Table Of Contents
Multiport T1/E1 ATM Port Adapters with Inverse Multiplexing over ATM
General Description of the ATM T1/E1 IMA Feature Set
Supported Standards, MIBs, and RFCs
Verifying the ATM Interface Configuration
Verifying the IMA Group Configuration
Monitoring and Maintaining ATM Inverse Multiplexing
ima differential-delay-maximum
Multiport T1/E1 ATM Port Adapters with Inverse Multiplexing over ATM
This document describes the Cisco IOS Inverse Multiplexing for ATM (IMA) features available with the introduction of Multiport T1/E1 ATM port adapters with IMA for the Cisco 7200 series routers and Cisco 7500 series routers.
This document includes the following sections:
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Supported Standards, MIBs, and RFCs
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Feature Overview
The inverse multiplexing over ATM (IMA) port adapter is a single-width port adapter that allows Cisco 7200 series and Cisco 7500 series routers to support inverse multiplexing over ATM. These port adapters allow WAN uplinks at speeds ranging from 1.544 Mbps to 12.288 Mbps for T1 connections and from 2.048 Mbps to 16.384 Mbps for E1 connections. (For details, see the "Bandwidth Considerations" section on page 4.)
With Cisco's scalable ATM IMA solution, network designers and managers can deploy only the bandwidth they need, using multiple T1 or E1 connections instead of more expensive T3 or OC-3 lines to bridge LANs and ATM WAN applications. Enterprises and branch offices can aggregate traffic from multiple lower-bandwidth physical transmission media, such as T1 or E1 pipes, to transmit voice and data at high-bandwidth connection speeds.
IMA Protocol Overview
In the transmit direction, IMA takes cells from the ATM layer and sends them in sequential distribution over the individual links that make up a logical link group called an IMA group (links can also be assigned as individuals rather than as group members). The IMA group performance is approximately the sum of the links, although some overhead is required for ATM header and control cells. At the receiving end, the cells are recombined to form the original cell stream and are passed up the ATM layer.
Filler cells are used to ensure a steady stream on the receiving side. IMA Control Protocol (ICP) cells control the operation of the inverse multiplexing function. For instance, using a frame length of 128 cells, one out of every 128 cells on each link is an ICP cell. The inverse multiplexing operation is transparent to the ATM layer protocols, and therefore the ATM layer can operate normally as if only a single physical interface is being used.
Figure 1 illustrates inverse multiplexing and demultiplexing with four bundled links, providing 5.52 Mbps of bandwidth for T1s for packet traffic, after subtracting the overhead of ATM cell headers and ICP cells. The transmitting side, from which cells are distributed across the links, is referred to as Tx, and the receiving side, where cells are recombined, is called Rx.
Figure 1
Inverse Multiplexing and Demultiplexing
General Description of the ATM T1/E1 IMA Feature Set
ATM networks were designed to handle the demanding performance needs of voice, video, and data, at broadband speeds of 34 Mbps and higher. However, the high cost and sporadic availability of long-distance broadband links limits broadband ATM WANs, preventing many organizations from taking advantage of ATM power. In response to these issues, the ATM Forum defined lower-speed ATM interface options for T1 or E1. However, this was not a complete solution, because a single T1 or E1 link often does not provide enough bandwidth to support either traffic among different router and switch locations or heavy end-user demand.
For this reason, many organizations find themselves caught between the bandwidth limitations of a narrowband T1 or E1 line and the much higher costs of moving to broadband links. In response to this dilemma, the ATM Forum defined IMA. Using Cisco 7200 series routers and Cisco 7500 series routers to provide ATM access gives branch offices and enterprises an affordable LAN-to-ATM interface.
ATM IMA T1 or E1 support on Cisco 7200 series routers and Cisco 7500 series routers includes the following features:
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Benefits
The following are benefits offered by the ATM T1 or E1 IMA features for Cisco 7200 series routers and Cisco 7500 series routers:
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Restrictions
This section describes general restrictions and ATM aspects that the ATM IMA feature does not support, as well as bandwidth considerations.
General Limitations
The following restrictions apply to the ATM IMA feature on Cisco 7200 series routers and Cisco 7500 series routers:
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Bandwidth Considerations
When planning IMA groups and payload bandwidths, consider the overhead required for ATM headers and ICP cells. Table 1 and Table 2 show approximate values for T1 and E1 IMA groups respectively, with a frame length of 128 cells, estimating ATM overhead at about 10 percent. The effective payload bandwidth varies based on packet size because the packets must be divided into an integer number of ATM cells leaving the last cell padded with filler bytes.
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Supported Platforms
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Supported Standards, MIBs, and RFCs
Standards
No new or modified standards are supported by this feature.
MIBs
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RFCs
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Prerequisites
Before you can configure a Cisco 7200 series router or Cisco 7500 series router to provide ATM T1 or E1 IMA service, you must perform the following tasks:
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PA_HARDWARE_A3_8T1IMA—Eight-port ATM IMA port adapter that provides T1 connectivity
PA_HARDWARE_A3_8E1IMA—Eight-port ATM IMA port adapter that provides E1 connectivity
For details about software configuration, see the Cisco IOS Release 12.0 software documents, Wide-Area Networking Configuration Guide and Wide-Area Networking Command Reference. For more information about the physical characteristics of the ATM T1 or E1 IMA port adapters for the Cisco 7200 series routers, or for instructions on how to install the port adapters, either see the Inverse Multiplexing over ATM (IMA) Port Adapter Installation and Configuration Guide that came with your ATM T1 or E1 IMA port adapter.
Configuration Tasks
This section describes the configuration tasks required to set up ATM IMA groups. You can also configure ATM links individually, but this feature description only includes those individual configuration steps that might pertain to ATM IMA groups. For complete information about ATM configuration, see the Cisco IOS Release 12.0 Wide-Area Networking Configuration Guide and Wide-Area Networking Command Reference.
See the following sections for configuration tasks that enable ATM inverse multiplexing. Each task in the list indicates if it is optional or required:
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Configuring the ATM Interface
Repeat the steps below to configure each ATM interface for ATM IMA operation. For complete information about ATM interface configuration, see the Cisco IOS Release 12.0 Wide-Area Networking Configuration Guide.
Step 1
Enter global configuration mode.
Step 2
Enters interface configuration mode and specifies the location of the interface.
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The Cisco IOS software creates the interfaces automatically when a port adapter is installed.
Step 3
Router(config-if)# clock source {line | internal}Sets the clock source for a link.
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Step 4
Router(config-if)# lbo long {gain26 | gain36} {-15db | -22.5db | -7.5db | 0db}or
lbo short {133 | 266 | 399 | 533 | 655}Sets a cable length longer than 655 feet for a T1 link.
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Sets a cable length 655 feet or shorter for a T1 link. There is no default for lbo short.
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If you do not set the cable length, the system defaults to a setting of lbo long gain260db (space between gain26 and 0db).
Step 5
Instead of configuring protocol parameters on the physical interface, you can set these up on the IMA group virtual interface.
Step 6
Enables the ATM bandwidth manager, which keeps track of bandwidth used by virtual circuits on a per-interface basis. When you specify the no form of the command, a check determines whether the ATM link is already oversubscribed. If it is, the command is rejected. Otherwise, the total bandwidth available on the link is recorded and all future connection setup requests are monitored to ensure that the link is not oversubscribed.
Step 7
Randomizes the ATM cell payload frames to avoid continuous nonvariable bit patterns and improve the efficiency of ATM's cell delineation algorithms. Normally the default setting for this command is sufficient, with no specific command required. By default, scrambling is off for T1 or E1 links.
Step 8
(For testing only) Loops all packets from the ATM interface back to the interface, as well as directs the packets to the network.
The default line setting places the interface into external loopback mode at the line.
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Step 9
Router(config-if)# fdl {ansi | att}(Optional) Sets the Facility Data Link (FDL) exchange standard for the Channel Service Unit (CSU) controllers. The FDL is a 4-Kbps channel used with the Extended Super Frame (ESF) framing format to provide out-of-band messaging for error-checking on a T1 link.
Changing the default allows better management in some circumstances, but can cause problems if your setting is not compatible with that of your service provider.
Step 10
Specifies that the link is included in an IMA group. Enter an IMA group number from 0 to 3. You can specify up to four groups per IMA port adapter. IMA groups usually span multiple ports on a port adapter.
Step 11
Ensures that the link is active at the IMA level.
1 It is recommended that if the link is already a port of an IMA group then remove it from the IMA group both at the near end and far end and then move the link to a desired IMA group.
Verifying the ATM Interface Configuration
Follow the steps below to verify configuration of ATM interfaces.
Step 1
Router#show interface atm 5/0ATM5/0 is up, line protocol is upHardware is IMA PAInternet address is 156.0.2.0/16MTU 4470 bytes, sub MTU 4470, BW 1536 Kbit, DLY 20000 usec,reliability 255/255, txload 1/255, rxload 1/255Encapsulation ATM, loopback not setKeepalive not supportedEncapsulation(s):AAL5512 maximum active VCs, 3 current VCCsVC idle disconnect time:300 seconds1 carrier transitionsLast input 00:43:16, output 00:43:16, output hang neverLast clearing of "show interface" counters neverInput queue:0/75/0 (size/max/drops); Total output drops:0Queueing strategy:weighted fairOutput queue:0/1000/64/0 (size/max total/threshold/drops)Conversations 0/0/256 (active/max active/max total)Reserved Conversations 0/0 (allocated/max allocated)5 minute input rate 0 bits/sec, 0 packets/sec5 minute output rate 0 bits/sec, 0 packets/sec4803 packets input, 5928671 bytes, 0 no bufferReceived 0 broadcasts, 0 runts, 0 giants, 0 throttles0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort4823 packets output, 5911619 bytes, 0 underruns0 output errors, 0 collisions, 1 interface resets0 output buffer failures, 0 output buffers swapped outStep 2
Router# show controller atm 1/ima0Interface ATM1/ima0 is upHardware is IMA PA - DS1 (1Mbps)Framer is PMC PM7344, SAR is LSI ATMIZER IIFirmware rev:G102, ATMIZER II rev:3idb=0x61DE9F10, ds=0x6185C0A0, vc=0x6187D3C0, pa=0x6184AF40slot 1, unit 9, subunit 0, fci_type 0x00BA, ticks 701720400 rx buffers:size=512, encap=64, trailer=28, magic=4Curr Stats:rx_cell_lost=0, rx_no_buffer=0, rx_crc_10=0rx_cell_len=0, rx_no_vcd=0, rx_cell_throttle=0, tx_aci_err=0Rx Free Ring status:base=0x3CFF0040, size=1024, write=320Rx Compl Ring status:base=0x338DCE40, size=2048, read=1275Tx Ring status:base=0x3CFE8040, size=8192, write=700Tx Compl Ring status:base=0x338E0E80, size=2048, read=344BFD Cache status:base=0x61878340, size=5120, read=5107Rx Cache status:base=0x61863D80, size=16, write=11Tx Shadow status:base=0x618641C0, size=8192, read=687, write=700Control data:rx_max_spins=12, max_tx_count=25, tx_count=13rx_threshold=267, rx_count=11, tx_threshold=3840tx bfd write indx=0x27, rx_pool_info=0x61863E20Control data base address:rx_buf_base = 0x038A15A0 rx_p_base = 0x6185CB40rx_pak = 0x61863AF0 cmd = 0x6185C320device_base = 0x3C800000 ima_pa_stats = 0x038E2FA0sdram_base = 0x3CE00000 pa_cmd_buf = 0x3CFFFC00vcd_base[0] = 0x3CE3C100 vcd_base[1] = 0x3CE1C000chip_dump = 0x038E3D7C dpram_base = 0x3CD80000sar_buf_base[0] = 0x3CE4C000 sar_buf_base[1] = 0x3CF22000bfd_base[0] = 0x3CFD4000 bfd_base[1] = 0x3CFC0000acd_base[0] = 0x3CE88360 acd_base[1] = 0x3CE5C200pci_atm_stats = 0x038E2EC0ATM1/ima0 is uphwgrp number = 1grp tx up reg= 0x5, grp rx up reg= 0x3, rx dcb reg= 0xD4 0x4, tx links grp reg=0x3, scci reg= 0x3C, ima id reg= 0x0, group status reg= 0xA2, tx timing reg= 0x20, tx test reg= 0x21, tx test pattern reg= 0x41, rx test pattern reg= 0x42, icpcell link info reg= 0xFC, icp cell link info reg= 0xFC, icp cell link info reg= 0x0, icp cell link info reg= 0x0, icp cell link info reg= 0x0, icp cell link info reg= 0x0, icp cell link info reg= 0x0, icp cell link info reg= 0x0
Configuring the IMA Groups
The ima-group command configures links on an ATM interface as IMA group members. When IMA groups have been set up in this way, you can configure settings for each group.
Step 1
Enters global configuration mode.
Step 2
Enters interface configuration mode and specify the slot location of the interface and IMA group number.
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Step 3
Sets protocol parameters for the whole group.
Step 4
If you are going to use SVCs, create an ATM PVC for ILMI management purposes and enter VC configuration mode. To set up communication with the ILMI, use a value of ilmi for ATM adaptation layer encapsulation; the associated vpi and vci values are ordinarily 0 and 16, respectively.1
Step 5
Enables the signaling for setup and tear-down of SVCs by specifying the Q.SAAL2 encapsulations; the associated vpi and vci values are ordinarily 0 and 5, respectively.
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Step 6
To complete configuration of a PVC, exit VC configuration mode.
Step 7
Router(config-if)# svc name nsap nsap-addressSets up SVCs for sending ATM information. Once you specify a name for an SVC, you can reenter the interface-ATM-VC configuration mode by simply entering svc name.
nsap-address is a 40-digit hexadecimal number.
Step 8
Specifies a protocol address for the SVC.
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Step 9
Exits VC configuration mode and returns to interface configuration mode.
Step 10
Sets the transmit clock mode for the group.
If all the links in the group should share a clock source, use the common keyword.
If each link uses a different clock source, use the independent clock source keyword. Using the port keyword, you can specify a link for common clocking. The default uses the common clock as the transmit clock source.
Step 11
When used with a number value from 1 to 8, specifies how many transmit links must be active in order for the IMA group to be operational. The setting you choose depends upon your performance requirements as well as the total number of links in the group. If fewer than the preset minimum are active, the group is automatically rendered inactive until the minimum number of links are up again. The default value is 1.
Step 12
Specifies the differential timing delay among the links in an IMA group by entering a milliseconds value from 25 to 250 for T1 and 25 to 190 for E1. If a link delay exceeds the specified maximum, the link is dropped; otherwise, the IMA feature adjusts for differences in delays so that all links in a group are aligned. A shorter value provides less resiliency in adjusting for variations than a higher value. However, a higher value might affect overall group performance, because increased differential delay adds more latency to the traffic that is transmitted across the group.
Step 13
Troubleshoots or diagnoses physical link connectivity. The IMA feature performs ongoing tests on all links in a group, to verify link connectivity. Use this command to specify a link to use for testing as well as a test pattern. The pattern is sent from the specified link and looped back from the receiving end in the multiplexing-demultiplexing process. A byte in the ICP cell identifies the pattern.
1 This command is new to Cisco 7200 series routers, but was introduced for other platforms in earlier releases. For more information about the command, see the Cisco IOS Release 12.0 documents, Wide Area Networking Configuration Guide and Wide Area Networking Command Reference.
2 Q Signalling ATM adaptation Layer
3 Subnetwork Access Protocol
4 To form an IMA group with independent clock mode, use the no shut command in the IMA interface only. To change the mode to independent from an already existing IMA group, use the no ima command on the IMA group links. Next, change the mode, add all the links, and then issue the no shut command in the IMA interface.
Verifying the IMA Group Configuration
Step 1
Important information is shown in bold.
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Router# show ima interface atm 1/ima0 detailATM1/ima0 is upImaGroupState:NearEnd = operational, FarEnd = operationalImaGroupFailureStatus = noFailureIMA Group Current Configuration:ImaGroupMinNumTxLinks = 2 ImaGroupMinNumRxLinks = 2ImaGroupDiffDelayMax = 25 ImaGroupNeTxClkMode = common(ctc)ImaGroupFrameLength = 128 ImaTestProcStatus = disabledImaGroupTestLink = 0 ImaGroupTestPattern = 0xFFIMA MIB Information:ImaGroupSymmetry = symmetricOperationImaGroupFeTxClkMode = common(ctc)ImaGroupRxFrameLength = 128ImaGroupTxTimingRefLink = 0 ImaGroupRxTimingRefLink = 0ImaGroupTxImaId = 0 ImaGroupRxImaId = 0ImaGroupNumTxCfgLinks = 2 ImaGroupNumRxCfgLinks = 2ImaGroupNumTxActLinks = 2 ImaGroupNumRxActLinks = 2ImaGroupLeastDelayLink = 1 ImaGroupDiffDelayMaxObs = 0IMA group counters:ImaGroupNeNumFailures = 78 ImaGroupFeNumFailures = 68ImaGroupUnAvailSecs = 441453 ImaGroupRunningSecs =445036IMA Detailed Link Information:ATM1/0 is upImaLinkRowStatus = LinkRowStatusUnknownImaLinkIfIndex = 0 ImaLinkGroupIndex = 0ImaLinkState:NeTx = activeNeRx = activeFeTx = activeFeRx = activeImaLinkFailureStatus:NeRx = noFailureFeRx = noFailureImaLinkTxLid = 0 ImaLinkRxLid = 0ImaLinkRxTestPattern = 65 ImaLinkTestProcStatus = disabledImaLinkRelDelay = 0IMA Link counters :ImaLinkImaViolations = 1ImaLinkNeSevErroredSec = 41 ImaLinkFeSevErroredSec = 34ImaLinkNeUnavailSec = 441505 ImaLinkFeUnAvailSec = 28ImaLinkNeTxUnusableSec = 2 ImaLinkNeRxUnUsableSec = 441542ImaLinkFeTxUnusableSec = 74 ImaLinkFeRxUnusableSec = 57ImaLinkNeTxNumFailures = 0 ImaLinkNeRxNumFailures = 15ImaLinkFeTxNumFailures = 4 ImaLinkFeRxNumFailures = 3ATM1/1 is upImaLinkRowStatus = LinkRowStatusUnknownImaLinkIfIndex = 1 ImaLinkGroupIndex = 0ImaLinkState:NeTx = activeNeRx = activeFeTx = activeFeRx = activeImaLinkFailureStatus:NeRx = noFailureFeRx = noFailureImaLinkTxLid = 1 ImaLinkRxLid = 1ImaLinkRxTestPattern = 65 ImaLinkTestProcStatus = disabledImaLinkRelDelay = 0IMA Link counters :ImaLinkImaViolations = 1ImaLinkNeSevErroredSec = 40 ImaLinkFeSevErroredSec = 42ImaLinkNeUnavailSec = 441389 ImaLinkFeUnAvailSec = 38ImaLinkNeTxUnusableSec = 2 ImaLinkNeRxUnUsableSec = 441427ImaLinkFeTxUnusableSec = 99 ImaLinkFeRxUnusableSec = 99ImaLinkNeTxNumFailures = 0 ImaLinkNeRxNumFailures = 16ImaLinkFeTxNumFailures = 4 ImaLinkFeRxNumFailures = 4Step 2
Router# show atm vcVCD / Peak Avg/Min BurstInterface Name VPI VCI Type Encaps SC Kbps Kbps Cells Sts1/1 1 0 50 PVC SNAP UBR 1000 INAC1/IMA3 2 0 5 PVC SAAL UBR 4000 UP1/IMA3 3 0 16 PVC ILMI UBR 4000 UP1/IMA3 first 1 13 PVC MUX VBR 640 320 80 UP1/IMA3 4 0 34 SVC SNAP VBR-RT 768 768 UP
Troubleshooting Tips
To troubleshoot ATM configuration and IMA group configuration, use the ping EXEC (user) or privileged EXEC command that checks host reachability and network connectivity. This command can confirm basic network connectivity on AppleTalk, International Organization for Standardization (ISO), Connectionless Network Service (CLNS), IP, Novell, Apollo, Virtual Integrated Network Service (VINES), DECnet, or Xerox Network Systems (XNS) networks.
For IP, the ping command sends Internet Control Message Protocol (ICMP) Echo messages. If a station receives an ICMP Echo message, it sends an ICMP Echo Reply message back to the source.
The extended command mode of the ping command permits you to specify the supported IP header options. This allows the router to perform a more extensive range of test options. To enter ping extended command mode, enter yes at the extended commands prompt of the ping command.
For detailed information on using the ping and extended ping commands, refer to the Cisco IOS Release 12.0 Configuration Fundamentals Command Reference.
If a ping command fails, check the following possible reasons for the connectivity problem:
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Tips
If a communication session is closing when it should not, an end-to-end connection problem can be the cause. The debug ip packet command is useful for analyzing the messages traveling between the local and remote hosts. IP debugging information includes packets received, generated, and forwarded. Because the debug ip packet command generates a significant amount of output, use it only when traffic on the IP network is low, so other activity on the system is not adversely affected.
Monitoring and Maintaining ATM Inverse Multiplexing
Configuration Examples
This section shows one sample configuration for a router that is set up for ATM T1 or E1 IMA.
T1 IMA Configuration
The following configuration example shows the setup of ATM interfaces, IMA groups, PVCs, and SVCs for T1 IMA.
version 12.0service timestamps debug uptimeservice timestamps log uptimeno service password-encryptionno service dhcp!hostname router!!!!!!ip subnet-zero!!!!!There are four links in IMA group 3. ATM interface 0/1 has a PVC configured on it, set to the default AAL5 SNAP encapsulation. The no scrambling cell-payload command is actually unnecessary, as this is the default for T1 links. Because the T1 default binary-eight zero substitution (B8ZS) line encoding is normally sufficient for proper cell delineation, this is the usual setting for T1 links, The scrambling setting must match the far-end receiver.
interface ATM0/0no ip addressno ip directed-broadcastloopback lineno atm ilmi-keepaliveima-group 3no scrambling cell-payloadno fair-queue!interface ATM0/1ip address 21.1.1.2 255.0.0.0no ip directed-broadcastno atm ilmi-keepalivepvc 0/50protocol ip 21.1.1.1 broadcast!ima-group 3no scrambling-payloadno fair-queue!interface ATM1/2no ip addressno ip directed-broadcastno atm ilmi-keepaliveima-group 3no scrambling-payloadno fair-queue!interface ATM0/3no ip addressno ip directed-broadcastno atm ilmi-keepaliveima-group 3no scrambling-payloadno fair-queue!!IMA group 3 has PVCs that are set up for SVC management and signaling. Two SVCs and a communications PVC are also set up on the group interface.
interface ATM0/IMA3no ip addressno ip directed-broadcastno atm ilmi-keepalivepvc 0/16 ilmi!pvc 0/5 qsaal!!pvc first 1/13vbr-nrt 640 320 80encapsulation aal5mux ip!!svc nsap 47.0091810000000002F26D4901.444444444444.01!The group commands below specify that three links must be active for the group to be operational. The common clock source is the first link, ATM 0/0, and ATM 0/1 is the test link. The differential delay maximum is set to 50 milliseconds (ms).
ima active-links-minimum 3ima clock-mode common 0ima differential-delay-maximum 50ima test link 1!interface Ethernet1/0no ip addressno ip directed-broadcastshutdown!interface Ethernet1/1no ip addressno ip directed-broadcastshutdown!ip classlessno ip http server!!!line con 0exec-timeout 0 0transport input noneline aux 0line vty 0 4login!!endCommand Reference
This section documents new or modified commands. All other commands used with this feature are documented in the Cisco IOS Release 12.0 command reference publications.
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bert pattern
To enable a bit error rate (BER) test pattern on a T1 or E1 line, use the bert controller configuration command. To disable a BER test pattern, use the no form of this command.
bert pattern {2^23 | 2^20 | 2^20-QRSS | 2^15 | 2^11 | 1s | 0s |alt-0-1} interval time
[no] bert pattern {2^23 | 2^20 | 2^20-QRSS | 2^15 | 2^11 | 1s | 0s |alt-0-1} interval time
Syntax Description
Defaults
Disabled
Command Modes
Controller configuration
Command History
11.1CC
The command was introduced.
12.0(5)XE
The command was enhanced as an ATM interface configuration command
Usage Guidelines
BER testing is supported on each of the T1 or E1 links and is done only over an unframed T1 or E1 signal, run on only one port at a time.
To view the BER test results, use the show controller atm EXEC command. The BERT results include the following information:
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When the T1 or E1 line has a BER test running, the line state is DOWN and the status field shows the current/last result of the test.
The bert pattern command is not written to NVRAM. This command is only used to test the T1 or E1 line for a short predefined interval and to avoid accidentally saving the command, which could cause the interface not to come up the next time the router reboots.
Examples
In the following example on a Cisco 7200 series router, a BER test pattern of all zeros is run for 30 minutes on T1 line 0 on the port adapter in slot 9:
int atm 9/0bert pattern 0s interval 30Related CommandsRelated Commands
framing
Use the framing controller configuration command to select the frame type for the T1 or E1 data line.
framing {sfadm | esfadm} (for T1 lines)
framing {crc4adm | pcm30adm | clear e1} (for E1 lines)
Syntax Description
Defaults
Extended Superframe (ESF) (for a T1 line)
Pcm30adm (for an E1 line)
Command Modes
Controller configuration
Command History
11.3
This command was introduced.
12.0(5)XE
The command was enhanced as an ATM interface configuration command.
Usage Guidelines
Use this command in configurations where the router or access server is intended to communicate with T1 or E1 fractional data line. The service provided determines which framing type, either sf, esf, or crc4, is required for your T1 or E1 circuit.
Examples
The following example selects Extended Superframe as the T1 frame type:
framing esfRelated Commands
lbo
Specifies the distance of the cable from the routers to the network equipment.
linecode
Selects the line-code type for a T1 or E1 line.
ima active-links-minimum
To set the minimum number of links that must be operational in order for an ATM IMA group to remain in service, execute the IMA interface configuration command ima active-links-minimum. The no form of the command removes the current configuration and sets the value to the default.
ima active-links-minimum number
no ima active-links-minimum number
Syntax Description
Defaults
One link
Command Modes
Interface configuration
Command History
Usage Guidelines
The minimum number of links that should be active for continued group operation depends upon the applications you are using and the speeds they require. ATM frame size and the number of links in a group affect the overhead required by ATM.
When planning, you should assume that only the bandwidth supplied by the minimal number of links will be available. If you decrease the value set in this command, make sure that virtual circuits of a higher bandwidth than the minimum supported by the command are torn down as necessary.
Examples
On Cisco 7200 series routers, the following example specifies that two links in IMA group 2 must be operational for the group to remain in service:
interface atm 2/ima2ima active-links-minimum 2ima clock-mode
To set the transmit clock mode for an ATM IMA group, execute the ima clock-mode IMA interface configuration command. If all the links in the group share a clock source, use the common keyword. If all the links use different clock sources, use the independent clock source keyword. The no form of the command removes the current configuration.
ima clock-mode {common <link_number> | independent}
no ima clock-mode
Syntax Description
Defaults
The default value is common. If no port is specified, the system automatically chooses an active link to provide clocking.
Command Modes
Interface configuration
Command History
Usage Guidelines
This command controls the clock for the IMA group as a whole. When the independent keyword is set, the clock source ATM interface configuration command is used under each interface to determine clocking individually. When the common keyword is set, the clock source ATM interface configuration command for the common link determines clocking for all the links in the group.
Because the system automatically chooses a replacement for the common link when it fails, any link in an IMA group potentially can provide the recovered transmit clock. For this reason, even when the common keyword is set with a specific link stipulated by the port value, it is a good idea to make sure that the clock source is configured correctly on each interface in the IMA group, using the ATM interface configuration clock-source command.
Examples
On Cisco 7200 series routers, the following example specifies that the links in IMA group 2 use a common clock source on link 0:
interface atm 1/ima2ima clock-mode common 0Related Commands
ima differential-delay-maximum
To specify a maximum differential timing delay among the links in an IMA group, use the ima differential-delay-maximum IMA interface configuration command. If a link delay exceeds the specified maximum, the link is dropped; otherwise, the IMA feature, while multiplexing and demultiplexing, adjusts for differences in delays so that all links in a group are aligned. The no form of the command restores the default setting.
ima differential-delay-maximum msec
no ima differential-delay-maximum msec
Syntax Description
msec
Specifies a value from 25 to 250 milliseconds for T1 and 25 to 190 for E1), to define the differential delay.
Defaults
25 milliseconds for T1
90 milliseconds for E1
Command Modes
Interface configuration
Command History
Usage Guidelines
This command controls latency in an IMA group by setting a limit on how much latency a slow link can introduce when links are aligned. Setting a high value allows a slow link to continue operating as part of the group, although such a setting means there is more potential for latency when a link is slow. A low setting provides better guaranteed bandwidth on active links and more resiliency than a high setting, although it can mean that the system takes a slow link out of operation.
When a link has been removed from service, it is automatically placed back in service when it meets the delay differential standard.
Examples
On Cisco 7200 series routers, the following example specifies that the links in IMA group 2 have a maximum differential delay of 50 ms:
interface atm 1/ima2ima differential-delay-maximum 50Related Commands
show ima interface atm [slot] /ima[group-number] [detail]
Displays differential delay information about an IMA group.
ima frame-length
To specify the number of cells in IMA frames, use the ima frame-length command. IMA frames are numbered sequentially and each contains an IMA Control Protocol (ICP) cell at a specific position. The no form of the command removes the current setting and restores the default value.
ima frame-length {32 | 64 | 128 | 256}
no ima frame-length {32 | 64 | 128 | 256}
Syntax Description
32
Specifies a value of 32 cells.
64
Specifies a value of 64 cells.
128
Specifies a value of 128 cells.
256
Specifies a value of 256 cells.
Defaults
The default value is 128 cells in a frame.
Command Modes
Interface configuration
Command History
Usage Guidelines
Frame length can affect performance, because the greater the total number of frames required to communicate a given number of cells, the greater the overhead for header and other control cells. In addition, shorter frame lengths might diminish performance when translated ATM-Frame Relay interworking occurs.
Examples
On Cisco 7200 series routers, the following example specifies that the links in IMA group 2 have a frame length of 64 cells:
interface atm 1/ima2ima frame-length 64ima-group
To define physical links as IMA group members, execute the ima-group configuration command for each group member. When you first perform the configuration or when you change the group number, the interface is automatically disabled, moved to the new group, and then enabled. The no form of the command removes the port from the group.
ima-group group-number
no ima-group group-number
Syntax Description
group-number
Enter an IMA group number from 0 to 3. IMA groups can span multiple ports on a port adapter but cannot span port adapters.
Defaults
Physical links are not part of IMA group by default.
Command Modes
Interface configuration
Command History
Examples
On Cisco 7200 series routers, the following example makes interface 1 on the ATM port adapter in
slot 1 a member of IMA group 1:interface atm 1/1ima-group 1Related Commands
ima test
To specify an interface and a test pattern, execute the ima test IMA configuration command. To verify link connectivity, the pattern is sent from the specified link and looped back from the receiving end in the multiplexing-demultiplexing process. This can help troubleshoot physical link connectivity or configuration problems at the remote end. All links in the group are tested, and testing is continuous. An ICP cell in each frame identifies the pattern. The no form of the command returns to default settings.
ima test [link port] [pattern pattern-id]
no ima test [link port] [pattern pattern-id]
Syntax Description
Defaults
There is no default for the port value. The default value for pattern-id is 0xFF (255).
Command Modes
Interface configuration
Command History
Usage Guidelines
When a link is not transmitting or receiving a pattern correctly, the command reports the link number where the problem exists.
Examples
On Cisco 7200 series routers, the following example configures link 4 to send test pattern 56.
interface atm 1/ima 2ima test link 4 pattern 5Related Commands
show ima interface atm [slot] /ima[group-number] [detail]
Shows the currently configured test link and test pattern for an IMA group.
interface atm ima
To configure an ATM IMA group and enter interface configuration mode, use the interface atm ima global configuration command. If the group does not exist when the command is issued, the command automatically creates the group.
interface atm slot/ima<group-number>
Syntax Description
Defaults
By default there are no IMA groups, only individual ATM links.
Command Modes
Global configuration
Command History
Usage Guidelines
When a port is configured for IMA functionality, it no longer operates as an individual ATM link.
Specifying ATM links as members of a group using the ima group interface command does not enable the group. You must use the interface atm slot/ima<group-number> command to create the group.
Examples
On Cisco 7200 series routers, the following example configures IMA group 0 on the port adapter in slot 1:
interface atm 1/ima0 ip address 255.255.255.0Related Commands
lbo
To set a cable length longer than 655 feet for a DS-1 link, use the lbo interface configuration command on the interface for a T1 link. The no form of this command deletes the lbo long value.
lbo {long {gain26 | gain36} {-15db | -22.5db | -7.5db | 0db} | short {133 | 266 | 399 | 533 | 655}}
no lbo
Syntax Description
Defaults
Gain26 and 0db
Command Modes
Interface configuration
Command History
11.3 MA
This command was introduced as a Cisco MC3810 controller configuration command.
12.0(5)XE
The command was introduced as an ATM interface command.
Usage Guidelines
This command is supported on T1 links only.
Each T1 port can operate in long-haul or short-haul mode. In long haul mode the user must specify the gain and the line build out. In short-haul mode, the user must specify the cable length in feet.
The transmit attenuation value is best obtained by experimentation. If the signal received by the far-end equipment is too strong, reduce the transmit level by entering additional attenuation.
Examples
On Cisco 7200 series routers, the following example specifies a pulse gain of 36 and a decibel pulse rate of -7.5 decibels:
interface atm 1/2lbo long gain36 -7.5dbloopback
To loop packets back to the interface for testing, enter the loopback interface configuration command with or without an optional keyword. The no form of the command removes the loopback.
loopback {diagnostic | local {payload | line} | remote {iboc | esf {payload | line}}}
(for T1 lines)loopback {diagnostic | local {payload | line}} (for E1 lines)
no loopback
Syntax Description
Defaults
No loopback
Command Modes
Interface configuration
Command History
11.1
This command was introduced as a controller configuration command for the Cisco MC3810.
12.0(5)XE
The command was introduced as an ATM interface configuration command.
Usage Guidelines
You can use a loopback test on lines to detect and distinguish equipment malfunctions caused either by line and channel service unit/data service unit (CSU/DSU) or by the interface. If correct data transmission is not possible when an interface is in loopback mode, the interface is the source of the problem.
The local loopback does not generate any packets automatically. Instead, the ping command is used.
Examples
On Cisco 7200 series routers, the following example sets up local loopback diagnostics:
interface atm 1/0loopback local linenational reserve
To set the E1 national bit, enter the national reserve interface configuration command. To return to the default E1 national bit, use the no form of this command.
national reserve <0-1><0-1><0-1><0-1><0-1><0-1>
no national reserve
Syntax Description
This command has no arguments or keywords.
Defaults
111111
Command Modes
Interface configuration
Command History
Usage Guidelines
This command applies only for E1. This command not only sets the national reserve bits but also the international bit as well. The far left digit represents the international bit. All six digits must be present for the pattern to be valid.
Examples
On Cisco 7200 series routers, the following example sets the national bit on interface 1 on the port adapter in slot 0 to no scrambling:
interface atm1/0national reserve 011011scrambling cell-payload
Scrambling improves data reliability by randomizing the ATM cell payload frames to avoid continuous nonvariable bit patterns and improve the efficiency of ATM cell delineation algorithms. The no form disables scrambling.
scrambling cell-payload
no scrambling cell-payload
Syntax Description
This command has no arguments or keywords.
Defaults
No scrambling
Command Modes
Interface configuration
Command History
Usage Guidelines
Normally, you do not issue the scrambling-payload command explicitly, because the default value is sufficient. On T1 links, the default b8zs line encoding normally assures sufficient reliability. The default for E1 is hdb3.
The scrambling setting must match that of the far-end receiver.
Examples
On Cisco 7200 series routers, the following example sets the link on interface 1 on the port adapter in slot 0 to no scrambling:
interface atm0/1no scrambling cell-payloadshow controllers atm
Use the privileged EXEC show controllers command to see information about an IMA group. Important information is shown in bold.
show controllers [atm slot/port-adapter/port] (physical port hardware information) (for Cisco 7500 series routers)
show controllers [atm slot/port-adapter/imagroup-number] (IMA group hardware information) (for Cisco 7500 series)
show controller [atm slot/port] (for the Cisco 7200 series routers)
show controllers [atm slot/imagroup-number] (for Cisco 7200 series routers )
Syntax Description
Defaults
No default behavior or values.
Command Modes
Privileged EXEC
Command History
Usage Guidelines
Use this command to monitor and diagnose ATM IMA links and groups.
Examples
On Cisco 7200 series routers, the following example displays detailed information about IMA group hardware related information. It includes the configuration of IMA hardware and IMA alarms.
Router# show controller atm 1/ima0Interface ATM1/ima0 is upHardware is IMA PA - DS1 (1Mbps)Framer is PMC PM7344, SAR is LSI ATMIZER IIFirmware rev:G102, ATMIZER II rev:3idb=0x61DE9F10, ds=0x6185C0A0, vc=0x6187D3C0, pa=0x6184AF40slot 1, unit 9, subunit 0, fci_type 0x00BA, ticks 701720400 rx buffers:size=512, encap=64, trailer=28, magic=4Curr Stats:rx_cell_lost=0, rx_no_buffer=0, rx_crc_10=0rx_cell_len=0, rx_no_vcd=0, rx_cell_throttle=0, tx_aci_err=0Rx Free Ring status:base=0x3CFF0040, size=1024, write=320Rx Compl Ring status:base=0x338DCE40, size=2048, read=1275Tx Ring status:base=0x3CFE8040, size=8192, write=700Tx Compl Ring status:base=0x338E0E80, size=2048, read=344BFD Cache status:base=0x61878340, size=5120, read=5107Rx Cache status:base=0x61863D80, size=16, write=11Tx Shadow status:base=0x618641C0, size=8192, read=687, write=700Control data:rx_max_spins=12, max_tx_count=25, tx_count=13rx_threshold=267, rx_count=11, tx_threshold=3840tx bfd write indx=0x27, rx_pool_info=0x61863E20Control data base address:rx_buf_base = 0x038A15A0 rx_p_base = 0x6185CB40rx_pak = 0x61863AF0 cmd = 0x6185C320device_base = 0x3C800000 ima_pa_stats = 0x038E2FA0sdram_base = 0x3CE00000 pa_cmd_buf = 0x3CFFFC00vcd_base[0] = 0x3CE3C100 vcd_base[1] = 0x3CE1C000chip_dump = 0x038E3D7C dpram_base = 0x3CD80000sar_buf_base[0] = 0x3CE4C000 sar_buf_base[1] = 0x3CF22000bfd_base[0] = 0x3CFD4000 bfd_base[1] = 0x3CFC0000acd_base[0] = 0x3CE88360 acd_base[1] = 0x3CE5C200pci_atm_stats = 0x038E2EC0ATM1/ima0 is uphwgrp number = 1grp tx up reg= 0x5, grp rx up reg= 0x3, rx dcb reg= 0xD4 0x4, tx links grp reg=0x3, scci reg= 0x3C, ima id reg= 0x0, group status reg= 0xA2, tx timing reg= 0x20, tx test reg= 0x21, tx test pattern reg= 0x41, rx test pattern reg= 0x42, icpcell link info reg= 0xFC, icp cell link info reg= 0xFC, icp cell link info reg= 0x0, icp cell link info reg= 0x0, icp cell link info reg= 0x0, icp cell link info reg= 0x0, icp cell link info reg= 0x0, icp cell link info reg= 0x0,Related Commands
show ima interface atm [slot] /ima[group-number] [detail]
Displays general and detailed information about IMA groups and the links they include.
show ima interface
The show ima interface command provides information about all configured IMA groups or a specific group.
show ima interface [atm slot/port-adapter/slot] [detail] (for Cisco 7500 series routers)
show ima interface [atm slot/port-adapter/ima group-number] [detail] (for Cisco 7500 series routers)
show ima interface [atm slot/port] [detail] (for Cisco 7200 series routers)
show ima interface [atm slot/port-adapter/ima group-number] [detail] (for Cisco 7200 series routers)
Syntax Description
Defaults
No default behavior or values.
Command Modes
Privileged EXEC
Command History
Usage Guidelines
Use this command to monitor the status of IMA group links.
Examples
On Cisco 7200 series routers, the following example displays detailed information about IMA group 0 on ATM interface 2. If you do not enter the detail keyword, the information beginning with "Detailed group Information:" does not appear.
Router#sh ima int atm 5/ima0 detailATM5/ima0 is upImaGroupState:NearEnd = operational, FarEnd = operationalImaGroupFailureStatus = noFailureIMA Group Current Configuration:ImaGroupMinNumTxLinks = 2 ImaGroupMinNumRxLinks = 2ImaGroupDiffDelayMax = 250 ImaGroupNeTxClkMode = common(ctc)ImaGroupFrameLength = 128 ImaTestProcStatus = disabledImaGroupTestLink = 0 ImaGroupTestPattern = 0xFFIMA MIB Information:ImaGroupSymmetry = symmetricOperationImaGroupFeTxClkMode = common(ctc)ImaGroupRxFrameLength = 128ImaGroupTxTimingRefLink = 0 ImaGroupRxTimingRefLink = 0ImaGroupTxImaId = 0 ImaGroupRxImaId = 0ImaGroupNumTxCfgLinks = 2 ImaGroupNumRxCfgLinks = 2ImaGroupNumTxActLinks = 2 ImaGroupNumRxActLinks = 2ImaGroupLeastDelayLink = 0 ImaGroupDiffDelayMaxObs = 0IMA group counters:ImaGroupNeNumFailures = 1 ImaGroupFeNumFailures = 2ImaGroupUnAvailSecs = 18 ImaGroupRunningSecs = 241IMA Detailed Link Information:ATM5/0 is upImaLinkRowStatus = activeImaLinkIfIndex = 1 ImaLinkGroupIndex = 47ImaLinkState:NeTx = activeNeRx = activeFeTx = activeFeRx = activeImaLinkFailureStatus:NeRx = noFailureFeRx = noFailureImaLinkTxLid = 0 ImaLinkRxLid = 0ImaLinkRxTestPattern = 64 ImaLinkTestProcStatus = disabledImaLinkRelDelay = 0IMA Link counters :ImaLinkImaViolations = 1ImaLinkNeSevErroredSec = 10 ImaLinkFeSevErroredSec = 10ImaLinkNeUnavailSec = 7 ImaLinkFeUnAvailSec = 8ImaLinkNeTxUnusableSec = 17 ImaLinkNeRxUnUsableSec = 16ImaLinkFeTxUnusableSec = 17 ImaLinkFeRxUnusableSec = 16ImaLinkNeTxNumFailures = 0 ImaLinkNeRxNumFailures = 2ImaLinkFeTxNumFailures = 1 ImaLinkFeRxNumFailures = 1ATM5/1 is upImaLinkRowStatus = activeImaLinkIfIndex = 2 ImaLinkGroupIndex = 47ImaLinkState:NeTx = activeNeRx = activeFeTx = activeFeRx = activeImaLinkFailureStatus:NeRx = noFailureFeRx = noFailureImaLinkTxLid = 1 ImaLinkRxLid = 1ImaLinkRxTestPattern = 64 ImaLinkTestProcStatus = disabledImaLinkRelDelay = 0IMA Link counters :ImaLinkImaViolations = 1ImaLinkNeSevErroredSec = 10 ImaLinkFeSevErroredSec = 10ImaLinkNeUnavailSec = 7 ImaLinkFeUnAvailSec = 8ImaLinkNeTxUnusableSec = 16 ImaLinkNeRxUnUsableSec = 16ImaLinkFeTxUnusableSec = 16 ImaLinkFeRxUnusableSec = 16ImaLinkNeTxNumFailures = 0 ImaLinkNeRxNumFailures = 2ImaLinkFeTxNumFailures = 1 ImaLinkFeRxNumFailures = 1Related Commands
show controllers [atm slot//ima group-number]
Displays detailed information about IMA groups and the links they include, as well as about current queues and ATM QoS settings.
show ima interface atm
The show ima interface atm command provides information about all configured IMA groups or a specific group.
show ima interface atm [slot] /ima[group-number] [detail]
Syntax DescriptionSyntax Description
Defaults
No default behavior or values.
Command Modes
Privileged EXEC
Command History
Usage Guidelines
Use this command to monitor the status of IMA group links.
Examples
On Cisco 7200 series routers, the following example displays detailed information about IMA group 0 on ATM interface 2. If you do not enter the detail keyword, the information beginning with "Detailed group Information:" does not appear.
Router#sh ima int atm 5/ima0 detailATM5/ima0 is upImaGroupState:NearEnd = operational, FarEnd = operationalImaGroupFailureStatus = noFailureIMA Group Current Configuration:ImaGroupMinNumTxLinks = 2 ImaGroupMinNumRxLinks = 2ImaGroupDiffDelayMax = 250 ImaGroupNeTxClkMode = common(ctc)ImaGroupFrameLength = 128 ImaTestProcStatus = disabledImaGroupTestLink = 0 ImaGroupTestPattern = 0xFFIMA MIB Information:ImaGroupSymmetry = symmetricOperationImaGroupFeTxClkMode = common(ctc)ImaGroupRxFrameLength = 128ImaGroupTxTimingRefLink = 0 ImaGroupRxTimingRefLink = 0ImaGroupTxImaId = 0 ImaGroupRxImaId = 0ImaGroupNumTxCfgLinks = 2 ImaGroupNumRxCfgLinks = 2ImaGroupNumTxActLinks = 2 ImaGroupNumRxActLinks = 2ImaGroupLeastDelayLink = 0 ImaGroupDiffDelayMaxObs = 0IMA group counters:ImaGroupNeNumFailures = 1 ImaGroupFeNumFailures = 2ImaGroupUnAvailSecs = 18 ImaGroupRunningSecs = 241IMA Detailed Link Information:ATM5/0 is upImaLinkRowStatus = activeImaLinkIfIndex = 1 ImaLinkGroupIndex = 47ImaLinkState:NeTx = activeNeRx = activeFeTx = activeFeRx = activeImaLinkFailureStatus:NeRx = noFailureFeRx = noFailureImaLinkTxLid = 0 ImaLinkRxLid = 0ImaLinkRxTestPattern = 64 ImaLinkTestProcStatus = disabledImaLinkRelDelay = 0IMA Link counters :ImaLinkImaViolations = 1ImaLinkNeSevErroredSec = 10 ImaLinkFeSevErroredSec = 10ImaLinkNeUnavailSec = 7 ImaLinkFeUnAvailSec = 8ImaLinkNeTxUnusableSec = 17 ImaLinkNeRxUnUsableSec = 16ImaLinkFeTxUnusableSec = 17 ImaLinkFeRxUnusableSec = 16ImaLinkNeTxNumFailures = 0 ImaLinkNeRxNumFailures = 2ImaLinkFeTxNumFailures = 1 ImaLinkFeRxNumFailures = 1ATM5/1 is upImaLinkRowStatus = activeImaLinkIfIndex = 2 ImaLinkGroupIndex = 47ImaLinkState:NeTx = activeNeRx = activeFeTx = activeFeRx = activeImaLinkFailureStatus:NeRx = noFailureFeRx = noFailureImaLinkTxLid = 1 ImaLinkRxLid = 1ImaLinkRxTestPattern = 64 ImaLinkTestProcStatus = disabledImaLinkRelDelay = 0IMA Link counters :ImaLinkImaViolations = 1ImaLinkNeSevErroredSec = 10 ImaLinkFeSevErroredSec = 10ImaLinkNeUnavailSec = 7 ImaLinkFeUnAvailSec = 8ImaLinkNeTxUnusableSec = 16 ImaLinkNeRxUnUsableSec = 16ImaLinkFeTxUnusableSec = 16 ImaLinkFeRxUnusableSec = 16ImaLinkNeTxNumFailures = 0 ImaLinkNeRxNumFailures = 2ImaLinkFeTxNumFailures = 1 ImaLinkFeRxNumFailures = 1Related Commands
show controllers [atm slot//ima group-number]
Displays detailed information about IMA groups and the links they include, as well as about current queues and ATM QoS settings.
yellow
The yellow command enables generation and detection of yellow alarm. This command is applicable to the T1 IMA port adapter.
yellow {generation | detection}
Syntax DescriptionSyntax Description
generation
This setting enables or disables generation of the yellow alarm.
detection
This setting enables or disables detection of the yellow alarm.
Defaults
Yellow alarm generation and detection are enabled.
Command Modes
Configuration mode
Command History
Usage Guidelines
Use this command to generate and detect yellow alarms.
Examples
The following example displays yellow generation and detection enabled on a Cisco 7500 series router:
interface atm 3/1/0yellow generationyellow detectionRelated Commands
show controllers [atm slot/ima group-number]
Displays detailed information about IMA groups and the links they include, as well as about current queues.
Glossary
AAL1—ATM adaptation layer 1. One of four AALs recommended by the ITU-T. AAL1 is used for connection-oriented, delay-sensitive services requiring constant bit rates, such as uncompressed video and other isochronous traffic.
AAL5—ATM adaptation layer 5. One of four AALs recommended by the ITU-T. AAL5 supports connection-oriented VBR services and is used predominantly for the transfer of classical IP over ATM and LANE traffic. AAL5 uses simple and efficient AAL (SEAL) and is the least complex of the current AAL recommendations. It offers low bandwidth overhead and simpler processing requirements in exchange for reduced bandwidth capacity and error-recovery capability.
ABR—available bit rate. QoS class defined by the ATM Forum for ATM networks. ABR is used for connections that do not require timing relationships between source and destination. ABR provides no guarantees in terms of cell loss or delay, providing only best-effort service. Traffic sources adjust their transmission rate in response to information they receive describing the status of the network and its capability to successfully deliver data.
AIS—alarm indication signal. In a T1 transmission, an all-ones signal transmitted in lieu of the normal signal to maintain transmission continuity and to indicate to the receiving terminal that there is a transmission fault that is located either at, or upstream from, the transmitting terminal.
ATM—Asynchronous Transfer Mode. International standard for cell relay in which multiple service types (such as voice, video, or data) are conveyed in fixed-length (53-byte) cells. Fixed-length cells allow cell processing to occur in hardware, thereby reducing transit delays. ATM is designed to take advantage of high-speed transmission media such as E3, SONET, and T3.
B8ZS—binary 8-zero substitution. Line-code type, used on T1 circuits, in which a special code is substituted whenever 8 consecutive zeros are sent over the link. This code is then interpreted at the remote end of the connection. This technique guarantees ones density independent of the data stream.
CPCS—common part convergence sublayer. One of the two sublayers of any AAL. The CPCS is service-independent and is further divided into the CS and the SAR sublayers. The CPCS is responsible for preparing data for transport across the ATM network, including the creation of the 48-byte payload cells that are passed to the ATM layer.
CS—convergence sublayer. One of the two sublayers of the AAL common part convergence sublayer (CPCS), which is responsible for padding and error checking. PDUs passed from the service specific convergence sublayer (SSCS) are appended with an 8-byte trailer (for error checking and other control information) and padded, if necessary, so that the length of the resulting PDU is divisible by 48. These PDUs are then passed to the SAR sublayer of the CPCS for further processing.
ESF—Extended Superframe. Framing type used on T1 circuits that consists of 24 frames of 192 bits each, with the 193rd bit providing timing and other functions. ESF is an enhanced version of SF.
FDL—Facility Data Link. A 4-Kbps channel, provided by the Extended SuperFrame (ESF) T1 framing format. The FDL performs outside the payload capacity and allows a service provider to check error statistics on terminating equipment, without intrusion.
ICP—IMA control protocol
ICMP—Internet Control Message Protocol. Network layer Internet protocol that reports errors and provides other information relevant to IP packet processing. Documented in RFC 792.
ILMI—Interim Local Management Interface. Specification developed by the ATM Forum for incorporating network-management capabilities into the ATM User-Network Interface (UNI).
IMA—Inverse Multiplexing for ATM, a standard protocol defined by the ATM Forum in 1997.
IMA group—Physical links grouped to form a higher-bandwidth logical link whose rate is approximately the sum of the individual link rates.
ISDN—Integrated Services Digital Network. Communication protocol, offered by telephone companies, that permits telephone networks to carry data, voice, and other source traffic.
OAM cell—Operation, Administration, and Maintenance cell. ATM Forum specification for cells used to monitor virtual circuits. OAM cells provide a virtual circuit-level loopback in which a router responds to the cells, demonstrating that the circuit is up, and the router is operational.
PDU—protocol data unit.
POTS—Plain Old Telephone Service. Basic telephone service supplying standard single-line telephones, telephone lines, and access to the public switched telephone network.
PVC—permanent virtual circuit. Virtual circuit that is permanently established. PVCs save bandwidth associated with circuit establishment and tear down in situations where certain virtual circuits must exist all the time. In ATM terminology, called a permanent virtual connection.
QoS—quality of service. Measure of performance for a transmission system that reflects its transmission quality and service availability.
SAR—segmentation and reassembly. One of the two sublayers of the AAL CPCS, responsible for dividing (at the source) and reassembling (at the destination) the PDUs passed from the CS. The SAR sublayer takes the PDUs processed by the CS and, after dividing them into 48-byte pieces of payload data, passes them to the ATM layer for further processing.
SF—Super Frame. Common framing type used on T1 circuits. SF consists of 12 frames of 192 bits each, with the 193rd bit providing error checking and other functions. SF is superseded by ESF, but is still widely used. Also called D4 framing.
SONET—Synchronous Optical Network. High-speed (up to 2.5 Gbps) synchronous network specification developed by Bellcore and designed to run on optical fiber. STS-1 is the basic building block of SONET.
SSCS—service specific convergence sublayer. One of the two sublayers of any AAL. SSCS, which is service dependent, offers assured data transmission. The SSCS can be null as well, in classical IP over ATM or LAN emulation implementations.
SVC—switched virtual circuit. Virtual circuit that is dynamically established on demand and is torn down when transmission is complete. SVCs are used in situations where data transmission is sporadic. Called a switched virtual connection in ATM terminology.
T3—Digital WAN carrier facility. T3 transmits DS-3-formatted data at 44.736 Mbps through the telephone switching network.
UBR—unspecified bit rate. Quality of Service (QoS) class defined by the ATM Forum for ATM networks. UBR allows any amount of data up to a specified maximum to be sent across the network, but there are no guarantees in terms of cell loss rate and delay.
UNI—User-Network Interface. ATM Forum specification that defines an interoperability standard for the interface between ATM-based products (a router or an ATM switch) located in a private network and the ATM switches located within the public carrier networks. Also used to describe similar connections in Frame Relay networks.
VBR—variable bit rate. QoS class defined by the ATM Forum for ATM networks. VBR is subdivided into a real time (RT) class and non-real time (NRT) class. VBR (RT) is used for connections in which there is a fixed timing relationship between samples. VBR (NRT) is used for connections in which there is no fixed timing relationship between samples, but that still need a guaranteed QoS.
VC—virtual circuit. Logical circuit created to ensure reliable communication between two network devices. A virtual circuit is defined by a VPI/VCI pair, and can be either permanent (PVC) or switched (SVC). Virtual circuits are used in Frame Relay and X.25. In ATM, a virtual circuit is called a virtual channel.
