CPSC 852 Intering A Whirlwind Introduction to the Internet Michele Weigle Department of Computer Science Clemson University mweigle@cs.clemson.edu http://www.cs.clemson.edu/~mweigle/courses/cpsc852 1 A Whirlwind Introduction to the Internet Overview What s the Internet local ISP* What s a protocol? Network edge Network core Access nets, physical media Performance: loss, delay Protocol layers, service models Backbones, NAPs, ISPs company regional ISP *Internet Service Provider 2
Just What is the Internet? The nuts and bolts view Millions of connected computing devices: hosts, end-systems» PCs, workstations, servers» PDAs, phones, toasters running applications Communication links» Different media (fiber, copper wire, radio, satellite)» Different transmission rates bits per second (bps) 10 3 (Kbps) to 10 6 (Mbps) to 10 9 (Gbps) Routers: forward packets of data though the local ISP company router server regional ISP workstation mobile 3 Just What is the Internet? The nuts and bolts view Protocols: control sending, receiving of messages» E.g., TCP, IP, HTTP, SMTP,. Internet: of s» Loosely hierarchical» Public Internet versus private intranet Internet standards» RFC: Request for comments» IETF: Internet Engineering Task Force local ISP company router server regional ISP workstation mobile 4
Just What is the Internet? The services view A communication infrastructure enabling distributed applications:» WWW, email, games, e- commerce, database, voting, Communication services provided:» Connectionless: No guarantees» Connection-oriented: Guarantees order and completeness local ISP company regional ISP 5 The Nuts & Bolts View What is a protocol? Main Entry: pro-to-col 1: An original draft, minute, or record of a document or transaction 2a: A preliminary memorandum often formulated and signed by diplomatic negotiators as a basis for a final convention or treaty b: The records or minutes of a diplomatic conference or congress that show officially the agreements arrived at by the negotiators 3a: A code prescribing strict adherence to correct etiquette and precedence (as in diplomatic exchange and in the military services) b: A set of conventions governing the treatment and especially the formatting of data in an electronic communications system 4: A detailed plan of a scientific or medical experiment, treatment, or procedure 6
The Nuts & Bolts View What is a protocol? Human protocols:» Do you have the time?» I have a question» Introductions Both:» Specific messages sent» Specific actions taken when messages (or other events) received Network protocols:» Machines rather than humans» All communication activity in Internet governed by protocols Protocols define format, order of of messages sent and received among entities, and actions taken on on message transmission, receipt 7 What is a protocol? A specification for a set of message exchanges Example:» Human protocols: Get the time from a stranger» Computer protocols: Get the class time from a web server Hi Hi Do you have the time? TCP connection request TCP connection reply Get http://www.cs.clemson.edu/~mweigle/courses/cpsc852 Yes! It s 2:00 Time <web page> 8
What is a Protocol? The Internet protocol food-chain (some examples) Network interface-to-transmission media» Media access protocols Router-to-router» Routing protocols Operating system-to-server» Name resolution protocols Transport protocol-to-transport protocol» Reliable transmission» Congestion and flow control Application-level protocols» File transfer, email, local ISP company regional ISP 9 A Whirlwind Introduction to the Internet Overview What s the Internet What s a protocol? Network edge Network core Access nets, physical media Performance: loss, delay Protocol layers, service models Backbones, NAPs, ISPs local ISP company regional ISP 10
The Structure of the Internet The physical makeup of the Internet Network edge:» Applications running on hosts host = end system Network core:» Routers» Network of s local ISP regional ISP In between: Access s» Physical media: communication links company 11 Network Structure The edge End systems (hosts)» Live at the edge of» Run applications Interaction paradigms:» Client/server model Client requests, receives service from server WWW browser/server; email client/server» Peer-to-peer model: Host interactions symmetric File sharing (Napster, MusicCity, Gnutella, ) 12
The Network Edge Connection-oriented service Goal: Transfer data between end systems» handshaking: setup data transfer ahead of time Hello, hello-back human protocol Set up state in two communicating hosts» Transmit data Connection-oriented service on the Internet:» TCP - Transmission Control Protocol [RFC 793] TCP service model» reliable, in-order byte-stream Losses handled by acknowledgements and retransmissions» flow control: Sender won t overwhelm receiver» congestion control: Senders slow down sending rate when congested 13 The Network Edge Connectionless service Goal: Transfer data between end systems» Same as before! Connectionless service on the Internet:» UDP - User Datagram Protocol [RFC 768] Unreliable data transfer No flow control No congestion control Applications using TCP:» HTTP (WWW), FTP (file transfer), Telnet (remote login), SMTP (email) Applications using UDP:» DNS (name to address mapping), streaming media, teleconferencing, Internet telephony 14
Network Structure The core A mesh of interconnected routers The fundamental question: How is data routed through the?» Circuit switching: dedicated circuit (path) per call used by all data (e.g., telephone)» Packet switching: data sent in discrete chunks (packets); each has a path chosen for it 15 Network Map 16
Network Structure The core A mesh of interconnected routers The fundamental question: How is data routed through the?» Circuit switching: dedicated circuit (path) per call used by all data (e.g., telephone)» Packet switching: data sent in discrete chunks (packets); each has a path chosen for it 17 The Network Core Circuit Switching Resources reserved end-to-end for the connection ( call )» Resources: Link bandwidth, switch capacity» Reservation: Dedicated fraction of available bandwidth, buffers, etc. Circuit-like (guaranteed) performance» Call setup required» Call rejection ( busy signal ) possible 18
Circuit Switching Allocating fractions of bandwidth Multiplexing Network bandwidth divided into transmission slots» Slots allocated to calls» Slots are unused ( idle ) if not used by owning call» No sharing of slots! How to divide link bandwidth into slots?» Frequency division multiplexing (FDM)» Time division multiplexing (TDM) Transmission Frequency FDM Time TDM 4 KHz Call 1 Call 2 Call 3 Call 4 Link capacity 1 2 3 4 1 2 3 4 1 2 3 4 Slot Call data Frame frames/sec X bits/slot = TDM per-call transmission rate 19 The Network Core Packet Switching Each sender divides its messages into packets (sequence of bits)» Senders packets share (compete for) resources» Each packet uses full link capacity until transmission completed» Resources allocated & used as needed Bandwidth division into slots Dedicated allocation Resource reservation But now we have resource contention!» Aggregate resource demand can exceed amount available» Congestion: packets queue, wait for link availability» Store and forward: packets move one hop at a time Transmit over link Wait turn at next link 20
Packet Switching Statistical multiplexing A 10 Mbps Ethernet statistical multiplexing C B queue of packets waiting for output link 1.5 Mbps 45 Mbps D E Packet-switching versus circuit switching:» Restaurant seating analogy» Other familiar analogies? 21 The Network Core Packet switching v. Circuit switching N users 1 Mbps link Packet switching allows more users to to use the the! Assume that on a 1 Mbps link:» Each user consumes 100Kbps when active» Each user active 10% of time Circuit-switching can support 10 users Packet switching can support 35 users» With 35 users the probability of more than 10 users active simultaneously is approximately 0.0004. 22
Packet Switching v. Circuit Switching Is packet switching a no brainer? Great for bursty data» Resource sharing» No call setup Excessive congestion: packet delay and loss» Protocols needed for reliable data transfer, congestion control How to provide circuit-like behavior?» Bandwidth guarantees needed for audio/video applications?» Still an unsolved problem (that s why we do research!) 23 Packet Switching Why switch packets instead of entire messages? 1.5 Mbps 5 seconds 5 seconds 5 seconds 7.5 Mb Message Message switching example» Transmit a 7.5 Mb message over a with 1.5 Mbps links» What is the total elapsed time? 24
Packet Switching Why switch packets instead of entire messages? 1.5 Mbps Time 7.5 Mb Message 5,000 Packets 11 22 33 44 55 4999 5000 11 22 33 44 11 22 33 11 22 4998 4999 5000 4997 4998 4999 5000 4996 4997 4998 4999 5000 0.000 0.001 0.002 0.003 0.004 4.998 4.999 5.000 5.001 5.002 Packet-switching: store and forward behavior» 1,500 bit packets, 1 packet forwarded every 1 ms 25 Network Taxonomy How this fits together Telecommunication s FDM Circuit-switched s TDM X.25, ATM Networks with VCs Packet-switched s IP Datagram Networks Datagram is not either connection-oriented or connectionless. Internet (IP) provides both connection-oriented (TCP) and connectionless services (UDP) to apps. 26
Packet Switching Routing The process of moving packets among routers from source to destination» Lots of path selection algorithms Datagram :» Each packet carries a destination address» Destination address used to look up next hop» Route (next hop) may change at any time local ISP company regional ISP Virtual circuit (path) :» Packets carry a tag (virtual circuit ID) that determines the next hop» Path determined at call setup time & remains fixed throughout call» Routers maintain per-call path state 27 Routing in Packet Switched Networks Virtual circuit routing a c b Inbound Interface a a c VC Number 127 32 127 Outbound Interface b b b New VC Number 19 8 63 A (static) route is computed before any data is sent Packets contain a VC identifier» Identifier replaced at every hop Routers maintain perconnection state and perform set-up/teardown operations Why does the router need to change the VC number? 28
Routing in Packet Switched Networks Datagram routing Network ID xxx.yyy. uuu.vvv. sss.ttt. Next Hop b b c a c b Packets contain a destination address» Address specifies both a and a host Each router examines the destination address and forwards packet towards the next router closest to the destination» Routers maintain a table of next hops to all s Routers maintain no per-connection state 29 The Structure of the Internet The physical makeup of the Internet Network edge:» Applications and hosts local ISP Network core:» Routers» Network of s regional ISP In between: Access s» Physical media: communication links company 30
Network Structure Access s and physical media How to connect end-systems to edge router?» Residential access nets» Institutional/enterprise access s» Mobile access s Issues:» Transmission speed (bits per second) of access» Shared or dedicated? 31 Access Networks and Physical Media Physical Media Transmission is the propagation of an electromagnetic wave (or optical pulse) through a physical medium Media types» Guided media signals propagate in solid media (copper, fiber)» Unguided media signals propagate freely (radio, infrared) What do you use?» Twisted Pair (UTP) Two insulated copper wires Category 3 UTP:» Traditional phone wires, 10 Mbps Ethernet Category 5 UTP:» 100Mbps Ethernet» Gigabit possible» Distance limited (100 m) 32
Physical Media Coaxial and fiber optic cable Coaxial cable» Wire (signal carrier) within a wire (shield) Baseband: single channel on cable Broadband: multiple channel on cable» Bi-directional transmission» Largely used for cable TV Fiber optic cable» Glass fiber carrying light pulses» Higher-speed operation: 100-1,000 Mbps Ethernet High-speed point-to-point transmission (e.g., 10 Gbps)» Low signal attenuation long distances» Low error rate 33 Physical Media Radio Signal carried in electromagnetic spectrum» No physical wire Bi-directional Physical environment effects propagation» Reflection» Obstruction by objects» Interference uplink base station Radio link types:» Microwave Up to 45 Mbps channels» LAN (e.g., 802.11) 2 Mbps, 11, 56 Mbps» Wide-area (e.g., cellular) CDPD, 10 s Kbps» Satellite Up to 50Mbps channel (or multiple smaller channels) 270 msec end-end delay Geosynchronous versus LEOS 34
Access Networks and Physical Media Residential access: point-to-point access Dialup via modem» Modem (modulator-demodulator) does digital analog signal conversions» Up to 56Kbps direct access to router ISDN: Integrated Services Digital Network» 128Kbps all-digital connection to router DSL: Digital Subscriber Line» Asymmetric speeds Up to 8 Mbps to the home Up to 1 Mbps from the home Distance-dependent, typical is 1-2 Mbps to home» Dedicated access 35 Access Networks and Physical Media Residential access: cable modems HFC (Hybrid Fiber-Coax)» Asymmetric speeds» Shared access Issues:» Congestion» Provisioning Providers:» Time Warner» AT&T» Cox» Comcast».. 200,000 400,000 homes 20,000 40,000 homes 2 Mbps to home 0.5 Mbps from home 500 1,000 homes 36
Access Networks and Physical Media Institutional access: local area s Local area (LAN) connects end system to edge router Ethernet is the dominant technology» Shared or dedicated cable connects end system and router» 10 Mbps, 100Mbps, 1Gbps Ethernet Deployment: institutions, home LANs 37 Access Networks and Physical Media Wireless access s Shared wireless access connects end-system to router Wireless LANs:» Radio spectrum replaces wire. e.g., Lucent Wavelan (2-12 Mbps) Wider-area wireless access» CDPD: wireless access to ISP router via cellular router base station mobile hosts 38
A Whirlwind Introduction to the Internet Overview What s the Internet What s a protocol? Network edge Network core Access nets, physical media Performance: loss, delay Protocol layers, service models Backbones, NAPs, ISPs local ISP company regional ISP 39