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Wide Area Networks (WANs)

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  • <Read the slide.>
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  • The first class of three WAN technologies is the of leased line, which we saw briefly in Chapter 6.
  • <Read the slide.>
  • <Read the box on the right.> <Then, note that there are many types of leased lines linking the sites.> [Telephone networking was the original use of leased line networks.]
  • <Read the slide.> The main difference between leased line networks for telephony and data, then, is whether the company has a PBX or a router at each site.
  • In a full mesh topology, there is a leased line between EACH PAIR of sites. A full mesh topology is highly reliable because if the line between two sites fails, there still is another path to carry traffic between the two affected sites. A full mesh topology is highly expensive because there are so many leased lines between distant sites.
  • In a pure hub-and-spoke topology, there is only one leased line from the hub site to each other site. A pure hub-and-spoke topology is very inexpensive because it uses the smallest possible number of leased lines to connect all of the sites. However, a pure hub-and-spoke topology is very unreliable because if a line to a site fails, there is no backup route. Few companies use either of these extreme topologies. They have some backup links.
  • Here we see the slowest two leased lines. Note that both use 2-pair data-grade UTP access lines. These must be run out to new customers, and this installation is very expensive. 56 kbps (sometimes 64 kbps) leased lines are rarely used today because they are so slow and expensive. However, T1 lines are very widely used because they are in the speed range of greatest corporate demand—128 kbps to a few megabits per second.
  • <Read the text box.> <Note the speeds of fractional T1 lines.> <Note that bonding is like link aggregation for Ethernet, which we saw in Chapter 4.>
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  • <Read the text box.> <Note rounded-off speeds of various SONET/SDH>
  • <Read the text box.> [Note to teacher: Because SONET/SDH is a carrier technology, we will not look at it further in this chapter. However, the telecommunications advanced module has more detail on carrier technology if you wish to cover it.]
  • We have been looking at leased lines, which require either new 2-pair UTP or optical fiber installations for each customer. By definition , DSL always uses 1-pair VG UTP, which is already installed; this avoids the cost of running a new line to the customer, making business-grade DSL lines more expensive. The most popular business DSL lines are HDSL, HDSL2, and SHDSL. HDSL is half as fast as a T1 circuit. HDSL2 is as fast as a T1 circuit. SHDSL offers flexible speeds up to the speed of an E1 line. Many firms are now replacing T1 and fractional T1 lines with business-grade DSL lines. Many carriers that install “T1” lines are really providing HDSL2 service.
  • Businesses have different needs than residential customers, so businesses do not use ADSL, which we saw in the last chapter. First, they need symmetrical throughput because they are used primarily for site-to-site traffic, which has symmetrical traffic needs. Second, they want QoS guarantees for minimum throughput. This makes them considerably more expensive than ADSL lines of similar speeds.
  • Now we will look at our second set of WAN technologies, public switched data networks or PSDNs.
  • <Read the slide.>
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  • A company has ten sites. It wants to use a PSDN. Question: Will it need leaded lines even if it is using a PSDN? Answer: Yes. Question: How many leased lines will it need? Answer: 10. One per site. Question: Where will each leased line go? Answer: From the site to the nearest PSDN POP.
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  • The first specific PSDN technology we will look at is Frame Relay.
  • Having discussed PSDNs in general, we will now look at several popular PSDN technologies, beginning with Frame Relay. <Read the slide.>
  • Let’s look at the elements of a Frame Relay Network. <Read the two text boxes, beginning at the top.>
  • For PSDNs, each site either uses a router or a dedicated access device, such as a Frame Relay access device (FRAD). At the physical layer, the company must have a CSU/DSU The CSU/DSU is either built into the router or access device or is a separate device between the router or access device and the carrier network.
  • <Read the slide.>
  • Note again, that you need a leased access line to the nearest POP. Fortunately, POPs usually are fairly close. This keeps the prices of leased access lines down.
  • <Read through the text boxes.>
  • Here, two PVCs are multiplexed over the leased line from Site 1 to the POP. <Read the slide.>
  • A PVC connects a site to a single other site. Here, PVCs from Site A to Sites B and C are Multiplexed over a Single Leased Line. PVC prices depend on PVC speed. PVC charges usually are collectively the second-most expensive part of Frame Relay service.
  • <Read the text box on the left.>
  • Now we will look at another PSDN technology. Some believe that it is the wave of the future. Others feel that other technologies will continue to eclipse it, just as Ethernet eclipsed ATM in the LAN market.
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  • Our old friend Ethernet blew other LAN technologies away with its low cost and (relatively) simple operation. Now, Ethernet is expanding to the WAN market and threatens to do the same for other PSDN technologies, at least over city-wide distances initially.
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  • The final PSDN technology we will look at is the carrier IP network.
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  • So far, we have seen leased line WANs and public switched data networks. The third major technology for WANs is the virtual private network or VPN.
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Transcript

  • 1. Wide Area Networks (WANs) Chapter 7 Panko’s Business Data Networks and Telecommunications, 6th edition Copyright 2007 Prentice-Hall May only be used by adopters of the book
  • 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. WAN Essentials
  • 4. Figure 7-1: Wide Area Networks (WANs)
    • Wide Area Networks (WANs)
      • Single networks that connect different sites
    • WANs and the Telephone
      • WAN technology usually uses the Public Switched Telephone Network transport system for transmission
      • Adds data switching and management
    • WAN Purposes
      • Internet access (Chapter 6)
      • Link sites within the same corporation
      • Provide remote access to individuals who are off site
  • 5. Figure 7-1: Wide Area Networks (WANs)
    • Site-to-Site Transmission within a Firm
      • Leased line networks
      • Public switched data networks (PSDNs)
      • Virtual Private Networks (VPNs)
  • 6. Figure 7-1: Wide Area Networks (WANs)
    • WANs are Characterized by High Cost and Low Speeds
      • High cost per bit transmitted compared to LANs
      • Consequently, lower speeds (most commonly 128 kbps to a few megabits per second)
        • This speed usually is aggregate throughput shared by many users
      • Much slower than LAN speeds (100 Mbps to 1 Gbps to the desktop)
  • 7. Figure 7-1: Wide Area Networks (WANs)
    • Carriers
      • Beyond their physical premises, companies must use the services of regulated carriers for transmission
        • Companies do not have rights of way to lay wires beyond their premises
      • Customers are limited to whatever services the carriers provide
      • Prices for carrier services change abruptly and without technological reasons
      • Prices and service availability vary widely from country to country
    突然地
  • 8. Leased Line Networks
  • 9. Leased Lines: Recap
    • Leased Line Characteristics
      • Point-to-point circuits
      • Always on
      • High speeds: 64 kbps (rare) to several gigabits per second
      • Leased for a minimum period of time
      • Usually offered by telephone companies
  • 10. Figure 7-2: Leased Line Networks for Voice and Data
  • 11. Figure 7-2: Leased Line Networks for Voice and Data
  • 12. Figure 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
  • 13. Figure 7-3: Full Mesh and Pure Hub-and-Spoke Topologies for Leased Line Data Networks 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.
  • 14. Figure 7-4: Leased Line Speeds Line Speed Typical Transmission Medium 56 kbps 56 kbps 2-Pair Data-Grade UTP T1 1.544 Mbps 2-Pair Data-Grade UTP North American Digital Hierarchy 56 kbps leased lines are hardly used today because they are so slow. T1 lines are very widely used because they are in the speed range of greatest corporate demand— 128 kbps to a few megabits per second.
  • 15. Figure 7-4: Leased Line Speeds, Continued Line Speed Typical Transmission Medium Fractional T1 128 kbps, 256 kbps, 384 kbps, 512 kbps, 768 kbps 2-Pair Data-Grade UTP T1 1.544 Mbps 2-Pair Data-Grade UTP North American Digital Hierarchy Bonded T1s (multiple T1s acting as a single line) A few multiples of 1.544 Mbps 2-Pair Data-Grade UTP T1 lines are very widely used. Fractional T1 lines offer lower speeds for companies that need them. Two or three T1 lines can be bonded for higher speeds. T1, Fractional T1, and Bonded T1s are the most widely used leased lines.
  • 16. Figure 7-4: Leased Line Speeds, Continued Line Speed Typical Transmission Medium North American Digital Hierarchy T3 44.736 Mbps Optical Fiber The jump from T1 to T3 speeds is extremely large. Few firms need T3 speeds, and they only need these speeds for some of their leased lines. Some carriers offer fractional T3 lines to bridge the T1-T3 gap. T3 lines and all faster leased lines use optical fiber. T1 1.544 Mbps 2-Pair Data-Grade UTP
  • 17. Figure 7-4: Leased Line Speeds, Continued Line Speed Typical Transmission Medium E3 34.368 Mbps Optical Fiber 64 kbps 64 kbps 2-Pair Data-Grade UTP E1 2.048 Mbps 2-Pair Data-Grade UTP CEPT Hierarchy In Europe, most countries use the CEPT hierarchy E1 lines are slightly faster than T1 lines E3 lines are slightly slower than T1 lines European Conference of Postal and Telecommunications Administrations
  • 18. Figure 7-4: Leased Line Speeds, Continued Line Speed (Mbps) Typical Transmission Medium OC3/STM1 155.52 Optical Fiber OS12/STM4 622.08 Optical Fiber SONET/SDH Speeds OC48/STM16 2,488.32 Optical Fiber OC192/STM64 9,953.28 Optical Fiber OC768/STM256 39,813.12 Optical Fiber For speeds above 50 Mbps, the world uses one technology Called SONET in the United States, SDH in Europe SONET speeds measured in OC numbers, SDH in STM numbers Speeds are multiples of 51.84 Mbps SONET: synchronous optical networking SDH: synchronous digital hierarchy
  • 19. Figure 7-4: Leased Line Speeds, Continued Line Speed (Mbps) Typical Transmission Medium OC3/STM1 155.52 Optical Fiber OS12/STM4 622.08 Optical Fiber SONET/SDH Speeds OC48/STM16 2,488.32 Optical Fiber OC192/STM64 9,953.28 Optical Fiber OC768/STM256 39,813.12 Optical Fiber Few commercial firms need SONET/SDH lines Primarily, carriers use them internally
  • 20. Figure 7-5: Business-Class Symmetric Digital Subscriber Line (DSL) Services HDSL HDSL2 SHDSL Uses Existing 1-Pair Voice-Grade UTP Telephone Access Line to Customer Premises?* Yes* Yes* Yes* Downstream Throughput 768 kbps 1.544 Mbps 384 kbps – 2.3 Mbps Upstream Throughput 768 kbps 1.544 Mbps 384 kbps – 2.3 Mbps *By definition , DSL always uses 1-pair VG UTP Many firms use HDSL and HDSL2 lines instead of T1 and fractional T1 speeds
  • 21. Figure 7-5: Business-Class Symmetric Digital Subscriber Line (DSL) Services HDSL HDSL2 SHDSL Symmetrical Throughput? Yes Yes Yes Target Market Businesses Businesses Businesses QoS Throughput Guarantees? Yes Yes Yes Businesses need symmetrical throughput and QoS
  • 22. Public Switched Data Networks (PSDNs)
  • 23. Figure 7-6: Public Switched Data Networks (PSDNs)
    • Recap: 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
  • 24. Figure 7-7: 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.
  • 25. Figure 7-7: 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)
  • 26. Leased Lines in PSDNs
    • A company has ten sites
    • It wants to use a PSDN
    • Will it need leased lines even if it is using a PDSN?
    • How many leased lines will it need?
    • Between what two locations will each leased line go?
  • 27. Figure 7-6: PSDNs
    • Costs
      • Carriers benefit from economies of scale in building and managing the large PSDN network
      • Consequently, the price to most companies is less than the cost of a network of leased lines
  • 28. Figure 7-6: 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
  • 29. Figure 7-8: Virtual Circuit Operation The internal cloud network is a mesh of switches. This creates multiple alternative paths. This gives reliability.
  • 30. Figure 7-8: Virtual Circuit Operation Mesh switching is slow because each switch must evaluate available alternative paths and select the best one. This creates expensive switching.
  • 31. Figure 7-8: 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.
  • 32. Figure 7-8: 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.
  • 33. Public Switched Data Networks (PSDNs) Frame Relay ATM Metropolitan Area Ethernet Carrier IP Networks
  • 34. Figure 7-9: 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
  • 35. Figure 7-10: Frame Relay Network Elements Switch POP Customer Premises B Customer Premises C 1. Access Device Customer Premises A Router or Dedicated Frame Relay Access Device And CSU/DSU CSU/DSU (Channel Service Unit/Data Service Unit)
  • 36. Figure 7-10: Frame Relay Network Elements 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)
  • 37. Figure 7-10: Frame Relay Network Elements
    • 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
  • 38. Figure 7-10: Frame Relay Network Elements Switch POP Customer Premises B Customer Premises C Customer Premises A 2. Leased Access Line to POP
  • 39. Figure 7-10: 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
  • 40. Frame Relay Network PVCs
    • Frame Relay PVC Numbers are called data link control indicators (DLCIs)
        • Pronounced “Dull’ seas”
        • Usually 10 bits long
        • 2 10 or 1,024 possible PVCs from each site
      • Multiplexed over the single leased line to the POP
        • Leased line must be fast enough to handle the combined PVC speeds
    Site 1 PSDN Leased Line Site 2 Site 3 POP PVC 1-2 PVC 1-2
  • 41. Figure 7-10: Frame Relay Network Elements Switch PVC 2 PVCs 1&2 POP PVC 2 PVC 1 Customer Premises B Customer Premises C Customer Premises A PVC 1 PVC 1 4. PVC Charges 2 PVCs are multiplexed over a single leased line PVC charges usually are collectively the second-most expensive part of Frame Relay service PVC prices depend on PVC speed
  • 42. Figure 7-10: Frame Relay Network Elements Switch PVC 2 PVCs 1&2 POP PVC 2 PVC 1 Customer Premises B Customer Premises C Customer Premises A PVC 1 PVC 1 5. Management Charges Frame Relay networks are managed by the carrier. For management of equipment on the customer premises, there is an extra charge.
  • 43. Public Switched Data Networks (PSDNs) Frame Relay ATM Metropolitan Area Ethernet Carrier IP Networks
  • 44. Figure 7-11: ATM
    • ATM (Asynchronous Transfer Mode) is a another PSDN
    • ATM Provides Speeds Greater than Frame Relay Can Provide
      • One megabit per second to several gigabits per second
    • Not a Competitor for Frame Relay
      • Most carriers offer both FR and ATM
      • Sell based on the customer’s speed range needs
      • May even interconnect the two services
  • 45. Figure 7-11: ATM, Continued
    • Designed to Run over SONET/SDH
    • Cell Switching
      • Most frames have variable length (Ethernet, etc.)
      • All ATM frames, called cells, are 53 octets long
        • 5 octets of header
        • 48 octets of data
      • Using fixed-length frames is called cell switching
      • Short length minimizes latency (delay) at each switch
  • 46. Figure 7-11: ATM, Continued
    • 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, however, ATM usually does NOT provide QoS guarantees!!
    • Manageability, Complexity, and Cost
      • Very strong management tools for large networks (designed for the PSTN)
      • Too complex and expensive for most firms
  • 47. Figure 7-11: ATM, Continued
    • ATM’s Future?
      • May flourish after firms outgrow Frame Relay speeds
      • However, metropolitan area Ethernet (discussed next) should be a strong competitor
    繁茂
  • 48. Public Switched Data Networks (PSDNs) Frame Relay ATM Metropolitan Area Ethernet Carrier IP Networks
  • 49. Figure 7-12: Metropolitan Area Ethernet
    • Metropolitan Area Networks (MANs)
      • MANs are carrier networks that are limited to a large urban area and its suburbs
      • Metropolitan area Ethernet (metro Ethernet) is available for this niche
      • New but growing rapidly
  • 50. Figure 7-12: Metro Ethernet, Cont.
    • Metro Ethernet Services
      • E-Line Service
        • Provides point-to-point connections between sites, like leased lines
      • E-LAN Service
        • Links multiple sites simultaneously
        • Virtual Private LAN Service (VPLS)
          • Makes the carrier service seem like a simple LAN segment
  • 51. Figure 7-12: Metro Ethernet, Cont.
    • Attractions of Metropolitan Area Ethernet
      • Very Low Prices Compared to Frame Relay and ATM
      • High Speeds: Tens of megabits per second
      • Familiar Technology for the Networking Staff
        • No need to learn a new technology
      • Rapid Provisioning
        • Setting up service to a customer
        • Changing the service (adding more capacity)
  • 52. Figure 7-12: Metro Ethernet, Cont.
    • Carrier Class Service
      • Basic Ethernet standards are insufficient for large wide area networks
      • Quality of service and management tools must be developed
      • The goal: provide carrier class services that are sufficient for customers
  • 53. Figure 7-12: Metro Ethernet, Cont.
    • 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
  • 54. Public Switched Data Networks (PSDNs) Frame Relay ATM Metropolitan Area Ethernet Carrier IP Networks
  • 55. Carrier IP Networks
    • Layer 2 Networks
      • Frame Relay, ATM, and Ethernet PSDNs Operate at the Data Link Layer
    • Some Carriers Now Offer IP Networks
      • Essentially, private Internets
      • Managed entirely by the carrier, so no overload in the Internet backbone from connected carries
      • Access is not open to everyone, so security is enhanced
      • Also called Private IP Networks
  • 56. Carrier IP Networks
    • Other Advantages
      • Allow companies to use familiar IP technology
      • Mature management and control standards
      • Carrier can manage everything if the customer desires that (and will pay)
      • Offer VoIP as well as data—convergence to reduce technology and management costs
  • 57. Virtual Private Networks (VPNs)
  • 58. Figure 7-13: Virtual Private Networks (VPNs)
    • Virtual Private Networks (VPNs)
      • Virtual private networks (VPN) use the Internet with added security for data transmission
    • The Attractions of Internet Transmission
      • Lowest cost per bit transmitted
      • Universal access to communication partners (Everybody uses the Internet)
  • 59. Figure 7-13: VPNs
    • Management
      • Self-managed corporate VPNs
      • VPNs managed by carriers
        • Cost more than self-managed VPNs
        • Reduce management labor and need for in-corporation expertise
  • 60. Figure 7-14: Virtual Private Networks (VPNs) There are 3 types of VPNs Remote access VPNs protect traffic for individual users
  • 61. Figure 7-14: Virtual Private Networks (VPNs) There are 3 types of VPNs Site-to-site VPNs protect traffic between sites Will dominate VPN traffic
  • 62. Figure 7-14: Virtual Private Networks (VPNs) There are 3 types of VPNs Host-to-host VPNs connect one client to one server
  • 63. Figure 7-13: VPNs
    • VPN Security Technologies
      • IPsec for any type of VPN
        • Offers very high security
      • SSL/TLS for low-cost transmission
        • Secure browser-server transmission
        • Remote access VPNs
  • 64. Figure 7-15: IPsec Transport and Tunnel Modes IPsec is the strongest VPN security technology. In transport mode, there is end-to-end 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.
  • 65. Figure 7-15: 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 setup on the individual hosts Inexpensive compared to transport mode
  • 66. Figure 7-16: 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.
  • 67. Figure 7-17: SSL/TLS with a Gateway SSL/TLS gateways turn SSL/TLS into a remote access VPN technology, Gives access to multiple internal webservers. Can “webify” some other applications for viewing on browsers as webpages. Can give access to other servers.
  • 68. SSL/TLS Versus IPsec
    • SSL/TLS
      • Limited to remote access VPNs
      • Only moderately strong security
      • Harder to use with many applications
    • IPsec
      • Both remote access and site-to-site VPNs
      • Offers extremely strong security
      • Costly to set up in the stronger transport mode
      • Economically attractive for site-to-site VPNs in tunnel mode
  • 69. Figure 7-18: 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
    迸發
  • 70. Figure 7-18: Market Perspective, Cont.
    • 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
  • 71. Figure 7-18: Market Perspective, Cont.
    • ATM
      • Much faster than Frame Relay
      • But most firms only need Frame Relay speeds
      • Very expensive because was designed to replace the core of the PSTN
        • It actually is doing this
      • The required sophistication in management is not needed for corporate networking
  • 72. Figure 7-18: Market Perspective, Cont.
    • Metro Ethernet
      • Price and speed are very attractive
      • Growing very rapidly
      • Limited to metropolitan area networking
      • Still somewhat immature technically
  • 73. Figure 7-18: Market Perspective, Cont.
    • Carrier IP Networks
      • PSDN vendors are beginning to offer IP service to their customers
      • Essentially, private Internets
      • Provide better congestion control and security than the global Internet
      • Most carriers want their customers to transition to IP offerings
      • Sprint will force this change in 2009
  • 74. Figure 7-18: Market Perspective, Cont.
    • Virtual Private Networks (VPNs)
      • IP is an base attractive technology for everything
      • Internet transmission is relatively inexpensive
      • Security and performance issues can be addressed
      • Growing rapidly
      • Dominates planning for the future in most firms
  • 75. Topics Covered
  • 76. WANs
    • Wide Area Networks
      • Carry data between different sites, usually within a corporation
      • High-cost and low-speed lines
        • 128 kbps to a few megabits per second
      • Carriers
      • Purposes
        • Internet access, site-to-site connections, and remote access for Individuals
      • Technologies
        • Leased line networks, public switched data networks, and virtual private networks
  • 77. Leased Line Networks
    • Leased Lines are Long-Term Circuits
      • Point-to-Point
      • Always On
      • High-speeds
    • Device at Each Site
      • PBX for leased line voice networks
      • Router for leased line data networks
    • Pure Hub-and-Spoke, Full Mesh, and Mixed Topologies
  • 78. Leased Line Networks
    • Many Leased Line Speeds
      • Fractional T1, T1, and bonded T1 dominate
      • Slowest leased lines run over 2-pair data-grade UTP
      • Above 3 Mbps, run over optical fiber
      • Below about 3 Mbps, 2-pair data grade UTP
      • Above 3 Mbps, optical fiber
      • North American Digital Hierarchy, CEPT, and other standards below 50 Mbps
      • SONET/SDH above 50 Mbps
      • Symmetrical DSL lines with QoS
  • 79. Public Switched Data Networks
    • PSDNs
      • Services offered by carriers
      • Customer does not have to operate or manage
      • One leased line per site from the site to the nearest POP
      • By reducing corporate labor, typically cheaper than leased line networks
      • Service Level Agreements
      • Virtual circuits
  • 80. Frame Relay PSDNs
    • Frame Relay
      • Most popular PSDN
      • 56 kbps to about 40 Mbps
      • Access devices, CSU/DSUs, leased access lines, POP ports, virtual circuits, management
        • Usually POP port speed charges are the biggest cost component
        • Second usually are PVC charges
      • Leased line must be fast enough to handle the speeds of all of the PVCs multiplexed over it
  • 81. Other PSDNs
    • ATM
      • High speed and cost
      • Cell switching
      • Low use
    • Metro Ethernet
      • Extending Ethernet to MANs
      • Very attractive speeds and prices
      • Small but growing rapidly
    • Carrier IP Networks
      • Essentially, private Internets with QoS and security
      • Carriers want to use it to replace Frame Relay
  • 82. Virtual Private Networks (PVCs)
    • The Internet is inexpensive and universal
      • VPNs add security to transmission over the Internet (or any other untrusted network)
    • IPsec
      • The strongest security for VPNs
      • Tunnel mode between sites is inexpensive
      • Transport mode between computers is expensive
    • SSL/TLS
      • First for browser communication with a single webserver
      • SSL/TLS gateways make it a full remote access VPN