Chapter 1. Introduction
11
May 2011
1.4 Typical System Applications
General
In a typical application (Figure 1-1), the ETU-01A is used in a point-to-point connection. The
synchronous data channels of each host are connected over an E1 line.
Figure 1-1 Point-to-Point Application
Fractional E1 data service is based on the assumption that the user data rate is a fraction of the
available E1 bandwidth, in multiples of 56K or 64K.
Figure 1-2 Fractional E1, Cascade Application
In the above figure, the available E1 Time Slots are divided (Fractional E1) and cascaded
(multiplexed). Various data interfaces are employed in each ETU-01A to provide connections
between hosts, LANs and servers across the E1 transmission facility.
1.5 E1 signal structure
The E1 line operates at a nominal rate of 2.048Mbps. The data transferred over the E1 line is
organized into frames, with each E1 frame containing 256 bits. The 256 bits are a total of the 32
time slots, each containing eight bits, carrying the data payload.
E1 transmission utilizes two main types of framing: Frame Alignment Signal (FAS) and Multi-
Frame Alignment Signal (MFAS). Framing is necessary in order for equipment receiving the E1
signal to be able to identify and extract the individual channels. PCM-30 (CAS) transmission
system use MFAS framing along with the FAS framing. PCM-31 (CCS) transmission system use
only FAS framing.
Frame Alignment Signal (FAS)
The 2.048 Mbps frame consists of 32 individual time slots (numbered 0-31). As described
previously, each time slot consists of an individual 64Kbps channel of data. In the FAS format,
time slot 0 of every other frame is reserved for the frame alignment signal pattern. Alternate
frames contain the FAS Distant Alarm indication bit and others bits reserved for national and
international use.
To Next Page
Loading...
Need help?
General