What is a Multilink Bundle?

Access server (Access Server) is also called network access server NAS or remote access server RAS, it is a kind of remote access equipment located between public telephone network (PSTN / ISDN) and IP network.

Access server (Access Server) is also called network access server NAS or remote access server RAS, it is a kind of remote access equipment located between public telephone network (PSTN / ISDN) and IP network.

Chinese name

Access server

Foreign name

Access Server

Also known as

Network access server

Belong to

Remote access access device

Access server background

Users can dial up to the access server through the public telephone network to access the IP network, to achieve remote access to the Internet, dial-up virtual private network (VPDN), construction of corporate intranet and other network applications. The access server can process the authentication, authorization and accounting (AAA) and tunnel IP packets sent to the ISP router. It can form an ISP local service site with the Web server, AAA server, DNS server, router and related supporting equipment. Generally, ports below 60 (including 60) are small access servers, ports 60 to 480 are medium access servers, ports 480 to 2880 are large access servers, and ports above 2880 are very large access servers.

Access server features and applications

1.Internet access service

Dial-up access is currently the most widely used way to access the Internet. The existing MODEM function enables users to both receive calls from third parties during online browsing and maintain the connection relationship with the central office modem. The ISDN basic rate interface BRI users use the 2B + D channel, that is, the maximum access rate reaches 128kbit / s to access the Internet. Compared with analog users, dialing MODEM to access the Internet has many advantages in all aspects, including a faster connection speed of 1s, which is stable. The relatively high-speed access rate, rich supplementary services, etc. Enterprise users can access the Internet through telephone lines or dedicated lines through the intranet. It is an important application supported by the access server. It provides interfaces including V.35 recommendations for connecting Frame Relay and dedicated line interfaces.

2. Support multi-link bundling

Multilink PPP is used to bundle multiple physical links in PPP to improve and use higher bandwidth. Multilink PPP is a protocol that divides, sequentially transmits, and reassembles PPP packets for multiple links that exist between two systems. MP bundling in the access server includes multiple bundling of two Bs and bundling of two modems, as well as bundling of one B and one modem. The access server can support analog-analog link bundling, analog-digital link bundling, digital-digital link bundling, and ISDN 30B + D link bundling.

3. Provide E1 interface

Supports various inter-office relay signaling such as China No.1, No.7 signaling (including TUP, ISUP signaling), ISDN PRI signaling, etc. No.7 signaling is one of the basic requirements of the current access server function. The access server can be connected to the telecommunication network through the inter-office PCM transmission system of the telecommunication office using a signaling relay. Because No.7 signaling management PCM transmission system supports data service transmission, it greatly supports the data exchange between the user's PC and the Internet.

4. Relay grouping function

The trunking function refers to the ability of the access server to process different called numbers (corresponding to different ISPs) from the same trunk group. The trunking group is applicable to the case where multiple ISPs share the same access server. Called number identification, different IP address allocation, and different access authentication system directions. The access server can support multiple access numbers in the same trunk group, and PSTN and ISDN users can access in the same trunk group, and the access numbers are the same.

5.Firewall function

The firewall function of the access server can be provided in two ways: IP Filter and IP Pool. The IP Filter method is an access server that provides IP packet filtering functions. It provides different levels of IP packet filtering functions to users with different permissions to achieve different user access capabilities. The IP Pool method works with corresponding routers to implement firewalls. Function, the access server reads IP addresses from different IP pools to the corresponding users according to the user's authorization, as the calling IP address of the user.

6. Access authentication, authorization and accounting functions

The access server is the initiator of the user access authentication request. It receives the user authentication response from the user access authentication server, and according to this response, grants the requesting user access permission and starts accounting. After the user access authentication passes, the access server starts accounting. When the user disconnects the normal modem or disconnects the normal modem, the access server stops charging. The difference between the time when the charging is stopped and the time when the charging starts is the user's access time. For users with dedicated line access, the access server can be charged according to the traffic meter.

7. Network Management Functions

The access server accepts the management of the IP network management system to implement network management functions such as configuration management, performance management, fault management, security management, and accounting management. A network management proxy module is set in the access server. The network management proxy module implements communication with network management, collects corresponding information of the network access server, and maintains the MIB library. The commonly used communication protocol is SNMP. The configuration and management of the access server can be implemented through Telnet. The number of times the network manager calls the user, the number of times that the user cannot connect, the average length of the user's visit, the average cost of the user's visit, the probability of free time, the probability of busy time, the average daily user curve, the monthly average user curve, the probability of failure of the device element, and the disconnection The number of times, the cause of abnormal termination and the frequency of occurrence are counted.

8.IP phone function

Provides IP phone functions, including Click to Dial, Click to fax, Email instructions, IP fax, IP voice mailbox, and Call Center.

9. Caller ID function

When the dial-in access user is already working in the IP network, the call indication requires the access server to receive the call message, process the call message, and send the call indication information to the user.

10.Callback function

After the user dials in the access server and passes the identity authentication, if the user applies for this function, the access server will automatically disconnect the call and call back the user. After the call connection is established, the user can access the Internet.

11.Virtual dial-up private network VPDN function

The VPDN function in the access server includes user qualification authentication for dial-up users requesting the establishment of a virtual data private network, and establishment of a virtual data private network tunnel, data packet transmission, and teardown of tunnels for users who have passed the qualification authentication. The access server can use VPN technology to realize a variety of new services. Enterprises only need to apply for VPN services in one place, and they can use VPN services in other places. When users dial into the local ISP access server, they can enjoy the corresponding services even without the local ISP account.

12. Build an intranet within your company

Users can access the access server through remote dial-up or router, and access to the corporate intranet through access authorization, authentication and authentication of the accounting server. Among them, you can dial through the remote user MODEM or ISDN, the remote branch office accesses the Internet through a telephone line or a dedicated line, and the SOHO user accesses the Internet through a telephone line or a dedicated line.

13.Data bypass function

The access server can be used as a new module of a new independent office or a large digital switch, so that the digital program-controlled switch has the function of remotely accessing the IP telephone gateway. In this way, the data users of this bureau can directly access the data network through the internal communication methods of large digital program-controlled switches, no longer occupy relay resources, reduce the blocking caused by Internet calls in the telecommunications network, and implement the data bypass function.

14. Equipment management functions

The access server has a remote dial-in function. The remote dial-up terminal or local console can be restarted after the failure of the access server is restored. The user's billing function can be modified to add or revoke the user's billing. It can achieve device security Control management, modify the user identification code (PIN), and forcibly remove the connection; it can be used to locate the fault of the device, determine the faulty MODEM, and stop using it, thereby implementing the maintenance and monitoring functions of the access server.

Access server development trend

From the market's requirements for access servers, carrier-class operational products will still be favored by users for their high stability, high reliability, flexible expansion and upgrade capabilities, large capacity, and high integration.

From a technical point of view, No. 7 signaling in the access server has become a basic functional requirement. No.7 signaling will have a dominant position in PSTN / ISDN due to its features such as rich service functions, high efficiency, fast connection speed, flexible networking, and advanced and universal public channel signaling.

In terms of operation, management, maintenance and security, having a larger range of centralized network management functions will become a higher requirement for the access server in the market. It requires that the network management function can manage not only the information on the data device side, but also the information on the telephone network side.

The vigorous development of data services, the integration of data and voice services, and other services will place higher requirements on the development of access servers in the future. Therefore, multi-service universal access platforms are also the trend of access server development in the future.

At present, China's broadband access market has started on a large scale, and operators have spared no effort in this aspect. As the number of dial-up and ISDN Internet users continues to increase, access servers that can fully utilize the telephone network's switching potential will still have great promise.