1. © 2009 Pearson Education, Inc. Publishing as Prentice Hall Wide Area Networks (WANs) Chapter 7 Panko’s Business Data Networks and Telecommunications, 7th edition © 2009 Pearson Education, Inc. Publishing as Prentice Hall May only be used by adopters of the book

2. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 7-2 Orientation Single Networks –Layers 1 and 2 (so OSI standards dominate) –Chapters 4-7: Local to long-distance for single networks Chapter 4: Wired Ethernet LANs Chapter 5: Wireless LANs (WLANs) Chapter 6: Telecommunications (and Internet Access) Chapter 7: Wide Area Networks (WANs) Chapter 8: TCP/IP Internetworking –To link multiple single networks

3. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 7-1: Wide Area Networks (WANs) Wide Area Networks (WANs) –Connect different sites WANs and the Telephone Network –Use the PSTN transport system for transmission –Add switching and management to create a WAN WAN Purposes –Provide remote access to individuals who are off site –Link sites within the same corporation –Provide Internet access 7-3 2

4. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 7-1: Wide Area Networks (WANs) Evolution of WAN Technology –Layer 1: Leased line service and networks –Layer 2: Public switched data networks (PSDNs) –Layer 3: Virtual Private Networks (VPNs) over the Internet and IP carrier networks 7-4

5. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 7-1: Wide Area Networks (WANs) Carriers –Beyond their physical premises, companies must use the services of regulated carriers for transmission –Companies are limited to whatever services the carriers provide –Prices for carrier services change abruptly and without technological reasons –Prices and service availability vary from country to country 7-5

6. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 7-1: Wide Area Networks (WANs) High Costs and Low Speeds –High cost per bit transmitted, compared with LANs –Consequently, lower speeds (most commonly 256 kbps to about 50 megabits per second) 7-6

7. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 7-2: Leased Line Networks for Voice and Data 7-7

8. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 7-2: Leased Line Networks for Voice and Data 7-8

9. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 7-9 7-3: Full Mesh and Pure Hub-and-Spoke Topologies for Leased Line Data Networks In a full mesh topology, there is a leased line between each pair of sites Highly reliable Highly expensive

10. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 7-3: Full Mesh and Pure Hub-and-Spoke Topologies for Leased Line Data Networks 7-10 In a pure hub-and-spoke topology, there is only one leased line from the hub site to each other site. Very inexpensive. Very unreliable. Few companies use either of these extreme topologies. They have some backup links. 1

11. © 2009 Pearson Education, Inc. Publishing as Prentice Hall Leased Lines Layer 1 Carrier WAN Service 7-11

12. © 2009 Pearson Education, Inc. Publishing as Prentice Hall Leased Lines Circuits between Two Sites Always On All digital High Speeds Physical layer operation 7-12

13. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 7-4: Leased Line Speeds 7-13 LineSpeedTypical Transmission Medium 56 kbps or 64 kbps (rarely offered) 56 kbps or 64 kbps*2-Pair Data-Grade UTP T11.544 Mbps*2-Pair Data-Grade UTP Fractional T1128 kbps, 256 kbps, 384 kbps, 512 kbps, 768 kbps *2-Pair Data-Grade UTP Bonded T1s (multiple T1s acting as a single line) Small multiples of 1.544 Mbps *2-Pair Data-Grade UTP T344.736 Mbps*Optical Fiber North American Digital Hierarchy *Usually must be pulled to the customer’s premises. *This is expensive,

14. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 7-4: Leased Line Speeds 7-14 LineSpeed (Mbps)Typical Transmission Medium OC3/STM1155.52Optical Fiber OC12/STM4622.08Optical Fiber OC48/STM162,488.32Optical Fiber OC192/STM649,953.28Optical Fiber OC768/STM25639,813.12Optical Fiber SONET/SDH Speeds Above 50 Mbps, the world uses the same standard, which has two slight variations: SONET and SDH. These two variants interoperate without problems.

15. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 7-5: Connecting to a Leased Line 7-15 Routers need CSU/DSUs to connect to leased lines. The CSU terminates the telephone line; protects the telephone system from harmful voltages and signals. The DSU converts between the router’s signals and the signals that the PSTN is expecting to receive from the firm. Conversion is needed because digital signals can vary along several dimensions.

16. © 2009 Pearson Education, Inc. Publishing as Prentice Hall Figure 7-6: ADSL versus Business-Class Symmetric Digital Subscriber Line (DSL) Services 7-16 ADSLHDSLHDSL2SHDSL Uses existing 1-pair voice-grade UTP telephone access line to customer premises?* Yes* Target MarketResidencesBusinesses Downstream Throughput A few megabits per second 768 kbps1.544 Mbps384 kbps– 2.3 Mbps Upstream ThroughputSlower than downstream 768 kbps1.544 Mbps384 kbps– 2.3 Mbps Symmetrical Throughput? NoYes QoS Throughput Guarantees? NoYes *By definition, ALL DSLs use 1-pair voice-grade UTP residential access lines.

17. © 2009 Pearson Education, Inc. Publishing as Prentice Hall Public Switched Data Networks (PSDNs) Layer 2 Carrier WAN Services 7-17

18. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 7-18 Public Switched Data Networks (PSDNs) Leased Line Data Networks –Use many leased lines, which must span long distances between sites –This is very expensive –Company must design and operate its leased line network Public Switched Data Networks –Carrier does more of the operational and management work –Total cost of technology, service, and management usually lower than leased line networks 1

19. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 7-19 7-8: Public Switched Data Network (PSDN) In Public Switched Data Networks, the PSDN carrier handles all switching. Reduces the load on the network staff. The PSDN central core is shown as a cloud to indicate that the user firm does not have to know how the network operates.

20. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 7-20 7-8: Public Switched Data Network (PSDN) In Public Switched Data Networks, the customer needs a single leased line from each site to one of the PSDN carrier’s points of presence (POPs)

21. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 7-21 7-7: PSDNs Service Level Agreements (SLAs) –Guarantees for services –Throughput, availability, latency, error rate, etc. –An SLA might guarantee a latency of no more than 100 ms 99.99 percent of the time SLA guarantees no worse than a certain worst-case level of performance

22. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 7-10: Frame Relay There are several PSDN services –Frame Relay –ATM –Metropolitan area Ethernet 7-22

23. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 7-23 7-10: Frame Relay Frame Relay is the Most Popular PSDN Service Today –56 kbps to 40 Mbps –This fits the range of greatest corporate demand for WAN speed –Usually less expensive than a network of leased lines –Grew rapidly in the 1990s, to be come equal to leased line WANs in terms of market share (about 40%) –Carriers have raised prices, reducing growth

24. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 7-24 7-11: Frame Relay Network Elements Switch POP Customer Premises B Customer Premises C 1. Access Device Customer Premises A

25. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 7-25 7-11: Frame Relay Network Elements Switch POP Customer Premises B Customer Premises C Customer Premises A 2. Leased Access Line to POP

26. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 7-26 7-11: Frame Relay Network Elements Switch POP Customer Premises B Customer Premises C Customer Premises A 3. Port Speed Charge at POP Switch POP has a switch with ports The port speed charge is based on the port speed used The port speed charge usually Is the biggest part of PSDN costs

27. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 7-12: ATM For Speeds Greater than Frame Relay Can Provide –1 Mbps up to several gigabits per second Not a Competitor for Frame Relay –Most carriers provide both FR and ATM –May even interconnect the two services 7-27

28. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 7-12: ATM Short Frames –Most frames have variable length –All ATM frames are a very short 53 octets in length 5 octets of header 48 octets of data (payload) No trailer 53 octets total –Short length minimizes latency (delay) at each switch 7-28

29. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 7-12: ATM ATM Has Strong Quality of Service (QoS) Guarantees for Voice Traffic –Not surprising because ATM was created for the PSTN’s transport core –For pure data transmission, ATM does not provide QoS guarantees Data gets whatever is left over. 7-29

30. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 7-12: ATM Manageability, Complexity, and Cost –Very strong management tools for large networks (designed for the PSTN) –Too complex and expensive for most firms ATM’s Future? –May flourish after firms outgrow Frame Relay speeds –However, metropolitan area Ethernet should be a strong competitor –ATM is flourishing in a different market, the PSTN core 7-30 1

31. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 7-13: Metropolitan Area Ethernet Metropolitan Area Network (MAN) –A carrier network limited to a large urban area and its suburbs –Metropolitan area Ethernet (metro Ethernet) is available for this niche –Metro Ethernet is new, but is growing very rapidly 7-31

32. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 7-13: Metropolitan Area Ethernet Attractions of Metropolitan Area Ethernet –Low prices –High speeds –Familiar technology for networking staff –Rapid provisioning 7-32

33. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 7-13: Metropolitan Area Ethernet Carrier Class Service –Basic Ethernet standards are insufficient for large WANs (wide area networks) –Quality of service and management tools must be developed –The goal: to provide carrier class services that are sufficient for customers 7-33

34. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 7-13: Metropolitan Area Ethernet Carrier Class Service –802.3ad standard Ethernet in the first mile Standard for transmitting Ethernet signals over PSTN access lines 1-pair voice-grade UTP, 2-pair data-grade UTP, optical fiber 7-34

35. © 2009 Pearson Education, Inc. Publishing as Prentice Hall Layer 3 Carrier WAN Service IP Carrier Networks The Internet withVirtual Private Networks 7-35

36. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 7-14: The Internet versus IP Carrier Networks IP Is Increasingly Important –Companies know it and are comfortable with it –There are two ways to use IP at Layer 3 for WAN transmission: Companies can use IP carrier networks just as they use PSDNs for Layer 2 WANs –Reduces corporate labor –Usually are ISPs –Sometimes are PSDNs that offer Layer 3 IP carrier service Companies can create their own IPsec VPNs 7-36

37. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 7-14: The Internet versus IP Carrier Networks Advantages using of the Internet as a WAN –Low cost per bit transmitted because of economies of scale in the Internet –Access to other companies, nearly all of which are connected to the Internet –IP carrier networks can offer QoS SLAs IP is only a best-effort protocol But companies can engineer their networks for full QoS Customers must connect all sites to the same ISP for this to work 7-37

38. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 7-14: The Internet versus IP Carrier Networks Security –If companies act on their own, they can add virtual private network (VPN) protection to their transmissions –IP Carrier Network Security IP Carrier Networks have some inherent security –Restrict access to business customers However, for real security, virtual private networks (VPNs) are needed –IP carrier networks provide cryptographic equipment at each site 7-38

39. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 7-15: Route-Based Virtual Private Network (VPN) in an IP Carrier Network 7-39

40. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 7-40 7-16: Virtual Private Networks (VPNs) Remote access VPNs protect traffic for individual users

41. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 7-41 7-16: Virtual Private Networks (VPNs) Site-to-site VPNs protect traffic between sites Will dominate VPN traffic

42. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 7-42 7-17: IPsec Transport and Tunnel Modes IPsec is the strongest VPN security technology. IPsec transport mode gives host-to-host security however, software must be added to each host, each host must have a digital certificate, and each host must be setup (configured). This is very expensive.

43. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 7-43 7-17: IPsec Transport and Tunnel Modes In IPsec tunnel mode, there is only security over the Internet between IPsec gateways at each site No security within sites, but no software, setup or certificates on the individual hosts Inexpensive compared to transport mode

44. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 7-44 7-18: SSL/TLS for Browser–Webserver Communication IPsec works at the internet layer. SSL/TLS works at the transport layer. Only protects SSL/TLS-aware applications. This primarily means HTTP. SSL/TLS is built into every browser and webserver.

45. © 2009 Pearson Education, Inc. Publishing as Prentice Hall Figure 7-20: Market Perspective Leased Line Networks –Dominated WAN transmission until the 1990s –But difficult to set up and expensive to run –Recent spurt in use because of reduced leased line prices and rising Frame Relay prices –Needed for access lines in PSDNs and VPNs anyway 7-45

46. © 2009 Pearson Education, Inc. Publishing as Prentice Hall Figure 7-20: Market Perspective Frame Relay –Grew explosively in the 1990s –Became very widely used –FR prices have risen recently in an effort by carriers to increase their profit margins –Widely used and familiar, but now considered a legacy technology 7-46

47. © 2009 Pearson Education, Inc. Publishing as Prentice Hall Figure 7-20: Market Perspective ATM –Very high speeds, but very high price –Not thriving in the corporate market 7-47

48. © 2009 Pearson Education, Inc. Publishing as Prentice Hall Figure 7-20: Market Perspective Metro Ethernet –Price and speed are very attractive –Growing very rapidly –Limited to metropolitan area networking, at least for now –Still somewhat immature technically 7-48

49. © 2009 Pearson Education, Inc. Publishing as Prentice Hall Figure 7-20: Market Perspective IP Carrier Networks and Internet Transmission with VPNs –The Internet offers a very low cost per bit transmitted VPNs provide security for Internet transmission –Companies can also subscribe to IP carrier services IP carrier services also offer QoS –IP WAN usage is growing rapidly 7-49