Telecom Dictionary

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E&M Leads Signaling
E&M Leads Signaling is an interface, used for connections between switches and transmission 
systems and between transmission systems themselves. Signaling information is transferred 
across the interface via 2-state voltage conditions on two leads, each with a ground return, 
separate from the leads used for message information. The message and signaling information 
are combined and separated by means appropriate to the transmission facility.

E-mail electronic mail
electronic mail

ECSA 
Exchange Carriers Standards Assoc

EKTS 
electronic key telephone system

Electrical Signal
An electrical signal is a signal consisting of an electrical current (i.e., a flow of electrons) that 
varies with time or space in accordance with specified parameters.

Electronic Mail
Electronic mail is a generic term for non-interactive communication of text, data, image or voice 
messages between a sender and designated recipients using telecommunications.

Electronic Switched Network (ESN) Service
ESN service is a private network service that provides user organizations with a uniform 
numbering plan and numerous call-routing features. The electronic tandem switching functions 
are furnished by either PBX or Centrex switching equipment.

EMI 
electromagnetic interference; also, exchange message interface

End Office (EO)
EO is a LEC (BOC or an ITC) switching system within a LATA where local loops to customer 
stations are terminated for purposes of interconnection with each other and with trunks. CO 
(central office) and EO are often used interchangeably.

Entrance Facilities
1. in a premises distribution system, the point of interconnection be tween the building wiring 
system and external telecommunications facilities (LEC networks, other buildings, etc.). Bellcore 
defines the interface with LEC networks as end-user points of termination (POT). 2. has a further 
specific meaning in interstate access, entrance facilities for interstate access (ENFIA).

EO 
end office

EPSCS 
enhanced private switched communications service

Equipment Room
In a premises distribution system, an equipment room is a special purpose room(s), with access 
to the backbone wiring, for housing elecommunications, data processing, security, and alarm 
equipment.

erlang
An erlang is an international dimensions unit of the average traffic intensity of a facility during a 
period of time; one erlang of traffic is equivalent to a single user who uses a single resource 
100% of the time. See centicall seconds.

ESF 
extended superframe

ESN 
electronic switched network

Exchange Carrier (or local exchange carrier LEC)
An exchange carrier is any company, BOC or independent which provides intra-LATA 
telecommunications within its franchised area.

Extended Superframe Format (ESF)
ESF is an extension of the superframe format of T1 carrier systems from 12 to 24 frames and the 
use of framing bits for error checking, a facilities data link (FDL) as well as frame 
synchronization. See superframe format.