Connecting to Remote Networks © 2004 Cisco Systems, Inc. All rights reserved. Using Packet Switching in WANs INTRO v2.0—7-1

© 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—7-2 Outline Overview Packet-Switched Communication Links X.25 Frame Relay Asynchronous Transfer Mode and Cell Switching DSL Cable Global Internet―the Largest WAN Summary

© 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—7-3 Packet Switching

© 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—7-4 WAN with X.25

© 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—7-5 Frame Relay

© 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—7-6 Frame Relay Devices and Virtual Circuits

© 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—7-7 ATM and Cell Switching

© 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—7-8 DSL

© 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—7-9 DSL Service Types Overview

© 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—7-10 DSL Considerations Advantages Speed Simultaneous voice and data transmission Incremental additions Always-on availability Backward compatibility with analog phones Disadvantages Limited availability Local phone company requirements Security risks

© 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—7-11 Cable-Based WANs

© 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—7-12 How Cable Modems Work

© 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—7-13 The Global Internet

© 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—7-14 Summary Packet-switched networks send data packets over different routes of a shared public network owned by a carrier to reach the same destination. The route that the packets take to reach the destination site, however, will vary. When the packets reach their destination, they are reassembled in order. X.25 is a network layer protocol and a data link layer protocol, and subscribers are provided with a network address. Virtual circuits can be established through the network with call request packets to the target address. The resulting SVC is identified by a channel number. Data packets labeled with the channel number are delivered to the corresponding address. Although the Frame Relay network layout appears similar to that for X.25, available data rates are commonly up to 4 Mbps, with some providers offering even higher rates. In addition, Frame Relay is a much simpler protocol that works at the data link layer rather than at the network layer.

© 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—7-15 Summary (Cont.) ATM is a type of cell-switched connection technology that is capable of transferring voice, video, and data through private and public networks. ATM is used primarily in service-provider networks and enterprise LAN backbones. ATM virtual circuits can be either PVC or SVC. DSL technology allows a service provider to offer high-speed (up to and exceeding the speed of a T1 connection) network services to customers, utilizing installed local-loop copper lines. DSL technology allows the local-loop line to be used for normal telephone voice connection and an always-on connection for instant network connectivity. There are several varieties of DSL, including ADSL, SDSL, HDSL, IDSL, and CDSL. There are both advantages (speed, always on, and so on) and disadvantages (availability) to DSL.

© 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—7-16 Summary (Cont.) WANs can also be connected by cable communications, requiring cable modems as the Layer 1 device. The global Internet grew from a U.S. Department of Defense plan to build a command-and-control network in the 1960s to its present state as the largest WAN on earth, with multiple ways to access it and multiple communication, research, and commercial uses.