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

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Presentation on theme: "Wide Area Networks (WANs) Chapter 7 Copyright 2003 Prentice-Hall Pankos Business Data Networks and Telecommunications, 4 th edition."— Presentation transcript:

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

2 2 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

3 3 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

4 4 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)

5 5 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

6 6 Figure 7.2: Telephone Modem Communication PSTN (Digital) Client A Server A Telephone 33.6 kbps Modem Digital Signal Modulated Signal Modem Need Modem at Each End Up to 33.6 kbps

7 7 Figure 7.2: Telephone Modem Communication PSTN (Digital) 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

8 8 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

9 9 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

10 10 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

11 11 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

12 12 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

13 13 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)

14 14 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

15 15 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

16 16 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

17 17 Figure 7.6: ADSL with Splitter Data WAN PSTN DSLAM ADSL Modem Splitter Telephone Subscriber Premises Telephone Company End Office Switch 1. Existing Pair of Voice-Grade UTP Wires PC

18 18 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

19 19 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

20 20 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

21 21 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

22 22 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

23 23 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. To Other Subscribers Sharing Neighborhood Capacity 6. Requires NIC or USB port

24 24 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

25 25 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 Appears stationary in sky (36,000 km or 22,300 mi) Far, so earth station needs dish antenna

26 26 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 (LEO) or tens of thousands of km (miles) (MEO) Closer, so omnidirectional transceivers can be used

27 27 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

28 28 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

29 29 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)

30 30 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

31 31 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 X.25 9,600 kbps to about 40 Mbps PacketReliableYesModerate Frame Relay 56 kbps to about 40 Mbps PacketUnreliableYesLow

32 32 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

33 33 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

34 34 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

35 35 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?

36 36 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) The Data Channel Uses 232 Serial Cable

37 37 Figure 7.12: Integrated Services Digital Network (ISDN) Personal Computer Desktop Telephone 64 kbps B Channel Analog Voice Signal On Telephone Wires ISDN Modem Internal Codec Converts Analog Voice Signal to Digital B Channel Signal at 64 kbps (000010000)) All-digital Service (1101001..) ISDN Wall Jack (RJ-45) The Voice Channel Uses Home Telephone Cord

38 38 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

39 39 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

40 40 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)

41 41 Figure 7.14: Pricing Elements in Frame Relay Service Switch POP Customer Premises B Customer Premises C 1. Access Device Customer Premises A

42 42 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

43 43 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

44 44 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

45 45 Figure 7.14: Pricing Elements in Frame Relay Service Switch POP Customer Premises B Customer Premises C Customer Premises A 5. Sometimes Traffic Charges and Other Charges 6. Management

46 46 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

47 47 Figure 7.15: Frame Relay Pricing Details 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 New Not in Book

48 48 Figure 7.15: Frame Relay Pricing Details 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, dont waste port speed by using a leased line much under its capacity New Not in Book

49 49 Figure 7.15: Frame Relay Pricing Details Example The Situation Headquarters and two branch offices. Branches communicate with HQ at 256 kbps Branches communicate with each other at 56 kbps HQ B1 B2 New Not in Book

50 50 Figure 7.15: Frame Relay Pricing Details 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 New Not in Book

51 51 Figure 7.15: Frame Relay Pricing Details 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 New Not in Book

52 52 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

53 53 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

54 54 Figure 7.17: Virtual Private Network VPN Server Corporate Site A VPN Server Corporate Site B Remote Customer PC (or site) Remote Corporate PC Tunnel Internet Extranet Remote Access for Intranet Site-to-Site for Internet

55 55 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 Internet reaches almost all sites Low transmission cost per bit transmitted

56 56 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

57 57 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 User dials into a remote access server (RAS) RAS often checks with RADIUS server for user identification information

58 58 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

59 59 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 intranetuse 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

60 60 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

61 61 Figure 7.19: IPsec in Tunnel 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

62 62 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

63 63 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

64 64 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 List of Allowable Security Associations List of Allowable Security Associations Party B Party A IPsec Policy Server


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