User guide

Canopy T1 / E1 Application Note
Issue 1, June 2005 1
5
In the context of T1/E1 the use of “RJ45” is widespread but probably inappropriate. The
telephony industry terms this jack as a “RJ48C” even though it is physically identical. As
Figure 9 illustrates the Tx and Rx pairs (often termed “tip” and “ring”) and pinouts; note
they are in a crossover arrangement. Crossover means that the TX pair at one cable end
becomes the Rx pair at the other cable end.
Figure 9. T1/E1 RJ45/RJ48C Pinouts
Contrast this circumstance to Ethernet RJ45 cable pinouts. Ethernet cable comes as
“straight through” or “crossover” versions (typically Ethernet ports “autosense” and work
with either version). Clearly Ethernet straight through can not work in the T1/E1 cable
environment. Figure 10 below indicates the Ethernet crossover cable pinouts. Note that
pins 1 and 2 map to pins 3 and 6 respectively, and visa-versa. The remaining pins 4, 5,
7, and 8 are often used to carry power, as indeed is the case for Canopy.
Figure 10. Ethernet Crossover Pinouts
The important point is that connecting the TMUX T1/E1 ports to telephony devices like a
PBX, ADM, DSC, or IP router T1/E1 requires special T1/E1 RJ48C cable. Ethernet cable
will not work. On the other hand, between the TMUX “Canopy Port” and a Canopy
BHRF20 unit an Ethernet RJ45 cable must be used (either crossover or straight through).
6.0 Summary and Conclusion
Laboratory testing shows that, when properly configured, the Canopy TMUX transparent
transport of T1/E1 is consistent with industry circuit standards of performance. But in any
radio environment transient conditions may temporarily cause unexpected and “random”
packet delays that, if sufficient to underflow a TMUX playout buffer, result in
unacceptable circuit performance. Additionally the challenges of Canopy’s half-duplex
operation and additional delays for packet payload accumulation may result in less than
common carrier-grade circuit performance on occasion. Consequently, it is necessary to
have realistic expectations when employing Canopy for circuit emulation.
Laboratory testing indicates that, when the Canopy TMUX is configured as described,
circuit emulation at the BER 10
-6
level is sustainable indefinitely. This is sufficient for
voice access, but slightly less than common carrier terrestrial performance goals.