Data Communications Networking Devices - 4th Ed.pdf

6.9 PORT-SHARING UNITS _________________________________________________________ 711Figure 6.58 Multiple applications can share the line.Through the use of a modem-sharingunit with a data communications equipment interface, a terminal distant from the clusterlocation 2) can share the same line segment computer to location 1) that is used totransmit data to those terminals at location 1.With a second application that requires aremote batch terminal at location 1, additional line economies can be derived by installingmultiport modems so both the polled terminals and the RBT can continue to share the use ofone leased line from the computer to location 1port selection, therefore, a large number of lines contend for a small number ofports. Users let go of a port by signing off in a way similar to that found in timesharingand RJE applications. You should refer to these sections for additionalinformation.6.9 PORT-SHARING UNITSAn alternative to the utilization of modem- and line-sharing units in a communicationsnetworkcan be obtained through the employment of devices known asport-sharing units. In addition, the proper employment of such devices can be usedto complement or supplement modem- and line-sharing units and in certainsituations may result in large economies being realized.When to considerPort-sharing units are devices that are installed between a host computer andmodem and that control access to and from the host for up to six terminals with thenumber of terminals limited by the capabilities of current hardware. In this way,port-sharing units are able to cut down on the number of computer ports needed for