Network Access and Backhaul

Question 1

What is ethernet medium access control?

Answer 1

Physical layer which uses network interface cards (NICs) to connect machines to a LAN. Each NIC has a globally unique address, frames are broadcast and NICs listen for frames with their address. Transmitting NICs listen for collisions with other messages and abort/reschedule communications as needed.

Question 2

What does OSI stand for?

Answer 2

Open systems interconnection

Question 3

What are the 7 layers of the OSI model?

Answer 3

Application 
Presentation
Session
Transport 
Network
Data link
Physical

Question 4

What is the TCP/IP network?

Answer 4

An alternative to OSI with fewer layers that are less strictly enforced. It’s heavily dependent on IP, IP packets transfer information between hosts. The IP layer in the router determines the next hop based on routing tables

Question 5

Describe ad-hoc networks

Answer 5

No base stations
Node to node transmission
Often used where infrastructure is limited

Question 6

Describe wireless networks

Answer 6

Nodes broadcast messages, broadcast domains have poorly defined boundaries and the domains often overlap. Interface range is larger than useful communications range. Nodes move.

Question 7

Name 2 components of wireless networks

Answer 7

Edge devices

Access points

Question 8

How does wireless MAC work?

Answer 8

Handshake protocol with terminal silencing:
o All backlogged nodes (ones that are waiting) choose a random number R
o Each node counts down, freezing countdown whenever a neighbouring node is transmitting a package
o Transmits a RTS when it counter zero
o RTS contains a Network Allocation Vector (NAV)
 All neighbours countdowns are frozen for T = (CTS + DATA + ACK(nowledgement)
o Receiver replies with CTS
 Includes NAV for DATA + ACK
 Neighbours update NAV
o Tx sends DATA, Rx confirms with ACK
o If RTS or DATA collide (not CTS/ACK received)
 Collision has occurred
 Tx chooses a new random number R