Networks (Week 10) Flashcards
What do Communication Systems do?
Transmit information from a source to a destination, typically over a network.
Networks can use either analog signals (e.g. old fashioned telephone) or digital signals (e.g. Wi-Fi).
At the source: convert information into a representation that can be transmitted over the chosen network
At the destination: convert signal back into the original representation
What is an example of an conversion for Communication Systems??
Well known example for such a conversion is Morse code.
Developed in the 1830s for telegraph communication
Every letter is encoded by a sequence of short and long signals (e.g. light or sound)
What is Bandwidth?
Bandwidth is about how fast a network can transmit data. If the bandwidth is large enough, data flows smoothly. If the bandwidth is constricted, data flow can halt or stutter.
How is Bandwidth measured?
The speed at which data can be transmitted (per direction) Bandwidth is measured in bits per second: kbps, Mbps, Gbps, Tbps
Kbps – kilobits per second
Mbps – Megabits per second (a megabit is over 1000x faster than a kilobit)
Gbps – Gigabits per second
Tbps – Terabits per second (fiber optic network that carry internet traffic across major expanses such as oceans or continents)
What is Latency or Delay?
How long does it take one particular chunk of information to get from the source to the destination?
What is Ping Time?
A term related to Latency or Delay.
Ping time is the time it takes for a packet of data to go from a device, to a server, and back to the device. This time is measured in milliseconds. A high ping means longer lag time.
In terms of online gaming, lower ping means smoother gameplay.
What is Jitter?
The variability of the delay in a system (high jitter degrades quality in transmissions involving live speech or live video).
Jitter is caused by the disruption of the normal sequence sending data sets or packets. Measured in milliseconds (ms)
What is Range?
Geographical size a network can cover depending on a given technology.
Local Area Networks can span several metres (LAN)
Metropolitan Area Network (MAN) can span over 50kms.
What are some Network Types?
Network types may be based on geographical size:
- WAN – wide area network, e.g. landline telephone system
- MAN – metropolitan area network, e.g. city fibre network
- LAN – Local area network, e.g. Camosun Campus Wi-Fi Network
- PAN – personal area network, e.g. smartphone connected to headphones via Bluetooth
What is the difference between Wired and Wireless Networks?
Wired networks require physical connections with different types of cables, typically containing electrical conductors
Wireless networks use radio frequency signals (electromagnetic waves) to transmit information
What is Broadcast?
Broadcast (one-to-many)
- Radio, TV, CB radio => one sender and multiple receivers are a desired
feature of the network type - Ethernet (both Wi-Fi and wired) => multiple receivers are an unwanted side effect (in most cases)
- In many usage scenarios, there is a need to consider security measures (e.g. to avoid eavesdropping)
What are some Network Types? (regarding how many receivers)
Unicast (one-to-one)
Multicast (one-to-many)
Broadcast (one-to-all)
What is the Point to Point network type?
Point to point (one-to-one)
* Telephone network (typically connects 1 sender and 1 receiver)
* Dedicated channel or line (e.g. for company networks)
What is Ethernet? (part 1)
Ethernet (both Wi-Fi and wired) => multiple receivers are an unwanted side effect (in most cases)
In many usage scenarios, there is a need to consider security measures to avoid eavesdropping
What is Ethernet? (part 2)
Ethernet is the predominant technology for local area networks
Uses a broadcast system (invented back in the 1960s)
* Messages are broadcasted to all connected workstations…
* …but are ignored by all except the destination workstation
Every workstation (WS) has it ́s unique ID – the Media Access Control Address (MAC address) => 12 digit hexadecimal number (48 bit)
What are TV Cable Networks?
Cable networks built for analog television are currently one of the options to get a high speed Internet connection:
Designed to carry multiple TV channels simultaneously => have enough excess capacity for upload and download of data in addition to TV channels
Originally a “broadcast” (one way) system, it had to be upgraded to allow two way communication
* e.g. to enable data uploads, allow pay per view options, etc.
Upload speeds tend to be slower as most traffic is downloading.
Internet cable users may experience slower speeds at peak times (due to shared access, e.g. in an apartment building)
Typically use coaxial cables
What is a Coaxial Cable?
Coaxial cable is reliable, accurate transmission.
Shielded design – transmit data quickly due to copper core, without succumbing to interference or damage from environmental factors.
There are limitations and fibre optic cable can replace the use of coaxial.
Typically Fibre Optic cable is more expensive to start. Is becoming more and more popular as residential neighbourhoods are being wired for Fibre Optic.
What are Fiber-Optic Cables?
Fiber-optic communication transmits data as light signals through an optical fibre (instead of copper wires). Advantages:
- Higher bandwidth (up to Tbps and more)
- Longer distances (between signal repeaters)
- Immunity to electromagnetic interference, e.g. from large electrical machinery, lightning strokes
Fibre is the technology of the future for wired high speed internet access (“fibre to the home”)
Fibre Optic vs Coaxial
Fibre Optic carries signals for several miles before needing a repeater.
Coaxial Cable signal loss is greater than Fibre Optic so it is better for shorter distances.
Fibre Optic is more expensive though carries more info.
Coaxial are easy to install and are durable
Coaxial is most common in residential.
TV Cable Networks
Use a “cable modem” to convert digital data to analog signals that are sent over the network
Upload and Download have different speeds (asymmetric), download speed is significantly higher. Bandwidth is typically higher to the home than out of the home.
What is a Digital Subscriber Loop (DSL)?
DSL modem is a device that connects a computer to a telephone line. This provides the DSL a connection to the Internet.
The DSL analog signals do not interfere with telephone voice traffic (you can talk and surf at the same time)
Allows high bandwidth connections over twisted pair cables of the telephone network, requires a DSL modem.
What is an Asymmetric Digital Subscriber Loop (ADSL)?
Often, ADSL (asymmetric DSL) is used because of higher bandwidth coming to the home than out of the home thus download speeds are faster than upload speeds.
You must live within approx. 5 km of a telephone switching location to get a decent performance
Does not use shared lines with neighbours as it uses a dedicated wire from your home to the phone company.
Basic Internet Service in Canada
Many rural communities in Canada have troubles getting basic Internet services at affordable prices => a major cause of the digital divide
Minimum service levels are essential to participate in the digital economy
Basic Internet service is defined by the Canadian Radio-television and Telecommunications Commission (CRTC) as 50 Mbps for downloads and 10 Mbps for uploads.
By the end of 2022, estimated 96% of Canadian homes and businesses are expected to have or exceed basic service.
Broadband Internet access through satellite
Various providers offer Internet access through a network of satellites.
Features lower bandwidth and higher latency than wired technologies, but can achieve basic Internet service levels as defined by CRTC
Improvements in coverage and speed are expected soon
* Satellite Internet operator Starlink (SpaceX) over 3,000 small satellites in orbit. 12,000 are planned.
Ethernet Network Details
Ethernet uses an error control mechanism
* If 2 or more workstations send at same time => collision Protocol calls for random delay, followed by re-broadcast
Data to be transmitted is split up into “Ethernet packets”
* Transmissions are encoded into packets of a specific size and form, e.g. contain MAC address of source and destination
Ethernet Transmission Medium (Part 1)
Most common: twisted pair cable (8 wires) with RJ45 connector (registered jack 45)
Wireless variant of Ethernet was added later
* Commonly known as Wi-Fi
* a.k.a.: IEEE 802.11 b/g/n/ac/ax (name of industry standard)
* Different encryption mechanisms are used to ensure privacy
What does IEEE stand for?
Institute of Electrical and Electronics Engineers
“IEEE is the world’s largest technical professional organization dedicated to advancing technology for the benefit of humanity” ieee.org
Ethernet Transmission Medium (Part 2, sniffer apps)
Good to be aware of:
* Packets are broadcasted to all participants of the network
* “Sniffer” programs can be used to receive all broadcasts
Sniffer apps monitor and capture data packets that flow through a network. Potential data at risk? Passwords and account information
Properties of Wi-Fi?
Bandwidth
* From 11 Mbps up to 9.6 Gbps (nominal values; actual is much less)
* Several variants available, traditional name: IEEE 802.11 a/b/g/n/ac/ax New rebranded name for n/ac/ax: Wi-Fi 4/5/6
Range of one access point
* Indoors typically up to 30 meters
* Outdoors typically up to 150 meters
To cover bigger areas (like a campus), multiple access points are used
Multiple antennas improve bandwidth
Cellular Networks (Mobile Networks)
Land area covered by the system is divided into cells (using different frequency bands) => cell phone
Each cell is usually served by one transceiver (radio tower); cell size: 100 m to 50 km
A device usually connects to the closest cell tower (that has the strongest signal => best quality)
When devices move from one cell to the other, a handover is performed, typically not noticed by user
Location of an device can be determined (the more towers “see” a device, the better)
Are broadcasting systems – require encryption and a unique identifier for each participant => International Mobile Equipment Identity IMEI (similar to MAC)
Different regions use competing technologies – not all phones are compatible
Evolution of cellular networks (Generations)
- 1G: analog system, voice only
- 2G: data rates up to several hundred kbps, introduced text messages
Standards: European GSM, American CDMA - 3G: data rates up to several tens of Mbps
Standards: European UMTS, American CDMA2000 - 4G: data rates up to several hundred Mbps (latency 20ms)
Standards: Long Term Evolution LTE (for voice and data), WiMAX (data only) - 5G: data rates up to 1.4 Gbps. Decrease in latency (1ms)
(Basically, more G’s are better)
5th Generation Cellular Networks – 5G
5G networks are now planned/built around the world
* First phone call made in Feb 2018
* Carriers in Canada started or will start rollout in 2020 and 2021
What kind of changes can we expect?
* Higher bandwidth (~20 x) and lower latency (~ 1 tenth)
* Higher maximum number of devices per cell
* Higher energy efficiency (batteries of phones last longer)
* This should boost applications like mobile virtual reality, self-driving cars, autonomous drones, and many others
Bluetooth
Low power personal area network (PAN) technology
Usage: connect computers or smartphones wirelessly to speakers, headsets, printers, cars, smart watches, etc.
Bandwidth: several Mbps
Range: up to 10 m
Devices are “paired” before they can interact with each other (security)
Uses same radio spectrum as Wi-Fi => interference is possible
Radio Frequency Identification (RFID)
Low power identification technology
Examples: implanted ID chips (e.g. dogs), shipping containers, passports, contactless paying with credit/debit cards, timing of marathon runners, etc.
Transceivers do not need to have their own power supply (and thus work without battery) Powered by energy of readers radio waves
Range: typically up to 10 cm (longer with active transceiver)
Bandwidth: up to 424 Kbps (quite slow in comparison to other technologies)
Satellite Navigation Systems
Multiple Systems are in currently in use or being built: GPS, GLONASS (Russia), BeiDou (China), Galileo (EU)
Satellites continuously broadcast very exact time information
With signals from 3 or more satellites, a receiver can calculate (a.k.a. triangulate) its latitude, longitude and elevation
Receivers can combine signals from different systems to improve accuracy
Only receivers know their position (satellites don ́t)
Wireless Networks for the Internet of Things –
Long Range Wide Area Network LoRaWAN
New wireless communication standards for the Internet of Things (IoT) are currently being rolled out, e.g. LoRaWAN,
Internet of Things: large networks with possibly millions of connected devices,
e.g. sensors to monitor the environment, smart buildings, vehicles, parcels, parking stalls, etc.
Long range (several km), low bandwidth (hundreds of kbps) and low energy consumption (enables months of battery life)
What is NFC?
NFC, or near-field communication, is a short-range wireless technology that allows your phone to act as a transit pass or credit card, quickly transfer data, or instantly pair with Bluetooth devices like headphones and speakers.
NFC isn’t some radically new technology. It’s simply an evolution of RFID (radio frequency identification)
Source : https://www.androidauthority.com/what-is-nfc-270730/
