منتدي منظمة أقباط الولايات المتحدة

منتدي منظمة أقباط الولايات المتحدة (http://www.copts.net/forum/index.php)
-   العلوم وتكنولوجيا الاتصالات (http://www.copts.net/forum/forumdisplay.php?f=36)
-   -   Networking Basics (http://www.copts.net/forum/showthread.php?t=11333)

InnerPeace 05-03-2006 11:08 AM

Networking Models
 
[LEFT][SIZE="4"][COLOR="Blue"][B] TCP/IP model [/B][/COLOR]


[COLOR="Green"]This page discusses the TCP/IP reference model, which is the historical and technical standard of the Internet. [/COLOR]

The U.S. Department of Defense (DoD) created the TCP/IP reference model, [U]because it wanted to design a network that could survive any conditions, including a nuclear war[/U]. In a world connected by different types of communication media such as copper wires, microwaves, optical fibers and satellite links, [U]the DoD wanted transmission of packets every time and under any conditions[/U]. This very difficult design problem brought about the creation of the TCP/IP model.

Unlike the proprietary networking technologies mentioned earlier, TCP/IP was developed as an open standard. This meant that anyone was free to use TCP/IP. This helped speed up the development of TCP/IP as a standard.

The TCP/IP model has the following four layers:

Application layer
Transport layer
Internet layer
Network access layer

Although some of the layers in the TCP/IP model have the same name as layers in the OSI model, the layers of the two models do not correspond exactly. Most notably, the application layer has different functions in each model.

The designers of TCP/IP felt that the application layer should include the OSI session and presentation layer details. They created an application layer that handles issues of representation, encoding, and dialog control.

The transport layer deals with the quality of service issues of reliability, flow control, and error correction. One of its protocols, the transmission control protocol (TCP), provides excellent and flexible ways to create [U]reliable, well-flowing, low-error network communications[/U].

TCP is a connection-oriented protocol. It maintains a dialogue between source and destination while packaging application layer information into units called segments. Connection-oriented does not mean that a circuit exists between the communicating computers. It does mean that Layer 4 segments travel back and forth between two hosts to acknowledge the connection exists logically for some period.

The purpose of the Internet layer is to divide TCP segments into packets and send them from any network. The packets arrive at the destination network independent of the path they took to get there. The specific protocol that governs this layer is called the Internet Protocol (IP). Best path determination and packet switching occur at this layer.

The relationship between IP and TCP is an important one. [U]IP can be thought to point the way for the packets, while TCP provides a reliable transport[/U].

The name of the network access layer is very broad and somewhat confusing. It is also known as the host-to-network layer. This layer is concerned with all of the components, both physical and logical, that are required to make a physical link. It includes the networking technology details, including all the details in the OSI physical and data link layers.

[CENTER][IMG]http://img64.imageshack.us/img64/5212/untitled7ed.png[/IMG][/CENTER]
Figure illustrates some of the common protocols specified by the TCP/IP reference model layers. Some of the most commonly used application layer protocols include the following:

File Transfer Protocol (FTP)
Hypertext Transfer Protocol (HTTP)
Simple Mail Transfer Protocol (SMTP)
Domain Name System (DNS)
Trivial File Transfer Protocol (TFTP)

The common transport layer protocols include:

Transport Control Protocol (TCP)
User Datagram Protocol (UDP)

The primary protocol of the Internet layer is:

Internet Protocol (IP)


The network access layer refers to any particular technology used on a specific network.

Regardless of which network application services are provided and which transport protocol is used, there is only one Internet protocol, IP. This is a deliberate design decision.[U] IP serves as a universal protocol that allows any computer anywhere to communicate at any time[/U].

A comparison of the OSI model and the TCP/IP model will point out some similarities and differences.

Similarities include:

Both have layers.
Both have application layers, though they include very different services.
Both have comparable transport and network layers.
Both models need to be known by networking professionals.
Both assume packets are switched. This means that individual packets may take different paths to reach the same destination. This is contrasted with circuit-switched networks where all the packets take the same path.

Differences include:

TCP/IP combines the presentation and session layer issues into its application layer.
TCP/IP combines the OSI data link and physical layers into the network access layer.
TCP/IP appears simpler because it has fewer layers.
TCP/IP protocols are the standards around which the Internet developed, so the TCP/IP model gains credibility just because of its protocols. In contrast, networks are not usually built on the OSI protocol, even though the OSI model is used as a guide.

Although TCP/IP protocols are the standards with which the Internet has grown, this curriculum will use the OSI model for the following reasons:

It is a generic, protocol-independent standard.
It has more details, which make it more helpful for teaching and learning.
It has more details, which can be helpful when troubleshooting.

Networking professionals differ in their opinions on which model to use. Due to the nature of the industry it is necessary to become familiar with both. Both the OSI and TCP/IP models will be referred to throughout the curriculum. The focus will be on the following:

TCP as an OSI Layer 4 protocol
IP as an OSI Layer 3 protocol
Ethernet as a Layer 2 and Layer 1 technology

Remember that there is a difference between a model and an actual protocol that is used in networking. The OSI model will be used to describe TCP/IP protocols. [/SIZE][/LEFT]

InnerPeace 05-03-2006 11:29 AM

Networking Models
 
[LEFT][SIZE="4"][COLOR="Blue"][B]Detailed encapsulation process [/B][/COLOR]


[COLOR="Green"]This page describes the process of encapsulation. [/COLOR]

All communications on a network originate at a source, and are sent to a destination. The information sent on a network is referred to as data or data packets. If one computer (host A) wants to send data to another computer (host B), the data must first be packaged through a process called encapsulation.

Encapsulation wraps data with the necessary protocol information before network transit. Therefore, as the data packet moves down through the layers of the OSI model, it receives headers, trailers, and other information.

[CENTER][IMG]http://img141.imageshack.us/img141/8324/untitled7gr1.png[/IMG][/CENTER]
To see how encapsulation occurs, examine the manner in which data travels through the layers as illustrated in Figure . Once the data is sent from the source, it travels through the application layer down through the other layers. The packaging and flow of the data that is exchanged goes through changes as the layers perform their services for end users.
[CENTER][IMG]http://img475.imageshack.us/img475/6892/untitled6an.png[/IMG][/CENTER]
As illustrated in Figure , networks must perform the following five conversion steps in order to encapsulate data:

[B]Build the data [/B]– As a user sends an e-mail message, its alphanumeric characters are converted to data that can travel across the internetwork.
[B]Package the data for end-to-end transport [/B]– The data is packaged for internetwork transport. By using segments, the transport function ensures that the message hosts at both ends of the e-mail system can reliably communicate.
[B]Add the network IP address to the header[/B] – The data is put into a packet or datagram that contains a packet header with source and destination logical addresses. These addresses help network devices send the packets across the network along a chosen path.
[B]Add the data link layer header and trailer[/B] – Each network device must put the packet into a frame. The frame allows connection to the next directly-connected network device on the link. Each device in the chosen network path requires framing in order for it to connect to the next device.
[B]Convert to bits for transmission[/B] – The frame must be converted into a pattern of 1s and 0s (bits) for transmission on the medium. A clocking function enables the devices to distinguish these bits as they travel across the medium. The medium on the physical internetwork can vary along the path used. For example, the e-mail message can originate on a LAN, cross a campus backbone, and go out a WAN link until it reaches its destination on another remote LAN. [/SIZE][/LEFT]

smile 05-03-2006 11:35 AM

[b]لا بقى دى كورس مكثف ولازم اثيته[/b]

InnerPeace 05-03-2006 11:36 AM

Summary
 
[LEFT][SIZE="4"][CENTER][FONT="Impact"][SIZE="5"]Summary [/SIZE][/FONT][/CENTER]

[COLOR="Green"]This page summarizes the topics discussed in this module.[/COLOR]

Computer networks developed in response to business and government computing needs. Applying standards to network functions provided a set of guidelines for creating network hardware and software and provided compatibility among equipment from different companies. Information could move within a company and from one business to another.

[U]Network devices[/U], such as repeaters, hubs, bridges, switches and routers connect host devices together to allow them to communicate. Protocols provide a set of rules for communication.

[U]The physical topology[/U] of a network is the actual layout of the wire or media. The logical topology defines how host devices access the media. The physical topologies that are commonly used are bus, ring, star, extended star, hierarchical, and mesh. The two most common types of logical topologies are broadcast and token passing.

[U]A local-area network[/U] (LAN) is designed to operate within a limited geographical area. LANs allow multi-access to high-bandwidth media, control the network privately under local administration, provide full-time connectivity to local services and connect physically adjacent devices.

[U]A wide-area network [/U](WAN) is designed to operate over a large geographical area. WANs allow access over serial interfaces operating at lower speeds, provide full-time and part-time connectivity and connect devices separated over wide areas.

[U]A metropolitan-area network[/U] (MAN) is a network that spans a metropolitan area such as a city or suburban area. A MAN usually consists of two or more LANs in a common geographic area.

[U]A storage-area network[/U] (SAN) is a dedicated, high-performance network used to move data between servers and storage resources. A SAN provides enhanced system performance, is scalable, and has disaster tolerance built in.

[U]A virtual private network[/U] (VPN) is a private network that is constructed within a public network infrastructure. Three main types of VPNs are access, Intranet, and Extranet VPNs. Access VPNs provide mobile workers or small office/home office (SOHO) users with remote access to an Intranet or Extranet. Intranets are only available to users who have access privileges to the internal network of an organization. Extranets are designed to deliver applications and services that are Intranet based to external users or enterprises.

The amount of information that can flow through a network connection in a given period of time is referred to as bandwidth. [U]Network bandwidth [/U]is typically measured in thousands of bits per second (kbps), millions of bits per second (Mbps), billions of bits per second (Gbps) and trillions of bits per second (Tbps). The theoretical bandwidth of a network is an important consideration in network design. If the theoretical bandwidth of a network connection is known, the formula T=S/BW (transfer time = size of file / bandwidth) can be used to calculate potential data transfer time. However the actual bandwidth, referred to as throughput, is affected by multiple factors such as network devices and topology being used, type of data, number of users, hardware and power conditions.

Data can be encoded on analog or digital signals. Analog bandwidth is a measure of how much of the electromagnetic spectrum is occupied by each signal. For instance an analog video signal that requires a wide frequency range for transmission cannot be squeezed into a smaller band. If the necessary analog bandwidth is not available the signal cannot be sent. In digital signaling all information is sent as bits, regardless of the kind of information it is. Unlimited amounts of information can be sent over the smallest digital bandwidth channel.

The concept of layers is used to describe communication from one computer to another. Dividing the network into layers provides the following advantages:

Reduces complexity
Standardizes interfaces
Facilitates modular engineering
Ensures interoperability
Accelerates evolution
Simplifies teaching and learning

Two such layered models are the Open System Interconnection (OSI) and the TCP/IP networking models. In the OSI reference model, there are seven numbered layers, each of which illustrates a particular network function: application, presentation, session, transport, network, data link, and physical. The TCP/IP model has the following four layers: application, transport, Internet, and network access.

Although some of the layers in the TCP/IP model have the same name as layers in the OSI model, the layers of the two models do not correspond exactly. The TCP/IP application layer is equivalent to the OSI application, presentation, and session layers. The TCP/IP model combines the OSI data link and physical layers into the network access layer.

No matter which model is applied, networks layers perform the following five conversion steps in order to encapsulate and transmit data:

Images and text are converted to data.
The data is packaged into segments.
The data segment is encapsulated in a packet with the source and destination addresses.
The packet is encapsulated in a frame with the MAC address of the next directly connected device.
The frame is converted to a pattern of ones and zeros (bits) for transmission on the media.

[/SIZE][/LEFT]

InnerPeace 05-03-2006 12:00 PM

[QUOTE=smile][b]لا بقى دى كورس مكثف ولازم اثيته[/b][/QUOTE]
[CENTER][SIZE="4"]فعلا يااسمايل هو كورس مكثف وهاتلاقى الديمو بتاعه [URL="http://www.cisco.com/web/learning/netacad/course_catalog/CCNA.html"]هنا[/URL][/SIZE][/CENTER]

InnerPeace 30-03-2006 12:49 PM

Module 3: Network Media
 
[LEFT][SIZE="4"][FONT="Impact"][COLOR="Red"][CENTER][SIZE="5"]Overview[/SIZE][/CENTER] [/COLOR][/FONT]


Copper cable is used in almost every LAN. Many different types of copper cable are available. Each type has advantages and disadvantages. Proper selection of cabling is key to efficient network operation. Since copper uses electrical currents to transmit information, it is important to understand some basics of electricity.

[I][U]Optical fiber [/U][/I]is the most frequently used medium for the longer, high bandwidth, point-to-point transmissions required on LAN backbones and on WANs. Optical media uses light to transmit data through thin glass or plastic fiber. Electrical signals cause a fiber-optic transmitter to generate the light signals sent down the fiber. The receiving host receives the light signals and converts them to electrical signals at the far end of the fiber. However, there is no electricity in the fiber-optic cable. In fact, the glass used in fiber-optic cable is a very good electrical insulator.

Physical connectivity allows users to share printers, servers, and software, which can increase productivity. Traditional networked systems require the workstations to remain stationary and permit moves only within the limits of the media and office area.

The introduction of wireless technology removes these restraints and brings true portability to computer networks. Currently, wireless technology does not provide the high-speed transfers, security, or uptime reliability of cabled networks. However, flexibility of wireless has justified the trade off.

Administrators often consider wireless when they install or upgrade a network. A simple wireless network could be working just a few minutes after the workstations are turned on. Connectivity to the Internet is provided through a wired connection, router, cable, or DSL modem and a wireless access point that acts as a hub for the wireless nodes. In a residential or small office environment these devices may be combined into a single unit.

Who complete this module should be able to perform the following tasks:

Discuss the electrical properties of matter
Define voltage, resistance, impedance, current, and circuits
Describe the specifications and performances of different types of cable
Describe coaxial cable and its advantages and disadvantages compared to other types of cable
Describe STP cable and its uses
Describe UTP cable and its uses
Discuss the characteristics of straight-through, crossover, and rollover cables and where each is used
Explain the basics of fiber-optic cable
Describe how fiber-optic cables can carry light signals over long distances
Describe multimode and single-mode fiber
Describe how fiber is installed
Describe the type of connectors and equipment used with fiber-optic cable
Explain how fiber is tested to ensure that it will function properly
Discuss safety issues related to fiber optics

[/SIZE][/LEFT]

constantin 03-04-2006 10:35 AM

شكرا على موضوعك
 
اخى الحبيب innerpeace456 شكرا شكرا على موضوعك
انا عاوزا اقولك انى نقلت الموضوع على الجهاز بعد ما قراته سريعا تمهيدا لقرآته بتدقيق
و عاوز اقول ان المعلومات دى اهم من البرامج الجاهزه مائة مرة
فلا تبخل علينا بالمعلومات فى اى مواضيع اخرى و مرحبا بمشاركاتك القيمة فى المنتدى
وشكرا

InnerPeace 09-04-2006 05:38 PM

[QUOTE=constantin]اخى الحبيب innerpeace456 شكرا شكرا على موضوعك
انا عاوزا اقولك انى نقلت الموضوع على الجهاز بعد ما قراته سريعا تمهيدا لقرآته بتدقيق
و عاوز اقول ان المعلومات دى اهم من البرامج الجاهزه مائة مرة
فلا تبخل علينا بالمعلومات فى اى مواضيع اخرى و مرحبا بمشاركاتك القيمة فى المنتدى
وشكرا[/QUOTE]

[CENTER][SIZE="4"]العفو يا constantin
الكورس مفيد جدا وحبيت انقله هنا للافادة ... بس الواضح انه محتاج متخصصين فى الشبكات علشان يفهموه
ربنا يسهل واكملكم الباقى بس الاقى موقع اقدر ارفع عليه فلاشات .. والاقى وقت (sml16) [/SIZE][/CENTER]


جميع الأوقات بتوقيت امريكا. الساعة الآن » 05:49 PM.

Powered by: vBulletin Version 3.8.6
Copyright ©2000 - 2022, Jelsoft Enterprises Ltd.

تـعـريب » منتدي الاقباط