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01 - Overview Prof. Dr.-Ing. Michael Mecking 01.10.2024 Reference Book. These lectures notes are based to a large extent on the book [KR21]...

01 - Overview Prof. Dr.-Ing. Michael Mecking 01.10.2024 Reference Book. These lectures notes are based to a large extent on the book [KR21] Computer Networking by Jim Kurose and Keith Ross. 2 THI | Computer Networks | Prof. Dr. M. Mecking | WS 2024/25 Chapter 1: Overview & History of Communication Networks. Chapter goal: Overview/roadmap: Get “feel,” “big picture,” History introduction to terminology What is the Internet? more depth, detail later in course What is a protocol? Network edge: hosts, access network, physical media Network core: packet/circuit switching, internet structure Performance: loss, delay, throughput Protocol layers: service models Security 3 THI | Computer Networks | Prof. Dr. M. Mecking | WS 2024/25 Meilensteine der Kommunikationstechnik. Signalgraphen 450 vChr. - 18 Jhd. Entdeckung Elektromagnetismus durch Oersted (1820) Morse-Telegraf (Anfang 19 Jhd.) Morse-Code (1837, patentiert 1840) Zeigertelegraf von Siemens (1847) Kommunikation über lange Distanzen mittels Relais (“Postkutschen”-Prinzip) 4 THI | Computer Networks | Prof. Dr. M. Mecking | WS 2024/25 Meilensteine der Kommunikationstechnik. Erfindung des Telefons durch Philipp Reis (1861) Verbesserung des Telefons durch Bell & Watson (1876) 5 THI | Computer Networks | Prof. Dr. M. Mecking | WS 2024/25 Meilensteine der Kommunikationstechnik. Theorie der elektromagnetischen Felder durch James Clerk Maxwell (1864-1867) Entdeckung der elektromagnetischen Wellen durch Heinrich Hertz (1885-1889) Erste drahtlose Datenübertragung durch Guglielmo Marconi (1897) “Are you ready?” 6 THI | Computer Networks | Prof. Dr. M. Mecking | WS 2024/25 Meilensteine der Kommunikationstechnik. Veröffentlichung “A Mathematical Theory of Communication” durch Claude Elwood Shannon (1948) → die Magna Charta des Informationszeitalters eine der meist zitierten (und immer noch lesenswertesten!) Veröffentlichungen weltweit Claude Shannon ist der Vater des digitalen Zeitalters und einer der einflussreichsten Wissenschaftler des 20. Jhd weitere wichtige, grundlegende Veröffentlichungen: “A Symbolic Analysis of Relay and Switching Circuits”, Master’s Thesis MIT (1937) “Communication Theory of Secrecy Systems” (1949) 7 THI | Computer Networks | Prof. Dr. M. Mecking | WS 2024/25 „A Mathematical Theory of Communication”, Claude Elwood Shannon [Sha48]. Random Choice “The fundamental problem of communication is that of reproducing at one point either exactly or approximately a message selected at another point.” “Frequently the messages have meaning; that is they refer to or are correlated according to some system with certain physical or conceptual entities. These semantic aspects of communication are irrelevant to the engineering problem.” “The significant aspect is that the actual message is one selected from a set of possible messages. The system must be designed to operate for each possible selection, not just the one which will actually be chosen since this is unknown at the time of design.” 8 THI | Computer Networks | Prof. Dr. M. Mecking | WS 2024/25 „A Mathematical Theory of Communication”, Claude Elwood Shannon [Sha48]. Kommunikation ist “digital” und “zufällig” erster Gebrauch des Wortes “bit” für “binary digit” Systematische Betrachtung von Unsicherheit, Information und Kommunikation Kommunikation wird zur Wissenschaft (→ Informationstheorie) fundamentale Theoreme zur Quellenkompression und Datenübertragung erste praktische Ansätze, um diese theoretischen Grenzen zu erreichen 9 THI | Computer Networks | Prof. Dr. M. Mecking | WS 2024/25 Meilensteine der Kommunikationstechnik. Telekommunikationsnetze mit Leitungsvermittlung von Hand - erste Hälfte 20 Jhd. Erstes elektronisches Fernsprechamt - 1962 in München Gründung Advanced Research Projects Agency (ARPA, 1958) Prinzip der Paketvermittlung in Netzen durch Leonard Kleinrock (Dissertation MIT, 1961) Committee Member: Claude Shannon! 10 THI | Computer Networks | Prof. Dr. M. Mecking | WS 2024/25 Meilensteine der Kommunikationstechnik. erste Host-to-Host Verbindung im ARPAnet zwischen L. Kleinrocks Rechner an der UCLA und Stanford Research Institute SRI (1969) Ziel: LOGIN von UCLA auf dem SRI Computer: “We sent an “L” - did you get the “L”? → YEP! “We sent an “O” - did you get the “O”? → YEP! “We sent a “G” – did you get the “G”? → CRASH!! ALOHA Satellitennetzwerk auf Hawaii (1970) durch Norman Abramson erste Email im ARPAnet durch Ray Tomlinson (1971) “something like QWERTYUIOP”, Nutzung des @-Symbols, um Nutzer und Rechneradresse zu trennen Ethernet-Kommunikation im Xerox Park (1976) “Internet”-Protokolle: smtp Email (1982), TCP / IP (1983), DNS (1983), FTP (1985) 11 THI | Computer Networks | Prof. Dr. M. Mecking | WS 2024/25 Meilensteine der Kommunikationstechnik. HTML, HTTP durch Tim Bernes-Lee (1990) @ CERN → Erfindung des WWW 12 THI | Computer Networks | Prof. Dr. M. Mecking | WS 2024/25 Meilensteine der Kommunikationstechnik. 1992 2000 2007 2011 2021 Mobile Mobiles Mobile Mobile Everything Telefonie Internet Apps Multimedia Mobile 2G 2.5G 3G 4G 5G GSM GPRS UMTS LTE HSPA LTE-A GSM Global System for Mobile Communica on GPRS General Packet Radio Service UMTS Universal Mobile Telecommunica on Network HSPA High-Speed Packet Access (HSxPA: HSDPA, HSUPA) LTE Long Term Evolu on LTE Long-Term Evolu on LTE-A Long-Term Evolu on Advanced 13 THI | Computer Networks | Prof. Dr. M. Mecking | WS 2024/25 ti ti ti ti ti Meilensteine der Kommunikationstechnik. Über die letzten zehn Jahre: Anzahl Geräte/Dinge im Internet Ausbau Breitbandzugriff DSL für HomeNetworks auf 10-100 Mbit/s, FTTH-Technologie (Fiber to the Home) Service Providers (Google, Facebook, Amazon) starten eigene Netzwerke für schnelle, verzögerungsfreie Datenübertragung “dicht am Kunden” (im “Edge”) Vergleich fixed / mobile Internet Unternehmen lagern Dienste in die Cloud aus (AWS, MS Azure) Ausbau HighSpeed Wireless Access Technologien (4G/5G, WLAN/WiFi) mehr drahtlose als feste Nutzer im Internet Internet of Things 14 THI | Computer Networks | Prof. Dr. M. Mecking | WS 2024/25 Quelle: Cisco 2022 Standardisierung in der Kommunikationstechnik. Kommunikation findet lokal, regional, national oder international statt — Standardisierung ist eine wesentliche Voraussetzung dafür. Auf dem Gebiet der Kommunikationstechnik werden standardisiert: Dienste (VoIP, Multimedia, WWW, E-Mail) → Kompatibilität sichern Schnittstellen (Ethernet, WiFi, 5G/6G, …) → Sicherung der Portabilität der Endgeräte, Dienstekompatibilität, Netzkooperation Standards sind Empfehlungen und kein Dogma: bilden Kompromiss zwischen (vielen) Interessengruppen und sind daher selten technisch optimal sind nicht statisch sondern werden weiterentwickelt (RFC - Request for Comments für IETF: Bsp. erstes HTTP, Version 0.9) Wichtige Organisationen in der Standardisierung sind nebenan aufgeführt. 15 THI | Computer Networks | Prof. Dr. M. Mecking | WS 2024/25 Overview / Roadmap Chapter 1. History of Communication Technology and Systems What is the Internet? What is a Protocol? ⟸ Network Edge: Hosts, Access Network, Physical Media Network Core: Packet / Circuit Switching, Structure of the Internet Performance: Loss, Delay, and Throughput Protocol Layers: Service Models Security Aspects of Communication Systems 16 THI | Computer Networks | Prof. Dr. M. Mecking | WS 2024/25 The Internet: a “Nuts and Bolts” View. Billions of connected mobile network computing devices: national or global ISP hosts = end systems running network apps at Internet’s “edge” Packet switches: forward local or packets (chunks of data) regional Internet ISP routers, switches home network content Communication links provider network datacenter fiber, copper, radio, satellite network Networks enterprise collection of devices, routers, links: network managed by an organisation 17 THI | Computer Networks | Prof. Dr. M. Mecking | WS 2024/25 The Internet: a “Nuts and Bolts” View. mobile network Internet: “network of networks” 5G national or global ISP Interconnected ISPs protocols are everywhere IP control sending, receiving of messages local or e.g., HTTP (Web), streaming video, regional Skype, TCP, UDP, IP, WiFi, 4/5/6 G, ISP Ethernet home network content Internet standards HTTP provider network datacenter IETF: Internet Engineering Task Force Ethernet network (RFC: Request for Comments) TCP IEEE, 3GPP, … enterprise network WiFi 18 THI | Computer Networks | Prof. Dr. M. Mecking | WS 2024/25 The Internet: a “Services” View. mobile network Streaming Infrastructure that provides services to video national or global ISP applications: Web, streaming video, multimedia teleconferencing, email, games, e-commerce, social media, Teams local or inter-connected appliances, … regional ISP provides programming interface to home network content distributed applications: provider HTTP network datacenter “hooks” allowing sending/receiving apps to network “connect” to, use Internet transport service provides service options, analogous to postal enterprise service network 19 THI | Computer Networks | Prof. Dr. M. Mecking | WS 2024/25 What is a Protocol? Human protocols: Network protocols: “what’s the time?” computers (devices) rather than humans “I have a question” all communication activity in Internet introductions governed by protocols Rules for: Protocols define the … specific messages sent format (syntax and semantics), … specific actions taken order of messages sent and received when message received, among network entities, and or other events actions taken on message transmission, receipt 20 THI | Computer Networks | Prof. Dr. M. Mecking | WS 2024/25 What is a Protocol? A human protocol and a computer network protocol: Hi TCP connection request Hi TCP connection Got the response time? GET https://www.thi.de/ 2:00 time Q: other human protocols? 21 THI | Computer Networks | Prof. Dr. M. Mecking | WS 2024/25 Overview / Roadmap Chapter 1. History of Communication Technology and Systems What is the Internet? What is a Protocol? Network Edge: Hosts, Access Network, Physical Media ⟸ Network Core: Structure of the Internet, Packet / Circuit Switching Performance: Loss, Delay, and Throughput Protocol Layers: Service Models Security Aspects of Communication Systems 22 THI | Computer Networks | Prof. Dr. M. Mecking | WS 2024/25 A Closer Look at the Internet Structure. mobile network Network edge: national or global ISP hosts: clients and servers servers often in data centres local or regional ISP Internet home network content provider network datacenter network enterprise network 23 THI | Computer Networks | Prof. Dr. M. Mecking | WS 2024/25 A Closer Look at the Internet Structure. mobile network Network edge: national or global ISP hosts: clients and servers servers often in data centers local or Access networks, physical media: regional Internet ISP wired, wireless communication links home network content provider network datacenter network enterprise network 24 THI | Computer Networks | Prof. Dr. M. Mecking | WS 2024/25 A Closer Look at the Internet Structure. mobile network Network edge: national or global ISP hosts: clients and servers servers often in data centers local or Access networks, physical media: regional Internet ISP wired, wireless communication links home network content provider Network core: network datacenter network interconnected routers network of networks → Internet enterprise network 25 THI | Computer Networks | Prof. Dr. M. Mecking | WS 2024/25 Access Networks and Physical Media. mobile network Q: How to connect end systems to national or global ISP edge router? residential access nets local or institutional access networks regional Internet ISP (school, company) mobile access networks (WiFi, 4/5G) home network content provider network datacenter network enterprise network 26 THI | Computer Networks | Prof. Dr. M. Mecking | WS 2024/25 Access Networks: Home Networks. Wireless and wired twisted devices pair coax to/from headend or central office often combined in single box cable or DSL modem optical fibre WiFi wireless access router, firewall, NAT point (100’s of Mbit/s) wired Ethernet (1 Gbit/s) 27 THI | Computer Networks | Prof. Dr. M. Mecking | WS 2024/25 Wireless Access Networks. Shared wireless access network connects end system to router via base station aka “access point” Wireless local area networks Wide-area cellular access networks (WiFi / WLAN) ▪ provided by mobile, cellular network operator (10’s km) ▪ typically within or around building (~30m) ▪ 10’s Mbit/s - ~Gbit/s ▪ WiFi 5/6/7 or 802.11 ac/ax/be: ▪ 4G/5G cellular networks (6G coming…) ~650 Mbit/s, ~1-3Gbit/s, ~6 Gbit/s transmission rate to Internet to Internet 28 THI | Computer Networks | Prof. Dr. M. Mecking | WS 2024/25 Access Networks: Enterprise Networks. Enterprise link to ISP (Internet) institutional router Ethernet institutional mail, switch web servers companies, universities, etc. mix of wired, wireless link technologies, connecting a mix of switches and routers Ethernet: wired access at 100 Mbit/s, 1 Gbit/s, 10 Gbit/s WiFi: wireless access points at several 10’s of Mbit/s … Gbit/s 29 THI | Computer Networks | Prof. Dr. M. Mecking | WS 2024/25 Access Networks: Data Center Networks. mobile network high-bandwidth links (10s to 100s Gbit/s) national or global ISP connect hundreds to thousands of servers together, and to Internet local or regional ISP home network content provider network datacenter network Courtesy: Massachusetts Green High Performance Computing Center (mghpcc.org) enterprise network 30 THI | Computer Networks | Prof. Dr. M. Mecking | WS 2024/25 Klassifikation der Kommunikationsnetze. Nach Größe / Ausdehnung als Nach der Organisation und PAN, LAN, MAN, WAN, … Management als Nach dem Anbieter als Infrastruktur oder ad hoc öffentlich (public) oder Nach der Art der transportierten privat (private) Daten als Nach dem Übertragungsmedium als analog oder digital sowie Telefon / Multimedia / Daten drahtlos (wireless) oder fest-verdrahtet (wired/wireline) 31 THI | Computer Networks | Prof. Dr. M. Mecking | WS 2024/25 Classification of Mobile Access Systems. 32 THI | Computer Networks | Prof. Dr. M. Mecking | WS 2024/25 Overview / Roadmap Chapter 1. History of Communication Technology and Systems What is the Internet? What is a Protocol? Network Edge: Hosts, Access Network, Physical Media Network Core: Structure of the Internet, Packet / Circuit Switching ⟸ Performance: Loss, Delay, and Throughput Protocol Layers, Service Models Security Aspects of Communication Systems 33 THI | Computer Networks | Prof. Dr. M. Mecking | WS 2024/25 Internet Structure: “Network of Networks”. Tier 1 ISP Tier 1 ISP Google IXP IXP IXP Regional ISP Regional ISP access access access access access access access access ISP ISP ISP ISP ISP ISP ISP ISP At “center”: small # of well-connected large networks “tier-1” commercial ISPs (e.g., Cogent, Level 3, and Telia in Germany), national & international coverage content provider networks (e.g., Google, Facebook): private network that connects its data centers to Internet, often bypassing tier-1, regional ISPs 34 THI | Computer Networks | Prof. Dr. M. Mecking | WS 2024/25 The Network Core. mobile network mesh of interconnected routers national or global ISP packet-switching: hosts break application- layer messages into packets network forwards packets from one router to the next, across links on path from local or source to destination regional ISP Internet home network content provider network datacenter network enterprise network 35 THI | Computer Networks | Prof. Dr. M. Mecking | WS 2024/25 Two Key Network-Core Functions. Forwarding: routing algorithm Routing: aka “switching” global action: local forwarding table local action: move header value output link determine source- arriving packets 0100 0101 3 2 destination paths from router’s input 0111 1001 2 1 taken by packets link to appropriate router output link →routing algorithms 1 3 2 1 011 destination address in arriving packet’s header 36 THI | Computer Networks | Prof. Dr. M. Mecking | WS 2024/25 Routing. routing 37 THI | Computer Networks | Prof. Dr. M. Mecking | WS 2024/25 Forwarding. forwarding forwarding 38 THI | Computer Networks | Prof. Dr. M. Mecking | WS 2024/25 Host: Sends Packets of Data. host sending function: takes application message two packets, breaks into smaller chunks, known L bits each as packets, of length L bits router transmits packet into access 2 1 network at link transmission rate R host aka link capacity, link bandwidth R: link transmission rate packet time needed to L τtrans = (bits) transmission = transmit L-bit = (bits/s) delay packet into link R 39 THI | Computer Networks | Prof. Dr. M. Mecking | WS 2024/25 Packet Switching: Store-and-Forward (Paket-Vermittlung). L bits per packet 3 2 1 source destination R bit/s R bit/s packet transmission delay: takes τtrans = L/R seconds One-hop numerical example: to transmit (push out) L-bit packet into link at R bit/s L = 10 kbit store and forward: entire packet must arrive at router R = 100 Mbit/s before it can be transmitted on next link one-hop transmission delay τtrans = 0.1 ms Q: what is the total delay for two hops/links? 40 THI | Computer Networks | Prof. Dr. M. Mecking | WS 2024/25 Packet Switching: Queueing (Warteschlangen). R = 100 Mbit/s C A D B R = 1.5 Mbit/s E queue of packets waiting for transmission over output link Queueing occurs when work arrives faster than it can be serviced: 41 THI | Computer Networks | Prof. Dr. M. Mecking | WS 2024/25 Packet Switching: Queueing (Warteschlangen). R = 100 Mbit/s C A D B R = 1.5 Mbit/s E queue of packets waiting for transmission over output link Packet queueing and loss: if arrival rate (in bit/s) to link exceeds transmission rate (bit/s) of link for some period of time: ▪ packets will queue, waiting to be transmitted on output link → delay ▪ packets can be dropped if memory (buffer) in router fills up → loss → Congestion control mechanisms required to prevent flooding of network 42 THI | Computer Networks | Prof. Dr. M. Mecking | WS 2024/25 Alternative to Packet Switching: Circuit Switching (Leitungsvermittlung). end-end resources allocated to, reserved for “call” between source and destination in diagram, each link has four circuits call gets 2nd circuit in top link and 1st circuit in right link. dedicated resources: no sharing circuit-like (guaranteed) performance circuit segment idle if not used by call commonly used in traditional telephone networks and first mobile networks 43 THI | Computer Networks | Prof. Dr. M. Mecking | WS 2024/25 Circuit Switching: FDM and TDM (Frequenz- und Zeitmultiplex). Frequency Division Multiplexing (FDM) 4 users optical, electromagnetic frequencies frequency divided into (narrow) frequency bands each call allocated its own band, can transmit at max rate of that narrow band time Time Division Multiplexing (TDM) time divided into slots frequency each call allocated periodic slot(s), can transmit at maximum rate of (wider) frequency band (only) during its time slot(s) time 44 THI | Computer Networks | Prof. Dr. M. Mecking | WS 2024/25 Packet Switching vs. Circuit Switching. Example: 1 Gbit/s link K ….. each user: users 1 Gbit/s link 100 Mbit/s when “active” active p = 10% of time Q: how many users can use this network under circuit-switching and packet switching? circuit-switching: K ≤ 10 users packet switching: with 35 users, probability > 10 active at same time is less than.0004 (trade-off queueing / link utilisation → Übungsaufgabe) 45 THI | Computer Networks | Prof. Dr. M. Mecking | WS 2024/25 Packet Switching vs Circuit Switching. Is Packet Switching (aka statistical multiplexing) a “Slam Dunk Winner”? great for “bursty” data – sometimes has data to send, but at other times not resource sharing improves link utilisation simpler, no call setup but: excessive congestion possible: packet delay and loss due to buffer overflow protocols needed for reliable data transfer, congestion control Q: How to provide circuit-like behaviour with packet-switching? “It’s complicated.” We’ll study various techniques that try to make packet switching as “circuit-like” as possible. Q: human analogies of reserved resources (circuit switching) versus on-demand allocation (packet switching)? 46 THI | Computer Networks | Prof. Dr. M. Mecking | WS 2024/25 Overview / Roadmap Chapter 1. History of Communication Technology and Systems What is the Internet? What is a Protocol? Network Edge: Hosts, Access Network, Physical Media Network Core: Structure of the Internet , Packet / Circuit Switching Performance: Loss, Delay, and Throughput ⟸ Protocol Layers: Service Models Security Aspects of Communication Systems 47 THI | Computer Networks | Prof. Dr. M. Mecking | WS 2024/25 Quality of Service / Communication Networks Design Parameter. Bandbreite Durchsatz Energieverbrauch Nachrichten- übertragungstechnik Datenrate Speicher Delay Rechenleistung Delay-Jitter Kosten Paket-Verluste Größe Nachrichten- übertragungstechnik Bitfehlerrate Kompatibilität #Nutzer Security 48 THI | Computer Networks | Prof. Dr. M. Mecking | WS 2024/25 Packet Delay: Four Sources. transmission A propagation B nodal queueing processing τnode = τproc + τqueue + τtrans + τprop τproc: nodal processing τqueue: queueing delay check bit errors time waiting at output link for transmission determine output link depends on congestion level of router typically < 1 μs can be considerable! 49 THI | Computer Networks | Prof. Dr. M. Mecking | WS 2024/25 Packet Delay: Four Sources. transmission A propagation B nodal queueing processing τnode = τproc + τqueue + τtrans + τprop τtrans: transmission delay τprop: propagation delay L: packet length (bits) d: length of physical link R: link transmission rate (bit/s) v: propagation speed ( ≈ 2 ⋅ 108 m/s) τtrans = L/R τprop = d/v very different 50 THI | Computer Networks | Prof. Dr. M. Mecking | WS 2024/25