© 2005 Cisco Systems, Inc. All rights reserved.INTRO v2.17-1 Connecting to Remote Networks Using Packet Switching in WANs. - презентация

1 © 2005 Cisco Systems, Inc. All rights reserved.INTRO v Connecting to Remote Networks Using Packet Switching in WANs

2 © 2005 Cisco Systems, Inc. All rights reserved.INTRO v Outline Overview Packet-Switched Communication Links X.25 Frame Relay Asynchronous Transfer Mode and Cell Switching Digital Subscriber Line DSL Types and Standards DSL Considerations Cable Global Internet: The Largest WAN Summary

3 © 2005 Cisco Systems, Inc. All rights reserved.INTRO v Packet Switching

4 © 2005 Cisco Systems, Inc. All rights reserved.INTRO v WAN with X.25

5 © 2005 Cisco Systems, Inc. All rights reserved.INTRO v Frame Relay

6 © 2005 Cisco Systems, Inc. All rights reserved.INTRO v Frame Relay Devices and Virtual Circuits

7 © 2005 Cisco Systems, Inc. All rights reserved.INTRO v ATM and Cell Switching

8 © 2005 Cisco Systems, Inc. All rights reserved.INTRO v DSL

9 © 2005 Cisco Systems, Inc. All rights reserved.INTRO v DSL Service Types Overview

10 © 2005 Cisco Systems, Inc. All rights reserved.INTRO v 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

11 © 2005 Cisco Systems, Inc. All rights reserved.INTRO v Cable-Based WANs

12 © 2005 Cisco Systems, Inc. All rights reserved.INTRO v How Cable Modems Work

13 © 2005 Cisco Systems, Inc. All rights reserved.INTRO v The Global Internet

14 © 2005 Cisco Systems, Inc. All rights reserved.INTRO v 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.

15 © 2005 Cisco Systems, Inc. All rights reserved.INTRO v 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, using 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.

16 © 2005 Cisco Systems, Inc. All rights reserved.INTRO v 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.

17 © 2005 Cisco Systems, Inc. All rights reserved.INTRO v