TCOM 540AgendaAccess and BackboneAccess and Backbone (2)Access and Backbone (3)RedundancyLocal Access Costs Are SignificantLocal Access Costs Are Significant (2)Local Access Costs Are Significant (3)Local Access Costs Are Significant (4)Local Access Design ExampleLocal Access Design Example (2)Local Access Design Example (3)Frame Relay (FR)Asynchronous Transfer Mode (ATM)ATM DefinitionsATM Definitions (2)Rules of ThumbRules of Thumb (2)Traffic ScaleTraffic Scale (2)One Speed, One CenterOne Speed, One Center (2)One Speed, One Center (3)Esau-Williams AlgorithmEsau-Williams Algorithm (2)Slide 27Esau-Williams Algorithm (3)HeapsHeaps (2)Heaps (3)Slide 32Esau-Williams ImplementationE-W Implementation (2)E-W Implementation (3)E-W Implementation (4)E-W Implementation (5)E-W Implementation (6)Creditability of E-WEsau-Williams Failure RateSharma’s AlgorithmSharma’s Algorithm (2)Sharma’s Algorithm (3)Multiple Link SpeedsMultiple Link Speeds (2)Predecessor FunctionAncestorsMultispeed CMST DefinitionMultispeed CMST Definition (2)MSLA Algorithm for Multispeed CMSTsSession 5 AssignmentTCOM 540/1 1TCOM 540Session 5TCOM 540/1 2Agenda•Quiz•Review Session 3 assignments•Access and backbone designTCOM 540/1 3Access and Backbone•We already encountered access and backbone in the first session•To over-simplify, access lines provide local connectivity, backbone provides long-distance transport•Balance between access and backbone costs can vary widelyTCOM 540/1 4Access and Backbone (2)AccessBackboneTCOM 540/1 5Access and Backbone (3)IXC1 POPIXC2 POPLECCentralOfficeLocalLoopsIXC1 BackboneIXC2 BackboneAccess lines to IXCsTo otherLEC COs(often SONET ring)TCOM 540/1 6RedundancyIXC1 POP2IXC2 POPLECCentralOffice1LocalLoopsIXC1 BackboneIXC2 BackboneAccess lines to IXCsTo otherLEC COsYour SiteLECCO2IXC2 POPTCOM 540/1 7Local Access Costs Are Significant•Relative cost of local access has been increasingSource: Bureau of Labor Statistics0.020.040.060.080.0100.0120.0140.0160.0180.0200.0838587899193959799YearLocal ResidentialInterstate ResidentialTCOM 540/1 8Local Access Costs Are Significant (2)•Situation regarding dedicated local access is less clear–Accurate information regarding real prices paid for dedicated access circuits is not easy to find–Probably has been some decrease, at least in areas where there is local access competitionTCOM 540/1 9Local Access Costs Are Significant (3)•The Telecommunications Reform Act of 1996 was supposed (among other things) to foster local competition–Appears to have been relatively unsuccessful–Competitive Local Access Carriers (CLECs) have been decimated by collapse of high-tech stocks–Relatively little facilities-based local competition (< 10% of market) – but this fraction is increasingTCOM 540/1 10Local Access Costs Are Significant (4)•Appears that whatever competition there is for at least residential local access (high speed) is coming from satellite and cable, not CLECs•Legislative action?TCOM 540/1 11Local Access Design ExampleFr. To BW1 2 120001 3 110001 4 90001 5 130001 6 80001 7 60001 2 3 4 5 6 71 400 1929 1985 1328 667 2112 16292 400 2814 2168 2031 1526 12253 400 1483 2044 3243 27144 400 1427 2551 20245 400 2136 16896 400 13277 400Traffic (symmetric)(Note: Site 1 is hub)Costs (symmetric)TCOM 540/1 12Local Access Design Example (2)•Use some nodes as concentrators$1929$1985$1328$667$2112$16291526122519296671328198512251327162913281483667$9650 $8660 $7659 (OPTIMAL)127654312765431276543TCOM 540/1 13Local Access Design Example (3)•If traffic grows by 50%, links (1,4) and (1,7) must be doubled 12251327325826561483667$10616127543132716291328667$8865 (OPTIMAL)1276543619291985IMPROVEMENTTCOM 540/1 14Frame Relay (FR)•Frame Relay Permanent Virtual Circuits (PVCs) use concepts of Committed Information Rate (CIR) and Port Speed•Charges for–Access–Port (connection to network)–CIR of PVC – does not vary with distanceTCOM 540/1 15Asynchronous Transfer Mode (ATM)•ATM uses similar concepts to FR–Constant Bit Rate (CBR)–Variable Bit Rate non-real-time (VBR-nrt)–Variable Bit Rate real-time (VBR-rt)–Available Bit Rate (ABR)–Unspecified Bit Rate (UBR)TCOM 540/1 16ATM DefinitionsConstant Bit Rate (CBR) - fixed bit rate in which bits are sent in a steady stream. A CBR is useful for applications requiring small but near constant transmission, for example, remote-site monitoring.Variable Bit Rate (VBR) - while overall transmission capacity (bits per second) is guaranteed, the rate at any given second may not equal the stated capacity. A VBR of 28 Kb/s, for example, may have periods where the transmission rate ranges from 23 to 33 Kb/s.VBR(rt) means a variable bit rate in real time transmission; VBR(nrt) means a variable bit rate transmission in near-real-time conditions. Both are used in voice and videoconferencing, where a quality channel is reserved but over which data does not flow evenly.Unspecified Bit Rate (UBR) - a transmission service which does not guarantee a fixed transmission capacity. Any application that can tolerate delays is ideally satisfied by an UBR.Source: BCE TeleglobeTCOM 540/1 17ATM Definitions (2)Available Bit Rate (ABR) -The bit rate left after the predictive and guaranteed service traffic (CBR/VBR) is served. In essence, it is simply a fair share of the remaining bandwidth amongst the VPs and VCs that have asked for this service.Source: cell-relay.indiana.eduTCOM 540/1 18Rules of Thumb•Cannot choose between a leased line and a FR/ATM design until both are done and costs compared–Availability of FR and ATM just complicates life …•Note that leased lines may have security advantagesTCOM 540/1 19Rules of Thumb (2)•If sites vary widely in size (traffic originated/terminated), choose the bigger sites as aggregation points–Define weight of a node as sum of all traffic flowing into and out of it•Design problem then has two parts–Access – gets traffic from small sites to backbone– Backbone – carries traffic between backbone nodes–Which comes first??TCOM 540/1 20Traffic Scale•Depends on relationship of node size to smallest desired link size–Smallest link size determined by factors such as packet size/delay1. Traffic from access node much smaller than smallest link we wish to use- Create access trees to group sites efficiently- Capacitated spanning treesTCOM 540/1 21Traffic Scale (2)2. Traffic from access node comparable to smallest link- Low speed link to hub vs.
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