E2 Frame Overview

Multiplexing E1 into E2

The E2 stream is the second level in the European PDH hierarchy. It is created by multiplexing four independent E1 tributary streams, each operating at 2.048 Mbit/s. While the combined data rate of the four tributaries is $4 \times 2,048 = 8,192 \text{ Mbit/s}$, the total bit rate of the resulting E2 stream is 8.448 Mbit/s.

This additional capacity ($8,448 - 8,192 = 0,256 \text{ Mbit/s}$ or 256 kbit/s) constitutes the overhead necessary for frame alignment, alarms, and, most importantly, the bit stuffing (justification) required to synchronize the four plesiochronous E1 streams.

The E2 Frame Structure

The 8.448 Mbit/s E2 stream is organized into a repeating frame structure that is precisely defined to accommodate both user data from the tributaries and the required overhead.

Key Frame Parameters:

• Total Frame Length: The E2 frame consists of 848 bits.
• Frame Duration: The time to transmit one frame is approximately 100.38 µs ($848 \text{ bits} / 8.448 \times 10^6 \text{ bits/s}$).
• Structure: The frame is divided into four equal blocks or sets, each containing 212 bits ($4 \times 212 = 848$).

Detailed Breakdown of the E2 Frame Blocks

Each of the four blocks within the E2 frame has a specific purpose, combining overhead information with interleaved data from the E1 tributaries.