Chapter 1
Introduction to Networking
&
7-Layer OSI Network Model
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Agenda
1. What is a computer network?
2. Network Models
-Topology
-P2P network model
-Client-server model
3. Client-Server Applications
4. Network Hardware
5. Open Systems Interconnection OSI Model vs. TCP/IP
Model
6. 7-layer OSI Model
Jackpotting I
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What is a computer network?
Two or more connected
computers that they can
communicate with each other
(send and receive)
1. The Internet is like a
postal mail system
(sender and receiver
addresses) with routers
connected together
2. IP address
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Components in a Network
• Major components in simple network
1. Client and server computers
2. Network interfaces card (N I C s)
3. Connection medium (wired & wireless)
4. Network Operating System (N O S)
5. Router, switch, modem, access point
6. More….such as?
A Simple Computer Network
A device to connect
outside networks
A simple network
What is the Internet?
Router
Switch
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Network Models
• Topology—How parts of a whole work together
• Physical topology—Mostly applies to hardware and describes how
computers, other devices, and cables fir together to form the
physical network
• Logical topology—Has to do with software and describes how
access to the network is controlled
• How users and programs initially gain access to the network
• Network operating system (N O S)—Controls access to the entire
network
• Required by client-server models
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Network Topology
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Peer-to-Peer Network Model (1 of 3)
• Peer-to-peer (P 2 P) network model—The OS of each computer
on the network is responsible for controlling access to its
resources
• No centralized control
• Computers, called nodes or hosts, form a logical group of
computers and users
• May share resources
• May prevent access to resources (Server – Client)
• Each computer user has a Windows local account
• Works only on that one computer
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Peer-to-Peer Network Model (2 of 3)
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Peer-to-Peer Network Model (3 of 3)
• Advantages
1. Simple configuration
2. Less expensive
-Compared to other network models
• Disadvantages
1. Not scalable
2. Not necessarily secure
3. Not practical for large installations
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Client-Server Network Model (1 of 5)
• Resources are managed by the Network Operating System (NOS)
via a centralized directory database
• Windows domain—A logical group of computers that a Windows
Server can control
• Active Directory (A D)—The centralized directory database that
contains user account information and security for the entire
group of computers
• A user can sign on to the network from any computer on the
network and gain access to the resources that AD allows
• This process is managed by Active Directory Domain Services (A
D D S)
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Client-Server Network Model (2 of 5)
• Client
• A computer making a request from another
• Clients don’t share their resources directly with each
other
• Access is controlled by entries in the centralized
domain database
• Client computers access resources on another computer
by way of the servers controlling the domain database
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Client-Server Applications
*The Internet is all about “Request ↔ Respond” cycle
on a Client-Server network model.
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Client-Server Network Model (3 of 5)
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Client-Server Network Model (4 of 5)
• The NOS (Network Operating System) is responsible for the
following activities:
1. Manages client data, resources
2. Ensures authorized user access
3. Controls user file access
4. Restricts user network access
5. Dictates computer communication rules
6. Supplies application to clients
• Server examples
• Windows Server 2016, Ubuntu Server, or Red Hat Enterprise
Linux
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NOS (Network Operating System)
Manage traffic in the network
Mail
Server
Database
Server
Web
Server
Client-Server Network Model (5 of 5)
• Servers that have a NOS installed require:
1. More memory, processing, and storage capacity
2. Equipped with special hardware
•Provides network management functions
• Advantages relative to peer-to-peer networks
1. User credential assigned from one central place
2. Multiple shared resource access centrally controlled
3. Central problem monitoring, diagnostics, and correction
capabilities
4. More scalable
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Client-Server Applications
• Network services—The resources a network makes available to its users
• Includes applications and the data provided by these applications
• In client-server applications
• A client computer requests data or a service from a second computer,
called the server
• Protocols
• Methods and rules for communication between networked devices
• Two primary protocols:
1. TCP (Transmission Control Protocol)
2. IP (Internet Protocol)
• T C P/I P suite of protocols is used by OSs for communication on a
network
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Client-Server Applications
• List of several popular client-server applications:
1. Web service
2. Email services
3. F T P service
4. Telnet service (command line on a remote computer)
5. Remote applications (Google Doc)
6. Remote Desktop
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Client-Server Applications
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Network Hardware
• Local area network (LAN)—Usually contained in a small space
• Such as an office or building
• Switch—Receives incoming data from one of its ports and
redirects it to another port or multiple ports
• Will send the data to its intended destination
• Hubs – function like switch, but dumb
• Star topology—All devices connect to one central device (usually a
switch)
• Network interface card (N I C)—A network port used to attach a
device to a network
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Network Hardware
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Network Hardware
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Network Hardware (4 of 9)
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Network Hardware
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Network Hardware
• Router—A device that manages traffic between two or more networks
• Can help find the best path for traffic to get from one network to another
• Routers can be used in small home networks to connect the home LAN to the
Internet
• Called a S O H O (small office-home office) network
• Industrial-grade routers can have several network ports, one for each network
it connects to
• Difference between router and switch:
• Router is like a gateway between networks and belongs to two or more local
networks
• Switch belongs only to its local network
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Network Hardware
Connect to other networks
Switch
Switch
Switch
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Network Hardware
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The Internet – Networks of Networks
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Open Systems Interconnection Model
(OSI Model)
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The Seven-Layer OSI Model (1 of 3)
• Compare two devices communicating on a network to two people
communicating by way of the U.S. Postal Service
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The Seven-Layer OSI Model (2 of 3)
• O S I (Open Systems Interconnection) reference model
• A seven-layer model developed to categorize the layers of
communication
• The layers are numbered in order, starting with Layer 1,
the Physical layer at the bottom
• Physical, Data Link, Network, Transport, Session,
Presentation, Application
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The Seven-Layer OSI Model (3 of 3)
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OSI vs. TCP/IP Model
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Layer 7: Application Layer
• Application layer—Describes the interface between two
applications, on separate computers
• Application layer protocols are used by programs that fall into two
categories:
1. Provide services to a user, such as a browser and Web server
2. Utility programs that provide services to the system, such as
SNMP that monitor and gather information about network
traffic
• Payload—Data that is passed between applications or utility
programs and the O S
*Simple Network Management Protocol (SNMP) is an Internet Standard protocol
for collecting and organizing information about managed devices on networks
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Layer 6: Presentation Layer
• Presentation layer—Responsible for reformatting,
compressing, and/or encrypting data in a way that the
receiving application can read
• Example:
• An email message can be encrypted at the
Presentation layer by the email client or by the OS
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Layer 5: Session Layer
• Session layer—Describes how data between applications is
synched and recovered if messages don’t arrive intact at the
receiving application
• The Application, Presentation, and Session layers are intertwined
• Often difficult to distinguish between them
• Most tasks are performed by the OS when an application makes
an API call to the OS
• Application Programming Interface (API) call is the method an
application uses when it makes a request of the OS
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Layer 4: Transport Layer (1 of 2)
• Transport layer—Responsible for transporting Application
layer payloads from one application to another
• Two main Transport layer protocols are:
1. T C P (Transmission Control Protocol)—Makes a connection with
the end host, checks whether data was received; called a
connection-oriented protocol
2. U D P (User Datagram Protocol)—Does not guarantee delivery by
first connecting and checking whether data is received; called a
connectionless protocol
3.
TCP is a connection-oriented protocol, whereas UDP is a connectionless
protocol.
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Layer 4: Transport Layer (2 of 2)
• Protocols add their own control information in an area at
the beginning of the payload (called a header)
• The Transport layer header addresses the receiving
application by a number called a port number
• If message is too large, T C P divides it into smaller
messages called segments
• In U D P, the message is called a datagram
• Encapsulation—Process of adding a header to the data
inherited from the layer above
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Encapsulation
Session Layer
Presentation Layer
Application Layer
Network Layer
Physical Layer
Data link Layer
Transport Layer
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Layer 3: Network Layer
• Network layer—Responsible for moving messages from one node to
another until they reach the destination host
• IP adds its own Network layer header to the segment or datagram
• The entire Network layer message is called a packet
• IP address—Assigned to each node on a network
• Network layer uses it to uniquely identify each host
• IP relies on several routing protocols to find the best route for a packet to take
to reach destination
• I C M P and A R P are examples
• Network layer protocol will divide large packets into smaller packets
• Process called fragmentation
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Layer 2: Data Link Layer
1. Layers 2 and 1 are responsible for interfacing with physical
hardware on the local network
• Protocols at these layers are programmed into firmware of a
computer’s N I C and other hardware
2. Type of networking hardware or technology used on a network
determine the Link Layer protocol used
• Ethernet and Wi-Fi are examples
3. The Link layer puts control information in a Link layer header
and at the end of the packet in a trailer
• Entire Link layer is called a frame
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Layer 2: Data Link Layer
• MAC (Media Access Control)
address—Hardware address of
the source and destination N I
Cs
• Also called a physical
address, hardware address,
or Data Link layer address
• Embedded on every network
adapter and are considered
short-range addresses that
can only find nodes on the
local network
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Layer 1: Physical Layer
• Physical layer—Simplest layer and is responsible for
sending bits via a wired or wireless transmission
• Can be transmitted as:
1. Wavelengths in the air
2. Voltage on a copper wire
3. Light (via fiber-optic cabling)
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OSI Model Recap
OSI 7-Layer Model
Application
7
SMTP, FTP, Telnet
Presentation
6
Format Data, Encryption
Session
5
Start & Stop Sessions
Transport
4
TCP, UDP, Port Numbers
Nework
3
IP Address, Routers
Data Link
2
MAC Address, Switches
Physical
1
Cable, Network Interface Card (NIC), Hubs
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Protocol Data Unit or PDU
• Protocol Data Unit (P D U)—The technical name for a group of bits as it moves
from one layer to the next and from one LAN to the next
• Technicians loosely call this group of bits a message or a transmission
• Table 1-1 Names for a P D U or message as it moves from one layer to another
OSI model
PDU Name
Layer 7, Application layer
Layer 6, Presentation layer
Layer 5, Session layer
Payload or data
Layer 4, Transport layer
Segment (T C P) or
datagram (U D P)
Layer 3, Network layer
Packet
Layer 2, Data Link layer
Frame
Layer 1, Physical layer
Bit or transmission
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Summary of How the Layers Work Together
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TCP (Transmission Control Protocol) (3 of 4)
• T C P uses a three-way handshake to establish a connection
• Three transmission sent before data transmission:
1. Step 1—Request for a connection (S Y N) ←
Knock on the door
2. Step 2—Response to the request (S Y N/A C K) ←
knock
3. Step 3—Connection established (A C K) ←
answer the
Now, we talk
• After the three initial messages, the payload or data is sent
• Sequence numbers will be increased by the number of bits
included in each received segment
-Confirms the correct length of message was received
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TCP (Transmission Control Protocol) (4 of 4)
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UDP (User Datagram Protocol) (1 of 2)
• UDP is an unreliable, connectionless protocol:
• No three-way handshake is performed
• Does not guarantee delivery of data
• UDP provides no error checking, sequencing, or flow control
• Makes UDP more efficient than TCP
• Useful for live audio or video transmissions over the Internet
• Also more efficient for carrying messages that fit within one data
packet
• An UDP header contains only four fields: Source port, Destination
port, Length, and Checksum
• Use of Checksum field in UDP is optional in IPv4, but required in
IPv6
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IP (Internet Protocol)
• IP operates at the Network layer (Layer 3) of the OSI model:
1.
Specifies where data should be delivered
2.
Identifies the data’s source and destination IP addresses
• IP enables TCP/IP to internetwork
• Traverse more than one LAN segment and more than one type
of network through a router
• IP is an unreliable, connectionless protocol
• Means that IP does not guarantee delivery of data and no session is
established before data is transmitted
• IP depends on TCP to ensure messages are put back together in the right
order and to ensure each message reaches the correct application on the
receiving host
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IP Address
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• What is GMU IP address?
IP addresses 129.174.182.0 to 129.174.182.255
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A R P (Address Resolution Protocol) on IPv4
Networks (1 of 4)
• A R P works in conjunction with IPv4 to discover the MAC address
of a host or node on the local network
• And to maintain a database that maps IP addresses to MAC
addresses on the local network
• A R P is a Layer 2 protocol that uses IP in Layer 3
• Operates only within its local network
• A R P relies on broadcasting
• ARP table—The database of IP-to-MAC address mappings
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ARP (Address Resolution Protocol) on IPv4 Networks (2 of 4)
MAC Address
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Jackpotting II – Taiwan ATM
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Jackpotting III - $$$
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