Communication Processor (CP)

Communication Processors (Networking)

The widespread perception of communication processors (CPs) is that they are general-purpose devices from a family of equipment types, including feeder multiplexers, packet assembler/disassemblers (PADs), terminal servers, and protocol converters. In the typical IBM mainframe environment, however, system administrators usually take a much narrower view, limiting the definition to FEPs, establishment controllers, and network gateway controllers.

Even though most mainframe central processors include parallel circuits and clocking mechanisms to handle I/O in a quasi-parallel fashion, they still consume a significant percentage of available CPU cycles for specialized, high-overhead, front-end applications. This has motivated system designers to find ways to offload these support processes onto less expensive resources. This motivation gave rise to the introduction of communications processor technology.

These special-purpose computers are designed to manage to complexities of computer communications such as protocol processing, data format conversion, data buffering and routing, error checking and correction, and network control. Depending on the environment, vender, or configuration, communications processors are commonly referred to as front-end processors (FEPs), local/remote concentrators or hubs, communication servers, gateway switches, intelligent routers, and controllers.

The market for communications processors is fully mature and dominated by one product, the IBM 3475 Communication Controller. Lately the term communications processor has been used increasingly to refer to network add-in boards for both PC and VMEbus system. The concept is the same - that these boards offload communications functions from the CPU.

Functions

The traffic management responsibilities of CPs include establishing, maintaining, and controlling any communications sessions between a host computer and dataterminal equipment (DTE), switching devices, other hosts (peer-to-peer), and intranet and Internet activities. Several venders have enhanced their CP offerings by adding features that include utilities for response time monitoring, event logging, terminal status indication, system administration, and diagnostic testing.

The original communication processors were relegated to mainframe systems. However, the advent of client/server computing and network topologies brought with them new, modernized devices for communications connectivity. Instead of a processor dedicated to servicing a single, central host, these newer communications servers offer front end for any number of processors connected via a local or enterprise-wide network.

Communications servers allow any piece of data communication equipment supporting the EIA-232 standard (terminals, modems, printers, hosts, and personal computers) to attach to a network. In some configurations, several operate concurrently in the same network, thereby providing an extensive range of communications services.

Communications processors, on the other hand, are generally classed by their range of features, flexibility, and capabilities. These include the number and types of host interfaces and protocols supported, aggregate bandwidth, and the types of terminal equipment and other devices supported. Creating an optimum configuration generally entails customizing the CP application software according to the functional and operational requirements of the system. This process, called System Generation (SYSGEN), prompts users through a series of questions about the desired configuration and estimates of data traffic. The result of this atrocity is a customized, resident program and associated tables that are automatically loaded and run each time the processor is initialized.

Communications processors support a number of protocols, including OSI, TCP/IP, IBM’s SNA/SDLC and 3270/3780 BSC, Ethernet, Fast Ethernet, token-ring, FDDI, ATM, X.25, frame relay, SONET, and Digital Equipment’s DECnet, and Local Area Transport (LAT) protocols. Anumber of CPs is able to operate in a multi-stack environment, supporting and translating multiple protocols concurrently.

From: http://what-when-how.com/networking/communications-processors-networking/