Wide Area Networks (WANs)

1. Wide Area Networks(WANs)

2. 7-1: Wide Area Networks (WANs) 1 • Wide Area Networks (WANs) • Connect different sites • (LANs connect hosts within sites) • WAN Purposes • Provide remote access to individuals who are off site • Link sites within the same corporation • Provide Internet access

3. 7-1: Wide Area Networks (WANs) • WANs and the Telephone Network • Most WANs use the PSTN transport system for transmission • Public data carrier services add switching and management to create a WAN

4. 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 often change abruptly and without technological reasons • Prices and service availability vary from country to country

5. 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)

6. 7-2: Leased Line Networks for Voice and Data

7. 7-2: Leased Line Networks for Voice and Data

8. 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

9. 7-3: Full Mesh and Pure Hub-and-Spoke Topologies for Leased Line Data Networks 1 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

10. 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

11. Leased Lines Layer 1 Carrier WAN Service

12. Leased Lines • Circuits between two sites • Always on • All-digital • High speeds • Physical layer operation only • Companies must add their own switching and management

13. 7-4: Leased Line Speeds North American Digital Hierarchy *Usually must be pulled to the customer’s premises. This is expensive

14. 7-4: Leased Line Speeds CEPT Hierarchy The CEPT hierarchy is widely used in Europe

15. 7-4: Leased Line Speeds SONET/SDH Speeds Above 50 Mbps, the world uses the same standard,which has two slight variations: SONET (UH) and SDH (Europe). These two variants interoperate without problems.

16. 7-5: Connecting to a Leased Line Routers need CSU/DSUs to connect to leased lines. The CSU terminates the telephone line and protects the telephone system from harmful voltages and signals. The DSU converts between the router’s data signals and the digital Signals that the PSTN is expecting to receive from the firm. Conversion is needed because digital signals can vary in transmission speed, voltage levels, clock cycle duration, etc.

17. Figure 7-6: ADSL versus Business-Class Symmetric Digital Subscriber Line (DSL) Services *By definition, ALL DSLs use 1-pair voice-grade UTP residential access lines

18. Public Switched Data Networks (PSDNs) Layer 2 Carrier WAN Services

19. Public Switched Data Networks (PSDNs) 1 • 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 (PSDNs) • Carrier does more of the operational and management work • Total cost of technology, service, and management usually lower than leased line networks

20. 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.

21. 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)

22. 7-7: PSDNs • PSDNs Typically Offer Service Level Agreements • Guarantees for 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

23. 7-9: Virtual Circuit Operation The internal cloud network is a mesh of switches. This creates multiple alternative paths. This gives reliability.

24. 7-9: Virtual Circuit Operation Mesh switching is slow becauseeach switch must evaluate each available alternative paths and select the best one. This creates expensive switching.

25. 7-9: Virtual Circuit Operation Before communication begins between sites, the PSDN computes a best path, called a virtual circuit. All frames travel along this virtual circuit.

26. 7-9: Virtual Circuit Operation Each frame has a virtual circuit number instead of a destination address. Each switch looks up the VC number in its switching table, sends the frame out the indicated port. VCs greatly reduce switching costs.

27. 7-10: Frame Relay • There are several PSDN services • Frame Relay • ATM • Metropolitan area Ethernet

28. 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 recently raised prices, reducing growth

29. 7-11: Frame Relay Network Elements The access device usually Consists of a router and CSU/DSU Or a Frame Relay Access Device (FRAD) and a CSU/DSU 1. Access Device Customer Premises A Switch POP Customer Premises B Customer Premises C

30. 7-11: Frame Relay Network Elements Customer Premises A 2. Leased Access Line to POP Switch POP There is a leased access line from each site to the POP Customer Premises B Customer Premises C

31. 7-11: Frame Relay Network Elements 3. Port Speed Charge at POP Switch Customer Premises A 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 Switch POP Customer Premises B Customer Premises C

32. 7-12: ATM • Asynchronous Transfer Mode • 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

33. 7-12: ATM Payload Header 53 Octets 5 Octets • 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

34. 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, and voice needs high quality of service • For pure data transmission, however, ATM does not provide QoS guarantees • Data gets whatever is left over after guaranteed capacity for voice and video

35. 7-12: ATM 1 • 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 • Rapidly replacing circuit switching in the PSTN core

36. 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 relatively new, but is growing very rapidly

37. 7-13: Metropolitan Area Ethernet 1 • Services • E-Line Service • Provides a point-to-point connection between sites, as leased lines do • E-LAN Service • Links multiple sites simultaneously

38. 7-13: Metropolitan Area Ethernet • Attractions of Metropolitan Area Ethernet • Low prices per bit transmitted • High speeds • Familiar technology for networking staff • Rapid provisioning • Rapid capacity increases for special events

39. 7-13: Metropolitan Area Ethernet • Carrier Class Service • Basic metro 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

40. 7-13: Metropolitan Area Ethernet • 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

41. Layer 3 Carrier WAN Service IP Carrier Networks The Internet with Virtual Private Networks

42. 7-14: The Internet Versus IP Carrier Networks • IP Is Increasingly Important • Companies know it and are comfortable with it • A common mantra is “IP over everything” • There are two ways to use IP at Layer 3 for WAN transmission: • IP carrier networks are like PSDNs but work at Layer 3 instead of Layer 2 • Companies can communicate over the Internet, adding a cryptographic VPN for security

43. 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

44. 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

45. 7-15: Route-Based Virtual Private Network (VPN) in an IP Carrier Network

46. 7-16: Cryptographic Virtual Private Networks (VPNs) Remote access VPNs protect traffic for individual users

47. 7-16: Cryptographic Virtual Private Networks (VPNs) Site-to-site VPNs protect traffic between sites Will dominate VPN traffic

48. Cryptographic VPN Technologies 1 • IPsec for any type of VPN • Offers very high security • Complex and expensive • SSL/TLS for low-cost transmission • Secure browser-server transmission • Remote access VPNs • Uses the Internet but does not use IP directly

49. 7-17: IPsec Transport and Tunnel Modes IPsec is the strongest VPN security technology. IPsec transport mode gives host-to-host securityhowever, software must be added to each host,each host must be given a digital certificate,and each host must be setup (configured). This is expensive if a firm has many hosts.

50. 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 nosoftware, setup or certificates on individual hosts Inexpensive compared to transport mode