The transmission mode refers to the manner in which the two devices in a network communicate with each other. A Communication channel where data transmission takes place in a physical transmission medium or a logical connection over a multiplexed medium. The physical transmission medium may be copper or fiber and logical connection can be a circuit/Packet switching connection such as wireless transmission.

There are three different modes of communication. They are

• Simplex Communication
• Half Duplex Communication
• Full Duplex communication

Simplex Communication

In this mode of communication, the network cable or communication channel can transfer data in only one direction. Simplex communication is permanent unidirectional communication. It is like a one-way road in which the traffic travels only in one direction, no vehicle from the opposite direction is allowed to enter.

The connectionless protocol should be used in simplex mode. This mode does not allow any acknowledgment to be sent back to the sender.

Example of Simplex communication

Radio – The radio signal is transmitted across and the receiver receives the signal. It is the responsibility of the receiver to check if the message is received correctly and there is no error

Television – Television also uses a simplex mode of communication since they cannot talk back to the satellites that are transmitting.

Keyboard and Monitor are the examples of the simplex mode as a keyboard can only accept the data from the user and the monitor can only be used to display the data on the screen.

simplex fiber optic cable – A simplex fiber optic cable consists of one single strand of glass of plastic fiber and one single outer jacket. Simplex fiber is most often used for applications that only require one-way data transfer.

Simplex mode of communication can be used for broadcasting and entire bandwidth can be used during the transmission.

Half Duplex Communication

The half-duplex mode communication can send the data in both directions but not simultaneously. It can either use the communication channel to send the data or the same channel can be used to receive the data at a time. In this mode of operation, the receiver detects the error in the data and ask the transmitter to send the corrupted data again.

It is still a one-way road, in which a vehicle traveling in the opposite direction of the traffic has to wait until the road is empty. The entire channel capacity is utilized by the transmitter, transmitting at that particular time.

Network hubs run in half-duplex mode

Walkie-talkie – It is a half-duplex device where the Push-to-talk button used to transmit. one party speaks, and another party listens. After a pause, the other speaks and the first-party listens. Speaking simultaneously not understood.

Full Duplex communication

The full-duplex communication permits data to be sent and received by the same communication channel simultaneously. The sender and receiver both can transmit and receive simultaneously at the same time. A full-duplex mode can greatly increase the efficiency of communication. The full-duplex transmission mode is like a two-way highway road in which traffic can flow in both the direction at the same time. Here the capacity of the channel is shared by both the transmitted signal traveling in the opposite direction.

telephone network – In the telephone system, people at both ends communicating with each other both can talk and listen at the same time.

Duplex fiber optic- A duplex fiber optic cable consists of two-strand fibers of glass or plastic, and it can be regarded as two simplex cables. here simultaneous, bi-directional data transfer. (One fiber transmits data one direction and another fiber transmits data in the opposite direction.)

Full-duplex Ethernet uses two pairs of wires at the same time instead of a single wire pair like half-duplex.

Configuring Speed and Duplex Mode in CISCO Switch/Router

Autonegotiation feature that allows the router/switches to negotiate the speed and duplex mode with the corresponding interface at the other end of the connection. By default Autonegotiation(auto) is enabled in Cisco Switch/Router. We can alter both mode and speed but not in all switches/Routers.

To set the mode of interface use duplex command  with mode auto, full, or half

Switch(config-if)#duplex ?
  auto  Enable AUTO duplex configuration
  full  Force full duplex operation
  half  Force half-duplex operation.

To set the speed of the interface use speed command  with mode auto,100, or 10

Switch(config-if)#speed ?
      10    Force 10 Mbps operation
      100   Force 100 Mbps operation
      auto  Enable AUTO speed configuration

Auto-MDIX– Switch-to-Switch or Switch-to-router requires using different Ethernet cable straight-through or crossover. Using the automatic medium-dependent interface crossover (auto-MDIX) feature on an interface eliminates this problem. either type of cable can be used to connect to other devices, and the interface automatically corrects for any incorrect cabling.

When using auto-MDIX on an interface, the interface speed and duplex must be set to auto so that the feature operates correctly.

Switch(config-if)#mdix ?
auto Enable automatic MDI crossover detection on this interface

Switch#configure terminal
Switch(config)#interface fa0/1
Switch(config-if)#speed auto
Switch(config-if)#duplex auto
Switch(config-if)#mdix auto

NOTE: The auto-MDIX feature is enabled by default on Catalyst 2960 and Catalyst 3560 switches but is not available on the older Catalyst 2950 and Catalyst 3550 switches.

Setting the Speed and Duplex Mode in Windows

Go to Start > Control Panel > Network and Internet > Network and Sharing Center. In the left-hand column, click Change adapter settings. A new screen will open with a list of network connections.

Right-click Local Area Connection >Properties >click on configure >Go to advance tab > search for Speed & Duplex default value on right side set as Auto Negotiation