Data Communications Networking Devices - 4th Ed.pdf

6.5 PACKET ASSEMBLER/DISASSEMBLER __________________________________________ 687ApplicationsThe primary use of PADs is to enable non-X.25 networking devices to be connectedto a packet switching network. There are many kinds of PADs, with their featuresand operation governing where they can be used to attach devices to an X.25network. Some PADs support only asynchronous terminals, while other PADssupport bisynchronous devices, SNA/SDLC devices or a mixture of terminalsusing different protocols.PADs are used in both public and private X.25 networks. A public X.25 networkis owned and operated by a communications carrier, which may sell or lease PADsto companies using the network. In addition, companies may purchase PADs foruse on a public networkonce the device is certi®ed by the communications carrierfor use on their network. A private X.25 network can be constructed by anorganization purchasing or leasing PADs and other networkequipment and circuitsFigure 6.43 Using PADs in an X.25 network. By installing a PAD at a location where twoor more terminals requiring access to an X.25 network are located the cost ofcommunications to that network can be reduced.At a computer site, a PAD can be usedto convert the X.25 packet network protocol to the protocol supported by a host computer