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This document describes the Cisco Cable Clock Card feature for the Cisco uBR7246 VXR universal broadband router. The cable clock card enables the cable router to synchronize to an external T1 timing reference and distribute the clock to its Cisco MC16S and MC16E cable modem cards. The synchronized Data-over-Cable System Interface Specification (DOCSIS) time stamps are then passed downstream to all cable modems. The clock card is designed for cable networks running Voice-over-IP (VoIP) applications where synchronized timing is vital for maintaining voice quality.
To use this feature, you must install a cable clock card in the Cisco uBR7246 VXR. For information about installing the cable clock card, see the Cisco Cable Clock Card Hardware Installation Guide.
This document includes the following sections:
Because voice streams are real-time and originate at a synchronized fixed rate, it is important to configure synchronous clocking for voice applications; otherwise overruns and underruns could occur at the cable modem coder-decoder (codec), resulting in data corruption and loss. By ensuring synchronized data transmission, the clock card enables high-quality delivery of IP telephony, fax, and analog modem services over DOCSIS-based networks.
The clock card locks to an external T1 timing signal supplied by a global positioning satellite (GPS) receiver or a T1 Building Independent Timing Source (BITS) reference from the Public Switched Telephone Network (PSTN). It drives the time stamp clock for its cable modem cards, which ultimately send the time stamp downstream to the cable modems, providing synchronized timing among the cable modems regardless of location. In addition, the clock card automatically provides the timing reference for the midplane TDM clock.
Figure 1 shows an example of the cable clock card passing synchronization downstream to Cisco uBR924 access routers.
The clock card operates in four modes, depending on the timing source:
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Note A port adapter that supports this feature is not currently available for the Cisco uBR7246 VXR. |
If the primary external source fails, the clock card enters holdover mode. After a few seconds, it switches over to the secondary external source. The clock card switches back to the primary external source when it becomes available.
Figure 2 shows an example of the clocking sources and distribution when the clock card is locked to the primary external source.
Standards
No new or modified standards are supported by this feature.
MIBs
No new or modified MIBs are supported by this feature.
For descriptions of supported MIBs and how to use MIBs, see the Cisco MIB web site on CCO at http://www.cisco.com/public/sw-center/netmgmt/cmtk/mibs.shtml.
RFCs
No new or modified RFCs are supported by this feature.
The Cable Clock Card feature requires specific service, software, and hardware:
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Note When the cable clock card is installed in the chassis, it automatically drives the DOCSIS time stamps for the Cisco MC16S and MC16E cable modem cards. No special configuration of these cable modem cards is required to support the clock card features. |
No configuration tasks are required to use the clock card after it is installed in the chassis. When the clock card is present, it becomes the midplane TDM clock reference source. See the following sections for optional configuration tasks:
No configuration tasks are required to use the cable clock card after it is installed in the chassis. If however, you want to select the external timing reference for the clock card when it is in holdover mode, perform the following optional task in global configuration mode:
| Command | Purpose |
|---|---|
Router(config)# cable clock force {primary | secondary}
| Overrides the default behavior of the clock card to allow you to select the external timing source, when the clock card is in holdover mode. |
The following steps use show commands to verify that the clock card is installed and operating correctly.
Router# show version ---- cut ---- cisco uBR7246VXR (NPE300) processor (revision B) with 122880K/40960K bytes of memory. Processor board ID SAB0329005N R7000 CPU at 262Mhz, Implementation 39, Rev 1.0, 256KB L2, 2048KB L3 Cache 6 slot VXR midplane, Version 2.0 Last reset from power-on X.25 software, Version 3.0.0. National clock card with T1 controller 1 FastEthernet/IEEE 802.3 interface(s) 2 Cable Modem network interface(s) 125K bytes of non-volatile configuration memory. ---- cut ----
Step 2 Use the show cable clock command to display the status of the external clock sources. Verify that the primary and secondary sources are present and whether the clock card is in holdover or free-running mode.
Router# show cable clock Clockcard primary input is present Clockcard secondary input is present Cable clock reference is clockcard primary input Cable3/0 Timestamp clock reference is from Clockcard Cable4/0 Timestamp clock reference is from Clockcard
Step 3 Use the show controllers clock-reference command to display hardware information, register values, and current counters for the clock card. The example below shows that the primary external timing source is available, and the secondary source is not.
Router# show controllers clock-reference National clock card with T1 controller Control register :0x4 Status register :0x54 LIU Config Register 0:0x0 LIU Config Register 1:0x0 1 events reported in 266636 seconds Primary active :1, LOS :0 Secondary active :0, LOS :1 Holdovers :0, HW faults :0
Step 4 Display the running configuration file with the show running-config command. Verify that the configuration is accurate for the system and for any optional clock card commands. For a sample configuration screen, see the "Configuration Examples" section.
The following commands are used to monitor and maintain the cable clock card:
| Command | Purpose |
|---|---|
Router# show cable clock | Displays the clock reference status information for the clock card. |
Router# show controllers clock-reference | Displays hardware information, register values, and current counters for the clock card. |
Router# cable clock clear-counters | Resets the counters that are displayed with the show controllers clock-reference command. |
The following example displays the screen output using the show running-config command:
! version 12.1 no service pad service timestamps debug datetime msec localtime service timestamps log datetime msec localtime no service password-encryption service udp-small-servers service tcp-small-servers ! hostname VXR1 ! boot system flash slot0:ubr7200-p-mz.121-0.8.T boot system bootflash: ! no cable qos permission create no cable qos permission update cable qos permission modems cable clock source-midplane no cable clock force primary no cable clock force secondary ! ! clock timezone PST -8 clock summer-time PDT recurring clock calendar-valid ip subnet-zero ip host abrick 192.168.255.255 ! ! interface FastEthernet0/0 ip address 10.0.0.0 10.255.255.255 no ip route-cache no ip mroute-cache no keepalive half-duplex ! interface Cable3/0 ip address 172.16.0.0 172.31.255.255 no keepalive cable downstream annex B cable downstream modulation 64qam cable downstream interleave-depth 32 cable upstream 0 frequency 20000000 cable upstream 0 power-level 0 no cable upstream 0 shutdown cable upstream 1 shutdown cable upstream 2 shutdown cable upstream 3 shutdown cable upstream 4 shutdown cable upstream 5 shutdown cable helper-address 10.0.0.2 ! interface Cable4/0 no ip address no keepalive shutdown cable downstream annex B cable downstream modulation 64qam cable downstream interleave-depth 32 cable upstream 0 shutdown cable upstream 1 shutdown cable upstream 2 shutdown cable upstream 3 shutdown cable upstream 4 shutdown cable upstream 5 shutdown ! ip default-gateway 10.0.0.0 ip classless ip route 172.16.0.0 10.0.0.0 10.255.255.255 no ip http server ! ! line con 0 exec-timeout 0 0 length 0 transport input none line aux 0 line vty 0 4 exec-timeout 0 0 no login ! end
This section documents new or modified commands. All other commands used with this feature are documented in the Cisco IOS Release 12.1 command reference publications.
New Commands
Modified Commands
In Cisco IOS Release 12.0(1)T or later, you can search and filter the output for show and more commands. This functionality is useful when you need to sort through large amounts of output, or if you want to exclude output that you do not need to see.
To use this functionality, enter a show or more command followed by the "pipe" character (|), one of the keywords begin, include, or exclude, and an expression that you want to search or filter on:
command | {begin | include | exclude} regular-expressionFollowing is an example of the show atm vc command in which you want the command output to begin with the first line where the expression "PeakRate" appears:
show atm vc | begin PeakRateFor more information on the search and filter functionality, refer to the Cisco IOS Release 12.0(1)T feature module titled CLI String Search.
To reset the counters that are displayed with the show controllers clock-reference command, use the cable clock clear-counters privileged EXEC command.
cable clock clear-countersSyntax Description
This command has no keywords or arguments.
Defaults
No default behavior or values.
Command Modes
Privileged EXEC
Command History
12.1(1)T This command was introduced.
Release
Modification
Usage Guidelines
This command resets any counters that were displayed from the last time the show controllers clock-reference command was used.
Examples
The following example resets all counters that are displayed for the clock card:
cable clock clear-counters
Related Commands
Displays the cable clock card's hardware information.
Command
Description
To select the external timing source when the clock card is in holdover mode, use the cable clock force global configuration command. To disable the selection and return to the default, use the no form of this command.
cable clock force {primary | secondary}
Syntax Description
primary Forces the primary source to act as the clock reference. secondary Forces the secondary source to act as the clock reference.
Defaults
The clock card automatically uses the primary external source, if available. If the primary source fails, the clock card enters holdover mode and after a few seconds, switches to the secondary external source. The clock card switches back to the primary source when it becomes available.
Command Modes
Global configuration
Command History
12.1(1)T This command was introduced.
Release
Modification
Usage Guidelines
This command overrides the default behavior of the clock card, when the clock card is in holdover mode. If the clock card is not in holdover mode, this command is ignored. You cannot force the reference to a port if the clock card is in free-running mode.
|
Note The clock card enters holdover mode if the forced reference is lost, even if the other external reference is available. |
Examples
The following example forces the timing reference for the cable clock card to come from the secondary external source, when the clock card is in holdover mode:
cable clock force secondary
Related Commands
Displays status information for the cable clock card. Displays hardware information, register values, and current counters for the cable clock card.
Command
Description
To make the midplane TDM clock the primary timing reference for the clock card, use the cable clock source-midplane global configuration command. To disable the selection and return to the default, use the no form of this command.
cable clock source-midplaneSyntax Description
This command has no keywords or arguments.
Defaults
The clock card does not get its timing reference from the midplane TDM clock.
Command Modes
Global configuration
Command History
12.1(1)T This command was introduced.
Release
Modification
Usage Guidelines
Because the clock card automatically provides the timing reference to the midplane TDM clock, the midplane cannot in turn act as the reference for the clock card. This means that the cable clock source-midplane command does not take effect unless a port adapter is configured as the primary clock reference source for the midplane.
|
Note Although the cable clock source-midplane command is configurable, it is ignored, until a port adapter that can serve as the midplane clock reference source is supported in the Cisco uBR7246 VXR. |
Examples
The following example sets the primary clock reference to the midplane TDM clock:
cable clock source-midplane
Related Commands
Displays status information for the cable clock card.
Command
Description
To display clock reference status information for the clock card, use the show cable clock privileged EXEC command.
show cable clockSyntax Description
This command has no keywords or arguments.
Defaults
No default behavior or values.
Command Modes
Privileged EXEC
Command History
12.1(1)T This command was introduced.
Release
Modification
Examples
The following sample output from the show cable clock command shows both external sources are available and the clock card is providing the clock reference:
Router# show cable clock Clockcard primary input is present Clockcard secondary input is present Cable clock reference is clockcard primary input Cable3/0 Timestamp clock reference is from Clockcard Cable4/0 Timestamp clock reference is from Clockcard
Related Commands
Displays hardware information, register values, and current counters for the cable clock card.
Command
Description
To display hardware information, register values, and current counters for the cable clock card, use the show controllers clock-reference privileged EXEC command.
show controllers clock-referenceSyntax Description
This command has no keywords or arguments.
Defaults
No default behavior or values.
Command Modes
Privileged EXEC
Command History
12.1(1)T This command was introduced.
Release
Modification
Usage Guidelines
To reset the counters that are displayed with the show controllers clock-reference command, use the cable clock clear-counters command.
Examples
The following is sample output from the show controllers clock-reference command:
Router# show controllers clock-reference National clock card with T1 controller Control register :0x4 Status register :0x54 LIU Config Register 0:0x0 LIU Config Register 1:0x0 1 events reported in 266636 seconds Primary active :1, LOS :0 Secondary active :0, LOS :1 Holdovers :0, HW faults :0
Related Commands
Clears the counters displayed with the show controllers clock-reference command.
Command
Description
To display diagnostic information for the cable modem cards, use the show diag privileged EXEC command.
show diagSyntax Description
This command has no keywords or arguments.
Defaults
No default behavior or values.
Command Modes
Privileged EXEC
Command History
11.3 XA This command was introduced. 12.1(1)T This command was modified to include information about the cable clock card.
Release
Modification
Usage Guidelines
Use the show diag command to display diagnostic information about the port adapters installed in the router. This command also displays information about the cable clock card, if installed.
Examples
The following is sample output from the show diag command displaying diagnostic information for the cable clock card:
router# show diag Clockcard:National clock card with T1 controller EEPROM contents at hardware discovery: Hardware Revision :1.1 Part Number :800-05867-02 Board Revision :11 Deviation Number :0-0 Fab Version :02 PCB Serial Number :CAB04046NXV RMA Test History :00 RMA Number :0-0-0-0 RMA History :00 EEPROM format version 4 EEPROM contents (hex): 0x00:04 FF 40 01 AC 41 01 01 C0 46 03 20 00 16 EB 02 0x10:42 31 31 80 00 00 00 00 02 02 C1 8B 43 41 42 30 0x20:34 30 34 36 4E 58 56 03 00 81 00 00 00 00 04 00
Table 1 describes the fields shown in the show diag display.
| Field | Description |
|---|---|
National clock card with T1 controller | The system has identified the cable clock card. |
EEPROM contents at hardware discovery | EEPROM programmed data present when the system identified the clock card. |
Hardware Revision | Version number of the card. |
Part Number | The part number of the card. |
Board Revision | Revision number (signifying a minor revision) of the card. |
Deviation Number | Revision number (signifying a minor deviation) of the card. |
Fab Version | Manufacturing fabrication version number. |
PCB Serial Number | Serial number of the printed circuit board. |
RMA Test History | Counter indicating how many times diagnostics have been performed on this card. |
RMA Number | Return material authorization number, which is an administrative number assigned if the card needs to be returned for repair. |
RMA History | Counter indicating how many times the card has been returned and repaired. |
EEPROM format version | Version number of the EEPROM format. |
EEPROM contents (hex) | Dumps of EEPROM programmed data. |
To display information about the midplane TDM clock reference, use the show frame-clocks privileged EXEC command.
show frame-clocksSyntax Description
This command has no keywords or arguments.
Defaults
No default behavior or values.
Command Modes
Privileged EXEC
Command History
12.0(T) This command was introduced. 12.1(1)T This command was modified to include the cable clock card as the current clock source.
Release
Modification
Examples
The following sample output from the show frame-clocks command shows that there are no clock sources configured and the clock card is the default clock source:
Router# show frame-clocks Priority 1 clock source:not configured input:none Priority 2 clock source:not configured input:none Priority 3 clock source:not configured input:none Priority 4 clock source:not configured input:none Current clock source:Clockcard, input:Primary, priority:5
Table 2 describes the fields shown in the show frame-clocks display:
| Field | Description |
|---|---|
Priority 1-4 clock source | The configuration of the four network clock sources. |
Current clock source | The current clock source, its input, and priority. In this example, the clock card is providing the clock source. |
Related Commands
Displays status information for the clock card. Displays the clock card's hardware information.
Command
Description
To display general information about the router when reporting a problem, use the show tech-support privileged EXEC command.
show tech-support [page] [password]
Syntax Description
page (Optional) Causes the output to display a page of information at a time. Use the Return key to display the next line of output or use the space bar to display the next page of information. If not used, the output scrolls (that is, does not stop for page breaks). password (Optional) Leaves passwords and other security information in the output. If not used, passwords and other security-sensitive information in the output are replaced with the label "<removed>" (this is the default).
Defaults
Display output without page breaks and remove passwords and other security information.
Command Modes
Privileged EXEC
Command History
11.2 This command was introduced. 12.1(1)T This command was modified to include information about the cable clock card.
Release
Modification
Usage Guidelines
Use this command to help collect general information about the router when you are reporting a problem. This command displays the equivalent of the following show commands:
Examples
For a sample display of the output of the show tech-support command, refer to the above show commands in the Cisco IOS Release 12.1 command references.
Related Commands
show buffers Displays statistics for the buffer pools on the network server. show controllers Displays information about a specific line card's interface controllers. show controllers tech-support Displays general information about a card when reporting a problem. show interfaces Displays interface information. show processes cpu Displays information about the active processes. show processes memory Displays memory used. show running-config Displays the running configuration. show stacks Displays the stack usage of processes and interrupt routines. Displays the configuration of the system hardware, the software version, the names and sources of configuration files, and the boot images.
Command
Description
To display the configuration of the system hardware, the software version, the names and sources of configuration files, and the boot images, use the show version EXEC command.
show versionSyntax Description
This command has no keywords or arguments.
Defaults
Display output without page breaks and remove passwords and other security information.
Command Modes
EXEC
Command History
10.0 This command was introduced. 12.1(1)T This command was modified to include information about the cable clock card.
Release
Modification
Examples
The following is sample output from the show version command for a Cisco uBR7246 VXR with the cable clock card installed:
Router# show version Cisco Internetwork Operating System Software IOS (tm) 7200 Software (UBR7200-P-M), Version 12.1(0.8)T, Copyright (c) 1986-2000 by cisco Systems, Inc. Compiled Wed 02-Feb-00 16:49 by ccai Image text-base:0x60008900, data-base:0x61192000 ROM:System Bootstrap, Version 12.0(19990210:195103) [12.0XE 105], VXR1 uptime is 2 days, 1 hour, 24 minutes System returned to ROM by power-on at 10:54:38 PST Sat Feb 5 2000 System restarted at 11:01:08 PST Sat Feb 5 2000 System image file is "slot1:ubr7200-p-mz.121-0.8.T" cisco uBR7246VXR (NPE300) processor (revision B) with 122880K/40960K bytes of memory. Processor board ID SAB0329005N R7000 CPU at 262Mhz, Implementation 39, Rev 1.0, 256KB L2, 2048KB L3 Cache 6 slot VXR midplane, Version 2.0 Last reset from power-on X.25 software, Version 3.0.0. National clock card with T1 controller 1 FastEthernet/IEEE 802.3 interface(s) 2 Cable Modem network interface(s) 125K bytes of non-volatile configuration memory. 16384K bytes of Flash PCMCIA card at slot 0 (Sector size 128K). 20480K bytes of Flash PCMCIA card at slot 1 (Sector size 128K). 4096K bytes of Flash internal SIMM (Sector size 256K). Configuration register is 0x0
Table 3 describes significant fields shown in these displays.
| Field | Description |
|---|---|
IOS (tm) 7200 Software (UBR7200-P-M), Version xx.x | Always specify the complete version number when reporting a possible software problem. In the example, the version number is 12.1(0.8)T. |
ROM: System Bootstrap, Version 12.0(19990210) [12.0XE 105], | Bootstrap version string. |
Router uptime is | The amount of time the system has been up and running. |
System restarted at | Also displayed is a log of how the system was last booted, as a result of normal system startup or system error. |
System image file is | If the software was booted over the network, the Internet address of the boot host is shown. If the software was loaded from onboard ROM, this line reads "running default software." |
cisco uBR7246VXR (NPE300) processor | The remaining output in each display shows the hardware configuration and any nonstandard software options. |
Configuration register is | The configuration register contents, displayed in hexadecimal notation. |
The output of the show version EXEC command can also provide certain messages, such as bus error messages. If such error messages appear, report the complete text of this message to your technical support specialist.
Related Commands
Displays diagnostic information for the cable modem cards. Displays general information about the router to use when reporting a problem.
Command
Description
codec---coder-decoder. Device that typically uses pulse code modulation to transform analog signals into a digital bit stream and digital signals back into analog.
DOCSIS---Data-over-Cable Service Interface Specifications. Defines technical specifications for equipment at both subscriber locations and cable operators' headends. Adoption of DOCSIS will accelerate deployment of data-over-cable services and ensure interoperability of equipment throughout system operators' infrastructures.
gateway---A gateway allows H.323 terminals to communicate with non-H.323 terminals by converting protocols. A gateway is the point at which a circuit-switched call is encoded and repackaged into IP packets.
GPS---global positioning satellite.
H.323---An International Telecommunication Union (ITU-T) standard that describes packet-based video, audio, and data conferencing. H.323 is an umbrella standard that describes the architecture of the conferencing system, and refers to a set of other standards (H.245, H.225.0, and Q.931) to describe its actual protocol.
HFC---hybrid fiber-coaxial. Technology being developed by the cable TV industry to provide two-way, high-speed data access to the home using a combination of fiber optics and traditional coaxial cable.
PSTN---Public Switched Telephone Network. General term referring to the variety of telephone networks and services in place worldwide. Sometimes called plain old telephone service (POTS) .
SGCP---Simple Gateway Control Protocol. Controls Voice over IP gateways by an external call control element (called a call-agent).
Stratum---Hierarchical clock reference in the PSTN network, where 1 represents the highest possible quality of clocking.
TDM---time-division multiplexing. Technique in which information from multiple channels can be allocated bandwidth on a single wire based on preassigned time slots. Bandwidth is allocated to each channel regardless of whether the station has data to transmit.
VoIP---Voice over IP. The ability to carry normal telephone-style voice over an IP-based internet with POTS-like functionality, reliability, and voice quality. VoIP is a blanket term which generally refers to Cisco's standards based (for example, H.323 or SGCP) approach to IP voice traffic.
Posted: Thu Mar 23 11:21:27 PST 2000
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