WEEK 6 DAY 2 : PERIPHERAL EQUIPMENT MODULE (PEM)

6.2 PERIPHERAL EQUIPMENT MODULE

        As we have discussed before PEMs are basically peripheries attached to the CEM which helps it to interact with outside world. These peripheries are basically huge chips called cards which are used for different applications. 

6.2.1 TYPES OF PERIPHERAL CIRCUIT CARDS

        There are several types of PEM cards but I will explain in detail only two of them.

1) TELEPHONE LINE CARD

        As the name suggests the telephone line card is basically used to connect telephone lines from individual telephones to exchange.

General Layout of Telephone line card

        Given above is a general layout for Telephone Line Card. No of circuit blocks can differ from card to card and model to model. The circuit circuit block shown above consists of relay with other elements like memory etc. 

        They can be divided into categories according to the number of circuit per cards. They are 8 , 16 , 24 , 32 circuit cards. Each line card can support a defined number of users (telephones) based on the number of circuit blocks a card has. These cards has to be programmed to work.

        When a user wishes to make a call it takes the headset of telephone equipment. When it does the relay in the Line card of that telephone goes to CEM (Control Equipment Module) which gives a dial tone to user. Now when he dials the number the CEM scans the number in its database and sends ring to the circuit card of dialled telephone. The relay in it gets into "Burst Mode" and gives ring to the concerned telephone using 75V 25Hz AC.

2) TRUNK CARD

        As you know each exchange can carry approximately 5000 lines. But sometimes we require two or three exchanges for greater capacity or we want to connect two exchanges. Here trunk card is used. They also have circuit blocks according to the capacity they have

       Basically there are 4 types of Trunk Cards which we will discuss below.

1) CO TRUNK

2) TIE TRUNK

3) E&M TRUNK ( EAR AND MOUTH )

4) 2 MB LINK (E1)

        OF these the first three cards are analog card while the last one is digital

1)  CO TRUNK (COBE 5B51 483 PIA) (4,8,16 Circuit)

        We were demonstrated the 8 circuit trunk card. The salient features are

• They use RJ-II connection.
• Telephone line is required from another exchange to connect them.
• It can also be connected to MTNL lines by giving it a code and then dialling the number.

2)  TIE TRUNK (LT1EFB51454) (4,8,16 Circuit)

        We were demonstrated the 4 circuit trunk card. The salient features are:-

• It has a single pair of connection
• It requires the tie card from another exchange if you wish to connect the exchanges
• Noise increases with distance. So it is only used for short distances only.

3) EAR & MOUTH (E&M) (LT1EFB51454) (4,8,16 Circuit)

• Very less noise.
• Other Exchange requires same card if they are to be connected together.
• There are two modes of connection

        1) Two wire mode (two pair)   2) Four wire mode (Three pair)

• Two Wire mode :- one pair each for transmitter and receiver
• Four Wire mode :- a) One pair each for transmitter and receiver b) One pair of wire for signal. This technique is cost ineffective

4) 2 MB link

• Four ports (2 for testing)
• Two connector are there which works as receiver and transmitter.
• 30 channels are supported at one time.
• Frequency multiplexing is employed for 30 channels.
• Same card is required at other exchange.
• It can also be connected directly to STM for fibre optic communication.
• It has a general output which can be connected to conference card etc.

NOTE:- For adding other three trunks, they can first be connected to 30 channel MUX and then connected to STM.

There are many other types of cards like PRI card (USED FOR E1) but we will not discuss it. That completes our exchange. Now let's proceed.

NEXT | HOME | PREVIOUS