Cisco Systems Network Router manual Cell Transfer Delay, Cell Delay Variation, Available Cell Rate

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Chapter 4 Planning Intermediate Route Selection

How MGX and SES Nodes Select Routes

You can change the AW on links to control network traffic. For example, you can reduce traffic on a backup link by increasing the AW to more than that on the desirable link. If the desirable link fails, the backup link becomes the lowest cost link and becomes available.

When AW is applied to a route, it is sometimes called the cumulative AW and is the sum of the AW values assigned to all links along a route. Some operations calculate the cumulative AW from the source to the destination, and other operations calculate the round trip cumulative AW. For example, if all links in a network use the default link AW, the source to destination AW for a route that uses two links is 10080. The round trip AW for the same route is 20160.

If you leave the AW set to the default value on all network links, routing using the lowest AW is the same as routing using the fewest hops. A hop is a connection segment through a node. Changing the AW on a link gives you the opportunity to make that link more or less desirable for routing.

Cell Transfer Delay

Cell transfer delay (CTD) is the measure of the delay an ATM cell encounters as it passes through an interface. Since each link has an interface at each end, each link CTD is the sum of the CTD at each end of the link.

The route CTD is the sum of the CTD values for all links through which the route passes and represents the time interval between a cell exiting the source node and entering the destination node.

The CTD used in MGX and SES nodes is a static value that is set by Cisco according to PNNI 1.0 standard and is based on the speed of the interface. Faster interfaces will have lower CTD values, and slower interfaces will have higher values.

Note Because the CTD is defined according to the PNNI 1.0 standard, the CTD for any specific link speed should match the CTD assigned to third-party interfaces that use that link speed.

Cell Delay Variation

Cell delay variation (CDV) is a measurement of the variation in CTD over links and through nodes. The route CDV is equal to the largest CDV along a route.

The CDV used in MGX and SES nodes is a static value that is set by Cisco and is based on the type of interface and node.

Available Cell Rate

Available cell rate (AvCR) is a dynamically generated value that indicates how much of the link bandwidth is available for the requested service class. AvCR is measured in cells per second (cps).

You cannot configure the AvCR for a link, but you can configure a parameter called the overbooking factor, which can change how the AvCR is advertised for new calls. After the PNNI controller calculates the AvCR for a route, it applies the overbooking factor to the AvCR before advertising the AvCR. The purpose of the overbooking factor is to allow you to purposely under book or over book a link.

For example, if link users are reserving more bandwidth than they actually need, bandwidth is being wasted. Overbooking allows you to make the wasted bandwidth available to other users. For example, if you estimate that 30% of the link bandwidth is not being used, you can configure the overbooking factor so that the advertised AvCR is 30% higher than the actual value. This enables the PNNI controller to

 

Cisco PNNI Network Planning Guide for MGX and SES Products, Release 5

4-2

Part Number OL-3847-01 Rev. D0, April, 2004

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Contents Corporate Headquarters Text Part Number OL-3847-01 Rev. D0Copyright 2003, Cisco Systems, Inc All rights reserved N T E N T S IiiCompatible Standards Worksheets Part Number OL-3847-01 Rev. D0, April G U R E S ViiViii B L E S Part Number OL-3847-01 Rev. D0, April Objectives AudienceOrganization Conventions XiiDocumentation Documentation Notes for the April 2004 Product ReleasesRelated Documentation XiiiTechnical Manual Order of Use XivTechnical Manual Titles and Descriptions TermsXvi Xvii Xviii Xix Reference Guides Xxi Document Title Description XxiiXxiii Xxiv Xxv Xxvi Obtaining Documentation Cisco.comOrdering Documentation XxviiChanges to This Document Chapter ChangesXxviii Obtaining Technical Assistance Documentation FeedbackCisco TAC Website Opening a TAC CaseObtaining Additional Publications and Information TAC Case Priority DefinitionsXxx Xxxi Xxxii Introduction to Pnni Pnni Network DatabaseSingle Peer Group Topology Hierarchical Pnni Network Topology Example Single Peer Group TopologyPeer group Ppeer Peer Group Leaders Simple Node RepresentationComplex Node Representation Simple Node RepresentationPnni Internetworking with Aini Border NodesHierarchical Pnni Network Benefits Pnni Internetworking with Iisp Example Pnni Internetworking with Aini TopologyPart Number OL-3847-01 Rev. D0, April Specifications Compatible StandardsPXM45 CapabilitiesPXM1E PXM45/BCapabilities SES SESConnection Limit Adjustments Connection Type Switch Connections CWM EndpointsSVC DAX SpvcInstall Redundant Hardware in Switches Parallel Links Between Adjacent SwitchesPhysical Network Planning Planning Guidelines for Individual Peer Groups Multiple Links Between Adjacent Peer GroupsMultiple Links to an External Network Multiple Paths Between Network NodesPlanning Guidelines for Hierarchical Networks Planning Guidelines for Peer Group LeadersPlanning Guidelines for Border Nodes Part Number OL-3847-01 Rev. D0, April Address and Closed User Group Planning Address Planning OverviewPnni Addressing Example Planning Address Configuration Settings Selecting an ATM Address FormatSupported Address Formats ESI SEL IDP DSPATM Field Description Default Values Guidelines for Selecting an Address FormatSelecting a Pnni Level Address Registration AuthoritiesCategory Type Authorities DCC4shows an example topology of a Pnni MPG WAN Part Number OL-3847-01 Rev. D0, April Length Level Peer Group ID Portion of ATM Address BytesDefault Peer Group ID Selecting the Pnni Peer Group IDSelecting the ATM Address 20-byte Node AddressSelecting the Ilmi Address Prefix Selecting the Spvc Address PrefixPlanning Address Prefixes for Aini and Iisp Links Selecting Static Addresses for UNI Ports Additional Guidelines for Creating an Address PlanClosed User Group Overview Closed User Group ExamplePlanning CUG Configuration Settings Selecting an Interlock CodeSelecting an Index Selecting Internal CUG Access Options Selecting CPE AddressesSelecting External CUG Access Options Specifying a Preferential CUGSelecting a Default CUG Address WorksheetsCUG Part Number OL-3847-01 Rev. D0, April Administrative Weight How MGX and SES Nodes Select RoutesLink and Route Metrics Cell Transfer Delay Cell Delay VariationAvailable Cell Rate Shortest Path Table Routing Maximum Cell RateShortest Path Tables Class of Service Tables Service Class Acronym Definition GuidelinesCTD CDV Traffic MetricHow SVCs and SVPs use the SPTs How SPVCs and SPVPs use the SPTsHow MGX and SES Nodes Select Links On-Demand RoutingLoad Balancing for SPT and On-Demand Routing Additional Routing Features in MGX and SES Nodes ServicePreferred Routing CLR0+12Priority Routing GroomingSoft Rerouting Priority BumpingBlocking Pass-Through Connections Nodal Point-to-Multipoint Branch RestrictionAXSM/A AXSM/BAXSM-E AXSM-XGFarthest Node Branching Part Number OL-3847-01 Rev. D0, April ABR AesaAini Ansi APSP2MP CBRCTD IN-2CUG CWMDIN IN-3IN-4 PGL PnniMGX SES IN-5IN-6 UBR UNITAC IN-7IN-8
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