1 Computer Networks: Internet InfrastructureRajesh Palit, Ph.D. North South University, Dhaka
2 Chapter 1: introductionour goal: get “feel” and terminology more depth, detail later in course approach: use Internet as example overview: what’s the Internet? what’s a protocol? network edge; hosts, access net, physical media network core: packet/circuit switching, Internet structure performance: loss, delay, throughput security protocol layers, service models history Introduction
3 Chapter 1: roadmap 1.1 what is the Internet? 1.2 network edgeend 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 Introduction
4 What’s the Internet: “nuts and bolts” viewsmartphone PC server wireless laptop millions of connected computing devices: hosts = end systems running network apps mobile network global ISP regional ISP home network institutional communication links fiber, copper, radio, satellite transmission rate: bandwidth wired links wireless Packet switches: forward packets (chunks of data) routers and switches router Introduction 4
5 “Fun” internet appliancesWeb-enabled toaster + weather forecaster IP picture frame Tweet-a-watt: monitor energy use Slingbox: watch, control cable TV remotely Internet refrigerator Internet phones Introduction
6 What’s the Internet: “nuts and bolts” viewmobile network global ISP regional ISP home network institutional Internet: “network of networks” Interconnected ISPs protocols control sending, receiving of msgs e.g., TCP, IP, HTTP, Skype, Internet standards RFC: Request for comments IETF: Internet Engineering Task Force Introduction
7 What’s the Internet: a service viewInfrastructure that provides services to applications: Web, VoIP, , games, e-commerce, social nets, … provides programming interface to apps hooks that allow sending and receiving app programs to “connect” to Internet provides service options, analogous to postal service mobile network global ISP regional ISP home network institutional Introduction
8 What’s a protocol? human protocols: network protocols:“what’s the time?” “I have a question” introductions … specific msgs sent … specific actions taken when msgs received, or other events network protocols: machines rather than humans all communication activity in Internet governed by protocols protocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt Introduction
9 What’s a protocol? a human protocol and a computer network protocol:Hi TCP connection request Hi TCP connection response Got the time? Get 2:00
10 Chapter 1: roadmap 1.1 what is the Internet? 1.2 network edgeend 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 Introduction 10
11 A closer look at network structure:network edge: hosts: clients and servers servers often in data centers mobile network global ISP regional ISP home network institutional access networks, physical media: wired, wireless communication links network core: interconnected routers network of networks Introduction
12 Access networks and physical mediaQ: How to connect end systems to edge router? residential access nets institutional access networks (school, company) mobile access networks keep in mind: bandwidth (bits per second) of access network? shared or dedicated? Introduction
13 Access net: digital subscriber line (DSL)central office telephone network voice, data transmitted at different frequencies over dedicated line to central office DSL modem splitter DSLAM DSL access multiplexer ISP 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) Introduction
14 Access net: cable networkcable headend … cable modem splitter Channels V I D E O A T C N R L 1 2 3 4 5 6 7 8 9 frequency division multiplexing: different channels transmitted in different frequency bands Introduction
15 Access net: cable networkcable headend … data, TV transmitted at different frequencies over shared cable distribution network cable modem splitter cable modem termination system CMTS ISP HFC: hybrid fiber coax asymmetric: up to 30Mbps downstream transmission rate, 2 Mbps upstream transmission rate network of cable, fiber attaches homes to ISP router homes share access network to cable headend unlike DSL, which has dedicated access to central office Introduction
16 to/from headend or central officeAccess net: home network wireless devices to/from headend or central office often combined in single box wireless access point (54 Mbps) router, firewall, NAT cable or DSL modem wired Ethernet (100 Mbps) Introduction
17 Enterprise access networks (Ethernet)institutional link to ISP (Internet) institutional router Ethernet switch institutional mail, web servers typically used in companies, universities, etc 10 Mbps, 100Mbps, 1Gbps, 10Gbps transmission rates today, end systems typically connect into Ethernet switch Introduction
18 Wireless access networksshared wireless access network connects end system to router via base station aka “access point” wide-area wireless access provided by telco (cellular) operator, 10’s km between 1 and 10 Mbps 3G, 4G: LTE wireless LANs: within building (100 ft) 802.11b/g (WiFi): 11, 54 Mbps transmission rate to Internet to Internet Introduction
19 Host: sends packets of datahost sending function: takes application message breaks into smaller chunks, known as packets, of length L bits transmits packet into access network at transmission rate R link transmission rate, aka link capacity, aka link bandwidth two packets, L bits each 2 1 R: link transmission rate host L (bits) R (bits/sec) packet transmission delay time needed to transmit L-bit packet into link = =
20 Physical media bit: propagates between transmitter/receiver pairsphysical link: what lies between transmitter & receiver guided media: signals propagate in solid media: copper, fiber, coax unguided media: signals propagate freely, e.g., radio twisted pair (TP) two insulated copper wires Category 5: 100 Mbps, 1 Gpbs Ethernet Category 6: 10Gbps Introduction
21 Physical media: coax, fibercoaxial cable: two concentric copper conductors bidirectional broadband: multiple channels on cable HFC fiber optic cable: glass fiber carrying light pulses, each pulse a bit high-speed operation: high-speed point-to-point transmission (e.g., 10’s-100’s Gpbs transmission rate) low error rate: repeaters spaced far apart immune to electromagnetic noise Introduction
22 Physical media: radio radio link types:terrestrial microwave e.g. up to 45 Mbps channels LAN (e.g., WiFi) 11Mbps, 54 Mbps wide-area (e.g., cellular) 3G cellular: ~ few Mbps satellite Kbps to 45Mbps channel (or multiple smaller channels) 270 msec end-end delay geosynchronous versus low altitude signal carried in electromagnetic spectrum no physical “wire” bidirectional propagation environment effects: reflection obstruction by objects interference Introduction
23 Chapter 1: roadmap 1.1 what is the Internet? 1.2 network edgeend 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 Introduction 23
24 The network core mesh of interconnected routerspacket-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 Introduction
25 Packet-switching: store-and-forwardL bits per packet 3 2 1 source destination R bps 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 one-hop numerical example: L = 7.5 Mbits R = 1.5 Mbps one-hop transmission delay = 5 sec end-end delay = 2L/R (assuming zero propagation delay) more on delay shortly … Introduction
26 Packet Switching: queueing delay, lossR = 100 Mb/s D R = 1.5 Mb/s B E queue of packets waiting for output link queuing and loss: If arrival rate (in bits) to link exceeds transmission rate of link for a period of time: packets will queue, wait to be transmitted on link packets can be dropped (lost) if memory (buffer) fills up Introduction
27 Two key network-core functionsrouting: determines source- destination 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 1 1 2 3 0111 dest address in arriving packet’s header Network Layer
28 Alternative core: circuit switchingend-end resources allocated to, reserved for “call” between source & dest: In diagram, each link has four circuits. call gets 2nd circuit in top link and 1st 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 telephone networks Introduction
29 Packet switching versus circuit switchingpacket switching allows more users to use network! example: 1 Mb/s link each user: 100 kb/s when “active” active 10% of time circuit-switching: 10 users packet switching: with 35 users, probability > 10 active at same time is less than * ….. N users 1 Mbps link Q: how did we get value ? Q: what happens if > 35 users ? * Check out the online interactive exercises for more examples Introduction
30 Packet switching versus circuit switchingis packet switching a “slam dunk winner?” great for bursty data resource sharing simpler, no call setup 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)? Introduction
31 Internet structure: network of networksEnd systems connect to Internet via access ISPs (Internet Service Providers) Residential, company and university ISPs Access ISPs in turn must be interconnected. So that any two hosts can send packets to each other Resulting network of networks is very complex Evolution was driven by economics and national policies Let’s take a stepwise approach to describe current Internet structure
32 Internet structure: network of networksQuestion: given millions of access ISPs, how to connect them together? access net …
33 Internet structure: network of networksOption: connect each access ISP to every other access ISP? access net … … connecting each access ISP to each other directly doesn’t scale: O(N2) connections.
34 Internet structure: network of networksOption: connect each access ISP to a global transit ISP? Customer and provider ISPs have economic agreement. access net … global ISP
35 Internet structure: network of networksBut if one global ISP is viable business, there will be competitors …. access net … ISP A ISP B ISP C
36 Internet structure: network of networks… and regional networks may arise to connect access nets to ISPS access net … ISP A IXP IXP ISP B ISP C regional net
37 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 … ISP A IXP Content provider network IXP ISP B ISP B regional net
38 Internet structure: network of networksaccess ISP Regional ISP IXP Tier 1 ISP Google 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
39 Chapter 1: roadmap 1.1 what is the Internet? 1.2 network edgeend 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 Introduction 39
40 How do loss and delay occur?packets queue in router buffers packet arrival rate to link (temporarily) exceeds output link capacity packets queue, wait for turn packet being transmitted (delay) A free (available) buffers: arriving packets dropped (loss) if no free buffers B packets queueing (delay) Introduction
41 Four sources of packet delaytransmission 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
42 Four sources of packet delaytransmission 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 dprop: propagation delay: d: length of physical link s: propagation speed in medium (~2x108 m/sec) dprop = d/s dtrans and dprop very different * Check out the Java applet for an interactive animation on trans vs. prop delay Introduction 42
43 Queueing delay (revisited)R: link bandwidth (bps) L: packet length (bits) a: average packet arrival rate average queueing delay traffic intensity = La/R 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! La/R ~ 0 * Check out the Java applet for an interactive animation on queuing and loss La/R -> 1 Introduction
44 Packet loss queue (aka buffer) preceding link in buffer has finite capacity packet arriving to full queue dropped (aka lost) lost packet may be retransmitted by previous node, by source end system, or not at all buffer (waiting area) packet being transmitted A B packet arriving to full buffer is lost * Check out the Java applet for an interactive animation on queuing and loss Introduction
45 Throughput throughput: rate (bits/time unit) at which bits transferred between sender/receiver instantaneous: rate at given point in time average: rate over longer period of time server, with file of F bits to send to client link capacity Rs bits/sec server sends bits (fluid) into pipe pipe that can carry fluid at rate Rs bits/sec) Rc bits/sec) link capacity Rc bits/sec Introduction
46 Throughput (more) Rs < Rc What is average end-end throughput?Rc bits/sec Rs bits/sec Rs > Rc What is average end-end throughput? Rs bits/sec Rc bits/sec link on end-end path that constrains end-end throughput bottleneck link Introduction
47 Throughput: Internet scenarioper-connection end-end throughput: min(Rc,Rs,R/10) in practice: Rc or Rs is often bottleneck Rs Rs Rs R Rc Rc Rc 10 connections (fairly) share backbone bottleneck link R bits/sec Introduction
48 Chapter 1: roadmap 1.1 what is the Internet? 1.2 network edgeend 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 Introduction 48
49 Protocol “layers” Question: 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
50 Layering of airline functionalityticket (purchase) baggage (check) gates (load) runway (takeoff) airplane routing departure airport arrival intermediate air-traffic control centers ticket (complain) baggage (claim gates (unload) runway (land) ticket baggage gate takeoff/landing layers: each layer implements a service via its own internal-layer actions relying on services provided by layer below Introduction
51 Why layering? dealing with complex systems:explicit structure allows identification, relationship of complex system’s pieces layered reference model for discussion modularization eases maintenance, updating of system change of implementation of layer’s service transparent to rest of system e.g., change in gate procedure doesn’t affect rest of system layering considered harmful? Introduction
52 Internet protocol stackapplication: supporting network applications FTP, SMTP, HTTP transport: process-process data transfer TCP, UDP network: routing of datagrams from source to destination IP, routing protocols link: data transfer between neighboring network elements Ethernet, (WiFi), PPP physical: bits “on the wire” application transport network link physical Introduction
53 ISO/OSI reference modelpresentation: allow applications to interpret meaning of data, e.g., encryption, compression, machine-specific conventions session: synchronization, checkpointing, recovery of data exchange Internet stack “missing” these layers! these services, if needed, must be implemented in application needed? application presentation session transport network link physical Introduction
54 Encapsulation source destination application transport network linkmessage M application transport network link physical segment Ht M Ht datagram Ht Hn M Hn frame Ht Hn Hl M link physical switch destination network link physical Ht Hn M Ht Hn Hl M M application transport network link physical Ht Hn M Ht M Ht Hn M router Ht Hn Hl M Introduction
55 Chapter 1: roadmap 1.1 what is the Internet? 1.2 network edgeend 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 Introduction 55
56 Network security field of network security:how bad guys can attack computer networks how we can defend networks against attacks how to design architectures that are immune to attacks Internet not originally designed with (much) security in mind original vision: “a group of mutually trusting users attached to a transparent network” Internet protocol designers playing “catch-up” security considerations in all layers! Introduction
57 Bad guys: put malware into hosts via Internetmalware can get in host from: virus: self-replicating infection by receiving/executing object (e.g., attachment) worm: self-replicating infection by passively receiving object that gets itself executed spyware malware can record keystrokes, web sites visited, upload info to collection site infected host can be enrolled in botnet, used for spam. DDoS attacks Introduction
58 Bad guys: attack server, network infrastructureDenial of Service (DoS): attackers make resources (server, bandwidth) unavailable to legitimate traffic by overwhelming resource with bogus traffic 1. select target 2. break into hosts around the network (see botnet) target 3. send packets to target from compromised hosts Introduction
59 Bad guys can sniff packetspacket “sniffing”: broadcast media (shared ethernet, wireless) promiscuous network interface reads/records all packets (e.g., including passwords!) passing by A C src:B dest:A payload B wireshark software used for end-of-chapter labs is a (free) packet-sniffer Introduction
60 Bad guys can use fake addressesIP spoofing: send packet with false source address A C src:B dest:A payload B … lots more on security (throughout, Chapter 8) Introduction
61 Chapter 1: roadmap 1.1 what is the Internet? 1.2 network edgeend 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 Introduction 61
62 Internet history 1961-1972: Early packet-switching principles1961: Kleinrock - queueing theory shows effectiveness of packet-switching 1964: Baran - packet-switching in military nets 1967: ARPAnet conceived by Advanced Research Projects Agency 1969: first ARPAnet node operational 1972: ARPAnet public demo NCP (Network Control Protocol) first host-host protocol first program ARPAnet has 15 nodes Introduction
63 Internet history 1972-1980: Internetworking, new and proprietary nets1970: ALOHAnet satellite network in Hawaii 1974: Cerf and Kahn - architecture for interconnecting networks 1976: Ethernet at Xerox PARC late70’s: proprietary architectures: DECnet, SNA, XNA late 70’s: switching fixed length packets (ATM precursor) 1979: ARPAnet has 200 nodes Cerf and Kahn’s internetworking principles: minimalism, autonomy - no internal changes required to interconnect networks best effort service model stateless routers decentralized control define today’s Internet architecture Introduction
64 Internet history 1980-1990: new protocols, a proliferation of networks1983: deployment of TCP/IP 1982: smtp protocol defined 1983: DNS defined for name-to-IP-address translation 1985: ftp protocol defined 1988: TCP congestion control new national networks: Csnet, BITnet, NSFnet, Minitel 100,000 hosts connected to confederation of networks Introduction
65 Internet history 1990, 2000’s: commercialization, the Web, new appsearly 1990’s: ARPAnet decommissioned 1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995) 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: more killer apps: instant messaging, P2P file sharing network security to forefront est. 50 million host, 100 million+ users backbone links running at Gbps Introduction
66 Internet history 2005-present ~750 million hostsSmartphones and tablets Aggressive deployment of broadband access Increasing ubiquity of high-speed wireless access Emergence of online social networks: Facebook: soon one billion users 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 EC2) Introduction