Computer networks introduction

• Computer and communication merging has deeply impacted computer systems organization
• Old single computer model has been replaced by interconnected computers or computer networks

Introduction to Computer Networking

• Transmission medium is the physical pathway connecting systems
• Protocols determine how systems communicate, acting as a set of rules
• Network protocol software dictates communication rules between machines
• Client-Server Model: Arrangement involves clients requesting work from servers
• Servers then processes tasks and returns the reply

Types of Networks

• Local Area Networks (LANs): confined to a specific location, use one transmission medium, and run at 10-100 mbps with low delay
• Metropolitan Area Networks (MANs): bigger version of LAN, uses same technology, covers corporate offices or a city, and has one or two cables
• Wide Area Networks (WANs): multiple connected LANs separated geographically, containing cables/telephone lines and routers
• Wireless Networks: fastest growing segment for mobile computers
• Internet works: collection of interconnected networks formed by connected LANs through WANs via routers and hosts

Topology

• Topology is the mapping of a LAN design
• Star topology connects devices to a central hub/switch, and follows Ethernet standards
• Bus topology connects devices to a linear cable, requires discharged ends, and is also called the backbone
• Ring topology connects devices in a closed loop, where each device acts as a repeater, and uses a token for data transmission
• Mesh Topology a local network topology where the infrastructure nodes connect directly, dynamically and non-hierarchically
• Mesh Topology requires the nodes to cooperate with one another to efficiently route data from/to clients

Basic Computer Networking

• Computer transmission media: uses cables and wireless technologies to connect network devices
• Networks are organized in layers to reduce design complexity, governed by layer protocols

Organizational Computational Models

• Centralized computing processes everything at a single location
• Distributed computing replaces dumb terminals with PCs that function separately but interact with servers
• Collaborative computing allows computers to share resources and processing through methods like borrowing processors or sharing processing with clients

Networking Models

• Peer-to-Peer: machines connect via networking cards without a server for resource sharing but lacks security
• Server-based network: implements user-level security based on user login authentication

Network Services

• File server: stores files for clients, provides central data location, enables backup operations, and ensures data safety through user-level security
• Print server: offers printing services to clients
• Application server: runs application for clients and transfers results after processing

Transmission Media

• Transmission media: Pathway network uses to contact each other
• Communication protocol includes cables & wireless technologies that allow network devices to contact each other

Repeaters

• Repeater: regenerates signals on the same network to extend transmission distance without amplifying
• It copies bits of data and regenerates with original strength, and it contains 2 ports

Hubs

• Hub: multiport repeater connecting multiple wires but cannot filter data and lack intelligence for optimal paths

Types of Hub

• Active Hub: clean, boost, and relay signals, acts as repeater and wiring center, and extends max distance between nodes
• Passive Hub: collect wiring from nodes and relay signals without cleaning/boosting
• Intelligent Hub: acts like active hub, includes remote management, enables admins to monitor & configure ports
• Bridge: repeats and filters content using MAC addresses for LAN interconnection, contains 2 ports

Types of Bridges

• Transparent Bridges: unaware of bridge presence, use bridge forwarding and learning processes
• Source Routing Bridges: routing is performed by the source station
• Switch: a faster multiport bridge with buffer design that enhances performance, performs error checking before forwarding data, divides the collision domain of hosts

Routers

• Router: routes data packets based on IP addresses, connects LANs/WANs, and uses updating routing tables
• Gateway: connects networks using different networking models like messenger agents

Pathways

• Shortest path routing minimizes distance/cost metric
• Longest path involves finding the longest simple path in a graph

The OSI Model

• The Open System Interconnection (OSI) model is a networking layering model
• The model was developed by the International Organization for Standardization (ISO)
• The American National Standards Institute (ANSI) is a member of ISO
• Standards are documented agreements containing technical specifications
• Open standards are public, while proprietary standards remain private

Layering

• Layering ensures standard interfaces between layers
• The operating system is said to provide an Application Programming Interface (API)
• There are companies specializing in hardware, BIOS, operating systems, and applications

Communications Layering

• Communications layering: The communication between two (or more) users on a network similarly is broken down into layers
• OSI serves as a "reference model" for how information is transmitted between any two points in a network.
• The OSI model comprises seven layers

The TCP/IP Model

• TCP/IP model: another model for understanding communications networks
• The OSI lower layers include the physical, data link, network and transport

Layer 1: Physical

• Physical (Layer 1): transmits raw data streams without interpretation and manages hardware-specific specifications (NIC speeds, cable types, voltages etc.)
• The physical layer involves protocols for actual transmission such as Ethernet, FDDI, RS232 and ATM

Layer 2: Data Link

• The data-link layer - considers bytes over bits
• The data-link layer examines the information content of the signal and error detection sequencing
• The data-link layer operates with bridges
• The data-link layer encodes, and decodes data packets into bits
• The data-link layer directs packets and handles errors from the physical layer.
• The data-link layer handles synchronization (timing)

Data Link Sublayers

• The MAC (Media Access Control) sublayer: interacts with physical transmission lines
• The LLC (Logical Link Control) sublayer: interprets signal as data, includes timing and error checking

Layer 3: Network Layer

• The network layer performs the function of routing
• Troubleshooting builds routing tables when there is lot of traffic and related packets are gathered (packet sequencing).

Layer 4: Transport Layer

• The transport layer manages verification
• The transport layer makes sure information is received intact and should be "transparent"

Layers 5, 6 and 7

• Layer 5 (The session layer): an agreement between a source and destination to communicate.
• Layer 6 (The presentation layer): This layer provides independence from differences in data representation
• Layer 7 (The application layer): This layer supports application and end-user processes.