to 9600 b/s. Up to 10 Bluegates can be located in one frame. Authorized terminals on the system can select the gateway and access the bisync environment.

Last year, GTE Telenet unveiled two new series of packet-switching network processors capable of handling up to eight times as much data traffic as previous models.

The TP 4200 uses a new central processing unit with increased RAM and a new release of Telenet Processor Operating System software to attain the higher performance level. It can handle up to 1200 packets per second (p/s), a capacity four times greater than previously achievable. A second switch, known as the TP 4800, will employ two CPU's in a design concept known as "co-processing" that was devised by GTE Telenet development engineers. Co-processing technology enables the TP 4800 to handle traffic loads of up to 2400 p/s.

Both switches can be interconnected using a new IEEE 802.3-compatible local-area network technology.

Going Beyond Stat Muxes

A number of modem and multiplexer suppliers also enhance their product lines with communications processors that go beyond conventional statistical multiplexing. Last year, Digital Communications Associates added a top-of-the-line model to its Series/300 family of communications processors based on the Norcross, Georgia, firm's Integrated Network Architecture. The System 375 is built on the proven technology of the popular System 355 communications processor, and offers the same flexibility, growth and network management capabilities, but at high speed. The 375 suppports up to 114 trunks, each with a capacity of 56 or 72 kb/s, and a bus speed of 4.27 Mb/s. Standard features include port contention and host-selection capability, as well as trunk-link multidrop multiplexing, and subnetting, which allows the network manager to create subnetworks to select and control the access of various terminals, or groups of terminals, to the host facilities.

Codex's 6050 Distributed Communications Processor provides adaptive routing, as well as adaptive data compression to eliminate the need for custom compression tables to handle different protocols. For added efficiency in network operation, user destination routing allows operators to access multiple hosts from a single terminal, and the 6050's contention feature increases cost-effectiveness by reducing the number of host ports required. Modular in design, the 6050 can be easily upgraded as networking requirements change. It is also downwardly compatible with the 6000 Series intelligent network processors.

Paradyne takes a different approach with its Pixnet-XL system, which extends the block or byte multiplexer channel of IBM mainframes to connect remote high-speed devices so they appear to the host as local peripherals. Pixnet-XL provides such networking functions as multiple CPU and application access, full-duplex line transmission and line concentration without traditional teleprocessing hardware, software and support personnel.

Pixnet-XL hardware and software are contained in control units or nodes. The Host Interface Node attaches to the system via the IBM computer channel. The local channel data stream is accepted by the interface, where it is compressed and formatted into HDLC frames suitable for transmission into the network. Data received from Pixnet-XL is presented to the CPU as though originating from a local device with all the communications error recovery and transmission information removed from the data stream.

The Remote Node provides the interface between the Pixnet-XL system and peripherals located at remote sites. It recreates the block multiplexer channel, resulting in remote peripheral performance which approaches that of direct-channel-attached devices. Pixnel-XL is priced at $95,000 to $125,000 per link in a point-to-point environment.

Micom's Micro860 concentrator switch connects up to eight Micro800/2 data concentrators and operates as the logical hub of a network to allow any asynchronous channel on one concentrator to communicate with any channel on that or other concentrator--all under centralized control. In effect, the Micro860 provides a number of add-on networking functions--add-on switching channel contention, queuing and centralized management--to what would otherwise be only a collection of point-to-point links. A command port and log port are provided for network management functions. The four-concentrator switch has a retail price of $2,550, and the eight-concentrator version is priced at $3,250.

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