Telecommunications and the
Information Age ET108B LM#8
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OSI Architecture
TCP/IP Architecture
Local Area Networks
Ethernet Protocol
Building a LAN
Interconnecting LANs
OSI Architecture
• The OSI reference model
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The basis of the architecture
• Is used universally as a method for teaching and
understanding network functionality
• Each layer of the OSI model defines a specific
function of the network.
• These functions are defined by the International Organization
for Standardization (ISO) and are recognized worldwide
• Following the OSI model when designing,
building, upgrading, or troubleshooting will
achieve greater compatibility and
interoperability between various network
technologies.
OSI Model Overview
Application
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Presentation
Session
Transport
Network
Data Link
Physical
http://computer.howstuffworks.com/osi.htm/printable
Reasons for using the OSI mode
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Divides the aspects of network operation
into less complex elements.
Enables engineers to specialize design and
development efforts on specific functions.
Prevents changes in one area from affecting
other areas, so that each area can evolve more
quickly.
Allows network designers to choose the right
networking devices and functions for that
layer.
Helps with testing and troubleshooting.
Physical layer (Layer 1)
• This layer provides
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The electrical, mechanical, procedural, and
functional means for activating and maintaining
whatever physical link exists between hosts.
• If the link between hosts or networks is
severed or experiencing problems, data
may not transmit.
• Networking media such as twisted-pair,
coaxial, and fiber-optic cable are layer 1
equipment
Data-link layer (Layer 2
• This layer deals with :
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Speed of transmission
• Flow control
• Error identification
• Topology.
• This layer recognizes special
identifiers that are unique to each
computer, called media access
control (MAC) addresses.
Network layer (Layer 3)
• The network layer adds logical or
network addresses
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Such as Internet Protocol (IP) addresses to
information that passes through it.
With the addition of this information, the frames are
now called packets.
• This layer is responsible for determining
the best way to move data from one
network to another.
• Routers perform this operation and are
thus referred to as Layer 3 devices.
Transport layer (Layer 4)
• This layer takes the data file
and divides it up into
segments to facilitate
transmission.
• This layer is also responsible
for reliable delivery of data
between the two hosts.
Session layer (Layer 5)
• The session layer establishes,
maintains, and manages
conversations, called sessions,
between two or more applications on
different computers
• The session layer is involved in
keeping the lines open for the
duration of the session and
disconnecting them at the conclusion.
Presentation layer (Layer 6)
• This layer provides formatting services to
the application layer by ensuring the data
that arrives from another computer can
be used by an application.
• For instance, it translates EBCDIC
characters from mainframe computers
into ASCII characters for PCs so that an
application can read the data.
• This layer is also responsible for
encryption and compression.
Application layer (Layer 7)
• The main function of the application
layer is to provide network services
to the end user.
• These network services include file
access, applications, and printing.
Application layer (Layer 7)
• The main function of the application
layer is to provide network services
to the end user.
• These network services include file
access, applications, and printing.
Layer 1 problems
• When there are problems with a network,
troubleshooting should begin with
Layer 1.
• It is estimated that about three-quarters
of all network problems are Layer 1
problems.
• Many of these could be avoided when
installing cable.
Data-link Layer Functions
• Data-link layer (Layer 2) LAN devices help
filter network traffic by looking at the MAC
addresses in the frame.
• These MAC addresses are physical
addresses burned into the network interface
cards (NICs) on PCs and devices.
• The data-link layer devices use these
addresses when performing their functions.
Switches
• A switch can divide the network into many
subnetworks or smaller networks depending
on the number of ports on the switch.
• A switch helps to keep network
communications from reaching beyond
where they are destined.
• A switch allows multiple connections within
it. When two hosts are communicating, they
use only a pair of ports.
Network Layer Functions
• The network layer (Layer 3) deals with
higher-level addressing schemes and path
determination. The network layer address is
the Internet Protocol (IP) address of a
computer.
• Each computer on a network has an IP
address to identify its location on the
network. It indicates to which network and
subnetwork a computer belongs.
Routers
• A router is a Layer 3 networking device that
connects network segments or entire
networks.
• It is considered more intelligent than Layer
2 devices because it makes decisions based
on information received about the network
as a whole.
• A router examines the IP address of the
destination computer to determine which
path is best to take to reach the destination.
Transport Layer Functions
• The transport layer (Layer 4) is responsible
for segmenting the data file and regulating
the flow of information from source to
destination.
• This end-to-end control is provided using a
variety of techniques, such as sequence
numbers, acknowledgements, and
windowing.
Session Layer Functions
• The session layer (Layer 5) is responsible
for managing the transmission session.
• The session layer sets up, maintains, and
then terminates sessions between hosts on
the network.
Presentation Layer Functions
• The presentation layer (Layer 6)
facilitates communication between
applications on diverse computer
systems to occur in such a way that it is
transparent to the applications. It does
so by reformatting the data.
Application layer functions
• The application layer (Layer 7) does
not provide services to any other OSI
layer.
• It provides services to applications
used by the end user.
TCP/IP Architecture
TCP/IP Architecture
• Four Layer Conceptual Model by DARPA
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Defense Advanced Projects Agency
Original version IP version 4 (IPv4)
Incoming version IP version 6 (IPv6)
• Sometimes referred to as IP Next Generation or Ipng
• Version 5 was skipped
• History of TCP/IP
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The key milestone in the development of the Internet
Protocol was the publishing of RFC 791, Internet
Protocol, in September 1981
TCP/IP Architecture
• Network Interface Layer
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Also called the Network Access layer
Functions
• Handles placing TCP/IP packets on the network medium
• Handles receiving TCP/IP packets off the network medium
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Interfaces TCP/IP to various physical layers
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Ethernet
Token Ring
X.25
Frame Relay
ATM
Etc.
TCP/IP Architecture
• Network Interface Layer
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New Network Interface protocols can be interfaced to
the Internet layer
• Then no changes to the Internet and above layers are needed
• Allows easy adaptation of TCP/IP to new interface protocols
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Encompasses the Data Link & Physical layers of the
OSI model
Network Interface optional services not used by
Internet Layer
• Sequence and Acknowledgement services
• Connection Reliability services
TCP/IP Architecture
• Internet Layer
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Functions Handled
• Addressing
• Packaging
• Routing
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Layer Protocols and their functions
• The Internet Protocol (IP) is a routable protocol that handles • IP addressing, routing, and the fragmentation and reassembly of
packets
• Address Resolution Protocol (ARP) handles –
• Resolution of an Internet layer address to a Network Interface layer
address, such as an Ethernet hardware address (MAC address)
TCP/IP Architecture
• Internet Layer
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Layer Protocols and their functions
• The Internet Control Message Protocol (ICMP)
handles –
• Providing diagnostic functions and reporting errors due to
the unsuccessful delivery of IP packets.
• The Internet Group Management Protocol (IGMP)
handles –
• Management of IP multicast group membership
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The Internet layer is analogous to the Network
layer of the OSI model.
TCP/IP Architecture
• Transport Layer
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Also known as the
• Host-to-Host Transport layer
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Handles providing the Application layer with session
and datagram communication services
Core Layer Protocols and Functions
• Transmission Control Protocol (TCP) handles
• One-to-one, connection-oriented, reliable communications
service
• Establishment of a TCP connection
• Sequencing and acknowledgment of packets sent
TCP/IP Architecture
• Transport Layer
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Core Layer Protocols and Functions
• Transmission Control Protocol (TCP) handles
• Recovery of packets lost during transmission
• User Datagram Protocol (UDP) handles
• Handles providing a one-to-one or one-to-many, connectionless,
unreliable communications service
• UDP is used when the amount of data to be transferred is small
(such as data that fits into a single packet)
• UDP is used when you do not want the overhead of establishing a
TCP connection
• UDP is used when the applications or upper layer protocols provide
reliable delivery.
TCP/IP Architecture
• Transport Layer
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The TCP/IP Transport layer encompasses the
responsibilities of the OSI Transport layer
• Application Layer
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Functions
• Lets applications access the services of the other layers
• Defines the protocols that applications use to exchange data
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Application Layer protocols and functions
• The Hypertext Transfer Protocol (HTTP) is used to transfer
files that make up the Web pages of the World Wide Web.
• The File Transfer Protocol (FTP) is used for interactive file
transfer
TCP/IP Architecture
• Application Layer
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Application Layer protocols and functions
• Simple Mail Transfer Protocol (SMTP) is used for the transfer
of mail messages and attachments
• Telnet, a terminal emulation protocol, is used for logging on
remotely to network hosts.
• The Domain Name System (DNS) protocol is used to resolve a
host name to an IP address
• Routing Information Protocol (RIP) is a routing protocol that
routers use to exchange routing information on an IP
internetwork
TCP/IP Architecture
• Application Layer
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Application Layer protocols and functions
• Simple Network Management Protocol (SNMP) is used
between a network management console and network devices
(routers, bridges, intelligent hubs) to collect and exchange
network management information
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TCP/IP Application Layer Interfaces Examples
• Windows Sockets provides a standard application
programming interface (API)
• NetBIOS is an industry-standard interface for accessing
protocol services such as sessions, datagrams, and name
resolution
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Same responsibilities of the OSI Session, Presentation,
and Application layers
Local-Area Networks
• Local-Area Network (LAN)
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Local computer
• Personal microcomputer-type system.
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LANs defined in terms of topology
(architecture) used to interconnect
networking equipment and protocol for
accessing network.
• Star
• Ring
• Bus
• Variations such as dual rings
Figure 11-13 Network topologies.
Local-Area Networks
• Local-Area Network (LAN)
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Carrier sense multiple access with
collision detection (CSMA/CD)
• Bus and star topologies;
• token passing;
• token-ring topology.
Figure 11-14 The tokenring topology.
Local-Area Networks
• Ethernet LAN
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Baseband CSMA/CD protocol local area
network system.
Capability for detecting data collisions
(collision detection).
Ethernet protocol provides information
regarding source and destination
addresses.
Figure 11-15 The bus topology.
Figure 11-16 The star topology.
Ethernet
• Characteristics
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Defined under IEEE 802.3
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Major use in Local Area Network (LAN) applications
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Example Versions
• 10Base-T
• 100Base-T
• Gigabit Ethernet
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Flexible Topology
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Cheap and easy to install
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Widely used to met networking Requirements
Ethernet
• History
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First developed by the Xerox Corporation as an
experimental coaxial cable based system in the 1970s
Used CSMA/CD protocol to allow multiple users
10 Mbps standard developed by Digital Equipment
Corporation, Intel and Xerox
• Ethernet Version 1 specification formed the basis for the first
IEEE 802.3 standard that was approved in 1983
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Published as an official standard in 1985
• A number of revisions have been undertaken to
update the Ethernet standard and keep it in line with
the latest technologies that are becoming available
Ethernet
• Ethernet network topologies
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Point to point:
• This is the simplest configuration as only two network units
are used.
• In this simple structure the cable is known as network link
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Coaxial bus:
• This type of Ethernet network is rarely used these days.
• The systems used a coaxial cable where the network units
were located along the length of the cable
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Star network:
• This type of Ethernet network has been the dominant
topology since the early 1990s.
Ethernet
• Ethernet network topologies
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Star network:
• It consists of a central network unit, which may be what is
termed a multi-port repeater or hub, or a network switch.
• All the connections to other nodes radiate out from this and are
point to point links.
• IEEE 802.3 (Ethernet) standards
Ranges from 802.3a in 1985 to 802.3at in 2005 to …..
• See Table on Article page 2
• New technologies are being added to the list of IEEE
802.3 standards to keep pace with technology.
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Ethernet
• Ethernet terminology
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Convention for describing the different forms of
Ethernet
• Example 10Base-T, 100Base-T, and 1000Base-T
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Designator consists of a three parts:
• The first number indicates the transmission speed in megabits
per second
• The second term indicates transmission type: BASE =
baseband; BROAD = broadband.
• The last number indicates segment length
• A 5 means a 500-meter (500-m) segment
• More recent versions of the IEEE 802.3 standard, letters replace
numbers
» T means unshielded twisted-pair cables
Ethernet
• Ethernet terminology
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Designator consists of a three parts:
• The last number indicates segment length
• More recent versions of the IEEE 802.3 standard, letters replace
numbers
» Further numbers indicate the number of twisted pairs available. For
example in 100BASE-T4, the T4 indicates four twisted pairs.
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The Ethernet IEEE 802.3 standards and Terminology
are continually being updated to ensure that the
generic standard keeps pace with constant advance
of technology
• The terminology used to define the different flavours is also
widely used for defining which Ethernet variant is used.
Ethernet
• Ethernet Frame Format / Structure
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Frame formats or frame structures are developed
within the MAC layer of the protocol stack
• Essentially the same frame structure is used for the different
variants of Ethernet
• There are some changes to the frame structure to extend the
performance of the system
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10 / 100 Mbps Ethernet MAC data frame format
• Preamble (PRE) - This is seven bytes long and it consists of a
pattern of alternating ones and zeros
Ethernet
• Ethernet Frame Format / Structure
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10 / 100 Mbps Ethernet MAC data frame format
• Start Of Frame delimiter (SOF) - This consists of one byte
and contains an alternating pattern of ones and zeros but
ending in two ones
• Destination Address (DA) - This field contains the address of
station for which the data is intended. Consists of 6-bytes
• Source Address (SA) - The source address consists of six bytes,
and it is used to identify the sending station.
• Length / Type - This field is two bytes in length. It provides
MAC information and indicates the number of client data
types that are contained in the data field of the frame. It may
also indicate the frame ID type if the frame is assembled using
an optional format.(IEEE 802.3 only
Ethernet
• Ethernet Frame Format / Structure
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10 / 100 Mbps Ethernet MAC data frame format
• Data - This block contains the payload data and it may be up
to 1500 bytes long.
• If the length of the field is less than 46 bytes, then padding data is
added to bring its length up to the required minimum of 46 bytes.
• Frame Check Sequence (FCS) - This field is four bytes long.
• It contains a 32 bit Cyclic Redundancy Check (CRC)
• Generated over the DA, SA, Length / Type and Data fields.
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1000 Mbps Ethernet MAC data frame format
• The basic MAC data frame format for Ethernet is modified
slightly for 1GE, IEEE 802.3z systems. For example:
• 1000Base-X standard, there is a minimum frame size of 416bytes
• 1000Base-T there is a minimum frame size of 520bytes
Ethernet
• Ethernet Frame Format / Structure
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1000 Mbps Ethernet MAC data frame format
• An extension is added as appropriate. This is a non-data
variable extension field to any frames that are shorter than
the minimum required length
• Half-duplex transmission
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Uses CSMA/CD
Ethernet
• Half-duplex transmission
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It was developed to enable several stations to share
the same transport medium without the need for
switching, network controllers or assigned time slots.
• Each station is able to determine when it is able to
transmit and the network is self organising.
• CSMA/CD
• Carrier Sense. Here each station listens on the network for
traffic and it can detect when the network is quiet
• Multiple Access aspect where the stations are able to
determine for themselves whether they should transmit
• Collision Detect element. If this occurs stations can detect this
and they will stop transmitting.
Ethernet
• Half-duplex transmission
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CSMA/CD
• They then back off a random amount of time before
attempting a retransmission
• Prevents the two stations starting to transmit together a second
time
• Full duplex
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Transmission in both directions
• Much simpler to implement than using the CSMA/CD
approach
• Much higher transmission throughput rates when the
network is being used
• Transmissions can be undertaken in both directions, thereby
doubling the effective bandwidth
Ethernet
• Ethernet addresses
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Every Ethernet network interface card (NIC) is given
a unique identifier called a MAC address
Assigned by the manufacturer of the card
• Each manufacturer that complies with IEEE standards can
apply to the IEEE Registration Authority for a range of
numbers for use in its products
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MAC address comprises of a 48-bit number
• First 24 bits identify the manufacturer and it is known as the
manufacturer ID or Organizational Unique Identifier (OUI)
• Second half of the address is assigned by the manufacturer
and it is known as the extension of board ID
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The MAC address is usually programmed into the
hardware so that it cannot be changed
Ethernet
• Ethernet addresses
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Because the MAC address is assigned to the NIC, it
moves with the computer.
• Even if the interface card moves to another location across the
world, the user can be reached because the message is sent to
the particular MAC address.
Assembling a LAN
• The Office LAN Example
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If network hardware and software
properly set up, all computers will be
able to access server, printer, other
computers.
• See Table 11-5: Common Numerics for LAN
Cabling
Table 11-5
Common
Numerics
for LAN
Cabling
Figure 11-19 An example of an
office LAN.
Assembling a LAN
• Assembling a Building LAN
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Network where multiple LANs within a
building are connected together.
Figure 11-20 An example of a building
LAN.
LAN Interconnection
• Open systems interconnection
(OSI) reference model
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Developed by International
Organization for Standardization (ISO).
LAN Interconnection
• Interconnecting LANs
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Switch
Routers
Gateways
Figure 11-22 Switch connecting two LANs.
Figure 11-23 Router connecting two LANs.
Figure 11-24 Gateway connecting two LANs.