Chapter 1 Computer Networks and the Internet A

Chapter 1 Computer Networks and the Internet 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. Computer Networking: A Top Down Approach 6 th edition Jim Kurose, Keith Ross Addison-Wesley March 2012 Thanks and enjoy! JFK/KWR All material copyright 1996 -2012 J. F Kurose and K. W. Ross, All Rights Reserved Introduction 1 -1

1. 1 What’s the Internet: “nuts and bolts” view v millions of connected PC computing devices: server § hosts = end systems wireless § running network apps laptop smartphonev communication links § coaxial cable, copper wire, optical fiber, radio spectrum, satellite wireless links § transmission rate: wired bandwidth (bits/second) links v Packet switches: forward packets (chunks of data) § routers used in the network core router § (link-layer) switches used in access network mobile network global ISP home network regional ISP institutional network Introduction 1 -2

1. 1 What’s the Internet : “Fun” internet appliances Web-enabled toaster + weather forecaster IP picture frame http: //www. ceiva. com/ Tweet-a-watt: monitor energy use Slingbox: watch, control cable TV remotely Internet refrigerator Internet phones Introduction 1 -3

1. 1 What’s the Internet: “nuts and bolts” view v Internet: “network of networks” mobile network § Interconnected ISPs (e. g. residential, corporate, university, Wi. Fi) v End systems, packet switches, and other pieces of the Internet run protocols that control sending, receiving of msgs global ISP home network regional ISP § e. g. , TCP, IP, HTTP, Skype, 802. 11 v Internet standards: Due to interoperatability of systems and products, it’s important that everyone agree on what each and every protocol does § RFC: Request for comments § IETF: Internet Engineering Task Force institutional network Introduction 1 -4

1. 1 What’s the Internet: a service view v Infrastructure that provides services to applications: mobile network § Web, Vo. IP, email, games, ecommerce, social nets, … v provides programming interface to apps § hooks that allow sending and receiving app programs to “connect” to Internet § provides service options, analogous to postal service global ISP home network regional ISP institutional network Introduction 1 -5

1. 1. What’s the Internet: what’s a protocol? human protocols: v v v “what’s the time? ” “I have a question” introductions … specific msgs sent … specific actions taken when msgs received, or other events network protocols: v v machines rather than humans all communication activity in Internet governed by protocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt Introduction 1 -6

1. 1. What’s the Internet: 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 time Q: other human protocols? Introduction 1 -7

1. 2 The Network Edge : A closer look at network structure v network edge: § § mobile network hosts (cf. application programs) : clients and servers often in data centers v access networks: physically connect an end system to the first router (a. k. a. edge router) v global ISP home network regional ISP network core: § interconnected routers § network of networks institutional network Introduction 1 -8

1. 2 The Network Edge : 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? Introduction 1 -9

1. 2 The Network Edge Access net: digital subscriber line (DSL) central office DSL splitter modem voice, data transmitted at different frequencies over dedicated line to central office v v v telephone network DSLAM ISP DSL access multiplexer DSL and cable are the most prevalent types of broadband residential access 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) The access is said to be “asymmetric” Introduction 1 -10

1. 2 The Network Edge Access net: cable network cable headend … cable splitter modem V I D E O V I D E O D A T A C O N T R O L 1 2 3 4 5 6 7 8 9 Channels frequency division multiplexing: different channels transmitted in different frequency bands Introduction 1 -11

1. 2 The Network Edge Access net: cable network cable headend … cable splitter modem data, TV transmitted at different frequencies over shared cable distribution network (i. e. every packet sent by the head end travels downstream on every link to every home and reverse way, too) v v CMTS cable modem termination system ISP HFC: hybrid fiber coax § asymmetric: up to 30 Mbps 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 Introduction 1 -12

1. 2 The Network Edge Access net: home network wireless devices to/from headend or central office often combined in single box cable or DSL modem wireless access point (54 Mbps) router, firewall, NAT wired Ethernet (100 Mbps) Introduction 1 -13

1. 2 The Network Edge : Enterprise access networks (Ethernet) institutional link to ISP (Internet) institutional router Ethernet switch v v v institutional mail, web servers a local area network (LAN) is typically used in companies, universities, and increasingly home settings 10 Mbps, 100 Mbps, 1 Gbps, 10 Gbps transmission rates today, end systems typically connect into Ethernet switch (note: by far most prevalent access technology) Introduction 1 -14

1. 2 The Network Edge : Wireless access networks v shared wireless access network connects end system to router § via base station aka “access point” wide-area wireless access wireless LANs: § within building (100 ft) § IEEE 802. 11 Tech. (a. k. a. Wi. Fi) : up to 54 Mbps transmission rate § provided by telco (cellular) operator, 10’s km § between 1 and 10 Mbps § 3 G, 4 G: LTE to Internet Introduction 1 -15

1. 2 The Network Edge Host: sends packets of data (p 37 of the textbook) host sending function: vtakes application message vbreaks into smaller chunks, known as packets, of length L bits vtransmits packet into access network at transmission rate R § link transmission rate, aka link capacity, aka link bandwidth packet transmission delay = two packets, L bits each 2 1 R: link transmission rate host time needed to transmit L-bit packet into link = L (bits) R (bits/sec) 1 -16

1. 2 The Network Edge: Physical media v v bit: propagates between transmitter/receiver pairs physical link: what lies between twisted pair (TP) transmitter & receiver v two insulated copper wires guided media: v least expensive an most § signals propagate in solid commonly used media such as copper, fiber, coax unguided media: § signals propagate freely in the atmosphere such as radio spectrum, wireless LAN Introduction 1 -17

1. 2 The Network Edge Physical media: coax, fiber coaxial cable: v v two concentric copper conductors common in cable TV systems bidirectional broadband: § achieves high data transmission rate § multiple channels on cable § HFC fiber optic cable: v v glass fiber carrying light pulses, each pulse a bit high-speed operation: § high-speed transmission (e. g. , 10’s 100’s Gpbs transmission rate) low error rate: § repeaters spaced far apart § immune to electromagnetic noise high cost of optical devices such as transmitters, receivers, and switches Introduction 1 -18

1. 2 The Network Edge Physical media: radio v v signal carried in electromagnetic spectrum no physical “wire” bidirectional depend significantly on the propagation environment: § reflection § obstruction by objects § interference radio link types: v terrestrial microwave § e. g. up to 45 Mbps channels v LAN (e. g. , Wi. Fi) § 11 Mbps, 54 Mbps v wide-area (e. g. , cellular) § 3 G cellular: ~ few Mbps v satellite § Kbps to 45 Mbps channel (or multiple smaller channels) § 270 msec end-end delay § geosynchronous versus low altitude Introduction 1 -19

1. 3 The network core v v mesh of interconnected routers packet-switching (routers and link-layer switches) § hosts break applicationlayer 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 Introduction 1 -20

1. 3 The Network Core Packet-switching: store-and-forward L bits per packet source 3 2 1 R bps destination takes L/R seconds to transmit (push out) L-bit packet into link at R bps one-hop numerical example: v store and forward: entire packet must arrive at router before it can be transmitted on next § L = 7. 5 Mbits link § R = 1. 5 Mbps v end-end delay = 2 L/R (assuming zero § one-hop transmission propagation delay) delay = 5 sec (cf. total elapse time = 4 L/R) v generally, end-end delay = N*(L/R) (where, N = # of links) v delay for P packets sent over a series of N links? (P 2 on p 71) Introduction 1 -21 v

1. 3 The Network Core Packet Switching: queuing 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 v For each attached link, the packet switch has an output buffer (a. k. a. output queue), which stores packets that the router is about to send into link. 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 Introduction 1 -22 § Figure 1. 12 on p 25

1. 3 The Network Core Two key network-core functions routing: determines source- forwarding: move packets from destination route taken by packets § routing algorithms 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 Network Layer 4 -23

1. 3 The Network Core Alternative core: circuit switching end-to-end resources allocated to, reserved for “call” between source & dest. (analogous to a restaurant that requires reservations): v 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 constant rate) performance v circuit segment idle if not used by call (no sharing) v Commonly used in traditional telephone networks Introduction 1 -24

1. 3 The Network Core Circuit switching: FDM versus TDM Example: FDM (Frequency-Division Multiplexing) 4 users frequency time TDM (Time-Division Multiplexing) frequency time Introduction 1 -25

1. 3 The Network Core Packet switching versus circuit switching is packet switching a “slam dunk winner? ” v great for bursty data § better sharing of transmission capacity § simpler, more efficient, and less costly to implement v excessive congestion possible: packet delay and loss § not suitable for real-time services such as telephone calls and video conference calls § protocols needed for reliable data transfer, congestion control v performance of packet switching can be superior to that of circuit switching § circuit switching pre-allocates use of the transmission link regardless of demand, with allocated but unneeded link time going unused § packet switching allocates link use on demand. Link transmission capacity will be shared on a packet-by-packet basis Introduction 1 -26

1. 3 The Network Core Internet structure: network of networks v v End systems connect to Internet via access ISPs (Internet Service Providers) § Residential, company and university ISPs Access ISPs in turn must be interconnected. v So that any two hosts can send packets to each other Resulting network of networks is very complex v Evolution was driven by economics and national policies Let’s take a stepwise approach to describe current Internet structure

1. 3 The Network Core 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 …

1. 3 The Network Core 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 … … access net …

1. 3 The Network Core Internet structure: network of networks Option: connect each access ISP to a global transit ISP? Customer and provider ISPs have economic agreement. Network Structure 1 access net … access net … … access net global ISP access net access net … access net …

1. 3 The Network Core Internet structure: network of networks But if one global ISP is viable business, there will be competitors …. Network Structure 2 access net … net access net … … ISP A access net ISP B ISP C access net access net … … access net

1. 3 The Network Core 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 … … access net

1. 3 The Network Core Internet structure: network of networks … and regional networks may arise to connect access nets to ISPS access net … … access net IXP access net … … ISP A IXP access net ISP B ISP C access net regional net access net … … access net

1. 3 The Network Core 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 … … access net … … ISP A access net

1. 3 The Network Core Internet structure: network of networks Tier 1 ISP IXP Regional ISP access ISP v access ISP Google access ISP IXP Regional ISP access ISP 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 Introduction 1 -35

1. 3 The Network Core Tier-1 ISP: e. g. , Sprint POP: point-of-presence to/from backbone peering … … … to/from customers Introduction 1 -36

1. 4 delay, loss, throughput in networks : 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 Introduction 1 -37

1. 4 delay, loss, throughput in networks : 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 dqueue: queueing delay § time waiting at output link for transmission § depends on congestion level of router Introduction 1 -38

1. 4 delay, loss, throughput in networks : 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 dprop: propagation delay: § d: length of physical link § s: propagation speed in medium (~2 x 108 m/sec) § dprop = d/s Introduction 1 -39

1. 4 delay, loss, throughput in networks : 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 § § § 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 Introduction 1 -40

1. 4 delay, loss, throughput in networks : 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. Introduction 1 -41

v v Since queuing delay can vary packet to packet, use statistical measures such as average queuing delay when characterizing queuing delay R : link bandwidth (bps) L : packet length (bits) a: average packet arrival rate (packets/sec) average queuing delay 1. 4 delay, loss, throughput in networks : Queuing delay (revisited) traffic intensity = La/R ~ 0 Introduction 1 -42

1. 4 delay, loss, throughput in networks : Packet loss v buffer (waiting area) A packet being transmitted B packet arriving to full buffer is lost Introduction 1 -43

1. 4 delay, loss, throughput in networks : “Real” Internet delays and routes what do “real” Internet delay & loss look like? v traceroute program: provides delay measurement from source to router along endend 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 Introduction 1 -44

1. 4 delay, loss, throughput in networks : “Real” Internet delays, routes traceroute: gaia. cs. umass. edu to www. eurecom. fr 3 delay measurements from gaia. cs. umass. edu to cs-gw. cs. umass. edu 1 cs-gw (128. 119. 240. 254) 1 ms 2 border 1 -rt-fa 5 -1 -0. gw. umass. edu (128. 119. 3. 145) 1 ms 2 ms 3 cht-vbns. gw. umass. edu (128. 119. 3. 130) 6 ms 5 ms 4 jn 1 -at 1 -0 -0 -19. wor. vbns. net (204. 147. 132. 129) 16 ms 11 ms 13 ms 5 jn 1 -so 7 -0 -0 -0. wae. vbns. net (204. 147. 136) 21 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 trans-oceanic 8 62. 40. 103. 253 (62. 40. 103. 253) 104 ms 109 ms 106 ms link 9 de 2 -1. de. geant. net (62. 40. 96. 129) 109 ms 102 ms 104 ms 10 de. fr 1. fr. geant. net (62. 40. 96. 50) 113 ms 121 ms 114 ms 11 renater-gw. fr 1. fr. geant. net (62. 40. 103. 54) 112 ms 114 ms 112 ms 12 nio-n 2. 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 r 3 t 2 -nice. cssi. renater. fr (195. 220. 98. 110) 126 ms 124 ms 15 eurecom-valbonne. r 3 t 2. ft. net (193. 48. 50. 54) 135 ms 128 ms 133 ms 16 194. 211. 25 (194. 211. 25) 126 ms 128 ms 126 ms 17 * * means no response (probe lost, router not replying) 18 * * * 19 fantasia. eurecom. fr (193. 55. 113. 142) 132 ms 128 ms 136 ms Introduction 1 -45

1. 4 delay, loss, throughput in networks : Throughput v v In addition to delay and packet loss, another critical performance measure in computer networks is end-to-end throughput: rate (bits/time unit) at which bits transferred between sender/receiver § instantaneous: rate at given point in time (ex) many applications display the instantaneous throughput during downloads in the user interface § average: rate over longer period of time (ex) a file consists of F bits and the transfer takes T seconds for Host B to receive all F bits from Host A F/T bits/sec server, with server sends bits file of F bits (fluid) into pipe to send to client linkpipe that can carry capacity Rs bits/secat rate fluid Rs bits/sec) linkpipe that can carry capacity Rc bits/secat rate fluid Rc bits/sec) Introduction 1 -46

1. 4 delay, loss, throughput in networks : 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? Rc Rs bits/sec Rc bits/sec bottleneck link on end-end path that constrains end-end throughput Introduction 1 -47

1. 4 delay, loss, throughput in networks : Throughput (Internet scenario) per-connection endend 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 Introduction 1 -48

1. 5 Protocol Layers & Their Service Models : 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? Introduction 1 -49

1. 5 Protocol Layers & Their Service Models : Organization of air travel v Human Analogy: Airline System ticket (purchase) ticket (complain) baggage (check) baggage (claim) gates (load) gates (unload) runway takeoff runway landing airplane routing v v To describe the series of actions you take (or others take for you) when you fly on an airline You are shipped from source to destination by the airline; a packet is shipped from source host to destination host in the Internet. Introduction 1 -50

1. 5 Protocol Layers & Their Service Models : 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 v v v 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 A layered architecture allows us to discuss a well-defined , specific part of a large and complex system. As long as the layer provides the same services to the layer above it, and uses the same services from the layer below it, the remainder of the system remains unchanged when a layer’s implementation is changed. Introduction 1 -51

1. 5 Protocol Layers & Their Service Models : Why layering? dealing with complex systems: v explicit structure allows identification, relationship of complex system’s pieces § the protocols of the various layers are called the protocol stack 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 v layering considered harmful? § One layer may duplicate lower-layer functionality (e. g. , error recovery on both a per-link basis and end-to-end basis) § Functionality at one layer may need information that is present only in another layer; this violates the goal of separation of layers (e. g. , a time-stamp value) Introduction 1 -52

1. 5 Protocol Layers & Their Service Models : Internet protocol stack v v application: supporting network applications § FTP (file transfer), SMTP (e-mail), HTTP (Web doc. ), DNS (human friendly-name to a 32 -bit network address) § an application-layer protocol is distributed over multiple end systems § refer the packet of information at the application layer as a message transport: process-process data transfer (i. e. transport applicationlayer messages between application endpoints) § TCP • connection-oriented service to its applications that includes guaranteed delivery of application-layer message and flow control (i. e. sender/receiver speed matching) • breaks long messages into short segment and provide a congestion-control mechanism § UDP • connectionless service to its application • no frills service that provides no reliability, no flow control, and no congestion control § refer to a transportation-layer packet as a segment application transport network link physical Introduction 1 -53

1. 5 Protocol Layers & Their Service Models : Internet protocol stack v network: routing of network-layer packets, known as datagrams, from source to destination § The Internet transport-layer protocol (TCP or UDP) in a source host passes a segment and a destination address to the network layer, then the network layer provides the application service of delivering the segment to the transport layer in the destination host transport § IP protocol defines the field in the datagram as well as how the end systems and routers act on these fields (note) only one IP protocol network § numerous routing protocols v v link: data transfer between neighboring network element (i. e. host or router) § Ethernet, 802. 111 (Wi. Fi), PPP (Point-to-Point Protocol), DOCSIS Protocol (for cable access network) § Refer to the link-layer packets as frames link physical: bits “on the wire” Introduction 1 -54

1. 5 Protocol Layers & Their Service Models : ISO/OSI reference model v Five-layer Internet protocol stack is not the only protocol stack around v The International Organizations for Standardization (ISO) proposed seven layers called the Open Systems Interconnection (OSI) model v v The functionality of five of these layers is roughly the same as their similarly named Internet counterparts 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? up to the application developer! application presentation session transport network link physical Introduction 1 -55

source message segment Ht M datagram Hn Ht M frame M Hl Hn Ht M application transport network link physical 1. 5 Protocol Layers & Their Service Models : Encapsulation link physical switch destination M Ht M Hn Ht Hl Hn Ht M M application transport network link physical Hn Ht Hl Hn Ht M M network link physical Hn Ht M router Introduction 1 -56

1. 5 Protocol Layers & Their Service Models : Encapsulation v Routers and link-layer switches are both packet switches and organize their networking h/w and s/w into layers link-layer switches (layers 1 and 2) v. s. routers (layers 1, 2, and 3) (meaning) - Internet routers are capable of implementing the IP protocol (a layer 3 protocol), while link-layer switches are not - While link-layer switches do not recognize IP addresses, they are capable of recognizing layer 2 addresses, such as Ethernet addresses v At each layer, a packet has two types of fields: header fields and payload field. The payload is typically a packet from the layer above § The transport-layer segment encapsulates the application-layer message. The added information (Ht) might include information allowing the receiver-side transport layer to deliver the messages up to the appropriate application, and error-detection bits. § The network-layer adds network-layer header information (Hn) such as source and destination end system addresses. Introduction 1 -57

1. 5 Protocol Layers & Their Service Models : Analogy v Introduction 1 -58