Full-duplex transmission allows for data transmission between two systems in both directions simultaneously. Both systems can send and receive at the same time. A telephone system uses full-duplex transmission in which both parties speak and hear at the same time. A full-duplex transmission over Ethernet is possible using twisted-pair and fiber-optic cabling where separate pairs and glass conductors are used for transmission in each direction thereby doubling the bandwidth capacity.

Configuring duplex setting on a Cisco Switch

The duplex interface configuration command is used to specify the duplex mode of operation for a port. There are three duplex modes Auto, Full and Half. By default Fast and Gigabit Ethernet ports are in Auto mode where Auto negotiation of duplex and speed takes place.

To change the duplex setting use the following command

SwitchA(Config)# Interface fastethernet 0/0

SwitchA(Config-if)# duplex {auto | full | half}

Microsegmentation is the segmentation of a collision domain into multiple segments. The main purpose behind this process is to segment the network in such a way that as many as possible collision domains can be created. A collision domain is a shared segment between two or possibly more devices that share the Ethernet segment and have to abide by the CSMA/CD rules, thus significant performance issues arise when multiple devices share the segment. This was the main reason why the initial Ethernet standard that used a shared coaxial cable had to be improved.

Bridges are devices that operate at Data-link layer of the OSI Model and are used to segment an Ethernet network. Due to segmentation bridges are able to solve two key problems in an Ethernet network which are the collision of frames and shared bandwidth. Collisions are part of the operation of Ethernet network, because many device share the same physical segment a collision occurs when two or more hosts attempt to communicate at the same time, thus they are said be in the same collision domain. This also implies that hosts will only get a percentage of available bandwidth due to shared connectivity.

Bridges allow an Ethernet network to be segmented into multiple collision domains thereby reducing the number of collisions and increasing the available bandwidth.


Figure 1

As shown in the picture above, a Bridge segments an Ethernet network into two collision domains. By doing so each host will share the bandwidth only with hosts in the same segment (collision domain).

Like bridges, switches perform the same function of segmenting the network into multiple collision domains, but they have many ports with each port usually connecting a single host and hence resulting in micro segmentation of the Ethernet network where each port is in a different collision domain. A switched Ethernet network replaces shared Ethernet network increasing network bandwidth because each switch port has access to full bandwidth.

Figure 2 shows a switched Ethernet network. Each host is in a different collision domain thereby increasing the bandwidth of each port to full bandwidth capacity.

Figure 2

This brings us to the end of this lesson in which we discussed duplex and microsegmentation which are one of the fundamental networking topics. Microsegmentation is one of the main concepts of Ethernet LANs and this will be helpful for us to understand the working of Spanning tree protocol (STP) in the upcoming lessons.