Network Criteria
A network must be able to meet a certain number of criteria. The most important of these are:1. Performance. Performance in a computer network can be assessed through various metrics, including transit time and response time:
How the components interconnect to form a network:
The router is connected to a switch for a LAN. Internet means the router may be connected to another switch from a different LAN forming an inter network.
- Transit Time: This is the time it takes for a message to travel from one device to another.
- Response Time: This measures the elapsed time between a request and the corresponding response.
Factors affect network performance, including:
- The number of users on the network
- The type of transmission medium (e.g., fiber optic, copper wire, wireless)
- The capabilities of the connected hardware (e.g., routers, switches)
- The efficiency of the network software
Performance is often evaluated using two key metrics:
- Throughput: The rate at which data is successfully transmitted over the network.
- Delay: The time it takes for data to travel from the source to the destination.
While higher throughput is desirable, it often comes at the cost of increased delay due to network congestion. Therefore, achieving an optimal balance between throughput and delay is crucial for network performance.
2. Reliability. In addition to accuracy of delivery, network reliability is measured by the frequency of
failure, the time it takes a link to recover from a failure, and the network’s robustness in
a catastrophe.
3. Security. Network security issues include protecting data from unauthorized access, protecting
data from damage and development, and implementing policies and procedures for
recovery from breaches and data losses.
Network Components
A network component is any part or device within a computer network that aids in the transmission and reception of data. These components collaborate to form the network infrastructure, which allows for communication between devices. Common network components:
1. Nodes
Node is a term used to refer to any computing devices such as computers that send and receive network packets across the network.
- End Nodes: These types of nodes are going to be the starting point or the end point of communication. E.g., computers, security cameras, network printers, etc.
- Intermediary Nodes: These nodes are going to be in between the starting point or end point of the end nodes. E.g., Switches, Bridges, Routers, cell towers, etc.
2. Cables
The physical medium that transmits data between network devices. Types: Ethernet cables (Cat5, Cat6), fiber optic cables. The data transmission capacity of these media varies based on their classification. When a network professional selects a medium for their work, they need to consider the following factors:
- The distance of the network.
- The amount of data and the speed of data transmission.
- The cost of installation.
3. Network Interface Cards (NICs)
NIC or Network Interface Card is a network adapter used to connect the computer to the network. It is installed in the computer to establish a LAN. It has a unique ID that is written on the chip, and it has a connector to connect the cable to it. The cable acts as an interface between the computer and the router or modem.
NIC can be wired or wireless, supporting a unique set of networking standards such as Ethernet, Wi-Fi, Bluetooth, and Fiber Channels. A wireless NIC uses antennae to connect to a wireless network, whereas a wired NIC uses a network cable and an RJ45 connector.
4. Switches
A switch is a hardware device that connects multiple devices on a computer network, offering more advanced features than a hub. A network switch operates on the data-link layer, or Layer 2. Unlike a hub, which broadcasts messages to the entire network, a switch uses an updated table to deliver messages directly to the correct destination based on the physical (MAC) address in the incoming message.
Data transmission between different computer network nodes is called “switching” in a computer network. Most common types of switching:
- Circuit switching: It creates a direct connection between two nodes. This unique route guarantees the transmission’s entire capacity by blocking all other traffic.
- Packet switching: It includes breaking data into smaller, more manageable parts called packets to ease the strain on the network. Through the network, the packets are sent to their final destination.
5. Routers
A Router is a device like a switch that routes data packets based on their IP (logical) addresses and transmits packet between different networks. The router is mainly a Network Layer device. Routers normally connect LANs and WANs and have a dynamically updating routing table based on which they make decisions on routing the data packets and finding the optimal path.
6. Repeaters
Extends the range of a network. Receives, amplify and retransmits signals to cover longer distances.
7. Hubs
A hub is a multi-port repeater that usually operate at the physical layer (Layer 1) that connect multiple devices on a local network. Hubs cannot filter data, so data packets are broadcast to all connected devices, creating a single collision domain for all hosts connected through the hub. Hubs lack a routing table to store port data and destination addresses.8. Servers
Provides resources, data, services, or programs to other computers, known as clients, over a network. File servers, web servers, database servers.
9. Modem
For transmission across an analog medium like a telephone line or cable, digital data must be converted via a networking device called a modem (short for modulator-demodulator). It is used to connect a computer or a router to an Internet service provider (ISP) via telephone lines or cable lines.
It is responsible for the conversion of digital signals originating from a computer or network into analog signals that are capable of being transmitted over a telephone or cable line. Upon reaching the terminal point of transmission, the analog signals undergo a conversion process by the modem located at the receiving end, which transforms them into digital signals that the recipient computer or network can understand.
How the components interconnect to form a network:
Types of Connection in a Computer Network
A network is two or more devices connected through links. A link is a communications pathway that transfers data from one device to another. For visualization purposes, it is simplest to imagine any link as a line drawn between two points. In this case there are two types of connections possible:
1. Point-to-Point. A point-to-point connection provides a dedicated link between two devices. The
entire capacity of the link is reserved for transmission between those two devices. When we change television channels by infrared remote control, we are
establishing a point-to-point connection between the remote control and the television’s
control system.
2. Multipoint. A multipoint (also called multidrop) connection is one in which more than two specific devices share a single link. In a multipoint environment, the capacity of the channel is shared, either spatially
or temporally. If several devices can use the link simultaneously, it is a spatially shared
connection. If users must take turns, it is a timeshared connection.
Physical Structures of a Computer Network
Physical Topology
The term physical topology refers to the way in which a computer network is laid out physically.
Two or more devices connect to a link forming a topology. The topology
of a network is the geometric representation of the relationship of all the links and
linking devices (usually called nodes) to one another. There are four basic topologies
possible: mesh, star, bus, and ring.
Mesh Topology
In a mesh topology, every device has a dedicated point-to-point link to every other
device. Dedicated means that the link carries traffic only between the two specific devices it connects. In a mesh topology for n devices -
- each node is connected to n-1 device.
- every device on the network must have n – 1 input/output (I/O) ports to be connected to the other n – 1 station.
- we need n*(n – 1) physical links for half duplex.
- we need n*(n – 1)/2 physical links for full duplex.
A mesh topology offers several advantages over other network topologies:
- Dedicated Links: Each connection carries its own data load, eliminating traffic problems associated with shared links.
- Robustness: The network remains operational even if one link fails, as there are multiple paths for data to travel.
- Privacy and Security: Messages travel on dedicated lines, ensuring that only the intended recipient can access the data.
- Fault Identification and Isolation: Point-to-point links facilitate easy identification and isolation of faults, allowing traffic to be rerouted around problem areas.
However, mesh topology also has significant disadvantages:
- Cabling and I/O Ports: The need for every device to be connected to every other device requires extensive cabling and a large number of I/O ports.
- Installation and Reconnection: The complexity of installation and reconnection is higher compared to other topologies.
- Space and Expense: The bulk of wiring may exceed available space, and the cost of hardware (cables and I/O ports) can be prohibitively high.
One practical example of a mesh topology is the connection of telephone regional
offices in which each regional office needs to be connected to every other regional
office.
Star Topology
In a star topology, each device has a dedicated point-to-point link only to a central controller, called a hub. A star topology does not allow direct traffic between devices, the devices are not directly linked to one another. The controller acts as: If one device wants to send data to another, it sends the
data to the controller, which then relays the data to the other connected device.
Advantages of Star Topology:
- Cost-Effectiveness: Requires fewer cables and I/O ports compared to a mesh topology, reducing overall costs.
- Ease of Installation and Reconfiguration: Simple setup with straightforward connections makes it easy to add, move, or remove devices.
- Reduced Cabling Needs: Although it requires more cables than ring or bus topologies, it requires significantly less than mesh topologies.
- Robustness: If one link fails, only that specific connection is affected, and the rest of the network continues to function normally.
- Fault Identification and Isolation: The central hub can monitor and identify link problems, isolating faults quickly to maintain network functionality.
- Scalability: Easy to expand by connecting additional devices to the central hub without significant changes to the network.
Disadvantages of Star Topology:
- Single Point of Failure: The entire network relies on the central hub. If the hub fails, the whole network goes down.
- Network Congestion: If the hub is overwhelmed by traffic, it can become a bottleneck, slowing down the entire network.
The star topology is used in local-area networks (LANs)
Bus Topology
The examples provided above all illustrate point-to-point connections. A bus topology uses multipoint connection. It uses a single long cable that act as a backbone to link all the devices in a network. Nodes are connected to the bus cable by drop lines and taps. Drop line is the connection between the device and the main cable. A tap serves as a connector that either integrates into the main cable or pierces the cable's sheathing to establish contact with the metallic core.
As a signal travels along the backbone, some of its energy is transformed into heat. Therefore, it becomes weaker and weaker as it travels farther and farther. For this reason, there is a limit on the number of taps a bus can support and on the
distance between those taps.
Advantages of Bus Topology:
- Ease of Installation: The backbone cable can be laid along an efficient path with drop lines connecting to the nodes, simplifying the setup process.
- Reduced Cabling: Uses less cabling than mesh or star topologies since only the backbone cable runs through the entire facility.
- Cost-Effective: Fewer cables and I/O ports are required, reducing the overall cost of installation and maintenance.
- Simplified Expansion: Adding new devices is relatively easy as they can be connected to the nearest point on the backbone.
Disadvantages of Bus Topology:
- Difficult Reconnection and Fault Isolation: Adding new devices or making changes to the network can be challenging. Identifying and isolating faults is also difficult.
- Signal Degradation: Signal reflection at the taps can degrade quality. This can be mitigated by limiting the number and spacing of devices, but it complicates adding new devices.
- Network Disruption: A fault or break in the backbone cable halts all transmission, even between devices on the same side of the problem and causes signal reflection and noise.
- Limited Scalability: The more devices added, the more likely signal degradation will occur, limiting the scalability of the network.
- Single Point of Failure: The backbone cable is a single point of failure; if it is damaged, the entire network can go down.
Traditional Ethernet LANs can use a bus topology, but they are less popular now.
Ring Topology
In a ring topology, each device has a dedicated point-to-point connection with only the
two devices on either side of it. A signal is passed along the ring in one direction, from
device to device, until it reaches its destination. Each device in the ring incorporates a
repeater. When a device receives a signal intended for another device, its repeater
regenerates the bits and passes them along.
Advantages of Ring Topology:
- Ease of Installation and Reconfiguration: Each device is connected to its immediate neighbors, making it straightforward to add or remove devices by changing only two connections.
- Simplified Fault Isolation: The continuous circulation of signals allows for easy detection of faults. If a device does not receive a signal within a specified time, it can raise an alarm to alert the network operator to the problem and its location.
- Organized Data Transmission: The orderly data transmission reduces the chances of packet collisions, leading to predictable network performance.
- Equal Access: Each device in the ring has equal access to the network, which can be beneficial in scenarios where fair resource allocation is important.
Disadvantages of Ring Topology:
- Unidirectional Traffic: In a simple ring topology, data travels in one direction. A break in the ring (such as a disabled station) can disable the entire network.
- Single Point of Failure: The entire network can be disrupted by a single break in the cable or a failure in any device. This issue can be mitigated by using a dual ring or switches capable of bypassing the failure, but it adds complexity and cost.
- Scalability Limitations: The maximum ring length and the number of devices are constrained by the medium and traffic considerations, potentially limiting network expansion.
- Latency: As the network grows, the time it takes for data to travel around the ring increases, potentially leading to higher latency.
