Hour 3

The Network Access Layer

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What You'll Learn in This Hour:

Physical addresses Ethernet frames LAN technologies

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Network Access Layer is the base of TCP/IP Model.

Collection of services and specifications that provide and manage access to the network hardware.

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This hour, you’ll be able to

Explain the Network Access layer Discuss how TCP/IP's Network Access layer

relates to the OSI networking model Explain a network architecture List the contents of an ethernet frame Identify the methods that ethernet, token ring,

and FDDI use for controlling access to the transmission medium

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Protocols and Hardware

The Network Access layer manages all the services and functions necessary to prepare the data for the physical network.

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The responsibilities include :

– Interfacing with the computer's network adapter.

– Coordinating the data transmission with the conventions of the appropriate access method. You'll learn more about access methods later in this hour.

– Formatting the data into a unit called a frame and converting that frame into the stream of electric or analog pulses that passes across the transmission medium.

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(Cont) The responsibilities include :

– Checking for errors in incoming frames.

– Adding error-checking information to outgoing frames so that the receiving computer can check the frame for errors.

– Acknowledging receipt of data frames and resending frames if acknowledgment is not received.

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There are many different types of Network Acess Layer for example – Ethernet – Token Ring– FDDI– PPP– Wireless Network

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The Network Access Layer and OSI Model

The Network Access Layer corresponds to OSI Physical and Data Link layer.– Physical layer

• turning the data frame into a stream of bit.• manage and synchronizes the electrical of analog pulse.

– Data Link layer • Media Access Control provides an interface with network

adapter.• Logical Link Control performs error checking.

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Network Architecture

network architecture is referred to as a LAN type or a LAN topology such as ethernet.

network architecture is a design for the physical network and a collection of specifications defining communications dependent on the physical details.

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Specifications such as the following– Access method (set of rules defining how

the computers will share the transmission medium)

– Data frame format (enclosed in the header necessary to deliver data on the physical network)

– Cabling type– Cabling rules (maximum and minimum

lengths for the cable)

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Physical Addressing The physical address is burned into the

card at the factory. Data frames sent across the LAN must

use this physical address to identify the source and destination adapters.

TCP/IP uses the Address Resolution Protocol (ARP) and Reverse Address Resolution Protocol (RARP) to relate IP addresses to the physical addresses

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Anatomy of a Frame

The Network Access layer software accepts a datagram from the Internet layer and converts that data to a form that is consistent with the specifications of the physical network

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Network Access layer performs the following:

1. Breaks IP layer data into smaller chunks2. Packages the chunks of data into frames 3. Passes the data frame to lower-level

components corresponding to OSI's physical layer

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Example of ethernet frame– Preamble– Recipient address– Source address– Length– Data– Frame Check Sequence

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LAN Technologies

Ethernet Token ring FDDI

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Ethernet

Ethernet and Fast Ethernet are the LAN technologies most commonly used today.

Ethernet cable is inexpensive and easily installed.

Ethernet uses CSMA/CD.

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Technology Name

Media Type Operating Speed

Maximum Distance

10BASE-2 Thin coax 10 megabits 185 meters

10BASE-5 Thick coax 10 megabits 500 meters

10BASE-T CAT3 or CAT5 UTP

10 megabits 100 meters

10BASE-F Fiber optic 10 megabits 2,000 meters

100BASE-TX CAT 5 UTP or STP

100 megabits 100 meters

100BASE-FX Fiber optic 100 megabits 2,000 meters

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Token Ring

This method is known as token passing.

Computers on the LAN are connected so that data is passed around the network in a logical ring.

Central hub called a MAU or MSAU

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FDDI

Fiber Distributed Data Interface (FDDI) is an expensive

Employs a pair of fiber-optic rings. One ring is considered primary and the

second ring is there to replace the primary ring in the event of a breakdown.

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