Introduction to two emerging broadband access technologies

Broadband access technology is still quite common, so I have studied the two new broadband access technologies that are currently emerging. I would like to share them with you here and hope they will be useful to you. In the past decade, two new modulation and demodulation technologies, Cable Modem and ADSL Asymmetric Digital user line, have emerged. Cable Modem implements data transmission up to 10 mbH/s on a hybrid optical fiber/coaxial network (HFCs), while ADSL Modem implements data transmission up to 6 Mbit/s on a twisted pair Cable, these two technologies have a broad market in Internet access networks, VOD, conference and television, distance learning, and other fields.

1. Comparison of Basic Technologies

The typical Cable Modem divides the spectrum of the transmission line into two sections, namely, the uplink channel of 5-50 MHz and the downstream channel above 50 MHz (outside the analog TV channel. Cable Modems is based on analog frequency division multiplexing technology. It integrates the application of analog and digital transmission technology, fiber-optic coaxial Cable technology and RF technology, therefore, analog TV signals and digital signals are transmitted simultaneously between 5-MHz, and 64QAM (orthogonal Amplitude Modulation) technology with commercial efficiency is used, the downstream channel speed can be up to 30 Mbit/d. The transmission rate of Cable Modem has nothing to do with the distance of transmission, but it is related to the noise of the optical fiber and the number of users of simultaneous broadband access technology.

ADSL divides the frequency spectrum of the transmission line into three sections, and transmits the ordinary telephone service (POTS) in the low frequency segment. The intermediate frequency band is the uplink digital channel, and the maximum transmission rate is 384 kbit/s; the rest are downstream digital channels that transmit 6 Mbit/s of digital information. ADSL uses two modulation schemes: CAP (no-carrier amplitude modulation) and DMT (discrete multi-tone modulation ). The CAP method is a two-dimensional transmission scheme similar to the QAM method, and DMT modulation is a form of multi-carrier modulation. DMT divides available bandwidth into N sub-channels. Based on the data transmission capability of sub-channels, the data is dynamically allocated to each sub-channel, greatly improving the bandwidth utilization and minimizing the error code and noise, this increases the system transmission capacity. In addition, ADSL uses the New Adaptive Filtering Technology, grid encoding, and the forward correction of intertwined methods to overcome Gaussian noise interference and increase the channel capacity, for the first time, the asymmetric echo cancellation technique (echo cancellation) was used to eliminate the echo. However, the transmission rate of ADSL is limited by the transmission distance. The long-distance transmission rate is no higher than 1.5 Mbit/s.

2. Basic Network Structure

2.1 Cable Modems System Structure
Cable Modem works on the HFCs network, while the HFCs network uses optical fiber cables for wire transmission, and the wiring and access lines make full use of the existing CATV Coaxial Cable networks to provide broadband access technology. Up to 100 broadband access technologies can be provided for each network line. Two-way amplifiers must be set on each line to support uplink channels. a Cable Modem must be installed on each client, install an IP router in the front-end device. It is worth noting that the coaxial cable network can be used as a data concentrator to avoid excessively concentrated use of the router. In some cases, high-speed buffers and proxy servers can be placed on front-end devices to ease data blocking. The broadband access technology of the hfcnetwork can be used to achieve the integration of the Telecom Network, CATV network and data network.

2.2 ADSL Network Structure
(L) SKIP (starter kit Internet platform) network structure 2, SKIP network structure is relatively simple, in each center set a router and a network switching device and ATU-C (ADSL Transceiver ), the network switching device sets the access line and enters the router for unified operations.

(2) network structure of the aim (asynchronous interface module. The ATM model installs an ATM switch in the local broadband access technology and transfer area and connects to the terminal access point through the transmission line DSI (or DS3, OC3). The terminal access point is connected to multiple independent ADSL users at the same time.

The common advantage of SKIP and AIM is that they can be designed on existing devices and can be developed and tested in a short period of time, while AIM is the first step in cross-to-full business network. SKIP is associated with AIM. The network switch of the SKIP network center is replaced by the Data concentrator and can be used as a terminal access point of AIM.

3. Performance Comparison between the two technologies

Multiple Cable Modem users share one communication line, which may cause serious leakage. Because ADSL is an end-to-end structure, it is extremely secure. However, password and authentication are very important to both systems, especially the Cable Modem system. If any line on the system is damaged, all the users on the road will be paralyzed, and there is no such problem for ADSL. As the architecture of the CATV is evolving, the CATV network uses a tree-like network topology to broadcast downstream TV signals at the lowest possible cost, the disadvantage is that the upstream bandwidth is much smaller than the downstream bandwidth. When the upstream channel is connected, the "funnel effect" of noise will seriously affect the quality of the uplink communication.

Relatively speaking, ADSL has higher security and reliability. ADSL is based on the existing telephone network. It does not require large-scale network transformation and will not affect the telephone business in the case of data service faults. Therefore, for commercial users, using the ADSL Broadband Access Technology is a relatively fast way, while the broadband access technology of the hfms is more suitable for domestic users.

With the opening of the telecom market and the emergence of new broadband services, building a full-fiber User Access Network FITL is an inevitable trend of the development of the communication network, but this requires a huge investment and a long construction period. Therefore, how to implement the "Last Mile" one-to-one broadband access technology of "information highway" is currently a hot topic. Currently, the ADSL technology and HFCs are ideal for sending users to the "Information Highway.

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