by Dinesh Thakur

A Wi-Fi network is made with many amenities, such as access points, antennas, bridges, controllers, etc. In this section, we will make an overview of the equipment in order to provide some features.

 
by Dinesh Thakur

A sensor array is defined as a set of sensors connected to one another, each sensor being provided with a transceiver. Sensor networks are a new generation networks with specific properties, which do not fall within the conventional architectures.

 
by Dinesh Thakur

Mesh networks (meshed networks) are ad-hoc networks in which routing points are immobile. Customers are connected by a wireless network access points and the access points are connected by wireless links.

 
by Dinesh Thakur

Routing is the primary element of an ad-hoc network. It takes routing software in each network node to manage the transfer of IP packets. The simplest solution is obviously to have a direct routing, as illustrated in Figure, in which each network station can directly reach another station, without going through an intermediary. The simplest case corresponds to a small cell, with a diameter less than 100 m, as in an 802.11 network in ad-hoc mode.

 
by Dinesh Thakur

Another big wireless network category is ad-hoc networks, where the infrastructure is composed as resorts themselves. The latter agreed to play the role of the router to allow the passages of information from one device to another, without these terminals are connected directly.



 
by Dinesh Thakur

Wireless networks are developing due to the flexibility of their interface, which allows a user to change positions while staying connected. Communications between terminals can be made directly or via base stations, called access points, or AP (Access Point). Communication between access points can be wireless or cable. The flow rates of these networks are tens of megabits per second.

 
by Dinesh Thakur

The local loop is to connect users to the first node, router or switch, the operator with whom the customer has a subscription. Broadband solutions is shared between the ATM for fixed links and Ethernet for wireless backhaul. One of the objectives in the Ethernet local loop is replaced by the ATM Ethernet solutions, particularly in the xDSL modems.

 
by Dinesh Thakur

Ethernet on the WAN aims to transport Ethernet frames over long distances while providing quality service. Its advantages are a very low cost, the possibility of oversizing of the network, highly granular, well known technology and very simple and finally simplified management, since Ethernet is everywhere. You can go very fast in throughput with different levels of 1 and 10 Gbit/s and soon the 100 Gbit/s. The register of difficulties include the lack of reliability, packet loss less controlled and quality of services more difficult to obtain. However, several technologies are currently being developed to address these issues and provide a royal way for the arrival of Ethernet on the WAN.



 
by Dinesh Thakur

After invading the world of business, Ethernet addresses the longer distances starting with the metropolitan area. The Metro Ethernet was born of this extension. This solution is supported in different settings but especially by the Forum MEF (Metro Ethernet Forum).

 
by Dinesh Thakur

SONET (Synchronous Optical Network) is a proposal by Bellcore (Bell Communications Research), SONET is a technique of transport between two nodes, which defines the interface adopted for the NNI (Network Node Interface). She initially concerned that the interconnection of telephone networks of major operators, PTT, carrier, etc. The difficulty of standardization has been to find a compromise between the American, European and Japanese interests to interconnect different operator networks and national networks.

 
by Dinesh Thakur

The LAP-F protocol (Link Access Protocol-Frame) was born with frame relay, designed to improve the performance of networks from the X.25 recommendation UITT. The latter has proved too heavy and therefore unable to increase rates, it took in search for a simplification.



 
by Dinesh Thakur

The frame level (layer 2) is to render a service to the next level just. This service is a transport node to node packet. Specifically, its role is to transport a package of three or message fragment layer of layer 4 from one node to another node. For this, the frame level asks his turn at just below, the physical level, a service of conveying the bits of the frame from one node to another node. This section provides the features necessary to achieve all these actions.

 
by Dinesh Thakur

Applications that are conventionally used on terminal equipment put in implement a point-to-point communication, that is to say the part of the communication micro to go look for information to only one other point. Many other applications involve the cooperation of several processes. For example, a search in a distributed database in which information is spread across multiple sites, uses a simultaneous request for information to several centers. To make this request, the application and all associated protocol layers must manage multipoint. This way of communicating is more powerful than that which is to apply a first site, and once the response, a second, and so on.



 
by Dinesh Thakur

The application of methods derived from INFORMATION THEORY to the detection and correcting of errors in DIGITAL data streams. Error correction is of the utmost importance in most areas of computing and communications technology. For example: Internet's TCP protocol provides error detection, CD-ROMS devote around 14% of their total data capacity to redundant error correction information (and music CDS only a little less), and modem speeds above 28 kilobits per second would be impossible over public telephone lines without error correcting PROTOCOLS such as v.90.



 
by Dinesh Thakur

(xDSL) A whole class of digital telecommunication technologies that can offer BROADBAND data rates, up to 50 megabits per second (Mbps), over the existing copper wires of the analogue public telephone system. By employing advanced modulation schemes, xDSL technologies support Internet or other data access simultaneously with voice telephone calls. In the meta-acronym xDSL, the x stands for the first letter of any of the individual acronyms used for these technologies: ADSL, HDSL, SDSL and VDSL.

 
by Dinesh Thakur

In the world of asynchronous communication (over Mac or PC serial ports), CTS stands for clear to send. When a computer needs to communicate with an outside device physically connected to it (peripheral), the two of them have to go through this preamble of making sure each of them is ready to hear what the other has to say, and confirm that they are going to be speaking the same language. Somewhere near the beginning of this preamble, one device will send an RTS (Request To Send) message. The receiving device will then reply with a CTS message "Yes, I'm now ready for anything you want to send me." I know, the whole thing sounds like you may be sitting there drumming your fingers on your desk, waiting for these flipping machines to get done with their senseless checklist. Relax. Like most processes done by a computer, this one takes less than a millisecond.



 
by Dinesh Thakur

BBS (Bulletin Board System): A single computer running special communications software that acts as a kind of electronic bulletin board. That allows remote users to dial in via a public telephone line to exchange messages and chat with one another. which is a service usually set up by an organization or a club to provide or exchange informationA BBS allows multiple people to use it at the same time in order to exchange ideas, offer help with software problems, and converse (through typed conversations) with other users currently connected to the BBS. You access the BBS through your modem , a device that transmits data through ordinary telephone lines. While connected to a BBS, a user can share information with other computer users, leave messages, and upload and download programs. One popular BBS is the Boston Computer Exchange, a place where members can buy, sell, or trade computers. Pay-for-use information services, such as CompuServe, Prodigy, and Internet are like BBS, but much larger. There are thousands of other BBSs across the globe offering a variety of topics and interests ranging from software support to dating services. To communicate with other computers, a modem is necessary.



 
by Dinesh Thakur

AAL (ATM Adaptation Layer) is a third example message level protocol. A software layer that accepts user data, such as digitized voice, video or computer data, and converts to and from cells for transmission over an ASYNCHRONOUS TRANSFER MODE network. AAL software mostly runs at the end-points of a connection, though in a few circumstances AAL software is run inside an ATM switch. AAL includes facilities to carry traffic that uses other network protocols, such as TCP/IP, over ATM.



 
by Dinesh Thakur

Asynchronous Transfer Mode (ATM) Also called cell relay, a high-speed switched network technology developed by the telecommunications industry to implement the next, BROADBAND generation of ISDN. ATM was designed for use in WANS such as the public telephone system and corporate data networks, though it has also been applied to create super-fast LANS. It can carry all kinds of traffic - voice, video and data – simultaneously at speeds up to 155 megabits per second.

 
by Dinesh Thakur

ISDN provides two basic types of interfaces to users.

 

  1. Basic Rate Interface (BRI)
  2. Primary Rate Interface (PRI)
 
by Dinesh Thakur

Products for ISDN technology from different vendors even with similar features and options may create some compatibility issues. CCITT after good deliberations over the years published the first significant ISDN standards in a number of red binders in 1984 and they were simply known as the Red Book standards. The group subsequently met four years later which culminated in the publication of the 1988 Blue Book standards. These international publications were the foundation for the evolving ISDN national standards. The CCITT eventually was reformed into the group, which is now called the ITU- T. The standards used to define ISDN make use of the OSI reference model with the first three layers of this OSI reference model.

 
by Dinesh Thakur

Integrated Services Digital Network (ISDN) is a set of CCITT /ITU standards for digital transmission over ordinary telephone copper wire as well as over other media. This technology uses ISDN adapters in place of modems and provides very fast speed up. ISDN requires adapters at both ends of the transmission.

 
by Dinesh Thakur

The earliest electronic network is the telephone system. This telephone network commonly uses analog technology that was quite different from digital technology used in the computer-based networks. The advantages of digital technology over the analog technology in terms of economics and services forced the telephone industry to move rapidly to install fiber and digital networks.

 
by Dinesh Thakur

The broadcast systems generally allow the possibility of addressing a packet to all destinations by using a special code in the address field. When a packet with this code is transmitted then it is received and processed by every machine on the network. This mode is called broadcasting.

 
by Dinesh Thakur

When data is sent to the receiver, flow control should be carried out so that the flow of data does not overwhelm the receiver. Any receiving device has a limited speed at which it can process the incoming data and a limited amount of memory to store the incoming data. The receiving device should be able to inform the sending device before these limits are reached so that the transmission is stopped or reduced, temporarily.



 
by Dinesh Thakur

Frame relay has evolved from X.25 packet switching and objective is to reduce network delays, protocol overheads and equipment cost. Error correction is done on an end-to-end basis rather than a link -to-link basis as in X.25 switching. Frame relay can support multiple users over the same line and can establish a permanent virtual circuit or a switched virtual circuit.



 
by Dinesh Thakur

X.25 is a standard used by many older public networks specially outside the U.S.

• This was developed in 1970s by CCITT for providing an interface between public packet-switched network and their customers.

 
by Dinesh Thakur

• Session Initiation Protocol (SIP) was designed by IETF and is described in RFC 3261.

 
by Dinesh Thakur

1. TDM is the digital multiplexing technique.

2. In TDM, the channel/link is not divided on the basis of frequency but on the basis of time.

3. Total time available in the channel is divided between several users.

4. Each user is allotted a particular a time interval called time slot or time slice during which the data is transmitted by that user.

 
by Dinesh Thakur

ISDN structure includes a central ISDN office. All the users are linked to this office through a digital pipe. This digital pipe may be of different capacities and may have different data transfer rates. These digital pipes between the customers and central office are organized into multiple channels of different size.

 
by Dinesh Thakur

Integrated Services Digital Network is a telephone system network. It is a wide area network becoming widely available. Prior to the ISDN, the phone system was viewed as a way to transport voice, with some special services available for data. The key feature of the ISDN is that it integrates speech and data on the same lines, adding features that were not available in the classic telephone system.

 
by Dinesh Thakur

The Token-Passing Protocol relies on a control signal called the token. A token is a 24-bit packet that circulates throughout the network from NIC to NIC in an orderly fashion. If a workstation wants to transmit a message, first it must seize the token. At that point, the workstation has complete control over the communications channel. The existence of only one token eliminates the possibility of signal collisions. This means that only one station can speak at a time.

 
by Dinesh Thakur

A communications device that multiplexes (combines) several signals for transmission over a single medium. A demultiplexer completes the process by separating multiplexed signals from a transmission line. Frequently a multiplexer and demultiplexer are combined into a single device capable of processing both outgoing and incoming signals. A multiplexer is sometimes called a mux.

 
by Dinesh Thakur

In Computer network, a proxy server is a server (a computer system or an application program) that acts as an intermediary for requests from clients seeking resources from other servers. A client connects to the proxy server, requesting some service, such as a file, connection, web page, or other resource, available from a different server.



 
by Dinesh Thakur

Divides Application Processing across multiple machines.Non-critical data and functions are processed on the client Critical functions are processed on the server

 
by Dinesh Thakur

Client/Server Architecture The client/server architecture significantly decreased network traffic by providing a query response rather than total file transfer. It allows multi-user updating through a GUI front end to a shared database. Remote Procedure Calls (RPCs) or standard query language (SQL) statements are typically used to communicate between the client and server.

 
by Dinesh Thakur

A server process (program) fulfills the client request by performing the task requested. Server programs generally receive requests from client programs, execute database retrieval and updates, manage data integrity and dispatch responses to client requests.

 
by Dinesh Thakur

The client is a process that sends a message to a server process requesting that the server perform a task. Client programs usually manage the user-interface portion of the application, validate data entered by the user, dispatch requests to server programs, and sometimes execute business logic.

 
by Dinesh Thakur

Server : A server is a computer in network that provides services to the client computers such as logon requests processing, files access and storage, internet access, printing access and many other types of services. Servers are mostly equipped with extra hardware such as plenty of external memory (RAM), more data store capacity (hard disks), high processing speed and other features.



 
by Dinesh Thakur

Frequency-Division Multiplexing (FDM) is a scheme in which numerous signals are combined for transmission on a single communications line or channel. It is analog technique. Each signal is assigned a different frequency (sub channel) within the main channel.