IP Technote

With the introduction of the Comrex BRIC-Link more questions have arisen regarding the use of Comrex Access and BRIC-Link across T1 circuits. Of specific interest have been point-to-point T1 type circuits.

Typically when the T1 is terminated by the Telco, it will be left on an RJ45 connector, to be interfaced to customer equipment. Ethernet interfaces will not connect directly to this point, as the protocols used here are not compatible. Typically, a device which has at least one Ethernet port and at least one T1 port will be needed here. Usually this job falls to a router. The router really has much more functionality than we need at this level, but it easily provides the bridge between T1 and Ethernet.

Some examples of routers that would work for this purpose include the Cisco 1600 and 1700 Series Small Business / Home Office Routers. These routers are no longer in production but may be found on the second hand market. Presently the Cisco 1800 Series is in production and can easily work in these applications. Typically the Cisco product line will have one Ethernet interface on board with the T1 interface being added by the end user (as an option). Other Cisco lines that could work here are the 2600 and 2800 series as well.

Adtran also has some offering in this area - the Adtran Total Access Series can be used for the purpose of connecting the Comrex IP products to a T1 circuit.

Although these devices would easily perform the tasks needed, there are also a line of media converters such as the Valiant Ethernet over 1 E1 Converter. These provide Ethernet transmission over T1. Although in theory these should be fine, I have little/no experience ever having used one.

Aside from the physical interface of the IP products to the T1, there are also concerns such as line coding, and clocking. In a point to point T1 there may or may not be any clocking provided by the Telco. If a router-based solution is used, the router can provide clocking to the circuit if required. In some cases one end of the T1 may have clocking enabled. In these cases the routers are simply set to use clocking provided by the Telco. In the majority of cases in the US, the line coding will be standard (B8ZS) and will be handled with no problem by the router.