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New Member

Clocking on Voice T1s - MGCP - CAS

There will be a total of 14 T1 CAS circuits on a 3845:

7 T1 CAS circuits from carriers:

3 from TDS and

4 from MCI

(These are all currently connected directly to a Siemens 9005. The plan is to terminate them on VWIC2-2MFT-T1/E1 modules on a 3845)

We will in turn feed 7 T1s to a Siemens Rolm 9005 (which is currently taking these circuits directly from carrier)

I need to configure clocking and want to ensure I do it correctly.

Since the carriers are providing clock I believe that I will want to take clock on the T1s from the carriers, possibly even specific clock from TDS and MCI separately.

And since the PBX is expecting to take clock from the line, I assume I should provide clock to the PBX.

I have read the “network-clock-participate” and “network-clock-select” info http://www.cisco.com/en/US/products/sw/iosswrel/ps5012/products_feature_guide09186a00800a18a4.html#wp1044918 but still am not sure how to do this correctly. It would be simple if there was a single T1 or even multiple from a single carrier… but that is not the case here.

This is what I have currently but I know it is wrong. Note: the first 7 T1s (0/0/0, 0/0/1. 0/1/0, 0/1/1, 0/2/0, 0/2/1 and 0/3/0) are from the carrier, the last 7 (0/3/1, 1/0, 1/1, 1/0/0, 1/0/1, 2/0, and 2/1) are to the PBX:

!

clock timezone cdt -6

clock summer-time CDT recurring

clock calendar-valid

network-clock-participate slot 1

network-clock-participate slot 2

network-clock-participate wic 0

network-clock-participate wic 1

network-clock-participate wic 2

network-clock-participate wic 3

ip subnet-zero

no ip source-route

ip cef

!

...

!

controller T1 0/0/0

framing esf

linecode b8zs

ds0-group 1 timeslots 1-24 type e&m-wink-start

description TDS DID Range 3000 to 3999

!

controller T1 0/0/1

framing esf

linecode b8zs

ds0-group 1 timeslots 1-24 type e&m-wink-start

description TDS DID Range 4500 to 4999

!

controller T1 0/1/0

framing esf

linecode b8zs

ds0-group 1 timeslots 1-24 type e&m-wink-start

description TDS DID Range 8600 to 8699 Analog

!

controller T1 0/1/1

framing sf

linecode ami

ds0-group 1 timeslots 1-23 type e&m-wink-start

description MCI TACM 007900

!

controller T1 0/2/0

framing sf

linecode ami

ds0-group 1 timeslots 1-22 type e&m-wink-start

description MCI TACM 042621

!

controller T1 0/2/1

framing esf

linecode b8zs

ds0-group 1 timeslots 2-8 type e&m-wink-start

ds0-group 2 timeslots 10-17 type e&m-wink-start

ds0-group 3 timeslots 19 type e&m-wink-start

ds0-group 4 timeslots 21-23 type e&m-wink-start

description MCI TACM 118331

!

controller T1 0/3/0

framing esf

linecode b8zs

ds0-group 1 timeslots 1-6 type e&m-wink-start

ds0-group 2 timeslots 8-20 type e&m-wink-start

ds0-group 3 timeslots 22 type e&m-wink-start

description MCI TACM 230005

!

controller T1 0/3/1

framing esf

linecode b8zs

ds0-group 1 timeslots 1-24 type e&m-wink-start

description (to PBX) TDS DID Range 3000 to 3999

!

controller T1 1/0

framing esf

linecode b8zs

ds0-group 1 timeslots 1-24 type e&m-wink-start

description (to PBX) TDS DID Range 4500 to 4999

!

controller T1 1/1

framing esf

linecode b8zs

ds0-group 1 timeslots 1-24 type e&m-wink-start

description (to PBX) TDS DID Range 8600 to 8699 Analog

!

controller T1 1/0/0

framing sf

linecode ami

ds0-group 1 timeslots 1-23 type e&m-wink-start

description (to PBX) MCI TACM 007900

!

controller T1 1/0/1

framing sf

linecode ami

ds0-group 1 timeslots 1-22 type e&m-wink-start

description (to PBX) MCI TACM 042621

!

controller T1 2/0

framing esf

linecode b8zs

ds0-group 1 timeslots 2-8 type e&m-wink-start

ds0-group 2 timeslots 10-17 type e&m-wink-start

ds0-group 3 timeslots 19 type e&m-wink-start

ds0-group 4 timeslots 21-23 type e&m-wink-start

description (to PBX) MCI TACM 118331

!

controller T1 2/1

framing esf

linecode b8zs

ds0-group 1 timeslots 1-6 type e&m-wink-start

ds0-group 2 timeslots 8-20 type e&m-wink-start

ds0-group 3 timeslots 22 type e&m-wink-start

description (to PBX) MCI TACM 230005

!

8 REPLIES

Re: Clocking on Voice T1s - MGCP - CAS

For the Rolm, we use the CMM in the 6500 series... Used the MGCP gateway and configured the clock source from the Rolm or "external"

B87s

ESF framing.

Everything is working... but we did have some clocking problems with the Rolm... the T1's came out of sync and we would get static on the lines... (IP phone to Rolm phone)

On the Rolm side, we used Digit translation to pump numbers of the Cisco, and of course the Cisco side is easy to route numbers over the T1 lines to the Rolm.

We have a bunch of old C/O and DID Trunks on the Rolm... on the Cisco side, we installed PRI's.. we will eventually swing all our DID's over the PRIs we are ready.. (basically get complete 100 blocks) The CO and DID trunks will be disconnected after the numbers ported over to the PRIs.

Silver

Re: Clocking on Voice T1s - MGCP - CAS

You can set the 7 T1's that connect to the service providers to clock from the line and use one of them to drive the clock for the 7 T1's that go to the PBX.

So for ports 0/0/0, 0/0/1. 0/1/0, 0/1/1, 0/2/0, 0/2/1 and 0/3/0, set the clock source to line under the controller.

Now chose one of them, say 0/0/0, as the Primary and say 0/1/0 as the Secondary to drive the clock for the T1's that go the PBX. (for redundancy this would be better, since they are in two different cards). If you see slips or errors, you might want to try using other ports and see which clock is more reliable.

network-clock-select 1 T1 0/0/0

network-clock-select 2 T1 0/1/0

Next, you have to configure the T1's that go the PBX to use the clock received on the above ports.

network-clock-participate slot 1

network-clock-participate slot 2

network-clock-participate wic 0

network-clock-participate wic 1

Set the clock source for ports 1/0, 1/1, 1/0/0, 1/0/1, 2/0, and 2/1 to internal

There is a problem with port 0/3/1. Since wic 3 terminates a T1 from the service provider and also from the PBX, you cannot have it participate as a slave.

If you happen to have another T1 card, you can move the T1 from the service provider to that one.

Regards,

Anup

New Member

Re: Clocking on Voice T1s - MGCP - CAS

This makes sense. I will need to put another card (possibly replace one of the VWIC2-2MFT-T1/E1 cards with two VWIC2-1MFT-T1/E1 cards)

I will let you know how it goes.

Thanks,

Casey

New Member

Re: Clocking on Voice T1s - MGCP - CAS

Anup,

A colleague of mine is also driving this issue and got the following recommendation wich is different than yours. Can you review it and let me know if it is viable? I would like to avoid adding T1 cards if it is not necessary but will as needed.

Thanks, Casey

_____________________________

dgahm - Network Engineer, Alaska USA Federal Credit Union, CCIE - Apr 12, 2006, 9:49pm PSTNew Message!

You have to select a clock source which will clock all voice T1s. Pick one of your carriers as the primary clock source, the other as the secondary. The PBX will need to be set to clock off the T1s from the 3845. All carriers have extremely accurate clocks synched to a stratum 1 source, so you should see no slips even though one source will clock T1s from both.

To set primary source network-clock-select 1 t1 X/X/X

Seconday source network-clock-select 2 t1 X/X/X

All other T1 ports network-clock-participate t1 X/X/X

A good doc:

http://www.cisco.com/en/US/customer/tech/tk652/tk653/technologies_tech_note09186a00804794c6.shtml

New Member

Re: Clocking on Voice T1s - MGCP - CAS

Anup,

Here is a Excerpt from our local Cisco office describing clocking:

- ISR HWIC slots MUST be "network clock participate" - you cannot turn this off, this is required to access the onboard DSPs across the ISR backplane.

- Access to the onboard DSPs are controlled by the ISR backplane clock - which is a single clock domain for all the ports accessing these DSPs.

- The ISR backplane is clocked by the system PLL when NO onboard T1 port is set to "network clock select" - an unlikely configuration. The ISR backplane is clocked by the designated port when 1 or more onboard T1 ports are set to "network clock select" (there is a priority scheme if multiple ports are set up this way) - the usual configuration.

- If you configure "clock source line" (i.e. external clocking) on a port that is designated as "network clock select", then that is the source of the backplane clock.

- If you configure "clock source line" (i.e. external clocking) on a port that is NOT designated as "network clock select", then the Rx buffer is clocked by the external clock received on the line, and the Tx buffer is clocked by the ISR backplane. The backplane clock is always used for DSP access. On this kind of port you could see clock slips, unless the line clock and the ISR backplane clock are derived from the same ultimate source (some Stratum 1 clock in the PSTN external to the ISR), and therefore in sync. The slips will most likely not show up on the ISR (although they could in "sh controllers" "x Slip Secs" field), but more likely will show up on the equipment (likely a CO) the ISR is connected to (because the Tx buffer is clocked by the backplane and may differ from the clocking supplied on the line to the ISR which controls the Rx buffer).

Based on this I was assuming that "all" WICs, regardless of what they connect to need the "network-clock participate" statement to allow them to participate in this single DSP clocking backplan. It's then a matter of configuring "how" the WIC will participate. This is done with Network-clock select as well as clock-source-line and/or internal.

Couldn't we have "network-clock participate" for WIC 3 and then line clocking for the port going to the PSTN and internal clocking for the port going to the PBX?

I could be all wrong on this.....

Silver

Re: Clocking on Voice T1s - MGCP - CAS

I didn't know that you cannot turn off "network-clock-participate" on HWIC slots. I was thinking that you don't need to set the cards that derive the clock from the PSTN to be part of "network-clock-participate". In my previous post, I typed the wrong cards. It should have been

network-clock-participate wic 2

network-clock-participate wic 3

Reading this post, I agree with your assumption of setting all the cards to "network-clock-participate" and use any two PSTN ports as "network-clock-source" and let the ports use the clock command to decide on the clocking.

Please post your findings after you do this.

Regard,

Anup

New Member

Re: Clocking on Voice T1s - MGCP - CAS

JR,

You mentioned that ISR HWIC slots MUST be "network clock participate". Does this include modules such as the WIC-1DSU-T1-V2 or the WIC-1T?

Thanks,

Dennis

Re: Clocking on Voice T1s - MGCP - CAS

Hi Dennis,

Strictly speaking, Data-only cards that do not leverage PVDM/DSP resources don't need to be sync'd with the TDM backplane. They should be sync'd with the carrier. But if not, higher level protocols can handle loss and error. I'm sure we've all seen occasions where the service-module was not configured for external clock, yet the circuit was still functional and carrying data, albeit with incrementing CRC and/or framing errors.

With voice cards, the carrier's bits must align with the PVDM/DSP else voice quality suffers significantly. PVDM/DSPs reside on the ISR back-plane, so the backplane must be synced in order for the DSP to be sync'd. The fundamental problem faced such multi-carrier scenarios is the potential both carriers and all switches may not be sync'd.

So the question becomes, What is the 'best' source of clock? The best would be, the source with the most devices are currently aligned to it.

Michael

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