Cisco Systems IGX 8400 manual Adding and Removing IMA Group Links, Line Redundancy

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Universal Switching Module Enhanced

Adding and Removing IMA Group Links

When you configure an IMA trunk through Cisco WAN Manager or the cnftrk command, you enter the number of retained links. This represents the number of ports that must remain active for the IMA trunk itself to remain active. If a physical line goes out of service, but the number of active lines is at least as great as the retained links value, the IMA trunk remains active even though the node goes into major alarm. Also, the available load bandwidth is adjusted according to physical line status, so the switch does not reroute connections after a line failure unless the used bandwidth becomes greater than the available bandwidth.

In Figure 4-6,the number of retained links is set to 3. If line 1 fails for example, trunk 8.1-4 will continue functioning, however, the node will show major alarm due to the physical line failure.

Figure 4-6

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The transmit and receive rate of an IMA trunk is the sum of all physical lines minus the IMA protocol overhead. The overhead for up to four lines is one DS0. Using the previous IMA trunk example, the maximum rates are as follows:

for trunk 8.1-4 (with T1 lines):

TX rate = Rx rate = 24 * 4 DS0s – 1 DS0 = 95 DS0s

You could configure the line receive rate to be the maximum bandwidth allowed on this trunk:

total bandwidth = RX rate = 95 DS0s

You could configure the line transmit rate to be the maximum bandwidth allowed on this trunk:

total bandwidth = RX rate = 95 DS0s

However, if a physical line fails (and the number of retained links are still active), the switch adjusts the total bandwidth. Using the example IMA trunk consisting of four physical T1 lines:

total bandwidth is 95 DS0s – 24 DS0s = 71 DS0s

4-16Cisco IGX 8400 Series Reference

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Contents Trunk Cards Trunk Interface Cards Trunk Front Cards Card Acronym Card NameTrunk Operating Modes Trunk Card MaintenanceLoopback Test Introduction to the UXM-E Trunk Mode Universal Switching Module EnhancedDetermining the UXM-E’s Mode of Operation Example Networks with UXM-EsUXM-E Trunk Features UXM-Es in a Network with Heterogeneous TrafficBack Cards for the UXM-E UXM-E InterfacesCard Name Card Description UXM-E Front Card Switchover to a Redundant UXM-E Maximum Number of UXM-EsCabled UXM-E Redundancy UXM-E Status LEDs Fail Active Standby Status of CardCard Mismatch Cellbus Bandwidth UsageUXM-E as a Clock Source Planning for Cellbus Bandwidth Allocation OC3Calculating Cellbus Bandwidth Changes ATM Across a Public ATM NetworkUXM-E in Trunk Mode Routing over Cell Trunks OnlyTypes of Supported Traffic Traffic from FastPacket-Based Cards Traffic TypeTypes of Connections on a UXM-E Trunk Inverse Multiplexing over ATM on IGX TrunksAdding an IGX Feeder Adding and Removing IMA Group Links Line RedundancyIMA Protocol Two-Segment ConnectionsRouting Feeder Connection Cell Endpoint a Endpoint B Type Gateway Type Routing Load TypeThree-Segment Connections Feeder Connection Cell Endpoint a Endpoint B TypeRT-VBR Gwtypenone ABR.FST GwtypenoneUXM-E Atfr Activation and Configuration of a UXM-E in Trunk ModeOC3 STM1 SMF 20Cisco IGX 8400 Series Reference Alarms for Physical Lines and Logical Trunks SCR and PCR Policing at Less than 50 CPS on UXM-EBXM IGX-UXM-ETrunk Statistics for Troubleshooting 10 PCR Policing Application ExampleSummary Statistics UXM-E Interface CardsConnector/Indicator Function Connectors and LEDs for SMF and MMF Back CardsOC-3/STM1 Back Cards 11 BC-UAI-4-155-SMF Faceplate T3 Back Cards 12 BC-UAI-2-155-SMF FaceplateConnectors/Indicator Function Connectors and LEDs for BC-UAI-6-T3 and BC-UAI-3-T3BC-UAI-6-T3 Faceplate E3 Back Cards 14 BC-UAI-3-T3 FaceplateConnectors and LEDs for BC-UAI-6-E3 and BC-UAI-3-E3 BC-UAI-6-E3 FaceplateT1 Back Cards 16 BC-UAI-3-E3 FaceplateBC-UAI-8-T1-DB-15 Faceplate E1 Back Cards 18 BC-UAI-4-T1-DB-15 FaceplateBC-UAI-8-E1 DB-15 Faceplate Port 21 BC-UAI-4-E1 DB-15 Faceplate 22 BC-UAI-4-E1 BNC Faceplate NTM Status Cable Redundancy for the NTMNetwork Trunk Module T1 Interface Card BC-T1 BC-T1 Faceplate Description23 BC-T1 Faceplate BC-T1 Connections and Status LEDsE1 Interface Back Card BC-E1 BC-E1 Connections and Status LEDs RX-TXSubrate Interface Card BC-SR Connection/Indicator Function BC-SR Connections and Status LEDsY1 Interface Back Card BC-Y1 RX MON BC-Y1 Connections and Status LEDsTX MON 46Cisco IGX 8400 Series Reference