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CEN604 Computer Networks Dr. Ibrahim Alsukayti [email protected] About the Course Credit Hours: 3 Mon (12:30-2:10 pm), Mon (2:30-4:10 pm) Marks: Mid-Term 1: 20% Homework and Quizzes: 10% Project: 20% Final Exam: 50% 1-2 Textbook Computer Networking: A Top Down Approach Jim Kurose, Keith Ross Addison-Wesley More:  Computer Networks: A Systems Approach (Peterson and Davie)  Data Communication and Networking (Behrous A. Forouzan) 1-3 Course Outline  Chapter 1: Computer Networks and The Internet  Chapter 2: Application Layer  Chapter 3: Transport Layer  Chapter 4: Network Layer  Chapter 5: Link Layer  Chapter 6: Wireless and Mobile Networks  Chapter 7: Multimedia Networking  Chapter 8: Security in Computer Networks  Chapter 9: Network Management 1-4 Chapter 1: introduction Chapter goal: Overview/roadmap:  Get “feel,” “big picture,”  What is a Network? introduction to terminology  What is the Internet? more depth, detail later in  Network edge: hosts, access network, course physical media  Network core: packet/circuit switching, internet structure  Performance: loss, delay, throughput  Protocol layers, service models  History Introduction: 1-5 Chapter 1: introduction What is a Network? Some Network types:  A network is a set of devices  Telephone networks (nodes) connected together handle a particular kind of data (voice) by communication links for connect special-purpose devices data transmission and  Cable TV networks sharing resources. handle a particular kind of data (video) a computer, printer, or any other device capable of sending connect special-purpose devices and/or receiving data  Computer Networks Text, voice, video general-purpose programmable hardware a wide range of applications Introduction: 1-6 Chapter 1: introduction A Data Communication System has five main components:  Data message  Sender  Receiver  Medium  Protocol Introduction: 1-7 Chapter 1: introduction The postal system involves:  Sender => Recipient: Addressing  Packages: Addressed (name, address)  POs Hierarchy: Local  Regional  Large packages divided Central  Local POs: connect to local destinations  POs redirect packages according to destination  Regional POs: interconnect local POs Store and send  Central POs: Use part of address (zip code) interconnect Reg. POs Each PO has a specific area to service Gateway to global couriers  Contents of packages: handled by  Access and Core: sender & recipients only (end-to-end) Access: parts we access (src/dst  local POs) Brocken: ask for replacement Core: parts managed by postal service provides Action on content  Delivery: Cars, Vans, Trucks, Plane  All are done following standards Speed Specific and agreed ways for processing Capacity Addressing, redirection, content Introduction: 1-8 Chapter 1: introduction A network can consist of:  two or more computers directly connected by some physical medium (a) point-to-point (c) (b) multiple-access  a set of nodes, each of which is attached to one or more point-to-point links (c) Switched network (d) Interconnection of networks  The Internet is built from a set of interconnected (d) Networks Introduction: 1-9 Chapter 1: introduction Host Network Switch Network Physical Components include:  Host: run user applications  Switch: store and forward data messages Link Router within a network  Router: route data messages from one network to another Access  Access Point: provide wireless connectivity Point  Links: Cable, Fiber, Wireless Introduction: 1-10 Chapter 1: introduction Networks also involve:  Addressing: Each device must have a unique address Used for identifying sources and destinations of communications  Protocols: a set of rules and procedures that enable devices and systems to communicate describes how communication is accomplished between one particular software or hardware element in two or more devices  Data (Applications) Different form of data: text, voice, video, … Data communication over the network is performed for specific application (e.g. email, file download,..) Introduction: 1-11 Chapter 1: introduction Common Examples of Computer Network Applications:  World Wide Web  Email  Online Social Network  Streaming Audio Video  File Sharing  Instant Messaging ……. Introduction: 1-12 The Internet: a “nuts and bolts” view Billions of connected mobile network computing devices: national or global ISP  hosts = end systems  running network apps at Internet’s “edge” Packet switches: forward local or packets (chunks of data) Internet regional ISP  routers, switches home network content Communication links provider network datacenter  fiber, copper, radio, satellite network  transmission rate: bandwidth Networks enterprise  collection of devices, routers, network links: managed by an organization Introduction: 1-13 The Internet: a “nuts and bolts” view mobile network 4G  Internet: “network of networks” national or global ISP Interconnected ISPs  protocols are everywhere Skype IP Streaming video control sending, receiving of messages local or regional ISP e.g., HTTP (Web), streaming video, Skype, TCP, IP, WiFi, 4G, Ethernet home network content provider HTTP network datacenter network Ethernet TCP enterprise network WiFi Introduction: 1-14 What’s a protocol? Human protocols: Network protocols:  Meetings  computers (devices) rather than humans  Classes  all communication activity in Internet  introductions governed by protocols Rules for: Protocols define the format, order of … specific messages sent messages sent and received among … specific actions taken network entities, and actions taken when message received, or other events on message transmission, receipt Introduction: 1-15 Chapter 1: roadmap  What is the Internet?  What is a protocol?  Network edge: hosts, access network, physical media  Network core: packet/circuit switching, internet structure  Performance: loss, delay, throughput  Protocol layers, service models  History Introduction: 1-16 A closer look at Internet structure mobile network Network edge: national or global ISP  hosts: clients and servers  servers often in data centers local or regional ISP home network content provider network datacenter network enterprise network Introduction: 1-17 A closer look at Internet structure mobile network Network edge: national or global ISP  hosts: clients and servers  servers often in data centers local or Access networks, physical media: regional ISP wired, wireless communication links home network content provider network datacenter network enterprise network Introduction: 1-18 A closer look at Internet structure mobile network Network edge: national or global ISP  hosts: clients and servers  servers often in data centers local or Access networks, physical media: regional ISP wired, wireless communication links home network content provider network datacenter Network core: network  interconnected routers  network of networks enterprise network Introduction: 1-19 Access networks and physical media Q: How to connect end systems mobile network national or global ISP to edge router?  residential access nets  institutional access networks (school, company) local or  mobile access networks (WiFi, 4G/5G) regional ISP home network content provider network datacenter network enterprise network Introduction: 1-20 Examples of network types: mobile network national or global ISP local or Internet regional ISP home network content connect hundreds to provider thousands of servers network datacenter together, and to Internet network In companies, universities, etc enterprise network Introduction: 1-21 Links: physical media  bit: propagates between Twisted pair (TP) transmitter/receiver pairs  two insulated copper wires  physical link: what lies Category 5: 100 Mbps, 1 Gbps Ethernet between transmitter & Category 6: 10Gbps Ethernet receiver  guided media: signals propagate in solid media: copper, fiber, coax  unguided media: signals propagate freely, e.g., radio Introduction: 1-22 Links: physical media Coaxial cable: Fiber optic cable:  two concentric copper conductors  glass fiber carrying light pulses, each pulse a bit  bidirectional  high-speed operation:  broadband: high-speed point-to-point multiple frequency channels on cable transmission (10’s-100’s Gbps) 100’s Mbps per channel  low error rate: repeaters spaced far apart immune to electromagnetic noise Introduction: 1-23 Links: physical media Wireless radio Radio link types:  signal carried in various  Wireless LAN (WiFi) “bands” in electromagnetic 10-100’s Mbps; 10’s of meters spectrum  wide-area (e.g., 4G cellular)  no physical “wire” 10’s Mbps over ~10 Km  broadcast, “half-duplex”  Bluetooth: cable replacement (sender to receiver) short distances, limited rates  propagation environment effects:  terrestrial microwave reflection point-to-point; 45 Mbps channels obstruction by objects  satellite Interference/noise up to 45 Mbps per channel 270 msec end-end delay Introduction: 1-24 Host: sends packets of data host sending function:  takes application message  breaks into smaller chunks, two packets, known as packets, of length L bits L bits each  transmits packet into access 2 1 network at transmission rate R link transmission rate, aka link host capacity, aka link bandwidth R: link transmission rate packet time needed to L (bits) transmission = transmit L-bit = delay packet into link R (bits/sec) Introduction: 1-25 Chapter 1: roadmap  What is the Internet?  What is a protocol?  Network edge: hosts, access network, physical media  Network core: packet/circuit switching, internet structure  Performance: loss, delay, throughput  Protocol layers, service models  History Introduction: 1-26 The network core  mesh of interconnected routers mobile network national or global ISP  packet-switching: hosts break data messages into packets network forwards packets from one router to the next, across links on local or regional ISP path from source to destination home network content provider network datacenter network enterprise network Introduction: 1-27 Two key network-core functions routing algorithm Routing: Forwarding: local local forwarding forwarding table table  global action: header value output link determine source-  aka “switching” 0100 3 destination paths  local action: 0101 2 move arriving 0111 1001 2 1 taken by packets packets from  routing algorithms router’s input link 1 to appropriate router output link 3 2 destination address in arriving packet’s header Introduction: 1-28 Packet-switching: store-and-forward L bits per packet 3 2 1 source destination R bps R bps  packet transmission delay: takes L/R seconds to One-hop numerical example: transmit (push out) L-bit packet into link at R bps  L = 10 Kbits  store and forward: entire packet must arrive at  R = 100 Mbps router before it can be transmitted on next link  one-hop transmission delay = 0.1 msec Introduction: 1-29 Packet-switching: queueing R = 100 Mb/s A C D B R = 1.5 Mb/s E queue of packets waiting for transmission over output link Introduction: 1-30 Packet-switching: queueing R = 100 Mb/s A C D B R = 1.5 Mb/s E queue of packets waiting for transmission over output link Packet queuing and loss: if arrival rate (in bps) to link exceeds transmission rate (bps) of link for some period of time:  packets will queue, waiting to be transmitted on output link  packets can be dropped (lost) if memory (buffer) in router fills up Introduction: 1-31 Alternative to packet switching: circuit switching end-end resources allocated to, reserved for “call” between source and destination  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 * Check out the online interactive exercises for more examples: http://gaia.cs.umass.edu/kurose_ross/interactive Introduction: 1-32 Packet switching versus circuit switching Is packet switching a “slam dunk winner”?  great for “bursty” data – sometimes has data to send, but at other times not resource sharing simpler, no call setup  excessive congestion possible: packet delay and loss due to buffer overflow protocols needed for reliable data transfer, congestion control  Q: How to provide circuit-like behavior with packet-switching? “It’s complicated.” We’ll study various techniques that try to make packet switching as “circuit-like” as possible. Q: human analogies of reserved resources (circuit switching) versus on-demand allocation (packet switching)? Introduction: 1-33 Internet structure: a “network of networks” mobile network  hosts connect to Internet via access national or global ISP Internet Service Providers (ISPs)  access ISPs in turn must be interconnected so that any two hosts (anywhere!) local or regional ISP can send packets to each other  resulting network of networks is home network content provider very complex network datacenter network evolution driven by economics, enterprise national policies network Let’s take a stepwise approach to describe current Internet structure Internet structure: a “network of networks” Question: given millions of access ISPs, how to connect them together? access access net net access net access access net net access access net net access access net net access net access net access net access net access access net access net net Introduction: 1-35 Internet structure: a “network of networks” Question: given millions of access ISPs, how to connect them together? access access net net access net access access net net access access net net connecting each access ISP to each other directly doesn’t scale: access access net O(N2) connections. net access net access net access net access net access access net access net net Introduction: 1-36 Internet structure: a “network of networks” Option: connect each access ISP to one global transit ISP? Customer and provider ISPs have economic agreement. access access net net access net access access net net access access net net global access net ISP access net access net access net access net access net access access net access net net Introduction: 1-37 Internet structure: a “network of networks” But if one global ISP is viable business, there will be competitors …. access access net net access net access access net net access access net net ISP A access net ISP B access net access ISP C net access net access net access net access access net access net net Introduction: 1-38 Internet structure: a “network of networks” But if one global ISP is viable business, there will be competitors …. who will want to be connected Internet exchange point access access net net access net access access net net IXP access access net net ISP A access net IXP ISP B access net access ISP C net access net access net peering link access net access access net access net net Introduction: 1-39 Internet structure: a “network of networks” … and regional networks may arise to connect access nets to ISPs access access net net access net access access net net IXP access access net net ISP A access net IXP ISP B access net access ISP C net access net access net regional ISP access net access access net access net net Introduction: 1-40 Internet structure: a “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 access net net access net access access net net IXP access access net net ISP A Content provider network access net IXP ISP B access net access ISP C net access net access net regional ISP access net access access net access net net Introduction: 1-41 Internet structure: a “network of networks” Tier 1 ISP Tier 1 ISP Google IXP IXP IXP Regional ISP Regional ISP access access access access access access access access ISP ISP ISP ISP ISP ISP ISP 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 networks (e.g., Google, Facebook): private network that connects its data centers to Internet, often bypassing tier-1, regional ISPs Introduction: 1-42 Chapter 1: roadmap  What is the Internet?  What is a protocol?  Network edge: hosts, access network, physical media  Network core: packet/circuit switching, internet structure  Performance: loss, delay, throughput  Protocol layers, service models  History Introduction: 1-43 How do packet delay and loss occur?  packets queue in router buffers, waiting for turn for transmission  queue length grows when arrival rate to link (temporarily) exceeds output link capacity  packet loss occurs when memory to hold queued packets fills up packet being transmitted (transmission delay) A B packets in buffers (queueing delay) free (available) buffers: arriving packets dropped (loss) if no free buffers Introduction: 1-44 Packet delay: four sources transmission A propagation B nodal processing queueing dnodal = dproc + dqueue + dtrans + dprop Introduction: 1-45 “Real” Internet delays and routes  what do “real” Internet delay & loss look like?  traceroute program: provides delay measurement from source to router along end-end Internet path towards destination. Introduction: 1-46 Real Internet delays and 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 1 ms 2 ms 3 delay measurements 2 border1-rt-fa5-1-0.gw.umass.edu (128.119.3.145) 1 ms 1 ms 2 ms 3 cht-vbns.gw.umass.edu (128.119.3.130) 6 ms 5 ms 5 ms to border1-rt-fa5-1-0.gw.umass.edu 4 jn1-at1-0-0-19.wor.vbns.net (204.147.132.129) 16 ms 11 ms 13 ms 5 jn1-so7-0-0-0.wae.vbns.net (204.147.136.136) 21 ms 18 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 22 ms 22 ms trans-oceanic link 8 62.40.103.253 (62.40.103.253) 104 ms 109 ms 106 ms 9 de2-1.de1.de.geant.net (62.40.96.129) 109 ms 102 ms 104 ms 10 de.fr1.fr.geant.net (62.40.96.50) 113 ms 121 ms 114 ms looks like delays 11 renater-gw.fr1.fr.geant.net (62.40.103.54) 112 ms 114 ms 112 ms 12 nio-n2.cssi.renater.fr (193.51.206.13) 111 ms 114 ms 116 ms decrease! Why? 13 nice.cssi.renater.fr (195.220.98.102) 123 ms 125 ms 124 ms 14 r3t2-nice.cssi.renater.fr (195.220.98.110) 126 ms 126 ms 124 ms 15 eurecom-valbonne.r3t2.ft.net (193.48.50.54) 135 ms 128 ms 133 ms 16 194.214.211.25 (194.214.211.25) 126 ms 128 ms 126 ms 17 * * * 18 * * * * means no response (probe lost, router not replying) 19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136 ms * Do some traceroutes from exotic countries at www.traceroute.org Introduction: 1-47 Throughput  throughput: rate (bits/time unit) at which bits are being sent from sender to receiver instantaneous: rate at given point in time average: rate over longer period of time link capacity pipe that can carry linkthat pipe capacity can carry Rsfluid bits/sec at rate Rfluid c bits/sec at rate serverserver, sends with bits (fluid) into pipe (Rs bits/sec) (Rc bits/sec) file of F bits to send to client Introduction: 1-48 Throughput: network scenario  per-connection end- Rs end throughput: Rs Rs min(Rc,Rs,R/10)  in practice: Rc or Rs is R often bottleneck Rc Rc Rc * Check out the online interactive exercises for more examples: http://gaia.cs.umass.edu/kurose_ross/ 10 connections (fairly) share backbone bottleneck link R bits/sec Introduction: 1-49 Chapter 1: roadmap  What is the Internet?  What is a protocol?  Network edge: hosts, access network, physical media  Network core: packet/circuit switching, internet structure  Performance: loss, delay, throughput  Protocol layers, service models  History Introduction: 1-50 Protocol “layers” and reference models Networks are complex, Question: is there any with many “pieces”: hope of organizing  hosts structure of network?  routers  links of various media  applications  protocols  hardware, software Introduction: 1-51 Example: Postal System Item preparing Action on item Item packaging & naming Unpacking & checking Addressing Receiving Handing out to Local PO Handing out from Local PO Addressing Delivery Delivery Handing out Delivery There is a structure and a series of steps with specific order Introduction: 1-52 Example: organization of air travel end-to-end transfer of person plus baggage ticket (purchase) ticket (complain) baggage (check) baggage (claim) gates (load) gates (unload) runway takeoff runway landing airplane routing airplane routing airplane routing How would you define/discuss the system of airline travel?  a series of steps, involving many services Introduction: 1-53 Example: organization of air travel ticket (purchase) ticketing service ticket (complain) baggage (check) baggage service baggage (claim) gates (load) gate service gates (unload) runway takeoff runway service runway landing airplane routing routing service airplane routing airplane routing layers: each layer implements a service  via its own internal-layer actions  relying on services provided by layer below Introduction: 1-54 Why layering? Approach to designing/discussing complex systems:  explicit structure allows identification, relationship of system’s pieces layered reference model for discussion  modularization eases maintenance, updating of system change in layer's service implementation: transparent to rest of system e.g., change in gate procedure doesn’t affect rest of system Introduction: 1-55 Layered Internet protocol stack  application: supporting network applications HTTP, IMAP, SMTP, DNS application application  transport: process-process data transfer TCP, UDP transport transport  network: routing of datagrams from source to destination network IP, routing protocols link  link: data transfer between neighboring network elements physical Ethernet, 802.11 (WiFi), PPP  physical: bits “on the wire” Introduction: 1-56 Services, Layering and Encapsulation M application Application exchanges messages to implement some application application service using services of transport layer Ht M transport Transport-layer protocol transfers M (e.g., reliably) from transport one process to another, using services of network layer network  transport-layer protocol encapsulates network application-layer message, M, with link transport layer-layer header Ht to create a link transport-layer segment Ht used by transport layer protocol to physical implement its service physical source destination Introduction: 1-57 Services, Layering and Encapsulation M application application Ht M transport Transport-layer protocol transfers M (e.g., reliably) from transport one process to another, using services of network layer network Hn Ht M network Network-layer protocol transfers transport-layer segment [Ht | M] from one host to another, using link layer services link link  network-layer protocol encapsulates transport-layer segment [Ht | M] with physical network layer-layer header Hn to create a physical network-layer datagram source Hn used by network layer protocol to destination implement its service Introduction: 1-58 Services, Layering and Encapsulation M application application Ht M transport transport network Hn Ht M network Network-layer protocol transfers transport-layer segment [Ht | M] from one host to another, using link layer services link Hl Hn Ht M link Link-layer protocol transfers datagram [Hn| [Ht |M] from host to neighboring host, using network-layer services physical physical  link-layer protocol encapsulates network datagram [Hn| [Ht |M], with link-layer header source Hl to create a link-layer frame destination Introduction: 1-59 Services, Layering and Encapsulation M application M application message Ht M transport Ht M transport segment network Hn Ht M Hn Ht M network datagram link Hl Hn Ht M Hl Hn Ht M link frame physical physical source destination Introduction: 1-60 message M source application Encapsulation: an segment datagram Hn Ht Ht M M transport network end-end view frame Hl Hn Ht M link physical link physical switch destination Hn Ht M network M application Hl Hn Ht M link Hn Ht M Ht M transport physical Hn Ht M network Hl Hn Ht M link router physical Introduction: 1-61 Chapter 1: roadmap  What is the Internet?  What is a protocol?  Network edge: hosts, access network, physical media  Network core: packet/circuit switching, internet structure  Performance: loss, delay, throughput  Protocol layers, service models  History Introduction: 1-62 Internet history 1961-1972: Early packet-switching principles  1961: Kleinrock - queueing  1972: theory shows effectiveness of ARPAnet public demo packet-switching NCP (Network Control Protocol)  1964: Baran - packet-switching first host-host protocol in military nets first e-mail program  1967: ARPAnet conceived by ARPAnet has 15 nodes Advanced Research Projects Agency  1969: first ARPAnet node operational Internet history 1972-1980: Internetworking, new and proprietary networks  1970: ALOHAnet satellite Cerf and Kahn’s internetworking network in Hawaii principles:  1974: Cerf and Kahn -  minimalism, autonomy - no architecture for interconnecting internal changes required to networks interconnect networks  best-effort service model  1976: Ethernet at Xerox PARC  stateless routing  late70’s: proprietary  decentralized control architectures: DECnet, SNA, XNA define today’s Internet architecture  1979: ARPAnet has 200 nodes Introduction: 1-64 Internet history 1980-1990: new protocols, a proliferation of networks  1983: deployment of TCP/IP  new national networks: CSnet,  1982: smtp e-mail protocol BITnet, NSFnet, Minitel defined  100,000 hosts connected to  1983: DNS defined for name- confederation of networks to-IP-address translation  1985: ftp protocol defined  1988: TCP congestion control Introduction: 1-65 Internet history 1990, 2000s: commercialization, the Web, new applications  early 1990s: ARPAnet late 1990s – 2000s: decommissioned  more killer apps: instant  1991: NSF lifts restrictions on messaging, P2P file sharing commercial use of NSFnet  network security to forefront (decommissioned, 1995)  est. 50 million host, 100 million+  early 1990s: Web users hypertext [Bush 1945, Nelson 1960’s] HTML, HTTP: Berners-Lee  backbone links running at Gbps 1994: Mosaic, later Netscape late 1990s: commercialization of the Web Introduction: 1-66 Internet history 2005-present: scale, SDN, mobility, cloud  aggressive deployment of broadband home access (10-100’s Mbps)  2008: software-defined networking (SDN)  increasing ubiquity of high-speed wireless access: 4G/5G, WiFi  service providers (Google, FB, Microsoft) create their own networks bypass commercial Internet to connect “close” to end user, providing “instantaneous” access to social media, search, video content, …  enterprises run their services in “cloud” (e.g., Amazon Web Services, Microsoft Azure)  rise of smartphones: more mobile than fixed devices on Internet (2017)  ~18B devices attached to Internet (2017) Introduction: 1-67 Chapter 1: summary We’ve covered a “ton” of material!  Internet overview  what’s a protocol? You now have:  network edge, access network, core  context, overview, packet-switching versus circuit- switching vocabulary, “feel” Internet structure of networking  performance: loss, delay, throughput  more depth,  layering, service models detail, and fun to  security follow!  history Introduction: 1-68

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