Network Fundamentals Summary

Objectives

• Understand basic principles of a computer network.

• Grasp the concept of layered architecture.

• Learn the layers of the OSI and TCP/IP models.

General Network Definition

• A network is a complex system of interconnected objects or people.

• Examples include:

  • Internet, postal service, TV/Radio.

  • Telephone, LAN/WAN.

  • Road networks, electrical grids.

  • Social networks, biological networks.

Telephone Networks

• Consist of an emitter (source) and a receiver (destination).

• Communication passes through several telephone centers.

• Computer networks utilize telephone network infrastructure.

Computer Networks

• Interconnection of entities:

  • Computers, printers, photocopiers, terminals.

• Networks connect machines, allowing applications to exchange information.

Why Networks?

• Networks address the need to avoid duplication of equipment and resources.

• They facilitate effective communication.

Benefits of Networks

• Sharing of hardware, software, and data resources.

• Communication between remote users/applications.

• Collaboration among remote users for common tasks.

• Fault tolerance through service continuation and data duplication.

Network Components

• Physical elements: interfaces, cables, connection equipment, computers.

• Logical elements: Browsers, protocols, services (web, mail, ftp).

Network Types (by coverage area)

• LAN (Local Area Network): Local networks.

• MAN (Metropolitan Area Network): Metropolitan networks.

• WAN (Wide Area Network): Long-distance networks.

LAN

• Manage local data communications.

• Limited geographical region (10m to 1 km).

• High transfer rates.

• Continuous connectivity to local services.

MAN

• Extend to a metropolitan area (city).

• Usually includes at least two LANs in a common geographic area (1 km to 100 km).

WAN

• Interconnect LANs over long distances.

• Allow communication over large distances (100 km to 10,000 km).

Network Topology

• Defines the structure of the network.

  • Physical topology: cabling configuration.

  • Logical topology: how machines access the media to send data.

Common Topologies

• Bus: All nodes connected to the same support.

• Ring: Each node connected to two others, forming a ring.

• Star: Centralized network; one node connected directly to all others.

• Extended Star: Connects individual stars by linking central nodes.

• Mesh: Any two nodes are connected to each other.

• Hierarchical: Distributed over several levels; nodes at the same level are not directly linked.

Protocol and Standardization

• Protocols and standardization address interoperability issues among different equipment and software manufacturers.

Protocol

• Ensures data transmission from source to destination.

• A protocol is a set of rules that govern communication within a network.

• Definition: A set of rules determining the format and transmission of data between sender and receiver.

• Example: HTTP (Hyper Text Transfer Protocol).

Standardization

• Addresses incompatibility issues between networks.

• Organizations establish common rules (norms and standards) for network design.

Standardisation Agencies

• ISO (International Organization for Standardization).

• ANSI (American National Standards Institute).

• AFNOR (Association Française de Normalisation).

• IEEE (Institute of Electrical and Electronic Engineers).

• ITU-T (International Telecommunication Union).

• IETF (Internet Engineering Task Force).

Network Design Models

• Two main models:

  • OSI Model.

  • TCP/IP Model.

• Both provide recommendations for network design and structure based on layering.

Layered Systems

• Layer: Set of entities contributing to communication.

• Service: Function provided by a layer.

  • Each layer offers services.

  • Layer N uses services from layer N-1.

  • Layer N provides services to layer N+1.

  • Layers N+1 and N-1 do not communicate directly.

Objectives of Layered Models

• Reduce design complexity.

• Standardize communication interfaces.

• Facilitate modular design.

• Ensure technology interoperability.

Communication in Layered Systems

• Each layer N communicates with the corresponding layer N at the receiving end via a layer N protocol.

Encapsulation

• Data from a source passes from the highest to the lowest layer (sender).

• Data is transported from the lowest to the highest layer (receiver).

• Each layer has a Protocol Data Unit (PDU).

• Lower layers encapsulate PDUs from upper layers.

OSI Model

• Published in 1984 by ISO.

• Abstract model for network design.

• Framework for understanding how information flows in a network.

OSI Layers

• Seven layers, each with a name and number.

  • Layer 1 (Physical).

  • Layer 7 (Application).

OSI Layers Functionality

• Physical: Defines electrical, mechanical, and functional specifications for data transmission.

• Data Link: Controls media access; detects and corrects transmission errors.

• Network: Addressing and routing; logical addressing; data routing.

• Transport: Reliable end-to-end data transport; error detection and correction; flow control.

• Session: Opens, manages, and closes sessions between systems; synchronizes dialogue.

• Presentation: Data presentation; ensures data readability; data format, structure, and coding.

• Application: Provides network services to user applications.

Encapsulation in OSI Model

• Data -> APDU -> PPDU -> SPDU -> TPDU -> Packet -> Frame -> Bits

TCP/IP Model

• Enables data exchange between computers worldwide.

• Standard on which the Internet is developed.

TCP/IP Layers

• Four Layers: Application, Transport, Internet, and Network Access.

  • TCP (Transmission Control Protocol).

  • IP (Internet Protocol).

TCP/IP Layers Functionality

• Network Access: Handles physical linking.

• Internet: Routes packets, identifies the best path (IP).

• Transport: Manages flow control, error correction (TCP, UDP).

• Application: High-level protocols, representation, code, and dialogue control.

TCP/IP Protocol Stack

• Application: Ping, HTTP, SMTP, FTP, DNS, TFTP.

• Transport: TCP, UDP.

• Internet: ICMP, IP, ARP/RARP.

Encapsulation in TCP/IP Model

• Data -> Message -> Segment -> Datagram -> Frame

TCP/IP vs. OSI Model

Similarities

• Both use layers.

• Both have application layers.

• Comparable network and transport layers.

Differences

• TCP/IP integrates presentation and session layers into its application layer.

• TCP/IP combines OSI's physical and data link layers into a single layer.

• OSI is a generic standard, while TCP/IP has defined protocols at each layer.

OSI Model Usefulness

• Universal standard, independent of protocol.

• More detailed, aiding teaching and study.

• Helpful for troubleshooting.