Internet: A Brief Overview. Chapter 1

Inter: 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 Inter as example overview: v what s the Inter? v what s a protocol? v work edge; hosts,, physical media v work core: packet/circuit switching, Inter structure v performance: loss, delay, throughput v protocol layers, service models

Chapter 1: roadmap 1.1 what is the Inter? 1.2 work edge end systems, works, links 1.3 work core packet switching, circuit switching, work structure 1.4 delay, loss, throughput in works 1.5 protocol, protocol layers, service models

What is the Inter?

What s the Inter: a service view v Infrastructure that provides services to applications: Web, VoIP, email, games, e- commerce, social s, v provides programming interface to apps hooks that allow sending and receiving app programs to connect to Inter provides service options, analogous to postal service mobile work home work institutional work global ISP regional ISP

What s the Inter: nuts and bolts view mobile work v Inter = work of works Interconnected ISPs Interconnected works home work global ISP regional ISP institutional work

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

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

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

Access works and physical media Access work: connect end systems (hosts) to edge routers Q: How to connect end systems to edge router? v residential s v institutional works (school, company) v mobile works keep in mind: v bandwidth (bits per second) of work? v shared or dedicated?

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

Common Access Network v Cable work v Digital subscriber line (DSL) v Home WiFi Network v Cellular (mobile) work v Ether v Fiber (optics work) v v Optional, read Chapter 1.2 for details

Access : digital subscriber line (DSL) central office telephone work DSL modem splitter voice, data transmitted at different frequencies over dedicated line to central office DSLAM DSL multiplexer ISP v use existing telephone line to central office DSLAM data over DSL phone line goes to Inter voice over DSL phone line goes to telephone v < 2.5 Mbps upstream transmission rate (typically < 1 Mbps) v < 24 Mbps downstream transmission rate (typically < 10 Mbps)

Access : cable work 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

Access : cable work cable headend cable modem splitter data, TV transmitted at different frequencies over shared cable distribution work CMTS cable modem termination system ISP v HFC: hybrid fiber coax asymmetric: up to 30Mbps downstream transmission rate, 2 Mbps upstream transmission rate v work of cable, fiber attaches homes to ISP router homes share work to cable headend unlike DSL, which has dedicated to central office

Access : home work wireless devices often combined in single box to/from headend or central office cable or DSL modem wireless point (54 Mbps) router, firewall, NAT wired Ether (100 Mbps)

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

Wireless works v shared wireless work connects end system to router via base station aka point wireless LANs: within building (100 ft) 802.11a/b/g (WiFi): 11, 54 Mbps transmission rate 802 11n/ac: hundreds of Mbps wide-area wireless provided by telco (cellular) operator, 10 s km between 1 and 10 Mbps 3G, 4G LTE LTE: ideally 100-300 Mbps to Inter to Inter

Physical media v bit: propagates between transmitter/receiver pairs v physical link: what lies between transmitter & receiver v guided media: signals propagate in solid media: copper, fiber, coax v unguided media: signals propagate freely, e.g., radio twisted pair (TP) v two insulated copper wires Category 5: 100 Mbps, 1 Gpbs Ether Category 6: 10Gbps

Physical media: coax, fiber coaxial cable: v two concentric copper conductors v bidirectional v broadband: multiple channels on cable HFC fiber optic cable: v glass fiber carrying light pulses, each pulse a bit v 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 electromagic noise

Physical media: radio v signal carried in electromagic spectrum v no physical wire v bidirectional v 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., WiFi) 11Mbps, 54 Mbps v wide-area (e.g., cellular) 3G cellular: ~ few Mbps v satellite Kbps to 45Mbps channel (or multiple smaller channels) 270 msec end-end delay geosynchronous versus low altitude

A So7ware- View mobile work v protocols control sending, receiving of msgs e.g., HTTP, Skype, TCP, IP, 802.11 v Inter standards RFC: Request for comments IETF: Inter Engineering Task Force home work global ISP regional ISP institutional work

What s a protocol? human protocols: v what s the time? v I have a question v introductions specific msgs sent in a specific order specific actions taken when msgs received, or other events work protocols: v machines rather than humans v all communication activity in Inter governed by protocols protocols define format, order of msgs sent and received among work entities, and actions taken on msg transmission, receipt

What s a protocol? a human protocol and a computer work protocol: Hi Hi Got the time? 2:00 time TCP connection request TCP connection response Get http://www.awl.com/kurose-ross <file> format, order of msgs, and actions

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

Two key work-core functions routing: determines sourcedestination route taken by packets routing algorithms forwarding: move packets from router s input to appropriate router output routing algorithm local forwarding table header value output link 0100 0101 0111 1001 3 2 2 1 3 2 1 dest address in arriving packet s header

Network core: Packet-switching 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 funcoon: v takes applicaoon message v breaks into smaller chunks, known as packets, of length L bits v transmits packet into work at transmission rate R link transmission rate, aka link capacity, aka link bandwidth 2 host 1 two packets, L bits each R: link transmission rate packet transmission delay time needed to transmit L-bit packet into link = = L (bits) R (bits/sec)

Packet-switching: store-and-forward L bits per packet source 3 2 1 R bps R bps desonaoon v 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-end delay = 2L/R (assuming zero propagation delay) 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 Example: 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) v Commonly used in traditional telephone works

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

Announcements v No class next week Online video lectures v HW1 is assigned today Due: Sep 16 (Tue)

Recap v Inter: hosts, communication links, routers, switches v Network edge Access works 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 work! example: 1 Mb/s link each user: 100 kb/s when active active 10% of time.. N users 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

More on how to calculate N? v Given N users, the probability that x users are active is P(N,x) P(N, x) = ( N x )px (1 p) N x v In order to afford N users, the probability that more than 11 (including 11) users are active at the same should be extremely small (e.g., < 0.1%) v Therefore, 10 P(N, x) (1 0.1%) = 0.999 x=0

More on how to calculate N? v Given N, we can obtain the probability of no more than x active users at the same time Calculator Program (sum them up) v Given the maximal probability of no more than x active users at the same time, how to calculate N? Approach #1: program (for loop, and increment N by 1 until it meets the threshold) Approach #2: Approximation via central limit theorem (optional)

More on how to calculate N? v Step 0: Xi: random variable, status of user i Xi = 1: user i is active Xi = 0: user i is not active P(Xi =1) = p = 0.1, P(Xi = 0) = 0.9 µ = E(Xi) =1* P(Xi =1)+ 0 * P(Xi = 0) = p σ 2 = Var(Xi) = E[(Xi E(Xi)) 2 ] = p(1 p) 2 + (1 p)p 2 = p(1 p) v Step 1: Z = sum(xi), another random variable The number of active users, given N users in total

v Step II: Z conforms to normal distribuoon Xi is iid (Independent and idenocally distributed) Central limit theorem µz = E[Z] = Np σ z 2 = Var(Z) = Np(1 p) Z conforms to normal distribuoon (Np, Np(1 p)) v Step III: look up the cumulaove distribuoon funcoon (CDF) for a normal distribuoon Given P(Z<= 10) > 99.9% Let us look up the standard normal distribuoon, we have (for simplicity) P(Z <= µz + 3σ z) > 99.9% Then, we have and then calculate N https://www.stat.tamu.edu/~lzhou/stat302/standardnormaltable.pdf µz + 3σ z 10

Packet switching versus circuit switching is packet switching a slam dunk winner? v great for bursty data resource sharing simpler, no call setup v excessive congestion possible: packet delay and loss protocols needed for reliable data transfer, congestion control Q: How to provide circuit-like behavior? bandwidth guarantees needed for audio/video apps still an unsolved problem (chapter 7) Q: human analogies of reserved resources (circuit switching) versus on-demand allocation (packet-switching)?

Packet switching versus circuit switching is packet switching a slam dunk winner? v great for bursty data resource sharing simpler, no call setup v 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)?

Inter structure: work of works (Read 1.3.3) v End systems connect to Inter via ISPs (Inter 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 work of works is very complex v Evolution was driven by economics and national policies v Let s take a stepwise approach to describe current Inter structure

Inter structure: work of works Question: given millions of ISPs, how to connect them together?

Inter structure: work of works Option: connect each ISP to every other ISP? connecting each ISP to each other directly doesn t scale: O(N 2 ) connections.

Inter structure: work of works Option: connect each ISP to a global transit ISP? Customer and provider ISPs have economic agreement. global ISP

Inter structure: work of works But if one global ISP is viable business, there will be competitors. ISP A ISP B ISP C

Inter structure: work of works But if one global ISP is viable business, there will be competitors. which must be interconnected Inter exchange point ISP A IXP IXP ISP B ISP C peering link

Inter structure: work of works and regional works may arise to connect s to ISPS ISP A IXP IXP ISP B ISP C regional

Inter structure: work of works and content provider works (e.g., Google, Microsoft, Akamai ) may run their own work, to bring services, content close to end users ISP A ISP B ISP B IXP Content provider work IXP regional

Inter structure: work of works Tier 1 ISP Tier 1 ISP Google IXP Regional ISP IXP Regional ISP IXP ISP ISP ISP ISP ISP ISP ISP ISP v at center: small # of well-connected large works tier-1 commercial ISPs (e.g., Level 3, Sprint, AT&T, NTT), national & international coverage content provider work (e.g, Google): private work that connects it data centers to Inter, often bypassing tier-1, regional ISPs

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

Host: sends packets of data (Recap) host sending funcoon: v takes applicaoon message v breaks into smaller chunks, known as packets, of length L bits v transmits packet into work at transmission rate R link transmission rate, aka link capacity, aka link bandwidth 2 host 1 two packets, L bits each R: link transmission rate packet transmission delay time needed to transmit L-bit packet into link = = L (bits) R (bits/sec)

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

Packet Switching: queuing delay, loss A R = 100 Mb/s C B queue of packets waiting for output link R = 1.5 Mb/s 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

How do loss and delay occur? packets queue in router buffers v packet arrival rate to link (temporarily) exceeds output link capacity v 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 A transmission propagation B nodal processing queueing d nodal = d proc + d queue + d trans + d prop d proc : nodal processing check bit errors determine output link typically < msec d queue : queueing delay time waiting at output link for transmission depends on congestion level of router

Four sources of packet delay A transmission propagation B nodal processing queueing d trans : transmission delay: d nodal = d proc + d queue + d trans + d prop L: packet length (bits) R: link bandwidth (bps) d trans = L/R d trans and d prop very different d prop : propagation delay: d: length of physical link s: propagation speed in medium (~2x10 8 m/sec) d prop = d/s * Check out the Java applet for an interactive animation on trans vs. prop delay

Caravan analogy ten-car caravan toll booth 100 km 100 km toll booth v cars propagate at 100 km/hr v toll booth takes 12 sec to service car (bit transmission time) v car~bit; caravan ~ packet v 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

Caravan analogy (more) 100 km 100 km ten-car caravan toll booth toll booth v suppose cars now propagate at 1000 km/hr v and suppose toll booth now takes one min to service a car v 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.

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

Real Inter delays and routes v what do real Inter delay & loss look like? v traceroute program: provides delay measurement from source to router along endend Inter 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

Real Inter delays, routes traceroute: www.eurecom.fr 3 delay measurements from ohio-state.edu to gw.cs.ohio-state.edu 1 se4-vl3000..ohio-state.edu (128.146.28.1) 1.795 ms 1.711 ms 1.432 ms 2 tc1-forg2-4..ohio-state.edu (164.107.2.190) 1.435 ms 1.793 ms 1.481 ms 3 tc6-teng2-1..ohio-state.edu (164.107.2.254) 1.559 ms 1.588 ms 1.534 ms 4 clmbt-r9-xe-0-0-2s333.bb.oar. (192.148.242.205) 1.503 ms 3.233 ms 1.632 ms 5 clmbk-r9-xe-1-1-0s101.core.oar. (192.153.38.37) 1.488 ms 3.239 ms 3.435 ms 6 clmbn-r0-xe-1-2-0s101.core.oar. (192.153.38.25) 2.971 ms 2.185 ms 1.773 ms 7 clmbn-r5-xe-4-2-0s101.core.oar. (192.153.38.13) 2.170 ms 2.024 ms 3.183 ms 8 clevs-r5-et-1-0-0s101.core.oar. (192.153.39.254) 6.488 ms 5.860 ms 6.281 ms * Do some traceroutes from exotic countries at www.traceroute.org trans-oceanic link 9 192.88.192.238 (192.88.192.238) 14.380 ms 15.203 ms 15.322 ms 10 abilene-wash.mx1.fra.de.geant. (62.40.125.17) 137.013 ms 128.416 ms 135.878 ms 11 ae1.mx1.gen.ch.geant. (62.40.98.108) 130.484 ms 144.101 ms 130.697 ms 12 ae4.mx1.par.fr.geant. (62.40.98.152) 137.941 ms 151.570 ms 138.500 ms 13 renater-lb1-gw.mx1.par.fr.geant. (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)

Packet loss v 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 A buffer (waiting area) 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 server, sends with bits (fluid) file of into F bits pipe to send to client link pipe capacity R s bits/sec that can carry fluid at rate R s bits/sec) link pipe capacity R c bits/sec that can carry fluid at rate R c bits/sec)

Throughput (more) v R s < R c What is average end-end throughput? R s bits/sec R c bits/sec v R s > R c What is average end-end throughput? R s bits/sec R c bits/sec bottleneck link link on end-end path that constrains end-end throughput

Throughput: Inter scenario v per-connection endend throughput: min(r c,r s,r/10) v in practice: R c or R s is often bottleneck R s R s R s R R c R c R c 10 connections (fairly) share backbone bottleneck link R bits/sec

What s the Inter: nuts and bolts view mobile work v protocols control sending, receiving of msgs e.g., HTTP, Skype, TCP, IP, 802.11 v Inter standards RFC: Request for comments IETF: Inter Engineering Task Force home work global ISP regional ISP institutional work

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 work?. or at least our discussion of works?

Organization of air travel ticket (purchase) baggage (check) gates (load) runway takeoff airplane routing airplane routing ticket (complain) baggage (claim) gates (unload) 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 airplane routing airplane routing airplane routing airplane routing departure airport 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?

Inter protocol stack v application: supporting work applications FTP, SMTP, HTTP v transport: process-process data transfer TCP, UDP v work: routing of datagrams from source to destination IP, routing protocols v link: data transfer between neighboring work elements Ether, 802.111 (WiFi), PPP v physical: bits on the wire application transport work link physical

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

segment datagram frame message H l H t H n H t H n H t M M M M source application transport work link physical Encapsulation link physical switch H l H n H n H t H t H t M M M M destination application transport work link physical H l H n H n H t H t M M work link physical H n H t M router

Advanced topic (optional) v Packet sniffer and analyzer tcpdump (command) > tcpdump i en0 > tcpdump -i en0 -c 10 -w test.cap > tcpdump r test.cap More usage via Google tcpdump Wireshark (UI)

Chapter 1: Overview v what s the Inter? v work edge hosts,, physical media v work core packet/circuit switching, Inter structure v performance: loss, delay, throughput v what s a protocol? v protocol layers, service models

Inter history 1980-1990: new protocols, a proliferation of works v 1983: deployment of TCP/ IP v 1982: smtp e-mail protocol defined v 1983: DNS defined for name-to-ip-address translation v 1985: ftp protocol defined v 1988: TCP congestion control v new national works: Cs, BIT, NSF, Minitel v 100,000 hosts connected to confederation of works

Inter history 1990, 2000 s: commercialization, the Web, new apps v early 1990 s: ARPA decommissioned v 1991: NSF lifts restrictions on commercial use of NSF (decommissioned, 1995) v early 1990s: Web hypertext [Bush 1945, Nelson 1960 s] HTML, HTTP: Berners-Lee 1994: Mosaic, later Netscape late 1990 s: commercialization of the Web late 1990 s 2000 s: v more killer apps: instant messaging, P2P file sharing v work security to forefront v est. 50 million host, 100 million+ users v backbone links running at Gbps

Inter history 2005-present v ~750 million hosts Smartphones and tablets v Aggressive deployment of broadband v Increasing ubiquity of high-speed wireless v Emergence of online social works: Facebook: soon one billion users v Service providers (Google, Microsoft) create their own works Bypass Inter, providing instantaneous to search, emai, etc. v E-commerce, universities, enterprises running their services in cloud (eg, Amazon EC2)

Introduction: summary covered a ton of material! v Inter overview v what s a protocol? v work edge, core, work packet-switching versus circuit-switching Inter structure v performance: loss, delay, throughput v layering, service models v security v history you now have: v context, overview, feel of working v more depth, detail to follow!