Common problems when constructing ADSL access network
Care should be taken when using ADSL to transmit broadband services over existing telephone cables. ADSL can only be used in areas where fiber access networks are not yet formed and cable transmission quality is better. ADSL is only a transitional measure in the early stage of broadband services. Once the penetration rate of broadband services exceeds 10%, ADSL is difficult to do. If the above-mentioned expensive transitional measures are widely applied, the opportunity to build a fiber optic network with a large bandwidth will inevitably be lost, and a new burden will be formed, resulting in a waste of investment.
The ADSL system has strict requirements on the wire pairs, and the transmission rate is very sensitive to the transmission distance, wire diameter, and copper wire quality. In the copper cable line constructed in the development peak of the previous years, a considerable number of line projects were built in a hurry. The plastic cable has not been checked for airtightness, and no inflation maintenance has been carried out. The cable joints are wet. The AC and DC performance indicators are low. In addition, due to the influence of factors such as echo noise and crosstalk between lines, currently only about 15% of the pairs of domestic local telephone cables can carry out ADSL services.
DSLAM configuration
According to factors such as user distribution map, number of users, cable layout, and coverage area, determine the DSLAM equipment configuration. In order to ensure the minimum bandwidth of users, the number of users at each DSLAM node should not be excessive. The construction of ADSL broadband access networks everywhere should be combined with the local urban fiber access network construction. In the initial stage of construction, based on the characteristics of ADSL technology and considering that there will not be too many user needs and users are widely distributed, DSLAM should be distributed in more offices, but the capacity of each node should not be too large for the time being; Before, DSLAM can be installed in the existing central office, using the existing local telephone cable. When the business develops to a certain extent, make the DSLAM as close to the user as possible in order to develop users and improve service quality.
Broadband access server configuration
In the ADSL network architecture, the setting of the broadband access server can be divided into three ways: centralized, distributed and centralized distributed.
Centralized is to set up a broadband access server at the exit of a city's ADSL broadband access network, which is responsible for aggregating the PPP connections of ADSL users in the entire city, providing information required for billing by time and traffic, and providing virtual dial-up users. Provide a dynamic IP address. The centralized type has the advantages of saving engineering investment and network operation costs, convenient management, and convenient business development. This method is suitable for small cities or medium-sized cities where the number of DSLAM nodes is small, broadband users are few, and the service volume is not large in the early stage of construction.
Centralized distribution is to set up several broadband access servers in a city, and each server is connected to multiple DSLAM nodes in the area, and the district handles the ADSL service connection, billing statistics, dynamic IP address allocation and other functions of the entire city. This method is suitable for large and medium cities with a large number of DSLAM nodes.
Distributed is to install a broadband access server at the access layer, complete the ADSL service connection, billing statistics, dynamic IP address allocation and other functions of the node at the DSLAM node. Because the broadband access server is more expensive, unless there are many broadband users and the business volume is large, considering the business volume and cost-effectiveness factors, it is generally not suitable.
ADSL network transmission mode
At present, there are two main network transmission modes of the ADSL system: Packet transmission mode and ATM transmission mode. Considering that the QoS mechanism of the ATM transmission mode can ensure the smooth development of large-capacity real-time video services, most traditional telecom equipment manufacturers still prefer to use ATM equipment in ATM transmission mode. In the ADSL system adopting the packet transmission mode, the uplink data interface of the DSLAM equipment at the central office and the user data interface of the RTU equipment at the customer premises are currently popular Ethernet interfaces; the format of the transmission data carried by the ADSL system can usually be based on the office premises. In response to changes in the functions of the user equipment, variable-length Layer 2 Ethernet frames or Layer 3 IP packets are used. In the ADSL system using the ATM transmission mode, the uplink data interface of the DSLAM equipment at the central office is usually a standard ATM interface, and can be connected to the ATM switch directly or through the local transmission network; the transmission data format carried by the ADSL system is ATM cells , And ATM25.6M interface or 10M Ethernet interface can usually be provided on the RTU equipment at the user end.
IP address planning
In the development of the Internet, due to the limitations of IPv4, IP addresses are very tight. Therefore, during the development of the ADSL broadband access network, you should apply for as many public IP addresses as possible. When planning a network, you should start applying for a public IP address. As for the applied IP addresses, it is necessary to plan public and private addresses within the entire network. The planning of IP addresses is critical to the scalability and stability of the network. When assigning IP addresses, class C addresses should be used as the allocation unit whenever possible.
User billing
At present, ADSL network billing generally adopts monthly billing, which is simple and reasonable in the initial stage of slow network deployment. However, as network bandwidth and users increase, this simple accounting The fee management model will bring many problems. First of all, this one-size-fits-all simple billing method cannot distinguish the actual usage of users. If users have very few network applications, but have to pay high fees, it will directly lead to user dissatisfaction, which will seriously affect the use of ADSL broadband access Enthusiasm; on the other hand, if users use a lot of network resources without restraint, it will indirectly cause losses to network service providers, and also lead to dissatisfaction of those network users with fewer network applications and normal network applications affected by it.
These problems can be effectively solved by adopting the method of charging by network. If users use more network resources, there will be more network traffic. Conversely, if they use less network, they will have less traffic. This billing method is more reasonable. The user can decide to pay the fee according to how much time the user has used the network. In addition, this billing method can also give network providers greater benefits and gain more revenue.
User Management
In terms of user management, it is mainly how to prevent user data from being stolen and traffic from being stolen.
Preventing the theft of user information is mainly to prevent the theft of users' addresses. Special attention should be paid to the circuit encapsulated by RFC1483 bridged protocol, because the encapsulation contains the hardware address in the AAL5 package, which usually requires IP address resolution. Therefore, it may cause serious security problems such as disguised addresses, denial of service attacks, and redirected traffic flow. This problem can be solved by secure ARP (AddressResoluTIonProtocol).
The realization of broadband access requirements is premised on the protection of narrow-band investments. The development of technology is often a leap forward process, and the growth of communication services shows a gradual and continuous development trend. The construction of communication networks should seek a future-oriented development path based on meeting the current needs of users. Therefore, the broadband construction of the network cannot be completed in one step, but on the basis of the existing narrow-band network, it is gradually evolving based on user needs. As a transitional solution, ADSL broadband access can basically meet the needs of current users in high-speed Internet access, LAN interconnection and IP-based broadband multimedia information services. At the same time, it has the characteristics of being able to deploy broadband networks faster. As long as we can grasp the construction strength of the ADSL broadband access network and pay attention to some problems in the construction, we can make full use of the existing copper cable resources of the telecommunications sector, reduce the unnecessary waste of copper cable user transformation, and meet the current business needs .
Prevent theft of traffic (ie prevent users from developing their own networks, but hide from the telecommunications department, and do not pay the corresponding network access fees), mainly to prevent users from using the Internet host device as a proxy server through ADSL, and then customers of the local area network The machine accesses external information resources through the proxy server. Under normal circumstances, users can PPPoE authentication and authorization through the broadband access server, and record the Internet time and traffic information, and find the user's abnormal conditions (such as long-time busy, large data traffic, etc.), accordingly, users can be conducted through Radius Charge by traffic, duration or prevent by restricting user access to the port.
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