Provides connection services and allows acknowledgement of recipients of messages
It is the most basic form of Flow Control i.e. controls the amount of data that is sent at once so that the receiver is not overloaded
Allows devices to make request to receive less data at a time or to replay some data
Provides basic error control feature allowing receiver to communicate that a data frame was not receiver or it was corrupted
This error handling is performed using Checksum

Communication Synchronization

Isochronous
Network devices use a common reference clock source and generate time slots for transmission
Less overhead as devices know when they can communicate and for how long

Synchronous
Network devices agree on a clocking method to indicate beginning and end of frames and can use control characters

Asynchronous
Network devices use there own internal clocks and use start and stop bits
No control on when the devices are allowed to communicate

Devices & Protocols

NIC/ Bridges/ Switches
MAC Address