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35 Cards in this Set
- Front
- Back
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What is a transport layer packet called? |
Segment |
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What is a link layer packet called? |
Frame |
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What is a network layer packet called? |
Datagram |
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What is the link layer responsible for? |
Transferring datagram from one mode to a physically adjacent node |
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What is a parity check? |
Check to make sure data has either odd or even number of 1 bits |
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How does CRC work?
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Sender and receiver both have r+1 bit pattern called generator, choose r bits, R such that DR divides by G, if the remained isnt 0 when checked we have an error |
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What four things do we want from a MAP? |
When one node transmits, it transmits at R When M nodes transmit, they transmit at R/M Full decentralised Simple |
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What are the 3 mac protocol types? |
Channel partitioning Random access Taking Turns |
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What is TDMA? |
Time division multiple access |
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What is FDMA? |
Frequency division multiple access |
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What are the properties of slotted aloha? |
All frames are the same size and divided by time to transmit 1 frame Nodes start to transmit at slot beginning Nodes are synchronised If 2 or more transmit in same slot, both detect collision |
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What is the efficiency of slotted aloha? |
.37 |
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What is unslotted aloha? |
Not split into slots, transmit immediately |
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What is the efficiency of unslotted aloha? |
.18 |
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What is CSMA? |
Listen before transmission Transmit only if channel idle
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How can collisions occur in CSMA? |
Propagation delay means nodes may not hear each others transmissions |
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What is CSMA/CD? |
CSMA with collision detection, can abort half way through transmission if detect collision |
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What is binary backoff? |
After mth collision, NIC chooses K at random from 0....2^m-1, and waits K.512 bit times then restarts |
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What is the efficiency of CSMA/CD? |
1 |
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What is polling? |
The master node invites slaves to transmit |
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What are disadvantages of polling? |
Overhead Latency Single point of failure |
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What is token passing? |
A token is passed around and nodes only transmit when they have it |
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What are issues with token passing? |
Token overhead latency Single point of failure |
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What is a LAN address? |
Mac address, administered by IEEE Manufacturers buy a portion of address space |
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What is ARP? |
Address resolution protocol, how to determine IP based on MAC? |
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What is an ARP table? |
Table that contains IP address, MAC and TTL for each IP node |
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What is an ARP query? |
Node asks for mac from IP, sent to everything on network |
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What is ethernet preamble used for? |
Syncing receiver/sender clock rates |
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What is in an ethernet frame? |
preamble, destination, source, type, data, CRC |
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Does ethernet use handshaking? |
No. |
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Why is ethernet unreliable? |
No acks or nacks used |
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What is ethernets MAC protocol? |
CSMA/CD with binary backoff |
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What does a switch table contain? |
MAC of host, interface its connected to, TTL |
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What does a switch do if it does not have a host in its switch table? |
Sends it to all interfaces |
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What is MPLS? |
Multiprotocol label switching, path to destination based off source and destination, not just destination |
