WLAN/GPRS Fusion network based on mobile IP

Source: Internet
Author: User
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Content Summary: First compares the WLAN and the GPRS two kinds of technology characteristic, then proposed a mobile IP support WLAN/GPRS network seamless roaming fusion scheme. It uses WLAN network and GPRS network in the technical complementarity, can quickly provide users with the support of seamless roaming data services. This scheme is based on the following basic ideas: Try not to make any changes to the GPRS network, but mainly through the adjustment of WLAN network structure to achieve the integration of the two. When describing the main workflow of this scenario, it includes the following aspects: Mobile contact Access/attachment, WLAN to GPRS roaming, GPRS to WLAN roaming, WLAN network availability judgment, billing, etc.

WLAN and GPRS provide data services, the characteristics of a great complementarity, if a mechanism to integrate the advantages of both, you can provide users with wide coverage, to ensure a certain data rate and in hot spots can be seamless switch to high speed unified mobile data Services.

Related Technology 1. Wlan

WLAN technology can not only be used as a supplement to the wired network, but also can be independent network, so as to solve the problem of mobile access network to some extent. WLAN mainstream physical layer technical standard has Bluetooth, IEEE 802.11 series, HiperLAN several. But most WLAN products now follow the IEEE 802.11 b standard. When used to provide a public access service in a hotspot area, the WLAN network structure is shown in Figure 1.

In Figure 1, WLAN user terminal is to support the 802.11 series standard wireless network card; access point (AP) provides the physical access channel for the end user and provides access authentication and billing service; the Access Controller (AC) assigns temporary IP addresses to end users and provides Internet access, as well as access authentication and billing services in AC; authentication server (as) interacts with the operator's attribution position Register (HLR) to complete the authentication and billing functions. (Computer science)


In the need to introduce mobile data services, GSM is a traditional Exchange Mode has become powerless, mainly in the bandwidth of the utilization of resources is not high. Therefore, the wireless resource based on dynamic allocation of GPRS, which is characterized by the user always maintain the connection with the network, but only the transfer of data to occupy the wireless resources, that is, according to the needs of users to dynamically allocate the physical channel, so as to improve the data transfer rate and bandwidth utilization. GPRS adopts packet switching mechanism to realize the cost of flowmeter. However, the use of GPRS to provide data services does not really increase the physical channel, in addition to the voice service and the contention for channel resources problems. Theoretically, GPRS can bundle up to 8 physical channels at the same time, and provide mobile data service with 115.2 kbit/s rate. However, operators in the actual operation to ensure the use of voice users, generally only allow a GPRS user bundled 3 physical channels, the highest data rate can only reach 43.2 kbit/s. And in hot areas, operators will use the voice business priority. The network structure of GPRS system implemented on GSM system is shown in Fig. 2.

In Figure 2, the base station subsystem (BSS) is the GSM mobile Access network, the GPRS Service Support node (SGSN) completes the access control function, provides authentication and authorization service to the user, and the GPRS Gateway Support Node (GGSN) provides the PDN interface with the packet data network. SGSN,GGSN and HLR constitute the switching system of GPRS network, which undertakes user mobility and routing management.

3. Mobile IP

The IP protocol does not effectively support moving across subnets because the IP address is associated with a particular network segment, and the movement of the terminal destroys the association so that communication does not work properly. The main purpose of the Mobile IP protocol is to provide a mechanism that allows the IP datagram to be transparently sent to the mobile node, as defined by the RFC2002 of the IETF. Unlike a specific host routing technology and a data link layer scenario, Mobile IP solves security and reliability problems and is not related to the transport media. The scalability of Mobile IP enables it to be applied across multiple heterogeneous networks.

To achieve these goals, Mobile IP introduces a new network entity:
• Mobile node: A host that changes its access point from one network or subnet to another network or subnet;

• Attribution Agent (Ha:home agent): A router located on the mobile node's home network that creates tunnels for the datagram when the mobile node is not home, and is responsible for maintaining the current location information of the mobile node;

• External agent (fa:foreign agent): A router that is located on a network accessed by a mobile node that provides routing services for registering mobile nodes.

When a mobile node leaves its own IP subnet segment, it must register its current IP subnet with the forwarding address (care-of addresses) of the tunnel services it provides. This referral address, if it is the address of the FA assigned to a mobile node, is referred to as a joint referral address and, if it is the address of the FA, an external proxy referral address. When Ha knows the current forwarding address of the mobile node, the packet received by HA can be forwarded to the forwarding address in a tunneled manner, and at the referral address, the original packet is removed from the tunnel and transferred to the mobile node. When a mobile node emits a packet, if the triangle is used by the (triangle Routing) method, the FA provides the routing function, the packet is sent directly to the destination node, and the source address is Ha's IP address; If you use a reverse tunnel (Reverse Tunnel) method, The packet is still sent to ha in a tunneled manner, which is forwarded externally by HA.

Mobile IP Certification and authentication by the registration (registration) message support, registration messages also include registration requests and registration response. In the overall structure of mobile IP, only the basic format of the message used for authentication is defined and the essential function requirements are expanded, but there is no definition and architecture of authentication and verification. Therefore, each Mobile IP product can have its own certification and authentication methods. For mobile operators, the Remote dial-up User Protocol (RADIUS) can be used to provide authentication and authenticate services. In the mobile IP protocol, there is no design for the billing information processing, but the HA and FA can collect information about the tunnel traffic, the time of use and the IP subnet roaming through, which can be processed by radius The accounting message is reported to the remote dial-up user server.

WLAN/GPRS Fusion network based on mobile IP

GPRS and WLAN advantages and disadvantages of a great complementarity. At present, GPRS and WLAN technology are mature. If you can develop two compatible equipment, give full play to GPRS network coverage and mature operation experience, can really support the user mobile and roaming, have a reliable security mechanism and billing model advantages, while giving play to the relatively high WLAN access rate, With the advantages of fast and flexible access and low cost of networking, operators will be able to effectively capture high-end users with high demand for data services and rapidly expand the market for mobile data services.

As compared to WLAN networks, the GPRS network of operators is a more complex and mature public mobile communication network. Therefore, the proposed scheme is based on the basic idea of not doing any modification to GPRS network, mainly through the adjustment of WLAN network structure to realize the fusion of the two. The network structure is shown in Figure 3.

When the mobile node is the user roaming to the GPRS network, GPRS system will assign a dynamic assigned IP address for each mobile node, this address is fixed when the mobile node uses GPRS, so HA can take the IP address designated by GPRS as its joint forwarding address. These addresses, which are usually private IP addresses, are not affected by insufficient IP addresses. At this time, mobile node can take the joint transfer address way to carry out mobile IP protocol communication, mobile node as the end of the tunnel directly with the HA Exchange data, do not need additional external agent equipment, thus eliminating the structure of the GPRS current network to change the risk.

In the WLAN network mode, commonly used is the authentication point in the AP program, at this time AC only provides data transmission and dynamic IP address allocation function, and an AC plus several AP can generally provide for a hotspot area coverage. Therefore, the replacement of an AC device, or its software upgrade only, provides the ability to provide an external agent that completes the communication between the mobile node and the HA based on the mobile IP protocol. Because in different hot spots, the mobile node can be assigned to the IP address of different subnet segments, so at this time mobile IP transfer address is the external proxy forwarding address, that is, the address of the FA as the address of the transfer. A link layer is used to transfer IP packets directly between FA and mobile nodes. Of course, if the hotspot area is large, then you can set up multiple external agents to complete the network.

The HA record moves the current forwarding address of the node and forwards the IP packets sent to the mobile node to the mobile node in tunnel mode. The setting of HA mainly provides the mobile node with the Data tunneling service based on mobile IP roaming, and it is not important for roaming users to return to their home network in order to provide roaming service to mobile nodes in the business. Therefore, HA is not suitable for any specific roaming user location, the best location should be the most efficient distance roaming users, the general choice of the province, the city's central room.

Programme main workflow 1. Mobile Node Access/attachment

Mobile IP is an IP layer based on another layer of protocol, its use presupposes that the underlying IP layer and link layer can already be used. Therefore, in the description of the access process, mainly for mobile IP layer access processing. The idea of the access process is to access the GPRS network first, and then look for the WLAN network which can provide higher business ability, compared with the service of the WLAN,GPRS service only in the hotspot area is almost everywhere. The main steps are as follows:

① Mobile node for GPRS attachment;

② mobile node to HA request authentication and certification, HA based on the current user status and user signing information to determine whether or not to provide mobile IP services;

③ such as the user through authentication, the GPRS network allocation of IP address report to ha, as a joint referral address, HA can provide users with GPRS on the tunnel services;

④ Mobile node to find an accessible WLAN network, if not, continue to use the GPRS network;

⑤ Apply for access if an available WLAN network is found;

⑥ access to the WLAN network, the use of mobile IP extended Internet Control Information Protocol (ICMP) in the ICMP Agent AD (ICMP agent advertisement), query the current available FA, if not then continue to use the GPRS network;

⑦ If there are available FA, the user will request authentication and certification to the FA, apply for mobile IP service;

⑧ such as the user through authentication, the FA notify Ha, the current user can use the tunnel services on the WLAN, at this time GPRS provides the IP layer to standby status.

In the above certification, ha or FA is only to provide users with authentication message interface, the real authentication process by the operator's RADIUS server completed.

2. WLAN to GPRS roaming

In the course of use, once the WLAN service is stopped, the mobile node will immediately use the IP Layer service provided by GPRS which is already in standby state, at this time the mobile node uses GPRS to assign the IP address as the joint forwarding address and notify ha with mobile IP registration message. At this point, the registration message does not interrupt the original tunnel service, but to ha notify the mobile node of the latest location, so that HA can quickly change the end of the tunnel location to the current GPRS in the joint transfer address.

3. GPRS to WLAN roaming

If the WLAN is restored to service, the mobile node will return to the WLAN again. If you are returning to a previously connected WLAN network, send a registration message informing HA to update the tunnel endpoint again to provide an external proxy referral address for the WLAN. If you arrive at a new WLAN network or if you first access your WLAN network, you will need to authenticate your access.

4. Availability of WLAN network judgment

Whether the WLAN network is available is determined by the client software on the mobile node, and the physical implementation is supported by the Gprs/wlan dual-mode NIC, which is based on whether the FA provides the service, not the link layer state. In Mobile IP protocol, the FA must broadcast the Agent Advertisement message periodically in ICMP mode, the standard time is 1/3 S, and the Mobile IP protocol stipulates that the frequency of roaming is not more than once per second, The FA has ceased service or found a new FA to provide services.

5. Billing

From the Mobile IP structure, the billing information that can be collected includes important information such as the time when users start and end roaming service, the roaming process subnet record, and the tunnel traffic provided by HA and FA in the course of roaming. With this information, the client can be timed or charged with the flow of traffic, but also can know the user in the subnet roaming process, the use of each subnet time and traffic. In the Mobile IP architecture protocol, there is no model design for the billing information processing, and HA and FA equipment manufacturers must provide the RADIUS billing message escalation function based on the operator's definition of billing message. Eventually, when all billing information is merged in the RADIUS server, the user will be given a single unified statement.


The above proposed a mobile IP based on the support of Gprs/wlan network seamless roaming fusion scheme, it utilizes the GPRS network and WLAN network in the technical complementarity, on the existing mobile network with a small number of additional devices can quickly provide support for seamless roaming data services. The Gprs/wlan network based on mobile IP has the following advantages over the original single GPRS or WLAN network:

• It can use the wide area coverage advantage of GPRS, as well as the advantages of high speed access that WLAN provides in hotspot area compared to wired access;

• Seamless roaming without user intervention;

• Reduce the cost of providing data services to users;

• Mitigate the contention of channel resources between GPRS and voice services, especially in hot spots, which can significantly improve the service quality of operators ' voice/data services.

• Support a variety of billing strategies to help operators provide differentiated services for market segments.

Of course, mobile IP is a layer of protocol attached to the original IP layer, so it will have some impact on efficiency and throughput, but on the whole, the WLAN/GPRS Fusion network based on mobile IP is still a better, more efficient and More feasible to provide data business solutions.

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