E1 Interface & Specification

Details and notes about the E1 interface, specification, connector types, signals, E1 lines, E1 cards, etc.

E Carrier telecommunications lines includes:
E Carrier basics E1 link & circuit E1 interface

The E1 interface requires accurate definition in a standard or specification to ensure that equipment from different suppliers is able to operate together.

With E1 systems and E1 lines widely deployed around Europe and the rest of the world, the E1 interface has been defined in a standard or specification to ensure its successful operation.

The E1 physical interface defines the various parameters required to ensure correct electrical operation of the circuit.

E1 interface basics

The E1 standard is defined under the specification or standard G.703 which is defined by the ITU-T - International Telecommunications Union, Telecommunication Standardisation Sector.

The ITU G.703 standard sets down the various physical parameters for the physical interface. These include a number of elements.

Parameter	Specification limits or details
Pulse shape	Normally rectangular
Conductor pairs in each direction	One coaxial line (i.e. centre and outer conductors)	One symmetrical pair (e.g. twisted conductor pair)
Test load impedance	75 ohms (resistive)	120 ohms (resistive)
Peak voltage of Mark condition	2.37 V	3 V
Peak voltage of space	0 ± 0.237 V	0 ± 0.3 V
Ratio of the amplitudes of positive and negative pulses at the centre of the pulse interval	0.95 - 1.05
Ratio of the widths of positive and negative pulses at the nominal half amplitude	0.95 - 1.05
Nominal pulse width	244 ns

The attenuation of the transmission lines used for carrying he data needs to be characterised as well. The standard assumes a √f law, and that the loss at the basic frequency of operation, 2048 kHz should be in the range 0 to 6 dB (minimum value). This loss must take into account any loss incurred in the digital distribution frame between the terminal equipments. In other words the loss required is between the driver and receiver.

Typical E1 interface connectors and implementation

The E1 interface uses a differential format using different transmit and receive pairs.

The most common physical formats for the data transmission are two coaxial cables terminated in BNC connectors, or twisted pairs terminated with RJ-48C connectors.

The RJ-48C connector has a total of eight connections.

Signal Name	RJ-48C Connector	BNC
Transmit Tip	5	TX BNC centre pin
Transmit Ring	4	TX BNC outer
Receive Tip	2	RX BNC centre pin
Receive Ring	1	RX BNC outer
Receive Shield	3
Transmit Shield	6
Not assigned	7
Not assigned	8

E1 lines are widely used for a variety of applications including Voice, Internet Access, X.25, Multiplexed data, ISDN, ATM and more. For example they are widely used for small exchanges and also for connecting mobile phone base stations to large switching centres. Both E1 lines are frequently connected to X.21, V.35 or other connections via network interface converters before connection to the communications equipment.