Wide Area Networks (WANs) Chapter 7 Copyright 2003 Prentice-Hall Panko’s Business Data Networks and Telecommunications, 4th edition

Figure 7.1: Wide Area Networks (WANs) The Telephone Network WAN technology often is based on telephone technology WAN Purposes Link sites within the same corporation Provide remote access to individuals who are off-site Internet access

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

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

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

Figure 7.2: Telephone Modem Communication Need Modem at Each End Up to 33.6 kbps Modulated Signal Digital Signal Modem Telephone 33.6 kbps Modem Telephone Server A Client A PSTN (Digital)

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

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 Other party must have a digital connection to the PSTN

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

Figure 7.3: Telephone Modem Modulation Standards and Speeds V.92 Usually uses V.44 compression, which downloads webpages twice as fast as the old standard for compression, V.42 bis

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

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

Figure 7.4: Leased Line Networks Leased Line (Private Line or Dedicated Line) Point-to-point connection Always on Lower cost per minute than dial-up service Must be provisioned (set up)

Figure 7.4: Leased Line Networks Trunk Line-Based Leased Lines Based on trunk lines discussed in the previous chapter Extend standard trunk line speeds to end-to-end circuits between two customer premises Require expensive data-grade copper or optical fiber Data-Grade UTP

Figure 7.4: Leased Line Networks Trunk Line-Based Leased Lines Fractional T1 lines offer low-speed choices between 56 kbps and T1, typically: 128 kbps 256 kbps 384 kbps 512 kbps 768 kbps

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

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

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

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

Figure 7.4: Leased Line Networks Digital Subscriber Lines (DSLs) 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 Speed not guaranteed

Figure 7.4: Leased Line Networks Digital Subscriber Lines (DSLs) HDSL Symmetric speed (768 kbps) over one voice-grade twisted pair HDSL2: 1.544 symmetric speed over one voice-grade twisted pair Needed in business. (ADSL primarily for home and small business access.) Speed guaranteed

Figure 7.4: Leased Line Networks Digital Subscriber Lines (DSLs) SHDSL Super High rate DSL Single voice-grade twisted pair; longer distances than ASDL, HSDL Symmetric speed Variable speed ranging from 384 kbps to 2.3 Mbps Speed guaranteed

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

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

Figure 7.8: GEO Satellite System 1. Geosynchronous Satellite 2. Point-to-Point Uplink 3. Broadcast Downlink 4. Footprint 5. Earth Station A Earth Station B Appears stationary in sky (36,000 km or 22,300 mi) Far, so earth station needs dish antenna

Figure 7.9: LEO and MEO Satellite Systems 1. Currently Responsible LEO or MEO 2. Next Responsible LEO or MEO 3. Small Omnidirectional Transceiver A few thousands (LEO) or tens of thousands of km (miles) (MEO) Closer, so omnidirectional transceivers can be used

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

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

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

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

Figure 7.11: Popular PSDN Services Typical Speeds Circuit- or Packet- Switched Reliable or Unreliable Virtual Circuits? Relative Price ISDN Two 64 kbps B channels One 16 kbps D channel Circuit Unreliable No Moderate X.25 9,600 kbps to about 40 Mbps Packet Reliable Yes Moderate Frame Relay 56 kbps to about 40 Mbps Packet Unreliable Yes Low

Figure 7.11: Popular PSDN Services Typical Speeds Circuit- or Packet- Switched Reliable or Unreliable Virtual Circuits? Relative Price ATM 1 Mbps to about 156 Mbps Packet Unreliable Yes High Ethernet 10 Gbps and 40 Gbps Packet Unreliable No Probably Low

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

Figure 7.12: Integrated Services Digital Network (ISDN) Personal Computer 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) 3. 64 kbps B Channel Analog Voice Signal On Telephone Wires 4. 16 kbps D channel is for Supervisory signaling 2B+D Desktop Telephone

Quiz 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?

Figure 7.12: Integrated Services Digital Network (ISDN) Internal DSU Converts Serial Port Signal to Digital B Channel Signal at 64 kbps (1010) Personal Computer 64 kbps B Channel Digital Signal On Serial Cable (1010) ISDN Wall Jack (RJ-45) “ISDN Modem” All-digital Service (1101001..) The Data Channel Uses 232 Serial Cable Desktop Telephone

Figure 7.12: Integrated Services Digital Network (ISDN) Personal Computer The Voice Channel Uses Home Telephone Cord ISDN Wall Jack (RJ-45) “ISDN Modem” 64 kbps B Channel Analog Voice Signal On Telephone Wires All-digital Service (1101001..) Internal Codec Converts Analog Voice Signal to Digital B Channel Signal at 64 kbps (000010000)) Desktop Telephone

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

Figure 7.14: Pricing Elements in Frame Relay Service Frame Relay Pricing Frame relay access device at site CSU/DSU at physical 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

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

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

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

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

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

Figure 7.14: Pricing Elements in Frame Relay Service 5. Sometimes Traffic Charges and Other Charges Customer Premises A 6. Management Switch POP Customer Premises B Customer Premises C

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

Figure 7.15: Frame Relay Pricing Details New Not in Book To Determine Needs For Each Site Determine needed speed to each other site You will need a virtual circuit of this speed Sum all the virtual circuit speeds You will need a leased line this fast Actually, you usually can get by with a least line 70% this fast because not all virtual circuits will always be in use

Figure 7.15: Frame Relay Pricing Details New Not in Book To Determine Needs For Each Site You need a port speed equal to or greater than the sum of the PVCs Again, you can get by with 70% Remember that port speed is more expensive than leased line speeds In general, don’t waste port speed by using a leased line much under its capacity

Figure 7.15: Frame Relay Pricing Details New Not in Book Example The Situation Headquarters and two branch offices. Branches communicate with HQ at 256 kbps Branches communicate with each other at 56 kbps B1 HQ B2

Figure 7.15: Frame Relay Pricing Details New Not in Book Example For HQ How many PVCs will HQ need? What are their speeds? If POP speeds are 56 kbps, 256 kbps, 512 kbps, what port speed will HQ need? What leased lines will HQ need if speeds are 56 kbps, 256 kbps, 512 kbps, or T1? HQ

Figure 7.15: Frame Relay Pricing Details New Not in Book Example For Each Branch How many PVCs will the branch need? What are their speeds? If POP speeds are 56 kbps, 256 kbps, 512 kbps, what port speed will the branch need? What leased lines will the branch need if speeds are 56 kbps, 256 kbps, 512 kbps, or T1? B1

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

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

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

Figure 7.16: Virtual Private Network (VPN) Issues Transmission over the Internet with added security Some analysts include transmission over a PSDN with added security Why VPNs PSDNs are not interconnected Internet reaches almost all sites Low transmission cost per bit transmitted

Figure 7.16: Virtual Private Network (VPN) Issues VPN Problems Latency Reduces by having all communication go through a single ISP Security PPTP for remote access is popular IPsec for site-to-site transmission is popular

Figure 7.18: ISP-Based PPTP Remote Access VPN Remote Access VPNs User dials into a remote access server (RAS) RAS often checks with RADIUS server for user identification information Local Access RADIUS Server PPTP RAS Internet Remote Corporate PC ISP PPTP Access Concentrator Corporate Site A

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 Secure tunnel between access concentrator and RAS at corporate site Some security limitations No security between user site and ISP No message-by-message authentication of user

Figure 7.16: Virtual Private Network (VPN) Issues Site-to-Site VPNs and Extranets Site-to-site networks link sites within a single company Often part of an intranet—use of TCP/IP transmission and applications internally TCP/IP transmission is low in cost TCP/IP applications are good, standardized, and inexpensive Extranet: communication with customers and suppliers with security over the Internet

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

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

Figure 7.16: Virtual Private Network (VPN) Issues IP Security (IPsec) At internet layer, so protects information at higher layers 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

Figure 7.16: Virtual Private Network (VPN) Issues IP Security (IPsec) Security associations: Agreement on how security options will be implemented Established before bulk of secure communication begins May be different in the two directions Governed by corporate policies

Figure 7.20: Policy-Based Security Associations in IPsec Security Association (SA1) for Transmissions From A to B Security Association (SA2) for Transmissions From B to A Party A Party B List of Allowable Security Associations List of Allowable Security Associations IPsec Policy Server