Cisco Systems Network Router Shortest Path Table Routing, Maximum Cell Rate, Shortest Path Tables

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Chapter 4 Planning Intermediate Route Selection

How MGX and SES Nodes Select Routes

route more calls for the link. Of course, if link users suddenly start using all link resources, some user-compliant traffic may be discarded when congestion occurs. Bandwidth overbooking can be configured on a per-service-class-basis for each interface in the node.

Note Beginning with Release 3.0, Cisco MGX and SES nodes also support connection overbooking, which is configured with the addcon command. When per-service-class overbooking and connection based overbooking are both configured, both are applied simultaneously to each affected connection.

For more information, see the Cisco MGX 8850 (PXM1E/PXM45), Cisco MGX 8950, Cisco MGX 8830, and Cisco MGX 8880 Configuration Guide, Release 5 or see the appropriate service module configuration guide.

For CBR, rtVBR, and nrtVBR traffic, the advertised AvCR represents the bandwidth available for calls. For ABR traffic, AvCR is the capacity available for minimum cell rate (MCR) reservation. AvCR does not apply to UBR traffic.

The AvCR for a route is equal to the lowest link AvCR along the route.

Maximum Cell Rate

The maximum cell rate (maxCR) is a static value that is configured for each logical interface and can be configured separately for each service class. The maxCR represents the maximum throughput available for PNNI connections and cannot be modified by the overbooking factor. To block traffic for a particular service class over a link, set the maxCR for that service class to 0.

The maxCR for a route is equal to the lowest link maxCR along the route.

Shortest Path Table Routing

Most routing attempts begin with a search for a route in the shortest path tables. The following sections introduce the shortest path tables and explain how the tables are used by SVCs, SVPs, SPVCs, and SPVPs.

The Shortest Path Tables

The PNNI routing protocol automatically builds shortest path tables (SPTs) that list optimized routes for each destination address. When an MGX or SES node receives a call request, it compares the destination ATM address with the addresses and address prefixes in the node’s routing tables. The node looks for a match between the first 19 bytes of the destination address and the address prefixes in its database. The longest match determines the routes that are eligible. If there is just one route for the longest matching entry, and if that route meets the QoS requirements for the call, that is the route selected.

When multiple routes are available for the longest match, other route selection parameters are used to determine the optimum route.

Note Border nodes can be configured with a 0-length prefix, which matches all ATM addresses. This 0-length prefix serves as a default destination or route for all calls that do not match up to a longer ATM address or prefix within the PNNI network. When a border nodes uses AINI or IISP links to communicate with

 

 

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

 

 

 

 

 

 

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

 

 

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Contents Text Part Number OL-3847-01 Rev. D0 Corporate HeadquartersCopyright 2003, Cisco Systems, Inc All rights reserved Iii N T E N T SCompatible Standards Worksheets Part Number OL-3847-01 Rev. D0, April Vii G U R E SViii B L E S Part Number OL-3847-01 Rev. D0, April Audience ObjectivesOrganization Xii ConventionsDocumentation Notes for the April 2004 Product Releases DocumentationRelated Documentation XiiiXiv Technical Manual Order of UseTerms Technical Manual Titles and DescriptionsXvi Xvii Xviii Xix Reference Guides Xxi Xxii Document Title DescriptionXxiii Xxiv Xxv Xxvi Cisco.com Obtaining DocumentationOrdering Documentation XxviiChapter Changes Changes to This DocumentXxviii Documentation Feedback Obtaining Technical AssistanceCisco TAC Website Opening a TAC CaseTAC Case Priority Definitions Obtaining Additional Publications and InformationXxx Xxxi Xxxii Pnni Network Database Introduction to PnniSingle Peer Group Topology Example Single Peer Group Topology Hierarchical Pnni Network TopologyPeer group Ppeer Simple Node Representation Peer Group LeadersSimple Node Representation Complex Node RepresentationBorder Nodes Pnni Internetworking with AiniHierarchical Pnni Network Benefits Example Pnni Internetworking with Aini Topology Pnni Internetworking with IispPart Number OL-3847-01 Rev. D0, April Compatible Standards SpecificationsCapabilities PXM45PXM1E PXM45/BSES Capabilities SESConnection Type Switch Connections CWM Endpoints Connection Limit AdjustmentsSVC DAX SpvcParallel Links Between Adjacent Switches Install Redundant Hardware in SwitchesPhysical Network Planning Multiple Links Between Adjacent Peer Groups Planning Guidelines for Individual 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 Planning Overview Address and Closed User Group PlanningPnni Addressing Example Selecting an ATM Address Format Planning Address Configuration SettingsESI SEL IDP DSP Supported Address FormatsGuidelines for Selecting an Address Format ATM Field Description Default ValuesAddress Registration Authorities Selecting a Pnni LevelCategory Type Authorities DCC4shows an example topology of a Pnni MPG WAN Part Number OL-3847-01 Rev. D0, April Level Peer Group ID Portion of ATM Address Bytes LengthSelecting the Pnni Peer Group ID Default Peer Group ID20-byte Node Address Selecting the ATM AddressSelecting the Spvc Address Prefix Selecting the Ilmi Address PrefixPlanning Address Prefixes for Aini and Iisp Links Additional Guidelines for Creating an Address Plan Selecting Static Addresses for UNI PortsClosed User Group Example Closed User Group OverviewSelecting an Interlock Code Planning CUG Configuration SettingsSelecting an Index Selecting CPE Addresses Selecting Internal CUG Access OptionsSpecifying a Preferential CUG Selecting External CUG Access OptionsWorksheets Selecting a Default CUG AddressCUG 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 Service Class Acronym Definition Guidelines Class of Service TablesCTD CDV Traffic MetricHow SPVCs and SPVPs use the SPTs How SVCs and SVPs use the SPTsOn-Demand Routing How MGX and SES Nodes Select LinksLoad Balancing for SPT and On-Demand Routing Service Additional Routing Features in MGX and SES NodesPreferred Routing CLR0+12Grooming Priority RoutingPriority Bumping Soft ReroutingBlocking Pass-Through Connections Nodal Point-to-Multipoint Branch RestrictionAXSM/B AXSM/AAXSM-E AXSM-XGFarthest Node Branching Part Number OL-3847-01 Rev. D0, April Aesa ABRAini Ansi APSCBR P2MPCTD IN-2CWM CUGDIN IN-3IN-4 Pnni PGLMGX SES IN-5IN-6 UNI UBRTAC IN-7IN-8
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