Chapter 11: WAN. Abdullah Konak School of Information Sciences and Technology Penn State Berks. Wide Area Networks (WAN)

Transcription

1 Chapter 11: WAN Abdullah Konak School of Information Sciences and Technology Penn State Berks Wide Area Networks (WAN) The scope of a WAN covers large geographic areas including national and international or global connections 2 1

2 WAN Alternatives WAN Technologies Point-to-Point Switched WAN T Lines Circuit Switched Packet Switched SONET public switched telephone network (PSTN) Datagram Virtual Circuit X.25 Frame Relay ATM 3 Point-to-Point Solution 4 2

3 Public Switched WAN 5 T-Lines T-carrier is the networking technology initially developed by AT&T in 1957 to provide a means for digital, long-haul transport of voice channels - Digitize the PSTN The Time Division Multiplexing nature of T- carrier made it ideal for data networking. Many corporations use a T leased line to access the Internet (or a fractional T-line services). 6 3

4 T-Lines Technology T-Carrier Systems First level (Intermediate level, US. hierarchy only) Second level Third level Fourth level Fifth level North American Mbit/s (DS1) (24 channels) (T1) Mbit/s (DS1C) Mbit/s (DS2) Mbit/s (DS3) (672 Channels) (T3) Mbit/s (DS4) (4032 Ch.) Mbit/s (5760 Ch.) 7 SONET Synchronous Optical Networking (SONET) is a standard for communicating digital information over optical fiber. A SONET network is made of an end-to-end optical fiber connection. Optical Level Line Rate (Mbps) OC OC-3 OC OC-48 2, OC-192 OC-768 9, ,

5 T-lines and Penn State Backbone Switched WAN Backbone networks in the Internet are usually switched WANs. These networks are usually mesh of point-topoint networks that connect switching stations (routers). Switched WAN Circuit Switched public switched telephone network (PSTN) Datagram X.25 Packet Switched Virtual Circuit ATM Frame Relay 10 5

6 LOAD ONB BAT Y PA T SS FAULT ESC Circuit-Switching Networks Switching node The circuit remains connected, and channel capacity is dedicated for the duration of connection. The blue path is called circuit. 11 Public Switched Telephone Network (PSTN) End Office (Exchange) Local Loop: Subscriber line UTP links Trunk Tandem (Toll) Offices Trunk Regional Offices End Office (Exchange) Trunk High capacity fiber optic or satellite links Carry multiple voice circuits using FDM or synchronous TDM PBX- Private branch exchange 12 6

7 DSL and ADSL Digital Subscriber Line (DSL) refers to a family of technologies that provide a digital connection over the copper wires of the local telephone network. Asymmetric Digital Subscriber Line (ADSL) is more common. 512 to 1,544 Kbps downstream, 128 kbps upstream data rate. The user has to be close to an exchange office. 13 ISDN (Integrated Services Digital Network) A digital service designed to run over existing telephone networks. ISDN combines voice, data, and video over the same connection. Never become popular in the US. Popular in Germany and France. 14 7

8 Packet-Switching Networks Data is broken into packets, each of which can be routed separately (store-and-forward) Advantages: better line efficiency, signals can always be routed, prioritization option Disadvantages: transmission delay in nodes, variable delays can cause jitter, extra overhead for packet addresses Packet Switched Datagram X.25 Virtual Circuit ATM Frame Relay 15 Packet-Switching Used in digital networks. Datagram Approach each packet treated independently and referred to as a datagram packets may take different routes, arrive out of sequence Virtual Circuit Approach preplanned route established for all packets similar to circuit switching, but the circuit is not dedicated 16 8

9 Packet-Switching Networks: Datagram C F 1 A D 2 G 3 3 E B 17 Packet-Switching Networks : Virtual Circuit C F A D G E 1 B 3 2 A preplanned route (virtualcircuit) is established before transmission. All of the packets follow this virtualcircuit. 18 9

10 X.25 A three-layer packet switching technology (virtual-circuit) introduced in the Designed for unreliable media; therefore, it has extensive error checking and flow control in the network and data link layer. Disappearing in the US. 19 Frame Relay Designed to replace X.25 Less overhead than X.25 (does not provide error checking and flow control in the network layer) High data rate Mbps to Mbps Supports bursty data (bandwidth on demand) Slowly being replaced by ATM 20 10

11 ATM (Asynchronous Transfer Mode) A packet switching (virtual circuit) network technology based on transferring data in small cells of a fixed size (53 bytes) instead of varying size packets. Designed for high-data rate transmission media (fiber optic) accurate and predictable delivery (quality-of-service) various applications, audio, data, and video. low cost transmission The small, constant cell size allows ATM equipment to transmit video, audio, and computer data over the same network, and assure that no single type of data hogs the line. Most common data rates for ATM service are 155Mbps and 622Mbps (9.2Gbps is also available) 21 ATM Asynchronous TDM 22 11