Basic knowledge of Broadband Access Server

The broadband access server is also a very important part of the access network system. It may not matter if many people do not know the concept and basic knowledge about the access server. After reading this article, you must have gained a lot, I hope this article will teach you more things.

1: Network Location of the Broadband Access Server

It should be said that the launch of broadband access servers is largely due to the large-scale application of ADSL. We know that in the past, ADSL used to implement broadband access network services by creating a corresponding PVC connection for a service of each user, then, end these large numbers of PVC directly on the vro. As you can imagine, the problem is that the network structure is huge, the user connection is complex, and the actual maintenance is difficult. In addition, this access network structure is mainly based on the static IP access mode, which will cause low utilization of network IP addresses and difficult management. It is impossible to effectively implement centralized user authorization authentication and corresponding billing management. These problems will seriously restrict the large-scale commercialization of broadband access networks. In response to the technical characteristics and application requirements of broadband access networks and the role of narrowband dial-up access servers, broadband access servers have emerged, it becomes a network access device for the transition from a non-IP/IP Access Network to a backbone IP network, to achieve integration of network IP Access, the data access of the broadband IP/ATM network is mainly for xDSL/Cable Modem/Ethernet Access/wireless broadband data access, this solution brings together broadband users in terms of business, traffic, and management, and enables the user terminal to flexibly, autonomously, and conveniently select a service network through only one network connection, it adapts to the development trend of broadband access network applications and becomes an important network unit between the access layer and the backbone edge layer.

2: System Requirements for Broadband Access Servers

At present, the performance of the broadband network is obviously improved: in terms of access bandwidth, the dial-up access is being transferred to xDSL, hfc-or high-speed man access, and the access bandwidth has been expanded hundreds of thousands of times; in terms of processing performance, the powerful urban FR/ATM network or high-speed local area network gradually replaces a single PSTN network. In response, the performance and functions of the broadband access server must meet the following requirements:

1). Hardware design structure
Obviously, the broadband access server must have a high-speed and efficient packet forwarding feature to effectively solve the problems caused by high performance, high load, and high burst of broadband networks, broadband Access Servers with poor performance will inevitably become the "bottleneck" of the network ". At present, it has more than 2 GB of switching backplane capacity, and more than KPPS of independent packet forwarding performance has become the industry's basic requirements for broadband access servers. From the perspective of the hardware system structure, the Broadband Access Server has evolved from the inefficient centralized packet processing structure to the current distributed processing structure, and the front and back Plug board interface board and processing board have become the mainstream design ideas. Using this system structure, the processing module can directly process user traffic from the same slot interface module, in addition, the network traffic output on the same slot can be directly forwarded without going through the system backplane and the switching matrix module, thus effectively reducing the system load. On the other hand, in order to achieve packet forwarding between different slots, the system structure must provide a system switching matrix module with high capacity, relatively independent, and redundant backup capabilities. Switch Fabric) and backplane bus of the corresponding capacity to ensure that the overall performance of the Broadband Access Server increases linearly with the increase of the interface module.

2). Interface Type and access method
Obviously, to support various broadband access types, the broadband access server must provide as many interface types as possible. Now, on the user side, the broadband access server can provide the DS3, OC3, and OC12 ATM optical interfaces to achieve pure ATM access or DSLAMDSL user concentrator) access, provides a 100/1000 M fast Ethernet interface to connect LAN users and HFCs users, and provides a high-density channelized or non-channelized E1/T1/DS3 frame relay interface to achieve access to frame relay users; on the network side, traffic aggregation and forwarding are generally achieved through the 100/1000 M fast Ethernet interface, OC3/OC12 ATM interface, or even OC12 POS interface, meet the bandwidth requirements of broadband services.

Unlike narrowband dial-up servers, the access process of Broadband Access Servers relies on the underlying data link layer, mainly the ATM layer and Ethernet layer) to encapsulate and reorganize data packets. Taking advantage of the technical features of the underlying layer, not only is the access networking flexible, but also can effectively bind the technical advantages of ATM and Ethernet to ensure service quality. Specifically, through RFC1490 and RFC1483 layer-2 bridging technologies, RFC1577 layer-3 IP routing technology can achieve static IP Access for broadband users; through PPP Over ATM and PPP Over Ethernet, you can access users' Dynamic IP addresses. Through L2 VPN tunnel technology of L2TP, you can achieve VPN access requirements for enterprise users and small ISPs. From the current trend of application access, PPP access must be the mainstream application direction for broadband access. In PPP access technology, because PPPOE can be applied to multiple access networks, its applications are flexible, and it is easy to choose services. It also protects the existing investment of users, and its application prospects are the most promising. To sum up, the following lists the protocols and interface types currently supported by the Broadband Access Server:

3). Access quantity
Since the dial-up access server used TDM technology in the past, the system receives data from the PSTN network through each DS0 time slot. the maximum number of accesses to the system is the number of DS0 time slots that the system can terminate, that is, the maximum number of Modem that can be integrated by the system. To expand the number of system access, this time slot-based switching technology can only be achieved by expanding the system integration level to some extent, with considerable limitations. In a broadband network, the interface processing module directly encapsulates and restructured various protocol stacks, such as PPPOE or PPPOA calls. Because of the introduction of ASIC dedicated ic) technology, the system packet processing capability is significantly improved, and the length of access implementation is usually less than 5 seconds, including the radius Authentication time ); the reasonable cooperation of the processing modules of the system makes the system more stable and can well schedule and process the concurrent access of multiple users.

At present, a medium-scale broadband access server should support more than 8000 concurrent PPP including PPPOA and PPPOE calls, and a large broadband access server can achieve million calls. The bandwidth access server has such processing capabilities that can fully meet the needs of large-scale broadband access applications.

In short, broadband access servers are currently in the early stage of large-scale application. With the development of the broadband network, it has a very broad development prospect.

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