Networks Year 9 PDF

NETWORKS A network consists of two or more computers linked together either by wires or wirelessly for sharing resources such as printers, files or allow electronic communication. NEWTORK TOPOLOGIES This is the physical arrangement of cables, computers and other peripherals devices to form a netwo...

NETWORKS A network consists of two or more computers linked together either by wires or wirelessly for sharing resources such as printers, files or allow electronic communication. NEWTORK TOPOLOGIES This is the physical arrangement of cables, computers and other peripherals devices to form a network. 1. Bus topology All devices are connected to a single cable called a "bus" with terminators at both ends. This cable serves as a shared communication medium, allowing all devices on the network to receive the same signal simultaneously. The terminator is used to absorb the signal when the signal reaches the end, preventing signal bounce. Computers and other devices including the server are connected to the cable for communication. Advantages Easy to install It does not require much cabling hence cheaper. The user can easily connect different types of nodes in the network. If any node in the network fails or malfunctions, it does not affect the performance of the rest of the network. Disadvantages If the backbone cable fails, the entire network stops working. In case the entire network shutdown, it becomes very difficult to locate the problem area. Data transmission is not secure because the data is transmitted to all the nodes along with the sender and receiving nodes. High possibility of data collision since the whole transmission occurs through the bus cable. As the number of nodes connected in the network increases, the possibility of data collision also increases. 1 of 9 2. Star topology Each network component is physically connected to a central node such as a router, hub or switch. If one device wants to send data to another device, it’s to first send the data to the switch/router then it transmits that data to the designated device. Advantages Centralized management of the network using the router, hub, or switch. Easy to add another computer to the network. If one computer on the network fails, the rest of the network continues to function normally. Easy to install. Disadvantages It may have a higher cost to implement, especially when using a switch or router as the central network device. The central network device determines the performance and number of nodes the network can handle. If the central computer, hub, or switch fails, the entire network goes down, and all computers are disconnected from the network. 3. Ring topology A type of network configuration in which each device on the network is connected to two other devices, forming a “ring.” Data travels around the ring in one direction only, from device to device, until it reaches its destination. Advantages Fewer cable wires are required. Easier to detect faults in the network. Data flows in one direction which reduces the chance of packet collisions. Equal access to the resources. Speed to transfer the data is very high in this type of topology. 2 of 9 Disadvantages Due to the Uni-directional Ring, a data packet (token) must have to pass through all the nodes. If one workstation shuts down, it affects whole network. It is slower in performance as compared to the bus topology. Difficult to add and remove of any node in a network because it requires rewiring and re- routing all the existing cables making it also expensive. For all the computer to communicate with each other, all computers must be turned on. NETWORK PROTOCOLS A protocol is the agreed set of rules that computers follow to communicate with each other over a network. 1. Transmission Control Protocol/Internet Protocol (TCP/IP) The Transmission Control Protocol (TCP) is responsible for breaking the data into smaller sections called packets. When sending data from one device to another on a network, TCP/ IP is the protocol used to break the data into packets, address the data, transmit the data, route the data and receive any data from other devices. The Internet Protocol (IP) adds the IP address of the sender and the receiver to the packet. Packet structure A packet is split up into: 1. A packet header the IP address of the sending device the IP address of the receiving device the sequence number of the packet - to ensure that all the packets can be reassembled into the correct order once they reach the destination. packet size - to ensure the receiving station can check if all the packets have arrived intact. 2. The payload - actual data in the packets. 3. The packet trailer consists of some way of identifying the end of the packet; to allow each packet to be separated from each other as they travel from sending to receiving station. 3 of 9 Packet switching When data is transmitted across a network, it is split up into small packets. When the packets are assembled, they are sent across the network. Packets can be sent across the network using different routes, travelling through many different devices before they reach their destination. The receiving computer will put the packets to check that they have all been received. If there have been any 'dropped packets', the receiver will re-request that packet and it will be transmitted across the network again. 2. HTTP and HTTPS Hypertext Transfer Protocol (HTTP) and Hypertext Transfer Protocol Secure (HTTPS) are protocols that exist to allow web browsers to fetch documents from web servers. Documents could include web pages, text, images or videos. HTTPS is encrypted, which can prevent unauthorised access if data is intercepted. Each time a user on a web browser tries to view a document on the world wide web, the device sends a request to the web server for the information NETWORK SCALABILITY FACTORS Network scalability means how well a network can cope if it suddenly needs to move a lot more data between more devices. Scalability factors that should be considered when designing networks. 1. Security - ensure the network remains stable and secure during rapid growth by using scalable firewalls and access control systems that can handle increased traffic and users. 4 of 9 2. Storage solutions - plan for additional storage capacity by upgrading file servers or adding new ones to accommodate more devices and data. 3. Data accessibility - avoid bandwidth issues and unstable connections by preventing network hardware overload. This can involve adding switches or wireless access points to distribute the load evenly. Challenges in designing scalable networks 1. Anticipating future needs - estimating the rate at which users, devices, and data traffic will increase can be difficult. 2. Emerging technologies -planning for new technologies that may require different infrastructure is challenging. 3. Balancing cost and scalability. 4. Ensuring performance - as the number of devices grows, ensuring sufficient bandwidth and low latency becomes increasingly complex. 5. Infrastructure expansion - adding new components like switches, routers, or wireless access points can complicate network management 6. Minimizing downtime - upgrading or expanding the network without disrupting services can be difficult. 7. Centralized management - managing large networks from a single point becomes increasingly complex. ERROR CHECKING METHODS When computers communicate, it is important that the information sent and received is correct. Several reasons why the data that is received could be incorrect. 1. Electrical spikes or power surges A power surge is a short burst of significantly more voltage coming through the electrical wire to an electrical device. Power surges can cause binary bits to flip between O and 1, causing an error in data transmission. They are usually caused by faulty wiring or lightning strikes. 2. Interference Interference occurs when several electrical devices are being used in a small area. 5 of 9 The electrical and radio waves can disrupt each other's signals. This can cause errors in binary data or causes devices to disconnect from the network. 3. Security breaches Security breaches can be caused by malware or by hackers. If a firewall hardware device were hacked, its rules could be changed to allow any data into the network, which could result in the system being overloaded and could cause errors in the binary data being transmitted. 4. Hardware failure If a network switch were to fail, this could cause errors in data transmission, with packets no longer routed to the correct places. PARITY-CHECKING This is a type of error check that ensures data has been transmitted correctly. Parity checks are used to make sure that data has been sent and received correctly. Devices transmitting data between each other agree to use either an odd or even protocol for parity checking. If devices have agreed that they will use an even number of bits, then any data received should have an even number of ls within it, so a byte would have two, four, six or eight ls in total. Byte is eight bits of data, e.g. 01010011 The parity bit is set to either 1 or 0 to ensure that the total number of ls is even. For example, assume even parity has been agree upon. If the first 7 bits are 1001100, then the parity bit would be set to 1 to make four ls in total. If the first 7 bits are 1001000, then the parity bit would be set to 0 as there is already an even number of ls in this byte. If any bytes are received that have an odd number of ls, then this data has an error and would need to be sent again. Where devices have agreed that an odd number of bits should be sent, if there are an even number of ls, then the data contains an error and would need to be sent again. Example 1 Computer 1 and Computer 2 have agreed to use an even checking system. Computer 1 sends the byte: 6 of 9  0 1 0 1 0 1 0 1 Computer 2 receives the byte: 0 1 0 1 0 1 0 1 The byte received by Computer 2 has four l s, which is an even number. There is no error. Computer 2 receives the byte: 1 1 1 1 1 1 0 1 There has been an electrical surge and the byte received by Computer 2 has seven l s, which is an odd number. There is an error. Example 2 A mobile phone and a tablet device have agreed to use an odd checking system. The tablet device receives the byte: 0 1 1 1 0 1 0 1 The byte received by Computer 2 has five ls, which is an odd number. There is no error. PARITY BLOCKS If two of the bits change value following data transmission, it may be impossible to locate the error using parity checking. A block of data is sent and a parity check is done in both horizontal and vertical directions. This method indicates where the error is. Example 1 Nine bytes of data have been transmitted. Agreement has been made that even parity will be used. Table below shows how the data arrived at the receiving end. It is necessary to check the parity of each byte horizontally and vertically. Each row and column where the parity has changed from even to odd should be flagged: 7 of 9 A careful study of the table shows the following: byte 8 (row 8) now has incorrect parity (there are three 1-bits) bit 5 (column 5) also now has incorrect parity (there are five 1-bits). At the intersection of row 8 and column 5, the position of the incorrect bit value can be found. The 1-bit at this intersection should be a 0-bit; this means that byte 8 should have been: This byte could therefore be corrected automatically or an error message could be relayed back to the sender asking them to re-transmit the block of data. NETWORK SECURITY Network managers need to make sure that the data on their networks are kept safe. Ways in which organisations can keep data safe on networks. 1. Firewalls This is a special type of network hardware or software that examines the incoming and outgoing network traffic to check for security risks and blocks any suspicious activity. Firewalls can protect data by blocking access to the data from outside the network or from specific parts of the network. 2. User access controls User access controls enable network managers to allow some users access to the data, but not others. 8 of 9 Some accounts will be grouped as administrator accounts, which is the type of account the network manager would have. 3. Password policies To prevent unauthorised access to a network, it is important to create strong password policies for their users. This helps to make sure that users create stronger passwords. Rules that may be included in the policy: Passwords must ▪ contain letters, numbers and symbols ▪ be longer than ten characters ▪ not contain the user's name ▪ not contain a date. Users must change their passwords regularly. Using long and unpredictable passwords helps to keep datasets secure, as it would take much longer for hackers to gain access using a brute force attack. Bruto force attack is type of unauthorised access to a computer system that uses a large dictionary to try multiple password combinations until it is successful. 4. Biometric security and two-factor authentication Biometric security requires a user to sign into systems using a biological password, such as a fingerprint, facial recognition or an iris scan. Two-factor authentication can be used to authenticate a user. This is where a user is asked to confirm their identity using a second device. Often a code is sent to the second device, such as a mobile phone, which must be entered via the main computer to complete the log-in process. This adds an additional layer of security, making it harder for someone to gain unauthorised access to the system. 5. Encryption The original data being sent is known as plaintext. Once it has gone through an encryption algorithm, it produces ciphertext: If data is sent between devices as plaintext, then a hacker could intercept the data and read the contents of the data packets. Network managers can make sure that all data is encrypted using secure protocols, such as HTTPS. 9 of 9