Ethernet

In the past, the Ethernet protocol required a coaxiale cable on which hosts interconnect. All the hosts electrically shared a bus.

In the past hosts ethernet interfaces were connected through a vampire tap junction.

Nowadays, the interfaces are connect to the cable using a T-junctions.

The difference between them is that the first one connects electrically to the cable (connecting it to a cable cut) and the second one is used only in ethernet cables that are physically composed by different cable (segments) and the T-junction is put at intersection of two segments.

The protocol supports Carriege Sense Multiple Access Collision Detection (CSMA/CD), used for coordination between hosts, that it's composed by two strategies:

• Carrier sense An host can't speak while anyone else is speaking Collision detection the protocol resolves conflicts raised during the contention time.

• Contention time the time in which people, that respect first rules, can also go in conflict starting talking together at the same moment.

Ethernet frame

• Preamble synchronization signal 10101010...1010 011 where the last three bits are called SFD().

• Destination address & Source address MAC (Medium Access Control) addresses, that are Hardware identifiers (broadcast= ff:ff:ff:ff:ff:ff ).

• Type type of upper layer protocol used (e.g. Internet Protocol = 0x0800 ).

• Payload payload of the ethernet frame.

• FCS Frame check sequence (FCS) is a CRC that allows detection of corrupted data within the entire frame as received on the receiver side.