Data Communications Networking Devices - 4th Ed.pdf

6.7 FRONT-END PROCESSORS _____________________________________________________ 705IBM 3746A relatively new addition to IBM's communications product line is its 3746.Although the 3746 of¯oads communications functions from System/390 host computers,it is marketed as a `multiprotocol controller' instead of a communicationscontroller. The key reason for this name change is the fact that the 3746 operatesas an Internet Protocol IP) router as well as supports APPN, enabling separateSNA and IP networks to be consolidated over a single multiprotocol transportnetwork.A key advantage associated with the use of a 3746 is its ability to supportcommunications without requiring the use of a NetworkControl Program NCP)on the host and a communications controller. Another advantage associated withthe use of the 3746 is its multiprotocol support capability which allows it to supportAPPN and IP over Token-Ring and Ethernet LANs, Frame Relay, SDLC, andpoint-to-point protocol PPP) links, the latter a dial-up version of IP.Hardware overviewA basic 3746 supports up to 16 adapters. Those adapters can consist of a mixture ofcommunications line adapters, ESCON channel adapters, and Token-Ringadapters. The communications adapter consists of a communications line processorCLP) which supports up to four line interface couplers. Each communications lineadapter can support up to 120 lines operating in half- or full-duplex, each runningSDLC, PPP, or Frame Relay at data rates from 600 bps to 2.048 Mbps. Via the useof a communications line adapter up to 500 active physical units can be supported,resulting from lines connected to control units which in turn support legacyterminals and PCs connected to the control unit.The ESCON adapter permits a 3746 to be connected via optical ®ber to thechannel on a S/390. Up to two ESCON adapters can be used to enhancetransmission to an attached S/390 while providing a duplicated path between the3746 and a S/390.The third type of adapter supported by the 3746 is a Token-Ring adapter. TheToken-Ring adapter used by the 3746 consists of a Token-Ring processor and oneor two Token-Ring couplers, permitting up to two rings to be directly connected tothe controller. Although the 3746 can operate as a stand-alone communicationsnetworking device, it can also operate in conjunction with the NCP on a 3745communications controller to expand the support of active devices. For example, asingle Token-Ring adapter with either one or two TICs can support up to 500active PUs. However, when a 3746 is connected to a 3745, PU support expands to2000, with the additional 1500 being controlled by the NCT in the 3745. Figure6.54 provides an example of the use of two 3746 multi-protocol controllers tointerconnect geographically separated corporate locations via a mixture of networkprotocols. In examining Figure 6.54, note that since a 3746 has an IP routingcapability, it provides the ability to connect a corporate networkto the Internet. Inaddition, since it supports Frame Relay, it permits you to consider the use of thatfast packet network as a substitute or supplement to leased lines. Thus, it provides a