User Manual

Chapter 13 ● Loopback testing backhaul links
160 Release 2.0, 910056 Rev01d
Understanding a typical T1/E1 backhaul network
Figure 22 shows a typical network in which T1s/E1s are used for backhaul link(s).
Figure 22 A typical T1/E1 backhaul network using DSXs (digital cross connects, T1/E1 multiplexors, or
similar)
Understanding Ethernet loopbacks
Like the T1/E1 loopback test, the Ethernet loopback test has two parts:
• Physically loopback the Ethernet
• Run the loopback test
The loopback can be done externally on the cable by physically connecting the receive wires (RXs) to the
transmit wires (TXs). The loopback can also be done internally on the hardware transceiver chip. Looping
back internally on the transceiver chip only tests limited hardware functionality and does not test the cable
connection or the punch down block. Looping back externally tests more. The Ethernet loopback test is not
a standard function of Ethernet but is a value-added proprietary feature.
Backhaul
1 to 4 T1s/E1s
IP-RN 8000
DSX
DSX
Router
RNC
PDSN
Internet
TDM
backhaul
punch block
Ethernet
External test: T1/E1 loopback to
carrier demarcation point
Carrier demarcation point