Types of Network 2 - Wireless computer networks

 

Learning Outcomes:

• Understand the basic features of a wireless computer network in terms of its underlying technologies and the hardware used.
• The common industry standards for wireless computer networks should be introduced to students. Relevant concepts including frequency, bandwidth, interference, and roaming, etc. are required.

• Explain the factors that need to be considered in choosing between wired and wireless computer networks.

• The strengths and weaknesses of both network solutions should be considered. The possibility of a hybrid solution should also be introduced to students.

 

Wireless computer networks

Wireless technologies

• NFC (near field communication): application e.g. Octopus card
• RFID (Radio frequency identification): application: e.g. trace or identify objects with the RFID tags
• Bluetooth: application: e.g. wireless headset
• Wi-Fi: application: formation of WLAN

 

Wireless network standard

• IEEE 802.11 is a standard for WLAN. 
• Different versions developed since its implementation. Latest ones are 802.11ac (WiFi 5) and 802.11ax (WiFi 6). 
• Different versions may have different frequency, bandwidth, data rate, MIMO (multiple input multiple output) and channels.

 

Collision handling

• CSMA-CA (Refer to basic concepts 2)

 

Devices

• Wireless network card/ wireless adapter
• Similar to network interface card, the adapter allows a device to connect to the wireless network.
• Access point/ Wireless access point (AP)
• A hardware that connects to a wired network. It allows wireless connections by other devices using Wi-Fi technology to access the wired network.
• Number of APs:
• inadequate number results in insufficient coverage, low throughput and cannot provide adequate number of connections
• Excessive number results in high installation cost and more complicated network management.

 

Setup

SSID (Service Set Identifier)

• Essentially the name of the wireless network. Different wireless networks can have the same SSID, just like 2 people can have the same name.  You may choose to broadcast or not to broadcast the SSID. (So that the network can or cannot be seen by others)
• BSSID (Basic Service Set Identifier) is the unique identifier, similar to the MAC address, that allows unique identification of the access point.
• Avoid using default SSID and password: to avoid confusion and reduce chance of being hacked

 

Password

• For authentication.
• Implementing password: reduce unauthorized access and sharing of bandwidth.
• Not implementing password: easy to use, decrease setup time and no decryption time needed.

 

Channel

• Using the 2.4GHz of 802.11n (Wi-Fi 4) as an example, the frequency ranges from 2400-2499MHz. This range is divided into 14 channels.  Channel 1 ranges from 2402-2422 and channel 2 from 2407-2427. There is certain overlap of frequencies among adjacent channels. Therefore, it is recommended to use non-overlapping channels i.e. channel 1, 6 and 11. (1: 2402-2422, 6: 2427-2447, 11: 2452-2472)
• If a nearby AP is using, for example, channel 1, it is better to use channel 6 or 11 for your AP.
• Another option is to use automatic channel selection, which selects channel with least inference.

 

Encryption

• Old methods: Wired equivalent privacy (WEP), WiFi Protected Access (WPA)
• Current methods: WPA2, WPA3
• Newer methods have security improvements over the older methods.

 

Roaming

• A device can remain connected to a network when moving from one AP to another of the same network, without any interruption. This is known as seamless roaming.
• Essential settings: the APs should have the same SSID, password and encryption methods.
• For roaming to succeed, the adjacent APs should have certain overlapping signals so that connection is not lost when moving from one AP to another AP. Since there is overlapping signals, their channels should be non-overlapping. Otherwise interference occurs.

 

Relevant pastpaper:

DSE ICT Elec B(SP-2017):  PP 1cii, 4abc. 2012 1bi,e. 2013 1d, 3aii,bcd. 2014 1e, 4cii. 2015 1bi, 3ei,ii. 2016 1abce. 2017 1d.

CE CIT Elec C(2005-2011): 2008 2bcd. 2009 1ef. 2011 1d, 2bc.

AS CA(2000-2013): 2007 9f. 2008 2b. 2011 1bc. 2012 7b, 10aii.

Choosing between wired and wireless computer networks

 

Advantages of wireless network (over wired network):

• Mobility
• No connection ports and cables needed
• Easier to relocate or expand the network

 

Disadvantages of wiresless network (over wired network):

• Security issues, more prone to interception
• Less stable
• Lower throughput in general
• Limited coverage
• More configuration needed

Relevant pastpaper:

DSE ICT Elec B(SP-2017):  2013 1e. 2014 1d, 2dii. 2015 3a.

CE CIT Elec C(2005-2011): 2005 2fg. 2007 2c. 2008 2a. 2009 1c. 2010 1d, 2bi. 2011 2a.

AS CA(2000-2013): 2008 2aii. 2012 10ai. 2013 10aii.

References:

https://www.rfwireless-world.com/Terminology/NFC-vs-RFID-vs-Bluetooth-vs-wifi.html

https://www.ciscopress.com/articles/article.asp?p=2999384&seqNum=3

https://www.makeuseof.com/tag/understanding-common-wifi-standards-technology-explained/

https://www.metageek.com/training/resources/why-channels-1-6-11.html

https://www.duckware.com/tech/wifi-in-the-us.html

https://www.netspotapp.com/wifi-encryption-and-security.html

https://www.dummies.com/programming/networking/wireless-network-administration-roaming/

 Types of Network 1

Learning Outcomes:

• Describe the characteristics of the different types of network, including the LAN, WAN and Personal Area Network (PAN).
• Describe the characteristics of basic network topology such as bus, ring and star.
• Describe the characteristics of a client-server network and a peer-to-peer network, and explain the factors that need to be considered in choosing between them as a network solution.
• The factors include the network services required, set-up and maintenance costs, and the workload of the network administrators, etc.

LAN, WAN, PAN

	WAN	LAN	PAN
Characteristics	Wide Area Network Not limited by locations e.g. a large company network with multiple LANs in different locations (interconnected by public network provided by internet service provider) e.g. internet Connect LANs together	Local Area Network Used in local area e.g. within a floor or building Connect local devices together: share resources and communicate with others	Personal Area Network Connect personal devices together e.g. Bluetooth headphone e.g. home office
Advantages	Large coverage	Faster than WAN Less complex than LAN Less expensive than LAN	Flexible and adhoc connection Easy to set up and use Low cost

 

Relevant past paper:

DSE ICT Elect B(SP-2017):  SP 1ai. 2013 4eii. 2017 4ai.

CE CIT Elec C(2005-2011): 2005 2cde. 2007 3a.

 

Basic Network Topology

Bus topology:

• Advantages: fewer cables needed, simple setup, lower cost (fewer cables, no active communication devices)
• Disadvantages: all nodes receive and examine signals, backbone failure causes failure of entire network

 

Ring topology:

• Advantages: only one station can send data at a time thus avoid collisions
• Disadvantages: failure of any nodes or cables causes failure of the entire network, longer data transmission time

 

Star topology:

• Advantages: centralized network management, easy to expand the network
• Disadvantages: central connecting device failure causes failure of the entire network, more expensive to setup

 

Tree topology:

• Advantages: easy to expand the network
• Disadvantages: delay in receiving data of the child node

 

Relevant past paper:

DSE ICT Elect B(SP-2017):  SP 4b. PP 1a. 2012 3e.

CE CIT Elec C(2005-2011): 2005 1def, 4a. 2006 3ab, 4b. 2007 3bc. 2008 1a. 2009 1a. 2010 1cii, iii. 2011 1ei.

AS CA(2000-2013): 2009 9ciii.

 

Client-server Network and Peer-to-peer (P2P) Network

	Client-server network	Peer-to-peer network
Characteristics	A server grade computer acts as the server to provide resources for its clients	No central server Each node can act as client or server i.e. request for or provide services Each node can control its own resource sharing
Advantages	Centralized management Easier to manage security	Less expensive and easier to setup No single point of failure
Considerations in choosing client-server / P2P network	Large number of users Centralized security management Centralized data management and backup Applications that require high processing power of the server	Small number of users Centralised security management not required Lower cost

 

Relevant past paper:

DSE ICT Elect B(SP-2017):  SP 2a, di. 2014 2c. 2015 2a.

CE CIT Elec C(2005-2011): 2007 4ci. 2010 1ci. 2011 4a.

AS CA(2000-2013): 2007 9gi,ii. 2008 10c.

 

References:

https://network-support.com/what-is-the-difference-between-a-lan-and-wan-network/#:~:text=As%20opposed%20to%20a%20LAN,or%20accessible%20to%20the%20public.

https://www.geeksforgeeks.org/overview-of-personal-area-network-pan/

https://www.dnsstuff.com/what-is-network-topology

https://techdifferences.com/difference-between-client-server-and-peer-to-peer-network.html

https://sourcedaddy.com/networking/selecting-network-type-client-server-or-peer-to-peer.html

Data Communications Basics 2 - Data transmission

Learning Outcomes:

• Identify and describe the three communication models: simplex, half-duplex and duplex.
• Compare asynchronous and synchronous transmission in terms of timing and overhead.
• Know the simple concept of multiplexing and its function in sharing the capacity of data transmission media.
• Explain briefly the mechanism used to co-ordinate data transmission in Ethernet and wireless networks.
• Knowledge of both Carrier Sense Multiple Access with Collision Detection (CSMA/CD) and Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) is required.
• Understand the simple concepts of circuit switching and packet switching.
• The basic function of each component of a packet including header, data and trailer should be known.

Communication models:

• Simplex: communication is unidirectional. One of the devices sends data only, while another one receives data only. E.g. Radio. Advantage: simple and easier setup.
• Half-duplex: Both devices can send and receive data, but not simultaneously. E.g. Walkie-talkie.
• Duplex: Both devices can send and receive data simultaneously. E.g. Telephone, interactive TV programmes.

Relevant past paper:

DSE ICT Elect B(SP-2017):  2012 3c. 2013 2bi, cii. 2015 1ei. 2017 3ai.

CE CIT Elec C(2005-2011): 2005 2b. 2007 2e. 2010 2ai,iii.

 

Asynchronous and synchronous transmission

• Synchronous transmission: Transmitter and receiver are synchronized with timing signals. Data transfer with continuous stream of data. Therefore, it is suitable for large amount of data.
• Advantage: faster transmission time c.f. asynchronous transmission
• Disadvantages: costly
• Asynchronous transmission: sender sends 1 character each time. Time gap exists between data.
• Advantage: economical (cheaper hardware) c.f. synchronous transmission
• Disadvantages: slower transmission, larger overhead (larger amount of control bits) 

Relevant past paper:

DSE ICT Elect B(SP-2017): 2013 2bii. 2017 3aii.

 

Multiplexing

• When multiple data signals use a single line of transmission medium, a device called multiplexor combines the data signals into a 1 single signal for transmission through the transmission medium. At the other end of the transmission medium, a demultiplexor will break down the single signal into the original multiple data signals.

 

Relevant past paper:

DSE ICT Elect B(SP-2017): 2012 3b.

Carrier Sense Multiple Access with Collision Detection (CSMA/CD) and Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA)

• CSMA/CD:
• Used in shared medium of a Ethernet
• The sender senses whether the transmission medium is in use or not. In case of a collision, the sender defers data transmission for a random period of time before retransmission.
• CSMA/CA:
• Mainly used in wireless medium as collision detection is not possible
• Aim at preventing collision
• The sender checks if the channel is in use or not. If the channel is in use, the sender waits for random time before resending checking signal.

Relevant past paper:

DSE ICT Elect B(SP-2017):  PP 1ci. 2012 1d. 2015 1eii. 2016 1d.

CE CIT Elec C(2005-2011): 2005 1a.

 

Circuit switching and packet switching

• Circuit switching:
• A dedicated connection is established. E.g. telephone system.
• Packet switching:
• A dedicated connection between two parties is not required.
• The data is divided into small parts known as packets. The packets are sent out and go through any network pathway that is readily available. The packets may then arrive at the receiving end in any possible orders.
• The receiving end will reassemble the packets in correct order and perform error checking.

 Relevant past paper:

DSE ICT Elect B(SP-2017):  2013 4c. 2017 3aiii.

AS CA(2000-2013): 2010 1ab.

 

Packet

• A data packet typically has 3 parts: Header, Body and Trailer.
• Examples of contents of each part:
• Header: packet length, source address, destination address, Header checksum
• Body: the actual data
• Trailer: bits that signify end of the packet

 Relevant past paper:

DSE ICT Elect B(SP-2017):  2015 1di. 2017 3aiii.

AS CA(2000-2013): 2011 4a.

 

References:

https://www.geeksforgeeks.org/transmission-modes-computer-networks/

https://www.guru99.com/difference-between-synchronous-and-asynchronous-transmission.html

https://www.tutorialspoint.com/difference-between-csma-ca-and-csma-cd

https://www.tutorialspoint.com/circuit-switching

https://www.tutorialspoint.com/packet-switching

https://computer.howstuffworks.com/question525.htm

Data Communication Basics 1 - Communications model and data encoding

Data Communication Basics 1 - Communications model and data encoding

Learning Outcomes:

Communications model and data encoding

1. Understand the simple model of communications.
• Components of the model include agent, input device, transmitter, transmission medium, receiver, and output device.
2. Know the basic concepts of data encoding.
• Distinction between data and signals should be known.
• Students should know that either form of digital and analog data can be coded into either form of digital and analog signal.
3. Understand some error detection methods.
• The error detection methods include parity check, checksum and cyclic redundancy check (CRC). Implementation arithmetic for parity check and checksum should be known.

Simple model of communications, Data encoding

Data vs Signal:

In simple term, data is the information that is in the form you can use or store.

When you want to transfer the data to another party over a network, the data will be converted into signal in order for it to be transferred over a transmission medium.

Analog vs Digital:

Analog data/signal: continuous in nature that varies with time. E.g. Sound wave, electromagnetic wave

Digital data/signal: a set of discrete values. E.g. data representation in computers – 1s and 0s

Transmitter: 

Convert data into signal for transmission. Depending on your data and transmission medium used, an appropriate transmitter is used. E.g. sending a file over an optical fibre means converting a digital data into digital signal for transmission. Broadcasting a CD with analog radio waves means converting digital data into analog signal. Details of the conversion are out of the exam scope.

Putting these into a simple communication model: 

An agent wants to send out something(data) which is stored or input into an input device. A transmitter will convert the data into appropriate signal (could be analog or digital depending on transmission medium) for transmission. The receiving end uses a receiver to convert the signal back into data. The output device can then use or store the data.

Relevant past paper:

DSE ICT Elect B(SP-2017):  2012 3a. 2013 2a.

Error detection methods:

Major source of error: interference or noise in the communication channel.

Parity check:

• Extra bit called parity bit is appended to each unit of data.
  10101010 1
• Odd parity check: the total number of 1s is odd number, as in above.
  Even parity check: the total number of 1s is even number. E.g. 10101010 0

Checksum:

• HKID and ISBN-10 use checksum.
• Example:
• ISBN number: 019852663-6 the last digit is check digit such that the weighted sum is divisible by 11.
• 0 x10 + 1 x9 + 9 x8 + 8 x7 + 5 x6 + 2 x5 + 6 x4 + 6 x3 + 3 x2 + 6 x1 = 231

Cyclic redundancy check:

                Details not required.

Comparison:

• Parity check: simple, but only able to detect odd number of error bits.
• Checksum: ease of computation, small overhead(single check digit attached to original data)
• CRC: able to detect burst error, which is more likely to happen. Easy to implement using hardware.

Relevant past paper:

DSE ICT Elect B(SP-2017):  2012 2c.

Reference:

https://isbn-information.com/the-10-digit-isbn.html

https://www.tutorialspoint.com/data_communication_computer_network/error_detection_and_correction.htm

https://freeitnetwoking.blogspot.com/2017/02/types-of-errors-in-data-transmission.html