touristsis wrote:
Hi,
I have a customer with a 7100. They have 3 T1 card in the system. T1 1/1, T1 2/1, and T1 2/2.
T1 2/1 and T1 2/2 are bonded together.
T1 1/1 are not in use.
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To what are the bonded T1 2/1 and T1 2/2 connected?
However under T1 1/1, there are two commands. system-timing primary and system-timing secondary.
Is this correct?
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Are you sure those are under T1 1/1 and not global commands?
They are reporting very slow connection and latency problem. Can this be the cause?
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It could be. Try the command "show interface t1 2/1 performance" and the same for 2/2 and look for slip seconds.
Here's the deal. T1 circuits are by nature point-to-point and synchronous.
- A T1 interface can either source timing (clock) or recover it from the T1 line.
- Every T1 circuit should have exactly one interface sourcing clock, the other end should recover it from the T1 line.
- If a circuit is connected to a carrier's equipment such as a Telco PRI or Internet router, then that side almost always will be providing an accurate clock.
- If a circuit is ordered as a point-to-point to connect two customer sites, then neither side will usually provide clock.
Case 1: Bonded T1 interfaces T1 2/1 and T1 2/2 are coming from a carrier such as an ISP or Telco-provided PRI, then you want the system timing to be primary to T1 2/1 and secondary to 2/2. This ensures that the system is in sync with what is being sent by the carrier. The carrier will provide clock on its interface and the Adtran will recover that clock from T1 2/1. Should T1 2/1 fail, then the carrier clock on T1 2/2 will be used. Because they're bonded and coming from the same carrier, the clock on T1 2/1 and 2/2 will be identical. Same deal with a single telco T1, set your device to take system timing from that interface.
Case 1a: Just like Case 1 but you also deliver PRI service to a customer PBX. Set your timing as above. Your local Adtran will recover the clock from the carrier and source it to the customer PBX. Tell the customer to set the PBX to recover clock from your PRI.
Case 2: No external T1 interface connects to a carrier or ISP. The only T1s in the system are the Adtran device itself providing T1/PRI service to a customer's PBX on premise. Set system timing to "Internal". Because there is no carrier-sourced clock, you'll generate one internally. Tell the customer to set the PBX to recover clock from your PRI.
Case 3: Two Adtran devices (or one and a Cisco, etc.) connected to no external carriers with only a T1 between them. Set one side to internal and the other to system timing from the T1 connected to the line. It doesn't matter which end is which, but one side must be internal and the other line.
Problem cases:
If both ends of a circuit provide clock and both are not connected to a high-accuracy source such as an atomic standard, then there will be slips as the clocks fight each other. These slips result in corrupt data, clicks in audio, and fax transmissions that print slanted.
If neither end of a circuit provides clock, the circuit will probably come up but then gradually drift either too high or too low in frequency for the electronics to handle, then go down and retrain. This may occur once every minute or once every six months and can be tough to troubleshoot.
Good practice:
Treat every T1 as a point-to-point circuit with two ends. Ensure that exactly one end provides the clock timing and the other recovers it from the T1 circuit. If a T1 is connected to equipment at a carrier or telco, its clock timing will likely be more accurate than what you can generate internally. Ask the provider if they are providing clock and set your gear to recover from the carrier.
