Internet A Brief Overview Chapter 1 Chapter 1

Internet: A Brief Overview Chapter 1

Chapter 1: introduction our goal: v get “feel” and terminology v more depth, detail later in course v approach: § use Internet as example overview: v v v 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

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, protocol layers, service models

What is the Internet?

What’s the Internet: “nuts and bolts” view mobile network global ISP v Internet = “network of networks” home network § Interconnected ISPs § Interconnected networks institutional network regional ISP

What’s the Internet: “nuts and bolts” view PC server v Hosts § wireless laptop smartphone § = end systems billions of connected computing devices running network apps v communication wireless links wired links § fiber, copper, radio, satellite § transmission rate: bandwidth v Routers router § and switches Packet switches: forward packets (chunks of data) mobile network global ISP home network institutional network regional ISP

Questions on hosts, links, routers v What else are hosts? mobile network global ISP v Are they comm. Links? § § v Phone-wireless AP? Phone-base station? Router-to-router? Router-to-server? home network How to differ routers and switches from end-hosts? § Routers: in-between § No network apps running (only interconnection, no web/email/etc) institutional network regional ISP

A closer look at network structure: v network edge: § § hosts: clients and servers often in data centers v access networks, physical media: wired, wireless communication links v network core: § interconnected routers § network of networks mobile network global ISP home network institutional network regional ISP

Access networks and physical media Access network: connect end systems (hosts) to edge routers 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?

Discussion: Your access networks? v What types of access networks did you use? v How do they perform? Your own experience? v What you care most? (What are essential features of access networks? )

Common Access Network v Cable network Digital subscriber line (DSL) Home Wi. Fi Network Cellular (mobile) network Ethernet Fiber (optics network) … v Optional, read Chapter 1. 2 for details v v v

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 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)

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

Access net: cable network cable headend … cable splitter modem data, TV transmitted at different frequencies over shared cable distribution network 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

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)

Enterprise access networks (Ethernet) institutional link to ISP (Internet) institutional router Ethernet switch v v v institutional mail, web servers typically used in companies, universities, etc 10 Mbps, 100 Mbps, 1 Gbps, 10 Gbps transmission rates today, end systems typically connect into Ethernet switch

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 a/b/g (Wi. Fi): 11, 54 Mbps transmission rate § 802 11 n/ac: hundreds of Mbps to Internet wide-area wireless access § provided by telco (cellular) operator, 10’s km § between 1 and 10 Mbps § 3 G, 4 G LTE § LTE: ideally 100 -300 Mbps to Internet

Physical media v v 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) v two insulated copper wires § § Category 5: 100 Mbps, 1 Gpbs Ethernet Category 6: 10 Gbps

Physical media: coax, fiber coaxial cable: v v v two concentric copper conductors bidirectional broadband: § multiple channels on cable § HFC fiber optic cable: v v glass fiber carrying light pulses, each pulse a bit high-speed operation: § high-speed point-to-point transmission (e. g. , 10’s-100’s Gpbs transmission rate) v low error rate: § repeaters spaced far apart § immune to electromagnetic noise

Physical media: radio v v signal carried in electromagnetic spectrum no physical “wire” bidirectional propagation environment effects: § 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

A Software-View mobile network v protocols control sending, receiving of msgs global ISP § e. g. , HTTP, Skype, TCP, IP, 802. 11 v Internet standards home network § RFC: Request for comments § IETF: Internet Engineering Task Force institutional network regional ISP

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. 6 networks under attack: security 1. 7 history

Discussion: How to transfer data? v v mesh of interconnected routers Role: send chunks of data from one host to another host ?

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

Network core: Packetswitching v 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

Host: sends packets of data host sending function: v takes application message v breaks into smaller chunks, known as packets, of length L bits v transmits 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)

Packet-switching: store-andforward L bits per packet source v v v 3 2 1 R bps 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 end-end delay = 2 L/R (assuming zero propagation delay) 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 …

Alternative core: circuit switching end-end resources allocated to, reserved for “call” between source & dest: v v Example: each link has four circuits. § call gets 2 nd circuit in top link and 1 st circuit in right link. dedicated resources: no sharing § circuit-like (guaranteed) performance circuit segment idle if not used by call (no sharing) Commonly used in traditional

Circuit switching: FDM versus TDM Example: FDM 4 users frequency time TDM frequency time

Announcements v No class next week § Online video lectures v HW 1 is assigned today § Due: Sep 16 (Tue)

Recap v. Internet: hosts, communication links, routers, switches v. Network edge § Access networks v Network core § Packet switching § Circuit switching

Packet switching versus circuit switching v. Q: Why packet switching is chosen?

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

Packet switching versus circuit switching is packet switching a “slam dunk winner? ” v v great for bursty data § resource sharing § simpler, no call setup excessive congestion possible: packet delay and loss (see the following slides) § protocols needed for reliable data transfer, congestion control Q: human analogies of reserved resources (circuit switching) versus on-demand allocation (packet-switching)?

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

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 …

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 …

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 … access net …

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 access net … … access net

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

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

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

Internet structure: network of networks Tier 1 ISP IX P Regional ISP access ISP v access ISP Google access ISP IX P 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

Tier-1 ISP: e. g. , Sprint POP: point-of-presence to/from backbone peering … … … to/from customers

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. 6 networks under attack: security 1. 7 history

Host: sends packets of data (Recap) host sending function: v takes application message v breaks into smaller chunks, known as packets, of length L bits v transmits 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)

Store-and-forward: transmission delay L bits per packet source v v v 3 2 1 R bps 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 end-end delay = 2 L/R (assuming zero propagation delay) 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 …

Follow-up questions v What if we have N hops? v What if we have P packets? § Back-to-back

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

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

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 * Check out the Java applet for an interactive animation on trans vs. prop delay

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

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.

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 La/R ~ 0 La/R -> 1

“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

“Real” Internet delays, routes traceroute: www. eurecom. fr 3 delay measurements from ohio-state. edu to gw. cs. ohio-state. edu 1 se 4 -vl 3000. net. ohio-state. edu (128. 146. 28. 1) 1. 795 ms 1. 711 ms 1. 432 ms 2 tc 1 -forg 2 -4. net. ohio-state. edu (164. 107. 2. 190) 1. 435 ms 1. 793 ms 1. 481 ms 3 tc 6 -teng 2 -1. net. ohio-state. edu (164. 107. 2. 254) 1. 559 ms 1. 588 ms 1. 534 ms 4 clmbt-r 9 -xe-0 -0 -2 s 333. bb. oar. net (192. 148. 242. 205) 1. 503 ms 3. 233 ms 1. 632 ms 5 clmbk-r 9 -xe-1 -1 -0 s 101. core. oar. net (192. 153. 38. 37) 1. 488 ms 3. 239 ms 3. 435 ms 6 clmbn-r 0 -xe-1 -2 -0 s 101. core. oar. net (192. 153. 38. 25) 2. 971 ms 2. 185 ms 1. 773 ms 7 clmbn-r 5 -xe-4 -2 -0 s 101. core. oar. net (192. 153. 38. 13) 2. 170 ms 2. 024 ms 3. 183 ms 8 clevs-r 5 -et-1 -0 -0 s 101. core. oar. net (192. 153. 39. 254) 6. 488 ms 5. 860 ms 6. 281 ms trans-oceanic link 9 192. 88. 192. 238 (192. 88. 192. 238) 14. 380 ms 15. 203 ms 15. 322 ms 10 abilene-wash. mx 1. fra. de. geant. net (62. 40. 125. 17) 137. 013 ms 128. 416 ms 135. 878 ms 11 ae 1. mx 1. gen. ch. geant. net (62. 40. 98. 108) 130. 484 ms 144. 101 ms 130. 697 ms 12 ae 4. mx 1. par. fr. geant. net (62. 40. 98. 152) 137. 941 ms 151. 570 ms 138. 500 ms 13 renater-lb 1 -gw. mx 1. par. fr. geant. net (62. 40. 124. 70) 141. 070 ms 127. 188 ms 141. 391 ms 14 193. 51. 179. 206 (193. 51. 179. 206) 149. 290 ms 161. 511 ms 160. 987 ms 15 193. 51. 179. 213 (193. 51. 179. 213) 143. 251 ms 158. 927 ms 143. 648 ms 16 * * means no response (probe lost, router not replying) * Do some traceroutes from exotic countries at www. traceroute. org

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

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) linkpipe capacity that can carry Rc bits/sec fluid at rate Rc bits/sec)

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-end path that constrains end-end throughput

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

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. 6 networks under attack: security 1. 7 history

What’s the Internet: “nuts and bolts” view mobile network v protocols control sending, receiving of msgs § e. g. , HTTP, Skype, TCP, IP, 802. 11 v global ISP home network Internet standards § RFC: Request for comments § IETF: Internet Engineering Task Force institutional network regional ISP

What’s a protocol? human protocols: v v v “what’s the time? ” “I have a question” introductions … specific msgs sent … in a specific order … 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

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 format, order of msgs, and actions

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?

Organization of air travel ticket (purchase) ticket (complain) baggage (check) baggage (claim) gates (load) gates (unload) runway takeoff runway landing airplane routing v a series of steps

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

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 v layering considered harmful?

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 § Ethernet, 802. 111 (Wi. Fi), PPP v physical: bits “on the wire” application transport network link physical

ISO/OSI reference model presentation: allow applications to interpret meaning of data, e. g. , encryption, compression, machine-specific conventions v session: synchronization, checkpointing, recovery of data exchange v Internet stack “missing” these layers! v § these services, if needed, must be implemented in application § needed? application presentation session transport network link physical

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 Hn Ht Hl Hn Ht M M network link physical Hn Ht M router

Advanced topic (optional) v Packet sniffer and analyzer § tcpdump (command) • > tcpdump –i en 0 • > tcpdump -i en 0 -c 10 -w test. cap • > tcpdump –r test. cap • More usage via Google “ tcpdump” § Wireshark (UI)

Chapter 1: Overview v what’s the Internet? v network edge § hosts, access net, physical media v network core § packet/circuit switching, Internet structure v performance: v what’s loss, delay, throughput a protocol? v protocol layers, service models

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. 6 networks under attack: security 1. 7 history (optional)

Internet history 1980 -1990: new protocols, a proliferation of networks v v v 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 v v new national networks: Csnet, BITnet, NSFnet, Minitel 100, 000 hosts connected to confederation of networks

Internet history 1990, 2000’s: commercialization, the Web, new apps v early 1990’s: ARPAnet late 1990’s – 2000’s: decommissioned v more killer apps: instant v 1991: NSF lifts restrictions on messaging, P 2 P file commercial use of NSFnet sharing (decommissioned, 1995) v network security to v early 1990 s: Web forefront § hypertext [Bush 1945, v est. 50 million host, 100 Nelson 1960’s] million+ users § HTML, HTTP: Berners-Lee v backbone links running at Gbps § 1994: Mosaic, later Netscape § late 1990’s: commercialization of the Web

Internet history 2005 -present v ~750 million hosts § v v v Smartphones and tablets Aggressive deployment of broadband access Increasing ubiquity of high-speed wireless access Emergence of online social networks: § Facebook: soon one billion users v v Service providers (Google, Microsoft) create their own networks § Bypass Internet, providing “instantaneous” access to search, emai, etc. E-commerce, universities, enterprises running their services in “cloud” (eg, Amazon EC 2)

Introduction: summary covered a “ton” of material! v v v v Internet overview what’s a protocol? network edge, core, access network § packet-switching versus circuit-switching § Internet structure performance: loss, delay, throughput layering, service models security history you now have: v v context, overview, “feel” of networking more depth, detail to follow!