* The first of these elements is the message source, or sender. Message sources are people, or electronic devices, that need to send a message to other individuals or devices. * The second element of communication is the destination, or receiver, of the message. The destination receives the message and interprets it. * A third element, called a channel, consists of the media that provides the pathway over which the message can travel from source to destination.
Components of the Network
* Devices and media are the physical elements or hardware of the network. Hardware is often the visible components of the network platform such as a laptop, a PC, a switch, or the cabling used to connect the devices. * Services and processes are the communication programs, called software, that run on the networked devices. Services include many of the common network applications people use every day, like e-mail hosting services and web hosting services. Processes provide the functionality that directs and moves the messages through the network.
End Devices and their Role on the Network
* The network devices that people are most familiar with are called end devices. * These devices form the interface between the human network and the underlying communication network. a. Computers (work stations, laptops, file servers, web servers) b. Network printers
c. VoIP phones
d. Security cameras
e. Mobile handheld devices (such as wireless barcode scanners, PDAs)
Intermediary Devices and their Role on the Network
* Networks rely on intermediary devices to provide connectivity and to work behind the scenes to ensure that data flows across the network. These devices connect the individual hosts to the network and can connect multiple individual networks to form an internetwork. f. Network Access Devices (Hubs, switches, and wireless access points) g. Internetworking Devices (routers)
h. Communication Servers and Modems
i. Security Devices (firewalls)
* Processes running on the intermediary network devices perform these functions: j. Regenerate and retransmit data signals
k. Maintain information about what pathways exist through the network and internetwork l. Notify other devices of errors and communication failures m. Direct data along alternate pathways when there is a link failure n. Classify and direct messages according to QoS priorities o. Permit or deny the flow of data, based on security settings
* Communication across a network is carried on a medium. The medium provides the channel over which the message travels from source to destination. p. Metallic wires within cables
q. Glass or plastic fibers (fiber optic cable)
r. Wireless transmission
* Criteria for Choosing a Network Media
s. The distance the media can successfully carry a signal. t. The environment in which the media is to be installed. u. The amount of data and the speed at which it must be transmitted. v. The cost of the media and installation
Local Area Networks
* Networks infrastructures can vary greatly in terms of:
* The size of the area covered
* The number of users connected
* The number and types of services available
* A LAN is usually administered by a single organization. * The administrative control that governs the security and access control policies are enforced on the network level.
Wide Area Networks
* Networks that connect LANs in geographically separated locations. * WANs use specifically designed network devices to make the interconnections between LANs.
* A global mesh of interconnected networks (internetworks) meets these human communication needs. * The most well-known and widely used publicly-accessible internetwork is the Internet.
* The term intranet is often used to refer to a private connection of LANs and WANs that belongs to an organization, and is designed to be accessible only by the organization's members, employees, or others with authorization.
Network Representations & Common Data Network Symbols
Network Interface Card - A NIC, or LAN adapter, provides the physical connection to the network at the PC or other host device. The media connecting the PC to the networking device plugs directly into the NIC.
Physical Port - A connector or outlet on a networking device where the media is connected to a host or other networking device.
Interface - Specialized ports on an internetworking device that connect to individual networks. Because routers are used to interconnect networks, the ports on a router are referred to network interfaces.
Switch - the most common device for interconnecting local area networks Firewall - provides security to networks
Router - helps direct messages as they travel across a network Wireless Router - a specific type of router often found in home networks Cloud - used to summarize a group of networking devices.
Serial Link - one form of WAN interconnection, represented by the lightning bolt-shaped line
Protocol Suites and Industry Standards
* A standard is a process or protocol that has been endorsed by the networking industry and ratified by a standards organization. * Institute of Electrical and Electronics Engineers (IEEE) * Internet Engineering Task Force (IETF).
* Networking protocol suites describe processes such as:
* The format or structure of the message
* The method by which networking devices share information about pathways with other networks * How and when error and system messages are passed between devices * The setup and termination of data transfer sessions
The Interaction of Protocols
* Hypertext Transfer Protocol (HTTP) is a common protocol that governs the way that a web server and a web client interact. * HTTP defines the content and formatting of the requests and responses exchanged between the client and server.
* Transmission Control Protocol (TCP) is the transport protocol that manages the individual conversations between web servers and web clients. * TCP divides the HTTP messages into smaller pieces, called segments, to be sent to the destination client. * It is also responsible for controlling the size and rate at which messages are exchanged between the server and the client.
* IP is responsible for taking the formatted segments from TCP, encapsulating them into packets, assigning the appropriate addresses, and selecting the best path to the destination host.
Network Access Protocols:
* Network access protocols describe two primary functions, data link management and the physical transmission of data on the media. * Data-link management protocols take the packets from IP and format them to be transmitted over the media. * The standards and protocols for the physical media govern how the signals are sent over the media and how they are interpreted by the receiving clients.
The Benefits of using a Layered Model
* Assists in protocol design, because protocols that operate at a specific layer have defined information that they act upon and a defined interface to the layers above and below. * Fosters competition because products from different vendors can work together. * Prevents technology or capability changes in one layer from affecting other layers above and below. * Provides a common language to describe networking functions and capabilities.
Two Basic Types of Networking Models
1.) Reference Model. A reference model provides a common reference for maintaining consistency within all types of network protocols and services. * The primary purpose of a reference model is to aid in clearer understanding of the functions and process involved.
* The Open Systems Interconnection (OSI) model is the most widely known internetwork reference model. It is used for data network design, operation specifications, and troubleshooting.
* Initially the OSI model was designed by the International Organization for Standardization (ISO) to provide a framework on which to build a suite of open systems protocols.
* The vision was that this set of protocols would be used to develop an international network that would not be dependent on proprietary systems.
2.) Protocol Model. A protocol model provides a model that closely matches the structure of a particular protocol suite. * The TCP/IP model is a protocol model because it describes the functions that occur at each layer of protocols within the TCP/IP suite.
Comparing OSI Model with the TCP/IP Model
The OSI Layers 1 and 2 discuss the necessary procedures to access the media and the physical means to send data over a network.
OSI Model Layer 3, the Network layer, almost universally is used to discuss and document the range of processes that occur in all data networks to address and route messages through an internetwork. The Internet Protocol (IP) is the TCP/IP suite protocol that includes the functionality described at Layer 3.
Layer 4, the Transport layer of the OSI model, is often used to describe general services or functions that manage individual conversations between source and destination hosts. These functions include acknowledgement, error recovery, and sequencing. At this layer, the TCP/IP protocols Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) provide the necessary functionality.
The OSI model Layers 5, 6 and 7 are used as references for application software developers and vendors to produce products that need to access networks for communications.
Protocol Data Units and Encapsulation
* Data - The general term for the PDU used at the Application layer * Segment - Transport Layer PDU
* Packet - Internetwork Layer PDU
* Frame - Network Access Layer PDU
* Bits - A PDU used when physically transmitting data over the medium
Getting Data to the End Device: Layer 2 is concerned with the delivery of messages on a single local network. Getting the Data through the Internetwork: Layer 3 protocols are primarily designed to move data from one local network to another local network within an internetwork. Getting the Data to the Right Application: At Layer 4, information contained in the PDU header does not identify a destination host or a destination network.
Addressing in the Network
* The OSI model describes the processes of encoding, formatting, segmenting, and encapsulating data for transmission over the network.