Networking Concepts Flashcards
What is the Internet?
Billions of interconnected devices.
Hosts = end systems
running network applications
What are the communication links?
fiber, satellite, copper, radio
transmit data
the transmission rate is measured in bandwidth
What do packet switches do?
Forward packets (chunks of data)
What do protocols do?
Control the sending and receiving of messages
define format, order of messages sent and received among network entities and actions taken on message transmission and receipt.
Examples: TCP, IP, 802.11, HTTP
What does TCP stand for?
Transmission Control Protocol
What is the network edge?
host: clients and servers
servers often in data centers
access networks, physical media: wired, wireless communication links
What is the network core?
interconnected routers, network of networks
How do we connect end systems to edge routers?
Through residential access networks, institutional networks (schools, companies), and mobile access networks.
What is NAT?
Network Address Translation: the process where a network device assigns a public address to a computer or group of computers on a private network.
Describe a home network setup?
devices are connected to either a wireless access point or wired ethernet. Which is connected to your local router (This is where the firewall is located as well as NAT occurs), your router is connected to a modem to your ISP.
Describe a enterprise network setup?
Devices are connected to either a wireless access point or directly to an ethernet switch. Which can be connected to a main router that links out to the ISP.
Describe packet switching:
hosts break application-layer messages down into packets which are forwarded from router to router until they get from the source to the destination.
L/R - transmission delay (Length of packet/rate of transmission)
What is queueing delay and how can it lead to packet loss?
if the arrival rate of packets exceeds the transmission rate of the link, packets will queue up and wait to be transmitted. Packets can be accidentally dropped if memory (buffer) fills up
What is the IP(Internet Protocol) stack?
Application Layer - supporting network applications (HTTP, SMTP)
Transport - proces-process data transfer (TCP, UDP)
Network - routing of datagrams from source to destination (IP, routing protocols)
Link: data transfer between neighboring network elements.
(Ethernet, 802.11)
Physical: bits on the wire
What is the OSI (Open systems interconnection) model?
Application
Presentation: Allows applications to interpret the meaning of data (encryption, compression)
Session: synchronization checkpointing, recovery of data exchange.
Transport
Network
Link
Physical
Explain TCP vs UDP (User Datagram Protocol) transport layer protocols?
TCP - reliable, in order delivery.
UDP - unreliable, unordered delivery.
- barebones
- Packets may be lost or out of order
- no handshaking
- small header size
- less delay
uses: streaming multimedia apps, DNS
What is in a UDP segment header?
source, destination, length, data, checksum
What is the goal of a checksum?
to detect “errors” (flipped bits) in transmitted segments
What is pipelining?
Sender allows multiple “in-flight”, yet to be acknowledged pkts.
Two generic forms:
Go-back-N
Selective Repeat
Explain Go-Back-N:
Sender can have up to N un-acknowledged packets in the pipeline.
receiver only sends cumulative ack.
sender has a timer for oldest unacked packet-when the timer expires, retransmit all unacked packets.
Explain Selective repeat:
Sender can have up to N un-acknowledged packets in a pipeline.
receiver sends individual acks for each packet.
sender maintains timer for each unacked packet.- when timer expires only resend the un-acked packet.
What is in a TCP segment structure?
source, destination, sequence number, ack number, receive window, length, checksum, data
What are some of the network layer functions?
Routing protocols - path selection (forwarding table)
IP - addressing conventions
packet handling conventions
datagram format
ICMP- error reporting
router signaling
What are some link layer services?
Flow control, error detection, error correction
What is parity checking ? (two dimensional bit parity)
detects and corrects single bit errors (remember even and odd parity)
What is Cyclic Redundancy Check (CRC)?
A more powerful error detection tool. View data bits as a Binary number ‘D’, Choose ‘r’ bits such that ‘D’/’G’ = will give exactly ‘r’.
If there is a non zero remainder there are errors detected. G is a generated bit pattern that is D is evenly divisible by.
What is an Ethernet Frame?
The encapsulated IP datagram (network layer protocol packet).
Contains: preamble, dest, source, type, data, CRC.
What are some examples of Single bit error detection.
1-D Parity, Checksum
What are some example of multi-bit error detection.
CRC, Hamming Code
What are some examples of single bit error correction
2-D parity, Hamming Code
What is an example of multi-bit error correction.
Convolution Codes
What are some characteristic of 1-D Parity Bit checking?
Simplest error checking mechanism - very limited reliability.
can be utilized alongside other detection correction methods
can only detect single bit,
cannot correct errors
if an error is found, it cannot tell if it is the actual parity bit that is wrong or a data bit.
What are some characteristics of Hamming Code error detection and correction?
Can correct single bit errors
Can detect 2-bit errors, but can only correct 1-bit errors
How do we determine the MAC address of a machine knowing its IP address?
Using ARP: Address resolution protocol
How do switches know which end devices are reachable through which interfaces?
They have a forwarding table - think of it like a routing table.
A switch will learn which hosts are connected to it through which interfaces as it receives transmissions from it. It will store the sender/location pair in its switch table
What are some characteristics that differentiate Wireless links from Wired links?
- decreased signal strength
- interference from other sources - standardized wireless network frequencies are shared by other devices - phones, roku etc
multipath propagation - radio signals reflect off objects, ground, and arrive at destination at slightly different times.
communication across wireless links are much more difficult
What is the hidden terminal problem?
multiple wireless senders and recievers create additional problems (beyond multiple access)
B,A - can hear each other
B, C - can hear each other
A,C - cannot hear each other, meaning they are unaware of their interference at B
What is UWSN ?
UnderWater Acoustic Sensor Networks (UW-ASN).
Uses sound as underwater wireless communication medium
What are some applications of underwater sensor networks?
Seismic monitoring Pollution Monitoring Ocean current monitoring equipment monitoring and control Autonomous Underwater Vehicles
Why use sound for underwater networks?
Optical or light - is affected by scattering
Radio waves- cannot transmit at high frequencies underwater. It would require an extremely large antennae to work.
What are some challenges faced by underwater networks?
Battery power is limited - solar energy charge cannot usually be exploited
available bandwidth is limited
long delays
high bit error rates
underwater sensors prone to corrosion
What year was bluetooth version 1.0 released?
1999
What is the name of the organization that founded Bluetooth?
SIG - Bluetooth special interest group
What band frequency does bluetooth operate at?
2.4 GHz
What are some ways you can make sure bluetooth does not interfere with Wifi?
TDM - Time division multiplexing
using 5GHz bandwidth
