3Com S330 manual Illustrates the loopbacks for OC3/STM-1

Using Loopbacks 181

OC3/STM-1 Loopbacks The following loopbacks are available for the OC3/STM-1 interface:

Network LIne—Loops the OC3/STM-1 received data back on the output side after the digital data has been recovered.

Local Card—Loops the transmit OC3/STM-1 output on the receive side; the transmitted data will continue to go on the output.

Figure 139 illustrates the loopbacks for OC3/STM-1.

Figure 139 OC3/STM-1 Loopbacks

OC3 Interface

Network Side

Local Card

Network Line

Payload

DS3 Loopbacks The DS3 module supports the following loopbacks:

Local Card—Loops the transmit DS3output on the receive side. All cells coming from the DS3 card are looped through the backplane and back to the DS3 card. The transmitted data will continue to go on the output.

Network Line—Loops the DS3 received data back on the output side after the digital data has been recovered.

Network Card—Loops the DS3 received cell payload back toward the line output.

Figure 140 illustrates the DS3 loopback options.

Figure 140 DS3 UNI Loopback Options

DS3 Interface

Network Side

Network Card

Network

Line

Bus Side

Local Card