NAVIGATION
My Investigation on Cable Modems
Investigation of CM's operation & architecture
Alternative Broadband Technologies
|
4. Cable Modem’s Alternatives 4.1 Dial up 4.2 DSL 4.3 ISDN 4.4 T1 4.5 Satellite Internet 4.5.1 Satellite internet options 4.6 MMDS (Wireless Internet) 4.7 Fast TCP
Alternatives to Cable Modems Cable modems have many things to offer as we have learned so far but they are not alone in the broadband market. Many alternatives ways to connect to the web exist nowadays since more and more companies from different areas want to offer internet with their services. Therefore these alternatives challenge cable modems with what have to offer. Below all major Cable modem alternatives are discussed for the search of the best technology. 4.1 Dial up The first modems developed were the dial-up modems since then many things changed but dial-up modems still exist in the market. Dial up modems are devices that can be used to establish connections between two points by manual or automatic dialling or answering. The quality of the circuit in not guaranteed since it depends on the quality of the telephone line and other factors but all major telecommunication companies establish standards which provide better quality services. The links are almost always 2-wire in order to avoid extra costs.
Pic. 7 Dial-up connection between two locations.
Analogue modems (dial-up modems) operate at a maximum of 56 Kbps. A comparison between dial-up and cable modems is very easy because of the big difference between their technologies. Moreover below are the advantages of cable modems over their predecessors:
4.2 DSL DSL is an acronym for Digital Subscriber Line. This technology uses the simple phone line to transfer its data between any two DSL modems. This link between the modems is used to transfer both low and high frequencies for voice and data respectively. DSL technology theoretically can achieve a maximum downstream rate of 52.8 Mbps from the Head-End and it can upload up to 2.3 Mbps to Head-End using asymmetric data transfer.
Pic. 8 DSL Configuration and connections Furthermore many variations of DSL technology exist nowadays (sometimes is called xDSL due to this). Some of these technologies are:
The most popular option is the ADSL which uses asymmetric data transfer. On the other hand HDSL and SDSL are very similar technologies but they use symmetric data and have a distance limit between the two ends at 3 Km. VDSL is still a developing technology and standards have not yet been fully established but data rates are expected to reach 52Mbps although distance limits still apply. One thing we need to highlight about xDSL and is a major technology difference when comparing it with a cable modem system is that the network’s performance depends on the distance between the user and the local Head-End. For example the ADSL technology can reach data rates described below in the table.
Data Rate Distance up to
Comparing cable modems to DSL we can find out that DSL is more secure and has higher data rates when it comes to file transfer but cable modems hit back offering convenience and speed when surfing the web. Also cable internet prices are more attractive to the user.
4.3 ISDN The Integrarated Services Digital Network (ISDN) line contains two 64 Kbps channels B and a 16 Kbps channel D. The B channels are used for voice and video transfer and can cooperate to reach speeds up to 128Kbps. Each channel is independent in order to be able to use the phone line while surfing the web.
Pic. 9 ISDN communication with the internet. The important thing about ISDN is its flexibility. We can see that from the way it is implemented. No new cabling is required since a simple telephone line can be used. The only thing that needs to be done in order to convert a simple line into ISDN is the change of a card in a local telecommunication centre that offers this service. Furthermore, another interesting thing about ISDN is that connections require to be dialled. The differences of ISDN technology compared to cable modems are:
4.4 T1 In 1960’s a new high speed digital network was developed by American telecommunication company AT & T in order to provide a network that could represent digitally the information (voice) that up till then existed only in its analogue form. This technology is capable of transmitting up to 1.544 Mbps between two points. It was designed for voice channels (24 per T1 line). Furthermore, the T1 technology existed successfully for a while and new variations of this technology started developing. Now after several years in 2003 four main variations of the previously developed T1 technology exist. Below is a table with all fives their transfer capabilities and the number of channels they occupy.
Technology Data rate Number of Voice Ch.
Table 4: T1 variations
These technologies might be very fast and have high capacity compared to cable modems and the other alternatives but exist only in the United States. Also their cost is much higher compared to all the other technologies discussed above.
4.5 Satellite Internet Satellite internet connections are developing more and more during the last years. The cost to implement such a system is bit high compared to cable modems but it gets cheaper and cheaper every day since more and more companies offer this technology to their services. Due to the high cost the target audience is usually people that have no other high-speed choices probably because no other internet service (DSL, ISDN, and Cable) is available in their area. In order to connect to such a system the user needs some important equipment. More specific the requirements for a satellite internet connection are:
As we can see the satellite internet needs a simple dial-up connection to a local ISP. This connection is used for the upstream direction and anything you need to send to the net is done by the dial-up modem. On the other hand the downstream comes from the satellite link and the data received is then passed from the dish to the satellite modem that operates as an interface between the user’s computer and the satellite network.
4.5.1 Satellite internet options There are three basic options offered by the satellite service providers. They are explained below: · Unicast. This option offers receiving of data through satellite while data sending is done by a simple dial-up or other connection. · Multicast. Multicast is very similar to unicast. The satellite ISP sends files through the satellite. These files are available for all users to download. · Two way satellite internet. This connection offers both sending and receiving of data through the satellite. It is much faster than the two other options but needs extra equipment to implement it and the cost increases dramatically.
Pic. 10 Two way satellite internet link
This technology has many differences compared to cable modems since it uses antennae network instead of a land cable network. Also the prices for implementing are much higher but their advantage is the global coverage they offer. 4.6 MMDS (Wireless Internet)
This is a very recently developed alternative technology to cable modems. This technology includes Multipoint Multichannel Distribution System. It provides broadband internet using a series of antennae around the country. The internet access in such a system is achieved by the used of many frequency bands. It can deliver up to 30Mbps in a 6MHz channel and provides high speed access. The available speed depends on the distance between your receiver and the antenna. The radius of the antenna depends on the frequency used and distance covered starts from 10 miles and can reach distances up to 35 miles. The operation of this technology is very similar to satellite internet. The data send from the user computer to the network is through a land line (ISDN, Cable) while the data received from the net are send from the antenna to the subscriber’s dish and then are forwarded to the computer. Furthermore there is always the option for a two way wireless communication but the cost increase enormously since the required equipment and services are still developing without having established a generally accepted standard.
Pic. 11 MMDS communication between two points. Red line used when one way MMDS is operating
4.7 Fast TCP
Finally a new alternative technology is in hybrid stages but has a very bright future as recent tests shown. This technology was developed by Stephen Low and his team in the California Institute of Technology. This technology is 6000 times faster than a typical dial-up modem but is still in testing stages. The last test done had the objective to send data from California to Geneva. The results were very satisfactory since the average data rate achieved was 925 Mbps. The data rate for cable modems network is much lower and this difference is the competitive advantage that this technology might have over the other competitive technologies in the market.
|
||||||||||||||||||||||||
