Network Topology

• The word topology originates from the Greek words "topos," meaning place, and "logos," meaning study.
• Topology is a branch of mathematics that deals with the properties of geometric figures that remain unchanged when distorted without tearing or bonding.
• Network topology refers to the arrangement of a network, including its nodes and connecting lines.
• Network topology is the schematic description of a network arrangement, connecting various nodes (sender and receiver) through lines of connection.
• Network topology is the pattern in which nodes (computers, printers, routers, etc.) are connected to a network via communication links, such as copper wire or optical fiber.
• There are two ways to define network geometry: physical topology and logical (or signal) topology.
• Physical topology is the actual geometric layout of workstations.
• Logical topology refers to the path signals follow from node to node, focusing on how devices communicate rather than how they are connected.

Bus Topology

• Every workstation is connected to a central cable called the bus or backbone.
• Each workstation is effectively directly connected to every other in the network.
• When one computer sends a signal, all computers receive the information, but only the one with the matching address accepts it.
• Bus topology is typically a passive topology because the cable is one or more wires without active electronics to amplify the signal.
• Bus topology is suitable for small, simple, or temporary network installations.

Advantages of Bus Topology

• Easy to use and understand.
• Inexpensive and easy to install for small networks as it requires the least amount of cable.
• It is easy to extend a bus by joining two cables with a BNC connector.

Drawbacks of Bus Topology

• Heavy traffic can slow a bus considerably as only one computer can send messages at a time.
• Difficult to troubleshoot; a cable break or loose connector causes reflection and stops all activity.

Ring Topology

• Each workstation connects to the next, with the last connected to the first, forming a closed loop.
• There is no termination because there is no end to the ring.
• Adjacent pairs of workstations are directly connected.
• Other workstations are indirectly connected.
• Each workstation retransmits what it receives from the previous computer.
• Messages flow around the ring in one direction.

Advantages of Ring Topology

• Each node has equal access.
• Capable of high-speed data transfer.

Drawbacks of Ring Topology

• Failure of one computer can affect the entire network.
• Difficult to troubleshoot the network.
• Token ring is a variation where signals travel in one direction, carried by a token from node to node.

Star Topology

• Cables run from computers to a central point connected by a hub or switch.
• Star networks are Relatively easy to install/manage
• Bottlenecks can occur since all data passes through a central device.
• Computers communicate via a central device that resends messages either to all computers (if a hub) or the destination computer (if a switch).
• Star topology is best when network expansion is expected and greater reliability is needed.

Advantages of Star Topology

• Easy to modify and add new computers without disrupting the rest of the network.
• The center of the star network is a good place to diagnose faults.
• Single computer failure does not necessarily bring down the entire network.

Drawbacks of Star Topology

• If the central device fails, the entire network fails.
• Star networking is expensive due to the amount of cable required.

Mesh Topology

• Employs either a full mesh or partial mesh scheme.
• In full mesh topology, each workstation is connected directly to each of the others.
• In partial mesh topology, some workstations are connected to most others, while some are connected only to nodes with which they exchange the most data.

Advantages of Mesh Topology

• A broken node won't disrupt data transmission.
• Additional devices do not affect the network connection.
• It can handle a high amount of traffic since each device is considered a node.

Drawbacks of Mesh Topology

• Maintaining mesh networks can be difficult.
• Expensive, as building this topology requires a lot of devices and capital investment.

Hybrid Topology

• Combines several basic network topologies.
• Examples of hybrid topology include the star-ring network and star-bus network.

Star-Ring Topology.

• Consists of two or more star topologies connected using a multi-station access unit (MAU) as a centralized hub.

Star-Bus Topology

• Consists of two or more star topologies connected using a bus trunk, which serves as the network's backbone.
• The central computers of the star networks are connected to a main bus.
• Star-Bus Topology is also known as a tree network, or bus network of star networks.
• The logical topology is often the same as the physical one, but not always; some networks are physically star-shaped but operate logically as bus or ring networks.

Network Service

• A function provided by the network infrastructure that adds value to the business process.
• An application running at the network application layer and above, providing data storage, manipulation, presentation, communication, or other capabilities.
• Often implemented using a client-server or peer-to-peer architecture based on application layer network protocols.
• Each service is typically provided by a server component on one or more computers and accessed through a network by client components on other devices.

Types of Network Services

• Configuration and Management (e.g., DHCP).
• Remote Access (e.g., SSH).
• File Management (e.g., FTP).
• Print Services (printer sharing).
• Information (e.g., WWW, video sharing, IPtv).
• Communication (e.g., email, chat, videoconference, IP telephony, online games).

Common Network Services

• Domain Name System (DNS) translates domain names to IP addresses.
• Dynamic Host Configuration Protocol (DHCP) assigns networking configuration information to network hosts.
• Authentication servers identify and authenticate users, provide profiles, and may log usage statistics.
• Directory service (name service) maps network resource names to respective addresses.
• Electronic-mail (email) exchange digital messages.
• File sharing distributes or provides access to digital media.
• Instant messaging (IM) offers real-time text transmission.
• Online game is a video game played through the Internet or another network.
• Print service (printer server) connects printers to computers; accepts print jobs and sends them to printers, queuing locally.
• File server provides shared disk access for files (documents, sound files, photos, etc.)
• Voice over Internet Protocol (Voice over IP, VoIP, and IP telephony) provides voice and multimedia communication over IP networks.
• Video on demand/display (VOD) allows users to select/watch video or audio content at will.
• Video telephony receives and transmits audio-video signals for communication between people in real-time.
• World Wide Web (WWW) is accessed via the Internet.
• Simple Network Management Protocol (SNMP) collects and organizes information about managed devices on IP networks
• Time service (time server) reads actual time from a clock and distributes this to clients.
• Wireless sensor networks (WSN) monitor physical/environmental conditions and cooperatively pass their data.