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