Wide Area Networks (WANs) Chapter 7 Updated Dec XU Zhengchuan Fudan University

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

7-3 WAN Concepts Wide Area Networks (WANs) –Single networks that connect different sites –So Layer 1 and Layer 2 operation WAN Purposes –Internet access (Chapter 6) –Link sites within the same corporation –Provide remote access to individuals who are off site 1.Point-to-point Leased Line Network 2.Public Switched Data Networks (PSDNs)

Leased Line Networks

7-5 Figure 7-2: Leased Line Networks for Voice and Data

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

7-7 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

7-8 Figure 7-4: Leased Line Speeds LineSpeedTypical Transmission Medium 56 kbps 2-Pair Data-Grade UTP T Mbps2-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.

7-9 Figure 7-4: Leased Line Speeds, Continued LineSpeedTypical Transmission Medium Fractional T1128 kbps, 256 kbps, 384 kbps, 512 kbps, 768 kbps 2-Pair Data-Grade UTP T Mbps2-Pair Data-Grade UTP North American Digital Hierarchy Bonded T1s (multiple T1s acting as a single line) A few multiples of 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.

7-10 Figure 7-4: Leased Line Speeds, Continued LineSpeed Typical Transmission Medium North American Digital Hierarchy T MbpsOptical 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. T Mbps2-Pair Data-Grade UTP

7-11 Figure 7-4: Leased Line Speeds, Continued LineSpeed (Mbps)Typical Transmission Medium OC3/STM Optical Fiber OC12/STM Optical Fiber SONET/SDH Speeds OC48/STM162,488.32Optical Fiber OC192/STM649,953.28Optical Fiber OC768/STM25639,813.12Optical 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 Mbps Used mostly by carriers

Public Switched Data Networks (PSDNs)

7-13 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 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

7-14 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.

7-15 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)

7-16 Figure 7-8: Virtual Circuit Operation The internal cloud network is a mesh of switches. This creates multiple alternative paths. This gives reliability.

7-17 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.

7-18 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.

7-19 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.

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

7-21 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 –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

7-22 Figure 7.14: Pricing Elements in Frame Relay Service Frame Relay Pricing –Frame relay access device at site CSU/DSU at physical layer (converts between internal, PSDN digital formats) Frame Relay at the Data Link 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

7-23 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

7-24 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)

7-25 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. It acts like a fuse in an electrical circuit. –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

7-26 Figure 7-10: Frame Relay Network Elements Switch POP Customer Premises B Customer Premises C Customer Premises A 2. Leased Access Line to POP

7-27 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

7-28 Figure 7-10: Frame Relay Network Elements Switch PVC 2 PVCs 1&2 POP PVC 2PVC 1 Customer Premises B Customer Premises C Customer Premises A 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

7-29 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 1-3

7-30 Figure 7-10: Frame Relay Network Elements Switch PVC 2 PVCs 1&2 POP PVC 2PVC 1 Customer Premises B Customer Premises C Customer Premises A 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.

7-31 Figure 7.15: Frame Relay Pricing Details To Determine Needs for Each Site Step 1: Determine PVC Needs –Determine needed speed from this site to each other site –You will need a virtual circuit to serve the needed speed to each other site –Sum all the virtual circuit speeds New Not in Book Site Being Analyzed 30 kbps needed 56 kbps PVC 800 kbps needed, 1 Mbps PVC Sum 1,056 kbps

7-32 Figure 7.15: Frame Relay Pricing Details Step 2: Determine Port Speed –You need a port speed equal to or greater than the sum of the PVCs –Don’t overdo port speed because port speed is most expensive component You can get by with 70% 70% of 1,056 kbps is 739 kbps Next-higher port speed may be 1 Mbps Don’t overdo port speed because port speed is most expensive component New Not in Book

7-33 Figure 7.15: Frame Relay Pricing Details Step 3: Determine Leased Line Speed –Remember that port speed is more expensive than leased line speeds In general, don’t waste port speed by using a leased line much under its capacity If port speed is 1 Mbps, leased line should be T1 with Mbps capacity New Not in Book

7-34 Figure 7.15: Frame Relay Pricing Details Example –The Situation Headquarters and two branch offices. Branches communicate with HQ at 200 kbps Branches communicate with each other at 40 kbps HQ B1 B2 New Not in Book

7-35 Figure 7.15: Frame Relay Pricing Details Example –For HQ How many connections will HQ need? What are their speeds? What will be their PVC speeds (0 kbps, 56 kbps, 256 kbps, 512 kbps, 1 Mbps) If port speeds are 56 kbps, 256 kbps, 384 kbps, 512 kbps, what port speed will be needed? What leased line will be needed if speeds are 56 kbps, 256 kbps, 512 kbps, or T1? HQ New Not in Book

7-36 Figure 7.15: Frame Relay Pricing Details Example –For Each Branch How many links will the branch need? What are their speeds? What will be their PVC speeds (0 kbps, 56 kbps, 256 kbps, 512 kbps, 1 Mbps) If port speeds are 56 kbps, 256 kbps, 384 kbps, 512 kbps, what port speed will be needed? What leased line will be needed if speeds are 56 kbps, 256 kbps, 512 kbps, or T1? B1 New Not in Book

7-37 Figure 7.15: Frame Relay Pricing Details Other Charges –Installation charges –Managed service charges –Service level agreement (SLA) charges Geographical Scope –Frame Relay systems with broader geographical scope cost more

7-38 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 percent of the time SLA guarantees no worse than a certain worst-case level of performance

Leased Line Networks Topology

7-40 Figure 7-2: Leased Line Networks for Voice and Data

7-41 Figure 7-2: Leased Line Networks for Voice and Data

7-42 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

7-43 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.

7-44 Test Your understanding Page Page Page 319 4

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

7-46 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

7-47 Figure 7-11: ATM, Continued Designed to Run over SONET/SDH Cell Switching ( 信元交换 ) –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

7-48 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 –Not thriving in the marketplace

7-49 Test Your understanding Page

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

7-51 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 very rapidly

7-52 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

7-53 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

7-54 Test Your understanding Page Page

Virtual Private Network (VPNs)

7-56 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)

7-57 Figure 7-14: Virtual Private Networks (VPNs) Remote access VPNs protect traffic for individual users

7-58 Figure 7-14: Virtual Private Networks (VPNs) Site-to-site VPNs protect traffic between sites Will dominate VPN traffic

7-59 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

7-60 Figure 7-15: 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.

7-61 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 software, setup or certificates on the individual hosts Inexpensive compared to transport mode

7-62 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.

7-63 Test Your understanding Page Page Page Page

7-64 Figure 7-18: Market Perspective Rapid Growth –VPNs –Metro Ethernet Stagnant –Leased line networks –Frame Relay –ATM

7-65 Test Your understanding Page

WAN Essentials

7-67 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)

7-68 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

7-69 Page 313 Test Your understanding 1

Topics Covered

7-71 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

7-72 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

7-73 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

7-74 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

7-75 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