Public Network. 1. Relatively long physical distance 2. Requiring a service provider (carrier) Branch Office. Home. Private Network.

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1 Introduction to LAN TDC 363 Week 4 Connecting LAN to WAN Book: Chapter 7 1 Outline Wide Area Network (WAN): definition WAN Topologies Choices of WAN technologies Dial-up ISDN T1 Frame Relay DSL Remote network connections Midterm 2 Branch Office What is WAN? Internet and Intranet Public Network Private Network Home Remote Headquarters Branch Office Branch Office 1. Relatively long physical distance 2. Requiring a service provider (carrier) Remote 3

2 WAN Interface Customer router CPE Enterprise Network Carrier Network Internet/ Internet ISP Demarcation point Central Office 4 WAN Topologies Wide area network (WAN) topologies Peer-to-peer Ring Star Mesh Tiered (Hierarchy) 5 Wide Area Network (WAN) Topologies (bus) T1 Note: You cannot use DSL for interoffice communications. 6

3 Ring Topology on WAN Each site is connected to two other sites so that entire WAN forms a ring pattern ISDN 7 Star Topology on WAN Single site acts as the central connection point for several other points 8 Meshed Topology on WAN Many directly interconnected locations forming a complex mesh 9

4 Tiered Topology on WAN Sites connected in star or ring formations are interconnected at different levels, with interconnection points organized into layers 10 WAN Technology Dial-up (PSTN) ISDN (BRI) ISDN (PRI) voice only X25 X.25 out of date Frame Relay Leased Line (T-carrier) Leased Line (OC-x) ATM too expensive xdsl Cable Modem SONET not for enterprise Ethernet Wireless 11 Technology Classification Leased Line Circuit Switching Packet Switching FT1 T1/E1 DS3/T3 OC-3c OC-x PSTN X.25 Frame Relay ISDN ATM Ethernet Q: where is IP? xdsl 12

5 PSTN (Public Switched Telephone Network Designed for voice traffic (not for data traffic) Also called plain old telephone service (POTS) PSTN for WAN connection: Modem (V.92) Downlink: 53 kbps, uplink: 48 kbps ISDN 13 PSTN to Internet Tandem Switch PSTN Local Switch modem Internet Local Switch ISDN-PRI/T1 router server T1 ISP Remote Access Server (modem pool) 14 ISDN BRI (Basic Rate Interface) International standard for transmitting data over digital lines BRI: Basic Rate Interface (2B+D) A variety of ISDN using two 64-kbps bearer (B) channels and one 16-kbps data (D) channel, as indicated by the following notation: Through bonding,, the two 64-kbps channels can be combined to achieve an effective throughput of 128-kbps ISDN PRI (23B+D) over T1 15

6 ISDN Network Connections Service Provider Customer A BRI 2B+D BRI 2B+D Customer B Customer C BRI 2B+D PSTN Central Office PRI 23B+D Cf. Fig.7-10, T-Carriers The most common T-carrier implementations are T1 and T3 Signal level (DS0, DS1, etc.) ANSI standard for T-carrier technology that refers to its Physical layer electrical l signaling characteristics ti DSO (digital signal, level 0) Equivalent of one voice channel (64K) Fractional T1 (FT1, n 64K) Arrangement allowing an organization to use only some channels on a T1 line, paying for what they use 17 Types of T-Carriers T1: 64K 24 = vs. (24 8+1) 8K = 1.544M channels: telephone calls 18

7 T-Carrier Connectivity Wiring Can use unshielded or shielded twisted-pair copper wiring CSU/DSU (Channel Service Unit/Data Service Unit) CSU provides termination for the digital signal and ensures connection integrity through error correction and line monitoring DSU converts the digital signal used by CPE into the digital signal sent via the outside cabling to the carrier. 19 T1: Data-only Service Customer router CSU/DSU Enterprise Network Carrier Network T1 Internet core router (built-in CSU/DSU) channelized DS3 multiplexer 20 DS3 Deployment Typically, fiber (often deployed as STS1/STS3) is used to transport the signals from the central office to the premise wiring closet where the STS1/STS3 fiber line is segmented into single or multiple DS3 coaxial lines for further deployment to individual offices or floors. Central Office fiber Network Device (router) coax 21

8 Need Higher Data Rate T1: 1.544M bps N T1 where N = 1, 2, 4, 6, 8 DS3 = 28 T1 = 45M bps OC-3 3 DS3 = 155M bps OC-12 = 4 OC-3 = 622M bps OC-48 = 4 OC-12 = 2.4G bps OC-192 = 4 OC-48 = 10G bps OC-768 = 4 OC-192 = 40G bps 22 Packet Switching Service X.25 Analog, packet-switched LAN technology optimized for long-distance data transmission Frame Relay Updated (and simplified) digital version of X.25 Variable rates: from 56K bps to 1.544M bps (new standards to 45M bps) 23 Frame Relay Router Frame Relay Overview CSU/DSU DCE or Frame Relay Switch Ethernet Virtual circuit connections One physical circuit Multiple virtual circuits Connection-oriented oriented service Permanent Virtual Circuit (PVC) 24

9 Frame Relay (cont.) Address: Data Link Connection Identifier (DLCI), 10-bit, local significance. CIR (committed information rate) Guaranteed minimum amount of bandwidth selected when leasing a frame relay circuit b t Can burst higher than CIR Users get more than they pay for. burst (512k) CIR (768k) 25 Why Frame Relay? (compared with T1) X.25 too much overhead, ATM too expensive A popular service for WAN The paragraph in the book is incorrect. (p. 355) Switched technology: not sensitive s to distance in pricing Cheaper than T1 for long distance Physical Connection: point to multi-points Significant cost saving for a mesh topology Logical Connection: point to point As secured as T1 Security: as good as PSTN (which is very secure) 26 Digital Subscriber Lines (DSL) Uses advanced data modulation techniques to achieve extraordinary throughput over regular phone lines (2-wire or 4-wire) DSL can span only limited distances. DSL types can be divided into two categories: Asymmetrical (download upload) Symmetrical (download = upload) 27

10 Types of DSL ADSL: Asymmetric DSL HDSL: High Bit Rate DSL (4-wire) SDSL: Symmetric (or Single line [one pair]) DSL VDSL: Very High Bit Rate DSL (not for WAN) New: ADSL2 and ADSL2+ New standards: HDSL2 (2-wire) g.shdsl, symmetric 28 DSL Connectivity Once inside the customer s home or office, the DSL line must pass through a DSL modem One RJ-11 port to PSTN One RJ-45 port to home/office LAN 29 ADSL Connectivity Note: ADSL requires a splitter at customer premise DSLAM: DSL Access Multiplexer 30

11 router DSL Connectivity (G.lite) DSL modem local loop splitter voice switch core router + (ATM Switch) filter DSLAM Note: G.lite does not need a splitter at customer premise Internet 31 Cable Modem Cable connections require that the customer use a special cable modem,, a device that transmits and receives digital signals for transmission and reception via cable wiring 32 Cable Modem Network Infrastructure fiber HFC: Hybrid Fiber Coax 33

12 Notes on Cable Modem Shared Medium Performance degradation if everyone is surfing. Security Concern Infrastructure Not available to the business community Comparison and Competing with xdsl There is no right answer. Note: Any packet switching technology allow multiple users to share the media. The goal is to improve the utilization of the media. Wherever there is resource sharing, there is potential bottleneck. The question is where the media is being shared. 34 SONET in Metro Network Core Router Carrier Central Office Metro SONET Ring Access Ring Access Ring T1 Access Ring c.f. Fig CPE 35 Add-Drop Multiplexer () SONET Ring Pass through drop add c.f. Fig

13 Notes on SONET SONET is a popular technology (and widely deployed) for a carrier to build its metro backbone. It may also used by an enterprise in a campus network. Government also builds its own SONET backbone. SONET is not the technology to access the Internet. An enterprise may connect its SONET to a carrier SONET via a leased trunk (OC-3 or higher). 37 SONET for Enterprise and Residential Users SONET Ring (owned by carrier) The is owned and maintained by a carrier, but it could be physically located at a company premise, or it could be at a multi-tenant environment (MTE). Example of MTE: office building, apartment complex. 38 Remote Connectivity Need: access private resources on the corporate network Remote access methods: Direct dial to the LAN The computer dialing into the LAN becomes a remote node on the network (see the slide on RAS/modem pool) Terminal Services (p. 386) Software running on both remote user s computer and LAN computer allows remote user to take over the LAN workstation. Web Portals (p. 387) Through a browser, a user at home or on the road connects to a LAN whose files are made visible to the Web through Web server software Virtual Private Network (VPN) a private data network over the public Internet 39

14 Virtual Private Networks (VPNs) VPN is a private network over a public network (internet). A VPN may or may not be IP- based. 40 Remote Access Remote Access Server Security Server PSTN Internet VPN Gateway Intranet Terminal server 41 Review Questions What are the characteristics distinguishing WAN from LAN? Speed of T-carrier and OC-x Comparison of T1 and Frame Relay. Give a scenario that you will use T1 and another scenario to use Frame Relay. Draw a network diagram to show the T1 connection to the Internet. (CSU/DSU + router + ) What is CSU/DSU? What is the addressing scheme of frame relay? Is there an addressing scheme for T1? Comparison of different DSL and their speeds. 42

15 Review Questions Describe the differences between ADSL and ADSL.lite (or G.lite). What is the network device to distribute traffic to/from SONET? Given a network diagram of three locations connected via Frame Relay, design the IP subnet scheme. What are the choices of remote access? What is VPN? 43 Midterm Exam 02/05 (Tuesday), 01:30pm Exam time: 90 minutes Exam seating will be given by the instructor. Exams are closed book, closed notes. Cl Calculator l is allowed db but no palm computer. You are allowed to bring a 2-page note (double sides) No make-up exam Study Guide: Review questions Homework 44