Comprehensive Analysis of Broadband Access Server Expansion

Broadband Access Servers are still quite common. So I have studied the questions about the expansion of broadband access servers. I would like to share them with you here, hoping they will be useful to you. In the planning process, the laying of optical cables should be conducted in one step. The selection of broadband network structure should be based on the characteristics of Broadband Access Point Distribution, routing and business requirements, comprehensive consideration, appropriate selection. It is necessary to fully consider the economic and technical nature of the network, as well as the development needs, as well as the narrow band requirements for broadband access servers and the flexibility of network operation and allocation, such as resizing, scheduling, and emergency response. The following two schemes are mainly used to describe the network structure of the broadband access network.

1. Star Mode

The master node is connected to the master node by a star node to form an active star or double star network structure. The advantage of this structure is that the structure is simple, easy to plan, and the investment of optical fiber cables is relatively small. The disadvantage is that many pipe holes are occupied, and each user uses a single route, resulting in poor security and reliability. It is an effective method for areas with sparse user density and recent changes that are far away from the local government.

2. Combination of ring and bus

The parent Bureau's receiving node adopts the two-way fiber loading method from the current node. The receiving ring consists of a large number of core trunk optical cables, and the ring optical cables adopt the non-decreasing method, generally, 4 ~ Six connection nodes. The gateway node uses a star-to-point connection to the corridor switch. The main advantage of this structure is that the convergence Ring Optical Cable occupies less pipe holes, the core usage is high, easy to schedule, and high security.

For other important connection nodes on the bus between parent and local communications nodes, to ensure the security of a single physical route, each optical node can be routed to two parent bureaus to form a two-way access method for this node. When one of the parent board's junction nodes fails, you can use the other parent board's junction node to clear the connection, increasing the reliability of the access service. At the same time, when the user's optical cable is surplus, it can be used as an inter-office relay. However, this method increases the load on the sink node device and makes the network structure complex, so it is not suitable to be used in large quantities. The comprehensive access method of the ring network has a series of detailed requirements on the network structure and laying of optical cables. The requirements for the number of main nodes in the self-healing Ring Network are 4 ~ 8 is recommended.

(1) It is mainly related to the optical transmission capacity. Taking UT Starcom's OMUX-400 as an example, in the self-healing Ring Network, the node of the Exchange Board or near the Exchange Board is set as the local endpoint COT ), the other nodes are set to the remote terminal RT), assuming that the local terminal COT in Figure 1) the node transmission system is 32 2 Mbit/s systems, and B, C, D, and E Remote RT) considering that the upstream and downstream traffic of a node are the same, the transmission system of each node is set to eight 2 Mbit/s systems. If the number of RT nodes increases, the number of transmission systems within the node will decrease, it cannot meet the business needs of the upstream and offline nodes.

2) It is related to the performance of optical transmission equipment for monitoring, switching, data services ,?? The increase in the number will undoubtedly complicate the control information and lead to a decline in transmission capacity and an increase in switching latency.

3) Optical Fiber Self-healing and environmental protection the loop formed by all fiber breaks between the two nodes in the loop. Its reliability is similar to the 1: N which is often used in the device segment. N here is the number of nodes ), that is, when the optical fiber between multiple nodes is interrupted, only one of them can be protected. If the number of points in the self-healing link increases, the protection reliability of the Self-healing Ring decreases. In addition, a ring-shaped network must have at least three nodes. Therefore, it is recommended that the minimum number of nodes be four.

In addition, it should be noted that the number of auxiliary optical fiber devices does not affect the capacity of transmission equipment: the capacity of each access point is only related to the performance of the equipment, for example, when an optical terminal outputs four E3 data streams, in actual work, some people understand that the larger the number of Optical Fiber entries into the access network, the larger the transmission capacity. This is incorrect.

Expansion of Broadband Access Server

The broadband access server is positioned at the edge of the backbone network. It mainly realizes the business convergence and traffic convergence of various access users, and highlights the access processing capabilities, it is obviously unrealistic to expect the Broadband Access Server to undertake various network functions. Therefore, to meet the current needs and application trends of broadband access, you can expand the function of broadband access servers to achieve more efficient broadband access.

1. Business Selection

The purpose of service selection is to achieve the user's Independent Selection of various services provided by the background network operator through a connection to the Broadband Access Server. On the one hand, the specific implementation of various services has different technical focuses and different network performance requirements. In this way, a proper business model is allocated on the Broadband Access Server to enable the system and its network resources to be bundled in a reasonable and orderly manner based on the characteristics of various businesses, so as to better implement various businesses with limited resources. On the other hand, from the perspective of the future development of network applications, the separation of the Network Content Service Provider ICP and the network access provider ISP is an inevitable trend.

2. VPN Virtual Private Network) Implementation

Virtual Private Network (VPC) is implemented on the public network platform for secure and efficient transmission, so that the network has good scalability and scalability. The core of VPN technology is data packet encryption and network transmission. IETF has developed some VPN Technical standards, such as L2 L2TP tunnel technology and L3 IP Sec encryption technology. The promulgation of these two technical standards laid a solid foundation for VPN applications. From the perspective of actual VPN applications, Most VPN services are implemented on the edge of the network, which is transparent to backbone network devices. As the role of network access and business convergence, the Broadband Access Server is often the initial initiator of a VPN application, which is crucial to the implementation of the VPN application. At present, in the VPN implementation of the second layer of the network, the Broadband Access Server provides L2TP tunnel encryption technology. Generally, it can be used as LACL2TP Access Concentrator or LNSL2TP network server) and flexible networking applications. In the VPN implementation on the third layer of the network, IP Sec is a newer protocol standard, so the implementation of this VPN is not popular yet. Currently, only some broadband access servers have begun to support this function.

3. Support for Multicast

From the perspective of the entire network, the broadband access server must support multicast to distribute the end Of the multicast video stream at the network layer. The network host installs the corresponding multicast application to support the multicast protocol. By actively submitting a multicast application, select the desired multicast service, connect it to a local vro or multicast server that supports IGMP. From the perspective of technical implementation and the current support for multicast by actual devices, the Broadband Access Server forwards multicast traffic between network terminals and multicast servers or routers that support IGMP. Generally, the first and second versions of the IGMP protocol are supported. However, to a large extent, they only play the role of IGMP Proxy) or IGMP spoofing Snooping, it is easy to transparently transfer and distribute multicast packets at the end of the network. End users do not feel the difference with the actual application.

4. IP traffic forwarding management and firewall functions

The IP traffic forwarding management of the Broadband Access Server is to provide corresponding access capabilities to users based on the actual permissions of different users, to a certain extent to complete the IP firewall function, to achieve internal network security. To a large extent, IP traffic forwarding management is bound with the VPN and Service Selection of the Broadband Access Server, and works with the upper-layer backbone edge router, flexibly and effectively implement IP separation for various business types. In terms of technology implementation, this function can Filter IP filters through its own IP packets), and flexibly allocate IP address segments and network-side NAT Network Address Translation for different services. At the same time, from the perspective of network security, broadband access servers should also provide protection against IP attacks and IP spoofing.

For IP address filtering technology, the system specifies the corresponding IP address filtering policy based on the selected service type while completing user access, and filters data packets of Layer 3 and Layer 4 to users with different permissions. This not only achieves the business needs, but also can effectively restrict the user's access permissions, to achieve the bundling with the corresponding business. The implementation of this function is independently implemented by the Broadband Access Server and does not require the cooperation of upper-layer routers.

For the allocation of IP addresses connected to users, the Broadband Access Server works with the backend RADIUS server, and the backend RADIUS server, it can even be attached to a DHCP server on the access server ?? To control IP traffic forwarding, you can set different routing forwarding policies for different IP address segments on the Broadband Access Server; on the other hand, the upper-layer router can filter or select routes for different IP sources and destination addresses through IP packet resolution to limit the access capabilities of different users. With the introduction of NAT technology, on the one hand, it can make full use of private network addresses to relieve the pressure on public network IP address resources. On the other hand, NAT achieves internal network security through one-way forwarding of IP traffic.

Networking applications of Broadband Access Servers

The broadband access server is mainly used to meet the current requirements of various DSL access applications, especially the application requirements of ADSL access. Currently, ADSL access is based on the ATM network platform, and is an ATM. However, the current network architecture is mostly pure IP and large. At the same time, the debate on ATM technology remains the focus of discussion in the industry. The further expansion of the ATM network is difficult, and it is of practical significance to achieve the requirement of ADSL direct IP Access. On the other hand, with the increasing integration of access devices on the Access side, a connected network unit, such as DSLAM, can often be connected to hundreds of users. For such a network distribution and so many single-point connected users, it is also an ideal choice to switch the Broadband Access Server from centralized access to decentralized access. It can even be directly integrated with edge access devices on the Access side to integrate IP addresses directly connected to the network. This networking scheme is not only conducive to simplifying the Broadband Access Server's own equipment, but also easy to implement user QoS, and directly aggregates the accessed user data IP into the edge router, it is easy to integrate with existing IP networks and saves network transmission devices and channels on the network access side and edge side. It should be said that such Broadband Access Servers are cheap and easy to design, and are often bundled for direct use as part of the access device. However, the function is relatively simple, and the network scalability and scalability are poor. Using this networking solution is feasible for accessing a single network with a single business, but it cannot be used for complex business networks. From the current actual business orientation, high-speed Internet access has become the mainstream service for broadband access networks, with a single business type and few additional services, in this situation, decentralized access has some advantages.

From the perspective of the whole network, the broadband access server is not only a single aggregation point for the whole network access service, but also a unified forwarding point for the user's business traffic. In this special network point, if it can implement joint networking applications with other dedicated network devices, it can greatly improve the overall network performance and the actual access speed of users. As you can imagine, for Internet services, the Broadband Access Server is directly attached to a dedicated Cache and a layer-4 switch. In this way, information frequently accessed by users can be obtained directly from the dedicated Cache through layer-4 switch filtering, thus bypassing a large number of user data streams, it reduces many repetitive and unnecessary network traffic, greatly reduces the backbone network load, improves the network utilization, and has high application value. The performance improvement of the Broadband Access Server focuses on the access processing capability, switching capacity, and interface bandwidth and density. The system performance requirements for the next generation of large Broadband Access Servers are as follows:

① The switching capacity should be at least 40 GB;
② The number of PPP calls supported at the same time reaches 20 k;
③ The number of configurable users reaches 100 k;
④ The forwarding capability of an independent package is greater than 1 Mbit/s.

The Development Trend of IP addresses indicates that the introduction of Multi-Protocol Label Switching MPLS can smoothly upgrade the network, making it easy to implement IP service quality assurance and VPN applications. These applications have incomparable advantages over other technologies. MPLS has become the industry's consensus on the development direction of next-generation IP addresses, and support for broadband access servers is an inevitable choice.