Lecture Sept 28, 2004

1
Lecture Sept 28, 2004

• Continuation of the Basics of Networking
  Chapter 2
• Analyze the OSI Model
• Analyze the OSI Model
• Analyze the TCP/IP Model
• Introduction to Cabling
• Remember Module 2 (chapter 2) test will be on
• Thursday 09/30/04 _at_ 3pm
• - TODAYS LAB
• Make a straight thru cable
• Make a cross over cable
• Make a roll over cable
• Test cable

2
Using layers to analyze problems in a flow of
materials

• The concept of layers is used to describe
  communication from one computer to another.
• The OSI and TCP/IP models have layers that
  explain how data is communicated from one
  computer to another.
• The models differ in the number and function of
  the layers.
• However, each model can be used to help describe
  and provide details about the flow of information
  from a source to a destination.

3
Using layers to describe data communication

• In order for data packets to travel from a source
  to a destination on a network, it is important
  that all the devices on the network speak the
  same language or protocol.
• A protocol is a set of rules that make
  communication on a network more efficient. (KNOW
  THIS)

4
OSI model

• To address the problem of network
  incompatibility, the International Organization
  for Standardization (ISO) researched networking
  models like Digital Equipment Corporation net
  (DECnet), Systems Network Architecture (SNA), and
  TCP/IP in order to find a generally applicable
  set of rules for all networks.
• Using this research, the ISO created a network
  model that helps vendors create networks that are
  compatible with other networks.
• The Open System Interconnection (OSI) reference
  model released in 1984 was the descriptive
  network model that the ISO created.
• It provided vendors with a set of standards that
  ensured greater compatibility and
  interoperability among various network
  technologies produced by companies around the
  world.

5
OSI layers
6
OSI layers

• Benefits of the OSI model
• Breaks network communication into smaller, more
  manageable parts.
• Standardizes network components to allow multiple
  vendor development and support.
• Allows different types of network hardware and
  software to communicate with each other.
• Prevents changes in one layer from affecting
  other layers.
• Divides network communication into smaller parts
  to make learning it easier to understand.

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Peer-to-peer communications

• In order for data to travel from the source to
  the destination, each layer of the OSI model at
  the source must communicate with its peer layer
  at the destination.
• This form of communication is referred to as
  peer-to-peer.
• During this process, the protocols of each layer
  exchange information, called protocol data units
  (PDUs). (KNOW THIS)
• Each layer of communication on the source
  computer communicates with a layer-specific PDU,
  and with its peer layer on the destination
  computer as illustrated in the figure above

8
TCP/IP model

• Unlike the proprietary networking technologies
  mentioned earlier, TCP/IP was developed as an
  open standard.
• This meant that anyone was free to use TCP/IP.
  This helped speed up the development of TCP/IP as
  a standard.
• Although some of the layers in the TCP/IP model
  have the same name as layers in the OSI model,
  the layers of the two models do not correspond
  exactly.

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TCP/IP model

• Some of the common protocols specified by the
  TCP/IP reference model layers. Some of the most
  commonly used application layer protocols include
  the following
• File Transfer Protocol (FTP)
• Hypertext Transfer Protocol (HTTP)
• Simple Mail Transfer Protocol (SMTP)
• Domain Name System (DNS)
• Trivial File Transfer Protocol (TFTP)
• The common transport layer
• protocols include
• Transport Control Protocol (TCP)
• User Datagram Protocol (UDP)
• The primary protocol of the
• Internet layer is
• Internet Protocol (IP)

10
TCP/IP model

• Networking professionals differ in their opinions
  on which model to use. Due to the nature of the
  industry it is necessary to become familiar with
  both. Both the OSI and TCP/IP models will be
  referred to throughout the curriculum. The focus
  will be on the following
• TCP as an OSI Layer 4 protocol
• IP as an OSI Layer 3 protocol
• Ethernet as a Layer 2 and Layer 1 technology
• Remember that there is a difference between a
  model and an actual protocol that is used in
  networking. The OSI model will be used to
  describe TCP/IP protocols.

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Detailed encapsulation process

• All communications on a network originate at a
  source, and are sent to a destination.
• The information sent on a network is referred to
  as data or data packets. If one computer (host A)
  wants to send data to another computer (host B),
  the data must first be packaged through a process
  called encapsulation.

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Detailed encapsulation process

• Networks must perform the following five
  conversion steps in order to encapsulate data
• Build the data.
• Package the data for end-to-end transport.
• Add the network IP address to the header.
• Add the data link layer header and trailer.
• Convert to bits for transmission.

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Data Encapsulation Example
Application Header data
Application Layer
Layer 4 Transport Layer
Layer 3 Network Layer
Layer 2 Network Layer
010010100100100100111010010001101000
Layer 1 Physical Layer
Let us focus on the Layer 2, Data Link, Ethernet
Frame for now.
14
Signaling over copper and fiber optic cabling

• INTRODUCTION TO TODAYS LAB
• In order for the LAN to operate properly, the
  receiving device must be able to accurately
  interpret the binary ones and zeros transmitted
  as voltage levels.
• Since current Ethernet technology supports data
  rates of billions of bits per second, each bit
  must be recognized, even though duration of the
  bit is very small.
• The voltage level cannot be amplified at the
  receiver, nor can the bit duration be extended in
  order to recognize the data.
• This means that as much of the original signal
  strength must be retained, as the signal moves
  through the cable and passes through the
  connectors.
• In anticipation of ever-faster Ethernet
  protocols, new cable installations should be made
  with the best available cable, connectors, and
  interconnect devices such as punch-down blocks
  and patch panels. 

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Attenuation and insertion loss on copper media

• Attenuation is the decrease in signal amplitude
  over the length of a link.
• Long cable lengths and high signal frequencies
  contribute to greater signal attenuation.

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Sources of noise on copper media

• Crosstalk involves the transmission of signals
  from one wire to a nearby wire.
• When voltages change on a wire, electromagnetic
  energy is generated.
• This energy radiates outward from the
  transmitting wire like a radio signal from a
  transmitter.
• Adjacent wires in the cable act like antennas,
  receiving the transmitted energy, which
  interferes with data on those wires.

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Sources of noise on copper media

• Twisted-pair cable is designed to take advantage
  of the effects of crosstalk in order to minimize
  noise.
• In twisted-pair cable, a pair of wires is used to
  transmit one signal.
• The wire pair is twisted so that each wire
  experiences similar crosstalk.
• Because a noise signal on one wire will appear
  identically on the other wire, this noise be
  easily detected and filtered at the receiver. 

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Cable testing standards

• The ten primary test parameters that must be
  verified for a cable link to meet TIA/EIA
  standards are
• Wire map
• Insertion loss
• Near-end crosstalk (NEXT)
• Power sum near-end crosstalk (PSNEXT)
• Equal-level far-end crosstalk (ELFEXT)
• Power sum equal-level far-end crosstalk
  (PSELFEXT)
• Return loss
• Propagation delay
• Cable length
• Delay skew
• This will be covered in Chapter 4

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Cable testing standards

• The Ethernet standard specifies that each of the
  pins on an RJ-45 connector have a particular
  purpose.
• A NIC transmits signals on pins 1 and 2, and it
  receives signals on pins 3 and 6.
• The wires in UTP cable must be connected to the
  proper pins at each end of a cable.

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Wiring Standards

• The pairs designated for 10BaseT Ethernet are
  orange and green. The other two pairs, brown and
  blue, are unused. The connections shown are
  specifically for an RJ45 plug. The wall jack may
  be wired in a different sequence because the
  wires may be crossed inside the jack. The jack
  should either come with a wiring diagram or at
  least designate pin numbers that you can match up
  to the color code below.
• There are two wiring standards for these cables,
  called T-568A and T-568B. They differ only in pin
  assignments, not in uses of the various colors.
  The illustration above shows both standards. 
  With the T-568B specification the orange and
  green pairs are located on pins 1, 2 and 3, 6
  respectively. The T-568A specification reverses
  the orange and green connections, so that the
  blue and orange pairs are on the center 4 pins,
  which makes it more compatible with the telco
  voice connections.
• T-568A is supposed to be the standard for new
  installations, and T-568B is the alternative

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Cable testing standards

• The wire map test insures that no open or short
  circuits exist on the cable.
• An open circuit occurs if the wire does not
  attach properly at the connector.
• A short circuit occurs if two wires are connected
  to each other.

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Cable testing standards

• The wire map test also verifies that all eight
  wires are connected to the correct pins on both
  ends of the cable.
• There are several different wiring faults that
  the wire map test can detect.