1 Internet Technology Fundamentals

2 Why Study Networks? Integral part of society Work, entertainment, community Pervasive Home, car, office, school, mall … Understand what they do, how they work, and limitations –Any jobs left? –What happened to IT? –Future of the IT industry.

3 Impact of the Net on People Anytime access to remote information –HW assignments from my server Person-to-person and group communication – , blogs, chat, meeting Form and strengthen communities –chat rooms, MUDs, newsgroups

4 Impact of the Net on Society Huge impact! –Continuation of technologies that reduce problems of time & space (e.g. railroads,phone,autos,TV) Good, bad and ugly –mirror of society Changes still on the horizon –Commerce, services, entertainment, socializing

5 Internet Roles Users Everyone (mom and pop, kids) work, leisure, serious, frivolous Designers protocol design and implementation performance, cost and scale Service Providers Administrators and ISPs Management, revenue, deployment

6 What is Internet Technology? What is an internet? –Network of networks What is the Internet? –A global internet based on the IP protocol To what does “Internet technology” refer? –Architecture, protocols and services

7 Sample Internet Applications Electronic mail Remote terminal File transfer Newsgroups File sharing Resource distribution World Wide Web Video conferencing Games

8 What is a Network? Carrier of information between 2 or more entities Interconnection may be any media capable of communicating information: –copper wire –lasers –microwave –satellite link

9 Some Definitions –Network: Collection of interconnected machines –Host: Machine running user application –Channel: Logical line of communication –Media: Physical process used –Protocol: Rules of communication –Router: decide were to send data next –Topology: How network is interconnected

10 How Do Computers Communicate? With 1’s and 0’s –Computers only deal with 1’s and 0’s –So do networks –Must build all further structures from this basic representation How do we transmit 1’s and 0’s in a network?

11 Physical Transmission A physical quantity (e.g. voltage), varying over time represents a digital 0 or 1

12 Concepts for this week Layering and encapsulation –IP Hourglass Core and Edge of the Internet Circuit, message and packet switching Single link transmission delay Multi-link transmission delay –Circuit switching –Message switching –Packet switching –Computing general pipelining delay

13 Layering and Encapsulation

14 Why Layering? Network communication is very complex Separation of concerns –Different vendors and organizations responsible for different layers –Testing and maintenance is simplified –Easy to replace a single layer with a different version

15 Protocol Hierarchy Use layers to hide complexity –Each layer implements a service Layer N uses service provided by layer N-1 layer N-1 provides a service to layer N –Protocols Each layer communicates with its peer by a set of rules Interface –A layers interface specifies the operations

16 Protocol Hierarchy (cont’d) Layer 7 Layer 6 Layer 5 Layer 4 Layer 3 Layer 2 Layer 1 Layer 7 Layer 6 Layer 5 Layer 4 Layer 3 Layer 2 Layer 1 Layer 7 Protocol Layer 4 Protocol Layer 3 Protocol Layer 2 Protocol Layer 6 Protocol Layer 1 Protocol Layer 5 Protocol Physical Medium Host AHost B

17 Different Layering Architectures ISO OSI 7-Layer Architecture TCP/IP 4-Layer Architecture –+ application layer = 5 layers in Kurose Novell NetWare IPX/SPX 4-Layer Architecture

18 Standards Making Organizations ISO = International Standards Organization ITU = International Teletraffic Union (formerly CCITT) ANSI = American National Standards Institute IEEE = Institute of Electrical and Electronic Engineers IETF = Internet Engineering Task Force ATM Forum = ATM standards-making body...and many more

19 Why So Many Standards Organizations? Multiple technologies Different areas of emphasis and history –Telecommunications/telephones ITU,ISO,ATM –Local area networking/computers IETF, IEEE –System area networks/storage ANSI

20 ISO OSI Layering Architecture Application Layer Presentation Layer Session Layer Transport Layer Network Layer Data Link Layer Physical Layer Application Protocol Transport Protocol Presentation Protocol Session Protocol Host AHost B Application Layer Presentation Layer Session Layer Transport Layer Network Layer Data Link Layer Physical Layer Network Layer Data Link Layer Physical Layer Network Layer Data Link Layer Physical Layer Router

21 ISO’s Design Principles A layer should be created where a different level of abstraction is needed Each layer should perform a well-defined function The layer boundaries should be chosen to minimize information flow across the interfaces The number of layers should be large enough that distinct functions need not be thrown together in the same layer out of necessity, and small enough that the architecture does not become unwieldy

22 Layer 1: Physical Layer Functions: –Transmission of a raw bit stream –Forms the physical interface between devices Issues: –Which modulation technique (bits to pulse)? –How long will a bit last? –Bit-serial or parallel transmission? –Half- or Full-duplex transmission? –How many pins does the network connector have? –How is a connection set up or torn down?

23 Layer 2: Data Link Layer Functions: –Provides reliable transfer of information between two adjacent nodes –Creates frames, or packets, from bits and vice versa –Provides frame-level error control –Provides flow control In summary, the data link layer provides the network layer with what appears to be an error-free link for packets

24 Layer 3: Network Layer Functions: –Responsible for routing decisions Dynamic routing Fixed routing –Performs congestion control

25 Layer 4: Transport Layer Functions: –Hide the details of the network from the session layer Example: If we want replace a point-to-point link with a satellite link, this change should not affect the behavior of the upper layers –Provides reliable end-to-end communication

26 Application Layer Presentation Layer Session Layer Transport Layer Network Layer Data Link Layer Physical Layer Application Protocol Transport Protocol Presentation Protocol Session Protocol Host AHost B Application Layer Presentation Layer Session Layer Transport Layer Network Layer Data Link Layer Physical Layer Network Layer Data Link Layer Physical Layer Network Layer Data Link Layer Physical Layer Router Transport Layer (cont’d) first end-to-end layer

27 Transport Layer (cont’d) Functions (cont’d): –Perform end-to-end flow control –Perform packet retransmission when packets are lost by the network

28 Layer 5: Session Layer May perform synchronization between several communicating applications or logical transmissions Groups several user-level connections into a single “session” Examples: –Banking session –Network meetings

29 Layer 6: Presentation Layer Performs specific functions that are requested regularly by applications Examples: –encryption –ASCII to Unicode, Unicode to ASCII –LSB-first representations to MSB-first representations

30 Layer 7: Application Layer Application layer protocols are application- dependent Implements communication between two applications of the same type Examples: –FTP –Quake –SMTP ( )

31 Encapsulation Treat the neighboring layer’s information as a “black box”, can’t look inside or break message Sending: add information needed by the current layer “around” the higher layers’ data –headers in front –trailers in back Receiving: Strip off headers and trailers before handing up the stack

32 Encapsulation Headers Trailer Application Layer Presentation Layer Session Layer Transport Layer Network Layer Data Link Layer Physical Layer Data AH DataPH DataSHDataTH DataNH DataDHDT DataPH

33 Internet “Hourglass” Architecture Defined by Internet Engineering Task Force (IETF) “Hourglass” Design … FTPHTTPRTP TFTP TCP UDP IP Ethernet PPP CAT-5Single-Mode Fiber RS-232

34 Internet Design Principles –Scale Protocols should work in networks of all sizes and distances –Incremental deployment New protocols need to be deployed gradually –Heterogeneity Different technologies, autonomous organizations –End-to-end argument Some functions can only be correctly implemented at the end hosts; the network should not provided these.

35 TCP/IP Layering Architecture A simplified model The network layer –Hosts drop packets into this layer, layer routes towards destination- only promise- try my best The transport layer –reliable byte-oriented stream Application Transport Internet/Network Host-to-Net

36 TCP/IP Layering Architecture (cont’d) Application Protocol Transport Protocol (TCP) Application Layer Transport Layer Network Layer Host-to- Net Layer Host AHost B Application Layer Transport Layer Network Layer Host-to- Net Layer Network Layer Host-to- Net Layer Network Layer Host-to- Net Layer IP

37 Internet Topology Current structure divides network into the “core” and “edge” networks Core ISP’s “tiers” –Tier 1: Biggest ISPs E.g. MCI, Sprint, AT&T –Tier 2 and 3: Regional and very small. Edges: –Companies, organizations with a “default route” E.g. Rutgers

38 Edge Networks Company A Company B Internet Service Provider 1 ISP 2 Edge router

39 Core Networks Company A Company B Internet Service Provider 1 ISP 2

40 Single link Network Performance A Brief Introduction

41 Why Study Network Performance Networks cost $ –OC-3 line ~= $10,000/month –Cable modem: $40/month –Are you getting your $/worth? Why is the network “slow”? Approach: –Build abstract models of network performance –Observe where real networks deviate from model –Simple Models: Tells us average/best/worse cases->useful, practical –Complex Models: Hard to understand -> useless

42 Digression: Units Bits are the units used to describe an amount of data in a network –1 kilobit (Kbit) = 1 x 10 3 bits = 1,000 bits –1 megabit (Mbit)= 1 x 10 6 bits = 1,000,000 bits –1 gigabit (Gbit)= 1 x 10 9 bits = 1,000,000,000 bits Seconds are the units used to measure time –1 millisecond (msec)= 1 x seconds = seconds –1 microsecond (  sec) = 1 x seconds = seconds –1 nanosecond (nsec) = 1 x seconds = seconds Bits per second are the units used to measure channel capacity/bandwidth and throughput –bit per second (bps) –kilobits per second (Kbps) –megabits per second (Mbps)

43 Types of Delay Processing –Time to execute protocol code Queuing –Time waiting in queue to be processed Transmission –Time to “get bits on wires” Propagation –Time for bits to “move across wires”

44 Some Definitions Packet length: size of a packet (units = bits or bytes) Channel speed: How fast the channel can transmit bits (units = bits/second) Packet transmission time: amount of time to transmit an entire packet (units = seconds) Propagation delay: Delay imposed by the properties of the link. Depends on the link’s distance (units = seconds)

45 Transmission vs. Prop. delay A single transmission link as a water pipe 1. The thicker the pipe, the more water it can carry from one end to the other 2. Water is carried from one end of the pipe to the other at constant speed, no matter how thick the pipe is Water = Data bits Thickness of the pipe = Channel capacity Speed of water through the pipe = Propagation delay

46 Transmission vs. Prop. Delay (cont) pipe 1. Propagation delay is how long takes to cross the pipe, irrespective of volume 2. Transmission (bandwidth delay) is related to how much water can be pushed in through the openning per unit time Assumption that inserting water and propagation overlap

x 8 bits Transmission Time How long does it take A to transmit an entire packet onto the link? Relevant information: packet length = 1500 bytes channel capacity = 100 Mbps Another way to ask this question: If the link can transmit 10 million bits in a second, how many seconds does it take to transmit 1500 bytes (8x1500 bits)? 100 Mbits 1 sec = t Solving for t… t = sec (or 120  sec)

48 Propagation Delay How long does it take a single bit to travel on the link from A to B? Relevant information: link distance = 500 m prop. delay factor = 5  sec/km Another way to ask this question: If it takes a signal 5  sec to travel 1 kilometer, then how long does it take a signal to travel 500 meters? 5  sec 1000 m = 500 m tSolving for t… t = 2.5  sec

49 Processing Delay Stylized format required to send data Analogy: adding and removing envelopes to letters Application Layer Transport Layer Network Layer Host-to- Net Layer Host How long does it take to execute all these layers? Why is this time important? Network Layer Host-to- Net Layer Router Application Layer Transport Layer Network Layer Host-to- Net Layer Host

50 Example Protocol Processing Time = 40  sec packet length = 1500 bytes channel capacity = 100 Mbps propagation delay factor = 5  sec/km AB 500 m 1. How long to format the data? 2. How long does it take a single bit to travel on the link from A to B? 3. How long does it take A to transmit an entire packet onto the link?

51 Timeline Method Time Protocol Delay Transmission time Propagation delay Protocol Delay Host AHost B st bit last bit Total time: =  sec

52 Queuing Delay Network Layer Host-to- Net Layer Router Packets arriving faster than processing or transmission delay => queuing (I.e. waiting in line) Router Packets waiting processing at input ports Packets waiting transmission at output ports

53 Switching Schemes How much “state” about the connection between two hosts does each node/router along a path through the network maintain?

54 Switching Schemes (1)Circuit Switching (2) Message Switching (Store-and-Forward) (3) Packet Switching (Store-and-Forward)

55 Circuit Switching Provides service by setting up the total path of connected lines hop-by-hop from the origin to the destination Example: Telephone network

56 Circuit Switching (cont’d) 1. Control message sets up a path from origin to destination 2. Return signal informs source that data transmission may proceed 3. Data transmission begins 4. Entire path remains allocated to the transmission (whether used or not) 5. When transmission is complete, source releases the circuit

57 Circuit Switching (cont’d) Time ABCD Data Call accept signal Call request signal Data Transmission Time Propagation Delay Routers/Switches Transmission Delay

58 Message Switching Each message is addressed to a destination When the entire message is received at a router, the next step in its journey is selected; if this selected channel is busy, the message waits in a queue until the channel becomes free Thus, the message “hops” from node to node through a network while allocating only one channel at a time Analogy: Postal service

59 Message Switching (cont’d) Time ABCD Msg Queueing Delay Routers/switches Transmission Delay Header

60 Packet Switching Messages are split into smaller pieces called packets These packets are numbered and addressed and sent through the network one at a time Allows Pipelining –Overlap sending and receiving of packets on multiple links

61 Packet Switching (cont’d) Time ABCD IMPs Pkt 1 Pkt 2 Pkt 3 Pkt 1 Pkt 2 Pkt 3 Pkt 1 Pkt 2 Pkt 3 Transmission Delay Header

62 Comparisons (1) Header Overhead Circuit < Message < Packet (2) Transmission Delay Short Bursty Messages: Packet < Message < Circuit Long Continuous Messages: Circuit < Message < Packet

63 Analytic Comparison Given choice of 2 switching schemes, how would you compare their performance? –What would you need to know? –What are the independent variables? –What is the dependent variable? Could you come up with a closed form expression based on your choices?

64 Example: Circuit Switching vs. Packet Switching Goal: Determine which is faster –Formal definition: Least time to move a fixed amount of data Approach: –Compute time where circuit switching and packet switching are equal based on all possible factors –A factor moving in one direction or the other will tip the balance in favor of one or the other –We’ll ignore wire-line propagation delay in this example

65 Factors: Number of bytes in the message: N Time to set up circuit: c Per-link bandwidth: B Size of the packet: p Size of the header: h Number of switches: s

66 Circuit Switching Time Time to send N bytes using circuit switching = Set-up cost + bandwidth delay

67 Pipelining “Parallelogram” for packet switching Time Host ASwitch 1Switch 2Host B Bandwidth Delay Propagation Delay Packet 1 Packet 2 Packet 3 Packet 4

68 Note on Pipelining The above analysis is very general: –Packets in a computer network Messages/packets are the unit of work. –Instructions in a processor Instructions are the unit of work. –Jobs through a batch Q in an operating system. Processes are the unit of work. Pipelining speeds up work over time. –How?

69 Packet Switching Time Transmission delay (also bandwidth delay): Time to push all the packets into the network + “Propagation” delay: Time for the last packet to cross - not really prop. delay in the traditional sense Delay = Transmission + “Propagation” delays

70 Packet Switching Time Number of packetsNumber of links/hops Time for each packet Transmission delay “Propagation” delay

71 Equilibrium Point Assuming all other factors equal, solve for C Q: Can you add link propagation delay to this example?

72 Homework Questions If we use message switching, how does the time increase as we scale s? How does packet switching reduce the impact of increasing s? Show, using an equation, how reducing the packet size and packet switching reduces the impact of increasing s. Where does the approach of reducing packet size fail to give any benefit?