INF1060 Introduction1 Introduction to Data Communication Kjell Åge Bringsrud (basert på lysark av Carsten Griwodz)

INF1060 Introduction2 Introduction Goal r Give an overview of the topic r Approach m Descriptive m Use Internet as example Content r What is the Internet? r What is a protocol? r End systems r Core networks r Access network and physical media r Throughput, loss and delay r Protocol layers, service models r Backbones, NAP’er, ISP’er r History

INF1060 Introduction3 What is the Internet? r Millions of interconnected devices: host computers, end systems m PCs, workstations, servers m PDAs, telephones, fridges … which run network applications r Communication links m Fiber, copper, radio, satellite r Routers m passing on packets of data through the network router workstation server mobile unit

INF1060 Introduction4 local ISP company networks regional ISP What is the Internet? r Internet: “network of networks” m Partly hierarchical m Public Internet versus private intranet m ISPs: Internet Service Providers r Protocols m Control sending, receiving of messages m E.g., TCP, IP, HTTP, FTP, PPP router workstation server mobile unit

INF1060 Introduction5 What is the Internet from a service view? r Communication infrastructure m Allows distributed applications: m WWW, , games, e- commerce, database., elections, m More? r Internet standards: m RFC: Request for comments m IETF: Internet Engineering Task Force

INF1060 Introduction6 End systems r End systems m Run application programs m E.g., web browser, web server, m At “the edge” of the net r Client/server model m Clients ask for, and get a service from the servers m E.g. WWW client (browser)/ server; client/server r Peer-to-peer model m Interactions are symmetrical m E.g. telephone conferences

INF1060 Introduction7 What is a protocol? Human protocols: r “What time is it?” r “I have a questions” r Formal phrases… … are special “messages” that are sent, which lead to … … defined events or actions when the message is received Network protocols: r Machine instead of people r All communication activity in the Internet is controlled by protocols Protocols define formats, order of sending and receiving of messages, and the actions that the reception initiates.

INF1060 Introduction8 What is a protocol? A human protocol and a computer protocol: Hi! TCP connect request Hi! TCP connect response 2.15 time What time Is it? GET

INF1060 Introduction9 What are protocol layers? Several layers of communication time Snakker du norsk? Sprechen Sie Deutsch? Do you speak English? Yes! Peter What’s your name? … Peter, have you met Paul? Use the language for all further messages! Use name in further messages now!

INF1060 Introduction10 What are protocol layers? Networks are complex r Many parts: m Hardware, software m End systems, routers m Links of different kinds m Protocols m Applications Question: Is it possible to organize the structure of a network? Or at least our discussion of networks?

INF1060 Introduction11 Why layering? Management of complex systems: r Modularisation simplifies m Design m Maintenance m Updating of a system r Explicit structure allows m Identification of the individual parts m Relations among them r Clear structure: layering m Layered reference model m Goal: different implementation of one layer fit with all implementations of other layers

INF1060 Introduction12 TCP/IP - protocol stack r application: supports network applications m ftp, smtp, http m Your applications r transport: data transfer from end system to end system m TCP, UDP r network: finding the way through the network from machine to machine m IP r (data) link: data transfer between two neighbors in the network m ppp, ethernet r physical: bits “on the wire” physical link network transport application

INF1060 Introduction13 physical link network transport session application OSI - model r A standard for layering of communication protocols m Open Systems Interconnection m by the ISO – International Standardization Institute r Two additional layers to those of the Internet stack r presentation: translates between different formats m XML, XDR m provides platform independence r session: manages connection, control and disconnection of communication sessions m RTP presentation application

INF1060 Introduction14 Layering: logical communication application transport network link physical application transport network link physical application transport network link physical application transport network link physical network link physical Each layer: r distributed r “units” implement functionality of each layer in each node r Units execute operations, and exchange messages with other units of the same layer

INF1060 Introduction15 Layering: logical communication application transport network link physical application transport network link physical application transport network link physical application transport network link physical network link physical data E.g. transport r Receive data from the application r Add receiver address, reliability check, information to create a “datagram” r Send datagram to the transport layer in the receiver node r Wait for “ack” from the transport layer in the receiver node r Analogy: post office data transport ack

INF1060 Introduction16 Layering: physical communication application transport network link physical application transport network link physical application transport network link physical application transport network link physical network link physical data

INF1060 Introduction17 Protocol layer and data Each layer takes data from next higher layer r Adds header information to create a new data unit (message, segment, frame, packet …) r Send the new data unit to next lower layer application transport network link physical application transport network link physical source destination M M M M H t H t H n H t H n H l M M M M H t H t H n H t H n H l message segment datagram frame

INF1060 Introduction18 A closer look at network structures r End systems m applications and host computers r Core networks m Routers m Network of networks r Access network, physical medium m Communication links

INF1060 Introduction19 Access network and physical media How to connect end systems to edge routers? r Home network r Company network (schools, companies) r Mobile access network Keep in mind when choosing a technology: r Bandwidth? r Shared or dedicated medium?

INF1060 Introduction20 Home network: point to point r Dial-up via modem m Up to 56Kbps direct access to the router (at least in theory) r ISDN: integrated services digital network m 128Kbps purely digital connection to the router r ADSL: asymmetric digital subscriber line m Up to 1 Mbps uplink (home-to- router) m Up to 8 Mbps downlink (router-to- home)

INF1060 Introduction21 Home network: cable modem/broadband An example r HFC: hybrid fiber coax m Asymmetrical: up to 10Mbps downlink, 1 Mbps uplink r Network of copper cable and optical fiber connects homes to ISP routers m Shared access to router for several homes m Problems: congestion, dimensioning fiber kabel router Coaxial cable hundreds of homes

INF1060 Introduction22 Institutional access networks (LAN) r Company/university local area network (LAN) connects end systems to the rest of the net r Ethernet: m Shared or dedicated cable connects end systems and routers m 10 Mbps, 100Mbps, Gigabit Ethernet

INF1060 Introduction23 Wireless access networks r Shared wireless access networks connect end systems to routers r Wireless LANs: m radio spectrum replaces cable m E.g. IEEE b - 11 Mbps IEEE a – 54 Mbps r Wireless access over long distances m GSM for example… base station mobile machines router

INF1060 Introduction24 Physical medium r Physical link: a sent bit propagates through the link r Closed media: m Signals propagate in cable media (copper, fiber) r Open media: m Signals propagate freely, e.g. radio. Twisted Pair (TP) r Two isolated copper cables m Category 3: traditional telephone cables, 10 Mbps Ethernet m Category 5 TP: 100Mbps Ethernet m Category 6 TP: 1Gpbs Ethernet

INF1060 Introduction25 Physical medium: coax, fiber Coaxial cable r Wire (signal carrier) in a wire (shielding) m baseband: a single channel on a cable m broadband: multiple channels on a cable r Bi-directional r Typically used for 10Mbs Ethernet. Fiber optic cable r Optical fiber that carries light impulses r High-speed transfer: m High-speed point-to-point transmission r Low error rate r Longer distances m 100Mbps, 1Gbps Ethernet

INF1060 Introduction26 Physical media: radio Radio r Signal in electromagnetic spectrum r No physical ”cable” r Bi-directional r Effects of environment on the distribution: m Reflection m Obstruction by blocking objects m Interferences Types of radio links r microwaves m E.g. up to 45 Mbps r LAN m 2Mbps, 11Mbps, 54Mbps r wide-area m GSM, 9,8 Kbps r satellite m Up to 50Mbps per channel (or several thinner channels) m 270 Msec end-to-end delay (limited by speed of light).

INF1060 Introduction27 Core networks r Graph of interconnected routers r One fundamental question: how is data passed through the net? m Circuit switching m Packet switching r Circuit switching m Dedicated line through the network r Packet switching m Discrete data units are sent through the network

INF1060 Introduction28 Core networks: Circuit Switching End-to-end resource reservation for a ”session” r Link bandwidth, router capacity r Dedicated resources (no sharing) r Guaranteed throughput r Setup phase is required

INF1060 Introduction29 Core networks: Circuit Switching Historical: r Analog telephone networks r Network consists of resources m Cables m Switches with relays r Establish a physical connection m Relays switch to connect cables physically m Create a circuit m Guaranteed resources m No difference between talking and silence Modern: r Networks consist of resources m Cables m Routers or switches m Network resources can be shared r Establish a connection m Switches reserve part of available resource r Division of link bandwidth into parts m Frequency division m Time division

INF1060 Introduction30 Core networks: Packet Switching Each end-to-end data stream is divided into packets r Data streams share network resources r Each packets uses the entire bandwidth of a link r Resources are used as needed Competition for resources: r Combined resource need can exceed the available resources r Congestion: packets are queued in front of “thin” links r Store and forward: packets move one link at a time m Send over a link m Wait for your turn at the next link Division of bandwidth Dedicated allocation Resource reservation

INF1060 Introduction31 Core networks: Packet switching A B C 10 Mbps Ethernet 1.5 Mbps 45 Mbps D E statistical multiplexing Queue of packets that wait for link access

INF1060 Introduction32 Packet switching versus circuit switching r 1 Mbps link r Each user m 100Kbps when “active” m Active 10% of the time, at random times r Circuit switching m max 10 users m Loss probability: 0% m Waste: ~90% capacity r Packet switching m >10 may be active concurrently! m Loss probability >0% m Waste: < 90% capacity Packet switching allows more users in the net! N users 1 Mbps link

INF1060 Introduction33 Packet switching versus circuit switching r Good for data with “bursty” behavior m Resource sharing m No ”setup phase” required r In a congested network: delay and packet loss m Protocols required for reliable traffic and congestion control r How to achieve a behavior like that of circuit switching? m Bandwidth guarantees are required for audio/video applications Unsolved problem so far! Is packet switching always the best approach?

INF1060 Introduction34 Delay in packet switching networks Packet experience delay on the way from sender to receiver r four sources of delay in each hop. r Node processing: m Checking for bit errors m Determining the output link r Queuing m Waiting for access to the output link m Depends on the congestion level of the router A B node processing queueing

INF1060 Introduction35 Delay in packet switching networks Transmission delay: r R = link bandwidth (bps) r L = packet size (bits) r Time required to send a packet onto the link = L/R Propagation delay: r d = physical link length (m) r s = propagation speed in the medium (~2x10 8 m/sec) r Propagation delay = d/s Note: s and R are of very different size! A B propagation transmission node processing queueing

INF1060 Introduction36 More about queueing delays r R= link bandwidth (bps) r L= packet length (bits) r a= average packet arrival rate traffic intensity = La/R r La/R ~ 0: average queuing delay is small r La/R -> 1: queuing delay grows r La/R > 1: more data is arriving at the link than it can handle  link goes into congestion (Average delay is infinite!)

INF1060 Introduction37 Packet switched network: Routing r Goal: move packets from router to router between source and destination m There are several methods to find the path of packets. r Datagram network: m Destination address determines the next hop. m Path can change during the sessions. m Routers need no information about sessions. m Analogy: ask for the way while you drive. r Virtual circuit network: m Each packet has a “tag” (virtual circuit ID), which determines the next hop. m Path is determined when connection is set up, and remains the same for the entire session. m Routers need state information for each virtual circuit.

INF1060 Introduction38 physical link network application transport Datagram and Virtual Circuit Networks

INF1060 Introduction Datagram and Virtual Circuit Networks Interface 1 Interface 2 Interface

INF1060 Introduction40 Datagram network …-… IF IF IF * * * * * * * …-…

INF1060 Introduction41 Datagram network

INF1060 Introduction Virtual circuit network …-… C1-IF1 C2-IF2 C3-IF3 …-…

INF1060 Introduction43 Network layer: IP Datagram switching r IP m Internet Protocol m Datagram service of the Internet m RFC 791 IP offers: r Datagram service m Unreliable m Unordered r Addressing r Routing IP networks can use virtual circuits r IPv4: circuit is one hop r IPv6: can have a tag

INF1060 Introduction44 Connection-oriented service Goal: data transfer between end systems r Start of communication m Handshaking m Initial preparation of data transfer m Hi!, hi! Is a human handshaking protocol m Creates a ”state” in the two machines that communicate. m End systems know their communication partners r During communication m Connection m End system expects messages from connected end system m End system know when messages belong to the connection r End of communication m Teardown m Bye! Bye! Is a human teardown protocol m New handshake required for re-establishing connection

INF1060 Introduction45 Connectionless service Goal: data transfer between end systems r As before! r Start of communication m No connection setup m No preparation for data transfer m Programs must expect messages at all times r During communication m No connection m No state in the machines m Senders don’t know whether messages are expected m Sender must identify itself in each message r End of communication m No teardown m Just stop sending

INF1060 Introduction46 Services over Switching Approaches r Services requested m Between end systems m Connection-oriented service m Connectionless service r Switching approaches m From host to host m Circuit switching m Packet switching Connection -oriented service Connection -less service Circuit switching Fits well Setup wasted Packet switching Additional work needed Fits well

INF1060 Introduction47 Transport layer: TCP Connection-oriented service r TCP m Transmission Control Protocol m Connection-oriented service of the Internet m RFC 793 TCP offers: r Connections m Handshake, end-system state, teardown r Reliable, ordered, stream- oriented data transfer m Loss: acknowledgements and retransmissions r Flow control: m Send not faster than receiver can receive r Congestion control: m Send slower when the network is congested.

INF1060 Introduction48 Transport layer: UDP Connectionless service r UDP m User Datagram Protocol m Connectionless service of the Internet m RFC 768 UDP offers: r No connections m Send immediately r Unreliable, unordered, packet- oriented data transfer m Loss: messages are simply lost m Messages arrive exactly as send r No flow control m Send as fast as programs want to r No congestion control m Ignore network problems

INF1060 Introduction49 Transport layer: applications Applications that use TCP: r HTTP (WWW) r FTP (file transfer) r SMTP ( ) r Telnet (remote login) Applications that use UDP: r Streaming media r Video conferencing r Internet telephony r NTP (network time protocol)

INF1060 Introduction50 Internet structure: network of networks r More or less hierarchical r National/international “backbone providers” (NBPs) m These interconnect either privately, or at so-called Network Access Point (NAPs) r regional ISPs m Connect to NBPs r local ISPs, companies m Connect to regional ISPs NBP A NBP B NAP regional ISP local ISP local ISP

INF1060 Introduction51 National Backbone Provider example BBN/GTE US backbone network

INF1060 Introduction52 History of the Internet r 1961: Kleinrock – queueing theory proves that packet switching is effective r 1964: Baran – packet switching in military networks r 1967: ARPAnet starts Advanced Reearch Projects Agency r 1969: first ARPAnet node operational r 1972: m ARPAnet publically demonstrated m NCP (Network Control Protocol) first machine- machine protocol m first program m ARPAnet has 15 nodes : Early packet-switching concepts

INF1060 Introduction53 History of the Internet r 1970: ALOHAnet satellite network on Hawaii r 1973: Metcalfe’s doctor thesis proposes Ethernet r 1974: Cerf and Kahn – architecture to the interconnection of many networks r End of the 70s: proprietary architectures: DECnet, SNA, XNA r 1979: ARPAnet has 200 nodes Cerf og Kahn’s internetworking principles: m Minimalism, autonomy – no internal network changes necessary to interconnect networks m best effort service model m Statekess routers m Decentralized control This defines mostly today’s Internet architecture : Internetworking – new, proprietary networks

INF1060 Introduction54 History of the Internet r 1983: first use of TCP/IP r 1982: protocol SMTP defined r 1983: DNS defined to translate a name into an IP address r 1985: ftp protocol defined r 1988: TCP congestion control r New national networks: Csnet, BITnet, NSFnet, Minitel r 100,000 machine connected to the Net : new protocols – the Net grows

INF1060 Introduction55 History of the Internet r Early 1990s: WWW m hypertext [Bush 1945, Nelson 1960’s] m HTML, http: Berners- Lee m 1994: Mosaic, later Netscape m late 1990s: commercialization of the WWW Late 1990s: r ca. 50 million machines on the Internet r ca. 100 million+ users r backbone links operate at 1 Gbps 1990’s: commercialization, WWW

INF1060 Introduction56 Summary Covering a large area! r Overview over the Internet r What is a protocol? r Network components r Throughput, loss, delay r Layering and service models r backbone, NAPer, ISPer Hopefully you have now: r A impression and overview of the area r More depth and details in later courses