آشنايي جامع و كامل با شبكه هاي بي سيم ( Wireless ) و تکنولوژي Wi-Fi

[Amir_P30]

آشنائي با شبكه هاي بي سيم
مقدمه
نياز روز افزون به پويايي كارها ، استفاده از تجهيزاتي مانند تلفن همراه ، پيجرها و ...
بواسطه وجود شبكه هاي بي سيم امكان پذير شده است.
اگر كاربر يا شركت يا برنامه كاربردي خواهان آن باشد كه داده و اطلاعات مورد نياز خود را به صورت متحرك در هر لحظه در اختيار داشته باشند شبكه هاي بي سيم جواب مناسبي براي آنها ست.
اين مقاله دربخش‌هاي مختلفي ارائه ميشود، در بخش حاضر فقط به بيان كلياتي در رابطه با شبكه‌هاي بي‌سيم و كابلي پرداخته شده، در بخش‌هاي بعدي به جزئيات بيشتري در رابطه با شبكه‌هاي بي‌سيم خواهيم پرداخت.

تشريح مقدماتي شبكه هاي بي سيم و كابلي
شبكه هاي محلي (LAN ) براي خانه و محيط كار مي توانند به دو صورت كابلي (Wired ) يا بي سيم (Wireless ) طراحي گردند . درابتدا اين شبكه ها به روش كابلي با استفاده از تكنولوژي Ethernet طراحي مي شدند اما اكنون با روند رو به افزايش استفاده از شبكه هاي بي سيم با تكنولوژي Wi-Fi مواجه هستيم .
در شبكه هاي كابلي (كه در حال حاضر بيشتر با توپولوژي ستاره اي بكار مي روند ) بايستي از محل هر ايستگاه كاري تا دستگاه توزيع كننده (هاب يا سوئيچ ) به صورت مستقل كابل كشي صورت پذيرد(طول كابل ازنوع CAT5 نبايستي 100 متر بيشتر باشد در غير اينصورت از فيبر نوري استفاده ميگردد) كه تجهيزات بكار رفته از دونوع غير فعال (Passive ) مانند كابل ، پريز، داكت ، پچ پنل و.......... . و فعال (Active )مانند هاب ،سوئيچ ،روتر ، كارت شبكه و........... هستند .
موسسه مهندسي IEEE استانداردهاي 802.3u را براي Fast Ethernet و 802.3ab و802.3z را براي Gigabit Ethernet ( مربوط به كابلهاي الكتريكي و نوري ) در نظر گرفته است.
شبكه هاي بي سيم نيز شامل دستگاه مركزي (Access Point ) مي باشد كه هر ايستگاه كاري مي تواند حداكثر تا فاصله 30 متر ي آن (بدون مانع ) قرار گيرد.

شبكه هاي بي سيم (Wlan ) يكي از سه استاندارد ارتباطي Wi-Fi زير را بكار مي برند:
802.11b كه اولين استانداردي است كه به صورت گسترده بكار رفته است .
802.11a سريعتر اما گرانتر از 802.11b مي باشد.
802.11g جديدترين استاندارد كه شامل هر دو استاندارد قبلي بوده و از همه گرانتر ميباشد.
هر دونوع شبكه هاي كابلي و بي سيم ادعاي برتري بر ديگري را دارند اما انتخاب صحيح با در نظر گرفتن قابليتهاي آنها ميسر مي باشد.
عوامل مقايسه

در مقايسه شبكه هاي بي سيم و كابلي مي تواند قابليتهاي زير مورد بررسي قرار گيرد:
نصب و راه اندازي
هزينه
قابليت اطمينان
كارائی
امنيت
نصب و راه اندازي
در شبكه هاي كابلي بدليل آنكه به هر يك از ايستگاههاي كاري بايستي از محل سويئچ مربوطه كابل كشيده شود با مسائلي همچون سوارخكاري ، داكت كشي ، نصب پريز و......... مواجه هستيم در ضمن اگر محل فيزيكي ايستگاه مورد نظر تغيير يابد بايستي كه كابل كشي مجدد و .......صورت پذيرد
شبكه هاي بي سيم از امواج استفاده نموده و قابليت تحرك بالائي را دارا هستند بنابراين تغييرات در محل فيزيكي ايستگاههاي كاري به راحتي امكان پذير مي باشد براي راه اندازي آن كافيست كه از روشهاي زير بهره برد:
Ad hoc كه ارتباط مستقيم يا همتا به همتا (peer to peer ) تجهيزات را با يكديگر ميسر مي سازد.
Infrastructure كه باعث ارتباط تمامي تجهيزات با دستگاه مركزي مي شود.
بنابراين ميتوان دريافت كه نصب و را ه اندازي شبكه هاي كابلي يا تغييرات در آن بسيار مشكلتر نسبت به مورد مشابه يعني شبكه هاي بي سيم است .

هزينه
تجهيزاتي همچون هاب ، سوئيچ يا كابل شبكه نسبت به مورد هاي مشابه در شبكه هاي بي سيم ارزانتر مي باشد اما درنظر گرفتن هزينه هاي نصب و تغييرات احتمالي محيطي نيز قابل توجه است .
قابل به ذكر است كه با رشد روز افزون شبكه هاي بي سيم ، قيمت آن نيز در حال كاهش است .

قابليت اطمينان
تجهيزات كابلي بسيار قابل اعتماد ميباشند كه دليل سرمايه گذاري سازندگان از حدود بيست سال گذشته نيز همين مي باشد فقط بايستي در موقع نصب و يا جابجائي ، اتصالات با دقت كنترل شوند.
تجهيزات بي سيم همچون Broadband Router ها مشكلاتي مانند قطع شدن‌هاي پياپي، تداخل امواج الكترومغناظيس، تداخل با شبكه‌هاي بي‌سيم مجاور و ... را داشته اند كه روند رو به تكامل آن نسبت به گذشته(مانند 802.11g ) باعث بهبود در قابليت اطمينان نيز داشته است .
كارائي
شبكه هاي كابلي داراي بالاترين كارائي هستند در ابتدا پهناي باند 10 Mbps سپس به پهناي باندهاي بالاتر( 100 Mbps و 1000Mbps ) افزايش يافتند حتي در حال حاضر سوئيچهائي با پهناي باند 1Gbps نيز ارائه شده است .
شبكه هاي بي سيم با استاندارد 802.11b حداكثر پهناي باند 11Mbps و با 802.11a و 802.11g پهناي باند 54 Mbps را پشتيباني مي كنند حتي در تكنولوژيهاي جديد اين روند با قيمتي نسبتا بالاتر به 108Mbps نيز افزايش داده شده است علاوه بر اين كارائي Wi-Fi نسبت به فاصله حساس مي باشد يعني حداكثر كارائي با افزايش فاصله نسبت به َAccess Point پايين خواهد آمد. اين پهناي باند براي به اشتراك گذاشتن اينترنت يا فايلها كافي بوده اما براي برنامه هائي كه نياز به رد و بدل اطلاعات زياد بين سرور و ايستگاهاي كاري (Client to Server ) دارند كافي نيست .

امنيت
بدليل اينكه در شبكه هاي كابلي كه به اينترنت هم متصل هستند، وجود ديواره آتش از الزامات است و تجهيزاتي مانند هاب يا سوئيچ به تنهايي قادر به انجام وظايف ديواره آتش نميباشند، بايستي در چنين شبكه هايي ديواره آتش مجزايي نصب شود.
تجهيزات شبكه هاي بي سيم مانند Broadband Routerها ديواره آتش بصورت نرم افزاري وجود داشته و تنها بايستي تنظيمات لازم صورت پذيرد. از سوي ديگر به دليل اينكه در شبكه‌هاي بي‌سيم از هوا بعنوان رسانه انتقال استفاده ميشود، بدون پياده سازي تكنيك‌هاي خاصي مانند رمزنگاري، امنيت اطلاعات بطور كامل تامين نمي گردد استفاده از رمزنگاري WEP (Wired Equivalent Privacy ) باعث بالا رفتن امنيت در اين تجهيزات گرديده است .
انتخاب صحيح كدام است؟
با توجه به بررسي و آناليز مطالبي كه مطالعه كرديد بايستي تصميم گرفت كه در محيطي كه اشتراك اطلاعات وجود دارد و نياز به ارتباط احساس مي شو د كدام يك از شبكه هاي بي سيم و كابلي مناسبتر به نظر مي رسند .
جدول زير خلاصه اي از معيارهاي در نظر گرفته شده در اين مقاله مي باشد . بعنوان مثال اگر هزينه براي شما مهم بوده و نياز به استفاده از حداكثر كارائي را داريد ولي پويائي براي شما مهم نمي باشد بهتر است از شبكه كابلي استفاده كنيد.
بنابراين اگر هنوز در صدد تصميم بين ايجاد يك شبكه كامپيوتري هستيد جدول زير انتخاب را براي شما ساده تر خواهد نمود.

انواع شبكه هاي بي سيم
WLANS(Wireless Local Area Networks )
اين نوع شبكه براي كاربران محلي از جمله محيطهاي(Campus) دانشگاهي يا آزمايشگاهها كه نياز به استفاده از اينترنت دارند مفيد مي باشد. در اين حالت اگر تعداد كاربران محدود باشند مي توان بدون استفاده از Access Point اين ارتباط را برقرار نمود .در غير اينصورت استفاده از Access Point ضروري است.مي توان با استفاده از آنتن هاي مناسب مسافت ارتباطي كاربران را به شرط عدم وجود مانع تاحدي طولاني تر نمود.

WPANS(Wireless Personal Area Networks )
دو تكنولوژي مورد استفاده براي اين شبكه ها عبارت از :IR (Infra Red ) و Bluetooth (IEEE 802.15 ) مي باشد كه مجوز ارتباط در محيطي حدود 90 متر را مي دهد البته در IR نياز به ارتباط مستقيم بوده و محدوديت مسافت وجود دارد .

WMANS(Wireless Metropolitan Area Networks )
توسط اين تكنولوژي ارتباط بين چندين شبكه يا ساختمان در يك شهر برقرار مي شود براي Backup آن مي توان از خطوط اجاره اي ،فيبر نوري يا كابلهاي مسي استفاده نمود .

WWANS(Wireless Wide Area Networks )
براي شبكه هائي با فواصل زياد همچون بين شهرها يا كشورها بكار مي رود اين ارتباط از طريق آنتن ها ي بي سيم يا ماهواره صورت مي پذيرد .


امنيت در شبكه هاي بي سيم
سه روش امنيتي در شبكه هاي بي سيم عبارتند از :

- WEP(Wired Equivalent Privacy )
در اين روش از شنود كاربرهايي كه در شبكه مجوز ندارند جلوگيري به عمل مي آيد كه مناسب براي شبكه هاي كوچك بوده زيرا نياز به تنظيمات دستي( KEY ) مربوطه در هر Client مي باشد.
اساس رمز نگاري WEP بر مبناي الگوريتم RC4 بوسيله RSA مي باشد.

- SSID (Service Set Identifier )
شبكه هاي WLAN داراي چندين شبكه محلي مي باشند كه هر كدام آنها داراي يك شناسه (Identifier ) يكتا مي باشند اين شناسه ها در چندين Access Point قرار داده مي شوند . هر كاربر براي دسترسي به شبكه مورد نظر بايستي تنظيمات شناسه SSID مربوطه را انجام دهد .

- MAC (Media Access Control )
ليستي از MAC آدرس هاي مورد استفاده در يك شبكه به AP (Access Point ) مربوطه وارد شده بنابراين تنها كامپيوترهاي داراي اين MAC آدرسها اجازه دسترسي دارند به عبارتي وقتي يك كامپيوتر درخواستي را ارسال مي كند MAC آدرس آن با ليست MAC آدرس مربوطه در AP مقايسه شده و اجازه دسترسي يا عدم دسترسي آن مورد بررسي قرار مي گيرد .اين روش امنيتي مناسب براي شبكه هاي كوچك بوده زيرا در شبكه هاي بزرگ امكان ورود اين آدرسها به AP بسيار مشكل مي باشد.

انواع استاندارد 802.11
اولين بار در سال 1990 بوسيله انستيتيو IEEE معرفي گرديد كه اكنون تكنولوژيهاي متفاوتي از اين استاندارد براي شبكه هاي بي سيم ارائه گرديده است .
802.11
براي روشهاي انتقال FHSS(frequency hopping spared spectrum ) يا DSSS (direct sequence spread spectrum ) با سرعت 1 Mbpsتا 2Mbps در كانال 2.4 GHz قابل استفاده مي باشد.
802.11a
براي روشهاي انتقال OFDM (orthogonal frequency division multiplexing ) با سرعت 54Mbps در كانال 5GHz قابل استفاده است.
802.11b
اين استاندارد با نام WI-Fi يا High Rate 802.11 قابل استفاده در روش DSSS بوده و در شبكه هاي محلي بي سيم نيز كاربرد فراواني دارد همچنين داراي نرخ انتقال 11Mbps مي باشد.
802.11g
اين استاندارد براي دستيابي به نرخ انتقال بالاي 20Mbps در شبكه هاي محلي بي سيم و در كانال 2.4GHz كاربرد دارد.

Bluetooth
نوع ساده اي از ارتباط شبكه هاي بي سيم است كه حداكثر ارتباط 8 دستگاه را با تكنولوژي Bluetooth پشتيباني مي كند دستگاههايي از قبيل PDA ، نوت بوك ، تلفن هاي همراه و كامپيوترهاي شخصي از جمله اين موارد هستند مي دهد اگرچه اين تكنولوژي ممكن است در صفحه كليدها ،موس ها و Headset و Hands-free تلفن هاي همراه نيز ديده شود اين تكنولوژي در سال 1994 توسط شركت اريكسون ايجاد شد در سال 1998 تعداد كوچكي از كمپانيهاي مشهور مانند اريكسون ،نوكيا ، اينتل و توشيبا استفاده شد . بلوتوس در فواصل كوتاهي بين 9 تا 90 متر كار مي كنند اين فاصله پشتيباني به امنيت اين تكنولوژي مي افزايد .چرا كه اگر كسي بخواهد ارتباط شما را شنود كند گر چه به ابزار خاصي نياز ندارد اما بايستي در فاصله نزديكي از شما قرار بگيرد مهمتري ويژگي بلوتوس اين است كه بر خلاف Infrared موانعي مانند ديوار تاثيري بر روي سيگنال آن ندارند از تكنولوژي راديوئي استفاده كرده كه خيلي گران نبوده و مصرف برق خيلي كمي دارد .

منبع:شركت همكاران سيستم
نويسنده: نادر ابوترابيان

[habibi]

سلام. دست شما درد نكنه. من تازگيها قابليت استفاده از شبكه‌هاي اينترنتي بي‌سيم رو روي چند نوع لپ تاپ جديد ديدم. البته اين دستگاهها مال فرانسه بود. ظاهرا اونجا يه شبكه اينترنت به طور موازي با موبايل هم وجود داره كه فعلا توي شهرهاي بزرگ فرانسه قابليت اجرايي داره. اميدوارم هرچي زودتر اين تكنولوژي وارد ايران هم بشه. اگرچه خودم زورم به خريدن لپ تاپ هم نمي‌رسه!

[pedramonline]

اين از بهترين مقاله ها بود

[hajHasan]

ديروز چند تا مقاله رو سايت cnet درباره شبكه بيسيم ديدم. گفتم متنشو اينجا بذارم اگر كسي مثل خودم علاقمند بود به اين موضوع ، اين تاپيك براش يه مرجع خوب باشه.در ضمن اطلاعات اين مقاله به روز و جديده.

In the modern day, setting up a wireless network is easy, and so is limiting its use, as long as you set it up properly. A well set up wireless network is virtually impossible to ---- (and in most cases not worth the effort, unless you're a government installation or bank). Thinking ahead and choosing your hardware and software settings with security in mind can save you a huge headache later on.

Hardware:
First off, decide which wireless standard you want to use. 802.11b, 802.11g, and Pre-N are the major types (in order from oldest to newest). 802.11b is fine for many purposes; 802.11g and Pre-N have advantages in speed and distance, but for a simple ADSL network 802.11b is not significantly different, unless you transfer large files (>1gigabyte) from one computer to another inside your network regularly. Each standard is backwards compatible, also - a computer with a 802.11b card can connect to a 802.11g network. I suggest getting 802.11g, unless the extra money for Pre-N is not a big deal, or you want to save a little money with 802.11b.

Then obtain an ADSL modem (if you don't already have one), a wireless router (aka Base Station) (appropriate to the standard you chose), wireless cards for your various PCs (notebook or desktop as needed), and if your home is larger than about half of the suggested range of the wireless router, any one of several options for wireless signal enhancement, such as a range expander or an external antenna. These should be purchased later if you find that you have significant 'dead areas' of low signal in your home, often caused by the base being on one side of the home rather than in the middle. Also, if the ADSL modem doesn't come with them, you'll have to buy telephone jack splitters for ADSL; otherwise your telephone and ADSL will disagree occasionally. Each telephone should have its own (unless you split the phone line already, in which case just one ADSL splitter is necessary for that one telephone jack); even if the telephone doesn't share a phone jack with the ADSL modem, you still need a line splitter for it. Also, you'll need a normal phone cord to connect the ADSL modem to the line splitter (probably 3-6' will do unless you have some seriously confusing architecture), an ethernet cord to connect the router to your base computer (at least temporarily), another ethernet cord to connect the router to the modem, and a surge protector if you don't have one already for the ADSL modem's power source. Make sure you have an ethernet port in one of your computers (either via a card or onboard); a lot of ADSL modems come with them, as well.

The wireless router chosen should include a firewall if possible. This will allow you to best protect your computers from intrusion over the internet; a software firewall on the PC will help as well, but the router is your first line of defense. Also choose one with WEP encryption, although that is fairly standard. To make the WEP encryption seamless, I recommend choosing wireless cards made by the same company as the router; it is not necessary, as pretty much all companies (PC and Mac alike, even, to most degrees) use the same standards, but they often have convenient encryption setup routines that work best when using the same brand of wireless card.

Wireless cards can either be internal or external. Desktops can benefit from an external wireless 'card', that connects to the USB port, if it is USB2 compliant; it runs just as fast, and can be placed in an area with good reception, while a PCI card often is near the ground and behind a table or something (in the back of the computer) and the electronics in the area can interfere with good reception. Notebooks generally use a PC card adapter, or can also use the USB adapter, although it is often annoying to carry another device along with your notebook, so the PC card is usually the choice for notebooks.

Wireless range expanders and antenna extenders are not hard to find, and pretty universal. You should wait until you've set up your network to get one, so you can test for areas that might need help; if you need one (because your wireless connection strength is <50% or so in parts of your house that you want to use your laptop or desktop), I recommend an antenna for a desktop (as it's not moving anywhere, and the antenna is usually cheaper and more effective) but a range expander for notebook connectivity (as notebooks move all over). An external antenna of any sort will help; some of the more expensive, focussed antennas can help a lot, but usually just the large-piece-of-plastic-with-wires-in-it types work fine. Range expanders often are just repeaters, IE they pick up a wireless signal, and re-broadcast it with greater strength, so if your 'base station' is on the east side of your home, and the west side has poor signal reception, putting a repeater in a spot to the west of your house that has decent reception itself will give the rest of that part of the house great reception, as if they had their own wireless base station.

Setup:
First, set up your ADSL modem per instructions. Often this came directly from the ISP, so follow their instructions to set up your primary computer. The network will be based out of the computer, so I recommend choosing the most central location in the house (for best wireless coverage). But don't drastically change your setup for this; there are many options for increasing range as needed. The ADSL modem will connect to the wall with a phone cord, and a ADSL splitter that cancels telephone noise (see above). It generally uses an ethernet cord to connect to your desktop or notebook computer; to start out you should set it up using this wired connectivity so any settings you need to choose can be easily set up, and if you ever lose your wireless connectivity (it happens sometimes!) or your network connectivity entirely, you can troubleshoot it directly rather than having one more source of errors. Make sure you connect the device in the order you are told by the manual; it is very important.

Then, once you have correct 'wired' functionality, follow the instructions that come with your router to set up the wireless network. Some general tips on initial setup: Usually you start by installing the software, and then connecting the router (although not always). Many routers now have HTTP interfaces to adjust their settings - you plug in a generic IP address, such as 157.0.0.1, into your web browser's URL field, and up comes the settings for your router. Choose a SECURE administrative password!! This is the first step to securing your wireless connection. Also, choose to disallow 'remote' connections to the administrative tools - that way, even if someone hacks your password, they can't change the settings.
Typically, from a hardware point of view, the router connects directly to your ADSL modem, through an ethernet cord, and then (optionally) connects to one or more computers through another ethernet cord. You should connect it to the computer that you set up the ADSL modem with to begin with, so that computer can change administrative settings on the network; if you decide to have a completely wireless network later, that's fine, as long as you fix the settings first.

Settings for the Router:

1. WEP encryption: Active, 64-bit at minimum. At least, if more secure (128-bit, ie) is available, go for it. This is the encryption that protects your wireless connection from being used by others. If you live in a heavily populated area, you'll undoubtedly see several people in your area that don't do this later on when setting up the remote computers; laugh at them and realize you have a safe connection while they're probably giving the whole neighborhood free internet access. The encryption either asks for a "hex" key (0-9 or A,B,C,D,E,F), or a "passkey" (a word that is used to generate a key) depending on the brand. If you use the "passkey", use the same rule you (hopefully) use for passwords - nothing from the dictionary, no names or other things related to you. Write it down - use something like QSNTHOE. Remember it if you don't write it down - you'll have to reset the whole system if you forget it later on. This secures your wireless connection from hijacking over the airwaves.

2. Firewall: The firewall is something you should set based on your usage. A router firewall will basically be a floodgate that you only open up for certain things; it is not as flexible as a desktop software firewall (nor should it be), but it is very powerful. If you play online games, use various protocol for accessing the internet like IRC or GUI chat programs (MSN, Yahoo!, ICQ, AIM, etc.), you will have to "open" the ports they use; each program should be able to tell you that, although it can take some research. Most firewalls will come preset to allow "normal" traffic, and block anything that's not usual; so if you're unusual, you will need to open ports yourself. If you are getting connection errors in some programs but not others, this is probably why. But, that also means that anyone trying to hijack your computer from the internet is also failing. This secures your computer from being hijacked over the internet.

3. Remote Access Settings: This is where you tell the router whether you want to limit the access to specific computers, or to any computer that knows your encryption settings. If you properly set up your WEP encryption, you probably don't need to limit it to specific computers; each time you add a new computer, or have a friend over who wants to use the internet on his laptop, or whatnot, you'd have to add that computer to the system. On the other hand, this is even more secure, if you're really worried about it.

4. Router Internet Access Settings: You will have to set up your router with your logon and password for the ADSL account. (If you were using a cable modem, for example, you wouldn't need this.) Once connected, you will have an 'always-on' connection - the router will maintain the internet connection even if all of your computers are asleep. (It is a good idea to every few weeks turn off your router and your modem and let them rest overnight; some brands of ADSL modem have a tendency to overheat over long periods.)

Remote setup:
To set up your 'remote' computers, again follow the instructions. In most cases it involves installing a small piece of software that will run whenever your computer is on, and telling that software what connection you want to use and what its password is. You probably named your router during the setup; that should be visible on the connection list. If it isn't, you may need a larger range for your network; unless you're very near to the router, in which case you have a problem with the router's settings. You will also likely see many other connections, most of which probably have low signal strength compared to yours; some of them require passwords, probably, and some don't, allowing pretty much anyone to freeload off of their internet connection. Yours should be one of the password-protected ones; if not, you need to look at the router's settings. Once you enter the settings for your password, you should be good to go (unless you set up your remote access settings to include only specific computers; then you'll have to make sure this specific computer is on that list). The card's program will run in the background, and maintain your network connection. The router probably has a light that indicates that the wireless network is being used; that light should come on sporadically to maintain the connection, as well as any time you download anything.

Finally, answering directly the last two parts of the question, as they are not directly answered as yet.

Restricting to IP addresses: You could mean two things by this. Probably, you mean that you would like to restrict the computers that can use this network; you've already done this, either through WEP encryption, through specifying on your router which computers may use the network, or both. You don't use IP addresses for this, but Ethernet addresses (MAC addresses, aka), which are the physical addresses of your computer's network hardware rather than the IP address (which is volatile and any one computer can have multiple IP addresses at different times or situations).
However, you could also mean restricting the IP addresses that your computer can access; this is usually accomplished by software, either through Internet Explorer or other browsers (like the company I work for uses), or through third-party software that either blocks IP addresses or allows only specific IP addresses to be accessed.

Notebook network conflicts: If you mean a conflict involving multiple wireless networks in the same physical location, not a problem. The router's physical address defines the network; essentially, your wireless card's software picks out the signal that has each packet of information start with that router's code. My computer at the moment sees 3 wireless networks, mine, another encrypted one, and a third that is unencrypted. A large amount of wireless networks in the same area can be slightly negative to each one, but usually the signal strength is so low from the others that it doesn't have a noticeable affect on your network.
Your notebook *will* be able to access other networks, say if you take it to work. The same wireless card can be set up to access *any* 802.11 based network (.b, .g, or Pre-N); most wireless card's software will allow you to save several pre-set password and router combinations, and it will either automatically select which one it finds, or you might have to choose the right one, but it should be easy to do that. That's the wonderful thing about wireless networking in the modern age - basically everything is cross-compatible, even if you have an older system.

Also, these networks run on the 2.4GHz frequency; so if you have a 2.4 GHz cordless phone, you may have some (usually minor) signal interference. Consider upgrading to a 5.8 GHz telephone (which has no signal interference) if it's a problem.

That's it! Hopefully this answers all of your questions. Remember, each pice of hardware is slightly different, so always refer to the manual that comes with the hardware for item-specific setup instructions; these suggestions are only a guide to getting it right! And if you have a problem with the functionality after you've gotten it to work (days after, for example), I always suggest turning first the router and then the ADSL modem off, then in the reverse order turning them on after a 15-20 second delay. This will fix a lot of temporary connectivity problems. (But don't turn off your ADSL modem for several days after you first plug it in; it uses the first few days to figure out your individual connection speed.)

Submitted by: Joe M. of Chicago, Illinois

[hajHasan]

اين هم يه مقاله ديگه. گر چه مطالب همونه

General Wireless

When installed properly, a wireless network is terrific alternative to having to run wires throughout your home or office. Today’s wireless routers and access points are more reliable, faster, easier to setup and lower cost than ever before. They still do not perform as well as a wired network when it comes to data transfer, but for most applications, they are plenty fast. I ran some tests a few months ago just to compare the time it took to move a 28 meg file from one computer in my house to another using some of the different standards versus using a wired network. If you are just accessing the internet, these numbers may not affect you, but if you are moving or backing up large files across your network, streaming video or music from one computer to another, it can make a big difference. Keep in mind that this is not a scientific study and results can and will vary depending on the distance between computer and router, the computer and router settings, the number of computers on the wireless network, manufacturer of the equipment and what type of antivirus software you are running.

Time to Copy 28mb file from one computer to another on the network:

Hard Wired Network 10/100 4 seconds
Wireless 802.11b 70 seconds
Wireless 802.11g 36 seconds
Wireless Pre-N 12 seconds

Note: The laptop to run this test was 15 feet and through one floor away from the Wireless Router and indicated that it was receiving and excellent signal.


Wireless Standards

There are several wireless standards to choose from for use in the consumer market as well as a few proprietary versions of those standards. Without getting into all the details, which I don’t even know, I will try to break it down into 4 main categories and discuss the pros and cons of each. Please keep in mind that much of this is based on my own tests and experience and that every installation is different.

1. Wireless 802.11b – This standard operates at 2.4ghz and has a maximum data rate of 11mbs. This is the most commonly used standard, but will be overtaken by 802.11G very soon. They can be purchased for very little money now, but unless you need are small and your computers are close together, I would pay the extra for G.

2. Wireless 802.11a – This standard operates at 5.8ghz and has a maximum data rate of 54mbs. This standard is not compatible with any of the others. You can find it used in some business applications or where someone is have a lot of interference problems with other devices running at 2.4ghz. I would not recommend using this standard. There are also a few 802.11a,b,g units out there that will work on all three of these standards.

3. Wireless 802.11g – This standard operates at 2.4ghz and has a maximum data rate of 54mbs. This is fast becoming the most popular standard and is compatible with older 802.11b systems as well. There are also some proprietary G units that have increased speed such as Speed Boost or Super G. These units are compatible with other b and g models as well but will only give you the speed increase when used with like cards from the same manufacturer.

4. Wireless 802.11n – This standard has not been approved yet, but there are units out there called Pre-N. They operate at 2.4ghz and have a maximum data rate of 108mbs. This standard will probably take over the market due to it’s increase in speed and range. I have installed several Pre-N systems and I have found that the range at least doubled if not tripled and is very fast. The Pre-N units are also backward compatible with both 802.11b and g but you will not realize the full potential of this standard without using the matching cards. However, you will experience an improvement in range even when used with pre-existing B and G cards.

Common Problems, Complaints and Concerns

1. Poor Range – One of the most common complaints I get is related to range. Wireless range is dependent on a large number of factors. Just to give you an idea of how varied it can be, I have had installations where a wireless laptop could not even receive a signal 20 feet away in the next room. Using the same equipment in another location, I was able to go over 100 feet. At these high frequencies, wireless signals are interfered, reflected and absorbed by all kinds of common household items. If you suspect an interference problem, I would suggest changing the default channel (usually chan 6) to either 1 or 11 to help eliminate interference from Cordless phones and other wireless networks. Here are a few of the common reasons for poor reception:

• Interference from cordless phones operating on the same 2.4ghz frequency.
• Interference from wireless speaker systems, baby monitors, wireless video cameras and security systems.
• The exact placement of the router and receiving computer.
• Other wireless networks in the building or neighborhood.
• Microwave Ovens
• Construction materials used in the walls or floors (metal studs, foil backed insulation, wire mesh).
• Large metal objects such as refrigerators in the room or in direct path of the signal.
• The type and amount of furniture in the house.
• Even the number of people in the room can alter reception.

2. Frequent Loss of Internet – It is not uncommon to loose your wireless connection to the internet every once and a while and may require resetting your router or modem or just waiting for it to come back on. This could be due to problems with your service provider or your equipment and is sometimes very difficult to determine where the problem lies. There are a number of steps you can take but I will have to save this for another time…

3. Security Concerns – You may hear a lot about security concerns associated with wireless networks. I don’t know about you, but my computer does not contain the security codes to the pentagon and I don’t store any of my passwords or account numbers on my computer. So if someone wants to steal this document, go for it… On the other hand, you should know that setting up a wireless network using the factory default setting has no security at all. Anyone driving by your house can access your internet connection. You will need to change some of the settings on your router to enable security features. I will get into some of the basics of this later on in this document (see Security Settings).

4. Too Slow – All of the wireless standards above are typically faster that most of the available DSL and Cable connections available to home users today. So under normal internet usage and reading email, speed is not usually an issue for a few computers on the network. However if you have many wireless computers on the same network and some are performing other tasks over the network or you plan to move a lot of large files over the network, you will want to take this into consideration when designing your network.

Layout the Plan

1. One computer hardwired – It is desirable to have at least one of your computers hardwired to the network to simplify setup and future troubleshooting. It is not necessary to keep it wired, but will make troubleshooting and setup much easier. You can make it wireless later if you want. If you are planning to use one computer as a server or central storage place for data and even a print server, you may want to keep this one hard wired to the network. It is still desirable to have as many computers hardwired as is conveniently possible and leave the rest for wireless.

2. Location of Hardware – Placement of your wireless router/access point is critical for optimum performance. Placing it in a central location equal distance from all the receiving computers is desirable. Also, installing it above the receiving computers is generally better than below. In other words, placing the router/access point in the attic is usually better than in the basement. Installing it in the far corner of the basement and expecting to get reception on the 3rd floor at the opposite end of the house is unlikely.

3. Avoid other objects – Place the router/access point away from other items in the room such as computers, wires and large objects. Move it to a location high up on a shelf away from your computer, monitor and printer.

4. Experiment First – If you have a laptop with wireless capability, you can use it to test your layout prior to finalizing your plans. You will need a Wireless Router or Access Point, but you do not need to connect the router to your DSL or Cable modem to run some placement tests.

1. First hardwire your wireless router/access point to one of your computers and go into setup (check your manual) and change the SSID (this is the routers name as it will seen by other computers) to anything other than the default. If you leave the default setting for the SSID, which is usually the name of the manufacturer (linksys, D-Link, Netgear), you might pick up someone else’s signal with out knowing it. I ran into this just the other day.

A new client called asking me to fix a problem they had been having for over a year, printing to a network printer in another room in the house. When I checked the computer in question, I found that it was not even on their own network. It had been receiving a wireless connection from the neighbor’s house next door for over a year. They were unaware of this because both houses had the same default SSID and this computer was out of range of there own network.

2. Now disconnect the Router/Access Point from the computer you used to set the SSID and move it to the location that you plan to test. Simply plug in the power to the router and walk around your house with the laptop. Go to each location of interest and check the signal strength. Each wireless card has some form of utility to view the status of your connection or you can just use the Windows indicator. In some cases they will even give you a nice bar graph (check your manual). There are several programs that you can download like netstumbler that can help survey your location. You can experiment with different locations for both your router/access point and your receiving computers. Keep in mind that sometimes simply moving the router a only a few inches away from an object can make a big difference.



Basic Network Layout

The following is a simplified diagram of a typical network setup with all the components you will need. Figures 1,2,3,and 4 all basically accomplish the same thing. Where Figure 1 shows all of the individual components and Figure 4 is a single box containing everything on one unit. You can either purchase all the components separately or purchase combo units that contain multiple components within a single box. The idea is similar to a stereo system. You can purchase a tuner, amplifier, CD player separately or purchase a complete Receiver with everything built-in.

1. MODEM – ROUTER – HUB/SWITCH – WIRELESS ACCESS POINT
2. MODEM – ROUTER(w/built in switch) – WIRELESS ACCESS POINT
3. MODEM – WIRELESS ROUTER (Built in Router, switch and Access Point)
4. A single Cable or ADSL GATEWAY(everything in one unit)


What You Will Need

I usually recommend purchasing all of the components from the same manufacturer. Even though most all brands are designed to work together, it may result in lower performance if you mix brands. Also, it will be a lot easier when it comes to technical support to be calling just one manufacturer for help. The same goes for mixing wireless standards, you could purchase an 802.11g router and a mix of 802.11b and 802.11g cards. It will work, but with reduced performance.

1. Cable or ADSL Modem – Broadband providers usually offer the modem for free or for rent. In the case of ADSL, the modem is usually provided for you. For cable modems the rental fee is usually a few dollars per month or you can chose to provide your own. If your provider is charging a dollar or two per month for the rental, I would go with that. If they are charging more, you may want to consider purchasing your own. Based on my experience so far, I have found that it is not uncommon for the modem to start exhibiting problems after about 2-3 years. Lightning strikes and power surges could be a contributing factor to these early failures. If you purchase a modem for $60 or rent for 3 years at $2 per month, it is about a wash. But that is your choice and may be completely different in Malaysia.

2. Cable/DSL Wireless Router or Access Point – You will need a Router and a Wireless Access Point or the more common Wireless Router (which contains both a router and an access point in one unit). Note: A few companies make a combination Modem, Router, Access Point and Switch all in one unit. You should also check the modem that may have come with your internet service, because some providers are starting to supply Modem/routers units. One other thing you need to check is that some providers have been known to supply a modem with only a USB connection and this can not be used for setting up this kind of network. Normally I would just go with wireless router, unless you have a situation where you need to place the access point in a different location than the router for better coverage or if you already own a router.


3. Wireless Cards for Each Computer – You will need a Wireless Card for each computer that you plan to use wirelessly.
Laptops – Depending on how old your laptops are, some of these my have wireless built-in. If not, you can purchase Wireless PCMCIA Cards for each.
Desktops – You can purchase either Wireless PCI cards that are installed into an available PCI slot inside the computer or an external USB Wireless Adapters. I would recommend the internal cards, especially if you already have several other devices connected through USB, such as Printers, Keyboards, Mice and WebCams.

4. Surge Protectors or UPS – I would make sure that the modem and router are both plugged into some form of surge protector. Better still would be to use a UPS (Uninterruptible Power Supply). These units have a built-in battery to power your equipment in the event that the power goes out. I have seen some of the smaller units going for as little as $30.


Preparing Computers For Networking

If you plan to share files or printers between computers, you will need to check some settings. I would suggest taking the time to make sure all the computers are in good working order before attempting to network them. At the very least you need to run a complete virus scan on each computer. Depending on your configuration and settings, a single computer that is infected with a virus can spread to your entire network infecting all of your computers. I would also run a good spyware scanner on each computer as well as perform some routine maintenance such as Disk Cleanup and defrag. Perform the following tasks:

1. Check Computer Name and Workgroup – Right Click on MY COMPUTER- Left Click PROPERTIES – Left Click COMPUTER NAME to check the Full Computer Name and Workgroup Name. You want to make sure each computer has a different full computer name and at the same time each computer is using the same workgroup name.

2. Turn off Firewalls – For the initial setup, it is usually easier to turn off or disable all software firewalls. You have one built into Windows, but you may also have others installed that may be included with Norton or McAfee internet security packages.

3. Shared Folder and Printers – If you are going to share files and/or printers with other computers on your network, you can select these now.


a. Sharing Printers – Select START – CONTROL PANEL – PRINTERS AND FAXES, Right Click on the printer to be shared and select the SHARING tab. Click the SHARE THIS PRINTER box. The Share Name box will now contain a default name for the printer. You can leave the default name or change it to whatever you want (keep the name to 8 characters). If your network has computers running anything other than Windows XP, you will need to add print drivers for the other versions of Windows (ADDITIONAL DRIVERS). Otherwise, click OK to exit. You should now see a hand under the printer icon, indicating that it is being shared. Perform the same steps above for any additional printers you want to share.

b. Sharing Files – If you would like to share some of your files with other computers. Navigate to the folder or file that you want to share using windows explorer or by drilling down through MY COMPUTER or MY DOCUMENTS. Right Click the folder or file name and select SHARING and SECURITY. Check the box next to SHARE THIS FOLDER,

Setting up the Network

1. Verify Broadband Connection – The first thing you want to do is connect a single computer directly to your cable modem or DSL modem. Run the setup disk that was given to you by your provider and check to make sure everything is working correctly. If your modem was already connected and running, you can skip this step. But if this is a new installation or you have moved your modem to a different location, test it with a single computer first before attempting to network.

2. Setting up the Router and First Computer – Now that you have determined that your internet connection and modem is in good working order, you can move onto setting up the router and first computer. Connect the Router to the modem and then plug your first computer into the router. Run the setup disk that came with you router to get the first computer up and running. You can run the Windows XP network wizard which will prompt you to create a setup disk for the remaining computers or choose to do everything manually. Note: I would recommend not applying any security until you have all the computers up and running on the network. I would change the default SSID, so that you will recognize your network later.

3. Setting up the Remaining Wired Computers – You can now proceed onto setting up each of the remaining computers. With the power off, plug in each additional wired computer and power on. Run the Windows Network Wizard or use the disk you created from before. If you plan to share any folders or printers, you can set those up as you go for each computer.

4. Setting up the Wireless Computers – If your laptops came with built-in wireless networking, you may need to first turn the wireless receiver on (Most laptops default setting is off to save power, see instructions for laptop). You should see a popup that indicates that the laptop has found a wireless connection. Click on this to see a listing of the available connections. If there are other wireless networks in your area you will see them listed. Scroll down until you see your network (whatever name you used for SSID), then click on that and connect. It will ask you if you are sure you want to connect to this unsecured network. Go ahead and connect. If you are installing wireless cards, follow the instructions that came with the card to install the drivers and then follow the instructions above.

Security Settings

You should have your network up and running now without any security or firewalls running. So it is time to start setting up your security. Keep in mind that the factory defaults for wireless has Zero security. Personally, I am not a fanatic about security and I don’t have anything that anyone would want, so I try not to get too carried away. But if it is a real concern, there are a number of security measures you can take depending on the type of hardware and software you have. Most Wireless Routers and Access Points have several setting you can adjust to add security to your network. I would recommend changing only one or two settings at a time and then testing your network before continuing.

1. Change all Default Passwords – The first thing to do is change all the default passwords for your router or access point. The default passwords are common knowledge to most anyone.

2. Change the SSID – I would change the SSID (network Name) as mentioned above, as well as you may want to turn off the broadcasting of the SSID. With broadcasting turned off, someone would have to know your network name before attempting to ----.

3. Enable WEP – Depending on your router you may have the option to enable 64 bit or 128 bit encryption. If this is enabled you will need to create a code and then write it down to apply it to each wireless computer that is going to be on the network. Someone would have to guess or try every possible combination to gain access.
4. WAP – The newer Wireless equipment may also offer this form of security which is considered to be more secure.

5. MAC Filtering – You can also select Mac filtering to allow only those computers that have a specific Mac Address to access your network. The Mac address is somewhat like a serial number for your computer. Someone could still access your network if they knew this address.

Firewalls - After you have applied all of the security settings you want, you should now go back to each computer and turn on any firewalls that you may have. This would include the Windows Firewall or any third party firewall software. You will have to go into the firewall settings for each computer and enable print and files sharing (if needed), and you may have to enable network activity by entering in the IP address range of you network computers.


Dana H.
Wayland Computers
[ برای مشاهده لینک ، با نام کاربری خود وارد شوید یا ثبت نام کنید ]

Submitted by: Dana H. of Wayland, Massachusetts

[Nesta]

سلام
دوسته عزيز من زياد تو اين سيستم وارد نيستم ميخواستم بدونم که اين شبکيه بی سيم بهتر از adsl جوم ميده و ميگن دکل ميخواد اين جرينش چيه ممنون ميشام

[hajHasan]

اين مقالات در كل براي راه اندازي شبكه بيسيم هستش. سوال شما در مورد اينترنت بيسيم هست.
البته تا اونجا كه من در مورد اينترنت بيسيم شنيدم مودم مخصوص (بيسيم) مي خواد كه داخل خود اتاق گذاشته ميشه و برخلاف دي اس ال ، محدوديت حجمي نداره ولي سرعتش بصورت اشتراكي(share) هست. محدوده فعليش هم قسمتهاي مركزي و شمال تهرانه. شرايط آب و هوايي روي كاراييش كمي تاثير ميذاره و امنيت پايينتري نسبت به دي اس ال داره. ( گر چه مشكل امنيتيش تو ايران اصلا مطرح نيست چون براي نفوذ به آن احتياج به ابزارهاي پيشرفته هست ). دكل هم مربوط ميشه به شركت ارائه دهنده خدمات بيسيم
شخصا اينترنت بيسيم را به دي اس ال فعلي ترجيح ميدم.

[Amir_P30]

ممنون حاجي جان

دستت درد نكنه

مرسي

[arash_irani]

سلام دوستان و دستتون درد نكنه
من خودم از اينترنت بيسيم يعني وايرلس استفاده ميكنم و در بندر لنگه هم زندگي ميكنم حدودا يه چند ماهي ميشه كه اين امكان رو ما داريم
ديال آپ در كل نميتونه بيشتر از 32 سرعت بده و با خط E1 ميشه تا 56 k بهره گرفت ولي اين سيستم در صورت اينكه ISP هم همكاري كنه يعني همه چيز بستگي داره به ISP و تا سرعت 11 MB هم ساپورت ميكنه ولي خب اين سرعت رو حتي يك كاربر اينترنت در آمريكا كه بيشترين سرعت رو آمريكايي ها دارند هم فعلا نداره تا جايي كه من خبر دارم حداكثر سرعتي كه به يك كاربر در آمريكا دادند 2 MB بوده در آمريكا و اين خودش ديگه آخر سرعته كه ما ايراني ها براي 32 چقدر جون ميكنيم و چقدر هم هزينه ميديم
ولي من الان تا سرعت 64 واقعي رو ميتونم استفاده كنم
راستي در سرعت 64 سرعت send من برا آپلود تا 60 الي 70 K در ثانيه ميرسه كه ديال آپ عمرا اگه بتونه به 6 يا 7 هم برسه
موفق باشيد
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[sara62]

كسي راجع به ارتباطات شبكه هاي بي سيم (Cooperative Communication In Wireless Networks) چيزي ميدونه؟