Another advantage of cable modems is that they are not the traffic bottlenecks on a cable data network. The cable modems have tremendous throughput capacity. It is the other components of the cable network and the Internet itself that slow traffic down. Some of the items that slow down a cable data network are the 1.5 Mbps T-1 cable Internet connection, the Ethernet PC interface card, current PC technology, and plain old Internet congestion. But all these items are being upgraded to allow ultra-fast data traffic. The Internet is going through growing pains and there is still a lot of growing to do (Medin, 1999).
Cable modem technology does have some disadvantages. Cable data networks are still in their infancy and are going to experience some growing pains as the rest of the Internet is upgraded to handle more traffic. Most of the disadvantages of cable data systems the result of legacy issues within the CATV systems. However, the cable companies were aware of these disadvantages before they got into the business, and they know how to overcome the problems. The solutions to the most of the problems of cable data networks are known. But, it will take a great deal of money to implement these solutions. The MSOs have invested already invested billions in creating cable data networks, and they are willing to invest more to remain competitive with the telephone industry.
The biggest legacy issue induced problem facing cable modem technology is that CATV systems were originally designed to carry TV programming from the cable operator to the subscriber’s home. The CATV systems were never intended to be used for two-way or point-to-point communications. The MSOs have the capability to upgrade their systems to deliver two-way data communications by switching to HFC plant, but there are no easy solutions to the point-to-point communication dilemma. The tree and branch configuration of a CATV system is not conducive to point-to-point communication. There was no need for sophisticated switching systems, like those used in a telephone system, when the CATV systems were first developed. Unfortunately for the MSOs, a switching network is essential for point-to-point communication.
Another disadvantage of cable data systems is slow upstream communication. But, fortunately for the MSOs, the high-speed telephone data technologies also have this problem. The root of the problem is that CATV systems were primarily designed for downstream delivery of TV programming. So, the majority of the coaxial cable bandwidth of a CATV system was dedicated to downstream traffic. There was very little bandwidth set aside for upstream traffic. To further complicate matters, the cable modem manufacturers are making their products use much narrower bandwidth, 2 MHz, for upstream communication.
The issue of shared bandwidth is also a disadvantage for the cable data systems. If the MSOs do not upgrade capacity as more people sign up, cable modem access speeds may become slower. Upgrading capacity is a fairly straightforward exercise for the MSOs. It is just a question of if the MSO’s are willing to invest the money to make the upgrades. Another shared bandwidth issue is security. All the downstream traffic in a cable data network goes to all the cable modems in the network and all the upstream bandwidth is shared by all the cable modems in a local loop. IP and network protocols are used to make sure traffic is secure and routed properly. Many of the non-standardized first generation cable modems did not have encryption capabilities, so users were able to access other user’s traffic. Second generation modems and CMTS equipment are built according to the DOCSIS specification, which contains security and data encryption requirements. Still another disadvantage of using a cable modem is that the user does not have a choice of ISPs. The only ISP available to a cable modem user is the local cable company. This is because cable TV lines do not have ‘common-carrier’ status as do phone lines. However, there are some efforts underway to change this.
The recommended application for cable modems is for private, not commercial use. Because of the shared bandwidth issue, most MSOs will not allow a subscriber to host a server with their cable modem. A cable modem subscriber who tried to host a server would use a great deal of the shared bandwidth, which would be detrimental to the other subscribers on the loop. But, for a private user, cable modem systems definitely offer the most bandwidth for the money. There are approximately 75 million cable TV subscribers in North America (Medin, 1999). As of August 1999, cable operators were offering two-way high-speed Internet service to about half of these customers (Medin, 1999). More than one million of these subscribers have signed up for cable modem service.
The future prospects of the cable modem are excellent. The current cable modem technology is stable and improvements are being developed at a rapid pace. Soon there will be internal cable modems on the market that will not need the Ethernet interface. There is tremendous upgrade capacity available to the MSOs and it appears that the MSOs are willing to make the capital investments required to make the upgrades. The MSOs have already moved the fiber-optic cable close to the end-users. It remains to be seen if the MSOs will move the fiber-optic cable all the way to the end-user. The coax portion of the HFC network that goes the “final mile” to the home is limiting factor to broad bandwidth. People are forecasting that the house of tomorrow will be totally networked. A great deal of bandwidth, more than there is available now, it going to be needed to accomplish this. Right now, there is speculation that as more and more people start using broadband access, there will come a point where there are so many high-speed users that the Internet’s backbone will be “broken”. But, this will not happen if backbone capacity is upgraded. If the Internet backbone is not upgraded, upgrading the cable data networks will be like building a new super fast off-ramp to the highway. Cable modem users will be able to get on the Internet highway much faster. But, they will find a traffic jam on the highway when they get there. Fortunately, the costs associated with upgrading the Internet backbone will be small in comparison to the cost of reworking other parts of the Internet to improve performance. Also, there is the issue of cable modems changing Internet usage patterns. As networks perform better, people are going to demand more and more out of them. To use the overused highway analogy, current Internet traffic is composed generally of small cars (e-mail) and some trucks (graphics) and only rarely a convoy of trucks (large audio/video files or programs). Traffic flows smoothly most of the time. However, if the composition of Internet traffic shifts heavily towards audio and video files, it would mean more and more truck convoys will be on the highway, taking up whole lanes and reducing the space available for other traffic. The future looks bright for cable modems, but the powers that be must insure the Internet can handle the increased traffic that will result from the growth of cable data networks.
The future holds a lot of competition for the cable modem industry. There are other high-speed data technologies on the horizon which are going to be in fierce competition with cable data networks. Right now, cable modems offer the simplest, fastest and cheapest broadband access. But this could easily change in the future. The phone companies are looking to give the cable companies some more competition in the high-speed Internet access market. Asynchronous Digital Subscriber Lines (ADSL) are just starting to come on line. ADSL speed should be comparable to cable modems. However, speed will depend on the user’s distance to the next telephone company switch. A potential ADSL customer can no be any further from 15,000 feet from the switch if 26-gauge twisted-pair wire is used. However, this distance increases to 18,000 feet if 24-gauge wire is used (Clark, 1999). With ADSL, the closer one is to the telco switch, the higher the connection speed. Like a traditional dial-up modem, ADSL will provide the user with a dedicated, always on, line to his ISP. Because there is a dedicated connection, there will not be any shared bandwidth concerns like there are for cable modems. ADSL uses filters to split the existing copper phone line into three separate frequency channels. A 0- to 4-KHz band carries the traditional analog telephone signal and a higher frequency band is used for upstream data transfers at rates up to 640 Kbps. The rest of the band is used to transmit data downstream, either from the Internet or as video-on-demand, at speeds of up to 8 Mbps. ADSL is likely to be more expensive than cable data access and it is too early to determine how fast ADSL will be in the real world (Clark, 1999)
Another source of competition for the MSOs is a satellite-based, high-speed Internet service called DirecPC, which is available through Hughes Network Systems (Clark, 1999). For $499, U.S. customers can purchase a kit that includes a satellite receiving dish, a PC interface card, and software. This price does not installation. With this service, upstream transmissions are sent via dial-up connections to the ISP. The upstream information requests go to the DirecPC satellite network operations center, which broadcasts the requested data down to the users from a Galaxy IV Satellite at rates up to 400 Kbps. This service starts at $9.95 per month, but goes up to $129.95 per month for the premium package. With the basic $9.95 rate, the user will also be charged 60 cents for each megabyte of information downloaded from the satellite (Clark, 1999).
Another future source of competition for cable modems is wireless cable. Wireless cable sounds like an oxymoron, but wireless cable TV is already an established business. Wireless cable works by using a satellite system to broadcast multichannel TV programming to homes equipped with dish antennas that operate in the 2- to 2.6-GHz range (Clark, 1999). The system can also be used to transmit data as well. The downstream data from the satellite is received by the dish, which passes the information through coaxial cable to a special modem that converts the signal into IP data the computer can computer understand. This process works for downstream data, but upstream data transmission involves using a standard analog telephone line. The industry is working to establish a wireless upstream path, but a viable solution is at least two years away (Clark 1999).
Cable modems are the wave of the future. Of all the current broadband technologies, cable modems offer the most benefits. Cable modems are simple to operate, do not require a great deal of extraneous hardware, offer the fastest connection speeds, and are the least expensive of all the alternatives. There are some disadvantages to cable modems and cable data systems, but there are solutions to these disadvantages. Just as computers have already done, networking will become a large part of everyday life. Better networking means having more speed, and having more speed takes having more bandwidth, and cable data networks provide that bandwidth. As more people begin to use cable modems, the MSOs will have to upgrade the capacity of the system. This means they will have increase the fiber-optic portions of the HFC networks. As the fiber-optic portions of the MSO’s HFC networks grow larger, fiber-optic cable will get closer and closer to the home. Cable modems are the harbinger of things to come because they will drive the need for fiber-optic to the home. Fiber-optic to the home is only a matter of time, and when this happens the Internet will become even bigger than anyone has imagined.
References
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