Your SlideShare is downloading. ×
0
Introduction to Data Networking
Introduction to this class <ul><li>Me: Stephan Bohacek </li></ul><ul><li>bohacek@udel.edu, 302-831-4274, skype: Stephan.Bo...
Syllabus (also online) <ul><li>Textbook: Kurose and Rose. Computer Networking, 2007 (the 4th edition). This book is requir...
Syllabus (also online)
Today – networking basics <ul><li>Movie on the history of the Internet </li></ul><ul><li>Core components of the Internet –...
Today – networking basics <ul><li>Movie on the history of the Internet </li></ul><ul><li>Core components of the Internet –...
Today – networking basics <ul><li>Movie on the history of the Internet </li></ul><ul><li>Core components of the Internet –...
Core components <ul><li>End-hosts </li></ul><ul><li>Applications </li></ul><ul><ul><li>?  </li></ul></ul><ul><li>Packets <...
Core components <ul><li>End-hosts </li></ul><ul><li>Applications </li></ul><ul><ul><li>Web </li></ul></ul><ul><ul><li>Emai...
Application Layer – where the applications live <ul><li>Email: </li></ul><ul><ul><li>Rules/protocols for how an end-host g...
Layers 1-4 <ul><li>End-hosts </li></ul><ul><li>Applications </li></ul><ul><ul><li>Web </li></ul></ul><ul><ul><li>Email </l...
Layers 1-4 <ul><li>End-hosts </li></ul><ul><li>Applications </li></ul><ul><ul><li>Web </li></ul></ul><ul><ul><li>Email </l...
Layers 1-4 <ul><li>End-hosts </li></ul><ul><li>Applications </li></ul><ul><ul><li>Web </li></ul></ul><ul><ul><li>Email </l...
Layers 1-4 <ul><li>End-hosts </li></ul><ul><li>Applications </li></ul><ul><ul><li>Web </li></ul></ul><ul><ul><li>Email </l...
Layers 1-4 <ul><li>End-hosts </li></ul><ul><li>Applications </li></ul><ul><ul><li>Web </li></ul></ul><ul><ul><li>Email </l...
Protocols <ul><li>End-hosts </li></ul><ul><li>Applications </li></ul><ul><ul><li>Web </li></ul></ul><ul><ul><li>Email </li...
Internet protocol stack <ul><li>application:  supporting network applications </li></ul><ul><ul><li>FTP, SMTP, HTTP </li><...
ISO/OSI reference model <ul><li>presentation:  allow applications to interpret meaning of data, e.g., encryption, compress...
Today – networking basics <ul><li>Movie on the history of the Internet </li></ul><ul><li>Core components of the Internet –...
Circuit switching versus Packet switching <ul><li>Packet switching brought the networking revolution </li></ul><ul><li>Cir...
Circuit switching <ul><li>Circuit switching </li></ul><ul><ul><li>Old style phone system </li></ul></ul><ul><ul><li>Each c...
Frequency division multiplexing toll office End office phone On each hop, the connection gets its own bandwidth TV is freq...
Time division multiplexing 64kbits 1 2 3 bytes 1/8000 sec per byte 7 bits of data and one bit for control (data or not), s...
Packet switching - Statistical multiplexing <ul><li>Data is in packets, not streams. </li></ul><ul><li>Must be digital </l...
Packet switching - Statistical multiplexing <ul><li>Data is in packets, not streams. </li></ul><ul><li>Must be digital </l...
Packet switching - Statistical multiplexing <ul><li>Data is in packets, not streams. </li></ul><ul><li>Must be digital </l...
Packet vs. Circuit Switching <ul><li>If usage is random (e.g., web surfing) statistical multiplexing is better.  </li></ul...
Packet Switching Case <ul><li>Now if there are 200 users, what is the probability that there are 150 or more  active  user...
Packet Switching Case <ul><li>What is the probability of more than 100 users being active? </li></ul>The probability of 10...
Packet Switching vs. Circuit Switching <ul><li>A couple of things: </li></ul><ul><li>This means that </li></ul><ul><li>whe...
Packet Switching vs. Circuit Switching <ul><li>If loss and delay are permissible and usage is random, then packet switchin...
Packet Switching: Statistical Multiplexing <ul><li>Sequence of A & B packets does not have fixed pattern, bandwidth shared...
Packet-switching: store-and-forward <ul><li>takes L/R seconds to transmit (push out) packet of L bits on to link at R bps ...
Today – networking basics <ul><li>Movie on the history of the Internet </li></ul><ul><li>Core components of the Internet –...
Losses and delay in packet switched networks <ul><li>Losses </li></ul><ul><ul><li>Transmission losses </li></ul></ul><ul><...
Queuing delay <ul><li>Queuing delay occurs for the same reason as congestion losses. </li></ul><ul><li>The more the networ...
Queuing delay <ul><li>Is it possible to have a network run at full utilization? </li></ul>No! The average delay would be i...
Delay in packet switched networks <ul><li>Delay </li></ul><ul><ul><li>Queuing delay </li></ul></ul><ul><ul><li>Transmissio...
Delay in packet switched networks <ul><li>Delay </li></ul><ul><ul><li>Queuing delay </li></ul></ul><ul><ul><li>Transmissio...
Fun with Propagation Delay How long is a bit? Suppose that a links transmits at 10mbps. How long is a bit? How long does i...
Delay in packet switched networks <ul><li>Routers take a bit of time to process packets. </li></ul><ul><li>moving packets ...
How to measure delay? <ul><li>Ping: > ping 216.109.124.73 </li></ul><ul><li>Ping  gives help </li></ul><ul><li>(linux) Pin...
Today – networking basics <ul><li>Movie on the history of the Internet </li></ul><ul><li>Core components of the Internet –...
Internet structure: network of networks <ul><li>roughly hierarchical </li></ul><ul><li>at center: “tier-1” ISPs  (e.g., Ve...
Tier-1 ISP: e.g., Sprint … to/from customers peering to/from backbone …. … … … POP: point-of-presence
Internet structure: network of networks <ul><li>“ Tier-2” ISPs: smaller (often regional) ISPs </li></ul><ul><ul><li>Connec...
Internet structure: network of networks <ul><li>“ Tier-3” ISPs and local ISPs  </li></ul><ul><ul><li>last hop (“access”) n...
Internet structure: network of networks <ul><li>a packet passes through many networks! </li></ul>Tier 1 ISP Tier 1 ISP Tie...
ISPs and the structure of the Internet <ul><li>Video of a Network Access Point (NAP) in Los Angeles </li></ul>
Said to be the most interconnected space in the world and the most expensive real estate in North America, the “Meet Me Ro...
Some 1,800 known conduits contain the fiber optic cables that flow through the building’s stairwells and vertical utility ...
Whenever a permit is pulled by a city contractor for any underground repairs outside One Wilshire, the various telco compa...
Computers generate a lot of heat, and maintaining a stable, cool temperature and a low humidity is essential in telco hote...
As tenants’ needs change, cables can go unused. Cable mining is performed to thin out the obsolete cables and future conge...
Power is supplied by DWP, but in the event of a blackout, the building’s five generators will kick in. It takes the genera...
On the roof, microwave antennas link up One Wilshire to transmission towers located around the city. Though fiber’s higher...
Much can be learned about a building’s function by examining its roof. The existence of telco hotels in the region around ...
The main fiber optic cables connecting One Wilshire to the world enter the building from under the street through closets ...
Said to be the most interconnected space in the world and the most expensive real estate in North America, the “Meet Me Ro...
Some 1,800 known conduits contain the fiber optic cables that flow through the building’s stairwells and vertical utility ...
Whenever a permit is pulled by a city contractor for any underground repairs outside One Wilshire, the various telco compa...
Computers generate a lot of heat, and maintaining a stable, cool temperature and a low humidity is essential in telco hote...
As tenants’ needs change, cables can go unused. Cable mining is performed to thin out the obsolete cables and future conge...
Power is supplied by DWP, but in the event of a blackout, the building’s five generators will kick in. It takes the genera...
On the roof, microwave antennas link up One Wilshire to transmission towers located around the city. Though fiber’s higher...
Much can be learned about a building’s function by examining its roof. The existence of telco hotels in the region around ...
The main fiber optic cables connecting One Wilshire to the world enter the building from under the street through closets ...
Homework <ul><li>Page 61. Questions (3, 7), 8, (9), (10), 11, 13, 14, 19, (20), 21, (22), (23) </li></ul><ul><li>Page 63. ...
Upcoming SlideShare
Loading in...5
×

Lecture: Introduction

426

Published on

0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total Views
426
On Slideshare
0
From Embeds
0
Number of Embeds
0
Actions
Shares
0
Downloads
9
Comments
0
Likes
0
Embeds 0
No embeds

No notes for slide

Transcript of "Lecture: Introduction"

  1. 1. Introduction to Data Networking
  2. 2. Introduction to this class <ul><li>Me: Stephan Bohacek </li></ul><ul><li>bohacek@udel.edu, 302-831-4274, skype: Stephan.Bohacek </li></ul><ul><li>http://www.eecis.udel.edu/~bohacek </li></ul><ul><li>Syllabus (online) </li></ul>
  3. 3. Syllabus (also online) <ul><li>Textbook: Kurose and Rose. Computer Networking, 2007 (the 4th edition). This book is required </li></ul><ul><li>Prerequisites: Introduction to probability, C/C++ programming </li></ul><ul><li>Grading: homework=1/3, projects=1/3, final=1/3. Homework and projects turned in late will be marked off 2.5% per day (including weekends). Grades of online discussion are based on the number and qualtiy of postings. These postings may be in the form of questions and answers. A good question will count toward your discussion grade. </li></ul><ul><li>There will be programming assignments. This can be done on Linux or on Windows with Visual Studio. Evans 132 has linux machines and remote access is possible. Also, with your EECIS user name and password, MS visual studio can be downloaded for free from here </li></ul>
  4. 4. Syllabus (also online)
  5. 5. Today – networking basics <ul><li>Movie on the history of the Internet </li></ul><ul><li>Core components of the Internet – the protocol stack </li></ul><ul><li>Multiplexing, circuit switching, and packet switching </li></ul><ul><li>Loss and delays </li></ul><ul><li>The structure of the Internet </li></ul><ul><li>This lecture covers much of chapter 1 in the textbook. </li></ul>
  6. 6. Today – networking basics <ul><li>Movie on the history of the Internet </li></ul><ul><li>Core components of the Internet – the protocol stack </li></ul><ul><li>Multiplexing, circuit switching, and packet switching </li></ul><ul><li>Loss and delays </li></ul><ul><li>The structure of the Internet </li></ul><ul><li>This lecture covers much of chapter 1 in the textbook. </li></ul>
  7. 7. Today – networking basics <ul><li>Movie on the history of the Internet </li></ul><ul><li>Core components of the Internet – the protocol stack </li></ul><ul><li>Multiplexing, circuit switching, and packet switching </li></ul><ul><li>Loss and delays </li></ul><ul><li>The structure of the Internet </li></ul><ul><li>This lecture covers much of chapter 1 in the textbook. </li></ul>
  8. 8. Core components <ul><li>End-hosts </li></ul><ul><li>Applications </li></ul><ul><ul><li>? </li></ul></ul><ul><li>Packets </li></ul><ul><ul><li>? </li></ul></ul><ul><li>Routers and gateways and groups of routers (ISPs) </li></ul><ul><li>Links </li></ul><ul><ul><li>? </li></ul></ul><ul><li>Protocols </li></ul>
  9. 9. Core components <ul><li>End-hosts </li></ul><ul><li>Applications </li></ul><ul><ul><li>Web </li></ul></ul><ul><ul><li>Email </li></ul></ul><ul><ul><li>File transfer </li></ul></ul><ul><ul><li>File sharing </li></ul></ul><ul><li>Packets </li></ul><ul><ul><li>TCP </li></ul></ul><ul><ul><li>UDP </li></ul></ul><ul><li>Routers and gateways and groups of routers (ISPs) </li></ul><ul><li>Links </li></ul><ul><ul><li>Fiber </li></ul></ul><ul><ul><li>Coaxial </li></ul></ul><ul><ul><li>Twisted pair </li></ul></ul><ul><ul><li>Wireless </li></ul></ul><ul><li>Protocols </li></ul>
  10. 10. Application Layer – where the applications live <ul><li>Email: </li></ul><ul><ul><li>Rules/protocols for how an end-host gets mail from the mail server </li></ul></ul><ul><li>Web: </li></ul><ul><ul><li>Rules/protocols for how the end-hosts gets a web page from the web servers </li></ul></ul><ul><li>Question: </li></ul><ul><ul><li>How is a networking application different from a non-networking application (e.g., MS Word). That is, why do we say that an application is a bunch of rules? MS-Word is not a bunch of rules? </li></ul></ul><ul><ul><li>Answer: The networking applications must communicate, and rules are required to define the communication. </li></ul></ul><ul><li>Roles that end-hosts play: </li></ul><ul><ul><li>Client, server, and peer </li></ul></ul><ul><ul><li>The client asks the server for a service. </li></ul></ul><ul><ul><ul><li>E.g., The client asks the server to send a mail for it. </li></ul></ul></ul><ul><ul><ul><li>The client asks the server for a web page </li></ul></ul></ul><ul><ul><ul><li>The client asks the server to translate a web address to an IP address. </li></ul></ul></ul><ul><ul><li>Peer: A host can act as both a client and a server. But usually in one transaction, the host takes only one role </li></ul></ul><ul><li>End-hosts </li></ul><ul><li>Applications </li></ul><ul><ul><li>Web </li></ul></ul><ul><ul><li>Email </li></ul></ul><ul><ul><li>File transfer </li></ul></ul><ul><ul><li>File sharing </li></ul></ul><ul><li>Packets </li></ul><ul><ul><li>TCP </li></ul></ul><ul><ul><li>UDP </li></ul></ul><ul><li>Routers and gateways and groups of routers (ISPs) </li></ul><ul><li>Links </li></ul><ul><ul><li>Fiber </li></ul></ul><ul><ul><li>Coaxial </li></ul></ul><ul><ul><li>Twisted pair </li></ul></ul><ul><ul><li>Wireless </li></ul></ul><ul><li>Protocols </li></ul>
  11. 11. Layers 1-4 <ul><li>End-hosts </li></ul><ul><li>Applications </li></ul><ul><ul><li>Web </li></ul></ul><ul><ul><li>Email </li></ul></ul><ul><ul><li>File transfer </li></ul></ul><ul><ul><li>File sharing </li></ul></ul><ul><li>Packets </li></ul><ul><ul><li>TCP </li></ul></ul><ul><ul><li>UDP </li></ul></ul><ul><li>Routers and gateways and groups of routers (ISPs) </li></ul><ul><li>Links </li></ul><ul><ul><li>Fiber </li></ul></ul><ul><ul><li>Coaxial </li></ul></ul><ul><ul><li>Twisted pair </li></ul></ul><ul><ul><li>Wireless </li></ul></ul><ul><li>Protocols </li></ul>client server Which are the end-host? Routers
  12. 12. Layers 1-4 <ul><li>End-hosts </li></ul><ul><li>Applications </li></ul><ul><ul><li>Web </li></ul></ul><ul><ul><li>Email </li></ul></ul><ul><ul><li>File transfer </li></ul></ul><ul><ul><li>File sharing </li></ul></ul><ul><li>Packets </li></ul><ul><ul><li>TCP </li></ul></ul><ul><ul><li>UDP </li></ul></ul><ul><li>Routers and gateways and groups of routers (ISPs) </li></ul><ul><li>Links </li></ul><ul><ul><li>Fiber </li></ul></ul><ul><ul><li>Coaxial </li></ul></ul><ul><ul><li>Twisted pair </li></ul></ul><ul><ul><li>Wireless </li></ul></ul><ul><li>Protocols </li></ul>client server Goal: move messages from server to the client Approach: break the problem into little pieces. Each piece is a layer in the “protocol stack” <ul><li>Why is this a good approach? </li></ul><ul><li>Small problems are easier </li></ul><ul><li>to understand/solve. </li></ul><ul><li>2.Different solutions can be </li></ul><ul><li>mixed and matched </li></ul>
  13. 13. Layers 1-4 <ul><li>End-hosts </li></ul><ul><li>Applications </li></ul><ul><ul><li>Web </li></ul></ul><ul><ul><li>Email </li></ul></ul><ul><ul><li>File transfer </li></ul></ul><ul><ul><li>File sharing </li></ul></ul><ul><li>Packets </li></ul><ul><ul><li>TCP </li></ul></ul><ul><ul><li>UDP </li></ul></ul><ul><li>Routers and gateways and groups of routers (ISPs) </li></ul><ul><li>Links </li></ul><ul><ul><li>Fiber </li></ul></ul><ul><ul><li>Coaxial </li></ul></ul><ul><ul><li>Twisted pair </li></ul></ul><ul><ul><li>Wireless </li></ul></ul><ul><li>Protocols </li></ul><ul><li>Top down approach of breaking problems into small pieces </li></ul><ul><li>Transport layer </li></ul><ul><ul><li>Reliability: The server must make sure that the client gets the data </li></ul></ul><ul><ul><li>Congestion control (or lack there of) </li></ul></ul><ul><ul><li>Congestion Control: The server should send data as fast as possible, but not too fast </li></ul></ul><ul><ul><li>TCP provides these features (services), while UDP does not </li></ul></ul><ul><li>Network layer (could be called the routing layer, but it isn’t) </li></ul><ul><ul><li>The packets must find their way through the network. </li></ul></ul><ul><ul><li>Each packet has the IP address of the destination </li></ul></ul><ul><ul><li>By examining the IP address, routers decide where to send the packet next </li></ul></ul><ul><li>Link Layer or MAC layer </li></ul><ul><ul><li>Links connect the routers/gateways and end-hosts </li></ul></ul><ul><ul><li>This layer provides logical and control for communicating across links. </li></ul></ul><ul><ul><li>Services that this layer might provide include </li></ul></ul><ul><ul><ul><li>congestion control, media access, error detection/correction </li></ul></ul></ul>client server
  14. 14. Layers 1-4 <ul><li>End-hosts </li></ul><ul><li>Applications </li></ul><ul><ul><li>Web </li></ul></ul><ul><ul><li>Email </li></ul></ul><ul><ul><li>File transfer </li></ul></ul><ul><ul><li>File sharing </li></ul></ul><ul><li>Packets </li></ul><ul><ul><li>TCP </li></ul></ul><ul><ul><li>UDP </li></ul></ul><ul><li>Routers and gateways and groups of routers (ISPs) </li></ul><ul><li>Links </li></ul><ul><ul><li>Fiber </li></ul></ul><ul><ul><li>Coaxial </li></ul></ul><ul><ul><li>Twisted pair </li></ul></ul><ul><ul><li>Wireless </li></ul></ul><ul><li>Protocols </li></ul><ul><li>Top down approach of breaking problems into small pieces </li></ul><ul><li>… .. </li></ul><ul><li>Link Layer or MAC layer </li></ul><ul><ul><li>Links connect the routers/gateways and end-hosts </li></ul></ul><ul><ul><li>This layer provides logical and control for communicating across links. </li></ul></ul><ul><ul><li>Services that this layer might provide include </li></ul></ul><ul><ul><ul><li>congestion control, media access, error detection/correction </li></ul></ul></ul><ul><li>Media access. The “air” is a shared medium. If two nodes transmit at the same time, there will be a collision. Thus, a scheme must be developed to determine which node transmits when. </li></ul><ul><li>Error detection/correction. If interference does occur, then errors might occur. If an error is detected, then </li></ul><ul><ul><li>the error could be corrected with forward error correction, or </li></ul></ul><ul><ul><li>the receiving link could request a retransmission </li></ul></ul>
  15. 15. Layers 1-4 <ul><li>End-hosts </li></ul><ul><li>Applications </li></ul><ul><ul><li>Web </li></ul></ul><ul><ul><li>Email </li></ul></ul><ul><ul><li>File transfer </li></ul></ul><ul><ul><li>File sharing </li></ul></ul><ul><li>Packets </li></ul><ul><ul><li>TCP </li></ul></ul><ul><ul><li>UDP </li></ul></ul><ul><li>Routers and gateways and groups of routers (ISPs) </li></ul><ul><li>Links </li></ul><ul><ul><li>Fiber </li></ul></ul><ul><ul><li>Coaxial </li></ul></ul><ul><ul><li>Twisted pair </li></ul></ul><ul><ul><li>Wireless </li></ul></ul><ul><li>Protocols </li></ul><ul><li>Top down approach of breaking problems into small pieces </li></ul><ul><li>Transport layer </li></ul><ul><ul><li>Reliability: The server must make sure that the client gets the data </li></ul></ul><ul><ul><li>Congestion control (or lack there of) </li></ul></ul><ul><ul><li>Congestion Control: The server should send data as fast as possible, but not too fast </li></ul></ul><ul><ul><li>TCP provides these features (services), while UDP does not </li></ul></ul><ul><li>Network layer (could be called the routing layer, but it isn’t) </li></ul><ul><ul><li>The packets must find their way through the network. </li></ul></ul><ul><ul><li>Each packet has the IP address of the destination </li></ul></ul><ul><ul><li>By examining the IP address, routers decide where to send the packet next </li></ul></ul><ul><li>Link Layer or MAC layer </li></ul><ul><ul><li>Links connect the routers/gateways and end-hosts </li></ul></ul><ul><ul><li>This layer provides logical and control for communicating across links. </li></ul></ul><ul><ul><li>Services that this layer might provide include </li></ul></ul><ul><ul><ul><li>congestion control, media access, error detection/correction </li></ul></ul></ul><ul><li>Physical layer </li></ul><ul><ul><li>Logical bits are encoded as physical quantities, e.g., as voltage levels, as shifts in phase, … </li></ul></ul><ul><ul><li>This course does not cover the physical layer </li></ul></ul>client server
  16. 16. Protocols <ul><li>End-hosts </li></ul><ul><li>Applications </li></ul><ul><ul><li>Web </li></ul></ul><ul><ul><li>Email </li></ul></ul><ul><ul><li>File transfer </li></ul></ul><ul><ul><li>File sharing </li></ul></ul><ul><li>Packets </li></ul><ul><ul><li>TCP </li></ul></ul><ul><ul><li>UDP </li></ul></ul><ul><li>Routers and gateways and groups of routers (ISPs) </li></ul><ul><li>Links </li></ul><ul><ul><li>Fiber </li></ul></ul><ul><ul><li>Coaxial </li></ul></ul><ul><ul><li>Twisted pair </li></ul></ul><ul><ul><li>Wireless </li></ul></ul><ul><li>Protocols </li></ul>protocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt Hi Hi Got the time? 2:00 TCP connection request TCP connection response Get http://www.awl.com/kurose-ross <file> time
  17. 17. Internet protocol stack <ul><li>application: supporting network applications </li></ul><ul><ul><li>FTP, SMTP, HTTP </li></ul></ul><ul><li>transport: process-process data transfer </li></ul><ul><ul><li>TCP, UDP </li></ul></ul><ul><li>network: routing of datagrams from source to destination </li></ul><ul><ul><li>IP, routing protocols </li></ul></ul><ul><li>link: data transfer between neighboring network elements </li></ul><ul><ul><li>PPP, Ethernet </li></ul></ul><ul><li>physical: bits “on the wire” </li></ul>application transport network link physical
  18. 18. ISO/OSI reference model <ul><li>presentation: allow applications to interpret meaning of data, e.g., encryption, compression, machine-specific conventions </li></ul><ul><li>session: synchronization, checkpointing, recovery of data exchange </li></ul><ul><li>Internet stack “missing” these layers! </li></ul><ul><ul><li>these services, if needed, must be implemented in application </li></ul></ul><ul><ul><li>needed? </li></ul></ul>application presentation session transport network link physical
  19. 19. Today – networking basics <ul><li>Movie on the history of the Internet </li></ul><ul><li>Core components of the Internet – the protocol stack </li></ul><ul><li>Multiplexing, circuit switching, and packet switching </li></ul><ul><li>Loss and delays </li></ul><ul><li>The structure of the Internet </li></ul><ul><li>This lecture covers much of chapter 1 in the textbook. </li></ul>
  20. 20. Circuit switching versus Packet switching <ul><li>Packet switching brought the networking revolution </li></ul><ul><li>Circuit switching </li></ul><ul><li>Virtual circuit networking </li></ul><ul><ul><li>A half-way point between packet switched and circuit switched networking </li></ul></ul>
  21. 21. Circuit switching <ul><li>Circuit switching </li></ul><ul><ul><li>Old style phone system </li></ul></ul><ul><ul><li>Each connection gets its own wire or bandwidth </li></ul></ul><ul><ul><li>Note: calls must be set-up. </li></ul></ul><ul><ul><li>E.g., </li></ul></ul><ul><ul><ul><li>Me: operator, get my the president. </li></ul></ul></ul><ul><ul><ul><li>Operator: one moment please. </li></ul></ul></ul><ul><ul><ul><li>Then she plugs a cable into a socket so now I have a physical wired between me and the president. </li></ul></ul></ul><ul><ul><li>Instead of each connection getting a whole wire, connections can share a wire via multiplexing </li></ul></ul><ul><ul><li>The first automatic circuit switching was developed by Almon Strowger – an undertaker. There were two undertakers in a small town and the switch board operator was the wife of the other undertaker. So Strowger invented an automatic circuit switch to rid both husband and wife of employment. </li></ul></ul>
  22. 22. Frequency division multiplexing toll office End office phone On each hop, the connection gets its own bandwidth TV is frequency division multiplexing phone End office 300 3400 100300 103400 200300 203400 300 3400
  23. 23. Time division multiplexing 64kbits 1 2 3 bytes 1/8000 sec per byte 7 bits of data and one bit for control (data or not), so it really 56kbps of data Overhead is 1 bit per 8*24 bits = 8000bps Note all the control overhead: if the bit is 1, then payload is control. Lots of control is needed to setup a circuit. How is it possible to get channels at each hop? Also, if there is not data, then nothing is sent. This wastes data. But the circuit is yours, guaranteed! 1 2 1 1 Multiplex 24 channels = 24*64kbps + overhead = 1.544Mbps DS1 (T1) Multiplex 28 DS1 = 28*24*64kbps + overhead = 44.736Mbps DS-3 Multiplexing 810 channels + overhead = 51.84 = STS-1/OC-1 STS is electrical and oc is optical OC3 = 155.52Mbps (150.336 payload) OC12 = 633.08 Mbps (601.344 payload) OC48 = 2.488Gbps (2.405Gbps) OC192 = 9.953Gbps (9.6Gbps payload) There are standard bit-rates that support multiplexing different numbers of calls
  24. 24. Packet switching - Statistical multiplexing <ul><li>Data is in packets, not streams. </li></ul><ul><li>Must be digital </li></ul><ul><li>Each packet has an address </li></ul><ul><li>A switch/router reads the whole packet, then reads the address and forwards the packet – store and forward </li></ul>client Server: address = 1 1 data packet. Note format specification specifies where the address is
  25. 25. Packet switching - Statistical multiplexing <ul><li>Data is in packets, not streams. </li></ul><ul><li>Must be digital </li></ul><ul><li>Each packet has an address </li></ul><ul><li>A switch/router reads the whole packet, then reads the address and forwards the packet – store and forward </li></ul>client Server: address = 1 A B C D F E If destination is 1, then next hop is B If destination is 1, then next hop is C If destination is 1, then next hop is 1 data 1 data 1 data 1 data
  26. 26. Packet switching - Statistical multiplexing <ul><li>Data is in packets, not streams. </li></ul><ul><li>Must be digital </li></ul><ul><li>Each packet has an address </li></ul><ul><li>A switch/router reads the whole packet, then reads the address and forwards the packet – store and forward </li></ul><ul><li>No reservations are needed. First come first serve. </li></ul><ul><li>Major benefit: </li></ul><ul><ul><li>If you need more bandwidth, then you can get it, it you don’t need it, then maybe someone else can use it. </li></ul></ul><ul><li>Major drawback: </li></ul><ul><ul><li>What happens if two packets arrive at a switch and both need to go to the same output interface. Picture. One packet is either dropped, or is placed in a buffer. Either way, something bad has happened, the packet is gone, or is delayed. This would never happen on a circuit switched network.  queuing delay and packet loss  </li></ul></ul>
  27. 27. Packet vs. Circuit Switching <ul><li>If usage is random (e.g., web surfing) statistical multiplexing is better. </li></ul><ul><li>Suppose that </li></ul><ul><li>A 5Mbps link </li></ul><ul><li>Each user needs 50kbps </li></ul><ul><li>And each user is active 20% of the time. (note that this condition does not matter for circuit switching. Why?) </li></ul>Circuit switching case The total number of users that can be accommodated with circuit switching is 5e6/50e3 = 100 users How many users can be accommodated under packet switching and how many can be accommodated under packet switching?
  28. 28. Packet Switching Case <ul><li>Now if there are 200 users, what is the probability that there are 150 or more active users? </li></ul><ul><li>In this case, there would be a problem, since the network cannot support more than 100 active users. </li></ul>Simpler questions: What is the probability of 150 particular users being active and 50 other being inactive?
  29. 29. Packet Switching Case <ul><li>What is the probability of more than 100 users being active? </li></ul>The probability of 101 users being active plus, 102 users being active, plus, …., 200 users being active, which is
  30. 30. Packet Switching vs. Circuit Switching <ul><li>A couple of things: </li></ul><ul><li>This means that </li></ul><ul><li>when you walk into the switching center, the probability of finding overload is 10^-8. </li></ul><ul><li>Or, if you random access the link, the probability of finding it in overload. </li></ul><ul><li>Once you find it in overload, or not, the probability that is will be in overload in the next second is more complicated and requires queuing theory. This analysis might reveal worst performance. </li></ul><ul><li>In this example, we assumed 20% user utilization (they were active 20% of the time) </li></ul><ul><li>Is this large or small? </li></ul><ul><li>If it the user utilization is smaller, then the difference between packet switching and circuit switching is even larger. But it is smaller, then there is less of a difference. </li></ul><ul><li>What is your user utilization? </li></ul><ul><li>For web surfing </li></ul><ul><li>For cell phone usage </li></ul><ul><li>For music streaming </li></ul>What does this probability really mean?
  31. 31. Packet Switching vs. Circuit Switching <ul><li>If loss and delay are permissible and usage is random, then packet switching is better than circuit switching. </li></ul><ul><li>If usage is very regular (e.g. TV!), circuit switching is best. </li></ul><ul><li>If losses and delay are not permissible, then circuit switching is best (e.g., remote controlled surgery). </li></ul><ul><li>With packet switching, congestion control is required. Also, there is more overhead for each packet. </li></ul><ul><li>For circuit switching, once the circuit is setup, it can be very efficient. But circuits must be set-up. </li></ul><ul><li>So, for short file transfer, packet switching is good but for long file transfers, circuit switching might be better. </li></ul>There is a subtle difference between packet switching and statistical multiplexing. Statistical multiplexing means to use the resource as needed. This leads to the performance improvements mentioned but also the complications (delay and loss). The phone network uses circuit switching, but the circuits are statistically multiplexed between users. In packet switching, links are statistically multiplexed.
  32. 32. Packet Switching: Statistical Multiplexing <ul><li>Sequence of A & B packets does not have fixed pattern, bandwidth shared on demand  statistical multiplexing . </li></ul><ul><li>TDM: each host gets same slot in revolving TDM frame. </li></ul>A B C 100 Mb/s Ethernet 1.5 Mb/s statistical multiplexing queue of packets waiting for output link D E
  33. 33. Packet-switching: store-and-forward <ul><li>takes L/R seconds to transmit (push out) packet of L bits on to link at R bps </li></ul><ul><li>store and forward: entire packet must arrive at router before it can be transmitted on next link </li></ul><ul><li>delay = 3L/R (assuming zero propagation delay) </li></ul><ul><li>Example: </li></ul><ul><li>L = 7.5 Mbits </li></ul><ul><li>R = 1.5 Mbps </li></ul><ul><li>transmission delay = 15 sec </li></ul>R R R L more on delay shortly …
  34. 34. Today – networking basics <ul><li>Movie on the history of the Internet </li></ul><ul><li>Core components of the Internet – the protocol stack </li></ul><ul><li>Multiplexing, circuit switching, and packet switching </li></ul><ul><li>Loss and delays </li></ul><ul><li>The structure of the Internet </li></ul><ul><li>This lecture covers much of chapter 1 in the textbook. </li></ul>
  35. 35. Losses and delay in packet switched networks <ul><li>Losses </li></ul><ul><ul><li>Transmission losses </li></ul></ul><ul><ul><ul><li>In fiber links, bit-error is 10^-12 or better (i.e., less). </li></ul></ul></ul><ul><ul><ul><ul><li>What is the probability of packet error when there are 1400 bytes in a packet? </li></ul></ul></ul></ul><ul><ul><ul><li>In wireless links, the bit-error rate can be very high </li></ul></ul></ul><ul><ul><li>Congestion losses. </li></ul></ul><ul><ul><ul><li>If too many packets arrive at the same time, then the buffers will fill up and packets are lost. </li></ul></ul></ul><ul><ul><ul><li>Increasing the link speeds or reducing the number of users can reduce the probability of loss. </li></ul></ul></ul><ul><ul><ul><li>Increasing the size of the buffer reduces losses, but also increases delay. </li></ul></ul></ul><ul><li>Delay </li></ul><ul><ul><li>Queuing delay </li></ul></ul><ul><ul><li>Transmission delay </li></ul></ul><ul><ul><li>Propagation delay </li></ul></ul><ul><ul><li>Processing delay </li></ul></ul>A B packet being transmitted (delay) packets queueing (delay) free (available) buffers: arriving packets dropped ( loss ) if no free buffers
  36. 36. Queuing delay <ul><li>Queuing delay occurs for the same reason as congestion losses. </li></ul><ul><li>The more the network is utilized, the high the queueing delay (and losses) </li></ul><ul><li>Utilization =  := actual use / maximum possible use </li></ul><ul><li>Suppose that </li></ul><ul><li>the link bit-rate is Z, </li></ul><ul><li>there are X users </li></ul><ul><li>Each users uses data rate Y, with probability P, and use no bandwidth with probability 1-p. </li></ul> = X*P/Z A B packet being transmitted (delay) packets queueing (delay) free (available) buffers: arriving packets dropped ( loss ) if no free buffers
  37. 37. Queuing delay <ul><li>Is it possible to have a network run at full utilization? </li></ul>No! The average delay would be infinite! From queuing theory Delay =  /(1-  ) 
  38. 38. Delay in packet switched networks <ul><li>Delay </li></ul><ul><ul><li>Queuing delay </li></ul></ul><ul><ul><li>Transmission delay </li></ul></ul><ul><ul><li>Propagation delay </li></ul></ul><ul><ul><li>Processing delay </li></ul></ul>How long does it take to transmit a packet? How long does it take to get all the bits from node on to the wire/air/fiber? <ul><li>Suppose </li></ul><ul><li>Link bit rate is 10 Mbps </li></ul><ul><li>Packet size is 1400 bytes </li></ul><ul><li>How long to transmit the packet? </li></ul>10*10^6 bits / sec 1400 *8 bits / packet = .0011 sec = 1.1 ms
  39. 39. Delay in packet switched networks <ul><li>Delay </li></ul><ul><ul><li>Queuing delay </li></ul></ul><ul><ul><li>Transmission delay </li></ul></ul><ul><ul><li>Propagation delay </li></ul></ul><ul><ul><li>Processing delay </li></ul></ul>How long does it take for a bit to travel along a wire/fiber/through the air? <ul><ul><li>Suppose </li></ul></ul><ul><ul><ul><li>Speed of light in a vacuum 3e8 m/s while in a fiber it is 2e8m/s </li></ul></ul></ul><ul><ul><ul><li>How long does it take to transmit a bit from NY to LA = 3962km </li></ul></ul></ul><ul><ul><ul><ul><li>20ms propagation delay </li></ul></ul></ul></ul><ul><ul><ul><li>How about from NY to Jakarta, Indonesia = 16,179km </li></ul></ul></ul><ul><ul><ul><ul><li>80ms </li></ul></ul></ul></ul><ul><ul><ul><li>How about to a Geostationary satellite? </li></ul></ul></ul><ul><ul><ul><ul><li>250-300 (up and back) </li></ul></ul></ul></ul><ul><ul><ul><li>Medium orbit satellites (e.g., GPS) </li></ul></ul></ul><ul><ul><ul><ul><li>120ms </li></ul></ul></ul></ul><ul><ul><ul><li>Low-earth orbit satellites (low earth? What about middle-earth?) </li></ul></ul></ul><ul><ul><ul><ul><li>Iridium at 10ms </li></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Note, Iridium paid 5 billion for the network and sold for 25million (1/2%->on sale 99.5% off, everything must go) </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><li>Teledesic. 10ms </li></ul></ul></ul></ul>
  40. 40. Fun with Propagation Delay How long is a bit? Suppose that a links transmits at 10mbps. How long is a bit? How long does it take to a bit? 1/10*10^6 = 10^-7 How far does the electric signal go in 10^7 sec? 10^-7 * 2e8 = 20 meters. How long many bits fit in a fiber at 10Mbps from NY to Jakarta? 16,179km*10^3/20 = 0.1 MB How long many bits fit in a fiber at 10 Gbps from NY to Jakarta? 16,179km*10^3/20 = 100 MB Satellite transmissions are subject to transmission loss (e.g., rain can cause interference), The satellite sending station could wait for and ACK from the other side and resend the data if no ACK appeared (a link layer solution) But this would cause out-of-order delivery So the satellite could hold the packets until the lost one is retransmitted. How large would the buffer need to be if the bit rate was 3Gbps? Answer .5*3e9/8=187MB (assuming no processor delay)
  41. 41. Delay in packet switched networks <ul><li>Routers take a bit of time to process packets. </li></ul><ul><li>moving packets inside the router </li></ul><ul><li>Finding which is the next hop </li></ul><ul><li>Applying security or QoS </li></ul><ul><li>Delay </li></ul><ul><ul><li>Queuing delay </li></ul></ul><ul><ul><li>Transmission delay </li></ul></ul><ul><ul><li>Propagation delay </li></ul></ul><ul><ul><li>Processing delay </li></ul></ul>
  42. 42. How to measure delay? <ul><li>Ping: > ping 216.109.124.73 </li></ul><ul><li>Ping gives help </li></ul><ul><li>(linux) Ping –I 10 216.109.124.73 > file.txt </li></ul><ul><li>Then read it in excel and plot delay </li></ul><ul><li>Traceroute (linux), tracert (windows) </li></ul><ul><li>Traceroute 216.109.124.73 gives the routers and an estimate of the delay to each router. </li></ul>
  43. 43. Today – networking basics <ul><li>Movie on the history of the Internet </li></ul><ul><li>Core components of the Internet – the protocol stack </li></ul><ul><li>Multiplexing, circuit switching, and packet switching </li></ul><ul><li>Loss and delays </li></ul><ul><li>The structure of the Internet </li></ul><ul><li>This lecture covers much of chapter 1 in the textbook. </li></ul>
  44. 44. Internet structure: network of networks <ul><li>roughly hierarchical </li></ul><ul><li>at center: “tier-1” ISPs (e.g., Verizon, Sprint, AT&T, Cable and Wireless), national/international coverage </li></ul><ul><ul><li>treat each other as equals </li></ul></ul>Tier 1 ISP Tier 1 ISP Tier 1 ISP Tier-1 providers interconnect (peer) privately
  45. 45. Tier-1 ISP: e.g., Sprint … to/from customers peering to/from backbone …. … … … POP: point-of-presence
  46. 46. Internet structure: network of networks <ul><li>“ Tier-2” ISPs: smaller (often regional) ISPs </li></ul><ul><ul><li>Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs </li></ul></ul>Tier 1 ISP Tier 1 ISP Tier 1 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP <ul><li>Tier-2 ISP pays tier-1 ISP for connectivity to rest of Internet </li></ul><ul><li>tier-2 ISP is c ustomer of </li></ul><ul><li>tier-1 provider </li></ul>Tier-2 ISPs also peer privately with each other.
  47. 47. Internet structure: network of networks <ul><li>“ Tier-3” ISPs and local ISPs </li></ul><ul><ul><li>last hop (“access”) network (closest to end systems) </li></ul></ul>Tier 1 ISP Tier 1 ISP Tier 1 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP local ISP local ISP local ISP local ISP local ISP Tier 3 ISP local ISP local ISP local ISP Local and tier- 3 ISPs are customers of higher tier ISPs connecting them to rest of Internet
  48. 48. Internet structure: network of networks <ul><li>a packet passes through many networks! </li></ul>Tier 1 ISP Tier 1 ISP Tier 1 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP local ISP local ISP local ISP local ISP local ISP Tier 3 ISP local ISP local ISP local ISP
  49. 49. ISPs and the structure of the Internet <ul><li>Video of a Network Access Point (NAP) in Los Angeles </li></ul>
  50. 50. Said to be the most interconnected space in the world and the most expensive real estate in North America, the “Meet Me Room” (a telco industry term) is the heart of One Wilshire. Here the primary fiber optic cables are routed, split, and shared. Because of the presence of so many telcos in this room and the ability to freely interconnect between them, rackspace here becomes extremely valuable. For comparison, the average price for office space in downtown Los Angeles is $1.75 per square foot per month. At the Meet Me Room, $250 per square foot would be a bargain. MEET ME ROOM
  51. 51. Some 1,800 known conduits contain the fiber optic cables that flow through the building’s stairwells and vertical utility corridors, called “risers.” Cable connects the commercial telco tenants on floors 5 through 29 to the 4th floor Meet Me Room, and to a new, “wireless” Meet Me Room constructed on the 30th floor. CABLE RISERS
  52. 52. Whenever a permit is pulled by a city contractor for any underground repairs outside One Wilshire, the various telco companies with cable in the area come out and paint the cable routes on the asphalt, creating a visible graphic of the complexity of what lies just under the surface. SURFACE CABLE MAP
  53. 53. Computers generate a lot of heat, and maintaining a stable, cool temperature and a low humidity is essential in telco hotels, so tenants sometimes demand to install their own cooling systems to safeguard their equipment. At One Wilshire, these units are installed primarily on the third floor roof. A new closed loop cooling system has been installed on the 30th floor roof. HVAC
  54. 54. As tenants’ needs change, cables can go unused. Cable mining is performed to thin out the obsolete cables and future congestion is alleviated through the installation of dedicated new ducts. CABLE MINING
  55. 55. Power is supplied by DWP, but in the event of a blackout, the building’s five generators will kick in. It takes the generators three seconds to start up and stabilize. During this brief period, the entire building runs on batteries. There are 11,000 gallons of diesel stored on site, enough to run the generators for 24 hours before being refueled. ELECTRICITY ELECTRICITY ELECTRICITY ELECTRICITY ELECTRICITY
  56. 56. On the roof, microwave antennas link up One Wilshire to transmission towers located around the city. Though fiber’s higher capacity has given it dominance over microwave at One Wilshire, microwave’s relatively low cost over long distances continues to make it economical for some applications. The roof’s clear line of sight to the south, west, and to other high-rises, along with the ability to interface with the fiber inside, continues to make One Wilshire an attractive location for microwave-based transmission. MICROWAVE
  57. 57. Much can be learned about a building’s function by examining its roof. The existence of telco hotels in the region around One Wilshire is indicated by the presence of new and extensive cooling units on the roofs of adjacent buildings, many of which were nearly vacant until the telco companies moved in. READING A ROOF
  58. 58. The main fiber optic cables connecting One Wilshire to the world enter the building from under the street through closets in the walls of the building’s parking garage. Given the importance of the building to the global communications network, access to the parking garage is controlled, and the building is said to be monitored continuously by federal security officials. POINT OF ENTRY
  59. 59. Said to be the most interconnected space in the world and the most expensive real estate in North America, the “Meet Me Room” (a telco industry term) is the heart of One Wilshire. Here the primary fiber optic cables are routed, split, and shared. Because of the presence of so many telcos in this room and the ability to freely interconnect between them, rackspace here becomes extremely valuable. For comparison, the average price for office space in downtown Los Angeles is $1.75 per square foot per month. At the Meet Me Room, $250 per square foot would be a bargain. MEET ME ROOM
  60. 60. Some 1,800 known conduits contain the fiber optic cables that flow through the building’s stairwells and vertical utility corridors, called “risers.” Cable connects the commercial telco tenants on floors 5 through 29 to the 4th floor Meet Me Room, and to a new, “wireless” Meet Me Room constructed on the 30th floor. CABLE RISERS
  61. 61. Whenever a permit is pulled by a city contractor for any underground repairs outside One Wilshire, the various telco companies with cable in the area come out and paint the cable routes on the asphalt, creating a visible graphic of the complexity of what lies just under the surface. SURFACE CABLE MAP
  62. 62. Computers generate a lot of heat, and maintaining a stable, cool temperature and a low humidity is essential in telco hotels, so tenants sometimes demand to install their own cooling systems to safeguard their equipment. At One Wilshire, these units are installed primarily on the third floor roof. A new closed loop cooling system has been installed on the 30th floor roof. HVAC
  63. 63. As tenants’ needs change, cables can go unused. Cable mining is performed to thin out the obsolete cables and future congestion is alleviated through the installation of dedicated new ducts. CABLE MINING
  64. 64. Power is supplied by DWP, but in the event of a blackout, the building’s five generators will kick in. It takes the generators three seconds to start up and stabilize. During this brief period, the entire building runs on batteries. There are 11,000 gallons of diesel stored on site, enough to run the generators for 24 hours before being refueled. ELECTRICITY ELECTRICITY ELECTRICITY ELECTRICITY ELECTRICITY
  65. 65. On the roof, microwave antennas link up One Wilshire to transmission towers located around the city. Though fiber’s higher capacity has given it dominance over microwave at One Wilshire, microwave’s relatively low cost over long distances continues to make it economical for some applications. The roof’s clear line of sight to the south, west, and to other high-rises, along with the ability to interface with the fiber inside, continues to make One Wilshire an attractive location for microwave-based transmission. MICROWAVE
  66. 66. Much can be learned about a building’s function by examining its roof. The existence of telco hotels in the region around One Wilshire is indicated by the presence of new and extensive cooling units on the roofs of adjacent buildings, many of which were nearly vacant until the telco companies moved in. READING A ROOF
  67. 67. The main fiber optic cables connecting One Wilshire to the world enter the building from under the street through closets in the walls of the building’s parking garage. Given the importance of the building to the global communications network, access to the parking garage is controlled, and the building is said to be monitored continuously by federal security officials. POINT OF ENTRY
  68. 68. Homework <ul><li>Page 61. Questions (3, 7), 8, (9), (10), 11, 13, 14, 19, (20), 21, (22), (23) </li></ul><ul><li>Page 63. Problems 2, (3), 6, 7, 8, (10), (11), (12) </li></ul><ul><li>Use trace route to determine the average number of hops between 10 destinations of your choice. </li></ul><ul><li>Use ping to determine the propagation delay. Specifically, send very small packets (these will be 24 bytes).Then send ICMP packets with larger payload. Compare the difference in the RTT and determine the transmission time. </li></ul><ul><li>Do links have time-varying delay? To answer this questions run trace route at different times of the day (e.g., the middle of the night, morning, afternoon, etc) and compare the delay times. </li></ul>
  1. A particular slide catching your eye?

    Clipping is a handy way to collect important slides you want to go back to later.

×