L2: Introduction to Communication Networks: Internet. Outline

Transcription

1 EECS 3213 Fall 2014 L2: Introduction to Communication Networks: Internet Sebastian Magierowski York University 1 Outline ARPANET A connectionless datagram network Internet A connectionless/connection-oriented datagram network best-effort service Local Area Networks Ethernet: connectionless protocol, medium access control 2 1

2 An internetwork Multi-tiered, decentralized organization A network of computers Powerful processing at network edge Move communication complexity towards the edge Develop sophisticated protocols Internet 3 Telephone vs. Internet Public Switched Telephone Network (PSTN) Switching office Distributed Switching System Toll office U.S. military dependent on PSTN in 50 s Easy to cripple by taking out switching centers RAND Corp. (Paul Baran) proposes a distributed network AT&T rejected the idea when asked to build prototype 4 2

3 ARPANET RAND idea implemented in late 60 s as network of computers between research centers SRI UTA MIT SRI UTA SRI UTA ILLINOIS MIT LINCOLN CASE UCSB UCSB SDC UCSB SDC CARN STAN UCLA UCLA RAND BBN UCLA RAND BBN ARVARD BURROUS Dec. 69 July 70 Mar. 71 SRI LBL MCCLELLAN UTA ILLINOIS MIT SRI NCAR WC LINCOLN CASE Apr. 72 RADC ILLINOIS Sept. 72 AMES MCCLELLAN UTA USC UCSB MIT STAN SDC CARN LINC MITRE ETAC UCLA RAND TINKER BBN ARVARD NBS CCA AMES TIP BBN AMES IMP ARVARD LINC X-PARC ABERDEEN STANFORD NBS ETAC FNWC RAND TINKER ARPA MITRE RADC UCSB UCSD SAAC BELVOIR CMU Retired in 90 at >100 hosts California - Norway 5 UCLA SDC USC NOAA WC CASE Nodes consisted of minicomputers connected to hosts Interface Message Processors (IMPs) Linked by 56-kbps lines leased from telephone company ost-imp protocol ARPANET: Basic Structure ost-host protocol Source IMP to destination IMP protocol IMP-IMP protocol IMP-IMP protocol ost Subnet Protocols developed for communication agreement/rules on how communications are to proceed IMP-IMP, S/IMP-D/IMP, ost-imp, ost-ost 6 IMP 3

4 Key ARPANET Characteristics Datagram service (just like telegraph) connectionless (contrast with connection-oriented) unreliable (unacknowledged) Packet switched messages up to 8063 bits could be sent BUT IMPs broke it up into 1008 bit (max) packets Automated routing no connection setup prior to packet transmission distributed routing algorithm to update routing tables Error control Congestion control Flow control 7 ARPANET Applications ARPANET introduced many new applications remote login file transfer SRI LBL MCCLELLAN UTA ILLINOIS MIT AMES TIP AMES IMP X-PARC STANFORD FNWC UCSB RAND UCSD TINKER ARVARD ABERDEEN NBS ETAC ARPA BBN MITRE SAAC CCA BELVOIR CMU LINC RADC UCLA SDC USC NOAA WC CASE 8 4

5 Internetworking ARPANET was a great WAN demonstration A robust network Capable of supporting a variety of applications But Its protocol structure did not support the merging of various networks well Not an internet E.g. ARPANET + packet radio + satellite performed poorly A reorganized design was proposed 9 TCP/IP New set of rules proposed to enable internetworking Kahn & Cerf argued for common rule layer ide differences between different networks instead of translation The layer was eventually separated into 2 protocols IP (Internet Protocol) A means of getting messages moving over multiple links: connectionless TCP (Transmission Control Protocol) A means of strengthening delivery guarantees between end-points: connection-oriented TTP SMTP DNS RTP 10 TCP Network Interface 1 IP Network Interface 2 UDP Network Interface 3 5

6 Layers & Structural Ideas With universally understood communication rules hosts in different types of network can talk to each other Net 1 Net 2 Routers talk IP, hosts talk TCP & IP Encapsulation router 11 IP Addressing and Routing Location based addressing ierarchical address: Net ID + ost ID IP packets routed according to Net ID Routers compute routing tables using distributed algorithm Net 1 Net 3 Net 5 Net 2 Net

7 Internet Today International ISPs (Tier 1) Data center Tier 1 ISP Backbone Router Fiber (FTT) Peering at IXP TorIX (Front & Uni.) 3 mobile phone Dialup DSL DSL modem DSLAM POP Other ISPs Data path Regional or National ISPs (e.g. Telus, SaskTel, Bell) Cable Cable modem CMTS 13 Tier-1 ISPs 1. Level 3 2. lobal Crossing 3. NTT 4. Sprint 5. TeliaSonera 6. Tinet 7. Tata 8. Cogent 9. Verizon 10. AT&T oogle, Facebook, etc. also setting up private pathways to move data between centers 14 7

8 Local Area Networks A major component of the internet are concentrated networks of computers university, business These simpler networks interface to the internet via routers but what happens inside? Basic components hubs bridges/switches A B C Port B1 4 4 Bridge 1 2 B2 3 D 1 ub E F A B C B1 1 2 Bridge (a) Port D E F 15 Popular LANs IEEE (WiFi) & IEEE (Ethernet) Best-effort connectionless service Access point To wired network Ports Ethernet switch To rest of network 16 8

9 Medium Access Control (MAC) A common challenge: communicating with multiple nodes over a shared medium Medium Access Controls for sharing were developed Example: Polling protocol on a multidrop line Access point To wired network Ports Ethernet switch To rest of network 17 LAN Addressing ow do LANs identify themselves? If they share a medium some means of identification is necessary lobally unique address MAC address, MAC-48, physical address consists of 48-bits burned inside network interface card (NIC) ow does this work with IP? The layering concept 18 9

10 Summary of Some Network Terms connectionless Send to source before you know that source is accepting connection-oriented Send to source only after you hear that it is willing to accept packet-switching Non-dedicated link to source made on fly for each chunk of message circuit-switching Dedicated link created to source for duration of message best-effort service not guaranteed datagram service unacknowledged connectionless service 19 10