TCSM2 Exchange Terminal modules¶

A working Nokia TCSM2 system requires a minimum of 1 and a maximum of 4 Exchange Terminal modules, either ET2E (2xE1) or ET2A (2xT1). The choice of ET module determines whether the TCSM2 system will operate in E1-based ETSI environment or T1-based ANSI environment. (More precisely, the selection between the two fundamental environments is done with a global configuration command on the TRCO - but in order to get a working system, that selection needs to match physically present ET hardware.)

ET2A for T1 circuits¶

I (falconia) do not currently have an ET2A to play with: unlike ET2E, ET2A does not show up in the online inventory system of the surplus vendor I currently work with, the one willing to sell to ultra-small customers who don't have compliance managers. I might ask them about it at a later time, though.

Compared to E1 modules examined below, ET2A has one distinct advantage: each of the two T1 interfaces is brought out on a standard RJ-48C jack. (Most people call it RJ-45, but RJ-48C is the official designation for this type of jack when it is used for a T1 interface per FCC specifications.) However, this advantage is effectively nullified by the problem that icE1usb supports only E1, and there is currently no solution for T1 that offers the same level of sanity. (Sanity as in something other than aftermarket Digium cards where the quality of driver code is atrocious, and it is not even clear if a non-working system is a driver problem or defective hardware.)

ET2E for E1 circuits¶

Even though RJ-48C is an official standard only for T1, many people have adopted the same convenient 8-position modular jack for E1 circuits, including the designers of the already mentioned icE1usb. But unfortunately, not Nokia: AFAICT Nokia never made a version of ET2E for TCSM2 that brings out the same convenient jacks. Instead ET2E for 2xE1 was made in two versions in terms of physical interfaces:

ET2E with a DIN 41612 half-C connector¶

The electrical interface for the two E1 circuits on this ET2E version is the same as it would have been if they had provided RJ-48C jacks, the same 120 ohm electrical interface one would connect directly to an icE1usb. But the connector is a difficult one: it is DIN 41612 of size "1/2 C", i.e., 3 rows with 16 pins in each row. It is the same E1 interface connector as used by the same manufacturer (Nokia) on the EKSOS N20 NCU. Official mating connectors that are meant to be mounted on cables (free-hanging inline) do exist, but only with a cost-prohibitive MOQ. I tried using the same approach that was used by laforge on the EKSOS - use a female connector that is officially meant for PCB rather than cable mounting - but I ran into an unexpected problem: the connector does not fit unless I destructively break off some plastic tabs from the connector housing on the ET2E module, which I am quite reluctant to do.

ET2E with coaxial E1 interfaces¶

The other version of ET2E brings out each E1 interface on a pair of SMB coaxial connectors - it is the 75 ohm unbalanced E1 interface. I don't have this ET2E-C module in my hands yet, but it is on order from the supplier. My current plan is to use it with external adapters that convert the 75 ohm coaxial E1 interface to the 120 ohm version on RJ-48C.

Different generations of ET2E¶

Aside from the coaxial vs 120 ohm balanced dichotomy, it appears that ET2E was made in 3 different evolutionary generations:

First generation: ET2E and ET2E-C¶

In the first generation, the 120 ohm balanced version (with the weird connector) was called simply ET2E, whereas the coaxial interface counterpart is ET2E-C. We currently have an ET2E-C module on order from shields-e; when it arrives, we'll be able to tell how it differs from the newer ET2E-T.

Second generation: ET2E-S and ET2E-SC¶

All we know is the name - we don't know if this version is closer to the original or to ET2E-T.

Third generation: ET2E-T and ET2E-TC¶

The only module we have on hand currently is ET2E-T, aka C105507. It appears to be a significantly redesigned implementation of ET module functionality compared to the original - but we will (hopefully) get a clearer picture when our ET2E-C arrives and we can compare the two.