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ISO OSI AND TCP/IP NETWORKING MODELS CHAPTER 1 1 3/2/2024 Basic Networking -Applied College- Example of a Computer Network 2 3/2/2024 Basic Networking -Applied College- What is a Computer network?37 3/2/2024 Basic Networking -Applied College- The Internet Layer At the Internet layer, the logical addresses of the source and destination devices are determined and placed on the package.It extracts the IP packet from this frame and resolves the information in the IP header, then does the same for the TCP and application headers, eventually extracting the HTTP application data for processing by a software program, such as a web browser or web server.o Network adapter or network interface card (NICs)--An NIC joins an end system host to network media (cabling or wireless) and enables it to communicate over the network by assembling and disassembling frames.3 3/2/2024 Basic Networking -Applied College- ISO The International Organization for Standardization (ISO) developed the Open Systems Interconnection (OSI) reference model (iso.org/standard/20269.html) to promote understanding of how components in a network system work.18 3/2/2024 Basic Networking -Applied College- Communication at layer 2 of the OSI model ...2.......?.????....???......??.?.......

ISO OSI AND TCP/IP
NETWORKING MODELS
CHAPTER 1
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Example of a Computer Network
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What is a Computer network?
A Computer network is two or more computer systems that are linked
by a transmission medium and share one or more protocols that enable
them to exchange data.
You can think of any network in terms of nodes and links. The nodes are
devices that send, receive, and forward data and the links are the
communications pathways between them.
Computer network aimed to
 Enable effective communication
 Share resources
 Facilitate centralized management of data
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ISO
The International Organization for Standardization (ISO)
developed the Open Systems Interconnection (OSI)
reference model (iso.org/standard/20269.html) to
promote understanding of how components in a network
system work.
It does this by separating the function of hardware and
software components to seven discrete layers. Each layer
performs a different group of tasks required for network
communication.
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OSI (Open System Interconnection)Model
The Open Systems Interconnection (OSI) model is used to simplify
some of this complexity.
It divides network technologies between seven functional layers.
This makes it easier to separate and focus on individual concepts
and technologies while retaining an understanding of
relationships to the functions of technologies placed in other
layers.
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Seven Layers of OSI Model
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Data Encapsulation and Decapsulation
A network protocol is a set of rules for exchanging data in a structured
format. A network protocol has two principal functions:

1. Addressing—Describing where data messages should go. At each
   layer, there are different mechanisms for identifying nodes and rules
   for how they can send and receive messages.


2. Encapsulation—Describing how data messages should be packaged
   for transmission. Encapsulation is like an envelope for a letter, with the
   distinction that each layer requires its own envelope. At each layer, the
   protocol adds fields in a header to whatever data (payload) it
   receives from an application or other protocol.
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   Data Encapsulation and Decapsulation
   A network will involve the use of many different protocols operating at
   different layers of the OSI model.
   At each layer, for two nodes to communicate they must be running the
   same protocol. The protocol running at each layer communicates with its
   equivalent (or peer) layer on the other node.
   This communication between nodes at the same layer is described as a
   same layer interaction.
   To transmit or receive a communication, on each node, each layer
   provides services for the layer above and uses the services of the layer
   below. This is referred to as adjacent layer interaction.
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   Data Encapsulation and Decapsulation
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   Data Encapsulation and Decapsulation
   When a message is sent from one node to another,
   it travels down the stack of layers on the sending node,
   reaches the receiving node using the transmission media,
   and then passes up the stack on that node.
   At each level (except the physical layer), the sending
   node adds a header to the data payload, forming a
   “chunk” of data called a protocol data unit (PDU). This is
   the process of encapsulation.
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   Data Encapsulation and Decapsulation
   For example, on the sending node, data is generated by an
   application, such as the HyperText Transfer Protocol (HTTP), which will
   include its own application header.
   At the transport layer, a Transport Control Protocol (TCP) header is
   added to this application data.
   At the network layer, the TCP segment is wrapped in an Internet
   Protocol (IP) header.
   The IP packet is encapsulated in an Ethernet frame at the data link
   layer, then the stream of bits making up the frame is transmitted over
   the network at the physical layer as a modulated electrical signal.
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   Data Encapsulation and Decapsulation
   The receiving node performs the reverse process, referred
   to as decapsulation.
   It receives the stream of bits arriving at the physical layer
   and decodes an Ethernet frame.
   It extracts the IP packet from this frame and resolves the
   information in the IP header, then does the same for the
   TCP and application headers, eventually extracting the
   HTTP application data for processing by a software
   program, such as a web browser or web server.
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   Layer 1—Physical
   The physical layer (PHY) of the OSI model (layer 1) is responsible
   for the transmission and receipt of the signals that represent bits
   of data from one node to another node. Different types of
   transmission media can be classified as cabled or wireless:
   • Cabled—A physical signal conductor is provided between two nodes.
   Examples include cable types such as copper or fiber optic cable.
   Cabled media can also be described as bounded media.
   • Wireless—Uses free space between nodes, such as microwave radio.
   Wireless media can also be described as unbounded media.
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   The Physical layer specifies the following:
    • Physical topology—The layout of nodes and links as established
   by the transmission media. An area of a larger network is called a
   segment. A network is typically divided into segments to cope with
   the physical restrictions of the network media used, to improve
   performance, or to improve security. At the Physical layer, a segment
   is where all the nodes share access to the same media.
    • Physical interface—Mechanical specifications for the network
   medium, such as cable specifications, the medium connector and pin-
   out details (the number and functions of the various pins in a network
   connector), or radio transceiver specifications.
   The process of transmitting and receiving signals over the network
   medium, including modulation schemes and timing/synchronization.
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   Devices that operate at the Physical layer include:
    Transceiver—The part of a network interface that sends and
   receives signals over the network media.
    Repeater—A device that amplifies an electronic signal to extend the
   maximum allowable distance for a media type.
    Hub—A multiport repeater, deployed as the central point of
   connection for nodes.
    Media converter—A device that converts one media signaling type
   to another.
    Modem—A device that performs some type of signal modulation
   and demodulation, such as sending digital data over an analog
   line.
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   Layer 2—Data Link
   The data link layer (layer 2) is responsible for transferring
   data between nodes on the same logical segment.
   At the Data Link layer, a segment is one where all nodes
   can send traffic to one another using hardware addresses,
   regardless of whether they share access to the same
   media.
   A layer 2 segment might include multiple physical
   segments. This is referred to as a logical topology.
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   Example of Nodes
   Nodes that send and receive information are referred to as
   end systems or as host nodes.
   This type of node includes
    computer,
    laptops,
    servers,
    Voice over IP(VoIP) phones,
    Smartphones,and
    printers.
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   The data link layer organizes the stream of bits arriving from the
   physical layer into structured units called frames.
   Each frame contains a network layer packet as its payload.
   The data link layer adds control information to the payload in the
   form of header fields.
   These fields include source and destination hardware addresses,
   plus a basic error check to test if the frame was received intact.
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   Communication at layer 2 of the OSI model
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   Devices that operate at the data link layer include:
    • Network adapter or network interface card (NICs)—An NIC joins an end
   system host to network media (cabling or wireless) and enables it to
   communicate over the network by assembling and disassembling frames.
    • Bridge—A bridge is a type of intermediate system that joins physical
   network segments while minimizing the performance reduction of having
   more nodes on the same network. A bridge has multiple ports, each of
   which functions as a network interface.
    • Switch—An advanced type of bridge with many ports. A switch creates
   links between large numbers of nodes more efficiently.
    • Wireless access point (AP)—An AP allows nodes with wireless network
   cards to communicate and creates a bridge between wireless networks and
   wired ones.
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   Layer 3—Network
   The network layer (layer 3) is responsible for moving data
   around a network of networks, known as an internetwork
   or the Internet.
   While the data link layer is capable of forwarding data
   by using hardware addresses within a single segment,
   The network layer moves information around an
   internetwork by using logical network and host IDs.
   The networks are often heterogeneous; that is, they use a
   variety of physical layer media and data link protocols.
   The main appliance working at layer 3 is the router.
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   Communications at layer 3 of OSI model
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   The network layer forwards information between
   networks by examining the destination network-layer
   address or logical network address.
   The packet is forwarded, router by router (or hop by
   hop), through the internetwork to the target network.
   Once it has reached the destination network,
   The hardware address can be used to deliver the
   packet to the target node.
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   It is usually important for traffic passing between
   networks to be filtered. A basic firewall operates at
   layer 3 to enforce an access control list (ACL). A
   network ACL is a list of the addresses and types of
   traffic that are permitted or blocked.
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   Layer 4—Transport
   The first three layers of the OSI model are primarily concerned with
   moving frames and datagrams between nodes and networks.
   At the transport layer—also known as the end-to-end or host-to-host
   layer—the content of the packets becomes significant.
   Any given host on a network will be communicating with many other
   hosts using many different types of networking data.
   One of the functions of the transport layer is to identify each type of
   network application by assigning it a port number.
   For example, data requested from an HTTP web application can be
   identified as port 80, while data sent to an email server can be
   identified as port 25.
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   At the transport layer, on the sending host, data from the
   upper layers is packaged as a series of layer 4 PDUs,
   referred to as segments.
   Each segment is tagged with the application’s port number.
   The segment is then passed to the network layer for delivery.
   Many different hosts could be transmitting multiple HTTP and
   email packets at the same time. These are multiplexed using
   the port numbers along with the source and destination
   network addresses onto the same link.
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   Communications at layer 4 (transport )of the
   OSI model
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    At the network and data link layers, the port number is ignored—it
   becomes part of the data payload and is invisible to the routers
   and switches that implement the addressing and forwarding
   functions of these layers.
    At the receiving host, each segment is decapsulated, identified by its
   port number, and passed to the relevant handler at the application
   layer. Put another way, the traffic stream is de-multiplexed.
    The transport layer can also implement reliable data delivery
   mechanisms, should the application require it. Reliable delivery
   means that any lost or damaged packets are resent.
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   Devices working at the transport layer include
    multilayer switches—usually working as load
   balancers—and many types of security appliances,
   such as more advanced firewalls and intrusion detection
   systems (IDSs).
    The upper layers of the OSI model are less clearly
   associated with distinct real world protocols. These
   layers collect various functions that provide useful
   interfaces between software applications and the
   transport layer.
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   Layer 5—Session
   Most application protocols require the exchange of
   multiple messages between the client and server. This
   exchange of such a sequence of messages is called a
   session or dialog. The session layer (layer 5)
   represents functions that administer the process of
   establishing a dialog, managing data transfer, and
   then ending (or tearing down) the session.
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   Layer 6—Presentation
   The presentation layer (layer 6) transforms data between the format
   required for the network and the format required for the application.
   For example, the presentation layer is used for character set
   conversion, such as between American Standard Code for Information
   Interchange (ASCII) and Unicode.
   The presentation layer can also be conceived as supporting data
   compression and encryption.
   However, in practical terms, these functions are often implemented by
   encryption devices and protocols running at lower layers of the stack or
   simply within a homogenous application layer.
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   Layer 7—Application
   The application layer (layer 7) is at the top of the OSI stack.
   An application layer protocol doesn’t encapsulate any other protocols
   or provide services to any protocol.
   Application-layer protocols provide an interface for software programs
   on network hosts that have established a communications channel
   through the lower-level protocols to exchange data.
   More widely, upper-layer protocols provide most of the services that
   make a network useful, rather than just functional, including web
   browsing, email and communications, directory lookup, remote printing,
   and database services.
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   OSI Model Summary
   The following image summarizes the OSI model, listing the PDUs at each layer,
   along with the types of devices that work at each layer..
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   The TCP/IP model
   The four layers of the TCP/IP model are as follows:

1. The Application Layer


2. The Transport Layer


3. The Internet Layer


4. The Network Access Layer
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   The Application Layer
   The Application layer is the user applications' interface to the
   networking process that is facilitated by TCPIIP.
   When a user attempts to access anything, the computer has to
   decide whether the object is located locally on the hard drive
   or is somewhere out on the network.
   If the computer determines that the network is required, the
   Application layer begins the process of creating the package
   (or series of packages, in most cases) that will be used to
   request the object or information from the remote device, or
   alternately to transfer requested information to another
   device.
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   The information that is contained in the package that will be handed down to
   the Transport layer includes the data itself (for example, a web page or a
   document) and all other information required to establish the session between
   the source and destination service or application and to manage the format or
   presentation of the data.
   In doing this, the Transport layer on the source device uses port numbers to
   identify protocols and services.
   These port numbers are used to communicate this infonnation to the Transport
   layer on the destination device.
   When routers make decisions about the handling of packets based on port
   numbers, it is said that they are operating at the Transport layer because the
   routers are using information that is placed in the packet at that layer.
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   The Transport Layer
   The parts of the TCP /IP suite dedicated to using the information
   provided by the port numbers are located at the Transport layer.
   UDP and TCP are the two sub protocols of TCP/IP that operate on this
   layer.
   The protocol selected at this layer will be a function of the transmission
   type (unicast, multicast, or broadcast) and the port number specified
   between the Application layer and the Transport layer.
   The protocol and port number required are added to the package,
   and the package is handed down to the Internet layer.
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   The Internet Layer
   At the Internet layer, the logical addresses of the source and
   destination devices are determined and placed on the package.
   This information, in the form of IP addresses, is used by the devices on
   the network that can operate at the Internet layer in the process of
   routing the package to its final destination.
   As you may have surmised by now, this is why routers are Internet layer
   devices. They use information placed in the package at the Internet
   layer (IP addresses) to make routing decisions.
   There are two more protocols operating at the Internet layer: ICMP
   and IGMP, which are covered in detail in Chapter “Network Protocols."
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   The Network Access Layer
   At the Network Access layer, the source and
   destination physical addresses are put on the front of
   the package in a part called the header.
   Information used to perform a frame check sequence
   on the message is placed at the back of the package
   in a section called the trailer.
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   Finally, the package is converted to ones and zeros in the format required by
   the physical medium in use.
   If the computer is connected with a cable, the format will be electrical
   impulses.
   If the computer is connected to a wireless network, the format will be radio
   waves.
   If the computer has a fiber-optic connection, the format will be light waves.
   This final operation is performed by the network adaptor in the computer,
   which is why you must have an Ethernet (wired), wireless, or fiber-optic network
   adaptor, respectively, in a computer to operate on those network types, so that
   the bit patterns (the ones and zeros) can be sent in the required format.
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   Comparing the OSI and TCP/IP Models
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   Comparing the OSI and TCP/IP Models
    There are seven layers in the OSI model and four in
   the TCPIIP model.
    The top three layers of the OSI model (Application,
   Presentation and Session) map to the Application
   layer of the TCP/IP model.
    The bottom two layers of the OSI model (Data-Link
   and Physical) map to the Network Access layer of
   the TCP/IP model.
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   Benefits of Computer Network

1. Sharing of Data and
   Information
    Important data
    Procedure manuals
    Database sharing
   2.Hardware Sharing
   3.Software Sharing
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