📡Systems Approach to Computer Networks Unit 2 – End Systems and Access Networks

Key Concepts

• End systems serve as the source and destination of data in computer networks enabling users to access network resources and services
• Access networks provide connectivity between end systems and the broader network infrastructure through various technologies (Ethernet, Wi-Fi, cellular)
• Network protocols define the rules and formats for data exchange ensuring interoperability across diverse systems and applications
• Interfaces specify the boundary between different network components or layers facilitating communication and data transfer
• Performance metrics measure network characteristics (bandwidth, latency, throughput) to assess the efficiency and quality of service
• Security considerations address the protection of data confidentiality, integrity, and availability in network communications through various mechanisms (encryption, authentication, firewalls)
• Real-world applications demonstrate the practical implementation of network concepts enabling services (email, web browsing, video streaming) that impact daily life

Network Architecture

• Defines the overall structure and organization of a computer network outlining the arrangement of components and their interactions
• Follows a layered approach dividing network functions into distinct levels (physical, data link, network, transport, application) for modularity and scalability
• Client-server architecture involves end systems requesting services from centralized servers promoting resource sharing and efficient management
• Peer-to-peer (P2P) architecture enables direct communication and resource exchange between end systems without relying on dedicated servers
  • Offers advantages in terms of scalability, fault tolerance, and load balancing
• Network topologies describe the physical or logical layout of devices and connections (bus, star, ring, mesh) influencing factors like performance and resilience
• Hierarchical designs separate the network into access, distribution, and core layers allowing for efficient traffic management and scalability
• Software-defined networking (SDN) decouples the control plane from the data plane enabling centralized network management and programmability

End Systems Overview

• End systems encompass devices that generate or consume data in a network including computers, smartphones, servers, and IoT devices
• Serve as the interface between users and the network enabling access to applications, services, and resources
• Host operating systems manage end system resources (memory, processing, storage) and provide an environment for running network applications
• Network interfaces (Ethernet adapters, Wi-Fi cards) enable end systems to connect to access networks and communicate with other devices
• End systems implement network protocols at various layers to facilitate data exchange, routing, and error handling
  • Examples include TCP/IP at the transport and network layers, HTTP at the application layer
• Resource sharing allows end systems to access and utilize remote resources (files, printers, databases) over the network
• Mobility support enables end systems to maintain network connectivity while moving across different access points or networks (cellular handoffs, Wi-Fi roaming)

Access Network Technologies

• Access networks bridge the gap between end systems and the core network infrastructure providing last-mile connectivity
• Ethernet is a widely used wired access technology offering high-speed (10 Mbps to 400 Gbps) and reliable connections over short distances
  • Utilizes twisted-pair cables (Cat5, Cat6) or fiber optic cables for data transmission
• Wi-Fi (IEEE 802.11) enables wireless access to local area networks (LANs) using radio frequencies in the 2.4 GHz and 5 GHz bands
  • Supports various data rates (11 Mbps to 6.9 Gbps) and security mechanisms (WPA2, WPA3)
• Cellular networks (3G, 4G, 5G) provide mobile access to wide area networks (WANs) through base stations and core network infrastructure
  • Offer voice and data services with increasing speeds and lower latencies in each generation
• Digital subscriber line (DSL) leverages existing telephone lines for broadband access delivering asymmetric data rates (ADSL) or symmetric rates (SDSL)
• Cable broadband utilizes coaxial cable television infrastructure for high-speed internet access sharing bandwidth among multiple users
• Fiber-to-the-home (FTTH) deploys optical fiber directly to individual premises enabling ultra-high-speed and low-latency connections
• Satellite internet relies on geostationary satellites to provide access in remote or underserved areas with higher latencies due to signal propagation

Network Protocols and Interfaces

• Network protocols establish the rules and formats for data communication between end systems and intermediate devices
• Interfaces define the boundaries and methods of interaction between different network components or layers
• Internet Protocol (IP) operates at the network layer providing logical addressing and routing capabilities for packet delivery across networks
  • IPv4 uses 32-bit addresses while IPv6 employs 128-bit addresses to accommodate the growing number of devices
• Transmission Control Protocol (TCP) ensures reliable, ordered, and error-checked delivery of data segments between end systems
  • Establishes virtual connections, performs flow control, and handles congestion
• User Datagram Protocol (UDP) offers a lightweight, connectionless alternative to TCP for applications tolerant to packet loss or requiring low latency
• Hypertext Transfer Protocol (HTTP) enables the retrieval and exchange of web resources between clients and servers at the application layer
• Domain Name System (DNS) translates human-readable domain names to IP addresses facilitating network resource access
• Application programming interfaces (APIs) specify the methods and formats for software components to interact and exchange data
  • Examples include socket APIs for network programming and RESTful APIs for web services
• Physical interfaces (Ethernet ports, Wi-Fi antennas) define the mechanical and electrical characteristics for connecting devices

Performance Metrics

• Performance metrics quantify the efficiency, reliability, and quality of service in computer networks
• Bandwidth measures the maximum rate at which data can be transmitted over a network link typically expressed in bits per second (bps)
  • Determines the capacity and speed of network connections
• Latency refers to the time delay experienced by data packets as they traverse the network from source to destination
  • Influenced by factors such as propagation delay, transmission delay, processing delay, and queuing delay
• Throughput represents the actual rate at which data is successfully transferred over a network link often lower than the theoretical bandwidth
  • Affected by factors like network congestion, protocol overhead, and data loss
• Packet loss occurs when data packets fail to reach their intended destination due to network errors, congestion, or device failures
  • Measured as a percentage of total packets sent and can impact the perceived quality of service
• Jitter describes the variation in latency or delay experienced by packets leading to inconsistent arrival times
  • Particularly detrimental to real-time applications (voice, video) requiring a steady flow of data
• Round-trip time (RTT) measures the time taken for a packet to travel from source to destination and back including processing and propagation delays
• Quality of service (QoS) refers to the ability of a network to prioritize and manage traffic based on application requirements (bandwidth, latency, jitter)
  • Achieved through techniques like traffic classification, queuing, and resource reservation

Security Considerations

• Security considerations aim to protect the confidentiality, integrity, and availability of data in computer networks
• Confidentiality ensures that data is accessible only to authorized parties preventing unauthorized disclosure or interception
  • Achieved through encryption techniques (symmetric, asymmetric) that scramble data using mathematical algorithms and keys
• Integrity guarantees that data remains unaltered during transmission or storage detecting and preventing unauthorized modifications
  • Ensured through mechanisms like checksums, digital signatures, and hash functions
• Availability ensures that network resources and services are accessible to authorized users when needed
  • Maintained through redundancy, load balancing, and protection against denial-of-service (DoS) attacks
• Authentication verifies the identity of users or devices before granting access to network resources preventing unauthorized access
  • Implemented through methods like passwords, biometric factors, and digital certificates
• Access control restricts and manages the permissions and privileges of authenticated users based on predefined policies
  • Enforced through techniques like role-based access control (RBAC) and access control lists (ACLs)
• Firewalls act as a barrier between trusted internal networks and untrusted external networks filtering traffic based on predefined rules
  • Can operate at the network layer (packet filtering) or application layer (stateful inspection)
• Virtual private networks (VPNs) establish secure and encrypted tunnels over public networks enabling remote access and data protection
  • Commonly used for remote work, branch office connectivity, and secure communication

Real-World Applications

• Email enables the exchange of electronic messages and attachments between end systems using protocols like SMTP, POP3, and IMAP
  • Relies on email servers for message storage, routing, and delivery
• Web browsing allows users to access and retrieve information from web servers using the HTTP protocol and web browsers as client applications
  • Supports the display of multimedia content, user interaction, and dynamic page generation
• Video streaming delivers continuous video content to end systems over the network adapting to available bandwidth and network conditions
  • Utilizes protocols like HTTP Live Streaming (HLS) and Dynamic Adaptive Streaming over HTTP (DASH) for adaptive bitrate streaming
• Voice over IP (VoIP) enables real-time voice communication over IP networks converting analog audio signals into digital packets
  • Employs protocols like Session Initiation Protocol (SIP) for call setup and Real-time Transport Protocol (RTP) for media transport
• File sharing allows users to share and access files stored on remote end systems or servers using protocols like File Transfer Protocol (FTP) and Server Message Block (SMB)
  • Enables collaboration, backup, and distribution of digital content
• Online gaming connects multiple end systems to facilitate real-time interactive gaming experiences over the network
  • Requires low-latency communication, synchronization, and efficient data exchange between game clients and servers
• Internet of Things (IoT) involves the interconnection of everyday devices (sensors, actuators) to the internet for data collection, analysis, and control
  • Enables applications like smart homes, industrial automation, and remote monitoring
• Cloud computing leverages network connectivity to provide on-demand access to shared computing resources (servers, storage, applications) over the internet
  • Offers scalability, flexibility, and cost-efficiency for various business and personal use cases