Wide Area Networking

1. Wide Area Networking

2. Wide Area Networks Link sites together Carriers and regulation Leased Line Networks Public Switched Data Networks (PSDNs) Virtual Private Networks Outline Topics

3. Wide Area Networks • WANs Link Sites (Locations) • Usually sites of the same organization • Sometimes, sites of different organizations Site B Site C Site A WAN

4. Carriers • You can only install wires on your own property • Called your customer premises • To send signals between sites or to customers, you must use a carrier • Carriers transport data and voice traffic between customer premises, charging a price for their services • Receive rights of way from the government to lay wires and radio links Carrier Customer Premises

5. Carrier Regulation • Traditionally, Carriers Have been Regulated • Given rights of way • Given monopoly protection from competition • In return, services normally must be tariffed • Tariff specifies exact terms of the service to be provided, and • Tariff specifies price to be charged • Prevents special deals, which would be inappropriate for a regulated monopoly • Regulators must approve price for reasonableness

6. Carrier Regulation • There is a Strong Trend Toward Deregulation • Gradual removal of monopoly protections • Allows competition, so lower prices and more service options • Fewer services need to be tariffed, allowing price negotiation

7. Carrier Regulation • Service Level Agreements (SLAs) • Even under competition, carriers may guarantee specific levels of service for certain service parameters in an SLA • Throughput • Latency • Availability • Error Rates, etc. • Penalties are paid to customers if carrier fails to meet agreed-upon service levels

8. High Cost of Long-Distance • LAN Communication is Inexpensive per Bit Transmitted • So most LANs operate at 10 Mbps to a few gigabits per second • Long-Distance Communication is Very Expensive per Bit Transmitted • So Most WANs use low speeds • Most WAN demand is 56 kbps to a few Mbps

9. Leased Lines • Leased Lines are Circuits • Often goes through multiple switches and trunk lines • Looks to user like a simple direct link • Limited to point-to-point communication • Limits who you can talk to • Carriers offer leased lines at an attractive price per bit sent to keep high-volume customers Switch Trunk Line Leased Line

10. Leased Line Meshes • If you have several sites, you need a mesh of leased lines among sites Mesh Leased Line

11. Leased Line Speeds • Largest Demand is 56 kbps to a few Mbps • 56 kbps (sometimes 64 kbps) digital leased lines • DS0 signaling • T1 (1.544 Mbps) digital leased lines • 24 times effective capacity of 56 kbps • Only about 3-5 times cost of 56 kbps • DS1 signaling

12. Leased Line Speeds • Fractional T1 • Fraction of T1’s speed and price • Often 128, 256, 384 kbps • T3: is the next step • 44.7 Mbps in U.S. • Europe has E Series • E1: 2.048 Mbps • E3: 34 Mbps • SONET/SDH lines offer very high speeds • 156 Mbps, 622 Mbps, 2.5 Gbps, 10 Gbps

13. SONET/SDH • Created as Trunk Lines for Internal Carrier Traffic • As were other leased lines • The Trunk Line Breakage Problem • Problem: unrelated construction products often break carrier trunk lines, producing service disruptions • The most common cause of disruptions X

14. SONET/SDH Uses a Dual Ring • Normally, Traffic Travels in One Direction on One Ring • If Trunk Line Breakage, Ring is Wrapped; Still a Ring, So Service Continues Switch Normal Operation Wrapped

15. Digital Subscriber Lines (DSLs) • Can Use Instead of Traditional Leased Lines • Less expensive • HDSL (High-Speed DSL) • Symmetrical: Same speed in each direction • HDSL: 768 kbps (Half a T1) on a single twisted pair • HDSL2: 1.544 Mbps (T1) on a single twisted pair

16. Digital Subscriber Line • Normal Leased Lines Used Data Grade Wires • High-quality, high-cost • Two pairs (one in each direction) • DSLs Normally Use Voice Grade Copper • Not designed for high-speed data • So sometimes works poorly • Usually one pair (ADSL, HDSL) • Sometimes two pairs (HDSL2)

17. Problems of Leased Lines • With many sites, meshes are expensive and difficult to manage • With N sites, N*(N-1)/2 leased lines for a mesh • May not need all links, but usually use many • User firm must handle switching and ongoing management • Expensive because this requires planning and the hiring, training, and retention of a WAN staff Sites Lines 5 10 10 45 25 300

18. T1 Leased Lines • Voice Requirements • Analog voice signal is encoded as a 64 kbps data stream • 8 bits per sample • 8,000 samples per second

19. T1 Leased Lines • T1 lines are designed to multiplex 24 voice channels of 64 kbps each • T1 lines use time division multiplexing (TDM) • Time is divided into 8,000 frames per second • One frame for each sampling period • Each frame is divided into 24 8-bit slots • One for each channel’s sample in that time period • (24 x 8) 192 bits • Plus one framing bit for 193 bits per frame

20. T1 Leased Lines • Speed Calculation • 193 bits per frame • 8,000 frames per second • 1.544 Mbps • Framing Bit • One per frame • 8,000 per second • Used to carry supervisory information (in groups of 12 or 24 framing bits)

21. PSDN PSDNs • Public Switched Data Networks • Designed for data rather than voice • Site-to-site switching is handled for you • You merely connect each site to the PSDN “cloud” (No need to know internal details)

22. PSDN PSDNs • Connect each site to the PSDN using one leased line • Only one leased line per site • With N sites, you only need N leased lines, not N* (N-1)/2 as with a full mesh 1 LeasedLine

23. PSDN PSDNs • Access Device Needed at Each Site • Connects each site to access line • Often a router • Sometimes a device specific to a particular PSDN Technology Access Device

24. PSDN PSDNs • Point of Presence (POP) • Place where you connect to the cloud • May be several in a city • May not have any POP close • Need leased line to POP • Separate from PSDN charges POP LeasedLine

25. PSDNs in Perspective • Simpler than Networks of Leased Lines • Less staffing • Fewer leased lines to support • Less Expensive than Networks of Leased Lines • Less staffing • PSDN prices are very low • PSDN is less expensive overall • PSDNs are replacing many leased line mesh networks

26. PSDN Circuit-Switched PSDNs • End-to-End Capacity is Guaranteed • If you need it, it is always there • When you don’t need it, you still pay for it • Expensive for data traffic, which usually has short bursts and long silences A bcd efg

27. Packet-Switched PSDNs • Messages are divided into small units called packets • Short packets load switches more effectively than fewer long messages

28. Packet-Switched PSDNs • Packet-Switched PSDNs Usually Operate at Layer 2 (Data Link Layer for Single Subnets) • Should be called frame-switched networks • Still called packet-switched networks

29. Packet Switched PSDNs • Packets are multiplexed on trunk lines • Cost of trunk lines is shared • Packet switching lowers transmission costs • Dominates PSDN service today Multiplexed Trunk Line

30. Packet Switched PSDNs: Virtual Circuits • All commercial packet switched PSDNs use virtual circuits • Eliminates forwarding decisions for individual packets • Reduces switching load, so reduces switching costs VirtualCircuit

31. Unreliable PSDNs • Most commercial PSDNs are Unreliable • (Only obsolete X.25 PSDN technology was reliable) • No error correction at each hop between switches • Reduces costs of switching • Note that both virtual circuits and unreliable service reduce switching costs

32. PSDN Cost Savings • Packet Switching • Reduces costs of transmission lines through multiplexing • Virtual Circuits • Reduces costs of switches because they do not have to make decisions for each frame • Unreliability • Reduces costs of switches because they do not have to do error correction

33. WAN Products ISDN X.25 Frame Relay ATM Virtual Private Networks (VPNs)

34. ISDN • Integrated Services Digital Network • 2B+D Basic Rate Interface (BRI)to the desktop • Two 64-kbps B channels • Can be bonded for 128 kbps service • One 16-kbps D channel, usually for supervisory signals 64 kbps BRI 2B+D 64 kbps ISDN Modem

35. ISDN ISDN • Primary Rate Interface (PRI) • Connection between firm and ISDN carrier • 23B+D (on a T1 line) • 30B+D (on an E1 line) • One 64 kbps D channel for supervision 2B+D 23B+D BRI PRI

36. ISDN • Circuit-Switched • Dedicated capacity • Expensive for data • Dial-Up Connection • Must connect each time you wish to communicate • Other PSDNs are dedicated (always on) • Unreliable • Only Popular PSDN that is either circuit-switched or dial-up

37. ISDN • Never achieved strong market use • Being overtaken by PSDNs that are both faster and less expensive • Often, ISDN is spelled out as “It still does nothing” • However, there is enough ISDN in use that you must know it • Also, if connectivity is only needed a short time each day, ISDN is still a good choice for low-speed transmission

38. X.25 • First Packet-Switched PSDN Standard • Developed in the 1970s • Now obsolete • But still used, especially in third-world countries and Europe • Slow: Usually 64 kbps or slower • Some faster X.25 services are available • Reliable, so costs of switches are high • So cost of service is high • But works even if transmission lines are poor

39. Frame Relay • Most Popular PSDN Today • Offers speeds of 64 kbps to about 40 Mbps; This covers the range of greatest corporate demand • Most demand is atthe low end of the range • Priced aggressively • Both reasonsare critical

40. Frame Relay • Low-Cost Service • Packet-Switched • Uses virtual circuits to cut costs • Unreliable • Relatively low speeds • Dedicated Connections • Always ready to sendand receive

41. ATM • Like Frame Relay: • Packet switched • Virtual circuits • Dedicated (Always On) Connections • Unlike Frame Relay • Much faster top speed • 1 Mbps, 25 Mbps, 45 Mbps, 156 kbps, 622 kbps, several Gbps • May offer quality of service (QoS) guarantees • Maximum latency for time-critical applications • Exact cell-by-cell timing

42. ATM • Very Expensive • Complexity because of basic transmission mechanisms • Complexity because of quality of service mechanisms • High-speed transmission

43. Frame Relay and ATM • Most Vendors Offer Both • To cover speeds from 56 kbps to a few gigabits per second • In general, a smooth price-speed curve across the two services • At some speed, may offer both • If so, usually price them the same FR Price ATM Speed

44. Frame Relay and ATM • Both are widely used • Frame Relay is more popular today because it serves the range of greatest corporate need (56 kbps to a few megabits per second) at an attractive price • As demand for higher-speed links grows, ATM should become more widely used • Unless other alternatives to ATM appear, such as 10 Gbps Ethernet for WANs

45. VPNs • Virtual Private Networks • Use the Internet for transmission instead of a PSDN • Sometimes called VPNs if use Frame Relay or ATM with added security • Why use the Internet? • Inexpensive • Business partners are already connected to the same network (the Internet) • May use different PSDNs, but everybody is connected to the Internet Internet

46. VPNs • Problems with the Internet • Congestion: slows transmissions • Reliability: cannot always connect, sometimes fails during transmissions • Lack of security

47. VPNs • IETF developing IPsec security standards • IP security • At the internet layer • Protects all messages at the transport and application layers E-Mail, WWW, Database, etc. TCP UDP IPsec

48. VPNs • IPsec Transport Mode • End-to-end security for hosts Local Network Internet Local Network Secure Communication

49. VPNs • IPsec Tunnel Mode • IPsec server at each site • Secure communication between sites Local Network Internet Local Network IPsec Server Secure Communication

50. VPNs • IPsec Modes Can be Combined • End-to-end transport mode connection • Within site-to-site tunnel connection Local Network Internet Local Network Tunnel Mode Transport Mode