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| title | aliases | tags | ||
|---|---|---|---|---|
| 21-data-link-layer-LAN |
|
data link layer services
- transfer datgram from one node to physically adjacent node over a link
- terminology
- hosts and routers: node
- communication channels between adjacent nodes: links
- wired
- wireless
- LANs
- layer-2 packet: frame, encapsulates datagram
services
- framing, link access:
- encapsulate datgram into frame, add head, trailer
- do not use IP address
- use MAC address in frame headers
- reliable delivery of data between adjacent nodes
- flow control: pacing between adjacent sending and recieving nodes
- error detection and correction
- errors from: signal attenuation, noise
- receiver detects errors and signals retransmission, or drops frame
- reciever identifies and correct bit error(s) without retransmission
implemented in network interface card: (NIC) or on a chip
- ethernet, WiFi card or chip
- implements link and physical layer
each NIC has a unique ID - MAC (medium access control)
- 48 bits: six groups of two hex digits
- also called physical address, ethernet hardware address
- manufacturer buys portion of MAC adress space (to assure uniqueness)