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Wide Area Networks (WANs) Chapter 7 (Modified April 2003) Copyright 2003 Prentice-Hall Pankos Business Data Networks and Telecommunications, 4 th edition

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2 Figure 7.1: Wide Area Networks (WANs) Chapters 4 and 5: LANs Customer premises operation, high speeds Chapter 6: Telephony LAN building wiring PSTN carrier service Chapter 7: WANs WAN technology often is based on telephone technology and services

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3 Figure 7.1: Wide Area Networks (WANs) WAN Purposes Link sites (usually) within the same corporation Provide remote access to individuals who are off- site Internet access 1. Link Sites 2. Remote Access 3. Internet Access

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4 Figure 7.1: Wide Area Networks (WANs) WAN Technologies Ordinary telephone line and telephone modem. Point-to-Point Leased lines Public switched data network (PSDN) Send your data over the Internet securely, using Virtual Private Network (VPN) technology PSDN VPN

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5 Figure 7.1: Wide Area Networks (WANs) High Speeds and Low Speeds High cost per bit transmitted compared to LANs Lower speeds (mostly commonly 56 kbps to a few megabits per second) LANs Cheap, WANs Expensive (per bit transmitted) LANs Fast, WANs Slow

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6 Figure 7.1: Wide Area Networks (WANs) WAN Technologies Ordinary telephone line and telephone modem. (low-speed access only) Point-to-Point Network of leased lines Public switched data network (PSDN) Send your data over the Internet securely, using Virtual Private Network (VPN) technology

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7 Figure 7.2: Telephone Modem Communication PSTN Client A Server A Telephone 33.6 kbps Modem Binary Data Analog Modulated Signal Modem Need Modem at Each End Up to 33.6 kbps

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8 Figure 7.2: Telephone Modem Communication PSTN Client B Server B Telephone Digital Access Line 56 kbps Modem For 56 kbps Download Speed Server Must Have a Digital Connection, Not a Modem

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9 Figure 7.3: Telephone Modem Modulation Standards and Speeds V.34 Send and receive at up to 33.6 kbps Fall back in speed if line conditions are not optimal V.90 Receive at up to 56 kbps Send at up to 33.6 kbps Asymmetric speed is good for WWW service. Other party must have a digital connection to the PSTN

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10 Figure 7.3: Telephone Modem Modulation Standards and Speeds V.92 Receive at up to 56 kbps Send at up to 33.6 kbps or higher if the line permits Other party must have a digital connection to the PSTN Modem on hold: can receive an incoming call for a short time without losing the connection Cuts call setup time in half

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11 Figure 7.3: Telephone Modem Modulation Standards and Speeds Compression V.92 modems usually use V.44 compression, which downloads webpages twice as fast as the old standard for compression, V.42 bis Data: 112.5 kbps Signal: 33.6 kbps

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12 Figure 7.1: Wide Area Networks (WANs) WAN Technologies Ordinary telephone line and modem. (low-speed access only) Point-to-Point Network of leased lines Public switched data network (PSDN) Send your data over the Internet securely, using Virtual Private Network (VPN) technology

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13 Figure 7.5: Trunk Line-Based Leased Line Computer Telephone Switch Telephone Switch Telephone Switch Server Access Line T1 Trunk Line (1.544 Mbps) T1 Leased Line (1.544 Mbps) End-to-End Circuit with Trunk Line Speed Trunk Line Extend trunk line speeds to end-to-end service

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14 Figure 7.4: Leased Line Networks Leased Line (Private Line or Dedicated Line) Point-to-point connection Always on Usually very fast (56 kbps or more) Usually digital instead of analog Lower cost per bit transmitted than dial-up service But speeds are higher, so higher total cost Must be provisioned (set up). Can take weeks or months

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15 Figure 7.4: Leased Line Networks Trunk Line-Based Leased Lines Require expensive optical fiber or (for 56 kbps, 64 kbps, T1 and E1 lines,) expensive data-grade copper UTP For data-grade UTP, need two pairsone for transmission in each direction. Called four-wire circuits. Data-Grade Copper UTP

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16 Figure 7.4: Leased Line Networks Trunk Line-Based Leased Lines 56 kbps Leased Lines Fractional T1 lines offer low-speed choices between 56 kbps and T1, typically: 128 bps, 256 kbps, 384 kbps, 512 kbps, 768 kbps T1 Leased Lines (1.544 Mbps) T3 Leased Lines SONET OC/SDM Leased Lines Highest Demand

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17 Figure 7.4: Leased Line Networks Digital Subscriber Lines (DSLs) Broadband speeds over single pair of voice-grade copper UTP for transmission in both directions Does not always work: distance limitations, etc. Where it does work, much cheaper than trunk line- based leased lines Existing Voice-Grade UTP Single Pair

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18 Figure 7.6: ASDL with Splitter Data WAN PSTN DSLAM ADSL Modem Splitter Telephone Subscriber Premises Telephone Company End Office Switch 1. Existing Single Pair of Voice-Grade UTP Wires PC 2. 3.

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19 Figure 7.6: ASDL with Splitter Data WAN PSTN DSLAM ADSL Modem Splitter Telephone Subscriber Premises Telephone Company End Office Switch PC 1. Data 256 kbps to 1.5 Mbps 2. 64 kbps to 256 kbps

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20 Figure 7.6: ASDL with Splitter Data WAN PSTN DSLAM ADSL Modem Splitter Telephone Subscriber Premises Telephone Company End Office Switch PC 1. Ordinary Telephone Service

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21 Figure 7.4: Leased Line Networks Asymmetric DSL (ADSL) Asymmetric speed Downstream (to customer): 256 kbps to over 1.5 Mbps Upstream (from customer): 64 kbps or higher Simultaneous telephone and data service DSL access multiplexer (DSLAM) at end telephone office Designed as consumer service, so speed is not guaranteed

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22 Figure 7.4: Leased Line Networks HDSL High-rate DSL Symmetric speed (768 kbps both ways) over one voice-grade twisted pair Needed in business. (ADSL primarily for home and small business access.) Speed guaranteed HDSL2 1.544 symmetric speed over one voice-grade twisted pair

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23 Figure 7.4: Leased Line Networks SHDSL Super High-rate DSL Single voice-grade twisted pair; longer distances than ASDL, HSDL Symmetric speed Variable speed ranging from 384 kbps to 2 Mbps Speed guaranteed

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24 Figure 7.7: Cable Modem Services PC Subscriber Premises 5. Cable Modem 4. Coaxial Cable to Premises 2. Optical Fiber to Neighborhood 3. Neighborhood Splitter ISP 1. Cable Television Head End 6. Requires NIC or USB port

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25 Figure 7.4: Leased Line Networks Cable Modem Delivered by cable television operator High asymmetric speed Up to 10 Mbps downstream 64 kbps to 256 kbps upstream Speed is shared by people currently downloading in a neighborhood In practice, medium ADSL speed or higher

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26 Figure 7.8: GEO Satellite System 2. Point-to-Point Uplink 3. Broadcast Downlink 4. Footprint 5. Earth Station A Earth Station B 1. Geosynchronous Satellite Satellite appears stationary in sky (35,785 km or 22,236 mi) Far, so earth station needs dish antenna

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27 Figure 7.9: LEO and MEO Satellite Systems 3. Small Omnidirectional Transceiver 1. Currently Responsible LEO or MEO 2. Next Responsible LEO or MEO A few thousands of km or miles (Low Earth Orbit) or tens of thousands of km (miles) (Medium Earth Orbit) Closer than GEO, so omnidirectional transceivers can be used User is served by a succession of satellites

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28 Figure 7.1: Wide Area Networks (WANs) WAN Technologies Ordinary telephone line and modem. (low-speed access only) Point-to-Point network of leased lines Public switched data networks (PSDN) Send your data over the Internet securely, using Virtual Private Network (VPN) technology PSDN

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29 Figure 7.10: Leased Line versus Public Switched Data Networks T3 Lease Line Site C Site A Site B OC3 Leased Line T1 Leased Line T1 Leased Line Site E Site D 56 kbps Leased Line 56 kbps Leased Line 56 kbps Leased Line Multisite Leased Line Mesh Network

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30 Figure 7.10: Leased Line versus Public Switched Data Networks Public Switched Data Network (PSDN) POP Site A Site B Point of Presence One leased line per site Site D Site C Site E Public Switched Data Network (PSDN)

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31 Figure 7.10: Leased Line versus Public Switched Data Networks Leased Line Network Many leased lines Individual leased line spans long distances Company must plan, buy switching equipment, and operate the network Public Switched Data Network Only need one leased line from each site to a POP Few and short-distance leased lines PSDN carrier provides planning, switching, and operation of the network

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32 Figure 7.11: Popular PSDN Services Service Typical Speeds Circuit- or Packet- Switched Reliable or Unreliable Virtual Circuits? Relative Price X.25 9,600 kbps to about 40 Mbps PacketReliableYesModerate Frame Relay 56 kbps to about 40 Mbps PacketUnreliableYesLow X.25 (Obsolete): Slow because of reliability Frame Relay Dominates PSDNs Today Unreliable for Lower Carrier Cost Speed Range is in Main Range of Corporate Demand

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33 Figure 7.11: Popular PSDN Services Ethernet 10 Gbps and 40 Gbps PacketUnreliableNo Probably Low ATM 1 Mbps to about 156 Mbps PacketUnreliableYesHigh Service Typical Speeds Circuit- or Packet- Switched Reliable or Unreliable Virtual Circuits? Relative Price ATM is Faster than Frame Relay Should Grow in Demand as Corporate Demand Outgrows FR However, Ethernet MANs are Appearing Should Offer Lower Prices for Comparable Speeds

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34 Frame Relay and ATM FR and ATM are Not Competitors Most PSDN carriers offer both so they can server any speed range Many interconnect their FR and ATM services, so that individual sites can use whatever service is best for them

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35 Figure 7.11: Popular PSDN Services Most PSDNs are packet-switched, unreliable, and use virtual circuits All of these are designed to reduce carrier transmission costs so that lower competitive prices can be set Packet switching multiplexes trunk line transmissions, reducing trunk line costs Unreliability and virtual circuits simply switching, reducing switching costs

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36 Figure 7.11: Popular PSDN Services Service Typical Speeds Circuit- or Packet- Switched Reliable or Unreliable Virtual Circuits? Relative Price ISDN Two 64 kbps B channels One 16 kbps D channel CircuitUnreliableNoModerate ISDN is Not Popular Expensive for its Slow Speed Has Niche in Backup Connections Because Dial-Up, So Only Pay for When Needed

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37 Figure 7.12: Integrated Services Digital Network (ISDN) Personal Computer Desktop Telephone 3. 64 kbps B Channel Analog Voice Signal On Telephone Wires 2. 64 kbps B Channel Digital Signal On Serial Cable (1010) 1. 3 Multiplexed Channels on One Pair of Telephone Wires (2B+D) ISDN Wall Jack (RJ-45) 4. 16 kbps D channel is for Supervisory signaling 2B+D

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38 Quiz In ISDN, how many bits per second are multiplexed over the single wire pair connected to the wall jack and to the single pair running from the customer premises to the carrier end office?

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39 Figure 7.12: Integrated Services Digital Network (ISDN) Personal Computer Desktop Telephone ISDN Modem 64 kbps B Channel Digital Signal On Serial Cable (1010) Internal DSU Converts Serial Port Signal to Digital B Channel Signal at 64 kbps (1010) All-digital Service (1101001..) ISDN Wall Jack (RJ-45) Bonding Use Both B Channels for Data Send and Receive at 128 kbps

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40 Figure 7.14: Pricing Elements in Frame Relay Service Frame Relay Pricing Frame relay access device at site CSU/DSU at physical layer (converts between internal, PSDN digital formats) Frame Relay at the Data Link Layer Leased line from site to POP Port on the POP Pay by port speed Usually the largest price component Permanent virtual circuits (PVCs) among communicating sites Other charges

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41 Figure 7.13: Access Devices CSU/DSU Channel service unit (CSU) protects the access line from unapproved voltage levels, etc. coming from the firm Data service unit (DSU) converts between internal digital format and digital format of access link to Frame Relay network. May have different baud rate, number of states, voltage levels, etc. DSU

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42 Figure 7.13: Access Devices Site A Site B PC Server T1 CSU/DSU at Physical Layer Frame Relay at Data Link Layer T3 CSU/DSU at Physical Layer ATM etc. at Data Link Layer T1 Line T3 Line Access Device (Frame Relay Access Device) Access Device (Router)

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43 Figure 7.14: Pricing Elements in Frame Relay Service Switch POP Customer Premises B Customer Premises C 1. Access Device Customer Premises A

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44 Figure 7.14: Pricing Elements in Frame Relay Service Switch POP Customer Premises B Customer Premises C Customer Premises A 2. T1 Leased Access Line to POP

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45 Figure 7.14: Pricing Elements in Frame Relay Service Switch POP Customer Premises B Customer Premises C Customer Premises A CIR = 56 kbps ABR = 1 Mbps 3. Port Speed Charge

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46 Figure 7.14: Pricing Elements in Frame Relay Service Switch PVC 2 PVCs 1&2 POP PVC 2PVC 1 Customer Premises B Customer Premises C Customer Premises A PVC 1 4. PVC Charges

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47 Figure 7.15: Frame Relay Pricing Details Other Charges Flat rate versus traffic volume charges Installation charges Managed service charges Service level agreement (SLA) charges Geographical Scope Frame Relay systems with broader geographical scope cost more

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48 Figure 7.15: Frame Relay Pricing Details To Determine Needs for Each Site Step 1: Determine PVC Needs Determine needed speed from this site to each other site You will need a virtual circuit to serve the needed speed to each other site Sum all the virtual circuit speeds New Not in Book Site Being Analyzed 30 kbps needed 56 kbps PVC 800 kbps needed, 1 Mbps PVC Sum 1,056 kbps

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49 Figure 7.15: Frame Relay Pricing Details Step 2: Determine Port Speed You need a port speed equal to or greater than the sum of the PVCs You can get by with 70% 70% of 1,056 kbps is 739 kbps Next-higher port speed may be 1 Mbps Dont overdo port speed because port speed is most expensive component New Not in Book

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50 Figure 7.15: Frame Relay Pricing Details Step 3: Determine Leased Line Speed Remember that port speed is more expensive than leased line speeds In general, dont waste port speed by using a leased line much under its capacity If port speed is 1 Mbps, leased line should be T1 with 1.544 Mbps capacity New Not in Book

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51 Figure 7.15: Frame Relay Pricing Details Example The Situation Headquarters and two branch offices. Branches communicate with HQ at 200 kbps Branches communicate with each other at 40 kbps HQ B1 B2 New Not in Book

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52 Figure 7.15: Frame Relay Pricing Details Example For HQ How many connections will HQ need? What are their speeds? What will be their PVC speeds (0 kbps, 56 kbps, 256 kbps, 512 kbps, 1 Mbps) If port speeds are 56 kbps, 256 kbps, 384 kbps, 512 kbps, what port speed will be needed? What leased line will be needed if speeds are 56 kbps, 256 kbps, 512 kbps, or T1? HQ New Not in Book

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53 Figure 7.15: Frame Relay Pricing Details Example For Each Branch How many links will the branch need? What are their speeds? What will be their PVC speeds (0 kbps, 56 kbps, 256 kbps, 512 kbps, 1 Mbps) If port speeds are 56 kbps, 256 kbps, 384 kbps, 512 kbps, what port speed will be needed? What leased line will be needed if speeds are 56 kbps, 256 kbps, 512 kbps, or T1? B1 New Not in Book

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54 Figure 7.1: Wide Area Networks (WANs) WAN Technologies Ordinary telephone line and modem. (low-speed access only) Point-to-Point Network of leased lines Public switched data networks (PSDN) Send your data over the Internet securely, using Virtual Private Network (VPN) technology VPN

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55 Figure 7.17: Virtual Private Network VPN Server Corporate Site A VPN Server Corporate Site B 2. Remote Customer PC (or site) 3. Remote Corporate PC Tunnel Internet Extranet Remote Access for Intranet 1. Site-to-Site

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56 Figure 7.16: Virtual Private Network (VPN) Issues Virtual Private Network (VPN) Transmission over the Internet with added security Some analysts include transmission over a PSDN with added security Why VPNs? PSDNs are not interconnected Only good for internal corporate communication But Internet reaches almost all sites in all firms Low transmission cost per bit transmitted

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57 Figure 7.16: Virtual Private Network (VPN) Issues VPN Problems Latency and Sound Quality Internet can be congested Creates latency, reduces sound quality Use a single ISP as for VoIP (see Chapter 6) Security PPTP for remote access is popular IPsec for site-to-site transmission is popular

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58 Figure 7.18: ISP-Based PPTP Remote Access VPN RADIUS Server PPTP RAS Internet ISP PPTP Access Concentrator Local Access Remote Corporate PC Corporate Site A Remote Access VPNs: ISP Mode User dials into a remote access server (RAS) RAS often checks with RADIUS server for user identification information. Allows or rejects connection Secure Tunnel Unsecure TCP Control Channel

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59 Figure 7.18: ISP-Based PPTP Remote Access VPN RADIUS Server PPTP RAS Internet Remote Corporate PC Corporate Site A Remote Access VPNs: Direct Mode End-to-End VPN protection to client PC Setup required on remote corporate PC Secure Tunnel Unsecure TCP Control Channel New

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60 Figure 7.16: Virtual Private Network (VPN) Issues Point-to-Point Tunneling Protocol Available in Windows since Windows 95 No need for added software on clients Provided by many ISPs PPTP access concentrator at ISP access point Some security limitations No security between user site and ISP No message-by-message authentication of user Uses unprotected TCP control channel New

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61 Figure 7.19: IPsec in Tunnel Mode Tunnel Only Between Sites Hosts Need No Extra Software Secure Tunnel Mode IPsec Server IPsec Server Local Network Local Network No Security In Site Network No Security In Site Network

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62 Figure 7.19: IPsec in Transfer Mode End-to-End (Host-to-Host) Tunnel Hosts Need IPsec Software Secure Tunnel Transfer Mode IPsec Server IPsec Server Local Network Local Network Security In Site Network Security In Site Network Module F

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63 Figure 7.16: Virtual Private Network (VPN) Issues IP Security (IPsec) Tunnel mode: sets up a secure tunnel between IPsec servers at two sites No security within sites No need to install IPsec software on stations Transfer mode: set up secure connection between two end hosts Protected even on internal networks Must install IPsec software on stations Module F

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64 Figure 7.16: Virtual Private Network (VPN) Issues IP Security (IPsec) At internet layer, so protects information at higher layers Transparent: upper layer processes do not have to be modified Internet Layer with IPsec Protection TCPUDP HTTPSMTPFTPSNMP Protected

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65 Figure 7.16: Virtual Private Network (VPN) Issues IP Security (IPsec) Security associations: Agreement on how security options will be implemented May be different in the two directions Security Association (SA1) for Transmissions From A to B Security Association (SA2) for Transmissions From B to A Party B Party A

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66 Figure 7.16: Virtual Private Network (VPN) Issues IP Security (IPsec) Security associations: Governed by corporate policies List of Allowable Security Associations List of Allowable Security Associations Party B Party A IPsec Policy Server

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67 PPTP and IPsec VPNs PPTP Simpler, software is on almost all client PCs Limited to remote access VPNs Only moderate security IPsec For both remote access and site-to-site VPNs Better security More difficult to implement As increasing numbers of clients and servers implement it, should become dominant

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68 Recap Reasons for WANs Remote access Site-to-site transmission Internet access

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69 Recap WAN Technologies Telephone modems and the PSTN (slow; only for remote access) Leased line meshes (offer whatever speed is needed; popular but use has peaked) DSLs and cable modems (leased line speeds over a single pair of inexpensive voice-grade UTP already going to the home) Public Switched Data Networks (offers any needed speeds; inexpensive, widely used, and growing) Virtual Private Networks (inexpensive but very new so just getting started)