LANs -> local area network technology

Terminology: -> host/routers: nodes -> communication channels/paths that connect nodes: links - wired, wireless - LANs -> layer 2 packet: frame

• The link layer has the responsibility of transfering datagram from one node to the physical adjacent one over a link

• Datagrams have different linking protocols depending on the link (wifi, ethernet, ...)

• Datagrams travel through differente links (wifi, ethernet, ...)

6.1.1 Link Layer Services

Framing: encapsulates datagrams into frames adding: -> header -> trailer(control bytes) -> If shared medium, channel access control -> MAC address

Reliable delivery: -> rarely used on low bit-error links
-> wireless links: high error rates

Flow control: -> pacing between adjacent sending and receiving nodes

Error Detection: ->errors caused by signal attenuation, noise.
->receiver detects errors, signals retransmission, or drops frame

Error Correction: -> receiver identifies and corrects bit error(s) without retransmission

Half-Duplex and Full-Duplex: ->with half duplex, nodes at both ends of link can transmit, but not at same time

6.1.2 Where Is the Link Layer Implemented?

• The link layer is implemented on every host as well as the physical layer in a chip or a Network Interface Card(NIC) (EX: Ethernet chip set)
• Combines hardware, software and firmware