Three access methods for Ethernet?

In the access network, currently available access methods are mainly PSTN, ISDN, DDN, LAN, ADSL, VDSL, Cable-Modem, PON and LMDS 9, they have their own advantages and disadvantages.

PSTN dial-up: the most widely used

PSTN (Published Switched Telephone Network, Public Switched Telephone Network) technology is the use of PSTN through the modem dialing to achieve user access. This access method is very familiar with a way of access, the current highest rate of 56kbps, has reached the channel capacity limit determined by the Xiannong theorem, this rate is far from being able to meet the broadband multimedia information transmission requirements; but because the telephone network is very popular, the user terminal equipment Modem is very inexpensive, about 100 to 500 yuan, and do not need to apply for an account, as long as the home computer, the telephone line, the telephone line, the telephone line, the telephone line, the telephone line, the telephone line, the telephone line, the telephone line, the telephone line and the telephone line. As long as there is a computer at home, the telephone line into the Modem can directly access the Internet. Therefore, the PSTN dial-up access method is more economical, and is still the main means of network access.

PSTN access method shown in Figure 2. With the development and popularization of broadband, this access method will be eliminated.

ISDN dial-up: talk to the Internet both

ISDN (Integrated Service Digital Network, Integrated Service Digital Network) access technology is commonly known as "one line", which uses digital transmission and digital switching technology, telephone, fax, data, images, and other services. It uses digital transmission and digital switching technology to integrate telephone, fax, data, image and other services into a unified digital network for transmission and processing. Users use an ISDN subscriber line, you can dial a phone, send and receive faxes while surfing the Internet, like two telephone lines. ISDN basic rate interface has two 64kbps information path and a 16kbps signaling path, referred to as the 2B + D, when a phone call is dialed in, it will automatically release a B channel to answer the call.

Just like ordinary dial-up Internet access to use Modem, the user to use ISDN also need special terminal equipment, mainly by the network terminal NT1 and ISDN adapter composition. The network terminal NT1 is as essential as the subscriber access box on the cable TV, which provides interfaces and access methods for ISDN adapters. ISDN adapters are divided into two categories, built-in and external, just like Modem, and the built-in ones are generally called ISDN built-in cards or ISDN adapters, while the external ISDN adapters are called TA. ISDN built-in cards are priced at 300-400 RMB, while TAs are priced at 1000 RMB. around, while the TA is around 1,000 dollars.

The ISDN access technology is shown in Figure 3. Users using ISDN dial-up access need to apply for an account, the initial installation fee will be different depending on the region, the general overhead ranging from a few hundred to 1,000 yuan. ISDN's limit bandwidth of 128kbps, a variety of test data show that the speed of dual-line Internet access can not be doubled from the point of view of the development trend, the narrow-band IS DN can not meet the high quality of the VOD and other broadband applications.

DDN Private Line: For Group Enterprises

DDN is the abbreviation of Digital Data Network, which is a new type of network developed rapidly with the development of data communication business. the backbone of the DDN transmission medium has optical fiber, digital microwave, satellite channels, etc., and the user side of the ordinary cables and twisted-pair wires. DDN combines digital communication technology, computer technology, fiber-optic communication technology and digital cross-connection technology organically to provide a high-speed, high-quality communication environment, which can provide users with point-to-point, point-to-multipoint transparent transmission of data leased line circuits for the transmission of data, images, sound and other information for the user.DDN communication rate can be selected according to the user's needs in the N × 64kbps (N = 1 to 32) between The faster the speed, the higher the rental cost.

Users need to apply for an account to rent DDN services. DDN charges can generally be monthly and traffic system, which is different from the general users of dial-up Internet access billing on time. For example, if China Telecom applies for a 128kbps DDN line in the district, the monthly rental fee is about 1000 RMB. Therefore, it is not suitable for community residential access, and is only attractive to commercial users in the community.

ADSL: The Personal Broadband Trend

ADSL (Asymmetrical Digital Subscriber Line) is a technology that provides broadband data services over ordinary telephone lines, and is a promising access technology. ADSL is known as the "network express" reputation, because of its high downlink rate, wide bandwidth, excellent performance, easy to install, do not need to pay the phone bill and other characteristics by the majority of users, and has become the Mod em, ISDN after a new and efficient way of access.

ADSL access technology schematic shown in Figure 4. ADSL program's most important feature is that there is no need to transform the signal transmission line, you can use ordinary copper telephone line as a transmission medium, with a dedicated Modem can realize high-speed data transmission. ADSL support uplink rate of 640kbps ~ 1Mbps, downlink rate of 1Mbps ~ 8Mb ps, the effective transmission distance of 3 ~ 5Mbps. ADSL supports uplink rate of 640kbps to 1Mbps and downlink rate of 1Mbps to 8Mb ps. In the ADSL access program, each user has a separate line connected to the ADSL bureau, and its structure can be regarded as a star structure, and the data transmission bandwidth is exclusively shared by each user.

VDSL: Higher Speed Broadband Access

VDSL is even faster than ADSL. With VDSL, the maximum downlink rate over a short distance can be up to 55 Mbps, and the uplink rate can be up to 2.3 Mbps (and in the future up to 19.2 Mbps, or even higher.) VDSL uses a pair of copper wires, and the effective transmission distance can be more than 1,000 meters. However, VDSL technology is still in the early stages of development, and long-distance applications still need to be tested, and the popularization of endpoint devices will take time.

Currently, there is an Ethernet-based VDSL that uses QAM modulation for access, and its transmission medium is also a pair of copper wires, which can achieve a symmetrical bidirectional 10Mbps transmission within 1.5 kilometers, i.e., at the rate of Ethernet. If this technology is used for access to broadband carrier communities, it can significantly reduce costs. The Ethernet-based VDSL access method is shown in Figure 5. The solution is to add VDSL switches at the server room end and place CPEs at the user end, which are connected by outdoor Category 5 cables, and only one CPE is placed in each building, while the indoor portion adopts a comprehensive cabling scheme as shown in Figure 6. The reason for this is: the last two years of broadband construction traction in the community user Internet access rate is low, generally in the 5% to 10% or so, in order to save access equipment and improve port utilization, so the use of this program.

We have measured the cost of community construction using VDSL technology and LAN technology, and found that for a 1,000-home community, if the Internet access rate is 8%, the use of VDSL solutions than the LAN solution to save 50,000 yuan of investment. Although the VDSL solution appears to increase the VDSL client and local equipment, it reduces construction costs by eliminating the need for fiber-optic modules and replacing fiber-optic cables with outdoor twisted-pair cables compared to the LAN solution.

Cable-modem: for cable networks

Cable-Modem (cable modem) is an ultra-high-speed Modem that has been tried and tested in the last two years, which utilizes the existing cable television (CATV) network for data transmission, and is a relatively mature technology. With the development and growth of CATV networks and the continuous improvement of people's quality of life, the use of Cable Modem to access the Internet through the CATV network has become a high-speed access method of increasing concern in the industry.

Because the cable network uses analog transmission protocols, the network needs to use a Modem to assist in the completion of the conversion of digital data. Cable-Modem and the previous Modem in principle are the data modulation in the Cable (cable) in a range of frequencies to transmit the reception of the demodulation, the transmission mechanism and the same as ordinary Modem, the difference is that it is through the cable TV (cable) in a frequency range of transmission. The difference lies in the fact that it is modulated and demodulated through one of the CATV transmission bands.

Cable Modem connection can be divided into two types: symmetrical rate type and asymmetrical rate type. The former has the same Data Upload rate and Data Download rate, both between 500kbps and 2Mbps; the latter has a Data Upload rate between 500kbps and 10Mbps, and a Data Download rate between 2Mbps and 40Mbps.

Using Cable-Modem The disadvantage of Internet access is that Cable Modem mode is a relatively backward bus-type network structure, which means that network users **** the same share of the limited bandwidth; in addition, the purchase of Cable-Modem and the initial installation fee is not very cheap, which hindered the popularity of Cable-Modem access in the country. However, its market potential is very large, after all, China's CATV network has become the world's largest cable TV network, its users have reached more than 80 million.

In addition, Cable-Modem technology is mainly used in the radio and television departments of the original cable TV lines on the renovation, such a program and the emerging broadband operators in the community to build a cost comparison does not make sense.

Passive optical network access: fiber to the home

PON (Passive Optical Network) technology is a point-to-multipoint fiber optic transmission and access technology, downstream broadcasting, upstream time division multiple access, can be flexibly composed of tree, star, bus and other topologies, in the light of the branch point does not require node equipment, only need to install a simple optical branching can be, with It has the advantages of saving fiber optic cable resources, bandwidth resources***, saving investment in equipment room, high security of equipment, fast network construction, and low cost of comprehensive network construction.

PON including ATM-PON (APON, that is, ATM-based passive optical network) and Ethernet-PON (EPON, that is, Ethernet-based passive optical network) two kinds of. APON technology developed earlier, it also has a comprehensive service access, QoS quality of service assurance and other unique features, ITU-T's G.983 recommendations regulate the network structure of ATM-PON. G.983 recommendation of ITU-T standardizes the network structure, basic composition and physical layer interface of ATM-PON, and China's Ministry of Information Industry has also formulated a perfect APON technical standards.

PON access equipment mainly consists of OLT, ONT, ONU, by passive optical splitting device will be OLT optical signals to the tree network of each ONU. an OLT can be connected to 32 ONT or ONU, an ONT can be connected to 8 subscribers, while the ONU can be connected to 32 subscribers, so that an OLT can be loaded with a maximum of 1024 subscribers. PO N technology of the The transmission medium of PO N technology adopts single-core optical fiber, and the maximum distance from the local office to the user end is 20 kilometers, and the total transmission capacity of the access system is 155 Mbps for uplink and downlink, and the bandwidth used by each user can be flexibly divided from 64 kbps to 155 Mbps, and the users connected to an OLT*** enjoy the bandwidth of 155 Mbps. For example, Fujitsu EPON product OLT equipment has A550, ONT equipment has A501, A550 maximum of 12 PON ports, each PON downstream to each A501 is 100Mbps bandwidth; and each PON port connected to the upstream bandwidth of the A501 is *** enjoy the PON access technology shown in Figure 7.

We have measured the community cost of using EPON technology and LAN technology, and found that for a community of 1,000 households, if the Internet access rate of 8%, the use of EPON solutions compared to LAN solutions (indoor cabling is optimized) in the cost advantage, but in the future maintenance will save maintenance costs. The difference in construction cost between the two LAN solutions with optimized indoor cabling and without optimization is large. The reason for this gap is: the optimized solution saves materials for indoor cabling, and the relative construction cost is also reduced. In addition, due to centralized management, the port utilization of switches is greatly increased, thus reducing the number of switches in the building, and accordingly reducing the investment in equipment.

LMDS access: wireless communication

This is a wireless access technology that can be used for community broadband access, and its schematic diagram is shown in Figure 8.

In this access method, a base station can cover an area with a diameter of 20 kilometers, and each base station can be loaded with 24,000 users, and the bandwidth of each end-user can be up to 25 Mbps.

However, the total bandwidth capacity is 600 Mbps. However, it has a total bandwidth capacity of 600Mbps, and the users under each base station*** enjoy the bandwidth, so if a base station loads more users, the bandwidth allocated to each user will be very small. Therefore, this technology is not suitable for community access, but it can be used for broadband operator's MAN interconnection by bundling the user side equipment together. The specific approach is: to build a base station at the aggregation point room, and the community room around the aggregation room can be used as the user side of the base station, the community room, if bundled with four user side, the aggregation room and the community room's bandwidth can be up to 100Mbps.

The advantage of adopting this program is that it can make the built broadband community quickly open operation, shorten the construction cycle. However, products using this technology are not yet available in China as a commodity market for cost evaluation.

LAN: Mature technology and low cost

LAN access is the use of Ethernet technology, the use of fiber optic cable + twisted pair of wires to the community for integrated cabling. Specific implementation plan is: from the community room laying fiber-optic cable to the residents of the unit building, building wiring using Category 5 twisted-pair cable laid to the user's home, twisted-pair cable length is generally no more than 100 meters, the user's computer at home through the Category 5 jumper access to the wall of the Category 5 module can be realized on the Internet. The exit of the community room is through the fiber optic cable or other media access to the metropolitan area network. LAN mode access schematic shown in Figure 9.

Using LAN access can take full advantage of the resources of the community LAN, providing residents with more than 10M **** enjoy bandwidth, which is more than 180 times faster than the current dial-up speed, and can be upgraded to more than 100M according to the user's needs.

Ethernet technology is mature, low-cost, simple structure, stability, scalability; easy to upgrade the network, and at the same time can realize real-time monitoring, intelligent property management, community/building/family security, home automation (such as remote control of home appliances, visual doorbells, etc.), remote meter reading, etc., which can provide intelligent, information-based office and home environment to meet the needs of people at different levels of information technology. Demand for informationization. According to statistics, the community using Ethernet access, the line cost per household can be controlled between 200 to 300 yuan; and for the user, the account opening fee of 500 yuan, the monthly Internet access fee of 100 to 150 yuan, which is much more economical than other ways of accessing the network.