Wide Area Networking Chapter 9 Copyright 2001 Prentice Hall Revision 2: July 2001

2 Orientation zChapters 6 & 7 ySimple Ethernet LAN zChapter 8 ySite Networks zChapter 9 yWide Area Networks yLink sites together yCarriers and regulation yLeased Line Networks yPublic Switched Data Networks (PSDNs) yVirtual Private Networks

3 Wide Area Networks zWANs Link Sites (Locations) yUsually sites of the same organization ySometimes, sites of different organizations WAN Site A Site C Site B

4 Carriers zYou can only install wires on your own property yCalled your customer premises zTo send signals between sites or to customers, you must use a carrier Carrier Customer Premises

5 Carriers zCarriers transport data and voice traffic between customer premises, charging a price for their services zReceive rights of way from the government to lay wires and radio links Carrier

6 Carrier Regulation zTraditionally, Carriers Have been Regulated yGiven rights of way yGiven monopoly protection from competition yIn return, services normally must be tariffed xTariff specifies exact terms of the service to be provided, and xTariff specifies price to be charged xPrevents special deals, which would be inappropriate for a regulated monopoly xRegulators must approve price for reasonableness

7 Carrier Regulation zThere is a Strong Trend Toward Deregulation yGradual removal of monopoly protections yAllows competition, so lower prices and more service options yFewer services need to be tariffed, allowing price negotiation

8 Carrier Regulation zService Level Agreements (SLAs) yEven under competition, carriers may guarantee specific levels of service for certain service parameters in an SLA xThroughput xLatency xAvailability xError Rates, etc. yPenalties are paid to customers if carrier fails to meet agreed-upon service levels

9 High Cost of Long-Distance zLAN Communication is Inexpensive per Bit Transmitted ySo most LANs operate at 10 Mbps to a few gigabits per second zLong-Distance Communication is Very Expensive per Bit Transmitted ySo Most WANs use low speeds yMost WAN demand is 56 kbps to a few Mbps

10 Types of U.S. Carriers zThe United States is divided into about 200 regions called local access and transport areas (LATAs) zWithin a LATA, services are provided by two types of local exchange carriers (LECs) yThe incumbent local area carrier (ILEC), which is the traditional telephone carrier within the LATA yCompetitive local area carriers (CLECs), which compete with the ILEC Module D

11 Types of U.S. Carriers zBetween LATAs, services are provided by inter- exchange carriers (IXCs) zSome carriers provide service both within and between LATAs yHowever, their services may be regulated differently when they act as ILECs/CLECs or IXCs Module D

12 Leased Lines zLeased Lines are Circuits (From Chapter 1) yOften goes through multiple switches and trunk lines yLooks to user like a simple direct link Switch Trunk Line Leased Line

13 Leased Lines zLeased lines yLimited to point-to-point communication xLimits who you can talk to yCarriers offer leased lines at an attractive price per bit sent to keep high-volume customers Leased Line

14 Leased Line Meshes zIf you have several sites, you need a mesh of leased lines among sites Leased Line Mesh

15 Leased Line Speeds zLargest Demand is 56 kbps to a few Mbps z56 kbps (sometimes 64 kbps) digital leased lines yDS0 signaling zT1 (1.544 Mbps) digital leased lines y24 times effective capacity of 56 kbps yOnly about 3-5 times cost of 56 kbps yDS1 signaling zFractional T1 yFraction of T1’s speed and price yOften 128, 256, 384 kbps

16 Leased Line Speeds zT3: is the next step y44.7 Mbps in U.S. zEurope has E Series yE1: Mbps yE3: 34 Mbps zSONET/SDH lines offer very high speeds y156 Mbps, 622 Mbps, 2.5 Gbps, 10 Gbps

17 SONET/SDH zCreated as Trunk Lines for Internal Carrier Traffic yAs were other leased lines zThe Trunk Line Breakage Problem yProblem: unrelated construction products often break carrier trunk lines, producing service disruptions yThe most common cause of disruptions X

18 SONET/SDH Uses a Dual Ring zNormally, Traffic Travels in One Direction on One Ring zIf Trunk Line Breakage, Ring is Wrapped; Still a Ring, So Service Continues Switch Normal OperationWrapped

19 Digital Subscriber Lines (DSLs) zCan Use DSLs Instead of Traditional Leased Lines yLess expensive zHDSL (High-Speed DSL) ySymmetrical: Same speed in each direction yHDSL: 768 kbps (Half a T1) on a single twisted pair yHDSL2: Mbps (T1) on a single twisted pair zSHDSL (Super-High-Speed DSL) yCan run at multiple rates up to 4.6 megabits/second ySymmetrical New

20 Digital Subscriber Line zNormal Leased Lines Used Data Grade Wires yHigh-quality, high-cost yTwo pairs (one in each direction) zDSLs Normally Use Voice Grade Copper yNot designed for high-speed data ySo sometimes works poorly yUsually one pair (ADSL, HDSL) ySometimes two pairs (HDSL2)

21 Problems of Leased Lines zWith many sites, meshes are expensive and difficult to manage zThere are many leased lines between the sites yEach site is likely to have several leased lines connected to it zThese leased lines tend to span long distances between sites New

22 Problems of Leased Lines zUser firm must handle switching and ongoing management yExpensive because this requires planning and the hiring, training, and retention of a WAN staff

23 T1 Leased Lines zVoice Requirements yAnalog voice signal is encoded as a 64 kbps data stream (see Chapter 5) y8 bits per sample y8,000 samples per second Mod B

24 T1 Leased Lines zT1 lines are designed to multiplex 24 voice channels of 64 kbps each zT1 lines use time division multiplexing (TDM) yTime is divided into 8,000 frames per second xOne frame for each sampling period yEach frame is divided into 24 8-bit slots xOne for each channel’s sample in that time period x(24 x 8) 192 bits xPlus one framing bit for 193 bits per frame Mod B

25 T1 Leased Lines zSpeed Calculation y193 bits per frame y8,000 frames per second y1.544 Mbps zFraming Bit yOne per frame y8,000 per second yUsed to carry supervisory information (in groups of 12 or 24 framing bits) Mod B

26 PSDNs zPublic Switched Data Networks yDesigned for data rather than voice ySite-to-site switching is handled for you yYou merely connect each site to the PSDN “cloud” (No need to know internal details) PSDN

27 PSDNs zConnect each site to the PSDN using one leased line yOnly one leased line per site yLine only runs a short distance—to the nearest PSDN access point 1 Leased Line PSDN New

28 PSDNs zAccess Device Needed at Each Site yConnects each site to access line yOften a router ySometimes a device specific to a particular PSDN Technology PSDN Access Device

29 PSDNs zPoint of Presence (POP) yPlace where you connect to the cloud yMay be several in a city yMay not have any POP close yNeed leased line to POP ySeparate from PSDN charges Leased Line PSDN POP

30 PSDNs in Perspective zSimpler than Networks of Leased Lines yLess staffing yFewer leased lines and shorter distances zLess Expensive than Networks of Leased Lines yLess staffing yPSDN prices are very low yPSDN is less expensive overall yPSDNs are replacing many leased line mesh networks

31 Circuit-Switched PSDNs zEnd-to-End Capacity is Guaranteed yIf you need it, it is always there yWhen you don’t need it, you still pay for it yExpensive for data traffic, which usually has short bursts and long silences A bcd efg PSDN

32 Packet-Switched PSDNs zMessages are divided into small units called packets yShort packets load switches more effectively than fewer long messages

33 Packet Switched PSDNs zPackets are multiplexed on trunk lines yCost of trunk lines is shared yPacket switching lowers transmission costs yDominates PSDN service today Multiplexed Trunk Line

34 Packet Switched PSDNs: Virtual Circuits zAll commercial packet switched PSDNs use virtual circuits yEliminates forwarding decisions for individual packets yReduces switching load, so reduces switching costs Virtual Circuit

35 Unreliable PSDNs zMost commercial PSDNs are Unreliable y(Only obsolete X.25 PSDN technology was reliable) yNo error correction at each hop between switches yReduces costs of switching yNote that both virtual circuits and unreliable service reduce switching costs

36 PSDN Cost Savings zPacket Switching yReduces costs of transmission lines through multiplexing zVirtual Circuits yReduces costs of switches because they do not have to make decisions for each frame zUnreliability yReduces costs of switches because they do not have to do error correction

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

38 ISDN zIntegrated Services Digital Network z2B+D Basic Rate Interface (BRI) to the desktop yTwo 64-kbps B channels yCan be bonded for 128 kbps service yOne 16-kbps D channel, usually for supervisory signals 64 kbps 64 kbps BRI 2B+D ISDN Modem

39 ISDN zPrimary Rate Interface (PRI) yConnection between firm and ISDN carrier y23B+D (on a T1 line) y30B+D (on an E1 line) yOne 64 kbps D channel for supervision ISDN PRI BRI 2B+D23B+D

40 ISDN zCircuit-Switched yDedicated capacity yExpensive for data zDial-Up Connection yMust connect each time you wish to communicate yOther PSDNs are dedicated (always on) yGood for backup since only pay when use zUnreliable zOnly Popular PSDN that is either circuit-switched or dial-up New

41 ISDN zNever achieved strong market use zBeing overtaken by PSDNs that are both faster and less expensive zOften, ISDN is spelled out as “It still does nothing” zHowever, there is enough ISDN in use that you must know it zAlso, if connectivity is only needed a short time each day, ISDN is still a good choice for low- speed transmission

42 X.25 zFirst Packet-Switched PSDN Standard yDeveloped in the 1970s yNow obsolete yBut still used, especially in third-world countries and Europe zSlow: Usually 64 kbps or slower ySome faster X.25 services are available zReliable, so costs of switches are high ySo cost of service is high yBut works even if transmission lines are poor

43 Frame Relay zMost Popular PSDN Today yOffers speeds of 64 kbps to about 40 Mbps; This covers the range of greatest corporate demand yMost demand is at the low end of the range yPriced aggressively yBoth reasons are critical

44 Frame Relay zLow-Cost Service yPacket-Switched yUses virtual circuits to cut costs yUnreliable yRelatively low speeds zDedicated Connections yAlways ready to send and receive

45 ATM zLike Frame Relay: yPacket switched yVirtual circuits yDedicated (Always On) Connections zUnlike Frame Relay yMuch faster top speed x1 Mbps, 25 Mbps, 45 Mbps, 156 kbps, 622 kbps, several Gbps yOffers quality of service (QoS) guarantees xMaximum latency for time-critical applications xExact cell-by-cell timing

46 Frame Relay and ATM zMost Vendors Offer Both zTo cover speeds from 56 kbps to a few gigabits per second zIn general, a smooth price-speed curve across the two services zAt some speed, may offer both yIf so, usually price them the same Speed Price ATMFR

47 Frame Relay and ATM zBoth are widely used zFrame 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 zAs demand for higher-speed links grows, ATM should become more widely used yUnless other alternatives to ATM appear, such as 10 Gbps Ethernet for WANs

48 Frame Relay Pricing zFrame Relay Access Device (FRAD) yDevice at each site to connect site network to Frame Relay WAN yPaid to PSDN carrier or an equipment manufacturer PSDN Access Device

49 Frame Relay Pricing zLeased Access Line xUsually paid to telephone company rather than PSDN xPSDN often includes a bundled pricing arrangement, but it must pay the telephone company if this is the case xIf POPs are not close, access line charges will be high PSDN Access Line

50 Frame Relay Pricing zPort Speed yAt the POP there is a connection port yPorts come in different speeds x56 or 64 kbps, 1 Mbps are very common yFaster ports are more expensive yMonthly port speed usually is the most expensive component of PSDN cost PSDN Port at POP

51 Frame Relay Pricing zSometimes, Two Port Speeds are Quoted yCommitted Information Rate (CIR) xFrames can be sent continuously at this speed yAvailable Bit Rate (ABR) xHigher speed xFrames sent above the CIR are on standby xIf congestion appears, will be discarded first PSDN Port at POP

52 Frame Relay Pricing zPort Speed and Access Line Speed yPort costs usually are higher than access line charges yAccess line must be as fast as port speed or faster to avoid wasting expensive port speed yFor example, if the port speed is 1 Mbps, you should get a T1 (1.544 Mbps) leased access line PSDN Port at POP Access Line

53 Frame Relay Pricing zPermanent Virtual Circuits (PVCs) yLeased line meshes had a leased line to each site yPSDNs, usually have PVCs wherever there were leased lines between sites in the previous leased line network xEases the transition to PSDNs from leased lines PVC Leased Access Line

54 Frame Relay Pricing zPermanent Virtual Circuits (PVCs) yPVCs to other sites are multiplexed over a site’s single leased access line yPay monthly charge per PVC, based on speed PVC Leased Access Line

55 Frame Relay Pricing zPermanent Virtual Circuits (PVCs) yLeased access line must be fast enough to handle all of the PVCs it is multiplexing yExample: if it multiplexes kbps PVCs, the access line must be 840 kbps (T1 line needed) PVC Leased Access Line

56 Frame Relay Pricing zOther Aspects of Pricing ySometimes only flat fees for access lines, ports, etc, but sometimes also charges based on traffic volume yOngoing (monthly) fees for leased lines, ports, PVCs, etc. yUsually also an initial setup or installation charge

57 Frame Relay Pricing zOther Aspects of Pricing yIf offer switched virtual circuits (which are set up on demand), usually a fee for each set up yMany vendors offer managed services that have them manage the Frame Relay network instead of the customer having to do it

58 Frame Relay Frame Structure zVariable Length Frames yStart flag ( ) to signal start of frame yAddress field has variable length (2-4 octets) yInformation field to carry data (variable) yCRC (Cyclical Redundancy Check) field to detect errors (2 octets) xIf find errors, switch discards the frame yStop flag ( ) to signal end of frame

59 Frame Relay Frame Structure zAddress Field of Frame Relay Frame yVariable Length: 2-4 octets y4-Octet form shown yComplex 0 7 DLCI (6 bits)C/RAE DLCIFECNBECNDEAE DLCIAE DLCIAE Bits

60 Frame Relay Frame Structure zAddress Extension Bit (AE) y0 unless last octet y1 if last octet 0 7 DLCI (6 bits)C/R0 DLCIFECNBECNDE0 DLCI0 1 Bits

61 Frame Relay Frame Structure zAddress Field of Frame Relay Frame yData Link Control Indicator (DLCI) yIndicates virtual circuit for switching yDoes not use destination addresses 0 7 DLCI (6 bits)C/RAE DLCI (4 bits)FECNBECNDEAE DLCI (7 bits)AE DLCI (7 bits)AE Bits

62 Frame Relay Frame Structure zAddress Field of Frame Relay Frame yIf address field is 2 octets long, DLCI is 10 bits long yIf address field is 3 octets long, DLCI is 17 bits long yIf address field is 4 octets long, DLCI is 24 bits long 0 7 DLCI (6 bits)C/RAE DLCI (4 bits)FECNBECNDEAE DLCI (7 bits)AE DLCI (7 bits)AE Bits

63 Frame Relay Frame Structure zAddress Field of Frame Relay Frame yDiscard Eligible Bit yIf send faster than committed rate, DE bit is set to 1 indicating that it may be discarded first 0 7 DLCI (6 bits)C/RAE DLCIFECNBECNDEAE DLCIAE DLCIAE Bits

64 Frame Relay Frame Structure zCongestion Notification yIf a switch detects congestion, it sets the FECN or BECN bit 0 7 DLCIC/RAE DLCIFECNBECNDEAE DLCIAE DLCIAE Bits

65 Frame Relay Frame Structure zCongestion Control yTraffic shaping (see Chapter 8) z The Backward Explicit Congestion Notification (BECN) bit is set to tell the station that receives the frame to slow down; This is easy to implement z The Forward Explicit Congestion Notification (FECN) bit is more complex; If a station receives this notification in an incoming frame, it should tell its communication partner at the other end of the Frame Relay network to slow down

66 Frame Relay Frame Structure zAddress Field of Frame Relay Frame yCommand/Response bit useful in applications that have commands and responses yNot widely used 0 7 DLCI (6 bits)C/RAE DLCIFECNBECNDEAE DLCIAE DLCIAE Bits

67 10 Gbps/40 Gbps Ethernet zNow Under Development yPotential alternative to PSDNs zHandle high data traffic loads zCost should be attractive zShould be limited to metropolitan area networks (MANs)—a city and its suburbs zOnly optical fiber; No UTP versions New

68 VPNs zVirtual Private Networks yUse the Internet for transmission instead of a PSDN ySometimes called VPNs if use Frame Relay or ATM with added security Internet

69 VPNs zWhy use the Internet? yInexpensive yBusiness partners are already connected to the same network (the Internet) xMay use different PSDNs, but everybody is connected to the Internet

70 VPNs zProblems with the Internet yCongestion: slows transmissions yReliability: cannot always connect, sometimes fails during transmissions yLack of security

71 VPNs zIETF developing IPsec security standards yIP security yAt the internet layer yProtects all messages at the transport and application layers IPsec TCPUDP , WWW, Database, etc.

72 VPNs zIPsec Transport Mode yEnd-to-end security for hosts Local Network Internet Local Network Secure Communication

73 VPNs zIPsec Tunnel Mode yIPsec server at each site ySecure communication between sites Local Network Internet Local Network Secure Communication IPsec Server

74 VPNs zIPsec Modes Can be Combined yEnd-to-end transport mode connection yWithin site-to-site tunnel connection Local Network Internet Local Network Tunnel Mode Transport Mode

75 VPNs zAnother Security System for VPNs is the Point- to-Point Tunneling Protocol (PPTP) yFor dial-up connections, based on PPP yConnects user with securely to a remote access server at a site Internet Local Network Remote Access Server Dial-Up Connection PPTP Connection Module F

76 Virtual Private Networks zOther Problems Remain zInternet Congestion is Still a Problem yInternet throughput tends to be low zInternet Reliability is Low yCannot get connections yBackbone fails occasionally

77 Virtual Private Networks zAlternative yAvoid the congested and unreliable backbone! yUse one ISP that serves all sites yShould offer QoS service level agreement (SLAs) for latency and reliability Site 1ISPSite 2

78 WANs in Perspective zBoth Leased Line Networks and PSDNs are widely used and will be for several years to come zLeased Line Networking is shrinking while PSDN networking is growing rapidly zVPN technology and standards are still immature and use will be very low for several years to come