Some Basic Theories on Open System Interconnection Reference

på


 by Aftab Ahmed

 The Open System Interconnection Reference Model or OSI Reference Model or OSI Model is basically a conceptual description for layered communications and computer network protocol design. It was created as part of the Open Systems Interconnection or OSI initiative. In its most fundamental form, it segments network architecture into seven distinct layers: the Application, Presentation, Session, Transport, Network, Data-Link, and Physical Layers. As a result it is frequently referred to as the OSI Seven Layer Model. A layer is a collection of theoretically similar functions that provide services to the layer directly above it and gets service from the layer beneath it. On each single layer an instance provides services to the instances at the layer above and requests service from the layer beneath. An example of this relates to a layer that provides error-free communications across a network which then provides the path needed by applications above it, while it calls the next lower layer to send and receive packets that comprise the contents of the path.

Work on a layered model of network architecture commenced in the year 1977. Simultaneously the International Organization for Standardization or ISO started to develop its OSI framework architecture. OSI has two major parts: an abstract model of networking, called the Basic Reference Model or seven-layer model and a set of specific protocols. It is important to note that the standard documents that describe the OSI model can be freely downloaded from the ITU-T as the X.200-series of recommendations. A number of the protocol specifications can also be accessed as part of the ITU-T X series. The equivalent ISO and ISO/IEC standards for the OSI model are available from ISO, however not all of these are available free.

Every area of the OSI design evolved from experiences with the CYCLADES network, which also had a large influence on the design of the internet. The latest design has been meticulously documented in ISO 7498 and several of its addenda. In this latest model, a networking system is segmented into layers. Within each layer, one or more entities proves its functionality. Each entity will interact directly only with the layer just below it, and enables facilities for use by the layer above it. Protocols will allow an entity in one host to interact with a corresponding entity at the same layer in another host. Service definitions ideally describe the functionality provided to an (N)-layer by an (N-1) layer, where N is one of the seven layers of protocols operating in the local host.

Neither the OSI Reference Model nor OSI protocols designate any programming interfaces, other than a purposely abstract service specifications. Protocol specifications precisely define the interfaces between multiple computers, but the software interfaces within computers are implementation-specific.

Take for example, Microsoft Windows' Winsock, and Unix's Berkeley sockets and System V Transport Layer Interface, are interfaces between applications (Layer 5 and above) and the transport (Layer 4). NDIS and ODI are interfaces between the media in Layer 2 and the network protocol in Layer 3. Interface standards, with the exception of the Physical Layer to media, are estimated implementations of OSI Service Specifications.

Free to Air Satellite

FTA is in certain circumstances delivered by satellite television, but in many different locations of the world free-to-air television channels are actually broadcast unencrypted on UHF or VHF bands. Despite the fact that these channels are described as free, in some cases the viewer may have to pay for them. Some of these channels are paid directly by payment of a licence fee, for example as seen with the BBC or by voluntary donation for example PBS. Others indirectly pay by paying for consumer products and services where a portion of the cost is used for television advertising and sponsorship.
Free-to-air is typically used for international broadcasting, making it in some way a video equivalent of shortwave radio. Most authorized FTA retailers will list free to air channel guides and content available in North America for free to air use.

There are many competing systems presently in use. Many of the older channels used C-band satellite dishes of several feet in diameter to receive signals which were at first analogue microwaves, and then digital microwave using the 3.9-4.2 GHz band. Currently, in the 11.7-12.2 GHz Ku band permits the use of under one-meter dishes chiefly with the DVB-S standard. Hence FTA can now be used from apartment balconies.

The most prevalent North American sources for free-to-air DVB satellite television includes:


NASA TV Multi-channel(NASA HD, NASA Public, NASA Media, NASA Education) Broadcast on AMC 6 (72W)
Retro Television Network on AMC 9 (83W)
TVU Music channel and This TV on AMC 3 (87W)
ABC News Now on Galaxy 28 (89W)
Eternal Word Television Network on Galaxy 17 (91W)
My Family TV on Galaxy 3C (95W).
AMGTV and BYU Television on Galaxy 19 (97W)
English and foreign language broadcasters RT (TV network), MHz Worldview, Ebru TV, IRINN, Al Jazeera English and more up-linked by GlobeCast World TV on Galaxy 25 (97W)
Christian broadcasters The Word Network, Emmanuel TV, Daystar Television Network, JCTV, Trinity Broadcasting Network, The Church Channel, God's Learning Channel and more promoted by Glorystar and Spiritcast Satellite Systems TV on Galaxy 25 (97W)
Pentagon Channel on AMC 1 (103W)
Jewish Life Television, ResearchChannel, and University of Washington TV on Galaxy 18 (123W)
Montana Public Broadcasting Service on AMC 21 (125W)
Louisiana Connection Network on Galaxy 13 (127W)
White Springs Television on Galaxy 27 (129W)
Classic Arts Showcase on Galaxy 15 (133W)
Football, Basketball, Baseball, Soccer, and Hockey wildfeeds on various satellites

Many of these signals are carried by United States satellites. There is a small number of or no free Canadian DVB-S content available to users of medium-size dishes as much of the available Ku-band satellite bandwidth is used by pay-TV operators Shaw Direct and Bell TV, however the large style dish of over 3 feet/90cm does have a few extra choices. FTA signals may be dispersed across multiple satellites needing a motor or multiple LNBs to receive everything.

Free-to-air satellite TV is a feasible addition to any home video system, not only because of the specialized content it makes available but also for use in areas where terrestrial ATSC over-the-air reception is not at acceptable levels and additional channels are needed.



Visit us at 3D Model to get online free Host 3D and share your Work 3D Models 3D and 2D Building Designs, AutoCAD Designer

Article Source: http://www.articlesphere.com/Article/Some-Basic-Theories-on-Open-System-Interconnection-Reference/252731

Comments

Post a Comment

Luxury Travel Blog for the Resident

We try to share with you this blog, tips, information knowledge, and experiences related to global tuirism. We have also frequently linked to some unbeatable price comparison services within the tourist industry where you can easily compare and book your next trip and accommodation.

As everyone understands, it costs to maintain web pages and blogs on the internet with up-to-date information that is regularly updated. Therefore, please feel free to support our business if you can. We gladly link to interesting articles and stories if you want to contribute with this.

For national, regional and local tourist agencies, travel companies, airlines etc. This way, through a number of channels, we can offer effective marketing opportunities. For example, we have our own adserver and adnetwork for Pay-Per Click advertising

We also offer the opportunity to advertise on this first page of our blog, if you want to be visible here with your tourist information then we can recommend that you hear from us so that we can set up a featured campaign for your advertising.

Featured ad here costs $ 300:-/year and we guarantee 50,000 unique visitors to your ad.



Featured Online Travel Booking Services - All inclusive travel planning

If you are really tight on the budget, booking an all-inclusive holiday package can save you a big chunk of money. Because these all-inclusive package holiday companies have close ties with hotels & popular tourist spots in the country, they can get a better rate than you can! Hence, normally, the discounts & savings will be passed on to you - the all-inclusive holiday customers, tourists & visitors!

Ever tried to cram all your travel plans into one small budget & short schedule? If you have, you will know the true meaning of a frugal & haphazard holiday. Some people think that all-inclusive holiday packages leave very little space for them to have fun & there is no flexibility. But they're wrong.
You can save money with an all-inclusive holiday package

All-inclusive vacations are hassle-free

Planning a holiday can give you headaches! When you book an all-inclusive holiday package, you are actually giving yourself the chance to enjoy the holiday without having to worry about the nitty-gritty details. Your accommodation, food, entertainment & travelling are all taken care of. The only thing that you & your relatives members have to worry about is how much fun you are going to have during the holiday. Some tourists & vacationers like to get an all-inclusive holiday package because there is lack of time. Some people have to contend with last minute plans. The all-inclusive holiday packages can be real life savers in this instance. Even honeymooners love all-inclusive packages because they don't require to have to worry about meals, entertainment, activities, transportation & accommodation when they should be focused on each other!

Mealtime fun with all-inclusive holiday packages

One of the most worrisome things for tourists is WHERE to eat. Because they're not familiar with the country & the booklets that they can get from airports are not very accurate (most of the time), meal times are worrying. When we are visiting another country, they require to try another delicacy, something old..and cheap. Who better to tell you where to find it than an all-inclusive holiday planner? they have all the ropes, hang on to them & enjoy the meal!

You can read all you require from the web or from books on the different cultures & religions in the country that you are visiting.and yet, whenever you are on an all-inclusive holiday package, the tourist guide will STILL tell you things that surprises you! & this is an important point because you don't really require to step on someone's toes when you are in THEIR country.

All-inclusive packages - tells you the cultural differences between races & religions

Besides all of that, with all-inclusive holiday packages, you don't have to worry about where to have fun because they plan everything for you. All-inclusive holiday packages are definitely worth it!


Cheap Airline Tickets: Great Ways To Save

A round-the-world trip remains the world's greatest journey. For two out of every three people, this is the ultimate travel experience, according to recent research. Needless to say, in a world obsessed by travel, travelers and travel agents are both looking for the cheapest tickets and airfares available.

Cheap airline tickets, in most cases, can be obtained from wholesale dealers and discounters.

If your requirements are simple - you want a round-trip ticket from one place to another, you have a particular airline on your mind and you have definite dates; then you can go directly to the source - to the ticket discount agency which buys cheap tickets in bulk from wholesalers and consolidators.

In real life most trips require more planning, and most people need a help from the agent to figure out what would be the best air ticket solution for their particular case. Cheap airfares to a particular region can often be found with local airlines that specialize in that country. Sometimes an agency that operates and retails tours to a particular country will have a discount agreement with the national carrier and will sell discount tickets on that airline.

With a bit of research through travel magazines aimed at the particular country of your choice, you can often find agencies dealing with national carriers for that country. For the cheapest possible airfare to many places the most affordable prices are often found in local travel agencies that deal with a particular destination selling round-trip discount airline flights - most likely to the capital of that country and a few main cities.

Sometimes you can find a really cheap air ticket with a discount retail agency that specializes in trips to a wider range of destinations or to multiple destinations. Through the sheer number of tickets that they sell they can command a reasonable discount. However, keep in mind that most advertised prices do not include taxes, luggage fee and airport tax, so the cheap airfare may end up being not so cheap. Best to read the small print to clarify exactly what you are getting before you purchase a ticket.

Another trick of the trade is for agencies to grab attention by indicating the lowest possible prices, which only apply on specific dates in low season. You’ll find that all agencies do this, even the most expensive ones so, don’t be surprised if you get a quote at double the price from what was displayed in the ad.

Airlines usually publish their scheduled flights and prices six months in advance. If you have decided on a destination it can be a good opportunity to get an ‘early bird’ discount by booking well in advance. Keep your eye on the travel press and also airline web-sites. There are often special discounts and incentives aimed at travelers who book online, as carrying out a booking online is cheaper for the company than through an intermediary who will take a commission.

However, although you can expect to get the cheapest air ticket if you start searching many months ahead, there are some exceptions. At times like Christmas or other periods of high demand the prices are usually inflated and planes fill up many months in advance. If you can be flexible and travel on actual holiday days such as Christmas day or New Years Eve you can find some pretty attractive discounts.


Pick A Hotel With Personality!

What does individuality mean in the hotel industry? As far as boutiques are concerned, it’s not just about being a little bit quirky; hanging modern art on the walls, sticking some designer chairs in the rooms or making all the fittings stainless steel. It’s about a design theme that runs through the hotel from start to finish and affects everything from the cushions on the sofas to the dessert menu in the restaurant.

Location

Where does the inspiration for this individuality and personality come from? For some hoteliers, it comes from the location. It’s unsurprising that boutique beach hotels are clean and simple, bringing the colours and textures of the coast into the building and using architectural design to allow guests to feel at one with the sea; large windows, folding doors and seawater pools for example. In contrast, small hotels that are based in cities often reflect either the present-day energy or the historic past of their location. Through the use of rich colours or minimal materials, antique furniture, period art and a variety of textiles, designers can create a hotel that truly reflects its location.

Culture

Many hotels show influences from different cultures – and not always from the culture that’s readily associated with the hotel’s location. Therefore, New England simplicity or Asian colours and textures can show up in hotels in London or Sydney and work well, as long as the concept is properly thought through and sensitively carried out. Extending a cultural theme to rooms and cuisine often requires a lot of research, particularly when it comes to sourcing the right furniture and accessories, but if the end result is a truly individual hotel, then the preparation is worthwhile.

Community

A true boutique hotel becomes an intrinsic part of the local community, and this is part of its individuality. Chain hotels are just places to stay; boutique hotels are places to be – whether it is locals using the restaurant or trendy city workers drinking in the bar; using the produce from the farm down the road or sharing spa facilities with a local retreat, boutique hotels make a real effort to integrate into their local community rather than being set apart from it.



Sincerely

Roger K. Olsson