Understanding the network.pdf - Back to Home

process. The T3 multiplexer adds stuffing bits (552Kbps worth) on the output
interface and strips them out on the input interface of the multiplexer on the far end
of the circuit. This behavior is different from the T2 multiplexing step, which adds
the stuff bits on the T1 input interface to the T2 multiplexer. The reason for the two
different stuffing methods is to provide the option to have the T2 interfaces come
from different locations. After the T3 circuit is complete, it might be multiplexed with
other T3 circuits to form a T4 interface (six T3 circuits), which is the common
interoffice trunk transport link (transmitted over fiber). This can be used as a
standalone interoffice trunk or terminated at a customer presence for clear channel
use. Figure 5.6 illustrates the T2-to-T3 multiplexing step.
Figure 5.6. T2-to-T3 multiplexing.
As a carrier trunking circuit, when the T3/T4 has reached the CO, a two or three step
demultiplexing process must be used to provision the transport at the T1/DS1 level.
As a clear channel data transport, the T3 terminates into a T3 DSU/CSU equipped
with a High-Speed Serial Interface (HSSI). HSSI was originally developed by Cisco
Systems and T3plus Network to provide a serial interface that could handle data
rates up to 52Mbps for T3/DS3 WAN applications. HSSI is now an ANSI and ITU-T