Network

A set of devices (nodes) connected by communication links.

• Performance: Measured by bandwidth, throughput, and delay.
• Reliability: Measured by frequency of failure, time for recovery, and network robustness.
• Security: Protects data from unauthorized access and damage, implements recovery policies.

Types of Connections

• Point-to-Point: Dedicated link between two devices; the entire capacity of the link is reserved.
• Multipoint: Multiple devices share a single link, capacity is shared.

Network Topology

Physical Topology

Describes where cables, workstations, nodes, routers, and gateways are located. Types include bus, ring, star, and mesh topologies.

Logical Topology

Refers to the paths that messages take from one user to another.

Bus Topology

All devices are connected to a central cable called the bus or backbone.

• Advantages: Ease of installation, less cabling.
• Disadvantages: Difficult to isolate faults, difficult to add new devices, inefficient with heavy traffic.

Star Topology

Central device (hub) manages network functions, acts as a repeater, uses RJ-45 connectors.

• Advantages: Less expensive, easy to reconfigure, robust.
• Disadvantages: Single point of failure (hub), more cabling than bus topology.

Ring Topology

Devices are connected in a closed loop, usually forming a star-wired ring topology.

• Advantages: Easy to install, consistent performance.
• Disadvantages: Media length limitations, a break in the ring can disable the entire network.

Mesh Topology

Redundant interconnection with full mesh connecting every node to every other node.

• Advantages: Security, privacy, robustness, easy fault identification.
• Disadvantages: Expensive, difficult to install, requires large wiring space.

Networking and Internetworking Devices

Repeater

An analog device that amplifies and retransmits signals over long distances, operates at the physical layer.

Hub

Physical layer device, like repeaters but designed for multiple input lines.

Bridge

Connects two or more LANs, isolates collision domains, and offers better performance than hubs.

Switch

Connects devices on a network, transmits data to specific devices, and operates at the Data Link Layer (Layer 2).

Router

Connects local networks, directs traffic at the Network Layer (Layer 3), and performs NAT (Network Address Translation).

Connection-Oriented vs Connectionless Services

Connection-Oriented

Modeled after the telephone system. A connection is established before communication, and the connection is released after use.

Connectionless

Modeled after the postal system. Each message carries the full destination address without needing to establish a connection.

Reference Models

OSI Reference Model

A model developed by ISO for standardizing network protocols, revised in 1995.

TCP/IP Reference Model

Used by ARPANET and its successor, the Internet, with design goals to connect multiple networks.

Transport Layer Protocols

Transmission Control Protocol (TCP)

• Connection-oriented
• Reliable delivery
• Ordered data reconstruction
• Flow control

User Datagram Protocol (UDP)

• Connectionless
• Unreliable delivery
• No ordered data reconstruction
• No flow control

Summary

Key topics: network topologies, internetworking devices, OSI reference model, TCP/IP protocols.