Comparison of Cable Modem over ADSL

In the narrowband access technology from the existing optical access solutions to end the process of evolution, there will be many very viable transition technology, which, based on ADSL technology and the telephone line cable of Cable Modem based technology is the mostpotential.

ADSL line rate with upper and lower asymmetric features, so its application is mainly applied to provide users with Internet access and VOD on demand and other services, does not apply to LAN interconnection services.Provide Internet access services using "ADSL + ATM / Ethernet" approach.ADSL client remote device configuration, the Council configure DSLAM (ADSL central office equipment), between them, with ordinary telephone twisted pair connections.

ADSL users PC, the remote device to provide Ethernet interface, DSLAM through the ATM or Fast Ethernet and connected to ISP. Through the network, users can achieve broadband Internet access.ISP DSLAM can be placed in the room, through the access network access to ISP; also be directly placed in the ISP engine room, and the ISP directly connected to the LAN access platform use.Using ADSL VOD video on demand service available, you can use "ADSL + ATM" approach.

Cable Modem is also a downlink and uplink bandwidth asymmetry of technology, to provide Internet access and VOD for the two businesses.Which can be used to provide Internet access service "HFC + Cable Modem + Ethernet / ATM" approach.Central Office needs with a HFC Headend Equipment, by ATM or Fast Ethernet and Internet connectivity, and complete signal modulation and mixing functions.Data signals through the HFC network (HFC) transmitted to the user at home, Cable Modem signal the completion of decoding, demodulation and other functions, and digital signal through the Ethernet port to send to the PC.Conversely, Cable Modem PC, came to receive the uplink signal, encoded, modulated pass through HFC head-end equipment.

ADSL and Cable Modem networking are two techniques can provide a variety of business and can basically meet the needs of current broadband services.ADSL bandwidth is lower than in the Cable Modem, but the use of HFC Cable Modem and to network in stability, reliability, power supply and operation and maintenance systems are still some problems.In addition, because of its network line bandwidth is shared, in fact, after the user reaches a certain size can not provide broadband data services, users share the bandwidth is very limited.The following is the author's comparison of these two technologies.

• Security.As the Cable Modem signal of all users were carried out with a coaxial cable transmission, so there is the risk of wiretapping.Problem solving wiretapping to protect the cable first, followed by the lines to understand the process of establishing a good set initialization parameters, the latter point is technically difficult to resolve.The ADSL not have this problem.


• Reliability.As the CATV network is a tree, so very easy to create a single point of failure, such as damage to the cable, amplifier failure, transmitter failure will cause the node's customer service interruption.The ADSL uses a star network, a fault will only affect ADSL equipment to a user.


• Stability.Cable Modem users will be able to enjoy the early stage of very high quality service, this is because the small number of users under bandwidth and band lines are very abundant.However, each addition of Cable Modem users will increase noise, occupied channel, reduce the impact of circuit reliability and quality of service on the existing users.This will be the Cable Modem urgent need to address a major problem.ADSL access network is not affected by the number of users and traffic impact.Of course, if the DSLAM bandwidth of less than all of the export total bandwidth users may need, there will be congestion at peak times, but this time as long as the bandwidth by increasing exports can solve this problem.


• Compatibility.Although the Cable Modem and ADSL have been introduced technical norms and standards, but there are different manufacturers of the products can not be compatible to the market expanding so bring some difficulties.


• Network cost.Cost in the network, ADSL equipment cost is clearly higher than the Cable Modem, but the latter need to be able to apply after the completion of HFC transformation.At present, China can only satisfy the majority of HFC 450MHz band of frequencies, while the use of HFC two-way business at least 750MHz bandwidth.This obviously does not meet the requirements need to replace all the coaxial cable.At the same time, to achieve a two-way HFC cable television line to replace the current use of one-way amplifier, this part of the reconstruction cost is very high.