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Designing A Flyback Converter with Si9113 for Feeding the TE from U-Interface In ISDN

Vishay Semiconductors 

AN728

Vishay Siliconix

110/220 VAC

TE1

R

TE2

110/220 VAC

Needed Only

for Long Loops

Battery Voltage

(48- to 60-V Typ.)

TE1

S

Si9113

U

U

dc-dc Converter

RG

NT

Central

Office

Switch

TA

Customer

Premises

Transmission

Line

Local Telephone

Exchange

FIGURE 12. ISDN Functional Groups and Reference Points

ISDN REFERENCE MODEL

Figure 12 is a reference model and shows how various

functional groups are connected together to gain access to the

ISDN network. The points which divide the functional groups

are referred to as reference (interface) points, and will typically

correspond to a particular physical interface connecting two

pieces of equipment.

The S-interface is also known as the user-network interface

(UNI) as it represents the common interface at which terminal

equipment (TE) can be connected to the ISDN. The functions

are:

D Terminal equipment, type 1 (TE1): examples are

telephones, fax machines and videophones which can be

directly connected to the S-interface and have the ability

to establish and terminate a call.

D Terminal equipment, type 2 (TE2): examples are analog

phones, computers, and communications terminal

equipment. TE2’s do not have an ISDN UNI and rely on a

terminal adapter (TA) to operate as the TE1 functional

group in order to connect to S-interface.

D Terminal adapter (TA): adapts a non-ISDN terminal to the

ISDN. It will contain functions which include layer 1

(physical layer) and higher layers (including call

processing) of the OSI reference model.

D Network Termination, type 1 (NT1): It marks the point at

which the public network ends and the customer premise

begins. NT1 equipment provides a conversion at the

physical layer between S-interface that runs inside a

customer premise and the subscriber loop cable at the

U-interface that connects to the local exchange. An

important function of NT1 is to feed power to the TE

either from the local mains supply or from the network as

a backup when the mains power fails.

D Network Termination, type 2 (NT2): Unlike NT1

equipment that provides only a physical translation

between S- and U-interfaces, NT2 equipment may also

incorporate more complex functions such as switching

and multiplexing. A private branch exchange (PBX),

inside customer premises, routes calls and provides its

users with internal voice services, as well as access to

external lines connected to the ISDN. Such an

ISDN-based PBX belongs to the NT2.

Line Termination (LT): LT marks the end of the ISDN subscriber

loop. It is typically located within the local exchange equipment

as a line card containing the terminations for a number of

subscriber lines. If the distance between LT and NT is greater

than that supported by the U-interface, a signal regenerator

(RG) is required.

U-Interface

To NT

Protection

Circuit

Protection

Circuit

To Local

Exchange

dc Voltage

Sink

www.vishay.com S FaxBack 408-970-5600

8

dc Voltage

Source

FIGURE 13. Power Feed Configuration at the U-Interface

Document Number: 71120

29-Feb-00

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