* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download notes
Survey
Document related concepts
Network tap wikipedia , lookup
Net neutrality law wikipedia , lookup
Computer security wikipedia , lookup
Wake-on-LAN wikipedia , lookup
Deep packet inspection wikipedia , lookup
Airborne Networking wikipedia , lookup
Cracking of wireless networks wikipedia , lookup
Computer network wikipedia , lookup
Internet protocol suite wikipedia , lookup
Zero-configuration networking wikipedia , lookup
Piggybacking (Internet access) wikipedia , lookup
List of wireless community networks by region wikipedia , lookup
Recursive InterNetwork Architecture (RINA) wikipedia , lookup
Transcript
EEC-484/584 Computer Networks Lecture 3 Wenbing Zhao [email protected] (Part of the slides are based on Drs. Kurose & Ross’s slides for their Computer Networking book) 2 Outline • Delay, loss and throughput in packetswitched networks • Protocol layers, reference models • Network standards • Internet history 5/25/2017 EEC-484/584: Computer Networks 3 Throughput • Throughput: rate (bits/time unit) at which bits transferred between sender/receiver – Instantaneous: rate at given point in time – Average: rate over longer period of time link capacity that can carry server, with server sends bits pipe Rs bits/sec fluid at rate file of F bits (fluid) into pipe Rs bits/sec) to send to client 5/25/2017 link that capacity pipe can carry Rfluid c bits/sec at rate Rc bits/sec) EEC-484/584: Computer Networks 4 Throughput (more) • Rs < Rc What is average end-end throughput? Rs bits/sec Rc bits/sec • Rs > Rc What is average end-end throughput? Rs bits/sec Rc bits/sec bottleneck link link on end-end path that constrains end-end throughput 5/25/2017 EEC-484/584: Computer Networks 5 Throughput: Internet Scenario • Per-connection end-end throughput: min(Rc,Rs,R/10) • In practice: Rc or Rs is often bottleneck 5/25/2017 Rs Rs Rs R Rc Rc Rc 10 connections (fairly) share backbone bottleneck link R bits/sec EEC-484/584: Computer Networks 6 Protocol “Layers” Networks are complex! • many “pieces”: – hosts – routers – links of various media – applications – protocols – hardware, software 5/25/2017 Question: Is there any hope of organizing structure of network? Or at least our discussion of networks? EEC-484/584: Computer Networks 7 Organization of Air Travel ticket (purchase) ticket (complain) baggage (check) baggage (claim) gates (load) gates (unload) runway takeoff runway landing airplane routing airplane routing airplane routing • A series of steps 5/25/2017 EEC-484/584: Computer Networks Layering of Airline Functionality ticket (purchase) ticket (complain) ticket baggage (check) baggage (claim baggage gates (load) gates (unload) gate runway (takeoff) runway (land) takeoff/landing airplane routing airplane routing airplane routing departure airport airplane routing airplane routing intermediate air-traffic control centers arrival airport Layers: each layer implements a service – Via its own internal-layer actions – Relying on services provided by layer below 5/25/2017 EEC-484/584: Computer Networks 8 9 Why Layering? Dealing with complex systems: • Explicit structure allows identification, relationship of complex system’s pieces – Layered reference model for discussion • Modularization eases maintenance, updating of system – Change of implementation of layer’s service transparent to rest of system – E.g., change in gate procedure doesn’t affect rest of system 5/25/2017 EEC-484/584: Computer Networks 10 Internet Protocol Stack • Application: supporting network applications – HTTP, DNS, SMTP • Transport: process-process data transfer – TCP, UDP • Network: routing of datagrams from source to destination – IP, routing protocols • Link: data transfer between neighboring network elements – PPP, Ethernet • Physical: bits “on the wire” 5/25/2017 EEC-484/584: Computer Networks Application Transport Network Link Physical 11 ISO/OSI Reference Model • Presentation: allow applications to interpret meaning of data, e.g., encryption, compression, machinespecific conventions • Session: synchronization, checkpointing, recovery of data exchange • Internet stack “missing” these layers! – these services, if needed, must be implemented in application 5/25/2017 EEC-484/584: Computer Networks Application Presentation Session Transport Network Link Physical source message segment M Ht M datagram Hn Ht M frame Hl Hn Ht M Encapsulation application transport network link physical link physical switch destination M Ht M Hn Ht Hl Hn Ht M M 5/25/2017 application transport network link physical Hn Ht Hl Hn Ht M M network link physical Hn Ht M router EEC-484/584: Computer Networks 12 13 Network Standardization • Why standard? – Only way to achieve interoperability – Standards also increase the market for products adhering to them – Two kinds of standards • De facto – from the fact (standards that just happened) • De jure – by law (formal, legal standards adopted by authorized organization) 5/25/2017 EEC-484/584: Computer Networks Treaty Organization between Nations United Nations ITU - International Telecommunications Union CCITT/ITU-T – telephone and data communications 5/25/2017 EEC-484/584: Computer Networks 14 15 Voluntary, Nontreaty Organization ISO (International Standards Organization) issues standards on wide range of topics 200 TC (Technical Committees) TC97 – computers and info processing SC (Subcommittees) WG (Working Groups) ANSI (American National Standards Institute) 5/25/2017 EEC-484/584: Computer Networks IEEE 802 Standards 5/25/2017 EEC-484/584: Computer Networks 16 17 Internet Standard Body • Internet Society (used to be Internet Architecture Board) – Internet Research Task Force (IRTF) • Concentrate on long term research – Internet Engineering Task Force (IETF) • Deal with short term engineering issues • Standardization process – Proposed standard: request for comments (RFCs) – Draft standard: after >= 4 month test by >= 2 sites – Internet standard: if convinced the idea is sound 5/25/2017 EEC-484/584: Computer Networks 18 Internet History 1961-1972: Early packet-switching principles • 1961: Kleinrock - queueing theory shows effectiveness of packet-switching • 1964: Baran - packetswitching in military nets • 1967: ARPAnet conceived by Advanced Research Projects Agency • 1969: first ARPAnet node operational 5/25/2017 • 1972: – ARPAnet public demonstration – NCP (Network Control Protocol) first host-host protocol – first e-mail program – ARPAnet has 15 nodes EEC-484/584: Computer Networks 19 Internet History 1972-1980: Internetworking, new and proprietary nets • 1970: ALOHAnet satellite network in Hawaii • 1974: Cerf and Kahn architecture for interconnecting networks • 1976: Ethernet at Xerox PARC • late70’s: proprietary architectures: DECnet, SNA, XNA • late 70’s: switching fixed length packets (ATM precursor) • 1979: ARPAnet has 200 nodes 5/25/2017 Cerf and Kahn’s internetworking principles: – Minimalism, autonomy - no internal changes required to interconnect networks – Best effort service model – Stateless routers – Decentralized control Define today’s internet architecture EEC-484/584: Computer Networks 20 Internet History 1980-1990: new protocols, a proliferation of networks • 1983: deployment of TCP/IP • 1982: SMTP e-mail protocol defined • 1983: DNS defined for name-to-IP-address translation • 1985: FTP protocol defined • 1988: TCP congestion control 5/25/2017 • New national networks: Csnet, BITnet, NSFnet, Minitel • 100,000 hosts connected to confederation of networks EEC-484/584: Computer Networks 21 Internet History 1990, 2000’s: commercialization, the Web, new apps • Early 1990’s: ARPAnet decommissioned • 1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995) • Early 1990s: Web – Hypertext [Bush 1945, Nelson 1960’s] – HTML, HTTP: Berners-Lee – 1994: Mosaic, later Netscape – Late 1990’s: commercialization Late 1990’s – 2000’s: • More killer apps: instant messaging, P2P file sharing • Network security to forefront • Est. 50 million host, 100 million+ users • Backbone links running at Gbps of the Web 5/25/2017 EEC-484/584: Computer Networks 22 Internet History 2007: • ~500 million hosts • Voice, Video over IP • P2P applications: BitTorrent (file sharing) Skype (VoIP), PPLive (video) • More applications: youtube, gaming • Wireless, mobility 5/25/2017 EEC-484/584: Computer Networks 23 Introduction: Summary Covered a “ton” of material! • Internet overview • What’s a protocol? • Network edge, core, access network – Packet-switching versus circuit-switching – Internet structure • Performance: loss, delay, throughput • Layering, reference models • Networking standards • History 5/25/2017 You now have: • Context, overview, “feel” of networking • More depth, detail to follow! EEC-484/584: Computer Networks 24 Exercise • A system has an n-layer protocol hierarchy. Applications generate messages of length M bytes. At each of the layers, an h-byte header is added. What fraction of the network bandwidth is filled with headers? 5/25/2017 EEC-484/584: Computer Networks