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

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

3. 3 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

4. 4 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

5. 5 ISDN zCircuit-Switched yDedicated capacity, no congestion yExpensive for data zDial-Up Connection yMust connect each time you wish to communicate yOther PSDNs are dedicated (most companies need) yGood for backup since only pay when use zUnreliable zOnly Popular PSDN that is either circuit-switched or dial-up

6. 6 X.25 zFirst Packet-Switched PSDN Standard yDeveloped in the 1970s for terminal-host yNow obsolete yUsed in legacy systems & in third-world countries and Europe zSlow: Usually 64 kbps or slower ySome faster X.25 services are available zReliable due to unreliable transmission lines ycosts of switches & service are high

7. 7 Frame Relay zMost Popular PSDN Today yOffers speeds of 64 kbps to about 40 Mbps; Range of greatest corporate demand yMost demand is at low end of the range ySimple zDedicated Connections zLow-Cost Service yPacket-Switched yUses virtual circuits to cut costs yUnreliable

8. 8 ATM zLike Frame Relay: yPacket switched yVirtual circuits yDedicated Connections zUnlike Frame Relay yMuch faster top speed x1 Mbps, 25 Mbps, 45 Mbps, 156 kbps xOffers quality of service (QoS) guarantees Maximum latency for time-critical applications Exact cell-by-cell timing

9. 9 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

10. 10 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

11. 11 Frame Relay Pricing zFrame Relay Access Device (FRAD) yConnects each site network to Frame Relay yPaid to PSDN carrier or equipment manufacturer zLeased Access Line xUsually paid to telephone company not PSDN xPSDN often includes bundled pricing arrangement, but it must pay the telephone company xHigher access line charges with POP long-distance PSDN Access Device PSDN Access Line

12. 12 Frame Relay Pricing zPort Speed yAt the POP there is a connection port yCommon Port speeds are 56 or 64 kbps, 1 Mbps yFaster ports are more expensive yMonthly port fee is usually most expensive PSDN cost ySometimes, Two Port Speeds are Quoted xCommitted Information Rate (CIR) Frames can be sent continuously at this speed xAvailable Bit Rate (ABR) Higher speed Frames sent above the CIR are on standby If congestion appears, will be discarded first PSDN Port at POP

13. 13 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

14. 14 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 xEases the transition to PSDNs from leased lines 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

15. 15 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 15 64 kbps PVCs, the access line must be 840 kbps (T1 line needed) PVC Leased Access Line

16. 16 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 yUsually an initial setup or installation charge yFor switched virtual circuits fee/set up (on demand) yMany vendors offer managed services that have them manage the Frame Relay network instead of the customer having to do it

17. 17 Frame Relay Frame Structure zVariable Length Frames yStart flag (01111110) 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 (01111110) to signal end of frame

18. 18 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

19. 19 Frame Relay Frame Structure zAddress Extension Bit (AE) y0 not last octet y1 if last octet 0 7 DLCI (6 bits)C/R0 DLCIFECNBECNDE0 DLCI0 1 Bits

20. 20 Frame Relay Frame Structure zAddress Field of Frame Relay Frame yData Link Control Indicator (DLCI) x2 octets long, DLCI is 10 bits long x3 octets long, DLCI is 17 bits long x4 octets long, DLCI is 24 bits long yIndicates virtual circuit for switching (Like ATM) 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

21. 21 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

22. 22 Frame Relay Frame Structure zCongestion Control yTraffic shaping (Congestion Notification) xIf switch detects congestion, FECN or BECN bit set to 1 xBackward Explicit Congestion Notification (BECN) tells receiving station to slow down; easy to implement  Forward Explicit Congestion Notification (FECN) tells its communication partner at the other end of the Frame Relay network to slow down; more complex 0 7 DLCIC/RAE DLCIFECNBECNDEAE DLCIAE DLCIAE Bits

23. 23 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

24. 24 VPNs zVirtual Private Networks yUse the Internet for transmission instead of a PSDN xInexpensive xBusiness partners already connected to Internet yDifferent PSDNs, but everybody is connected to Internet ySometimes called VPNs if use Frame Relay or ATM with added security Internet

25. 25 VPNs zProblems with the Internet yCongestion: slows transmissions yReliability: cannot always connect, sometimes fails during transmissions yLack of security

26. 26 VPNs zIETF developing IPsec security standards yIP security yAt the internet layer yProtects all messages at the transport and application layers IPsec TCPUDP E-Mail, WWW, Database, etc.

27. 27 VPNs zIPsec Transport Mode yEnd-to-end security for hosts Local Network Internet Local Network Secure Communication

28. 28 VPNs zIPsec Tunnel Mode yIPsec server at each site ySecure communication between sites Local Network Internet Local Network Secure Communication IPsec Server

29. 29 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

30. 30 Virtual Private Networks zOther Problems Remain yInternet Congestion is Still a Problem xInternet throughput tends to be low yInternet Reliability is Low xCannot get connections xBackbone fails occasionally 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