When a host connects to a switch port, the switch creates a dedicated connection. When two connected hosts communicate with each other, the switch consults the switching table and establishes a virtual connection, or microsegment, between the ports.
The switch maintains the virtual circuit (VC) until the session terminates. Multiple virtual circuits are active at the same time. Microsegmentation improves bandwidth utilization by reducing collisions and by allowing multiple simultaneous connections.
Switches can support either symmetric or asymmetric switching. Switches that have ports of all the same speeds are termed symmetric. Many switches, however, have two or more high-speed ports. These high-speed, or uplink ports, connect to areas that have a higher demand for bandwidth. Typically, these areas include:
Connections to other switches
Links to servers or server farms
Connections to other networks
Connections between ports of different speeds use asymmetric switching. If necessary a switch stores information in memory to provide a buffer between ports of different speeds. Asymmetric switches are common in the enterprise environment.
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Typically, when connecting different types of devices, use a straight-through cable. And when connecting the same type of device, use a crossover cable.
1. Straight-through UTP Cables
Identifying the cable standard used allows you to determine if you have the right cable for the job. More importantly, it is a common practice to use the same color codes throughout the LAN for consistency in documentation.
Use straight-through cables for the following connections:
- Switch to a router Ethernet port
- Computer to switch
- Computer to hub
2. Crossover UTP Cables
For two devices to communicate through a cable that is directly connected between the two, the transmit terminal of one device needs to be connected to the receive terminal of the other device.
The cable must be terminated so the transmit pin, Tx, taking the signal from device A at one end, is wired to the receive pin, Rx, on device B. Similarly, device B's Tx pin must be connected to device A's Rx pin. If the Tx pin on a device is numbered 1, and the Rx pin is numbered 2, the cable connects pin 1 at one end with pin 2 at the other end. These "crossed over" pin connections give this type of cable its name, crossover.
To achieve this type of connection with a UTP cable, one end must be terminated as EIA/TIA T568A pinout, and the other end terminated with T568B pinout.
To summarize, crossover cables directly connect the following devices on a LAN:
- Switch to switch
- Switch to hub
- Hub to hub
- Router to router Ethernet port connection
- Computer to computer
- Computer to a router Ethernet port
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