Digital & Analog loops

Level: - Beginners
Platform: - Telecom Modems
Keywords: - : What are digital and analog loops, local loop
Author: - Surender Singh

In the world of telecom we often hear a technician telling another to give a local loop or a digital loop. The modems have keywords like local loop, digital loops written on them. It is very important to understand the meaning of these basic terms. This article tries to explain the meaning of these simple terms.

Digital Loop:
Modem will give a loop towards service providers PCM channel and can be checked in all the PCM in between on a point to point link using any loop tester. That’s how Telco decides the quality and errors on a link, as they can measure the frame loss and CRC on digital loop. When you activate a digital loop on your modem the remote router interface shows as looped since it is sensing this loop.
Analog loop:
Modem will initiate a loop towards to your router interface. On practical scenario, when an analog loop active your router interface goes down. You can use it to check your v.35 cable or g.703 cable and even the router interface. Analog loop can be used to check connectivity form your modem to router connectivity.

Local loop
Local loop is the circuitry from the demarcation point (where the service provider cable/system ends at customer premise) up to Telco MDF or PCM. Local loop is the connection between your equipment and the service providers equipment....


It is the method used to self test if an interface is working or not.... loopback testing is supported by most of the equipments.... what is actually does is cross connecting TX and RX and sending some signals and receiving them and check to see if they are received properly and also for errors... this helps to isolate where there problem actually is - is it a defective equipment or link problems....

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