1 DT 066 Distributed Information Systems Chapter 1

1 DT 066 Distributed Information Systems Chapter 1 Introduction Adapted from: Computer Networking, Kurose/Ross 1 -1

The book and copyrights A note on the use of these ppt slides: We’re making these slides freely available to all (faculty, students, readers). They’re in Power. Point form so you see the animations; and can add, modify, and delete slides (including this one) and slide content to suit your needs. They obviously represent a lot of work on our part. In return for use, we only ask the following: v If you use these slides (e. g. , in a class) that you mention their source (after all, we’d like people to use our book!) v If you post any slides on a www site, that you note that they are adapted from (or perhaps identical to) our slides, and note our copyright of this material. Thanks and enjoy! JFK/KWR Computer Networking: A Top Down Approach 6 th edition Jim Kurose, Keith Ross Addison-Wesley March 2012 All material copyright 1996 -2012 J. F Kurose and K. W. Ross, All Rights Reserved Adapted from: Computer Networking, Kurose/Ross 1 -2

Chapter 1: introduction our goal: v get “feel” and terminology v more depth, detail later in course v approach: § use Internet as example Adapted from: Computer Networking, Kurose/Ross overview: v v v what’s the Internet? what’s a protocol? network edge; hosts, access net, network core: switching, Internet structure performance: loss, delay, throughput protocol layers, service models 1 -3

What’s the Internet: “nuts and bolts” view PC server v millions wireless laptop smartphone of connected computing devices: § hosts = end systems § running network apps v communication wireless links wired links § fiber, copper, radio, satellite § transmission rate: bandwidth v Packet switches: router forward packets (chunks of data) Adapted from: Computer Networking, Kurose/Ross and switches § routers mobile network global ISP home network regional ISP institutional network Adapted from: Computer Networking, Kurose/Ross 1 -4

What’s the Internet: “nuts and bolts” view v Internet: “network of networks” mobile network § Interconnected ISPs v protocols control sending, receiving of msgs § e. g. , TCP, IP, HTTP, Skype, 802. 11 v global ISP home network Internet standards regional ISP § RFC: Request for comments § IETF: Internet Engineering Task Force institutional network Adapted from: Computer Networking, Kurose/Ross 1 -5

What’s the Internet: a service view v Infrastructure that provides services to applications: § Web, Vo. IP, email, games, e-commerce, social nets, … v mobile network global ISP home network regional ISP provides programming interface to apps § hooks that allow sending and receiving app programs to “connect” to Internet § provides service options, analogous postal Adapted from: Computer Networking, to Kurose/Ross institutional network 1 -6

What’s a protocol? a human protocol and a computer network protocol: Hi TCP connection request Hi TCP connection response Got the time? Get http: //www. awl. com/kurose-ross 2: 00 <file> time Q: other human protocols? Adapted from: Computer Networking, Kurose/Ross 1 -7

A closer look at network structure: v network edge: § § hosts: clients and servers often in data centers – the “Cloud” access networks, physical media: wired, wireless v communication network core: links v v mobile network global ISP home network regional ISP § interconnected routers § network of networks Transmission rate: § Bits transmitted per second on a institutional network link Adapted from: Computer Networking, Kurose/Ross § Capacity, Bandwidth. “Bandbredd” 1 -8

Access networks and physical media Q: How to connect end systems to edge router? v v v residential access nets institutional access networks (school, company) mobile access networks keep in mind: v v bandwidth (bits per second) of access network? shared or dedicated? Adapted from: Computer Networking, Kurose/Ross 1 -9

Access net: home network wireless devices Internet Service Provider, ISP. E. g. Telia, Com. Hem, Bredbandsbolaget often combined in single box wireless access point (54+ Mbps) Adapted from: Computer Networking, Kurose/Ross Fiber, cable or ADSL modem router, firewall, NAT wired Ethernet (100 Mbps) 1 -10

Wireless access networks v shared wireless access network connects end system to router § via base station aka “access point” wireless LANs: § within building (100 ft) § 802. 11 b/g/n/a (Wi. Fi): 11, 54, 108 Mbps transmission rate wide-area wireless access § provided by Mobile operators (Telenor, Tre, etc) , 10’s km § between 1 and 30 Mbps § 3 G, 4 G: LTE to Internet Adapted from: Computer Networking, Kurose/Ross 1 -11

Host: sends packets of data host sending function: v takes application two packets, message L bits each v breaks into smaller chunks, known as packets, of length L bits 2 1 v transmits packet into access network at R: link transmission rate host transmission rate R § link transmission rate, aka link capacity, aka link bandwidth time needed to packet L (bits) transmission = transmit L-bit = R (bits/sec) packet into link delay Adapted from: Computer Networking, Kurose/Ross 1 -12

Packet-switching: store-andforward L bits per packet source 3 2 1 R bps takes L/R seconds to transmit (push out) L-bit packet into link at R bps v store and forward: entire packet must arrive at router before it can be transmitted on next link v end-to-end (E 2 E) delay = 2 L/R (assuming zero Adaptedpropagation from: Computer Networking, delay) Kurose/Ross v R bps destination one-hop numerical example: § L = 7. 5 Mbits § R = 1. 5 Mbps § one-hop transmission delay = 5 sec more on delay shortly … 1 -13

Packet Switching: queueing delay, loss A B C R = 100 Mb/s R = 1. 5 Mb/s queue of packets waiting for output link D E queuing and loss: v 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 Adapted from: Computer Networking, Kurose/Ross 1 -14

Two key network-core functions routing: determines source- forwarding: move packets destination route taken by packets § routing algorithms from router’s input to appropriate router output routing algorithm local forwarding table header value output link 0100 0101 0111 1001 1 3 2 2 1 3 2 11 01 dest address in arriving packet’s header Adapted from: Computer Networking, Kurose/Ross 4 -15

Circuit switching end-end resources allocated to, reserved for “call” between source & dest: In diagram, each link has four circuits. § call gets 2 nd circuit in top link and 1 st circuit in right link. v dedicated resources: no sharing § circuit-like (guaranteed) performance v circuit segment idle if not used by call (no sharing) Adapted from: Computer Networking, Kurose/Ross v Commonly used in traditional v 1 -16

Circuit switching: FDM versus TDM Example: Frequence Division Multiplexing 4 users frequency Time Division Multiplexing time frequency time Adapted from: Computer Networking, Kurose/Ross 1 -17

Packet switching versus circuit switching packet switching allows more users to use network! example: § 1 Mb/s link § each user: …. . N users • 100 kb/s when “active” • active 10% of time 1 Mbps link v circuit-switching: § 10 users v packet switching: Q: how did we get value 0. 0004? § with 35 users, probability > 10 active at same time is less than. 0004 * Q: what happens if > 35 users ? * Check out the online interactive exercises for more examples Adapted from: Computer Networking, Kurose/Ross 1 -18

Internet structure: network of networks Question: given millions of access ISPs, how to connect them together? access net … access net … … access net access net … Adapted from: Computer Networking, Kurose/Ross access net … access net 1 -19

Internet structure: network of networks Option: connect each access ISP to every other access ISP? access net … access net … … connecting each access ISP to each other directly doesn’t scale: O(N 2) connections. … … access net access net … … Adapted from: Computer Networking, Kurose/Ross … access net 1 -20

Internet structure: network of networks Option: connect each access ISP to a global transit ISP? Customer and provider ISPs have economic agreement. access net … access net … … access net global ISP access net access net … Adapted from: Computer Networking, Kurose/Ross access net … access net 1 -21

Internet structure: network of networks But if one global ISP is viable business, there will be competitors …. access net … access net access net … … ISP A access net ISP B ISP C access net … Adapted from: Computer Networking, Kurose/Ross access net … access net 1 -22

Internet structure: network of networks But if one global ISP is viable business, there will be competitors …. which must be interconnected Internet exchange point access net … … net access net IXP access net … … ISP A IXP access net ISP B ISP C access net peering link access net … Adapted from: Computer Networking, Kurose/Ross access net … access net 1 -23

Internet structure: network of networks … and regional networks may arise to connect access nets to ISP: s access net … … access net IXP access net … … ISP A IXP access net ISP B ISP C access net regional net access net … Adapted from: Computer Networking, Kurose/Ross access net … access net 1 -24

Internet structure: network of networks … and content provider networks (e. g. , Google, Microsoft, Akamai ) may run their own network, to bring services, content close to end users access net … … access net IXP access net Content provider network IXP access net ISP B access net regional net access net … Adapted from: Computer Networking, Kurose/Ross access net … … ISP A access net 1 -25

Internet structure: Clouds … and Service providers (e. g. , Google Drive, Microsoft, Amazon, Dropbox ) may run services for the users on their server farms. access net … … access net Cloud access net IXP access net … … ISP A IXP access net ISP B access net regional net access net … Adapted from: Computer Networking, Kurose/Ross access net … access net 1 -26

How do loss and delay occur? packets queue in router buffers v v packet arrival rate to link (temporarily) exceeds output link capacity packets queue, wait for turn packet being transmitted (delay) A B packets queueing (delay) free (available) buffers: arriving packets dropped (loss) if no free buffers Adapted from: Computer Networking, Kurose/Ross 1 -27

Four sources of packet delay transmission A propagation B nodal processing queueing dnodal = dproc + dqueue + dtrans + dprop dproc: nodal processing § § § check bit errors determine output link typically < msec Adapted from: Computer Networking, Kurose/Ross dqueue: queueing delay § time waiting at output link for transmission § depends on congestion level of router 1 -28

Four sources of packet delay transmission A propagation B nodal processing queueing dnodal = dproc + dqueue + dtrans + dprop dtrans: transmission delay: § L: packet length (bits) § R: link bandwidth (bps) § dtrans = L/R dtrans and dprop very different Adapted from: Computer Networking, Kurose/Ross dprop: propagation delay: § d: length of physical link § s: propagation speed in medium (~2 x 108 m/sec) § dprop = d/s * Check out the Java applet for an interactive animation on trans vs. prop delay 1 -29

Caravan analogy 100 km ten-car caravan v v 100 km toll booth 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 2 nd toll booth? toll booth § § § Adapted from: Computer Networking, Kurose/Ross time to “push” entire caravan through toll booth onto highway = 12*10 = 120 sec time for last car to propagate from 1 st to 2 nd toll both: 100 km/(100 km/hr)= 1 hr A: 62 minutes 1 -30

Caravan analogy (more) 100 km ten-car caravan v v v toll booth 100 km toll booth 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 2 nd booth before all cars serviced at first booth? § A: Yes! after 7 min, 1 st car arrives at second booth; three cars still at 1 st booth. Adapted from: Computer Networking, Kurose/Ross 1 -31

v v v R: link bandwidth (bps) L: packet length (bits) a: average packet arrival rate average queueing delay Queueing delay (revisited) traffic intensity = La/R ~ 0: avg. queueing delay small La/R -> 1: avg. queueing delay large La/R > 1: more “work” arriving than can be serviced, average delay infinite! * Check out the Java applet for an interactive animation on queuing and loss Adapted from: Computer Networking, Kurose/Ross La/R ~ 0 La/R -> 1 1 -32

“Real” Internet delays and routes what do “real” Internet delay & loss look like? v traceroute program: provides delay measurement from source to router along end -end Internet path towards destination. For all i: v § 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 Adapted from: Computer Networking, Kurose/Ross 1 -33

Adapted from: Computer Networking, Kurose/Ross 1 -34

Adapted from: Computer Networking, Kurose/Ross 1 -35

Adapted from: Computer Networking, Kurose/Ross 1 -36

Packet loss queue (aka buffer) preceding link in buffer has finite capacity v packet arriving to full queue dropped (aka lost) v lost packet may be retransmitted by previous node, by source end system, or not at all v buffer (waiting area) A packet being transmitted B packet arriving to full buffer is lost Adapted from: Computer Networking, Kurose/Ross * Check out the Java applet for an interactive animation on queuing and loss 1 -37

Throughput v 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 bits server sends file of into F bits (fluid) pipe to send to client linkpipe capacity that can carry Rs bits/sec fluid at rate Rs bits/sec) Adapted from: Computer Networking, Kurose/Ross linkpipe capacity that can carry Rc bits/sec fluid at rate Rc bits/sec) 1 -38

Throughput (more) v Rs < Rc What is average end-end throughput? Rs bits/sec v Rc bits/sec Rs > Rc What is average end-end throughput? Rs bits/sec Rc bits/sec bottleneck link on end-to-end path that constrains end-to-end throughput Adapted from: Computer Networking, Kurose/Ross 1 -39

Adapted from: Computer Networking, Kurose/Ross 1 -40

Throughput: Internet scenario per-connection end -end throughput: min(Rc, Rs, R/10) v in practice: Rc or Rs is often bottleneck v Rs Rs Rs R Rc Rc Rc 10 connections (fairly) share backbone bottleneck link R bits/sec Adapted from: Computer Networking, Kurose/Ross 1 -41

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? Hierarchical Layers ? Adapted from: Computer Networking, Kurose/Ross 1 -42

Organization of air travel – layering? ticket (purchase) ticket (complain) baggage (check) baggage (claim) gates (load) gates (unload) runway takeoff runway landing airplane routing v a series of steps Adapted from: Computer Networking, Kurose/Ross 1 -43

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 departure airport 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 Adapted from: Computer Networking, Kurose/Ross 1 -44

Why layering? dealing with complex systems: v explicit structure allows identification, relationship of complex system’s pieces § layered reference model for discussion v 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 Adapted from: Computer Networking, Kurose/Ross 1 -45

Internet protocol stack v application: supporting network applications § FTP, SMTP, HTTP v transport: process-process data transfer § TCP, UDP v network: routing of datagrams from source to destination § IP, routing protocols v link: data transfer between neighboring network elements application transport network link physical § Ethernet, 802. 111 (Wi. Fi), PPP v physical: bits “on the wire” Adapted from: Computer Networking, Kurose/Ross 1 -46

ISO 7 -layer reference model application transport presentation network session link physical Introduction 1 -47

Encapsulation source message segment Ht M datagram Hn Ht M frame M Hl Hn Ht M application transport network link physical switch destination M Ht M Hn Ht Hl Hn Ht M M application transport network link physical Adapted from: Computer Networking, Kurose/Ross Hn Ht Hl Hn Ht M M network link physical Hn Ht M router 1 -48