From GSM to LTE: An Introduction to Mobile Networks and Mobile Broadband

1.3 Transmission Speeds

The smallest transmission speed unit in a classic circuit-switched telecommunication network is the digital signal level 0 (DS0) channel. It has a fixed transmission speed of 64 kbit/s. Such a channel can be used to transfer voice or data, and thus it is usually not called a speech channel but simply referred to as a user data channel.

The reference unit of a telecommunication network is an E-1 connection in Europe and a T-1 connection in the United States, which use either a twisted pair or coaxial copper cable. The gross datarate is 2.048 Mbit/s for an E-1 connection and 1.544 Mbit/s for a T-1. An E-1 is divided into 32 timeslots of 64 kbit/s each, as shown in Figure 1.3 while a T-1 is divided into 24 timeslots of 64 kbit/s each. One of the timeslots is used for synchronization, which means that 31 timeslots for an E-1 or 23 timeslots for a T-1, respectively, can be used to transfer data. In practice, only 29 or 30 timeslots are used for user data transmission while the rest (usually one or two) are used for SS-7 signaling data (see Figure 1.3). More about SS-7 can be found in Section 1.4.

Figure 1.3 Timeslot architecture of an E-1 connection.

A single E-1 connection with 31 DS0s is not enough to connect two switching centers with each other. An alternative is an E-3 connection over twisted pair or coaxial cables. An E-3 connection is defined at a speed ...