I’m going to identify and describe the different types of internet & intranet connections, detailing the advantages and disadvantages of each. Then detail the effect of download time in relation to large website files.
Dial Up
Is the slowest technology used to connect either computer to computer, or directly to an ISP for internet access, transferring data at 56KBPS, requiring a standard Dial-Up Modem, built into most computers.
Advantages:
• You can use dial-up at any spare telephone point.
• It only costs the charge of a local phone call.
• Available anywhere, where there is a phone line.
Disadvantages:
• Ties up the phone line.
• Painfully slow.
3G
3G Technologies is the latest Mobile Technology used in data transfer from Mobile Devices (Phones, Laptops) at speeds of up to 384KBPS. Applications including Video Telephone Calls, Web Browsing and accessing files from your home PC can all be done over the mobile network, via the Internet.
Advantages:
• Reasonably Fast
• Mobile
Disadvantages:
• Not available everywhere.
ADSL
Asymmetric Digital Subscriber Line is a high bandwidth technology used over telephone lines. Usually the subscriber will get a maximum upload speed of 256kbps and a maximum download speed of approximately 8mbps. Although this is shared between up to 50 users, depending on the contention ratio.
Advantages:
• High Speed
• Uses a phone line, which is usually already installed but doesn’t tie it up. Therefore you can have a convosation over the phone and browse the internet at the same time.
Disadvantages:
• For a reasonable performance, the location using ADSL services needs to be within 5km of the local telephone exchange serving the ADSL line.
SDSL
This is the same as ADSL only the upload and download speed is the same. SDSL is a acronym for Symmetric Digital Subscribers Line, usually more expensive and with a lower contention ratio than ADSL lines.
The same Advantages & Disadvantages with ADSL also apply with SDSL.
CABLE
Cable Internet Access is where the future is as it is capable of much faster transfer speeds than ADSL or SDSL can provide. This is because Cable providers have laid Fibre Optics in the streets which can transfer much more data than a standard telephone line. This also means cable has absolutely no effect on a telephone line at all.
A Cable modem works in much the same way as Cable TV, the provider (in the UK that is usually NTL or Telewest) install a box on the wall, from this a COAX cable is connected from this box to your modem. The Box on the wall leads to a cabinet situated out in the street somewhere. Your modem then plugs into either a Router or directly into your computer via USB/Ethernet.
Telewest are currently offering Cable on speeds of upto 10MBPS, which is already much faster than ADSL services available.
Advantages:
• Much faster than any other broadband on the market today.
• It’s likely to increase to 50MBPS this year.
Disadvantages:
• Availability is even more limited than ADSL, Telewest must have laid cable in the streets for the persons to be able to get Cable Internet Access.
• Much higher Contention Ratios than ADSL, your sharing your 10MBPS with many more people.
ISDN
Intergrated Services Digital Network: is a faster dial up connection using a different connection, not commonly used for Internet access anymore, however it is Point to Point (not directly through the internet) making it much securer for business to business communications so it is still used occasionally.
Transfer rates of up to 128kbps.
Contention
Contention is how many users share the bandwidth. You never experience the full amount of bandwidth offered by your ISP this is because your on a 50:1 Contention Ratio (in usual circumstances) so at peak times the broadband being used could be 50 times slower than advertised.
Data centres
Data Centres are large warehouses with Huge Internet Connections and in some circumstances Backbones routing Internet Traffic to the appropriate servers or actually supplying WebPages. Depending on the data centres purpose.
Data Centre Speeds
Data Centres used multi-homed connections, meaning instead of having a single service provider they will usually have between 2 – 20. The advantage of using this, if one service provider crashes all servers remains reachable.
The transfer speeds of these lines (individually) are usually 10,100 or 1000 MBPS and have absolutely no contention.
Data Centres situated closely to each other will also sometimes link to each other to further reduce traffic, with fibre optics. This allows them to share providers and reduce traffic. The benefit of this is Trace Routes become shorter, meaning the user gets to there destination quicker.
Speed Testing (How long it takes to download a 1MB file, at best)
56KBPS (Dial Up) Two Minutes and Twenty Two Seconds.
128KBPS (ISDN) One Minute and Two Seconds.
1MBPS (Cable/ADSL/SDSL) Seven Seconds.
2MBPS
(Cable/ADSL/SDSL) Three Seconds.
10MBPS or Above Less than one second.
Again, these speeds are based on a 1:1 Contention Ratio.
Other Optimization
Image compression is commonly used to increase speed in which a page loads. This can have advantages and disadvantages.
Images will indeed load much quicker, improving the browse speed and site usability. However the quality of image will degrade considerably as a consequence of doing this.
Webmasters are capable of doing a small amount of image optimization without compromising the look and feel of the website.
Other types of compression can include placing downloads in a .zip file, compressing the files, making them smaller in file size therefore quicker to download.
This is a very good idea; however .zip files can occasionally corrupt.
Intranet/Internal Networks
Internal Networks and Intranets transfer over Ethernet; this is 10, 100 or 1000mbps depending on the Network Card in the System.
Usually desktop machines have a 100mbps and a server (e.g. Web server hosting the Intranet) will have 1000mbps network hard, so it can handle all the requests sent to it.
Downloads made Internally should be very close to the above time quoted, as there shouldn’t be virtually any contention, this does depend on how many users are logged on in the facility.
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