Switched Ethernet vs. Classic Ethernet

Ethernet is a set of technologies and protocols that are used primarily in LANs. It was first standardized in 1980s as IEEE 802.3 standard.

Ethernet can be broadly classified into two types −

What are Classic Ethernet and Switched Ethernet?

Classic Ethernet is the original form of Ethernet that provides data rates between 3 to 10 Mbps. The stations are connected by hubs that allow each station to communicate with every other station in the LAN. There are a number of varieties of classic Ethernet, commonly referred as 10BASE-X. Here, 10 is the maximum throughput, i.e. 10 Mbps, BASE denotes use of baseband transmission, and X is the type of medium used.

The common varieties of classic Ethernet are −

• Thick coax (10BASE-5)
• Thin coax (10BASE-2)
• Twisted pair (10BASE-T)
• Ethernet over Fiber (10BASE-F)

In switched Ethernet, the hub connecting the stations of the classic Ethernet is replaced by a switch. The switch connects the high-speed backplane bus to all the stations in the LAN. The switch-box contains a number of ports, typically within the range of 4 - 48. A station can be connected in the network by simply plugging a connector to any of the ports. Connections from a backbone Ethernet switch can go to computers, peripherals or other Ethernet switches and Ethernet hubs.

Architecture of Classic Ethernet and Switched Ethernet

Classic Ethernet is simplest form of Ethernet. It comprises of an Ethernet medium composed of a long piece of coaxial cable. Stations can be connected to the coaxial cable using a card called the network interface (NI). The NIs are responsible for receiving and transmitting data through the network. Repeaters are used to make end-to-end joins between cable segments as well as re-generate the signals if they weaken. When a station is ready to transmit, it places its frame in the cable. This arrangement is called the broadcast bus.

Unlike classic Ethernet in which the channel is shared by the stations, in switched Ethernet, each station gets a dedicated connection. When a port of the switch receives a frame, it checks the destination address in the frame and then sends the frame to the corresponding port, for outgoing data.

In switched Ethernet, collisions do not occur in the channel due to the presence of dedicated connection to each station. However, collisions may still occur in a destination port if it receives frames from more than one ports simultaneously. In a switch, each port has its own individual collision domain and resolves it individually.

Key Differences

Frame Formats

The frames for transmission of both classic Ethernet and switched Ethernet are same except for one field. Both of them have seven fields. The difference between the two is that while classic Ethernet has a Type field, switched Ethernet has Length field. The fields are −

• Preamble: It is a 7 bytes starting field that provides alert and timing pulse for transmission.
• Destination Address: It is a 6 byte field containing physical address of destination stations.
• Source Address: It is a 6 byte field containing the physical address of the sending station.
• Type/Length: It a 2 bytes field. In classic Ethernet it is 'Type' field that instructs the receiver which process to give the frame to. In switched Ethernet, it is 'Length' field that stores the number of bytes in the data field.
• Data: This is a variable sized field carries the data from the upper layers. The maximum size of data field is 1500 bytes.
• Padding: This is added to the data to bring its length to the minimum requirement of 46 bytes.
• CRC: CRC stands for cyclic redundancy check. It contains the error detection information.