How to build a large-scale VoWLAN

The application of wireless technology has become the focus of our attention. Here we will detail how to make WLAN Technology mature and how to build a large-scale VOWLAN.

To implement a WLAN that supports a maximum of 2000 wireless voice users, a single planar voice network is not a feasible solution, but a subnet should be designed.

Use a WLAN Switch

The network structure selected during WLAN implementation may be very important here. The most important choice is whether to use a bloated access point structure or a WLAN switch structure. If you already have a WLAN Based on a large number of access points, the best way is to centralize these access points on several/24 VLANs and connect these VLANs to the WLAN switch at the same time, to process subnet roaming with a large number of access points.

However, if no access point is deployed here, the WLAN switch structure is much more suitable than large-scale WLAN deployment. The WLAN switch integrates security, information packet processing, and RF management functions, and makes all layers of the protocol stack transparent. Therefore, only the WLAN switch structure can ensure the advantages of voice communication in the air and network.

Control broadcast package

In a data network, it is generally recommended to divide the network into smaller subnets to reduce broadcast traffic. Broadcast traffic is sent to all systems on the LAN subnet. However, if the network expands and the broadcast traffic increases with the increase of the number of users, this will reduce the network performance. Broadcast traffic also affects the terminal system. This is because the number of received information packets has increased, and the information packets must be used in the terminal system.

The two most common broadcast information packages are Address Resolution Protocol (ARP) requests and NetBIOS. ARPRFC 826) is the main part of broadcasting. The terminal system uses ARP to determine which MAC address to send the IP packet to another system. By using ARP, the system sends the broadcast packets to all systems on the subnet, and then asks which system has the IP address you are trying to send the packets. Each receiving system checks the request and determines whether the IP address of the request is its own address. If it is its own address, the system sends a response. In a large network that has not been divided into small subnets, this will cause a sharp increase in network traffic. By dividing the network into small subnets, you can limit the broadcast traffic to each subnet of the network, and use the gateway/router to forward information packets between different subnets.

It is generally recommended that the subnet size be 254 hosts, also known as the "/24" subnet). However, this is not a hard rule. You can select a larger or smaller subnet, depending on the expected broadcast traffic.

Some WLAN switch architectures no longer need to divide small subnet segments because they intelligently manage broadcast domains to restrict broadcast traffic such as ARP requests and thus prevent broadcasts from being sent to all hosts. This is especially important for wireless systems because bandwidth is restricted in the air. To improve network performance, it is very important to reduce unnecessary information packet transmission volumes.

Reduces roaming latency

When dividing a wireless network into multiple subnets, make sure that the WLAN switch and access point can support access point roaming for almost zero time and subnet roaming for the entire network range. Sometimes, when a user calls one call, the phone will be transferred from one access point to another. You certainly do not want the user to be disturbed in this case, so this is especially important for wireless voice deployment. Large-scale deployment of 2000 voice customers) The problem is that voice applications require much higher than data applications. Packet loss or delay may be nothing for data communication, but it is enough to disrupt voice calls.

In June 802.11, we all know that it is up to the customer to decide when and where to associate) and transmit hand off), and they are both independent. In large-scale general deployment, this will lead to a ping-pong effect. The customer spends a lot of time from one access point to another, rather than transmitting or receiving data. Therefore, the voice quality is damaged, the number of times of delivery is too high, or the transmission time is too long.) or the call cannot continue. The reason for this is that the voice stream is a digital sampling, usually one sample every 30 ms. If the information package is lost, the signal cannot be completely restored, resulting in low speech quality. The worst case is that this loss of voice may cause a call interruption. In general deployment, there will be several hundred access points, which means that during a voice call, your VoIP receiver may be exchanged several hundred times between access points. If the communication between access points exceeds several milliseconds, the service center will receive a large number of complaints about the quality of calls. In fact, the problem is not on the phone, but on the WLAN infrastructure.

Implement Mobile IP Address

The key to mobility is to be able to track the movement of a customer's device from one access point to another, and then forward information packets as appropriate, rather than forcing the user to obtain a new IP address. In a single subnet, this can be achieved by using the customer's MAC address. However, this method is not suitable when more than one subnet exists. It makes the Administrator unable to effectively manage the network.

For subnet roaming, wireless products must be able to track the IP addresses used by the customer's devices to move on the third layer ). In addition, the infrastructure must be able to execute some basic IP connection functions such as ARP on behalf of the customer, so that the existing IP infrastructure will not be aware of the customer's movement. One way to solve this problem is to implement proxy Mobile IP, but the configuration of this method is complicated and you need to change the LAN Routing infrastructure.

There is also a good way to solve the mobility problem, that is, to use another signal transmission mechanism, usually known as "edge channel" edge tunneling. In this method, the wireless switch is responsible for tracking roaming customers. By combining the LWAPP channel with the edge channel, the network routing will not know the actual location of the customer's IP address. No matter where the mobile device is connected to the network, the wireless switch will think that the customer has never moved, thus forming a seamless movement. Several groups of wireless switches automatically establish a mobile channel between each other, and the connections between several subnets are maintained. To use this method, you do not need to change the underlying network infrastructure.