ww.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. X.25, Internets, Intranets, and Extranets X.25, Internets, Intranets, and Extranets Figure 7-10 Added protocols for X.25. 2600 Maders 00000000 The PAD-to-host arrangement is controlled by the X.29 protocol. Control information is exchanged between a PAD (X.3) and a packet mode DTE or another PAD (X.3). This is shown in Figure 7-10. In this case, as the communication is established between these devices, the X.3 PAD sets the parameters of the remote device. This could be the speed, format, control parameters, or anything that would be appropriate in the file transfer. The X.29 parameters can also provide keyboard conversion into network-usable information. The internetworking capability of an X.25 network uses a protocol called X.75. Although this should be user transparent, the network needs the X.75 parameters to provide a gateway between two different packet networks or between networks in different countries. In each case, the gateway function is something that should only concern the network carrier. However, as more organizations install their own pri- vate network-switching systems, the need to interconnect to the public data networks rises. Therefore, the internetworking capability is mov- ing closer to the end user's door. Figure 7-11 shows a representation an X.75 interconnection. Other Forms of Packet Another form of packet switching, called a datagram, is used in the indus- try. A datagram transfer is a form of packet switching. Typically, the Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. X.25, Internets, Intranets, and Extranets Chapter 7 Figure 7-11 internetworking. Non Packet Mode X.75 Interface X.25 PSN Non Packet Mode Packet Mode Computer Non Packet Mode X.25 PSN 