Test: 9 common Internet access methods

When it comes to access networks, we must first involve a bandwidth problem. With the continuous development and improvement of Internet technology, the bandwidth of access networks is divided into narrowband and broadband. Industry experts generally think that broadband access is the future direction of development.

The network structure of the broadband carrier is shown in 1. The entire city network consists of the core layer, convergence layer, edge convergence layer, and access layer. The access part from the Community end to the end user is usually the last kilometer, as shown in location 1 in the entire network.

In the access network, the following access methods are available: PSTN, ISDN, DDN, lan, ADSL, VDSL, cable-modem, pon, and lmds9. Each of them has its own advantages and disadvantages.

PSTN Dialing: the most widely used

PSTN (published Switched Telephone Network, public telephone exchange network) technology uses PSTN to implement user access through MODEM dialing. This access method is a very familiar access method. Currently, the maximum rate is 56 kbps, which has reached the channel capacity limit determined by Xiannong's theorem, this speed is far from enough to meet the transmission needs of broadband multimedia information. However, due to the popularity of telephone networks, user terminal equipment modem is very cheap, which is about 100 ~ An account can be opened between RMB 500 and no application is required. If you have a computer at home, you can directly access the Internet by connecting the telephone line to the modem. Therefore, PSTN dial-up access is relatively economical and is still the main means of network access.

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

 

ISDN dialing

ISDN (Integrated Service Digital Network) access technology is commonly known as "one-line communication". It uses digital transmission and digital exchange technology, integrates telephone, fax, Data, images, and other services into a unified digital network for transmission and processing. Using an ISDN User line, users can call and send and receive faxes while surfing the Internet, just like two telephone lines. The basic ISDN Rate Interface has two 64kbps information channels and a 16 kbps signaling channel, 2B + D for short. When a call is made, it automatically releases a B channel for telephone answering.

Just like using a modem for dial-up Internet access, you also need a dedicated terminal device for using ISDN, which is mainly composed of a network terminal nt1 and an ISDN adapter. The network terminal nt1 is as essential as a user access box on a cable TV. It provides interfaces and access methods for the ISDN adapter. The ISDN adapter and modem are also divided into two types: Internal and External. the built-in ones are generally called ISDN built-in cards or ISDN adapter cards. The external ISDN adapter is called Ta. The price of the ISDN built-in card is 300 ~ It is about 400 yuan, while Ta is about 1000 yuan.

Figure 3 shows the ISDN access technology. The user needs to apply for an account to access through ISDN dial-up. The initial installation fee varies depending on the region, and the cost generally ranges from several hundred to 1000 yuan. The maximum bandwidth of ISDN is 128 Kbps. Various test data shows that the speed of Dual-line access cannot be doubled. From the development trend, narrowband ISDN cannot meet the needs of high-quality broadband applications such as VOD.

Ddnleased line: for Group Enterprises

DDN is short for digital data network. It is a new type of network that rapidly develops with the development of data communication services. DDN's backbone network transmission media include optical fiber, digital microwave, satellite channels, and so on. Common cables and twisted pair wires are used on the user end. DDN combines digital communication technology, computer technology, optical fiber communication technology, and digital cross-connection technology to provide a high-speed and high-quality communication environment, A leased line lease circuit for point-to-point and point-to-point transparent data transmission is provided to transmit data, images, sounds, and other information to users. DDN communication rate can be at N × 64 Kbps (n = 1 ~ 32), of course, the faster the speed, the higher the rental fee.

You need to apply for an account to rent a DDN business. DDN charges can generally be based on monthly subscription and traffic calculation, which is different from the pay-as-you-go billing method for dial-up Internet access. The rental fee of DDN is expensive, and ordinary individual users cannot afford it. DDN is mainly for enterprises that need comprehensive use such as group companies. DDN charges vary according to different bandwidth rates. For example, if China Telecom applies for a 1000 kbps ddnleased line in the region, the monthly rental fee is about yuan. Therefore, it is not suitable for access by community residents and is only attractive to community commercial users.

ADSL: Personal Broadband popularity

Asyuncrical Digital Subscriber Line (Asymmetric Digital user loop) is a technology that provides broadband data services through common telephone lines. It is also a promising access technology. ADSL is well known as "network express" and is favored by many users due to its high downlink rate, high bandwidth, excellent performance, convenient installation, and no need to pay telephone bills, it has become another new and efficient access method after modem and ISDN.

Figure 4 of ADSL access technology. The biggest feature of the ADSL solution is that there is no need to transform the signal transmission line. You can use a common copper telephone line as the transmission medium and use a dedicated modem to achieve high-speed data transmission. ADSL supports the uplink speed of kbps ~ 1 Mbps, downlink speed 1 Mbps ~ 8 Mbps, with a valid transmission distance of 3 ~ Within 5 kilometers. In the ADSL access scheme, each user has a separate line connected to the ADSL local terminal. Its structure can be viewed as a star structure, and the data transmission bandwidth is exclusive to each user.

VDSL: higher-speed broadband access

VDSL is faster than ADSL. With VDSL, the maximum downloading rate within a short distance can reach 55 Mbps, And the upload speed can reach 2.3 Mbps (19.2 Mbps or higher in the future ). VDSL uses a pair of copper wires, with a valid transmission distance of more than 1000 meters. However, the VDSL technology is still in its infancy, long-distance applications still need to be tested, and the popularization of endpoint devices also takes time.

At present, there is a VDSL Based on Ethernet, the access technology uses the QAM modulation method, its transmission medium is also a pair of copper lines, within the range of 1.5 kilometers can achieve bidirectional symmetric 10 Mbps transmission, that is, the Ethernet speed is reached. If this technology is used to access the broadband operator community, the cost can be greatly reduced. The Ethernet-based VDSL access method is shown in Figure 5. The solution is to add a VDSL switch to the data center and place the CPE on the user end. The two are connected by five types of cables outdoors, with only one CPE in each building, the indoor part adopts the Integrated Wiring Scheme shown in figure 6. The reason for doing so is: in the past two years, the Internet access rate of Community users is low, generally between 5% and ~ About 10%. This solution is used to save access devices and improve port utilization.

We calculated the cost of Community Construction Using VDSL and LAN technologies respectively, and found that for a community of 1000 users, if the Internet access rate is 8%, the VDSL solution saves about 50 thousand yuan of investment compared with the LAN Solution. Although the VDSL solution adds VDSL clients and local devices, it saves the photovoltaic module and replaces the optical cable with an outdoor twisted pair cable, thus reducing the construction cost.

In addition, cable-modem technology is mainly used when the original cable TV line of the Radio and Television Department is transformed. This solution is meaningless compared with the community construction cost of emerging broadband operators.

Passive Optical Network Access: Optical Fiber entry

Pon (Passive Optical Network) is a point-to-multiple-point Optical Fiber Transmission and access technology. downlink broadcast and uplink time-division multiplexing are used, A tree, Star, bus, and other topology structures can be flexibly formed. You only need to install a simple optical splitter when you do not need a node device at the optical pivot, it has the advantages of saving optical fiber resources, sharing bandwidth resources, saving investment in data centers, high equipment security, fast network construction, and low overall network construction costs.

 

Pon includes ATM-PON (APON) and Ethernet-pon (EPON. APON technology has developed early, it also has the unique characteristics of integrated service access, QoS service quality assurance, ITU-T g.983 suggests to standardize the ATM-PON network structure, basic composition and physical layer interface, the Ministry of Information Industry of China has also formulated sound APON technical standards.

Pon access devices are mainly composed of OLT, ont, and ONU. The OLT optical signals are divided into the ONU of the tree network by the passive optical splitter. One OLT can be connected to 32 ont or ONU, one ont can connect to 8 users, and The ONU can connect to 32 users. Therefore, an OLT can load up to 1024 users. The PON technology uses a single-core optical fiber for transmission. The maximum distance from the local terminal to the user side is 20 kilometers. The total transmission capacity of the Access System is 155 Mbps for both the uplink and downlink, the bandwidth used by each user can be flexibly divided from 64 Kbps to 155mbps. The user connected to an OLT shares the bandwidth of 155mbps. For example, the Fujitsu EPON product OLT device has a550, The ont device has a501, And the a550 device has up to 12 Pon ports, and each Pon downstream route to each a501 is mbps; the a501 uplink bandwidth connected to each Pon port is shared. The PON access technology is shown in figure 7.

We calculated the cost of Community investment using EPON and LAN respectively, and found that for a community of 1000 users, if the Internet access rate is 8%, the use of the EPON solution has no advantages over the LAN Solution (the indoor wiring is optimized), but it will save maintenance costs in the future. However, there is a large gap in the construction cost between the two LAN schemes that adopt optimization and those that do not adopt optimization. The reason for this gap is that the optimization solution saves the indoor cabling materials and reduces the construction cost. In addition, the port utilization rate of the switch is greatly increased due to the centralized management, this reduces the number of corridor switches and the investment in equipment.

LMDS access: Wireless Communication

This is currently a wireless access technology that can be used for community broadband access. See figure 8.

In this access mode, a base station can cover a region of 20 kilometers in diameter. Each base station can load 24 thousand users, and the bandwidth of each end user can reach 25 Mbps. However, the total bandwidth is 600 Mbps, and users under each base station share the bandwidth. Therefore, if a base station has a large number of users, the bandwidth allocated to each user is very small. Therefore, this technology is not suitable for the access of Community users, but its client devices can be bundled together and used for the interconnection of man networks of broadband operators. The specific practice is to create a base station in the data center of the aggregation point, and the Community data center around the aggregation data center can be used as the user end of the base station. If the Community data center is bound with four users, the bandwidth of the aggregation and Community data centers can reach 100 Mbps.

The advantage of using this solution is that it can enable the established broadband community to quickly activate operations and shorten the construction cycle. However, currently, products using this technology have not yet formed a commodity market in China and cannot be evaluated for costs.

Lan: low cost for mature technologies

LAN access uses Ethernet technology and optical fiber cables and twisted pair wires to perform integrated wiring for the community. The specific implementation scheme is: laying optical cables from the Community machine room to the residential unit building, and laying cables in the building using five twisted pair wires to the user's home. The total length of twisted pair wires is generally no more than 100 meters, the user's home computer can access the Internet through the five modules on the wall through the five jumpers. The egress of the Community data center is connected to the man through optical cables or other media. Figure 9 shows LAN access.

LAN access can take full advantage of the resources of the residential area network to provide residents with a shared bandwidth of more than 10 MB, which is more than 180 times faster than dial-up, and can be upgraded to m or above according to the user's needs.

Mature Ethernet technology, low cost, simple structure, stability, and good scalability; easy to upgrade the network, at the same time, real-time monitoring, intelligent property management, residential/building/home security, Home Automation (such as remote control appliances, visual doorbell, etc.), remote meter reading, etc, it provides an intelligent and information-based office and home environment to meet the needs of people at different levels of information technology. According to statistics, the community uses Ethernet Access, and each household's line cost can be controlled at 200 ~ For users, the account opening fee is between 300 yuan, and the monthly Internet access fee is between 500 and 100 ~ 150 yuan, which is much more economical than other network access methods.