NETWORK CLASSIFICATION

LAN (LOCAL AREA NETWORK)

·         A LAN connects network devices over a relatively short distance.

·         A networked office building, school, or home usually contains a single LAN, though sometimes one building will contain a few small LANs (perhaps one per room), and occasionally a LAN will span a group of nearby buildings.

·         In TCP/IP networking, a LAN is often but not always implemented as a single IP subnet.

·         In addition to operating in a limited space, LANs are also typically owned, controlled, and managed by a single person or organization.

·         They also tend to use certain connectivity technologies, primarily Ethernet and Token Ring.

WAN (WIDE AREA NETWORK)

·         As the term implies, a WAN spans a large physical distance. The Internet is the largest WAN, spanning the Earth.

·         A WAN is a geographically-dispersed collection of LANs. A network device called a router connects LANs to a WAN. In IP networking, the router maintains both a LAN address and a WAN address.

·         A WAN differs from a LAN in several important ways. Most WANs (like the Internet) are not owned by any one organization but rather exist under collective or distributed ownership and management. WANs tend to use technology like ATM, Frame Relay and X.25 for connectivity over the longer distances.

MAN (METROPOLITAN AREA NETWORK)

·         Network that interconnects users with computer resources in a geographic area or region larger than that covered by even a large local area network (LAN) but smaller than the area covered by a wide area network (WAN). The term is applied to the interconnection of networks in a city into a single larger network (which may then also offer efficient connection to a wide area network). It is also used to mean the interconnection of several local area networks by bridging them with backbone lines. The latter usage is also sometimes referred to as a campus network.

PAN (PERSONAL AREA NETWORK)

·         Computer network organized around an individual person. Personal area networks typically involve a mobile computer, a cell phone and/or a handheld computing device such as a PDA. You can use these networks to transfer files including email and calendar appointments, digital photos and music.

·         Personal area networks can be constructed with cables or wirelessly. USB and FireWire technologies often link together a wired PAN while wireless PANs typically use Bluetooth or sometimes infrared connections. Bluetooth PANs are also called piconets.

·         Personal area networks generally cover a range of less than 10 meters (about 30 feet).

What Email is and How It Works

Email and Postal Mail

• The email message - Instead of using a pen to write a letter on paper, you're using your keyboard to type an email message in an email program on your computer.
• Sending the email - When the email is finished and has been addressed to the recipient's email address, you don't put a stamp on it and post it but press the Send button in the email program. This makes the email message go on its journey.
• Email transport - Like postal services transport letters and parcel, email servers transmit email messages from sender to recipient. Usually, emails are not delivered to the recipient directly, though, but waiting at the "nearest" mail server to be picked up by them.
• Fetching new mail - If you've got new mail in your mailbox, you go and fetch it. Similarly, your email program can check for new email messages at your mail server and download them for you to read.

The benefits and wonders of email include

• Convenience - If a desktop computer, laptop or mobile phone is around, you can type your email message wherever you want, save it for later use and send it at any time without having to worry about envelopes, stamps and tariffs.
• Speed - Emails typically arrive within seconds or minutes — anywhere in the world, something that can be said only about a negligible number of the letters I've sent via postal mail.
• Attachments - You can attach any file on your computer to an email message easily, regardless of its type and, mostly, size. It's as easy to send a long master's thesis around the world as it is to email a spread sheet, a report, pictures, or a saved game of your favorite game.
• Accessibility - Emails can be stored conveniently in your email program. Good programs make it easy to organize, archive and search your emails, so any information contained in an email is always readily accessible.
• Cost - Safe for the fee you pay for accessing the internet, sending and receiving emails is typically free.

Email's Problem

Unfortunately, the last beneficial wonder in particular is also responsible email's big problem: spam — unsolicited emails that are sent in huge numbers and clog mail servers as well as email programs.

With hundreds of these junk mails in your inbox, the occasional good email can be hard to spot. Fortunately, though, sophisticated filters exist that go through your new messages and sort out the unwanted ones automatically.

NETWORK TOPOLOGY

Architecture

·         One of the 2 major type of network architecture

Ø  Peer to peer

      Communications between diplomats of the same rank. In the networking environment, "peer to peer" refers to communications between similar processes running in different computers, or communication between devices that are equal with regard to how they exchange information and control communications.

Ø  Client and server

      Server-powerful computer or process dedicated to managing disk drivers (file server), printer (print server), or network traffic (network servers).

      Clients-PC’s or workstations on which users run applications. Client rely on server for resources such as files, devices and even processing power.

Topology

·         Geometric arrangement of network.

Protocol

·         Command set of rules and signal competence on the network use to communicate.

Network topology

·         Bus wire

·         Star ring

·         Star

·         Tree

Linear bus

Ø  One computer can transfer information at a time.

Ø  Suitable for small area.

Ø  Each end of terminator (device that absorb the signal transmitted on the network cable). The terminator prevent signal from being bounce back a long the cable and cause interference.

Ø  Node (devices-computer, printer, and others).

Star

Ø  Individual connected to a center point of the network (hub/concentrator).

Ø  All information passes through hub.

Ø  Cable length between computers and hub should be less than 100 meter.

Ø  Hub commonly connects for 8 and 16 computers.

Ø  Office or large buildings of each floor of the building have to have its own hub.

Ø  In the middle of the star should have a hub.

Ø  Information going to the hub first.

Ø  Hub is functioning as a repeater.

Star-wired

Ø  Individual computer connected at each in a single ring cable.

Ø  Information travel in one direction only.

Ø  Next computer that will not address will pass to the next, continue pass until it reach its destinations.

Ø  There is no beginning or end.

Tree

Ø  Combines characteristics of linear bus and star topology.

Ø  Tree topologies integrate multiple star topologies together onto a bus. In its simplest form, only hub devices connect directly to the tree bus, and each hub functions as the "root" of a tree of devices. This bus/star hybrid approach supports future expandability of the network much better than a bus (limited in the number of devices due to the broadcast traffic it generates) or a star (limited by the number of hub connection points) alone.

How WiFi Works

Wireless Technology

Wireless Networking Hardware

network cables, for example, between two rooms or two buildings. However,
recent advances in wireless networking technology make wireless networking
practical and affordable. New wireless standards have facilitated the
development of wireless products with good performance and the ability to
integrate easily into a wired Ethernet network.
The Ethernet standard for wireless networking is the IEEE 802.11b
wireless standard. The 802.11b standard supports wireless connections at
speeds up to 11 Mps, comparable to 10 Mbps wired Ethernet. Wireless
industry leaders formed the Wireless Ethernet Compatibility Alliance
(WECA) to certify cross-vendor compatibility with the 802.11b standard.
These products display the WECA "Wireless Fidelity" (Wi-Fi†) logo.


Suppose you want to network a few computers together in a small area
where it would be expensive to have network cabling installed in an existing building. Or perhaps you just have a desktop computer and a notebook
computer at home and you would like to be able to roam the house with the
notebook computer and perhaps even browse the Web from the hammock in
the back yard. Wireless Ethernet makes all this possible. You can install
wireless adapters in each computer and form a wireless network.

Building a Simple Network

Sharing an Internet Connection
If you already have access to the Internet from one computer on your
network, you can share that Internet connection with other computers on the
network. Then all the computers on your network can browse the Web at the
same time, using this single Internet connection.
Networking Components
To network computers together, you need to install networking hardware and
software. Every network includes these three components:
􀂄 The computers that are connected together. Computers and similar
devices are called nodes when connected to a network.
􀂄 The networking hardware that connects the computers together,
including hardware installed in your computer, network cables, and
devices that connect all the cables together.
􀂄 Networking software that runs on each computer and enables it to
communicate with other computers on the network.
Networking Hardware
Here is the networking hardware you need to set up a small network:
􀂄 Network adapter cards: expansion cards that provide the physical
connection between each computer and the network. The card installs
into a slot on your computer, just like a sound card or modem card.
Some newer computers have a network adapter already built into the
system. Laptop computers often use a card that slides into a PC card
slot.
Chapter 1: Introduction to Networking 5
Figure 1.5 Network Adapter Card
􀂄 Network hub: the central connection point for network cables that
connect to computers or other devices on a network. The hub has
several network cable jacks or ports that you use to connect network
cables to computers. The hub contains circuitry that enables each
computer to communicate with any other computer connected to
the hub.
Figure 1.6 Network Hub
􀂄 Network cables: special, unshielded twisted-pair (UTP) cables used
to connect each computer to the hub. The cable you need is Category
5 UTP cable with a square plastic RJ-45 connector on each end.
6 Building a Simple Network
Figure 1.7 Network Cable with RJ-45 Connector
All the networking hardware described here is known as Ethernet.
Ethernet is the industry-wide standard for computer networks. Standard
Ethernet networks transmit data at 10 million bits per second (Mbps).
A newer Ethernet standard, called Fast Ethernet, transmits data at 100 Mbps.
Computer networks often contain a mixture of 10 Mbps and 100 Mbps
devices.

Sharing a Printer

If you have a printer connected to your computer, you can share the printer
with other computers on the network. Then instead of buying a printer for
every computer, all the computers can print across the network to the printer.
Suppose you want to print a document on a color laser printer that is
connected to another computer in the office. Instead of copying your file to a
disk, going to the other computer, and interrupting the person using that
computer, you can print directly over the network.

Sharing Files and Drives

If your computers are connected to a network, each computer can make its
resources available to other computers in your office by sharing them over the
network. Instead of working in isolation as you do on a single computer not
linked to a network, you can work collectively, within a system that shares
resources among a group of computer users.
Each computer on your network can share folders, entire disk drives, or a
CD-ROM drive. Then other computers on your network can access
documents and other files stored in the folders and on the drives. Instead of
copying a document to a diskette and giving it to another person to view,
anyone can open and view the document using the network.
If you want to view the company’s annual report stored on a co-worker’s
computer, you can use the network to access the document on that computer.
If you want to listen to music stored on a computer in another room, you can
use the network to access the music files.

What Can I do With a Simple Network

Without a network, you can access resources only on your own computer.
These resources may be devices in your computer, such as a folder or disk
drive, or they may be connected to your computer, such as a printer or CDROM
drive. These devices, accessible only to you, are local resources.
Networking allows you to share resources among a group of computer
users.

What is a Network

A computer network is simply two or more computers connected together so
they can exchange information. A small network can be as simple as two
computers linked together by a single cable.

Lapisan (Layer) ATM

Sel ATM mengandungi 53 oktet: lima yang pertama merupakan “header” dan
48 yang selebihnya merupakan lapangan maklumat. Beberapa lapangan sel
pada user network interface (UNI) ditunjukkan dalam Rajah 4-2.
Secara ringkas, empat bit header yang pertama mengandungi Generic Flow
Control (GFC); ia membekalkan mekanisme simple flow control pada lapisan
ATM. Lapan bit yang berikutnya merupakan Virtual Path Identifier (VPI) , diikuti
dengan 16-bit Virtual Channel Identifier (VCI). Dua lapangan ini menentukan
saluran logikal dalam penyambungan ATM. Lapangan Payload Type Indicator
(PTI) ialah 3 bit panjang dan menerangkan jenis data yang dibawa lapangan
maklumat sel. Bit Cell Loss Priority (CLP) menunjukkan kepada penerima
adakah ia sel khas yang boleh dibuang jika kesesakan rangkaian berlaku.
Lapangan Header Error Control (HEC) mempunyai 8 bit parity dalam empat oktet
yang pertama pada header. Kegunaannya ialah supaya penerima boleh
mengesan kesalahan yang mungkin telah berlaku di dalam header semasa
transmisi. Format sel pada Network-to-Network Interface (NNI) adalah sama,
kecuali pada NNI ia tiada lapangan GFC. Ini disebabkan ia menggunakan 12 bit
lapangan VPI. Dalam B-ISDN, beberapa pre-assigned nilai header telah
disimpan untuk operasi, pentadbiran dan penyelenggaraan (OA&M) yang
digunakan pada lapisan fizikal. Jadual 4-1 menunjukkan sebahagian senarai nilai
header .

The ATM Protokol Stack

Untuk mengendalikan perkhidmatan yang berbeza dengan berkesan, lapisan
senibina telah dibina di dalam protokol, setiap lapisan menjalankan fungsi yang
spesifik. Rajah 4-1 menunjukkan the genetic protokol stack. Lapisan protokol
yang teratas menggolongkan di antara semua, lapisan aplikasi, lapisan
pengangkutan dan lapisan rangkaian. Contoh bagi lapisan aplikasi ialah file
transfer protokol (FTP) untuk memindahkan fail, simple mail transfer protokol
(SMTP) untuk memindahkan mesej elektronik, protokol telnet yang menyediakan
perkhidmatan virtual terminal dan lain-lain. Transmission control protocol (TCP)
dan internet protocol adalah lapisan pengangkutan dan lapisan rangkaian
protokol masing-masing .
ATM Adaptation Layer (AAL), adalah lapisan yang mempunyai ciri-ciri
lapisan penyesuaian service-dependent. Tujuan lapisan penyesuaian ini adalah
untuk memformat data daripada lapisan aplikasi . Ia mengambil panjang paket
43
yang berubah-ubah daripada lapisan teratas, menambahkan header trailer dan
jika perlu beberapa akan memenuhi beberapa oktet, bergantung kepada aplikasi
yang digunakan, segmen keputusan paket kepada paket yang lebih kecil supaya
dapat dipadankan dengan saiz sebenar sel ATM dan kemudian menghantar
segmen tersebut ke lapisan ATM. Berpandukan daripada fungsi-fungsi tersebut,
lapisan penyesuaian dapat dibahagikan kepada 2 sublapisan : sublapisan
pemuratan (Convergence Sublayer - CS) dan segmentasi dan Reassembly
Sublayer (SAR). Lapisan CS sendiri mengandungi 2 sublapisan: the servicespecific
convergence sublayer (SSCS) dan the common-part convergence
sublayer (CPCS).

pengenalan ATM

4.1 Pengenalan
ATM merupakan sejenis protokol paket di mana data daripada sumber
yang berbeza dapat dihantar kepada saluran fizikal yang sama dengan
menggunakan prosedur mod pemindahan tak serentak (asnychronous).
Protokol ini telah direkabentuk untuk memenuhi keperluan pengguna yang
menggunakan aplikasi yang berbeza. Sebagai contoh, ia tidak hanya sesuai
untuk penyambungan perkhidmatan data tanpa wajar dalam pelbagai kadar bit,
malah dalam LANs , ia juga menyokong pemindahan penyambungan,
berstruktur, circuit- switched data dan 64-kb/s PCM speech signals. Begitu
juga, ia boleh digunakan untuk mengangkut data pengguna serta “call control
messages” untuk membuat penyambungan. Dalam bab ini, kita dapat
mengetahui tentang asas-asas dalam protokol ATM [1]-[4].

DESKTOP AND VIDEO CONFERENCING

DESKTOP AND VIDEO CONFERENCING

Videoconferencing is the conduct of a videoconference (also known as a video conference or videoteleconference) by a set of telecommunicationtechnologies which allow two or more locations to interact via two-way video and audio transmissions simultaneously. It has also been called 'visual collaboration' and is a type of groupware.

Videoconferencing differs from videophone calls in that it's designed to serve a conference rather than individuals. It is an intermediate form of videotelephony, first deployed commercially by AT&T during the early 1970s as part of their development of Picturephone technology.

TECHNOLOGY

The core technology used in a videoconferencing system is digital compression of audio and video streams in real time. The hardware or software that performs compression is called a codec (coder/decoder). Compression rates of up to 1:500 can be achieved. The resulting digital stream of 1s and 0s is subdivided into labeled packets, which are then transmitted through a digital network of some kind (usually ISDN or IP). The use of audio modems in the transmission line allow for the use of POTS, or the Plain Old Telephone System, in some low-speed applications, such as videotelephony, because they convert the digital pulses to/from analog waves in the audio spectrum range.

The other components required for a videoconferencing system include:

§  Video input : video camera or webcam

§  Video output: computer monitor , television or projector

§  Audio input: microphones, CD/DVD player, cassette player, or any other source of PreAmp audio outlet.

§  Audio output: usually loudspeakers associated with the display device or telephone

§  Data transfer: analog or digital telephone network, LAN or Internet

§  Computer: a data processing unit that ties together the other components, does the compressing and decompressing, and initiates and maintains the data linkage via the network.

There are basically two kinds of videoconferencing systems:

1.     Dedicated systems have all required components packaged into a single piece of equipment, usually a console with a high quality remote controlledvideo camera. These cameras can be controlled at a distance to pan left and right, tilt up and down, and zoom. They became known as PTZ cameras. The console contains all electrical interfaces, the control computer, and the software or hardware-based codec. Omnidirectional microphones are connected to the console, as well as a TV monitor with loudspeakers and/or a video projector. There are several types of dedicated videoconferencing devices:

-          Large group videoconferencing are non-portable, large, more expensive devices used for large rooms and auditoriums.

-          Small group videoconferencing are non-portable or portable, smaller, less expensive devices used for small meeting rooms.

-          Individual videoconferencing are usually portable devices, meant for single users, have fixed cameras, microphones and loudspeakers integrated into the console.

2.     Desktop systems are add-ons (hardware boards, usually) to normal PCs, transforming them into videoconferencing devices. A range of different cameras and microphones can be used with the board, which contains the necessary codec and transmission interfaces. Most of the desktops systems work with the H.323 standard. Videoconferences carried out via dispersed PCs are also known as e-meetings.

CONFERENCING LAYERS

The components within a Conferencing System can be divided up into several different layers: User Interface, Conference Control, Control or Signal Plane and Media Plane.

Video Conferencing User Interfaces could either be graphical or voice responsive. Many of us have encountered both types of interfaces, normally we encounter graphical interfaces on the computer or television, and Voice Responsive we normally get on the phone, where we are told to select a number of choices by either saying it or pressing a number. User interfaces for conferencing have a number of different uses; it could be used for scheduling, setup, and making the call. Through the User Interface the administrator is able to control the other three layers of the system.

Conference Control performs resource allocation, management and routing. This layer along with the User Interface creates meetings (scheduled or unscheduled) or adds and removes participants from a conference.

Control (Signaling) Plane contains the stacks that signal different endpoints to create a call and/or a conference. Signals can be, but aren’t limited to, H.323 and Session Initiation Protocol (SIP) Protocols. These signals control incoming and outgoing connections as well as session parameters.

The Media Plane controls the audio and video mixing and streaming. This layer manages Real-Time Transport Protocols, User Datagram Packets (UDP) and Real-Time Transport Control Protocols (RTCP). The RTP and UDP normally carry information such the payload type which is the type of codec, frame rate, video size and many others. RTCP on the other hand acts as a quality control Protocol for detecting errors during streaming.

Multipoint videoconferencing

Simultaneous videoconferencing among three or more remote points is possible by means of a Multipoint Control Unit (MCU). This is a bridge that interconnects calls from several sources (in a similar way to the audio conference call). All parties call the MCU unit, or the MCU unit can also call the parties which are going to participate, in sequence. There are MCU bridges for IP and ISDN-based videoconferencing. There are MCUs which are pure software, and others which are a combination of hardware and software. An MCU is characterised according to the number of simultaneous calls it can handle, its ability to conduct transposing of data rates and protocols, and features such as Continuous Presence, in which multiple parties can be seen on-screen at once. MCUs can be stand-alone hardware devices, or they can be embedded into dedicated videoconferencing units.

The MCU consists of two logical components:

1.    

2.     Multipoint Processors (MP), sometimes referred to as the mixer.

The MC controls the conferencing while it is active on the signaling plane, which is simply where the system manages conferencing creation, endpoint signaling and in-conferencing controls. This component negotiates parameters with every endpoint in the network and controls conferencing resources While the MC controls resources and signaling negotiations, the MP operates on the media plane and receives media from each endpoint. The MP generates output streams from each endpoint and redirects the information to other endpoints in the conference.

Some systems are capable of multipoint conferencing with no MCU, stand-alone, embedded or otherwise. These use a standards-based H.323 technique known as "decentralized multipoint", where each station in a multipoint call exchanges video and audio directly with the other stations with no central "manager" or other bottleneck. The advantages of this technique are that the video and audio will generally be of higher quality because they don't have to be relayed through a central point. Also, users can make ad-hoc multipoint calls without any concern for the availability or control of an MCU. This added convenience and quality comes at the expense of some increased network bandwidth, because every station must transmit to every other station directly.

VIDEOCONFERENCING MODES

Videoconferencing systems have several common operating modes that are used:

1.     Voice-Activated Switch (VAS);

2.     Continuous Presence.

In VAS mode, the MCU switches which endpoint can be seen by the other endpoints by the levels of one’s voice. If there are four people in a conference, the only one that will be seen in the conference is the site which is talking; the location with the loudest voice will be seen by the other participants.

Continuous Presence mode display multiple participants at the same time. The MP in this mode puts together the streams from the different endpoints and puts them all together into a single video image. In this mode, the MCU normally sends the same type of images to all participants. Typically these types of images are called “layouts” and can vary depending on the number of participants in a conference.