Networking Fundamentals: Understanding Communication Networks, Study notes of Computer Systems Networking and Telecommunications

Download Networking Fundamentals: Understanding Communication Networks and more Study notes Computer Systems Networking and Telecommunications in PDF only on Docsity! Page 1 Chuah, Fall 2004 1 Lecture 1: Overview § Introduction to Networking - Circuit vs. packet switching - Connection oriented vs. connectionless - Multiplexing § Fundamental Issues in Networking Readings: Chapter 1.1-1.2 Chuah, Fall 2004 2 What is a Communication Network? (End-system Centric View) § Network offers a service: move information - Bird, fire, messenger, post, telegraph, telephone, Internet … § What distinguish different types of networks? - The services they provide § What distinguish the services? • Latency • Bandwidth • Loss rate • Number of end users/systems • System interface (how to invoke the service) • Others ¢reliability, real-time, etc. Chuah, Fall 2004 3 What is a Communication Network? (Infrastructure Centric View) § Communication medium: electron, photon § Network components - Links – carry bits from one place to another (or maybe multiple places): fiber, copper, satellite, … - Interfaces – attach devices to links - Switches/routers – interconnect links: electronic/optic, crossbar/Banyan - Hosts – communication endpoints: workstations, PDAs, cell phones, toasters § Protocols – rules governing communication between nodes - TCP/IP, ATM, MPLS, SONET, Ethernet, X.25 § Applications: Web browser, X Windows, FTP, ... Chuah, Fall 2004 4 Network Components (Examples) Fibers Coaxial Cable Links Interfaces Switches/routers Ethernet card Wireless card Large router Telephone switch Page 2 Chuah, Fall 2004 5 Types of Networks § Information type - Data vs. telecommunication networks § Application type - Special purpose (e.g., airline reservation network, banking network) vs. general purpose network (e.g., Internet) § Geographical distance: LAN, MAN, WAN § Right to use: private vs. public § Technologies - terrestrial vs. satellite - wired vs. wireless, protocols Chuah, Fall 2004 6 § Communication networks can be classified based on the way in which the nodes exchange information: A Taxonomy of Communication Networks Communication Network Switched Communication Network Broadcast Communication Network Chuah, Fall 2004 7 § Broadcast communication networks - Information transmitted by any node is received by every other node in the network • examples: usually in LANs (Ethernet, WLAN) - Challenge: coordinate the access of all nodes to the shared communication medium (Multiple Access Problem) § Switched communication networks - Information is transmitted to a sub-set of designated nodes • examples: WANs (Telephony Network, Internet) - Challenge: how to forward information to intended node's) • this is done by special nodes (e.g., routers, switches) running routing protocols Broadcast vs. Switched Communication Networks Chuah, Fall 2004 8 Switched Networks - two or more nodes connected by a link, or - two or more networks connected by two or more nodes § A network can be defined recursively as... Page 5 Chuah, Fall 2004 17 Statistical Multiplexing § Time division, but on demand rather than fixed § Reschedule link on a per -packet basis § Packets from different sources interleaved on the link § Buffer packets that are contending for the link § Buffer buildup is called congestion § This is packet switching, used in computer networks Chuah, Fall 2004 18 Why Statistically Share Resources § Efficient utilization of the network § Example scenario - Link bandwidth: 1 Mbps - Each call requires 100 Kbps when transmitting - Each call has data to send only 10% of time § Circuit switching - Each call gets 100 Kbps: supports 10 simultaneous calls § Packet switching - Supports many more calls with small probability of contention • 35 ongoing calls: probability that > 10 active is < 0.0017! Chuah, Fall 2004 19 Circuit Switching vs Packet Switching Queuing delayCall blockingEffect of congestion On every packetAt setup timeWhen can congestion occur Not NeededRequiredCall setup NoYesEach packet follows the same route YesNoStore-and -forward transmission NoYesPotentially wasted bandwidth DynamicFixedBandwidth available NoYesDedicated “copper” path Packet-switchedCircuit-switchedItem Chuah, Fall 2004 20 Packet-Switching vs. Circuit-Switching § Most important advantage of packet-switching over circuit switching is its ability to exploit statistical multiplexing: - efficient bandwidth usage; ratio between peek and average rate is 3:1 for audio, and 15:1 for data traffic - great for bursty data § However, packet-switching needs to deal with congestion: - more complex routers - harder to provide good network services (e.g., delay and bandwidth guarantees) § In practice they are combined: - IP over SONET, IP over Frame Relay Page 6 Chuah, Fall 2004 21 Overview § Introduction to Networking - Circuit vs. packet switching - Connection oriented vs. connectionless - Multiplexing § Fundamental Issues in Networking Chuah, Fall 2004 22 An Example: Computer Network § A set of computer and/or switches connected by communication links (coax cable, optical fiber, ...) § Many topologies possible: Ring Bus Star General mesh § Network provides connectivity! § Network is a shared resource! - Allows shared access to computing resources and distributed services/applications Chuah, Fall 2004 23 Fundamental Issues in Networking § Naming/Addressing - How to find name/address of the party (or parties) you would like to communicate with - Address: byte-string that identifies a node - Types of addresses • Unicast: node-specific • Broadcast: all nodes in the network • Multicast: some subset of nodes in the network § Routing/Forwarding: process of determining how to send packets towards the destination based on its address - Finding out neighbors, building routing tables Chuah, Fall 2004 24 Fundamental Problems in Networking § What can go wrong? - Bit-level errors: due to electrical interferences - Packet -level errors: packet loss due to buffer overflow/congestion - Out of order delivery: packets may takes different paths - Link/node failures: cable is cut or system crash § What can be done? - Add redundancy to detect and correct erroneous packets - Acknowledge received packets and retransmit lost packets - Assign sequence numbers and reorder packets at the receiver - Sense link/node failures and route around failed links/nodes § Goal: to fill the gap between what applications expect and what underlying technology provides