Network Devices


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Network Devices

  1. 1. Chapter 1: Internetworking <ul><li>Internetworking Basics </li></ul><ul><li>Network segmentation </li></ul><ul><li>How bridges, switches, and routers are used to physically segment a network </li></ul><ul><li>How routers are used to create internetwork </li></ul><ul><li>OSI model </li></ul>
  2. 2. Internetworking Models <ul><li>Most networks are designed as a stack of layers , each one built upon the one below it. Why? </li></ul>Layer 3 Layer 2 Layer 1 Layer 3 Layer 2 Layer 1 Physical Medium Layer 3 protocol Layer 2 protocol Layer 1 protocol Layer 2/3 interface Layer 1/2 interface Host 1 Host 2
  3. 3. <ul><li>Each layer provides services to the higher levels. </li></ul><ul><li>Each layer behaves as a black box. </li></ul><ul><li>Layer n on one machine talks to layer n on another machines. </li></ul><ul><li>The corresponding layer in the layered structure are called peers . </li></ul><ul><li>The communication between peers must follow certain rules, known as protocol . </li></ul><ul><li>No data are directly transferred between layers. Actual communication is through a physical medium below layer 1. </li></ul>
  4. 4. An Analogy Ik vind konijnen leuk L: Ducth Fax:# Ik vind konijnen leuk L: Dutch I like rabbits Message Information for the remote translator Information for the remote secretary Ik vind konijnen leuk L: Ducth Fax:# Ik vind konijnen leuk L: Ducth J’aime bien les lapins Urdu & English Chinese & French Professor B Translator Secretary use fax use Dutch Secretary Translator Professor A
  5. 5. Open Systems Interconnection (OSI) Reference Model Application Presentation Session Transport Network Data Link Physical <ul><li>Provides user interface </li></ul><ul><li>Initiates services </li></ul><ul><li>Transfer data into standard format before transmission </li></ul><ul><li>Keeps data different applications’ data separate </li></ul><ul><li>Control the data exchange </li></ul><ul><li>End-to-end data error free data transmission </li></ul><ul><li>Logical addressing for data packets Routing and error handling </li></ul><ul><li>Moves bits between devices </li></ul><ul><li>Specifies voltages, cables, and cables </li></ul><ul><li>NIC software function </li></ul><ul><li>How data in packaged </li></ul><ul><li>Error detection </li></ul>The lower levels The upper levels
  6. 6. Reasons for Layering <ul><li>Simplifies the network model </li></ul><ul><li>Enables programmers to specialize in a particular level or layer of the networking model </li></ul><ul><li>Provides design modularity </li></ul><ul><li>Encourages interoperability </li></ul><ul><li>Allows for standardized interfaces to be produced by networking vendors </li></ul>
  7. 7. The Application Layer (Layer 7) <ul><li>The layer where users communicate to the computer </li></ul><ul><li>Contains protocols and utilities that provides services to network applications </li></ul><ul><ul><li>(True/False) MsWord, Eudora Mail, Netscape are in the application layer. </li></ul></ul><ul><ul><li>Eudora (application) uses SMTP (Simple Mail Transfer Protocol) (protocol). </li></ul></ul><ul><li>E-mail: </li></ul><ul><ul><li>Message formats such as RFC 822 </li></ul></ul><ul><ul><li>SMTP, POP3 (Post Office Protocol Version 3), IMAP (Internet Message Access Protocol) </li></ul></ul><ul><li>WWW: </li></ul><ul><ul><li>HTML (The HyperText Markup Language), XML (eXtensible Markup Language), XSL (eXtensible Style Language) </li></ul></ul><ul><ul><li>HTTP (The HyperText Transfer Protocol) </li></ul></ul>
  8. 8. The Presentation Layer (Layer 6) <ul><li>The presentation layer prepares the data from the application layer for transmission over the network or from the network to the application layer. </li></ul><ul><li>Include protocols specifying how to represent data (MPEG, JPEG, PIC, WAV) </li></ul><ul><li>Responsible for data translation, formatting, encryption, compression. </li></ul><ul><li>We need these services because different computers use different internal representation for data (integers and characters) </li></ul>
  9. 9. The Session Layer (Layer 5) <ul><li>Enables two applications on the network to have an ongoing conversation </li></ul><ul><li>Provide following services </li></ul><ul><ul><li>Communication setup and teardown </li></ul></ul><ul><ul><li>Control for data exchange </li></ul></ul><ul><ul><li>Data synchronization definition </li></ul></ul><ul><ul><li>Failure recovery </li></ul></ul><ul><li>Examples: </li></ul><ul><ul><li>Structured Query Language (SQL) </li></ul></ul><ul><ul><li>X Windows </li></ul></ul><ul><ul><li>AppleTalk Session Protocol (ASP) </li></ul></ul>
  10. 10. The Transport Layer (Layer 4) <ul><li>Provides </li></ul><ul><ul><li>end-to-end error free data transport services </li></ul></ul><ul><ul><li>establish a logical connection </li></ul></ul><ul><ul><li>data segmentation into maximum transmission unit size </li></ul></ul><ul><ul><li>messaging service for session layer </li></ul></ul><ul><li>Protocols in this layer can be </li></ul><ul><ul><li>connection-oriented : require an acknowledgment of the receipt of data packets. </li></ul></ul><ul><ul><li>connectionless : do not require an acknowledgment of the receipt of data packets. </li></ul></ul>
  11. 11. <ul><li>Connection-oriented protocols: </li></ul>sender receiver Synchronize Negotiate connection Connection Establish Synchronize Acknowledge Data Transfer Virtual Circuit
  12. 12. <ul><li>Flow Control </li></ul>sender receiver Buffer full GO <ul><li>The segments delivered back to the sender upon their reception </li></ul><ul><li>Any segment not acknowledged are retransmitted. </li></ul><ul><li>Segments are sequence back into their proper order upon arrival at their destination </li></ul><ul><li>Manageable data flow is maintained in order to avoid congestion </li></ul>
  13. 13. <ul><li>Windowing : The quantity of data segment (in bytes) is sent without receiving an acknowledgment (ack) is called a window. </li></ul>sender receiver receive 1 ack. 2 send 1 send 2 receive 2 ack. 3 send 3 sender receiver send 1 send 2 ack. 4 send 3 send 4 Window size of 1 Window size of 3
  14. 14. <ul><li>Acknowledgments : </li></ul>sender receiver send 1 send 2 ack. 4 send 3 send 4 send 5 send 6 ack. 5 send 5 Connection lost! ack. 7 1 2 3 4 5 6 1 2 3 4 5 6 Positive Acknowledgment with retransmission
  15. 15. The Network Layer (Layer 3) <ul><li>Provides services </li></ul><ul><ul><li>to manage devices addressing </li></ul></ul><ul><ul><li>to tracks the location of devices on the network </li></ul></ul><ul><ul><li>to determine the best way to move data on the network </li></ul></ul><ul><li>The network layer must transport traffic between devices that are not directly connected. </li></ul><ul><li>Routers are specified at this layer. </li></ul>
  16. 16. The Data Link (Layer 2) <ul><li>Services </li></ul><ul><ul><li>Identification of the source and destination nodes via their physical address (Media Access Control (MAC) address) </li></ul></ul><ul><ul><li>Definition of how data is packaged for transport as frames </li></ul></ul><ul><ul><li>Error detection </li></ul></ul><ul><ul><li>Flow control of information sent across the link </li></ul></ul><ul><li>Has two sublayers: </li></ul><ul><ul><li>Media Access Control (MAC) 802.3 </li></ul></ul><ul><ul><li>Logical Link Control (LLC) 802.2 </li></ul></ul>
  17. 17. The Physical Layer (Layer 1) <ul><li>This layer communicates directly with the various types of actual communication media </li></ul><ul><li>Services </li></ul><ul><ul><li>definition of the physical characteristics of the network hardware, including cable and connector </li></ul></ul><ul><ul><li>Encoding </li></ul></ul><ul><ul><li>Transmission of signals on the wire </li></ul></ul>
  18. 18. Example: 568B twisted pair wiring scheme
  19. 19. Layer 1 Network Devices: Repeaters <ul><li>The number of nodes on a network and the length of cable used influence the quality of communication on the network </li></ul><ul><li>Attenuation </li></ul><ul><ul><li>Natural degradation of a transmitted signal over distance </li></ul></ul><ul><li>Repeaters work against attenuation by repeating signals that they receive on a network </li></ul><ul><li>Why are repeaters Layer 1 devices? </li></ul>
  20. 20. Layer 1 Network Devices: Hubs <ul><li>Generic connection device used to tie several networking cables together to create a link between different stations on a network </li></ul>
  21. 21. <ul><li>Hubs that are plugged into electric power are called active hubs </li></ul><ul><li>A hub that merely connects different cables on a network and provides no signal regeneration is called a passive hub and is not a repeater </li></ul><ul><li>“ Hub” is a generic term applied to many different network-connection devices </li></ul><ul><li>If a hub in some way segments or subdivides the traffic on a network, it is an intelligent , or switching, hub </li></ul><ul><li>For the purpose of the CCNS exam, the term hub—by itself—is a device that does not segment the network </li></ul>
  22. 22. Network Segmentation <ul><li>Segmentation </li></ul><ul><ul><li>Process of breaking a network into smaller broadcast or collision domains </li></ul></ul><ul><li>Ethernet network, which are characterized by IEEE 802.3 standard, define the use of a Carrier Sense Multiple Access with Collision Detection (CSMA/CD) access method </li></ul><ul><ul><li>Backoff algorithm : Mathematical calculation performed by computers after a collision occurs on a CSMA/CD network </li></ul></ul><ul><ul><li>Backoff period : Random time interval used after a collision has been detected on an Ethernet network </li></ul></ul>
  23. 23. Network Segmentation via Bridges
  24. 24. Layer 2 Devices: Bridges <ul><li>Operate at the Data Link layer of the OSI model </li></ul><ul><li>Filters traffic between network segments by examining the destination MAC address </li></ul><ul><ul><li>Based on this destination MAC address, the bridge either forwards or discards the frame </li></ul></ul><ul><ul><li>When a client sends a broadcast frame to the entire network, the bridge will always forward the frame </li></ul></ul>
  25. 25. <ul><li>Transparent Bridges : Also called learning bridges because they build a table of MAC addresses as they receive frames </li></ul><ul><ul><li>This means that they “learn” which addresses are on which segments </li></ul></ul><ul><ul><li>Ethernet networks mainly use transparent bridges </li></ul></ul><ul><li>Source-routing bridges : Rely on the source of the frame transmission to provide the routing information </li></ul><ul><ul><li>Usually employed by Token Ring networks </li></ul></ul><ul><li>Translation bridges : Can connect networks with different architectures </li></ul>
  26. 26. Layer 2 Devices: Switches <ul><li>Increase network performance by reducing the number of packets transmitted to the rest of the network </li></ul><ul><li>Like bridges, operate at the Data Link layer of the OSI model </li></ul><ul><li>In an Ethernet network, computers are usually connected directly to a switch </li></ul><ul><li>Virtual circuit </li></ul><ul><ul><li>Private connections between two points created by a switch that allows the two points to use the entire available bandwidth between those two points without contention </li></ul></ul>