how to order PRI Synchronization clock Source?

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Sep 20th, 2008

hello all,

i have router equiped with 6 E1. 3 for PSTN and other 3 E1 trunk QSIG with othe othe vendor PBX. Cisco is the gateway for the pbx users to call out. we are facing an issue in high traffic hours call get error tone or busy tone when trying to call from the pbx user. in normal times calls get through without any porblem. anyway i suspect in synrchronization issue.

how should i programm the PRI clock source and synchronization for each of them? for the PSTN side and also for the E1 Qsig side?

I have this problem too.
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Marwan ALshawi Sat, 09/20/2008 - 17:32

set up the clocking for the TDM bus in the gateway. Begin in global configuration mode by entering the network-clock-participate slot 1 and network-clock-participate slot 2 commands. Set up one E1 as priority 1 clock source using the network-clock-select 1 e1 1/0 command. The 1 indicates that this is the clock that will be selected first for use if it is available. Use the network-clock-select 2 e1 2/0 command to set up the other PSTN connection as a backup clock

and so on ..

You can verify proper clocking configuration by using the show network-clocks command

go to the serial1/1:15 interface and enter the isdn protocol-emulate network command. This makes the voice gateway the network side of the PBX connection just as the PSTN was, helping to meet the requirement of minimizing changes to the PBX (ISDN configuration)

where the erial port number is ur serial port numer on ur gateway

When setting up tie trunks to a PBX, it is always preferable to use a PRI or QSIG trunk if you can. Some PBX systems do not have PRI capability, which might force you to use a channel-associated signaling (CAS) trunk. If you must use an E1 R2 or T1 CAS connection, be sure to select a supported signaling method that provides the highest level of reliability and functionality

good luck

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t-alkhalidi Sat, 09/20/2008 - 21:34

thank you much for the info. the tie trunk is QSIG E1 . its already working . but i dont understand how who is clock source primary external and who is internal.

Now for PRI with PSTN "i will make it clock external"

and for those QSIG tie trunk will use " clock source internal "

Marwan ALshawi Sat, 09/20/2008 - 23:00

u right the link from GW to the PBX should be clock source internal

and to the PSTN

clock source line

the clock source line command instructs the voice gateway to use the clock recovered from the bit stream received on that interface as a clock source, rather than the internal clock

good luck

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t-alkhalidi Sat, 09/20/2008 - 23:16

thank you .

well what is the difference between clock source ? and network participate? whats relation ship between them?

and please how can i trace specific call on voice gateway on the PRI interface?

how to check if i have errors on the link ? what is slips? how to correct it

Marwan ALshawi Sat, 09/20/2008 - 23:26

It is important that you understand how clocking will be set up on a digital trunk. Improper clocking configuration shows up as clock slips on the controller interface. Slips can cause a wide variety of voice problems, including poor voice quality, static, echo, and one-way audio. Understanding how to set up a stable clocking domain prevents these problems.

In addition to the trunks, Cisco voice gateways that have a built-in TDM bus must be clocked correctly for voice traffic to flow properly and to avoid problems. By default, the time-division multiplexing (TDM) bus uses the internal oscillator as a clock source. However, this causes problems with connected circuits that use a different clock source. You can use the show network-clocks command to see which of the available clock sources is currently being used to time the TDM bus

show network-clocks

Network Clock Configuration

Priority Clock Source Clock State Clock Type

1 T1 1/0 GOOD T1

2 T1 1/1 LINK DOWN T1

10 Backplane GOOD PLL

Current Primary Clock Source

Priority Clock Source Clock State Clock Type

1 T1 1/0 GOOD T1

In Cisco Integrated Services Routers (ISR), you must synchronize the clock for the digital signal processor (DSP) resources on the motherboard with the circuit to be used. The DSP resources are clocked from the TDM bus.

When selecting a clock source to use, choose the best available one. PSTN circuits are generally the best clock sources available. Most PBX systems can pass the clock from a "master" source, such as a PSTN circuit, to other trunk ports. If the PBX has a PSTN circuit attached and can use that circuit as a master clock source, use the PBX timing on the tie trunk and set the voice gateway for loop timing

The network-clock-participate command enables the module on slot 1 to be a clock source for the TDM bus. The network-clock-select command sets clocking recovered on T1 1/0 to be used as the priority 1 clock for the TDM bus. If additional clock sources are available, you can add them as candidates using the network-clock-select command and different priorities. Only one clock is in use at any given time. In controller configuration mode, the clock source line command instructs the voice gateway to use the clock recovered from the bit stream received on that interface as a clock source, rather than the internal clock

You can also reverse this configuration. If the PSTN trunk goes to the Cisco voice gateway instead of the PBX, the voice gateway can recover the clock from the PSTN circuit and use it to clock both the internal TDM bus and the tie trunk to the PBX, thus providing clocking for the PBX

by using the show controller t1 | e1 slot/subunit/port command. The output shows a great deal of information about the current state of the link, in addition to historical information. This information can help you isolate problems with line coding, framing, and clocking of the link

show controller

hope this helpful

t-alkhalidi Sun, 09/21/2008 - 11:23

i have done those command show controllers there is no errors at all. should i do clock source line for PSTN , then do network-participate for PSTN E1?

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