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Chapter 1 Introduction Computer Networking: A Top Down Approach

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1 Chapter 1 Introduction Computer Networking: A Top Down Approach
7th edition Jim Kurose, Keith Ross Pearson/Addison Wesley April 2016 Introduction

2 Chapter 1: roadmap 1.1 what is the Internet? 1.2 network edge
end systems, access networks, links 1.3 network core packet switching, network structure 1.5 protocol layers, service models Introduction

3 What’s the Internet: “nuts and bolts” view
components configurations smartphone PC server wireless laptop billions 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 switches: forward chunks of data (packets) routers and switches router Introduction 3

4 “Fun” Internet-connected devices
Web-enabled toaster + weather forecaster Internet picture frame Tweet-a-watt: monitor energy use Slingbox: watch, control cable TV remotely sensorized, bed mattress Internet refrigerator Internet phones Introduction

5 What’s the Internet: “nuts and bolts” view
tying it all together mobile network global ISP regional ISP home network institutional Internet “network of networks” interconnected networks transport data protocols control sending, receiving of information – data exchange between end devices e.g., TCP, IP, HTTP, Skype, Internet standards IETF: Internet Engineering Task Force RFC: Request for comments IEEE: Inst. of Electrical & Electronic Eng. ITU: Intl Telecomm. Union (UN) Introduction

6 What’s the Internet: a service view
an infrastructure that provides services to applications: Web, VoIP, , games, e-commerce, social nets, … it provides programming interface to apps software modules (socket) that allow sending and receiving application programs to “connect” to Internet service options (options/choices) necessary for the functionality of applications mobile network global ISP regional ISP home network institutional Introduction

7 Postal Service Analogy
Postal Service Rules  Internet Rules Stamp From address To address Delivery  Transmission Letter  Data Service Options: first class, registered, 2-day delivery….. Trans options: priority, guaranteed error free, high speed…. Delivery Options (registered, certified, priority)  Trans. Options (error control, priority) Envelope  Packet Introduction

8 What’s a protocol? human protocols: network protocols:
asking a question in a classroom introductions a courtroom dinner conversation network protocols: machines rather than humans diverse devices type of application: queries reports/files protocols define format, order of messages sent and received and actions taken on message 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 Courtroom, dinner table…… <file> Bye time Disconnect Bye Disconnect Introduction

10 Chapter 1: roadmap 1.1 what is the Internet? 1.2 network edge
end systems, access networks, links 1.3 network core packet switching, network structure 1.5 protocol layers, service models Introduction 10

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

12 Access networks and physical media
Q: How to connect end devices to edge router? mobile access networks residential access nets institutional access networks (school, company) Access network: Shared (multiple access) or dedicated (point to point) Introduction

13 Physical media bit: propagates between transmitter/receiver pairs
physical link: what lies between transmitter & receiver guided media: signals propagate in solid media: copper, fiber, coax unguided media: signals propagate freely in space, e.g., radio, cellular Introduction

14 Chapter 1: roadmap 1.1 what is the Internet? 1.2 network edge
end systems, access networks, links 1.3 network core packet switching, network structure 1.5 protocol layers, service models Introduction 14

15 The network core mesh of interconnected switches referred to as routers packet-switching: hosts break application-layer data into chunks and put 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

16 End devices: generate data
host sending function: takes application data 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 over link = = Introduction

17 Packet-switching: store-and-forward
L bits per packet 3 2 1 source destination R bps R bps store and forward: entire packet must arrive at router before it can be transmitted on next link – hop by hop Introduction

18 Packet Switching: queueing delay, loss
R = 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

19 Two key network-core functions
routing: determines source- destination route taken by packets routing algorithms forwarding: move packets from router’s input (port) to appropriate router output (port) based on forwarding table created by routing algorithm routing algorithm local forwarding table header value output link 0100 0101 0111 1001 3 2 1 1 2 3 0111 destination address in arriving packet’s header Introduction

20 Internet structure: network of networks
… … access net access net access net access net access net access net access net ISP A … … ISP B access net access net ISP C access net access net access net regional net access net … access net access net … access net Introduction

21 Chapter 1: roadmap 1.1 what is the Internet? 1.2 network edge
end systems, access networks, links 1.3 network core packet switching, network structure 1.5 protocol layers, service models Introduction 21

22 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

23 Analogy: Organization of air travel
ticket (purchase) baggage (check) gates (load) runway takeoff airplane routing ticket (complain or not) baggage (claim) gates (unload) runway landing a series of steps Introduction

24 Layering of airline functionality
ticket (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

25 Why layering? dealing with complex systems:
layered structure allows breakdown of a complex system into smaller, well identified modules with explicit responsibilities/relationships to each other layered reference model – up/down relationships only - well defined modularization eases maintenance/updating of system change of implementation of a layer’s service transparent to rest of system – internals are hidden e.g., change in gate procedure doesn’t affect rest of system operation, a flight is still a flight, passenger still gets to destination but a change in a layer’s service could impact performance of end system -> passengers may not be happy with a new gate procedure – unless reflected in their ticket purchase layering considered harmful? Overlap in functionality (e.g., error control), dependency wrt specific requirements (e.g., timestamps) – not fully independent Change runway, change airplane, change baggage carrousel….. It could impact “quality” of service, but you will still be serviced, changing implementation of layer is different than changing a service. Introduction

26 Internet protocol stack - layers
application: supporting networked applications, process to process transfer – data stream  managed as messages FTP, SMTP, HTTP,…. transport: process to process message transfer  managed as segments/datagrams TCP, UDP network: routing of data segments from source to destination hop by hop  managed as datagrams IP (Internet Protocol) link: data transfer between neighboring network elements  managed as frames Ethernet, (WiFi), PPP physical: data “on the wire” managed as bits optical, electrical, electromagnetic….. application transport network link physical Introduction

27 Layers: Functionality & Services
Data Link Layer: Transmission of frames Functions: Framing, media access control, error checking, flow control Network Layer: Forwarding of packets (datagrams) Functions: Network addressing, hop by hop routing, header checking, loop prevention Transport Layer: Transfer of “chunks of application data” Functions: Connection establishment/termination, error control, flow control, congestion control Application Layer: Application specific – display/presentation Functions: Synchronization/timing, error recovery Introduction

28 IEFT Protocol Stack Example
Introduction

29 Protocols in Action IP Router Argon 128.143.137.144 Neon 128.143.71.21
Data in segment is for HTTP Send HTTP Request to neon Establish a connection to Neon Open TCP connection to Neon IP datagram is a TCP segment Send connection request to Neon Forward IP datagram to Neon Send IP datagram to Neon Frame is an IP datagram Frame is an IP datagram for Neon Forward datagram to next hop - Router Forward the datagram to Neon IP Router Send Ethernet frame to Router Send Ethernet frame to Neon Introduction 29

30 Encapsulation with layering comes encapsulation
each layer adds control bits used to process the information to provide the desired type of service to the layer above it and ultimately to the application the packet grows in size as it drops from application to datalink at the source the packet is stripped of bits as it travels back up the stack to the application layer Introduction

31 IETF Encapsulation link layer frame with header Hl
transport layer segment with header Ht network layer datagram with header Hn link layer frame with header Hl linkh networkh transporth linkt message Introduction

32 Example source X destination application transport network link
message M application transport network link physical segment Ht M Ht datagram Ht Hn M Hn Ht Hn Hl M frame 1 Tl Ht Hn Hl M frame 1 Tl link physical switch Ht Hn Hl M frame 1 Tl destination network link physical Ht Hn M Ht Hn Hl M application transport network link physical Ht Hn Hl M frame 2 Tl X router Ht Hn M Ht Hn Hl M frame 1 Tl Introduction

33 Chapter 4: Network Layer
4.3 IP: Internet Protocol IPv4 addressing Network Layer: Data Plane

34 Internet Addressing: Introduction
Internet address: 32-bit identifier for host, router interface interface: connection between host/router and physical link router’s typically have multiple interfaces each interface creates a distinct/separate network host typically has one or two interfaces (e.g., wired Ethernet, wireless ) interfaces may or may not be on a same network Internet address associated with each interface = 223 1 1 1 Network Layer: Data Plane

35 What is an Internet address?
Internet address is usually referred to as the IP (Internet Procotol) address. henceforth we will refer to it as IP address an IP address is a unique global address for a network interface an IP address: is a 32 bit long identifier – 4bytes encodes a network number referred to as network prefix and a device number referred to as host address human analogy: network prefix  street name host number  house number

36 IP Dotted Decimal Notation
IP addresses are written in a dotted decimal format each byte is identified by a decimal number in the range [0….255] – 28 example 1st Byte = 128 2nd Byte = 143 3rd Byte = 137 4th Byte = 144

37 Network prefix and host number
the network prefix identifies a network and the device number identifies a specific device (actually, interface on the network as a device can have more than 1 ”network card”, and each card will have a unique IP address). real life analogy? - street name and house number how do we know how long the network prefix is? the network prefix used to be implicitly defined (class-based addressing, A,B,C,D…) the network prefix now is flexible and is indicated by a prefix/netmask (classless). network prefix host number

38 Example Example: argon.cs.virginia.edu IP address is 128.143.137.144
is that enough info to route/forward a datagram??? -> No. must indicate a network prefix for every IP device (host and router) using prefix notation an IP address is: /x e.g., x = 16 means network prefix is16 bits long the prefix is identified by a network mask: prefix =16  mask consists of 16 ‘one’s i.e., mask is represented as: or hex format: ffff0000 --> network prefix (or ID or address) (IP address AND netmask) is: --> host number (IP address AND inverse of netmask(=0000ffff) is:

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