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- 1. Computer and Communication Networks Lecture 1 – Introduction Lec Amara Umar amaraumar@mcs.nust.edu.pk
- 2. About Instructor Amara Umar PhDWireless Communication and Networks (in progress) • SEECS, National University of Sciences and Technology (NUST), Islamabad MS Electrical Engineering (Comm. and Networks) • COMSATS University Islamabad. Research Interests Aerial access and edge computing networks, 6G networks, Mobile Edge Computing, Routing solutions for mobile ad hoc networks (MANETs), Wireless channel access protocols, Performance evaluation and resource optimization in wireless network
- 3. Grading Policy Exam Score Quizzes 10% Assignments 10% Midterm 30% Final 40% Project/Presentations 10% (To be carried out in groups of maximum 3 students. Presentations 2 weeks before exams)
- 4. Introduction Introduction our goal: get “feel” and terminology more depth, detail later in course approach: use Internet as example overview: what’s the Internet? what’s a protocol? network edge; hosts, access net, physical media network core: packet/circuit switching, Internet structure performance: loss, delay, throughput protocol layers, service models history 1-4
- 5. Introduction What’s the Internet:“nuts and bolts” view millions of connected computing devices: hosts = end systems running network apps communication links fiber, copper, radio, satellite transmission rate: bandwidth Packet switches: forward packets (chunks of data) routers and switches wired links wireless links router mobile network global ISP regional ISP home network institutional network smartphone PC server wireless laptop 1-5
- 6. Introduction “Fun” internet appliances IP picture frame http://www.ceiva.com/ Web-enabled toaster + weather forecaster Internet phones Internet refrigerator Slingbox: watch, control cable TV remotely 1-6 Tweet-a-watt: monitor energy use
- 7. Introduction Internet: “network of networks” Interconnected ISPs protocols control sending, receiving of msgs e.g.,TCP, IP, HTTP, Skype, 802.11 Internet standards RFC: Request for comments IETF: Internet EngineeringTask Force What’s the Internet:“nuts and bolts” view mobile network global ISP regional ISP home network institutional network 1-7
- 8. What’s the Internet: a service view Infrastructure that provides services to applications: Web,VoIP, email, games, e- commerce, social nets, … provides programming interface to apps hooks that allow sending and receiving app programs to “connect” to Internet provides service options, analogous to postal service mobile network global ISP regional ISP home network institutional network Introduction 1-8
- 9. Introduction What’s a protocol? human protocols: “what’s the time?” “I have a question” introductions … specific msgs sent … specific actions taken when msgs received, or other events network protocols: machines rather than humans all communication activity in Internet governed by protocols protocols define format, order of msgs sent and received among network entities, and actions taken on msgs transmitted/received 1-9
- 10. Introduction a human protocol and a computer network protocol: Hi Hi Got the time? 2:00 TCP connection response Get http://www.awl.com/kurose-ross <file> time TCP connection request What’s a protocol? 1-10
- 11. Introduction A closer look at network structure: network edge: hosts: clients and servers servers often in data centers access networks, physical media: wired, wireless communication links network core: interconnected routers network of networks mobile network global ISP regional ISP home network institutional network 1-11
- 12. ISP Introduction Access network: digital subscriber line (DSL) central office telephone network DSLAM voice, data transmitted at different frequencies over dedicated line to central office use existing telephone line to central office DSLAM • data over DSL phone line goes to Internet • voice over DSL phone line goes to telephone net < 2.5 Mbps upstream transmission rate (typically < 1 Mbps) < 24 Mbps downstream transmission rate (typically < 10 Mbps) DSL modem splitter DSL access multiplexer 1-12
- 13. ISP Introduction data, TV transmitted at different frequencies over shared cable distribution network cable modem splitter … cable headend CMTS cable modem termination system HFC: hybrid fiber coax • asymmetric: up to 30Mbps downstream transmission rate, 2 Mbps upstream transmission rate network of cable, fiber attaches homes to ISP router • homes share access network to cable headend • unlike DSL, which has dedicated access to central office Access network: cable network 1-13
- 14. Introduction Access network: home network to/from headend or central office cable or DSL modem router, firewall, NAT wired Ethernet (1 Gbps) wireless access point (54 Mbps) wireless devices often combined in single box 1-14
- 15. Introduction Access network: cable network cable modem splitter … cable headend Channels V I D E O V I D E O V I D E O V I D E O V I D E O V I D E O D A T A D A T A C O N T R O L 1 2 3 4 5 6 7 8 9 frequency division multiplexing: different channels transmitted in different frequency bands 1-15
- 16. Introduction Enterprise access networks (Ethernet) typically used in companies, universities, etc. 10 Mbps, 100Mbps, 1Gbps, 10Gbps transmission rates today, end systems typically connect into Ethernet switch Ethernet switch institutional mail, web servers institutional router institutional link to ISP (Internet) 1-16
- 17. Introduction Wireless access networks shared wireless access network connects end system to router • via base station aka “access point” wireless LANs: within building (100 ft.) 802.11b/g/n (WiFi): 11, 54, 450 Mbps transmission rate wide-area wireless access provided by telco (cellular) operator, 10’s km between 1 and 10 Mbps 3G, 4G: LTE to Internet to Internet 1-17
- 18. Introduction Physical media bit: propagates between transmitter/receiver pairs physical link: what lies between transmitter & receiver guided media: • signals propagate in solid media: copper, fiber, coax unguided media: • signals propagate freely, e.g., radio twisted pair (TP) two insulated copper wires • Category 5: 100 Mbps, 1 Gbps Ethernet • Category 6: 10Gbps 1-18
- 19. Introduction Physical media: coax, fiber coaxial cable: two concentric copper conductors bidirectional broadband: • multiple channels on cable • HFC fiber optic cable: glass fiber carrying light pulses, each pulse a bit high-speed operation: • high-speed point-to-point transmission (e.g., 10’s-100’s Gbps transmission rate) low error rate: • repeaters spaced far apart • immune to electromagnetic noise 1-19
- 20. Introduction Physical media: radio signal carried in electromagnetic spectrum no physical “wire” bidirectional propagation environment effects: • reflection • obstruction by objects • interference radio link types: terrestrial microwave • e.g. up to 45 Mbps channels LAN (e.g.,WiFi) • 54 Mbps wide-area (e.g., cellular) • 4G cellular: ~ 10 Mbps satellite • Kbps to 45Mbps channel (or multiple smaller channels) • 270 msec end-end delay • geosynchronous versus low altitude 1-20
- 21. Introduction mesh of interconnected routers packet-switching: hosts break application-layer messages into packets forward packets from one router to the next, across links on path from source to destination each packet transmitted at full link capacity The network core 1-21
- 22. Host: sends packets of data host sending function: takes application message breaks into smaller chunks, known as packets, of length L bits transmits packet into access network at transmission rate R link transmission rate, aka link capacity, aka link bandwidth R: link transmission rate host 1 2 two packets, L bits each packet transmission delay time needed to transmit L-bit packet into link L (bits) R (bits/sec) = = 1-22
- 23. Introduction Packet-switching: store-and-forward takes L/R seconds to transmit (push out) L-bit packet into link at R bps store and forward: entire packet must arrive at router before it can be transmitted on next link one-hop numerical example: L = 7.5 Mbits R = 1.5 Mbps one-hop transmission delay = 5 sec more on delay shortly … 1-23 source R bps destination 1 2 3 L bits per packet R bps end-end delay = 2L/R (assuming zero propagation delay)
- 24. Introduction Packet Switching: queueing delay, loss A B C R = 100 Mb/s R = 1.5 Mb/s D E queue of packets waiting for output link 1-24 queuing and loss: If arrival rate (in bits) to link exceeds transmission rate of link for a period of time: packets will queue, wait to be transmitted on link packets can be dropped (lost) if memory (buffer) fills up
- 25. Network Layer 4-25 Two key network-core functions forwarding: move packets from router’s input to appropriate router output routing: determines source- destination route taken by packets routing algorithms routing algorithm local forwarding table header value output link 0100 0101 0111 1001 3 2 2 1 1 2 3 0111 dest address in arriving packet’s header
- 26. Internet structure: network of networks End systems connect to Internet via access ISPs (Internet Service Providers) Residential, company and university ISPs Access ISPs in turn must be interconnected. So that any two hosts can send packets to each other Resulting network of networks is very complex Evolution was driven by economics and national policies Let’s take a stepwise approach to describe current Internet structure
- 27. Internet structure: network of networks Question: given millions of access ISPs, how to connect them together? access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net … … … … … …
- 28. Internet structure: network of networks Option: connect each access ISP to every other access ISP? access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net … … … … … … … … … … … connecting each access ISP to each other directly doesn’t scale: alot of connections.
- 29. Internet structure: network of networks access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net … … … … … … Option: connect each access ISP to a global transit ISP? Customer and provider ISPs have economic agreement. global ISP
- 30. Internet structure: network of networks access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net … … … … … … But if one global ISP is viable business, there will be competitors …. ISP B ISP A ISP C
- 31. Internet structure: network of networks access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net … … … … … … But if one global ISP is viable business, there will be competitors …. which must be interconnected ISP B ISP A ISP C IXP IXP peering link Internet exchange point
- 32. Internet structure: network of networks access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net … … … … … … … and regional networks may arise to connect access nets to ISPs ISP B ISP A ISP C IXP IXP regional net
- 33. Internet structure: network of networks access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net … … … … … … … and content provider networks (e.g., Google, Microsoft, Akamai ) may run their own network, to bring services, content close to end users ISP B ISP A ISP B IXP IXP regional net Content provider network
- 34. Introduction Internet structure: network of networks at center: small # of well-connected large networks “tier-1” commercial ISPs (e.g., Level 3, Sprint,AT&T, NTT), national & international coverage content provider network (e.g, Google): private network that connects it data centers to Internet, often bypassing tier-1, regional ISPs 1-34 access ISP access ISP access ISP access ISP access ISP access ISP access ISP access ISP Regional ISP Regional ISP IXP IXP Tier 1 ISP Tier 1 ISP Google IXP
- 35. Introduction Tier-1 ISP: e.g., Sprint 1-35
- 36. Introduction How do loss and delay occur? packets queue in router buffers packet arrival rate to link (temporarily) exceeds output link capacity packets queue, wait for turn A B packet being transmitted (delay) packets queueing (delay) free (available) buffers: arriving packets dropped (loss) if no free buffers 1-36
- 37. Introduction Four sources of packet delay dproc: nodal processing check bit errors determine output link typically < msec A B propagation transmission nodal processing queueing dqueue: queueing delay time waiting at output link for transmission depends on congestion level of router dnodal = dproc + dqueue + dtrans + dprop 1-37
- 38. Introduction dtrans: transmission delay: L: packet length (bits) R: link bandwidth (bps) dtrans = L/R dprop: propagation delay: d: length of physical link s: propagation speed in medium (~2x108 m/sec) dprop = d/s dtrans and dprop very different Four sources of packet delay propagation nodal processing queueing dnodal = dproc + dqueue + dtrans + dprop 1-38 A B transmission
- 39. Introduction Caravan analogy cars “propagate” at 100 km/hr toll booth takes 12 sec to service car (bit transmission time) car~bit; caravan ~ packet Q: How long until caravan is lined up before 2nd toll booth? time to “push” entire caravan through toll booth onto highway = 12*10 = 120 sec time for last car to propagate from 1st to 2nd toll both: 100km/(100km/hr)= 1 hr A: 62 minutes toll booth toll booth ten-car caravan 100 km 100 km 1-39
- 40. Introduction Caravan analogy (more) suppose cars now “propagate” at 1000 km/hr and suppose toll booth now takes one min to service a car Q: Will cars arrive to 2nd booth before all cars serviced at first booth? A:Yes! after 7 min, 1st car arrives at second booth; three cars still at 1st booth. toll booth toll booth ten-car caravan 100 km 100 km 1-40
- 41. Introduction “Real” Internet delays and routes what do “real” Internet delay & loss look like? traceroute program: provides delay measurement from source to router along end- end Internet path towards destination. For all i: sends three packets that will reach router i on path towards destination router i will return packets to sender sender times interval between transmission and reply. 3 probes 3 probes 3 probes 1-41
- 42. Introduction “Real” Internet delays, routes 1 cs-gw (128.119.240.254) 1 ms 1 ms 2 ms 2 border1-rt-fa5-1-0.gw.umass.edu (128.119.3.145) 1 ms 1 ms 2 ms 3 cht-vbns.gw.umass.edu (128.119.3.130) 6 ms 5 ms 5 ms 4 jn1-at1-0-0-19.wor.vbns.net (204.147.132.129) 16 ms 11 ms 13 ms 5 jn1-so7-0-0-0.wae.vbns.net (204.147.136.136) 21 ms 18 ms 18 ms 6 abilene-vbns.abilene.ucaid.edu (198.32.11.9) 22 ms 18 ms 22 ms 7 nycm-wash.abilene.ucaid.edu (198.32.8.46) 22 ms 22 ms 22 ms 8 62.40.103.253 (62.40.103.253) 104 ms 109 ms 106 ms 9 de2-1.de1.de.geant.net (62.40.96.129) 109 ms 102 ms 104 ms 10 de.fr1.fr.geant.net (62.40.96.50) 113 ms 121 ms 114 ms 11 renater-gw.fr1.fr.geant.net (62.40.103.54) 112 ms 114 ms 112 ms 12 nio-n2.cssi.renater.fr (193.51.206.13) 111 ms 114 ms 116 ms 13 nice.cssi.renater.fr (195.220.98.102) 123 ms 125 ms 124 ms 14 r3t2-nice.cssi.renater.fr (195.220.98.110) 126 ms 126 ms 124 ms 15 eurecom-valbonne.r3t2.ft.net (193.48.50.54) 135 ms 128 ms 133 ms 16 194.214.211.25 (194.214.211.25) 126 ms 128 ms 126 ms 17 * * * 18 * * * 19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136 ms traceroute: gaia.cs.umass.edu to www.eurecom.fr 3 delay measurements from gaia.cs.umass.edu to cs-gw.cs.umass.edu * means no response (probe lost, router not replying) trans-oceanic link 1-42
- 43. Introduction Packet loss queue (aka buffer) or the preceding link in buffer has finite capacity packet arriving to full queue dropped (aka lost) lost packet may be retransmitted by previous node, by source end system, or not at all A B packet being transmitted packet arriving to full buffer is lost buffer (waiting area) 1-43
- 44. Introduction 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 server, with file of F bits to send to client link capacity Rs bits/sec link capacity Rc bits/sec server sends bits (fluid) into pipe pipe that can carry fluid at rate Rs bits/sec) pipe that can carry fluid at rate Rc bits/sec) 1-44
- 45. Introduction Throughput (more) Rs < Rc What is average end-end throughput? Rs bits/sec Rc bits/sec Rs > Rc What is average end-end throughput? link on end-end path that constrains end-end throughput bottleneck link Rs bits/sec Rc bits/sec 1-45
- 46. Introduction Throughput: Internet scenario 10 connections (fairly) share backbone bottleneck link R bits/sec Rs Rs Rs Rc Rc Rc R per-connection end- end throughput: min(Rc,Rs,R/10) in practice: Rc or Rs is often bottleneck Bottle-neck link is at network edge 1-46
- 47. Introduction Protocol “layers” Networks are complex, with many “pieces”: hosts routers links of various media applications protocols hardware, software Question: is there any hope of organizing structure of network? …. or at least our discussion of networks? 1-47
- 48. Introduction 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 layering considered harmful? 1-48
- 49. Introduction Internet protocol stack application: supporting network applications FTP, SMTP, HTTP 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 Ethernet, 802.111 (WiFi), PPP physical: bits “on the wire” application transport network link physical 1-49
- 50. Introduction ISO/OSI reference model presentation: allow applications to interpret meaning of data, e.g., encryption, compression, machine-specific conventions session: synchronization, checkpointing, recovery of data exchange Internet stack “missing” these layers! these services, if needed, must be implemented in application needed? application presentation session transport network link physical 1-50
- 51. Introduction source application transport network link physical Ht Hn M segment Ht datagram destination application transport network link physical Ht Hn Hl M Ht Hn M Ht M M network link physical link physical Ht Hn Hl M Ht Hn M Ht Hn M Ht Hn Hl M router switch Encapsulation message M Ht M Hn frame 1-51
- 52. Introduction Chapter 1: roadmap 1.1 what is the Internet? 1.2 network edge end systems, access networks, links 1.3 network core packet switching, circuit switching, network structure 1.4 delay, loss, throughput in networks 1.5 protocol layers, service models 1.7 history 1-52
Editor's Notes
- #5: End systems, also known as hosts, are devices connected to a network that run applications and generate or consume data. A packet switch is a network device that forwards data packets from one network node to another based on their destination address.
- #7: A protocol is a set of rules that define how data is transmitted, received, and interpreted between devices in a network.
- #12: Uses twisted pair copper wires Also asymmetric Service quality greatly effected by the distance between the house and central office, as distance increases the quality degrades
- #13: It’s a shared network so your neighbour’s data transmission and reception rates effect yours Asymmetric: different rates in DL and UL as we are majorly the consumers of data instead of prodeucers
- #17: WLANs are Wifi networks
- #39: 120 sec is the transmission delay and 1 hour is the propagation delay
- #45: In upper case its Rs and in lower case its Rc, as they are the bottle-neck links and are controlling max allowable output