Cisco Systems Network Router manual Peer Group Leaders, Simple Node Representation

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Chapter 1 Introduction to PNNI

The Hierarchical PNNI Network Topology

Hierarchical networks can support thousands of nodes because each higher level summarizes information for all lower levels. For example, suppose a level 64 peer group were added below Peer Group 2 in Figure 1-3. All nodes in the new level 64 peer group would be summarized by the peer group leader for Peer Group 2. The impact on the hierarchical network would be the following:

•Peer Group 2 would support one less physical node because it would have to add one LGN to represent the level 64 child peer group.

•The level 64 child peer group could support as many as 155 physical nodes (160 nodes - 1 LGN for each of the 5 peer groups at the higher levels.

•There would still be plenty of room for adding more physical nodes to levels above and below those shown in Figure 1-3.

The following sections provide additional information the peer group leaders that operate at higher levels in a PNNI hierarchy and introduce the border nodes that connect one peer group to another.

Peer Group Leaders

A peer group leader (PGL) is a higher level node (such as the level 40 nodes in Figure 1-3) that summarizes data for a child peer group (such as the level 56 nodes in Figure 1-3). A child peer group is a peer group that operates one level below the PGL that supports it. Each PGL works with other PGLs at the same level to build and maintain network data that it summarizes and distributes to its child peer group. The PGL also receives summarized data from a parent PGL if another level exists above the PGL’s level. Network data from levels above the PGL is also summarized and distributed to child peer groups.

Network administrators can use configuration commands to control which node becomes the PGL. The configuration process assigns a PGL election priority to each node in the peer group. When PNNI nodes start up, an election is held to determine which node has the highest PGL priority, and that node becomes the PGL. If the PGL node fails, a new election is held among the operating nodes to determine a new PGL. There is just one peer group leader for each peer group.

Each higher level peer group is made up of LGNs that represent the peer groups at the next lower level. These LGNs collect and manage information that is needed to communicate with the peer groups represented. As with the lowest level, these LGNs elect a PGL, which is responsible for determining communications paths to PNNI groups not represented within the peer group.

Note Network administrators add higher levels by adding LGNs with the addpnni-nodecommand. The PGL election priority is configured with the cnfpnni-electioncommand.

The PGL task adds to the work load of a PNNI node. The PGL must not only collect and manage data for communications outside the peer group, it must also collect and manage data for communications within the peer group. Because the PGL task adds to the work load of a PNNI node, it is good design practice to choose peer group leaders (and backup peer group leaders) carefully. Consider reducing the load on switches that serve as peer group leaders, and avoid using border nodes as peer group leaders.

Simple Node Representation

When a LGN presents its child peer group information to other peer groups, the default representation is called simple node representation. To other peer groups, the local peer group is represented as a single node with no nodal state parameters. Figure 1-4illustrates simple node representation.

 

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

1-6

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 Organization ObjectivesAudience Conventions XiiRelated Documentation DocumentationDocumentation Notes for the April 2004 Product Releases XiiiTechnical Manual Order of Use XivTechnical Manual Titles and Descriptions TermsXvi Xvii Xviii Xix Reference Guides Xxi Document Title Description XxiiXxiii Xxiv Xxv Xxvi Ordering Documentation Obtaining DocumentationCisco.com XxviiXxviii Changes to This DocumentChapter Changes Cisco TAC Website Obtaining Technical AssistanceDocumentation Feedback Opening a TAC CaseXxx Obtaining Additional Publications and InformationTAC Case Priority Definitions 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 RepresentationHierarchical Pnni Network Benefits Pnni Internetworking with AiniBorder Nodes Pnni Internetworking with Iisp Example Pnni Internetworking with Aini TopologyPart Number OL-3847-01 Rev. D0, April Specifications Compatible StandardsPXM1E PXM45Capabilities PXM45/BCapabilities SES SESSVC Connection Limit AdjustmentsConnection Type Switch Connections CWM Endpoints DAX SpvcPhysical Network Planning Install Redundant Hardware in SwitchesParallel Links Between Adjacent Switches Multiple Links to an External Network Planning Guidelines for Individual Peer GroupsMultiple Links Between Adjacent Peer Groups Multiple Paths Between Network NodesPlanning Guidelines for Border Nodes Planning Guidelines for Hierarchical NetworksPlanning Guidelines for Peer Group Leaders 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 FormatCategory Type Authorities Selecting a Pnni LevelAddress Registration 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 AddressPlanning Address Prefixes for Aini and Iisp Links Selecting the Ilmi Address PrefixSelecting the Spvc Address Prefix Selecting Static Addresses for UNI Ports Additional Guidelines for Creating an Address PlanClosed User Group Overview Closed User Group ExampleSelecting an Index Planning CUG Configuration SettingsSelecting an Interlock Code 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 Link and Route Metrics Administrative WeightHow MGX and SES Nodes Select Routes Available Cell Rate Cell Transfer DelayCell Delay Variation Shortest Path Tables Shortest Path Table RoutingMaximum Cell Rate CTD CDV Class of Service TablesService Class Acronym Definition Guidelines Traffic MetricHow SVCs and SVPs use the SPTs How SPVCs and SPVPs use the SPTsLoad Balancing for SPT and On-Demand Routing How MGX and SES Nodes Select LinksOn-Demand Routing Preferred Routing Additional Routing Features in MGX and SES NodesService CLR0+12Priority Routing GroomingBlocking Pass-Through Connections Soft ReroutingPriority Bumping Nodal Point-to-Multipoint Branch RestrictionAXSM-E AXSM/AAXSM/B AXSM-XGFarthest Node Branching Part Number OL-3847-01 Rev. D0, April Aini ABRAesa Ansi APSCTD P2MPCBR IN-2DIN CUGCWM IN-3IN-4 MGX SES PGLPnni IN-5IN-6 TAC UBRUNI IN-7IN-8
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