2. Link layer and LAN

2. Link layer and LAN - Why link layer? a protocol in the...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
Why link layer? a protocol in the link layer (layer 2) provides services to the protocols in the network layer (layer 3). The most basic service of any link-layer protocol is to move a datagram from one node to an adjacent node over a single communication link . Data-link layer has responsibility of transferring datagram from one node to adjacent node over a link Error-detection and –correction techniques, e.g. parity check, cyclic redundancy check (CRC) Single Bit Parity: Detect single bit errors Two Dimensional Bit Parity : Detect and correct single bit errors Multiple access methods: TDMA, FDMA, CDMA, CSMA (e.g. ALOHA, Slotted ALOHA, CSMA/CD, CSMA/CA) (concepts) TDMA TDMA: time division multiple access access to channel in "rounds" each station gets fixed length slot (length = pkt trans time) in each round unused slots go idle example: 6-station LAN, 1,3,4 have pkt, slots 2,5,6 idle
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
FDMA FDMA: frequency division multiple access channel spectrum divided into frequency bands each station assigned fixed frequency band unused transmission time in frequency bands go idle example: 6-station LAN, 1,3,4 have pkt, frequency bands 2,5,6 idle CDMA CSMA/CD: carrier sensing, deferral as in CSMA collisions detected within short time colliding transmissions aborted, reducing channel wastage Collision detection: easy in wired LANs: measure signal strengths, compare transmitted, received signals difficult in wireless LANs: received signal strength overwhelmed by local transmission strength Human analogy: the polite conversationalist CSMA Listen before transmit: If channel sensed idle: transmit entire frame If channel sensed busy, defer transmission human analogy: don’t interrupt others! Collisions
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 02/26/2012 for the course CSC 138 taught by Professor Jingsong during the Spring '11 term at CSU Chico.

Page1 / 6

2. Link layer and LAN - Why link layer? a protocol in the...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online