CL21E1B20

CL21E1B20 is a trunk cable for Huawei transmission equipment, 20 m long. Pre-made assemblies exist because the connectors on transmission equipment are often not field-terminable, and because a factory-terminated cable of a known length is more reliable than one made up on a rack at the end of a long day.

It is a 120 ohm cable, and that figure is not interchangeable. E1 circuits exist in two forms: 75 ohm unbalanced on coax, and 120 ohm balanced on twisted pair. Both carry the same signal and the equipment ends can look similar, but mixing them creates an impedance mismatch, and a mismatch causes reflections rather than an outright failure. The circuit comes up, passes a quick test, then throws errors under load, which makes it one of the slower faults to track down. Check what the distribution frame and the far end actually use before ordering. This assembly carries 21 E1 circuits in one cable, which is how a tributary card is taken to a distribution frame without running 21 separate leads.

The jacket is low smoke zero halogen. That is a fire-safety property rather than an electrical one: in a fire the sheath gives off less smoke and no halogen gases, which matters where cables run through escape routes, tunnels, underground stations or enclosed public spaces. In many of those locations it is a regulatory requirement rather than a preference, and substituting standard PVC is not a saving worth making.

This is SDH-generation equipment, and SDH is a legacy transport technology. The industry moved to packet and to OTN years ago, and the OSN 500 is not a platform anyone is designing a new network around in 2026.

That is not the same as saying it is useless. A great deal of SDH is still in service carrying E1 and STM-n circuits that work perfectly well, in utilities, rail, broadcast, defence and government networks where the circuits outlive the fashion in transport technology. If that is what you are maintaining, this keeps it running. If you are being offered SDH for something new, push back.

Length is the thing to get right first. These are fixed assemblies, so the length cannot be adjusted on site: too short is useless, and too long has to be coiled somewhere, which on fibre risks bending it past its minimum radius and introducing loss that appears and disappears as the bundle is moved. Measure the actual route, including the rise up the rack and the slack for maintenance loops, rather than the straight-line distance. Tell us the route and the equipment at both ends and we will confirm the right assembly and length.

Green Code Technologies supplies Huawei transmission equipment together with the racks, power, cabling and installation parts that go with it. We are a supplier of Huawei alongside HPE, Dell, Cisco, Samsung and Netgear, and we would rather confirm a part against Huawei’s own documentation than sell you the wrong one, which on OSN 500 equipment is worth doing. Send us the site, the power available there and what the node has to contain and we will come back with a straight answer.