2021-05-11 MAC ARP

two types of links:

1. point to point 

2.broadcast(shared wire or medium)

-Multiple access protocol:

distributed algorithm that determines how nodes share channel,  i.e., determine when node can transmit

communication about channel sharing must use channel itself!

-MAC protocols: taxonomy

three broad classes:

§ channel partitioning ( divide channel into smaller “pieces” (time slots, frequency, code) • allocate piece to node for exclusive use)

TDMA: time division multiple access

FDMA: frequency division multiple access

§ random access (channel not divided, allow collisions • “recover” from collisions）

slotted ALOHA

ALOHA

CSMA: listen before transmit: if channel sensed idle: transmit entire frame; if channel sensed busy, defer transmission; human analogy: don’t interrupt others!

CSMA/CD:collision detection: carrier sensing, deferral as in CSMA; collisions detected within short time; colliding transmissions aborted, reducing channel wastage

CSMA/CA

§ “taking turns”( nodes take turns, but nodes with more to send can take longer turns )

Summary of MAC protocols

§ channel partitioning, by time, frequency or code

• Time Division, Frequency Division

§ random access (dynamic),

• ALOHA, S-ALOHA, CSMA, CSMA/CD

• carrier sensing: easy in some technologies (wire), hard in others (wireless)

• CSMA/CD used in Ethernet

• CSMA/CA used in 802.11

§ taking turns

• polling from central site, token passing

• Bluetooth, FDDI, token ring

ARP:https://blog.csdn.net/u014042372/article/details/80564594