Role of Sockets & Connectors

  • Sockets, also known as jacks, act as the terminating end point of the Transceiver/PHY.
  • Connectors, also known as plugs, act as the terminating end point of the telecommunication link cable.
  • Together, the sockets and connectors, act as an interface between the PHY and the telecommunication link, to carry the electrical/electromagnetic/optical signals for data transmission and reception.
  • Sockets and Connectors come in different sizes, shapes, functionalities and are interface/protocol specific. For e.g. Ethernet interface typically use RJ-45 sockets, serial interfaces use V.xx sockets etc.

The diagram given below shows a few types of sockets and their respective connectors:

Examples of socket/connector pairs

Examples of socket/connector pairs

In the diagram shown above, all the sockets are female type sockets (i.e. they have holes and not pins) and all the cable connectors are male type plugs (i.e. they have pins at their end). For some interfaces like serial, the reverse types are also possible, where the sockets are  of type male and the cable connectors are of  type female.

Mechanical, Electrical and Functional Specifications for sockets/connectors

  • For each  socket and connector type, there is  a standard mechanical specification that specifies the mechanical properties of the socket/connector,  like size, shape, number of pins.
  • Similarly, for each socket/connector type, there is an electrical specification, that specifies the roles of each pin (like transmit, receive, ground, clock etc.) and the corresponding voltage/signal value to be used on that pin. For e.g., in a specific socket, pin number 4 may have to be set to +0.85V for a duration of 5 ms to transmit a  digital 1 bit. 
  • Additionally, for each socket/connector type, there is a functional specification, that defines the sequence of steps required to transmit and receive data through these sockets. For e.g. in serial cables, the DTE pin has to be enabled before transmitting data. Similarly, the DCD (data carrier detect) pin has to be enabled before receiving data from the cable.
  • All these socket/connector specifications like mechanical, electrical and functional are considered to be part of the physical layer.

The diagram gives below an example pin assignment for a RJ-45 jack:

Example pin functionality assignments for a RJ-45 jack

Example pin functionality assignments for a RJ-45 jack

In the diagram above, out of the 8 pins, four pins, namely pins 4,5, 7 and 8 are unused. While pin numbers 1 and 2 are used for transmission of data, pin numbers 3 and 6 are used for reception of data.

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