Elective B - Compulsory topics that appear in the elective part

 Elective B - Compulsory topics that appear in the elective part

 

Transfer speed calculation

 

MB/s ≠ Mbps

 

• Mbps = megabits per second
• MB/s = megabytes per second

• 1 GB = 1024 MB
• 1 MB = 1024 KB
• 1 KB = 1024 B
• 1 B = 8 bits ***

 

You are usually provided with

• Data size e.g. 20 MB
• Transfer speed e.g. 10 Mbps

Calculate the transfer time

 

Steps:

1. Convert the data size to bits.
   20 MB = 20 x 1024 KB = 20 x 1024 x 1024 B = 20 x 1024 x 1024 x 8 bits
   
   
2. Convert the transfer speed to bits.
   Actually it is already in bits! Mega- here stands for 1000000. i.e. 10 Mb = 10 x 1000000 bits
   
   
3. Data size/transfer speed is the answer.
   20 x 1024 x 1024 x 8 / (10 x 1000000) = 16.78 seconds.

 

Other calculations: 

• Calculate data size from transfer time and speed. 
• Calculate the number of users the devices can support using transfer speed (calculate using individual device’s speed instead of the total speed).

 

Relevant past paper:

DSE ICT Elect B(SP-2017): 2015 2b. 2016 3bi. 2017 2a, 3c.

CE CIT Elec C(2005-2011): 2006 1g. 2007 4di. 2008 3b. 2009 3dii. 2010 3ai.

 

Methods for Internet access

• Wireless network: e.g. Satellite, mobile phone network, 2G – 5G network
• Leased line (compared with broadband): fixed bandwidth (not shared with others), secure, stable and expensive

 

Relevant past paper:

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

CE CIT Elec C(2005-2011): 2010 2bii.

AS CA(2000-2013): 2006 10d.

 

References:

https://www.rfwireless-world.com/Terminology/wired-network-vs-wireless-network.html

https://www.actcorp.in/blog/what-is-leased-line-and-how-it-works

Network Security

 

Learning Outcomes:

• Describe the potential risks caused by the common network security threats.
• The threats include virus, worm and Trojan programs, spyware, unauthorised access, interception, and Denial of Service (DoS) attack, etc.
• Propose effective measures to improve network security for both wired and wireless networks.
• The measures include anti-virus software, authentication, access and user right control, packet filtering, firewall, public and private key encryption, Wired Equivalent Privacy (WEP), and IPsec used in Virtual Private Network (VPN), etc.
• Encryption mechanisms to guarantee a message is both authentic and private should be known. Detailed implementation algorithms of public and private key encryption are not required. Technical details on how a VPN is constructed are not required.

 

Network security threats

 

Virus: malicious program that injects malicious code into existing applications in order to spread.

Worm: malicious program that can self-replicate and infect other computers. This affects system performance and consumes network bandwidth.

Trojan programs: malware that disguises as legitimate software.

Spyware: malware that tries to keep itself hidden and steals sensitive information.

Adware: malware that hijacks your system and displays advertisements in your computer.

Denial of Service (DoS) attack: prevent users from accessing resources by overloading the network/system with fake communication requests. E.g. ping flood – overwhelm the victim with huge number of ping requests.

 

Relevant past paper:

DSE ICT Elect B(SP-2017): SP 4g. 2015 2cii. 2016 4d.

CE CIT Elec C(2005-2011): 2006 4g. 2008 1h. 

Network security measures

 

Antivirus

• Mechanism e.g. signature analysis: identify the specific code/pattern that the virus carries.
• Therefore, it is important to keep it up-to-date and active.

 

Authentication

• Password recommendations:
• Minimum 8-character length
• Multi-factor authentication
• Avoid common passwords or using personal information as password
• (regularly changing password and mixing uppercase/lowercase/non-alphanumeric characters are not recommended now)

 

Access and user right control

• Software control: block different ports e.g. USB port. Block certain IP addresses. User rights of operating system.
• Hardware control: MAC filtering (feasible if MAC addresses of devices known and infrequent update needed)

 

Firewall

• Mechanism: Packet filtering based on access control list. (Control inbound and outbound communications)
• Block packets based on criteria such as source IP addresses and port number.
• In terms of security, proxy server helps to hide the internal network IP addresses and restrict access to certain websites, while firewall filters unwanted packets.

 

Public and private key encryption (Asymmetric key encryption)

 

Sender A	Receiver B	Result
Use B’s public key for encryption	Use own private key for decryption	Only B can read the message
Use own private key for encryption	Use A’s public key for decryption	Message is really from A. (Digital signature)

Encrypt twice with both methods can serve both purposes. But it is also more time consuming.

 

Wired Equivalent Privacy(WEP)

See wireless network

 

IPsec used in Virtual Private Network (VPN)

• IPsec is used to set up encrypted connections between devices. IPsec is also implemented in IPv6.
• Virtual Private Network (VPN) establishes communication channel between you and the VPN server with the data encrypted.
• Disadvantages: complicated in configuration and connection speed can be slow.

 

Protocols with encryption

• HyperText Transfer Protocol Secure (HTTPS). Encrypted using TLS.
• Secure Sockets Layer (SSL). The newer one is Transport Layer Security (TLS).
• Secure Shell (SSH). For communication between computers.

 

Relevant past paper:

DSE ICT Elect B(SP-2017): SP 3b,ci, 4f. PP 2a(P1), 3ai,b,c, 4c. 2012 1bii. 2013 1bii,ci. 2014 3abii,c, 4aiii,ci. 2015 1bii, 2ci, 3c. 2016 2ci. 2017 1bii,c, 2cii.

CE CIT Elec C(2005-2011): 2005 4efg. 2006 3g, 4f. 2007 4f. 2008 2e, 4de. 2009 1bd. 2010 3e, 4bvi.

AS CA(2000-2013): 2003 10dii. 2004 9ci. 2006 4b, 10ceg. 2007 7, 9e. 2009 1a, 9f. 2010 9fii. 2011 8dg. 2013 10f.

For interest only: AS CA: 2003 10abcdi. 2005 2.

 

References:

https://securitytrails.com/blog/top-10-common-network-security-threats-explained

https://www.usnews.com/360-reviews/antivirus/how-does-antivirus-software-work

https://docs.microsoft.com/en-us/microsoft-365/admin/misc/password-policy-recommendations?view=o365-worldwide

https://www.tutorialspoint.com/network_security/network_security_firewalls.htm

https://www.preveil.com/blog/public-and-private-key/

https://www.gov.hk/en/residents/communication/infosec/digitalcert.htm

https://www.cloudflare.com/learning/network-layer/what-is-ipsec/

https://www.usnews.com/360-reviews/vpn/what-is-a-vpn

https://blog.robertelder.org/what-is-ssh/

 Network Management

 

Learning Outcomes:

• Develop the basic skills of monitoring and fine-tuning the performance of a simple network.
• Students should be able to use some simple network monitoring software to interrogate devices to determine their status and to obtain statistics about the networks for monitoring and fine-tuning purposes.
• Develop the basic skills of analyzing problems of a networked environment and performing troubleshooting for it.
• The problems may involve cabling, Network Interface Card (NIC), driver, Network Operating System (NOS), and configuration of a network, etc.
• Be aware of the importance of backup in disaster planning and recovery measures.
• Know the common hardware and software components of a network backup solution.
• Students should be introduced to the different components/technologies of a network backup solution including network backup servers, network backup and recovery software, Uninterruptible Power Supply (UPS), and Redundant Array of Independent Disks (RAID), etc.

 

Network performance

• Proxy server can improve network performance by caching a copy after a website being visited.
• This does not happen if
• First time visit (no local copy)
• Connection via HTTPS (no cache for HTTPS connection unless special configuration made)
• Live streaming

 

• Wireless network speed can be affected by
• Hardware – e.g. old standard WiFi router, access point location
• Interference – from channels with significant overlap
• Number of connected devices – sharing of bandwidth
• Network configuration – maximum speed is set

 

• Network speed can be affected by
• Cable vs wireless network
• Hardware – older devices/routers
• The service provided by ISP
• Computer processing power – both the client and the server
• Network traffic

 

Relevant past paper:

DSE ICT Elect B(SP-2017): 2013 2ci. 2014 3biii. 2017 2b.

CE CIT Elec C(2005-2011): 2007 2diii, 4dii. 2008 3c, 4b. 2010 3aii.

 

Network troubleshooting

 What to check

• Hardwares e.g. network interface card, cable, router
• Command tools
• Ipconfig: check the values of current default gateway and IP address
• Ping: check connectivity. Whether it can reach certain IP address.
• Tracert: show the details about the path that a packets take from the computer to destination.
• Nslookup: look for any DNS server issue. (or visit different websites)
• Other issues
• Port number related: e.g. Visit websites with different port number e.g. HTTPS, HTTP
• Device configuration: e.g. firewall setting
• Website related: e.g. web server issues, DNS server errors
• Network congestion

 

Relevant past paper:

DSE ICT Elect B(SP-2017):  SP 4c. PP 2bc. 2016 4c.

CE CIT Elec C(2005-2011): 2008 3fii. 2009 2e.

AS CA(2000-2013): 2011 8f.

 

Network backup solution

 

• Uninterruptible Power Supply (UPS)
• Functions: 
• Protect against power failure by providing temporary power supply
• Protect against voltage drop by providing stable power supply
• During power interruption, UPS allows time for 
• backup creation
• the computer/server can shut down properly.

 

• Redundant Array of Independent Disks (RAID)
• Two or more drives working in parallel
• RAID 1 – mirroring: both drives have the same set of data. Requires at least 2 drives.
• RAID 5 – striping with parity: the data are striped across the drives together with parity data.  Requires at least 3 drives
• RAID 10 – combining RAID 1 and RAID 0 (mirroring + striping). Requires at least 4 drives
• These RAID configurations can protect against single drive failure. (but not RAID 0)

 

• Backup medium
• Magnetic Tape: Large amount of data with low cost
• Second Hard drive for RAID 1: see above
• External Hard drive: portability
• Network attached storage: storage with network capability. Essentially a drive within your network. Additional features may include access control, RAID and UPS.
• Cloud storage: Storage managed by third party and accessible through the internet.
• Advantages: Maintenance also by third party. Choose storage size according to need.
• Disadvantages: Security concern. Requires internet access.

 

• Backup
• How?
• Full backup: all data are copied.
• Advantages: easy to recover the data when needed.
• Disadvantages: slow backup time.
• Incremental backup: record the changes since last backup.
• Advantages: fast backup time.
• Disadvantages: slow recovery time. To restore data, need to have full backup copy + all incremental backup copies.
• When?
• Usually overnight, when the server/computer usage is low.

 

Relevant past paper:

DSE ICT Elect B(SP-2017): PP 2a. 2012 4c. 2013 4d. 2014 1f. 2015 2d, 4b. 2016 2abcii,iii. 2017 1e.

CE CIT Elec C(2005-2011): 2007 3d.

AS CA(2000-2013): 2003 10e. 2007 9c. 2008 10f. 2010 9a. 2013 4.

 

References:

https://network-data-cabling.co.uk/blog/Wi-Fi-17-factors/

https://www.techguide.com.au/news/10-things-affecting-internet-speed/

https://www.dnsstuff.com/network-troubleshooting-steps

https://www.ia.omron.com/support/guide/572/introduction.html

https://www.prepressure.com/library/technology/raid

https://www.aomeitech.com/nas/what-is-nas-storage-and-how-it-works-1234.html

http://www.nssit.com/how-to-choose-a-data-backup-medium/

https://www.business.org/it/cloud-computing/cloud-vs-network-attached-storage-pros-cons/

https://phoenixnap.com/kb/full-vs-incremental-vs-differential-backup

https://cloudpockets.com/best-time-to-backup/

 

 Network Design and Implementation

 

Learning Outcomes:

• Conduct a simple needs analysis on a proposed network and translate the needs identified into requirements and specifications.
• Design a network to meet the requirements generated in the needs analysis and represent it in a diagram.
• Justify their designs based on technical, cost effectiveness and other considerations.
• Set up simple Ethernet and wireless networks.
• Students should know the use of a subnet and know which subnet an IP address belongs to from a simple subnet mask.
• Share various resources among the networked computers/stations.
• The resources include files, printers and Internet connection, etc
• Set folder/ file sharing permissions, including read, write and execute rights, etc.
• Design a simple test plan based on the requirements and specifications to validate a network system.
• Document the user requirements, a schematic diagram for the network and specifications of the network.
• Documentation of industry standards is not required.
• Be aware of the importance of adequate end user support and training for the attainment of the benefits sought.
• Appreciate and value the use of various networking technologies in meeting different user requirements.

 

Network Diagram

 

Correct arrangement of the network devices.

Beware of the maximum number of ports.

 

Relevant past paper:

DSE ICT Elect B(SP-2017): 2017 4d.

CE CIT Elec C(2005-2011): 2005 4c. 2007 3cii. 2009 3ci. 2010 3b.

AS CA(2000-2013): 2005 10c. 2008 10a. 2009 9diii. 2012 7a.

 

Design Justification

 

• Connect device to switch or router?
• Considerations:
• Loading on the switch (number of connected devices)
• Router allows centralized management and security management
• Connecting to a switch allows easier access to the network within the switch (access not controlled by router)

•  Proxy server in front of or behind the router?
• In front of the router: hide IP address of the router for better security
• Behind the router: filter incoming data therefore reduce the loading on the server

 

Relevant past paper:

DSE ICT Elect B(SP-2017):  2014 4ai,ii. 2016 3bii. 2017 2di.

 

Setup Network

 

• General considerations for setting up network
• User requirement
• Cost
• Network type
•  Default gateway = local IP address of the router

 

Relevant past paper:

DSE ICT Elect B(SP-2017):  PP 1dii. 2013 1aii. 2014 2a. 2015 3dii. 2016 3cii,4bii.

CE CIT Elec C(2005-2011): 2010 1a. 2011 3c.

AS CA(2000-2013): 2010 4c.

 

Resource Sharing

 

Printer without intrinsic network capability:

• Connect to a host in a network. This host can make the printer sharable and manage the printing queue.
• Other hosts in the network can use the printer after installing the printer driver.

 

Network printer:

• It has a Ethernet port. Therefore, it can directly connect to a network or connect to a host.

 

Relevant past paper:

DSE ICT Elect B(SP-2017):  PP 1e. 2015 1c.

CE CIT Elec C(2005-2011): 2007 4cii,iii. 2008 3e,g. 2011 1eii.

AS CA(2000-2013): 2009 7.

 

File Permission

 

Correct assignment of read, write and execute rights. (Access rights)

Device configuration e.g. firewall setting, OS setting.

 

Relevant past paper:

DSE ICT Elect B(SP-2017): 2014 2b. 2015 4d. 

AS CA(2000-2013): 2007 9giii. 2010 4d.

 

 

Test Plan

 

Design a test plan that is able to achieve the objective of the network. A test plan shall consist of test cases and test items.

Test cases E.g. stress test with higher than expected maximum load, performance test to check the response time.

 

Relevant past paper:

DSE ICT Elect B(SP-2017):  2013 3ai. 2015 4ci.

CE CIT Elec C(2005-2011): 2007 3e. 2011 2div,4c.

 

Documentation

 

• user requirements
• schematic diagram for the network
• specifications of the network e.g. IP configuration

 

Relevant past paper:

DSE ICT Elect B(SP-2017):  2015 4cii.

CE CIT Elec C(2005-2011): 2007 3f. 2009 4a. 2011 2diii.

AS CA(2000-2013): 2011 8a.

 

Other questions: Feasibility study, user training, survey, stages, system administrator manual

Relevant past paper:

CE CIT Elec C(2005-2011): 2010 1b. 2011 2di,ii,v.

AS CA(2000-2013): 2012 10c. 2013 1.

 

References:

https://www.toolbox.com/tech/enterprise-software/blogs/creating-a-network-test-plan-040508/

https://www.tutorialspoint.com/software_testing_dictionary/test_plan.htm

 Network Applications

 

Learning Outcomes:

• Describe the services provided by common network servers.
• The common network servers include the Dynamic Host Configuration Protocol (DHCP) server, domain controller, file server, proxy server, and gateway, etc.
• Describe and appreciate the applications of various networks.
• The applications include resources sharing, web serving, and telecommunicating, etc.
• Simple knowledge of the latest mobile computing applications and their role in supporting the mobile business, mobile government services and mobile life initiatives should be discussed.
• Describe the different personnel involved in a networking environment.
• The types of personnel should include network engineers and network administrators.

 

Common network servers:

DHCP server, domain controller, file server, proxy server, gateway

 

DHCP server

• Function: dynamically assign IP addresses to devices on a network
• Advantages:
• Automatically assign IP addresses i.e. no need for manual configuration
• All assigned IP addresses are unique
• Released IP addresses can be reassigned automatically
• Disadvantages:
• A server is required
• Increase network traffic between device and server
• More difficult to identify individual devices as IP addresses are dynamic i.e. not fixed

Relevant past paper:

DSE ICT Elect B(SP-2017): PP 1diii. 2012 1ci. 2013 1biii. 2016 3ci.

CE CIT Elec C(2005-2011): 2005 4dii. 2006 1j. 2008 3fi.

AS CA(2000-2013): 2007 9d. 2012 10bi. 2013 10 bii,c.

 

More on static/dynamic IP address:

CE CIT Elec C(2005-2011): 2007 1e. 2009 3b. 2010 3c,4bi,ii. 2012 10bii.

 

Domain controller (DO NOT confuse with DNS – Domain Name System)

• Function: authentication and authorization
• Authentication: manage authentication/login requests
• Authorisation: access rights to different resources
• Server with similar purpose: RADIUS server for authentication

 

Relevant past paper:

DSE ICT Elect B(SP-2017): SP 2dii. PP 4ciii. 2017 4b,ci.

 

File server

• Central server for storage of files
• Advantages: 
• centralized management allows better security management. 
• High power server allows efficient sharing of files.

 

Relevant past paper:

CE CIT Elec C(2005-2011): 2009 2di. 2011 3ei.

AS CA(2000-2013): 2005 10biii.

 

Proxy server

• Functions:  Make a copy of a visited website. Block the visit to certain websites.
• Advantages: Faster access to websites which is previously visited. Reduced network traffic as no need to repeatedly download the content. Better security and network access management.
• Risks: leaking of sensitive data as any information passing through the proxy can be logged and subsequently stolen.

Tips: compare with firewall in terms of filtering. i.e. website filtering vs packet filtering.

 

Relevant past paper:

DSE ICT Elect B(SP-2017):  PP 3a. 2012 1cii. 2014 3aii,bi. 2015 3b. 2017 2dii,iii.

CE CIT Elec C(2005-2011): 2008 1e. 2009 4f. 2011 3eiii.

AS CA(2000-2013): 2008 10d.

 

Gateway

• Functions: allow communication between different networks which may have different protocols.
• Technically speaking, it combines the function of a modem and a router.

Relevant past paper:

DSE ICT Elect B(SP-2017): 2013 1bi. 2016 3ciii.

CE CIT Elec C(2005-2011): 2010 4biii.

 

Other servers:

Domain Name System (DNS) server – refer to compulsory part

Printer server

Relevant past paper:

CE CIT Elec C(2005-2011): 2005 3bc. 2006 4cd. 2008 4bii. 2010 4bv. 2011 3eii,4fi,ii.

AS CA(2000-2013): 2009 9eii,iii. 2012 10di.

 

Applications of various networks

 

• This part focuses on applications of network use in different real life situations.
• Examples: e-commerce, farming, online exam system
• Considerations in designing a system:
• Network traffic
• Front-end applications
• Security

 

Relevant past paper:

DSE ICT Elect B(SP-2017):  SP 1b, 2c. 2013 4b. 2014 1b, 2di,iii.

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

AS CA(2000-2013): 2006 10a.

 

Personnel

 

• Network administrator
• Installation, maintenance and update of network
• Network documentation, monitoring
• Troubleshooting and security management

• Network engineering
• Design and setup network
• Design test plan
• Documentation
• User training

 

Relevant past paper:

DSE ICT Elect B(SP-2017):  SP 4a. 2012 4e.

CE CIT Elec C(2005-2011): 2006 4a.

References:

https://www.efficientip.com/what-is-dhcp-and-why-is-it-important/

https://www.varonis.com/blog/domain-controller/

https://www.cisco.com/c/en/us/support/docs/security-vpn/remote-authentication-dial-user-service-radius/12433-32.html

https://www.varonis.com/blog/what-is-a-proxy-server/

https://www.allconnect.com/blog/difference-between-gateway-modem-router

https://www.bmc.com/blogs/network-engineer-vs-network-administrator-roles-responsibilities-and-job-descriptions/#:~:text=In%20general%2C%20the%20network%20engineer,network%20once%20it's%20been%20developed.

 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

 TCP/IP protocol suites 2
 

Learning Outcomes:

• Know the basic concepts of IP addressing including the scheme and classes of IP addresses.
• Compare TCP/IP protocol suites such as Internet Protocol version 4 (IPv4) and Internet Protocol version 6 (IPv6) from an evolutionary perspective.
• Different versions of TCP/IP protocol suites are compared in terms of address size and their support for audio and video.

Internet Protocol (IP):

Features: Similar to UDP, it is unreliable and connectionless

Functions: IP addressing, encapsulation, routing and ultimately delivery of the IP packets to correct destination

 

IPv4 vs IPv6:

IPv4 address is 32-bit long. The number cannot cope with the huge demand from the expanding network. Thus, IPv6 is developed with its address which is 128-bit long. Additional features are also available.

Features of IPv6:

128-bit long addresses

Efficient packet handling: e.g. simplified header, traffic class, flow label

Improved performance: multicast – sending datagrams to multiple receivers in a single transmission

Improved security: e.g. IPsec fully integrated

Relevant past paper:

DSE ICT Elect B(SP-2017): 2012 2d.

CE CIT(2005-2011): 2009 2c.

 

IPv4

Address classes:

Binary notation 11000000.10101000.00000000.00000001

Decimal notation 192.168.0.1

The IP address is separated by dots into 4 parts. Each part is called an octet. The leading bits determine the class.

Network address is for identifying the network while the host address is for identifying the devices in that network.

Class	leading bits	1st octet	Network address portion	Host address portion
A	0-------	0-127	1st octet	2nd-4th octet
B	10------	128-191	1st-2nd octet	3rd-4th octet
C	110-----	192-223	1st-3rd octet	4th octet
D	1110----	224-239
E	1111----	240-255

Class D and E are not important for the exam purpose.

 

Relevant past paper:

DSE ICT Elect B(SP-2017):  SP 4e. PP 1di. 2012 4ai.

CE CIT(2005-2011): 2006 4e. 2007 2b. 2008 1f. 2011 3f.

 

Local(private) vs global(public) IP address:

Some IP addresses are reserved for private use (use in a LAN). i.e. it cannot be used to identify a network/host through the internet.

A router is in a special location where it is between 2 different networks, usually a LAN and the internet. The ISP assigns a public IP address for the router to use so that others can identify and reach the router through the internet. The router also has a private/local IP address so that devices in the LAN can reach the router. 192.168.0.1 is used by many routers as the default (local) IP address.

Relevant past paper:

DSE ICT Elect B(SP-2017):  2017 2ci.

CE CIT(2005-2011): 2009 2f. 2010 4bvii.

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

 

Network address translation (NAT):

The translation of local IP address into global IP address and vice versa. This allows the hosts in a LAN to communicate with the outside world.

A special form of NAT called NAT overload allows multiple hosts in a LAN to communicate with the outside world using 1 public address only. This helps to reduce the demand of the limited number of IP addresses. Port number is used to identify different hosts in the LAN.

NAT table:

Local IP address and source port	Port number used in NAT
192.168.0.3:10100	20000

 

When data is sent out from an application of a host, the router received the information 192.168.0.3:10100. This information is saved in the NAT table in the router and mapped to a new port number. Suppose the public IP address of the network is 11.100.100.100. The outgoing data will now have a source IP address and port number as 11.100.100.100:20000.

When returning data targeting 11.100.100.100:20000 reaches the router, it maps the port number 20000 to the local IP address and port 192.168.0.3:10100. The data will therefore be directed to the relevant host and application.

Relevant past paper:

DSE ICT Elect B(SP-2017):  PP 1div.

CE CIT(2005-2011): 2009 4c. 2010 4biv.

AS CA(2000-2013): 2007 2c.

 

Subnetting:

Reason for subnetting:

Usual IP address can be divided into network and host number based on its class as mentioned before. This represents 1 network with certain number of hosts. To facilitate network management, for example a large company, we want to divide the single network into a number of networks.

Use binary notation for understanding

Without subnet:

IP address                      192.168.123.132         11000000.10101000.01111011. | 10000100

(Default) subnet mask   255.255.255.0               11111111.11111111.11111111. | 00000000

                                                                                       Network address             Host address

The subnet mask determines which point to divide the IP address into network address and host address.

The default subnet masks for class A, B and C addresses are 255.0.0.0, 255.255.0.0 and 255.255.2552.0, respectively.

 

Subnetting a private network:

To divide a network into 4 networks, we use subnet mask 255.255.255.192 for a class C address.

IP address           192.168.123.0                11000000.10101000.01111011.00 | 000000

Subnet mask      255.255.255.192                11111111.11111111.11111111.11 | 000000

                                                                                    Network address             Host address

So, the four networks are:

11000000.10101000.01111011.00(000000)          192.168.123.0                     host addresses: 1-62

11000000.10101000.01111011.01(000000)          192.168.123.64                  host addresses: 65-126

11000000.10101000.01111011.10(000000)          192.168.123.128                host addresses: 129-190

11000000.10101000.01111011.11(000000)           192.168.123.192                host addresses: 193-254

For a class C network:

No of subnets	Subnet mask 255.255.255.x x =	In binary notation x =	Number of subnets	Number of host addresses in each subnet	Number of hosts in each subnet *
2	128	10000000	21	27=128	128-2
4	192	11000000	22	26=64	64-2
8	224	11100000	23	25=32	32-2
16	240	11110000	24	24=16	16-2
32	248	11111000	25	23=8	8-2
64	252	11111100	26	22=4	4-2

* The first and last address of a subnet cannot be assigned to a host.

 

Advantages of subnetting:

• Access control
• Data traffic management

Disadvantages of subnetting:

• Increased hardware cost
• Network management work more complicated

 

Relevant past paper:

DSE ICT Elect B(SP-2017):  PP 1dii. 2012 4aii. 2013 1aii. 2014 1c, 2a. 2015 3di. 2016 4a, bi. 2017 4c.

CE CIT(2005-2011): 2009 4d.

AS CA(2000-2013): 2008 3ab. 2009 9cii, di, ii. 2012 7bc, 10dii. 2013 10 bi.   

References:

https://www.plixer.com/blog/network-layers-explained/

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

http://www.internet-computer-security.com/Firewall/Protocols/Ports-Protocols-IP-Addresses.html

https://www.tutorialspoint.com/what-is-network-port

https://www.tutorialspoint.com/internet_technologies/internet_protocols.htm

https://www.tutorialspoint.com/ipv6/ipv6_features.htm

https://www.geeksforgeeks.org/network-address-translation-nat/

http://cactus.io/tutorials/ethernet/what-is-a-mac-address