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Transcript
Outlines Received due 13 March 2000 24 % Homework Review for Midterm (1 March 2000) Research Paper Readings [9] “MPLS: Special Delivery” [10] “Diversifying Internet Delivery” Frame Relay ANSI Standard covering OSI Layer 2 Accessed by Routers or FRAD’s Derived from X.25 Protocol Dumps almost all error checking Requires fiber on the long haul Uses Permanent Virtual Circuits (PVC’s) VC differs from Datagram Long Term Connection Requires Carrier intervention to change Frame Relay Committed Information Rate (CIR) Is a Quality of Service Guarantee ‘Guaranteed’ minimum Bandwidth Should be set > average traffic during appropriate peak period Port Connection Speed a.k.a. Port Speed or Burst Speed Bandwidth you can burst to provided network capacity exists. Ex) 1.54 Mbps Leased Lines Detroit OKC IXC Leased Line Network NYC IXC & Local Carriers dedicate 1.54 Mbps to our use via Circuit Switching & TDM. Router Carrier Leased Line Network Cross-Connect Leased Line ‘Cloud’ Trunks use TDM & Circuit Switching Ex) Frame Relay Detroit IXC Frame Relay Network OKC Router NYC Local Carriers dedicate 1.54 Mbps to our use. IXC provides random Packet Switched StatMux connectivity via PVC’s. Frame Relay Backbone FR Switch Frame Relay ‘Cloud’ Trunks use StatMux & Packet Switching Ex) Internet Detroit ISP Network OKC Router NYC Local Carriers dedicate 1.54 Mbps to our use. ISP provides random Packet Switched StatMux connectivity via datagrams. Internet Service Provider Backbone Router ISP ‘Cloud’ Trunks use StatMux & Packet Switching WAN Design (Link Reduction) Start with Traffic Matrix Examine Full Mesh Consider eliminating lightly used links Compare costs at each iteration Circuit Switched connections waste bandwidth for bursty traffic. traffic NYC to OKC 1.54 Mbps Line Speed 146 Kbps Average time Idle Time >> Active Time Frame Relay End-to-End Delay Frame Relay > equivalent sized Leased Line Network Cost Tendency Frame Relay < equivalent sized Leased Line Network Frame Relay (Inside the Cloud) Examined a specific case Frame Relay Switch 100 Mbps Trunk ?? 1.54 Mbps Connections P(Access Line is Active) = 10% How many access lines can this switch support? Availability Bounds on Packet Switch Carrying Capacity 100 Mbps Trunk, 1.54 Mbps Inputs with 154 Kbps average loads Lower 90% 559 99% 494 99.9% 452 99.99% 421 Where switch probably operates Upper 649 649 649 649 Where switch could operate Given 100 Mbps of Bandwidth... 64 421 - 649 1.54 Mbps Circuit Switched TDM Customers 1.54 Mbps Packet Switched StatMux Customers with 154 Kbps average load & 99.99% availability More Bursty Data Traffic can be moved with the Packet Switched StatMux network. Network Cost... Can be spread over 64 Leased Line customers Can be spread over 421 Frame Relay customers Frame Relay & the Internet Are Packet Switched StatMux network Largely hauling bursty data traffic Effectively haul bursty data traffic Inexpensive (compared to a Leased Line) Switched Network Carrying Capacities Packet Switch StatMux Circuit Switch TDM 0% Data 100% TST Offered Load 100% Data 0% TST Voice Over Frame Relay Many of same problems as Voice over IP Designed for data One Priority Quality is worse than Telephone System Quality is better than Internet Voice CIR guarantees Bandwidth FRAD can prioritize voice Video over FR products now available Priorities are a double edged sword... There is only so much pie to go around Frame Relay Switch Hi Priority Voice PVC’s Lo Priority Data PVC’s 100 Mbps Trunk If voice gets preference, data will suffer! QoS DE bit used by FR switches to police network Traffic > CIR enters switch in a 1 second interval? Marked DE If you are behaving... ...and other users exceed their CIR’s... ...and FR switch becomes congested... ...then other users’ traffic gets dumped 1st... ...your traffic is protected. Helps shelter you from behavior of others Internet Performance Probability of dropped packets Average Delay for delivered packets 0% Trunk Offered Load 100% Frame Relay Performance Probability of dropped packets* Average Delay for delivered packets 0% Trunk Offered Load 100% *Dashed: If we are transmitting at > CIR Solid: Provided we are transmitting at < CIR Worldwide Frame Relay Revenues Source: Data Communications