Cisco Systems Network Router manual How MGX and SES Nodes Select Links, On-Demand Routing

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Chapter 4 Planning Intermediate Route Selection

How MGX and SES Nodes Select Links

Any route selected from the SPTs must conform to all specified metrics. If a conforming route is not available in chosen SPT, on demand routing is used to find a conforming route.

On PXM1E cards and service modules, you can change this with the addcon command.

On-Demand Routing

When the SPTs cannot produce a route for a connection, the switch performs on-demand routing. A SPT can fail to produce a route because the shortest route or routes in the table have failed. On-demand routing is also required when a connection specifies multiple routing metrics and the SPT routes do not conform to all of the metrics.

During on-demand routing, the switch searches the PNNI database for routes that match the specified criteria. On demand routing takes more time than SPT routing. However, on-demand routing can access more of the PNNI database and select better routes.

As a switch administrator, you can choose what action the controller takes when it discovers the first acceptable on-demand route. You can configure the controller for first fit, which produces the fastest route selection, or you can configure the switch for best fit. When the controller is configured for first fit on-demand route selection, it selects the first route that satisfies all connection requirements. When the controller is configured for best fit on-demand route selection, it identifies all routes that meet the call requirements, and then it chooses the route based on the setting of the load balancing option.

Load Balancing for SPT and On-Demand Routing

The load balancing option, which applies to SPT routing and on-demand routing, is a configurable parameter that allows you to control how a route is chosen when multiple routes offer the same level of service. You can configure the load balancing option to choose randomly from multiple routes or choose according to the best AvCR. If you select the random method, the PNNI controller considers the conforming routes equal and balances the load by randomly assigning calls to each. If you choose the route based on the AvCR, the route with the highest available cell rate is chosen.

How MGX and SES Nodes Select Links

The SPTs are built by calculating routes that are optimized for lowest AW, CTD, or CDV. However, for most service classes, each link along a route must conform to additional parameters. If no route is found in the SPTs, on-demand routing must be used to calculate a conforming route from the PNNI database.

The link parameter requirements for a service class establishes the quality of service (QoS) required for a call. Table 4-3shows the link parameters that must be satisfied for each service class.

 

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

4-6

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 Audience ObjectivesOrganization 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 XxviiChapter Changes Changes to This DocumentXxviii Obtaining Technical Assistance Documentation FeedbackCisco TAC Website Opening a TAC CaseTAC Case Priority Definitions Obtaining Additional Publications and InformationXxx 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 RepresentationBorder Nodes Pnni Internetworking with AiniHierarchical 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 SpvcParallel Links Between Adjacent Switches Install Redundant Hardware in 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 Peer Group Leaders Planning Guidelines for Hierarchical NetworksPlanning 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 Spvc Address Prefix Selecting the Ilmi 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 ExampleSelecting an Interlock Code Planning CUG Configuration SettingsSelecting 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 How MGX and SES Nodes Select Routes Administrative WeightLink and Route Metrics Cell Delay Variation Cell Transfer DelayAvailable Cell Rate Maximum Cell Rate Shortest Path Table RoutingShortest 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 SPTsOn-Demand Routing How MGX and SES Nodes Select LinksLoad 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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