Fixed digital services (or leased lines) are fully digital, end-to-end point-to-point links with no analogue conversion. They replaced analogue leased lines in the 1980s and 1990s for corporate WAN connections.

1. Service E0 (64 kbps)

The standard 64 kbps digital service has been designated E0 within the European telecommunications sector. The analogue modem is replaced by an NTU (Network Terminating Unit) and the interface standard used is X.21/V.11. The data remains in digital format throughout the connection, which improves quality and reduces latency.

2. Service E1 (2,048 Mbps)

When speeds need to exceed 64 kbps, an E1 link is the solution. This type of line provides a fully digital service at 2.048 Mbps (European standard). The NTU is replaced by an LTE (Line Termination Equipment) and the interface with the customer’s unit complies with the G.703 standard.

There are two types of E1 links:

Unstructured link: the total bandwidth of 2.048 Mbps is provided as a transparent service (a single data channel).

Structured link: the link is pre-divided into 32 time slots (Time Slots) of 64 kbps. 30 channels are available for data, 1 for frame synchronisation (TS0) and 1 for signalling (TS16).

3. European and American numerical hierarchies

European Standards

Flow rate

American Standards

Flow rate

E0

64 kbps (1-channel DS0)

DS0

sixty-four kilobits per second

E1

2.048 Mbps (30 B-channels)

T1

1.544 Mbps (24 channels)

E2

8,448 Mbps (4×E1)

T2

6,312 Mbps

E3

34,368 Mbps (4×E2)

T3

44,736 Mbps

E4

139,264 Mbps (4×E3)

T4

274,760 Mbps

ℹ E1 in modern networks

E1 access (2 Mbps) was the standard WAN connection for businesses from 1990 to 2010. It has now largely been replaced by Ethernet access (10/100/1000 Mbps over fibre optic) and high-speed internet connections (VDSL2, FTTH). E1 links remain in use in certain telephone signalling networks (SS7, ISDN PRI) and in developing countries where fibre has not yet been rolled out.

Modifié le: vendredi 9 octobre 2026, 09:46