Transcript OSI Model Review Layer 1

Chapter 2 Networking Basics
Copyright 2003
Fundamentals of Voice and Data Cabling 1.2
Cisco Networking Academy Program
Network Definition
• A network is a system of interconnected objects or
people. There are many different types of
networks. A computer network is defined as
having two or more devices such as workstations,
printers, and servers linked together for the
purpose of sharing information.
Copyright 2003
Fundamentals of Voice and Data Cabling 1.2
Cisco Networking Academy Program
A Typical Computer Network
Copyright 2003
Fundamentals of Voice and Data Cabling 1.2
Cisco Networking Academy Program
Computer Networks Using Voice Cable
• Telephone lines are often used for transmitting
data between computers, particularly for home
and small business Internet users. Although this is
a slow connection method, it is fairly inexpensive,
and for many home users, the only option
available.
• New telco (short for telephone company) data
services are bringing higher bandwidths at
reasonable costs to home and small business
users over the same copper wires that carry voice
calls .
Copyright 2003
Fundamentals of Voice and Data Cabling 1.2
Cisco Networking Academy Program
Goals of the Network
The network should be:
• Simple
• Manageable
• Adaptable and scalable
• Reliable
• Transparent
Copyright 2003
Fundamentals of Voice and Data Cabling 1.2
Cisco Networking Academy Program
Benefits of Networking
• Sharing Output Devices - Printers, other output
devices, and fax machines can be shared.
• Sharing Input Devices - High-end devices are
typically used occasionally and are often
expensive so it makes sense to configure them for
multiple users on the network.
• Sharing Storage Devices - Files can be saved on
these storage devices and accessed from
anywhere on the network.
Copyright 2003
Fundamentals of Voice and Data Cabling 1.2
Cisco Networking Academy Program
More Benefits of Networking
• Sharing Internet Connections - With the proper
software, an entire LAN can connect to the
Internet through one phone line and a single ISP
account.
• Security – It is much easier to secure data and
resources when policies and enforcement are
centralized and managed.
• Sharing Data and Applications - Sharing data files
result in the efficient use of disk space and easier
collaboration on multi-user projects.
Copyright 2003
Fundamentals of Voice and Data Cabling 1.2
Cisco Networking Academy Program
Role of cabling in a network
• In the past, data and voice networks were
separate. Today, the wiring systems are integrated
creating organized and standards-driven
structured cabling systems.
• Such systems pull wires for both data and voice
networks at the same time, sometimes even using
the same kind of wiring for both.
Copyright 2003
Fundamentals of Voice and Data Cabling 1.2
Cisco Networking Academy Program
Networking media
• The most common networking medium is copper
wiring, which uses electrical current to send
signals.
• Fiber-optic cable uses pulses of light to transmit
signals along thin strands of glass.
• Wireless media include radio waves, infrared, or
microwave waves.
Copyright 2003
Fundamentals of Voice and Data Cabling 1.2
Cisco Networking Academy Program
Server Location Issues
• One feature of any structured cabling installation
is the ability to provide services from any location
on the network.
• Peer-to-peer networks have no central server.
Every network member shares files with every
other member.
• Servers contain information or applications that
can be accessed by many users.
Copyright 2003
Fundamentals of Voice and Data Cabling 1.2
Cisco Networking Academy Program
Types of Computer Networks
• A local area network (LAN) is a computer
network that connects a cluster of users and
devices within a building and is managed on site.
• Multiple LANs can be internetworked together to
form Building Area Networks (BANs) or
Metropolitan Area Networks (MANs).
• LANs, BANs, and MANs can be internetworked
together over large geographical regions to form
Wide Area Networks (WANs).
Copyright 2003
Fundamentals of Voice and Data Cabling 1.2
Cisco Networking Academy Program
Global and regional voice networks
• The telephone system is a
global network allowing
users from virtually
anywhere in the world to
call another user. The
global telephone network
is composed of smaller
telephone networks from
each country.
Copyright 2003
Fundamentals of Voice and Data Cabling 1.2
Cisco Networking Academy Program
Local voice network
• A localized voice network is basically a private
telephone network confined to an organization.
These are called private branch exchanges
(PBXs), and are found in many large
organizations.
• PBXs allow users to access other users on the
network by only dialing their extension rather
than the entire phone number. Users of the PBX
share a certain number of outside lines for
making telephone calls external to the PBX.
Copyright 2003
Fundamentals of Voice and Data Cabling 1.2
Cisco Networking Academy Program
Local Area Networks
• A computer network that
connects users and
devices within a building
or campus and is
managed on site is
called a Local-Area
Network (LAN). LANs
are found in businesses,
schools, governments,
and even homes.
Copyright 2003
Fundamentals of Voice and Data Cabling 1.2
Cisco Networking Academy Program
Metropolitan Area Networks
• When two or more
LANs are linked
within a city or
limited geographic
area, it is called a
metropolitan-area
network (MAN).
Copyright 2003
Fundamentals of Voice and Data Cabling 1.2
Cisco Networking Academy Program
Wide Area Networks
• A wide-area network (WAN) has few geographic limits.
WANs can cover a city, country, or even the entire
world.
• The Internet is an example of a WAN.
Copyright 2003
Fundamentals of Voice and Data Cabling 1.2
Cisco Networking Academy Program
Network topologies
• Computer networks have physical and logical
topologies.
• Physical topologies are the layout of the
networking cables, devices, and workstations.
• Logical topologies dictate the path data takes
between devices and workstations.
• Every network has both a logical and a physical
topology.
Copyright 2003
Fundamentals of Voice and Data Cabling 1.2
Cisco Networking Academy Program
Physical Topologies
•Physical topologies describe the actual
physical layout of the network.
Copyright 2003
Fundamentals of Voice and Data Cabling 1.2
Cisco Networking Academy Program
The Bus Topology
• A physical bus topology uses a single length of
cable that runs from one end of the network to
the other.
• Users are connected to the central cable by
segments of cable.
Copyright 2003
Fundamentals of Voice and Data Cabling 1.2
Cisco Networking Academy Program
Ring and Dual Ring Topologies
• In a physical ring topology, all devices are connected
by a circle of wire.
• The dual-ring topology provides additional reliability
since it has two pathways for traffic to flow.
Dual Ring
Ring
Copyright 2003
Fundamentals of Voice and Data Cabling 1.2
Cisco Networking Academy Program
The Star and Extended Star Topology
• A star topology connects all cables to a central point.
• An extended star topology is created by linking
together several star topologies to a central point.
Ring
Extended Star
Star
Copyright 2003
Fundamentals of Voice and Data Cabling 1.2
Cisco Networking Academy Program
The Hierarchical Topology
• The hierarchical topology imposes order on the
network by grouping hosts based on their
physical location on the network.
Hierarchical
Copyright 2003
Fundamentals of Voice and Data Cabling 1.2
Cisco Networking Academy Program
Mesh Topology
• A mesh topology provides redundancy for a
network by connecting each host to every other
host.
Mesh
Copyright 2003
Fundamentals of Voice and Data Cabling 1.2
Cisco Networking Academy Program
The OSI reference model
• The OSI reference model is used universally as
a method for teaching and understanding
network functionality.
• Following the OSI model when designing,
building, upgrading, or troubleshooting will
achieve greater compatibility and interoperability
between various types of network technologies.
Copyright 2003
Fundamentals of Voice and Data Cabling 1.2
Cisco Networking Academy Program
The OSI reference model
Copyright 2003
Fundamentals of Voice and Data Cabling 1.2
Cisco Networking Academy Program
Reasons for using the OSI model
• 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.
Copyright 2003
Fundamentals of Voice and Data Cabling 1.2
Cisco Networking Academy Program
Physical layer (Layer 1)
• This layer provides 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.
Copyright 2003
Fundamentals of Voice and Data Cabling 1.2
Cisco Networking Academy Program
Data-link layer (Layer 2)
• This layer deals with speed of transmission, flow
control, error identification, and topology.
• This layer recognizes special identifiers that are
unique to each computer, called media access
control (MAC) addresses.
Copyright 2003
Fundamentals of Voice and Data Cabling 1.2
Cisco Networking Academy Program
Network layer (Layer 3)
• The network layer adds logical or network
addresses, 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.
Copyright 2003
Fundamentals of Voice and Data Cabling 1.2
Cisco Networking Academy Program
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.
Copyright 2003
Fundamentals of Voice and Data Cabling 1.2
Cisco Networking Academy Program
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.
Copyright 2003
Fundamentals of Voice and Data Cabling 1.2
Cisco Networking Academy Program
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.
Copyright 2003
Fundamentals of Voice and Data Cabling 1.2
Cisco Networking Academy Program
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.
Copyright 2003
Fundamentals of Voice and Data Cabling 1.2
Cisco Networking Academy Program
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.
Copyright 2003
Fundamentals of Voice and Data Cabling 1.2
Cisco Networking Academy Program
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.
Copyright 2003
Fundamentals of Voice and Data Cabling 1.2
Cisco Networking Academy Program
Bridges
• A bridge keeps a table with all MAC addresses
on the network.
• This table enables the bridge to recognize which
MAC addresses are on each side of the bridge.
• A bridge works by keeping traffic destined for
one side of the bridge to that side alone.
Copyright 2003
Fundamentals of Voice and Data Cabling 1.2
Cisco Networking Academy Program
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.
Copyright 2003
Fundamentals of Voice and Data Cabling 1.2
Cisco Networking Academy Program
Network Layer Functions
• The network layer (Layer 3) deals with higherlevel 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.
Copyright 2003
Fundamentals of Voice and Data Cabling 1.2
Cisco Networking Academy Program
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.
Copyright 2003
Fundamentals of Voice and Data Cabling 1.2
Cisco Networking Academy Program
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.
Copyright 2003
Fundamentals of Voice and Data Cabling 1.2
Cisco Networking Academy Program
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.
Copyright 2003
Fundamentals of Voice and Data Cabling 1.2
Cisco Networking Academy Program
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.
Copyright 2003
Fundamentals of Voice and Data Cabling 1.2
Cisco Networking Academy Program
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.
Copyright 2003
Fundamentals of Voice and Data Cabling 1.2
Cisco Networking Academy Program
OSI Model Review Layer 1
Copyright 2003
Fundamentals of Voice and Data Cabling 1.2
Cisco Networking Academy Program
OSI Model Review Layer 2
Copyright 2003
Fundamentals of Voice and Data Cabling 1.2
Cisco Networking Academy Program
OSI Model Review Layer 3
Copyright 2003
Fundamentals of Voice and Data Cabling 1.2
Cisco Networking Academy Program
OSI Model Review Layer 4
Copyright 2003
Fundamentals of Voice and Data Cabling 1.2
Cisco Networking Academy Program
OSI Model Review Layer 5
Copyright 2003
Fundamentals of Voice and Data Cabling 1.2
Cisco Networking Academy Program
OSI Model Review Layer 6
Copyright 2003
Fundamentals of Voice and Data Cabling 1.2
Cisco Networking Academy Program
OSI Model Review Layer 7
Copyright 2003
Fundamentals of Voice and Data Cabling 1.2
Cisco Networking Academy Program