Wide Area Networks WANs Chapter 7 Panko s Business

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 2

WAN Essentials

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 4

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) 5

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) 6

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 突然地 technological reasons – Prices and service availability vary widely from country to country 7

Leased Line Networks

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 9

Figure 7 -2: Leased Line Networks for Voice and Data 10

Figure 7 -2: Leased Line Networks for Voice and Data 11

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 12

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. 13

Figure 7 -4: Leased Line Speeds North American Digital Hierarchy Line 56 kbps T 1 Speed Typical Transmission Medium 56 kbps 2 -Pair Data-Grade UTP 1. 544 Mbps 2 -Pair Data-Grade UTP 56 kbps leased lines are hardly used today because they are so slow. T 1 lines are very widely used because they are in the speed range of greatest corporate demand— 128 kbps to a few megabits per second. 14

Figure 7 -4: Leased Line Speeds, Continued North American Digital Hierarchy Line T 1 Fractional T 1 Bonded T 1 s (multiple T 1 s acting as a single line) Speed Typical Transmission Medium 1. 544 Mbps 2 -Pair Data-Grade UTP 128 kbps, 256 kbps, 2 -Pair Data-Grade UTP 384 kbps, 512 kbps, 768 kbps A few multiples of 2 -Pair Data-Grade UTP 1. 544 Mbps T 1 lines are very widely used. Fractional T 1 lines offer lower speeds for companies that need them. Two or three T 1 lines can be bonded for higher speeds. T 1, Fractional T 1, and Bonded T 1 s are the most widely used leased lines. 15

Figure 7 -4: Leased Line Speeds, Continued North American Digital Hierarchy Line T 1 T 3 Speed Typical Transmission Medium 1. 544 Mbps 2 -Pair Data-Grade UTP 44. 736 Mbps Optical Fiber The jump from T 1 to T 3 speeds is extremely large. Few firms need T 3 speeds, and they only need these speeds for some of their leased lines. Some carriers offer fractional T 3 lines to bridge the T 1 -T 3 gap. T 3 lines and all faster leased lines use optical fiber. 16

Figure 7 -4: Leased Line Speeds, Continued CEPT Hierarchy Line 64 kbps E 1 E 3 Speed Typical Transmission Medium 64 kbps 2 -Pair Data-Grade UTP 2. 048 Mbps 2 -Pair Data-Grade UTP 34. 368 Mbps Optical Fiber In Europe, most countries use the CEPT hierarchy E 1 lines are slightly faster than T 1 lines E 3 lines are slightly slower than T 1 lines European Conference of Postal and Telecommunications Administrations 17

Figure 7 -4: Leased Line Speeds, Continued SONET/SDH Speeds Line SONET: synchronous optical networking SDH: synchronous digital hierarchy Speed (Mbps) Typical Transmission Medium OC 3/STM 1 155. 52 Optical Fiber OS 12/STM 4 622. 08 Optical Fiber OC 48/STM 16 2, 488. 32 Optical Fiber OC 192/STM 64 9, 953. 28 Optical Fiber OC 768/STM 256 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 18

Figure 7 -4: Leased Line Speeds, Continued SONET/SDH Speeds Line Speed (Mbps) Typical Transmission Medium OC 3/STM 1 155. 52 Optical Fiber OS 12/STM 4 622. 08 Optical Fiber OC 48/STM 16 2, 488. 32 Optical Fiber OC 192/STM 64 9, 953. 28 Optical Fiber OC 768/STM 256 39, 813. 12 Optical Fiber Few commercial firms need SONET/SDH lines Primarily, carriers use them internally 19

Figure 7 -5: Business-Class Symmetric Digital Subscriber Line (DSL) Services HDSL Uses Existing 1 -Pair Voice-Grade UTP Telephone Access Line to Customer Premises? * HDSL 2 SHDSL 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 HDSL 2 lines instead of T 1 and fractional T 1 speeds 20

Figure 7 -5: Business-Class Symmetric Digital Subscriber Line (DSL) Services HDSL Target Market HDSL 2 SHDSL Businesses Symmetrical Throughput? Yes Yes Qo. S Throughput Guarantees? Yes Yes Businesses need symmetrical throughput and Qo. S 21

Public Switched Data Networks (PSDNs)

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 23

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. 24

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) 25

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? 26

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 27

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 28

Figure 7 -8: Virtual Circuit Operation The internal cloud network is a mesh of switches. This creates multiple alternative paths. This gives reliability. 29

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. 30

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. 31

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. 32

Public Switched Data Networks (PSDNs) Frame Relay ATM Metropolitan Area Ethernet Carrier IP Networks

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 34

Figure 7 -10: Frame Relay Network Elements Customer Premises A 1. Access Device Router or Dedicated Switch Frame Relay Access Device POP And CSU/DSU Customer Premises B Customer Premises C CSU/DSU (Channel Service Unit/Data Service Unit) 35

Figure 7 -10: Frame Relay Network Elements Site A Access Device (Frame Relay Access Device) T 1 CSU/DSU at Physical Layer T 1 Line Frame Relay at Data Link Layer PC Site B Server Access Device (Router) T 3 CSU/DSU at Physical Layer ATM etc. at Data Link Layer T 3 Line 36

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 37

Figure 7 -10: Frame Relay Network Elements Customer Premises A 2. Leased Access Line to POP Switch POP Customer Premises B Customer Premises C 38

Figure 7 -10: Frame Relay Network Elements 3. Port Speed Charge at POP Switch Customer Premises A POP has a switch with ports Switch The port speed charge is based on the port speed used POP The port speed charge usually Is the biggest part of PSDN costs Customer Premises B Customer Premises C 39

Frame Relay Network PVCs • Frame Relay PVC Numbers are called data link control indicators (DLCIs) • Pronounced “Dull’ seas” • Usually 10 bits long • 210 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 PVC 1 -2 POP Site 1 Leased Line Site 2 PSDN PVC 1 -2 Site 3 40

Figure 7 -10: Frame Relay Network Elements PVC charges usually Customer are collectively Premises A the second-most expensive part of Frame Relay service Switch 2 PVCs are multiplexed over a single leased line 4. PVC Charges PVCs 1&2 POP PVC 2 PVC prices depend on PVC speed PVC 1 PVC 2 Customer Premises B PVC 1 Customer Premises C 41

Figure 7 -10: Frame Relay Network Elements 5. Management Charges Frame Relay networks Customer are managed by the carrier. Premises A For management of equipment on the customer premises, Switch there is an extra charge. PVC 2 PVCs 1&2 POP PVC 1 PVC 2 Customer Premises B PVC 1 Customer Premises C 42

Public Switched Data Networks (PSDNs) Frame Relay ATM Metropolitan Area Ethernet Carrier IP Networks

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 44

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 45

Figure 7 -11: ATM, Continued • ATM Has Strong Quality of Service (Qo. S) 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 Qo. S guarantees!! • Manageability, Complexity, and Cost – Very strong management tools for large networks (designed for the PSTN) – Too complex and expensive for most firms 46

Figure 7 -11: ATM, Continued • ATM’s Future? – May flourish after firms outgrow Frame Relay speeds 繁茂 – However, metropolitan area Ethernet (discussed next) should be a strong competitor 47

Public Switched Data Networks (PSDNs) Frame Relay ATM Metropolitan Area Ethernet Carrier IP Networks

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 49

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 50

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) 51

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 52

Figure 7 -12: Metro Ethernet, Cont. • Carrier Class Service – 802. 3 ad 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 53

Public Switched Data Networks (PSDNs) Frame Relay ATM Metropolitan Area Ethernet Carrier IP Networks

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 55

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 Vo. IP as well as data—convergence to reduce technology and management costs 56

Virtual Private Networks (VPNs)

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) 58

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 incorporation expertise 59

Figure 7 -14: Virtual Private Networks (VPNs) There are 3 types of VPNs Remote access VPNs protect traffic for individual users 60

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 61

Figure 7 -14: Virtual Private Networks (VPNs) There are 3 types of VPNs Host-to-host VPNs connect one client to one server 62

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 63

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. 64

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 65

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. 66

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. 67

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 68

Figure 7 -18: Market Perspective • Leased Line Networks – Dominated WAN transmission until the 1990 s – But difficult to set up and expensive to run 迸發 – Recent spurt in use because of reduced leased line prices and rising Frame Relay prices – Needed for access lines in PSDNs and VPNs anyway 69

Figure 7 -18: Market Perspective, Cont. • Frame Relay – Grew explosively in the 1990 s – 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 70

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 71

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 72

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 73

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 74

Topics Covered

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 76

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 77

Leased Line Networks • Many Leased Line Speeds – Fractional T 1, and bonded T 1 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 Qo. S 78

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 79

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 component • Second usually are PVC charges – Leased line must be fast enough to handle the speeds of all of the PVCs multiplexed over it 80

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 Qo. S and security – Carriers want to use it to replace Frame Relay 81

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 82