Chapter 1 - Introduction-3.pdf

04-641: Fundamentals of Telecommunications and Computer Networks Edwin Mugume, PhD Assistant Professor Chapter 1 Introduction Computer Networking: A Top-Down Approach Seventh Edition Jim Kurose, Keith Ross Pearson/Addison Wesley April 2016 Introduction 1-2 Chapter 1:...

04-641: Fundamentals of Telecommunications and Computer Networks Edwin Mugume, PhD Assistant Professor Chapter 1 Introduction Computer Networking: A Top-Down Approach Seventh Edition Jim Kurose, Keith Ross Pearson/Addison Wesley April 2016 Introduction 1-2 Chapter 1: Introduction Our goal: Overview: ▪ get “feel” and ▪ what’s the Internet? terminology ▪ what’s a protocol? ▪ network edge: hosts, access ▪ more depth, detail network, physical media later in course ▪ network core: packet and circuit ▪ approach: switching, Internet structure use Internet as ▪ performance: packet loss, delay, throughput example ▪ security ▪ protocol layers, service models ▪ history Introduction 1-3 Chapter 1: Introduction 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 Introduction 1-4 Chapter 1: Introduction 1.1 What is the Internet? ❑ A “nuts and bolts” description ▪ The basic hardware and software components that make up the Internet ❑ A Services description ▪ A networking infrastructure that provides services to distributed applications Introduction 1-5 Chapter 1: Some key facts Source: Cisco Annual Internet Report (2018–2023) White Paper Introduction 1-6 Chapter 1: Some key facts Internet users as a percentage of regional population Introduction 1-7 Chapter 1: Some key facts Introduction 1-8 Chapter 1: Some key facts Introduction 1-9 Chapter 1: Some key facts Number of DDoS attacks Introduction 1-10 Chapter 1: Introduction 1.1 What is the Internet? ❑ A “nuts and bolts” description ▪ The basic hardware and software components that make up the Internet ▪ A computer network that interconnects billions of computing devices throughout the world* ▪ End systems or hosts connect to the Internet ▪ Traditionally, desktop PCs, servers, etc. ▪ Non-traditional devices: laptops, phones, sensors, cars, gaming consoles, watches, etc. Introduction 1-11 What’s the Internet: A “nuts and bolts” view PC ▪ billions of connected mobile network server computing devices: wireless laptop hosts = end systems global ISP smartphone running network apps home ▪ communication links network regional ISP wireless fiber, copper, radio, links satellite wired links transmission rate: bandwidth in bps ▪ packet switches: forward router packets (chunks of data) institutional routers and link-layer network switches Introduction 1-12 “Fun” Internet-connected devices Web-enabled toaster + weather forecaster IP picture frame http://www.ceiva.com/ Tweet-a-watt: Slingbox: watch, monitor energy use control cable TV remotely sensorized, bed mattress Internet refrigerator Internet phones Introduction 1-13 What’s the Internet: “nuts and bolts” view ▪ Internet: “network of networks” mobile network Interconnected ISPs End systems access the Internet global ISP through ISPs Lower-tier ISPs are interconnected through national and international home upper-tier ISPs network regional ISP An upper-tier ISP has high-speed routers interconnected with high- speed fiber-optic links ▪ Protocols control sending, receiving of messages e.g., TCP, IP, HTTP, Skype, 802.11 institutional network Introduction 1-14 What’s the Internet: “nuts and bolts” view ▪ Protocols control sending, receiving mobile network of messages TCP and IP are among the most global ISP important protocols IP specifies format of packets sent though routers home ▪ TCP/IP protocol stack network regional ISP ▪ Internet standards Developed by Internet Engineering Task Force (IETF) Uses standard documents called Request for Comments (RFCs) ▪ Over 9,000 RFCs exist ▪ RFCs are very detailed and technical Other bodies define other standards institutional network ▪ E.g., IEEE 802 LAN/MAN standards committee for Ethernet and WiFi Introduction 1-15 What’s the Internet: A Service view ▪ Infrastructure that provides services to applications: Web, VoIP, email, games, e-commerce, social networks, … Applications are distributed in different hosts that exchange data to use them ▪ Provides programming (socket) interface to applications This API sets the rules that a sending app must follow so that the Internet can deliver data to the destination ▪ Analogous to the postal service Introduction 1-16 What’s a Protocol? A human protocol and a computer network protocol Introduction 1-17 What’s a Protocol? Human protocols: Network protocols: ▪ “what’s the time?” ▪ Machines rather than humans ▪ “I have a question” ▪ All communication activity on ▪ Introductions the Internet is governed by protocols … specific messages sent … specific actions taken A protocol defines the format and when messages the order of messages exchanged received, or other between two or more events communicating entities, as well as the actions taken on the transmission and/or receipt of a message or other event. Introduction 1-18 Chapter 1: Introduction 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 Introduction 1-19 A closer look at network structure: ▪ Network edge: Hosts: clients and servers Clients are typically PCs, phones, laptops, sensors, etc. Servers tend to be more powerful, and they store and distribute data such as web pages, email, etc. Most servers are found in large data centers e.g. Google ▪ Access networks and physical media: An access network connects an end system to its immediate (first) router, e.g., a LAN ▪ Network core: Interconnected routers Network of networks Introduction 1-20 Introduction 1-21 Access networks and physical media Qn: How do we connect end systems to the edge router? ▪ Residential access networks ▪ Institutional access networks (school, company) ▪ Mobile access networks Keep in mind: ▪ What is the bandwidth (bits per second) of the access network? ▪ Is the link shared or dedicated? Introduction 1-22 Introduction 1-23 Access network: digital subscriber line (DSL) central office telephone network DSL splitter modem DSLAM ISP voice, data transmitted at different frequencies over a DSL access dedicated line to central office multiplexer ▪ Use existing telephone line to the CO DSLAM Data over DSL phone line goes to Internet (upstream: 4 kHz to 50 kHz; down: 50 kHz to 1 MHz) Voice over DSL phone line goes to telephone net (0 to 4 kHz band) ▪ < 2.5 Mbps upstream transmission rate (typically < 1 Mbps) ▪ < 24 Mbps downstream transmission rate (typically < 10 Mbps) Introduction 1-24 Access network: digital subscriber line (DSL) Introduction 1-25 Access network: cable network cable head end … cable splitter cable modem modem CMTS termination system data, TV transmitted at different frequencies over shared cable ISP distribution network ▪ HFC: hybrid fiber coax (HFC) Employs fiber (to neighborhood level junctions – supporting thousands of homes) and cable to the home Asymmetric: up to 30Mbps downstream transmission rate and 2 Mbps upstream transmission rate ▪ Network of cable and fiber attaches homes to ISP router homes share access network to cable head end This is unlike DSL which has dedicated access to central office Introduction 1-26 Access network: cable network Introduction 1-27 Access network: cable network cable headend … cable splitter modem C O V V V V V V N I I I I I I D D T D D D D D D A A R E E E E E E T T O O O O O O O A A L 1 2 3 4 5 6 7 8 9 Channels Frequency division multiplexing: different channels transmitted in different frequency bands Introduction 1-28 Access network: FTTH ▪ Direct fiber: each home is connected by a dedicated fiber ▪ Shared fiber: homes share the fiber link which is separated later Passive optical networks (PONs) is shown ▪ Each home has an optical network terminator (ONT) with a dedicated connection to a neighborhood optical splitter ▪ Splitter connects to an optical line terminator (OLT) in the CO ▪ Active optical networks (AONs) Introduction 1-29 Access network: FTTH ▪ FTTH can provide Gbps speeds in theory ▪ Actual rates depend on rate packaging/offerings ▪ The higher the rate, the more costly it is ▪ Rates can reach up to 150 Mbps (check Liquid Telecom Rwanda rates) ▪ If cable, DSL or FTTH do not exist, other options are: ▪ Satellite, microwave (e.g., WiMAX 802.16 standard) Introduction 1-30 Enterprise access networks (Ethernet) ▪ 10 Mbps, 100Mbps, 1Gbps connection to the Ethernet switch ▪ Servers may have 1 Gps or 10Gbps transmission rates ▪ Today, end systems typically connect into Ethernet switch ▪ In addition, wireless LANs are prevalent in all settings (homes, offices, etc.) Introduction 1-31 Enterprise access networks (Ethernet) institutional link to ISP (Internet) institutional router Ethernet institutional mail, switch web servers ▪ Typically used in companies, universities, etc. ▪ End systems connected to the router through LANs enabled by Ethernet switches ▪ Ethernet (twisted pair copper) is by far the most common access technology in such networks Introduction 1-32  Access network: home network wireless devices to/from headend or central office often combined in single box cable or DSL modem wireless access router, firewall, NAT point (54 Mbps) wired Ethernet (1 Gbps) Introduction 1-33 Access network: WiMAX ▪ Wireless Interoperability for Microwave Access Speeds above 50 Mbps Introduction 1-34 Wireless access networks ▪ A shared wireless access network connects an end system to a router Via a base station a.k.a an access point Wireless LANs: Wide-area wireless access ▪ Within building (~100 ft.) ▪ Provided by telcos (cellular ▪ 802.11b/g/n (WiFi): 11, 54, 450 operators) Mbps transmission rates ▪ 10’s of kilometers ▪ 1 to 10 Mbps and beyond ▪ 3G, 4G LTE, 5G to Internet to Internet Introduction 1-35 Physical media ▪ Bit: propagates between Twisted pair (TP) transmitter/receiver pairs ▪ two insulated copper ▪ Physical link: what lies wires between transmitter & Category 5: 100 Mbps, 1 receiver Gbps Ethernet ▪ Guided media: Category 6: 10Gbps Signals propagate in solid media: copper, fiber, coax ▪ Unguided media: Signals propagate freely, e.g., radio Introduction 1-36 Physical media Introduction 1-37 Physical media: coax, fiber Coaxial cable: fiber optic cable: ▪ Two concentric copper ▪ Glass fiber carrying light pulses, conductors each pulse is a bit ▪ Bidirectional ▪ high-speed operation: ▪ Broadband: 10’s-100’s Gbps transmission rate Multiple channels on cable ▪ low error rate: HFC in cable applications repeaters spaced far apart immune to electromagnetic noise Introduction 1-38 Ref: https://www.submarinenetworks.com/en/stations/africa Introduction 1-39  Submarine Cable Map Interactive Map Ref: https://www.submarinecablemap.com/ Introduction 1-40 Physical media: Radio ▪ Signal carried in Radio link types: electromagnetic spectrum ▪ Terrestrial microwave ▪ No physical “wire” e.g., up to 45 Mbps channels ▪ Bidirectional ▪ LAN (e.g., WiFi) ▪ Propagation environment 54 Mbps effects: ▪ Wide area (e.g., cellular) Reflection 4G cellular: ~ 10 Mbps Obstruction by objects ▪ Satellite Interference kbps to 45 Mbps channel (or Noise multiple smaller channels) Diffraction Geosynchronous (GEO) versus Multipath fading lower altitude (MEO, LEO) Up to 270 ms end-end delay in GEO Introduction 1-41 Introduction 1-42 Physical media: Radio Satellite ▪ Geostationary orbit (GEO) Launched 35,870 km above earth Support long-distance communication Has high delay (latency up to 270 ms) but large coverage (three satellites cover two-thirds of the earth) ▪ Medium earth orbit (MEO) Not commonly used for communications ▪ Low earth orbit (LEO) Orbit up to 500 km above earth Common for localized provision Starlink is a common provider These show very minimal delay Introduction 1-43 Chapter 1: Introduction 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 Introduction 1-44 The Network Core ▪ The core is a mesh of interconnected routers ▪ In packet-switching, hosts break application-layer messages into packets Forward packets from one router to the next, across links on the path from source to destination Each packet is transmitted at full link capacity Introduction 1-45 Host: sends packets of data Host sending function: ▪ Takes application message ▪ Breaks it into smaller two packets, chunks, known as L bits each packets, of length L bits ▪ transmits packet into access network at a 2 1 transmission rate R R: link transmission rate Link transmission rate host a.k.a link capacity, a.k.a link bandwidth packet time needed to L (bits) transmission = transmit L-bit = delay packet into link R (bits/sec) Introduction 1-46 Introduction 1-47 Introduction 1-48 Introduction 1-49 Packet-switching: store-and-forward L bits per packet 3 2 1 source destination R bps R bps ▪ Takes L/R seconds to transmit (push out) one L-bit packet into link at R bps ▪ In store and forward, the entire packet must arrive at the router before it can be transmitted on to the next link ▪ End-end delay = 2L/R (assuming zero more on delay later … propagation delay) Introduction 1-50 Packet-switching: store-and-forward L bits per packet 3 2 1 source destination R bps R bps Numerical examples: One packet over one hop: One packet over two hops: ▪ L = 7.5 Mbits ▪ Two-hop transmission delay = ▪ R = 1.5 Mbps 10 sec = 2L/R ▪ One-hop transmission ▪ Generally, delay = 5 sec ▪ Delay = HL/R, where H is the number of hops Introduction 1-51 Packet-switching: store-and-forward Multiple packets 3 2 1 source destination R bps R bps For multiple packets, transmission delay is: ▪ At time L/R, router receives first packet and source begins loading the second packet ▪ At time 2L/R, destination receives first packet, router receives second packet, source begins to load the third packet ▪ At 3L/R, destination receives second packet and router receives third packet ▪ At time 4L/R, destination receives the third packet Introduction 1-52 Packet-switching: store-and-forward Multiple packets 3 2 1 source destination R bps R bps Multiple packets over a multiple-hop link: ▪ N packets [assume N=2 packets] ▪ L bits per packet ▪ For H = 2 hops: Delay = 3L/R = (N+1)L/R ▪ For H = 3 hops: Delay = 4L/R = (N+2)L/R ▪ For H = 4 hops: Delay = 5L/R = (N+3)L/R Introduction 1-53 Packet-switching: store-and-forward Multiple packets 3 2 1 source destination R bps R bps Multiple packets over a multiple-hop link: ▪ N packets [assume N=3 packets] General case: ▪ L bits per packet It appears that: ▪ For H = 2 hops: Delay = 4L/R = (N+1)L/R ▪ For N packets and H ▪ For H = 3 hops: Delay = 5L/R = (N+2)L/R hops: ▪ For H = 4 hops: Delay = 6L/R = (N+3)L/R ▪ Delay = (N+H-1)L/R Introduction 1-54 Packet Switching: queueing delay, loss R = 10 Mb/s C A D R = 1.5 Mb/s B queue of packets E waiting for output link Queuing and Loss: ▪ If arrival rate (in bits) to the link exceeds transmission rate of link for a period: Packets will queue and wait to be transmitted on link Queuing delays depend on level of congestion Packets can be dropped (lost) if memory (buffer) fills up Introduction 1-55  Two key network core functions Routing: determines source- Forwarding: move packets from destination route to be taken by router’s input to appropriate packets based on IP address router output ▪ Routing algorithms ▪ Determined from a forwarding table that maps IP addresses to the outbound links ▪ Based on routing protocols routing algorithm local forwarding table header value output link 0100 3 1 0101 2 0111 2 3 2 1001 1 destination address in arriving packet's header Introduction 1-56 Circuit switching End-to-end resources allocated to or reserved for “call” between source & destination ▪ Resources: buffer space, transmission rate, etc. A and B communicating: ▪ A network establishes a ▪ Each link has four circuits. connection before sending any information 2nd circuit in top link and 1st circuit in right link ▪ This is maintained throughout the dedicated to the call duration of the call A 1 Mbps link means 250 ▪ Reserved transmission rate gives a kbps per circuit guaranteed rate to the receiver Introduction 1-57 Multiplexing in CSNs: FDM versus TDM Example: FDM 4 users frequency time TDM frequency time Introduction 1-58 Multiplexing in CSNs: FDM versus TDM Introduction 1-59 Example on CSNs Question: Answer: ▪ Consider how long it takes ▪ Link rate of 1.536 Mbps to send a file of 640,000 bits means that the rate per from A to B over a CSN time slot = 1.536 Mbps/24 = ▪ All links in the network use 64 kbps. TDM with 24 time slots and ▪ The file is sent through one have a bit rate of 1.536 time slot per frame, Mbps. requiring: ▪ Assume that it takes 500 ms 640,000 bits / 64 kb/s = to establish an end-to-end 10 seconds circuit. ▪ Hence, total time is 10 sec + 0.5 sec = 10.5 seconds. Introduction 1-60 Packet Switching vs Circuit Switching ▪ CS better supports real-time services like video, voice, etc. ▪ PS supports more users (better sharing) and is cheaper, more efficient, and less costly than CS. Example 1: N ▪ 1 Mb/s link; Each user requires a users rate of 100 kbps; Users active 10% of the time. 1 Mbps link ▪ Circuit-switching: Only 10 users can use the link The link/frame can have 10 circuits, each dedicated to one user 90% of the frame is essentially wasted, due to idleness of users ▪ In other words, each circuit is idle 90% of the time. * Check out the online interactive exercises for more examples: http://gaia.cs.umass.edu/kurose_ross/interactive/ Introduction 1-61 Packet switching versus circuit switching Example 1: ▪ Packet switching: For 35 users (each 10% active), N the probability of 11 or more users users active simultaneously is 1 Mbps link less than 0.0004. So: for 35 users, there is a 0.04% chance of a user being blocked. ▪ Qn: how did we get 0.0004? For 99.96% of the time, See Homework Problem P8 transmission happens with no ▪ Qn: what happens if you have issue more than 35 users? Queues With 10 or less users, the performance is like in CS develop. 1-62 * Check out the online interactive exercises for more examples: http://gaia.cs.umass.edu/kurose_ross/interactive/ Introduction Packet switching versus circuit switching Example 2: ▪ 1 Mb/s link, 10 users. 9 users idle, 1 user generates one thousand 1,000-bit packets (or N 1,000,000 bits) users Each user has 100 kbps rate. 1 Mbps link ▪ What time does it take to transmit it? ▪ Circuit switching: ▪ Packet switching: Data will be sent over 10 All packets sent in 1 second seconds All other users are idle The other slots remain idle, This sharing of bandwidth causing wastage of bandwidth makes PS very efficient Introduction 1-63 Packet switching versus circuit switching Is packet switching a “slam dunk winner?” ▪ Great for bursty data resource sharing simpler, no call setup ▪ Excessive congestion possible leading to 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 Q: Human analogies of reserved resources (circuit switching) versus on-demand allocation (packet-switching)? Introduction 1-64 Internet structure: network of networks ▪ End systems connect to the Internet via access Internet Service Providers (read about ISPs here) Residential, company and university ISPs Access ISPs can use wired or wireless: DSL, cable, FTTH, etc. ▪ Access ISPs in turn must be interconnected so that any two hosts can send packets to each other This creates a network of networks ▪ Let us take a stepwise approach to describe current Internet structure Introduction 1-65 Internet structure: 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 1-66 Internet structure: network of networks Option 1: connect each access ISP to every other access ISP? access access net net access net access access net net access access net net connecting each access ISP to access access net each other directly doesn’t scale. net access net access net access net access net access access net access net net Introduction 1-67 Internet structure: network of networks Option 2: 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 1-68 Internet structure: network of networks Option 3: But if one global ISP is a 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 net ISP C access net access net access net access access net access net net Introduction 1-69 Internet structure: network of networks ▪ Creates a two-tier hierarchy ▪ Customer-Provider relation Global transit ISPs reside above Access ISPs pay regional ISPs Access ISPs below them. Regional ISPs pay Tier-1 ISPs Assumption: global ISPs can get Some regional ISPs are bigger close to every access ISP than others, creating a multi- ▪ This is not economically tier hierarchy viable ▪ The Internet also has: ▪ Regional ISPs cover regions Points of Presence Access ISPs connect to them Multi-homing They also connect to global Peering ISPs (called Tier-1 ISPs) Internet Exchange Points Although Tier-1 ISPs exist, they don’t cover every city Content Provider Networks Introduction 1-70 Internet structure: network of networks ▪ PoPs ▪ Peering A PoP is a group of routers in a provider The amount paid by a ISP’s network (at the same location) customer ISP to a provider ISP where customer ISPs can connect to the reflects amount of traffic provider ISP exchanged PoPs exist at all levels, except at access A pair of nearby ISPs at the ISP level same level can interconnect to A customer ISP can connect to a PoP via reduce costs a high-speed microwave link or fiber. Traffic between them passes directly, rather than going ▪ Multi-homing through upstream ISPs Any ISP (except Tier-1) can connect to Peering is usually settlement- two or more provider ISPs free. An access ISP may multi-home with Tier-1 ISPs also peer regional ISPs and/or with a Tier-1 ISP settlement-free Multi-homing provides redundancy and other economic benefits Introduction 1-71 Internet structure: network of networks ▪ IXPs A third-party company can create a Google tries to “bypass” upper tier meeting point where multiple ISPs can ISPs by peering with low-tier ISPs peer together or connecting to them at the IXPs This is an IXP, a standalone facility with (settlement-free) its own switches. ▪ Google connects to Tier-1 ISPs for cases where access ISPs Over 760 IXPs exist today, according to are unreachable Packet Clearing House* ▪ Google pays for this traffic exchange ▪ CPNs ▪ CPNs: (a) reduce payment to Google is a main example, with their other ISPs ; (b) control how their services are delivered to many data centers across the world end users. Servers are interconnected via Google’s CPNs same as Content Delivery TCP/IP private network that spans the Networks (CDNs) globe * https://www.pch.net/ixp/summary Introduction 1-72 Internet structure: network of networks Introduction 1-73 Internet structure: network of networks Single Server Distribution vs CDN Approach Introduction 1-74 Internet structure: network of networks ▪ There is no authority that defines tiers of ISPs participating in the Internet. ▪ A well-accepted definition of a Tier 1 ISP is a network that can reach every other network on the Internet without purchasing IP transit or paying for peering. ▪ Ref: https://en.wikipedia.org/wiki/Tier_1_network Introduction 1-75 Internet structure: network of networks But if one global ISP is viable business, there will be competitors …. which must be interconnected access access Internet exchange point net net access net access access net net access IXP access net net ISP A access net IXP ISP B access net access net ISP C access net access peering link net access net access access net access net net Introduction 1-76 Internet structure: network of networks … and regional networks may arise to connect access networks to Tier-1 ISPs access access net net access net access access net net access IXP access net net ISP A access net IXP ISP B access net access net ISP C access net access net regional net access net access access net access net net Introduction 1-77 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 access net net access net access access net net access IXP access net net ISP A Content provider network access net IXP ISP B access net access net ISP C access net access net regional net access net access access net access net net Introduction 1-78 Internet structure: 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 the center is a small number of well-connected large networks Tier-1 ISPs (e.g., Level 3, Sprint, AT&T, NTT): national & international coverage Content provider network (e.g., Google): private network that connects its data centers to Internet, often bypassing tier-1 and regional ISPs Introduction 1-79 Tier-1 ISP: e.g., Sprint POP: point-of-presence to/from backbone peering … … … … … to/from customers Introduction 1-80 Chapter 1: Latency 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 Introduction 1-81 How do loss and delay occur? Packets queue in router buffers ▪ packet arrival rate to the link (temporarily) exceeds output link capacity ▪ packets queue and wait for their turn packet being transmitted (delay) A B packets queueing (delay) free (available) buffers: arriving packets dropped (loss) if no free buffers Introduction 1-82 Four sources of packet delay transmission A propagation B nodal processing queueing dnodal = dproc + dqueue + dtrans + dprop dproc: nodal processing dqueue: queueing delay ▪ check bit errors ▪ time waiting at output link for ▪ determine output link (routing) transmission (~ ms) ▪ typically ~ ms ▪ depends on congestion level at router ▪ zero delay if the queue is empty Introduction 1-83 Four sources of packet delay transmission A propagation B nodal processing queueing dnodal = dproc + dqueue + dtrans + dprop dtrans: transmission delay: dprop: propagation delay: ▪ L: packet length (bits) ▪ d: length of physical link ▪ R: link bandwidth (bps) ▪ s: propagation speed (~2x108 m/s) ▪ dtrans = L/R dtrans and dprop ▪ dprop = d/s ▪ typically ~ ms very different ▪ typically ~ ms in WANs * Check out the online interactive exercises for more examples: http://gaia.cs.umass.edu/kurose_ross/interactive/ * Check out the Java applet for an interactive animation on trans vs. prop delay Introduction 1-84 Caravan analogy 100 km 100 km ten-car toll toll caravan booth booth ▪ cars “propagate” at ▪ time to “push” entire 100 km/hr caravan through toll ▪ toll booth takes 12 sec to booth onto highway = service car (bit transmission 12*10 = 120 sec = 2 mins time) ▪ time for last car to ▪ car ~ bit; caravan ~ packet propagate from 1st to ▪ Q: How long until caravan is 2nd toll both: 100 km / lined up before 2nd toll (100 km/hr) = 1 hour booth? ▪ A: 62 minutes Introduction 1-85 Caravan analogy 100 km 100 km ten-car toll toll caravan booth booth ▪ suppose cars now “propagate” at 1,000 km/hr ▪ and suppose toll booth now takes one min to service a car ▪ Q: Will some cars arrive to the 2nd booth before all cars are serviced at the first booth? ▪ Answer: Yes! After 7 min, the first car arrives at second booth; three cars still at first booth Introduction 1-86 Queueing delay (revisited) ▪ R: link bandwidth (bps) ▪ L: packet length (bits/packet) ▪ a: average packet arrival rate (packets/sec) La/R ~ 0 ▪ Hence: La is bits/sec La/R is the traffic intensity ▪ La/R ~ 0: average queueing delay small ▪ La/R 1: average queueing delay large ▪ La/R > 1: more packets arriving La/R 1 than can be serviced, average delay infinite! * Check online interactive animation on queuing and loss Introduction 1-87 “Real” Internet delays and routes ▪ What do “real” Internet delay & loss look like? ▪ Traceroute program: provides delay measurement from source to router along end-to-end Internet 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 calculates interval between transmission and reply. 3 probes 3 probes 3 probes Introduction 1-88 “Real” Internet delays, routes traceroute: cs-gw to cis.poly.edu * Do some traceroutes from exotic countries at www.traceroute.org Introduction 1-89 “Real” Internet delays, routes traceroute: gaia.cs.umass.edu to www.eurecom.fr 3 delay measurements from gaia.cs.umass.edu to cs-gw.cs.umass.edu 1 cs-gw (128.119.240.254) 1 ms 1 ms 2 ms 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 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 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 link 10 de.fr1.fr.geant.net (62.40.96.50) 113 ms 121 ms 114 ms 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 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 1-90  Packet Loss ▪ Queue (or buffer) preceding the link has a finite capacity ▪ Packets arriving to a full queue are dropped (i.e., lost) ▪ Lost packets may be retransmitted by the previous node, by the source host, or not at all buffer packet being transmitted A (waiting area) B packet arriving to full buffer is lost 1-91 * Check out the Java applet for an interactive animation on queuing and loss Introduction  Throughput ▪ Throughput: rate at which bits are transferred between sender and receiver measured in bits/unit time (bps usually) instantaneous: rate at a given point in time average: rate over a longer period link capacity link capacity server, with Rc bits/sec file of F bits Rs bits/sec to send to client Introduction 1-92  Throughput ▪ Rs < Rc : What is average end-to-end throughput? Rs bits/sec Rc bits/sec ▪ Rs > Rc : What is average end-to-end throughput? Rs bits/sec Rc bits/sec bottleneck link link on end-to-end path that constrains end-to-end throughput Introduction 1-93  Throughput: Internet scenario ▪ (a): bottleneck = min(Rc , Rs ) For a file of ▪ 32 million bits ▪ Rs = 2 Mbps ▪ Rc = 1 Mbps Transmission time = 32 seconds. The constraint is usually the access (bottleneck) link as the core network is often over-provisioned * Check out the online interactive exercises for more examples: http://gaia.cs.umass.edu/kurose_ross/interactive/ Introduction 1-94  Throughput: Internet scenario ▪ (b): If R >> (Rc, Rs): Rate = min(Rc , Rs ) bottleneck link If R has many competing data streams, it can become a bottleneck ▪ If R ~ (Rc, Rs): It becomes the bottleneck link * Check out the online interactive exercises for more examples: http://gaia.cs.umass.edu/kurose_ross/interactive/ Introduction 1-95  Throughput: Internet scenario ▪ per-connection end-to- end throughput: Rs min ( Rc , Rs , R/10 ) Rs Rs ▪ In practice: Rc or Rs is often a bottleneck R Rc Rc 10 connections (fairly) share backbone bottleneck link of R bits/sec Rc * Check out the online interactive exercises for more examples: http://gaia.cs.umass.edu/kurose_ross/interactive/ Introduction 1-96 Chapter 1: Protocol Layers 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 Introduction 1-97 Protocol “layers” Networks are complex, with many “pieces”: Question: ▪ hosts is there any hope of ▪ routers organizing structure of ▪ links of various media network? ▪ applications ▪ protocols …. or at least our discussion of networks? ▪ hardware, software Introduction 1-98 Why layering? Dealing with complex systems: ▪ explicit structure allows identification, relationship of complex system’s pieces layered reference model ▪ modularization eases maintenance, updating of system change of implementation of layer’s service is transparent to rest of system ▪ e.g., change in gate procedure doesn’t affect the rest of system Introduction 1-99 Why layering? Layers: ▪ Provide structure to the design of protocols and associated hardware and software ▪ A layer provides services to the immediate upper layer (service model of a layer) ▪ Each layer provides service: ▪ via its own internal-layer actions ▪ relying on services provided by the layer below Example: ▪ Layer below may provide unreliable delivery of packets from edge device to edge device ▪ Layer above has functionality to detect and retransmit lost messages using the layer(s) below Introduction 1-100 Protocol Stacks Introduction 1-101 Internet protocol stack [TCP/IP] ▪ A protocol is implemented in software, hardware or a application combination of the two Application-layer protocols are usually implemented in software transport ▪ FTP, SMTP, HTTP Transport layer protocols too network ▪ Physical and data link layers handle link communications over the link Implemented in the network interface physical cards such as Ethernet, WiFi ▪ This is both hardware and software Introduction 1-102 Internet protocol stack ▪ application: supporting network applications FTP, SMTP, HTTP application ▪ transport: process-process data transfer transport TCP, UDP ▪ network: routing of datagrams from source to destination network IP, routing protocols link ▪ link: data transfer between neighboring network elements Ethernet, 802.11 (WiFi), Point-to-Point physical Protocol (PPP) ▪ physical: bits “on the wire” Introduction 1-103 ISO/OSI reference model ▪ presentation: allow applications to interpret meaning of data, e.g., encryption, application compression, format translation, etc. Often also called translation or syntax layer presentation ▪ session: provides mechanism for opening, session closing, and managing a session between applications transport synchronization, checkpointing, recovery of data network exchange ▪ Internet stack “missing” these layers! link these services, if needed, must be implemented in the application layer physical the application developer decides this, and then builds the functionality into the application Introduction 1-104 Encapsulation ▪ Every end system implements all 5 application layers of the TCP/IP protocol stack Consistent with the view of putting most complexity in the network edge transport ▪ Routers and link-layer switches are network packet switches that use layering They implement lower layer protocols link ▪ Routers: layers 1-3 ▪ Link-layer switches: 1-2 physical Introduction 1-105  Encapsulation ▪ Encapsulation: adding additional information to the payload/data at every layer Meant for the receiver to use this info Encapsulation starts in the application layer, down the stack Ref: Cory Beard and William Stallings,Wireless Communication Networks and Systems, Pearson, 2016 Introduction 1-106 Encapsulation Introduction 1-107  message M source application Encapsulation segment Ht M transport datagram Hn Ht M network 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 1-108  End-to-end communication Ref: Cory Beard and William Stallings,Wireless Communication Networks and Systems, Pearson, 2016 Introduction 1-109 Chapter 1: Security 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 Introduction 1-110 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 1-111 Bad guys put malware into hosts via Internet ▪ Malware can get in host from: virus: self-replicating infection by receiving/executing an object (e.g., email attachment) worm: self-replicating infection by passively receiving an object that gets itself executed ▪ Spyware malware can record keystrokes, web sites visited, etc., and upload info to a collection site ▪ infected host can be enrolled in a botnet and: used as a source in DDoS attacks or for spam email distribution ▪ Most malware is self-replicating: once it infects a host, it seeks entry into other hosts on the Internet Introduction 1-112 Bad guys: attack server, network infrastructure Denial of Service (DoS): ▪ attackers make resources (server, bandwidth) unavailable to legitimate traffic by overwhelming resource with bogus traffic Web servers, email servers, DNS servers, networks, all vulnerable ▪ Vulnerability attack: send well-crafted messages to a vulnerable application or operating system to gain access Can run malicious code, install malware, steal sensitive data ▪ Bandwidth flooding: send deluge of packets to the target host Clog the target’s access link and prevent legitimate packets ▪ Connection flooding: establish many TCP connections at the host, bog it down to frustrate legitimate connections Introduction 1-113 Bad guys: attack server, network infrastructure Denial of Service (DoS): 1. Select target 2. Break into hosts around the network (see botnet) 3. Send packets to target from target compromised hosts Introduction 1-114 Bad guys can sniff packets packet “sniffing”: ▪ works on broadcast media (shared Ethernet, wireless) ▪ promiscuous network interface (receiver) reads/records all packets (including passwords!) passing by ▪ Sniffed packets analyzed offline for important data A C src:B dest:A payload B ▪ Wireshark software used for end-of-chapter labs is a (free) packet-sniffer Introduction 1-115 Bad guys can use fake addresses IP spoofing: send packet with false source address Important to determine if a packet originates from the source it claims A C src:B dest:A payload B … lots more on security (throughout, Chapter 8) Introduction 1-116 Chapter 1: Internet 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 Introduction 1-117 Internet history 1961-1972: Early packet-switching principles ▪ 1961: Kleinrock - ▪ 1972: queueing theory shows ARPAnet public demo effectiveness of packet- NCP (Network Control switching Protocol) first host-host ▪ 1964: Baran - packet- protocol switching in military nets first e-mail program ▪ 1967: ARPAnet ARPAnet has 15 nodes conceived by Advanced Research Projects Agency ▪ 1969: first ARPAnet node operational Introduction 1-118 Internet history 1972-1980: Internetworking, new and proprietary nets ▪ 1970: ALOHAnet satellite network in Hawaii Cerf and Kahn’s ▪ 1974: Cerf and Kahn - internetworking principles: architecture for interconnecting minimalism, autonomy - no networks internal changes required to ▪ 1976: Ethernet at Xerox PARC interconnect networks best effort service model ▪ Late70’s: proprietary architectures: DECnet, SNA, stateless routers XNA decentralized control ▪ late 70’s: switching fixed length define today’s Internet packets (ATM precursor) architecture ▪ 1979: ARPAnet has 200 nodes Introduction 1-119 Internet history 1980-1990: new protocols, a proliferation of networks ▪ 1983: deployment of ▪ new national networks: TCP/IP CSnet, BITnet, NSFnet, ▪ 1982: smtp e-mail Minitel protocol defined ▪ 100,000 hosts connected ▪ 1983: DNS defined for to confederation of name-to-IP-address networks translation ▪ 1985: ftp protocol defined ▪ 1988: TCP congestion control Introduction 1-120 Internet history 1990, 2000’s: commercialization, the Web, new apps ▪ early 1990’s: ARPAnet late 1990’s – 2000’s: decommissioned ▪ more killer apps: instant ▪ 1991: NSF lifts restrictions on messaging, P2P file sharing commercial use of NSFnet ▪ network security to (decommissioned, 1995) forefront ▪ early 1990s: Web ▪ est. 50 million hosts, 100 hypertext [Bush 1945, million+ users Nelson 1960’s] ▪ backbone links running at HTML, HTTP: Berners-Lee Gbps 1994: Mosaic, later Netscape late 1990’s: commercialization of the Web Introduction 1-121 Internet history 2005-present ▪ ~ 5B devices attached to Internet (2016) smartphones and tablets ▪ aggressive deployment of broadband access ▪ increasing ubiquity of high-speed wireless access ▪ emergence of online social networks: Facebook: ~ one billion users ▪ service providers (Google, Microsoft) create their own networks bypass Internet, providing “instantaneous” access to search, video content, email, etc. ▪ e-commerce, universities, enterprises running their services in “cloud” (e.g., Amazon EC2) Introduction 1-122 Introduction: summary covered a “ton” of material! you now have: ▪ Internet overview ▪ context, overview, “feel” ▪ what’s a protocol? of networking ▪ network edge, core, access ▪ more depth, detail to network follow! packet-switching versus circuit-switching Internet structure ▪ performance: loss, delay, throughput ▪ layering, service models ▪ security ▪ history Introduction 1-123  Chapter 1 Additional Slides Introduction 1-124  application (www browser, packet email client) analyzer application OS packet Transport (TCP/UDP) Network (IP) capture copy of all Ethernet Link (Ethernet) (pcap) frames sent/received Physical