[From Beginner to Expert - WLAN Common Terms] Section 14 - Air Interface

Definition

In the WLAN field, air interfaces can be considered as virtual logical interfaces on APs and STAs. 802.11 defines a series of wireless transmission standards on air interfaces, including the frequency, bandwidth, access time, and encoding method of each wireless channel.

Air interfaces are invisible. Links between air interfaces are called wireless links, through which APs and STAs communicate with each other and APs set up wireless bridges. Corresponding to air interfaces, wired interfaces are fixed on devices, including optical and electrical interfaces.

Figure 1 shows the relationship between air interfaces and wired interfaces.

Figure 1. Relationship between air interfaces and wired interfaces

More information

Air interface transmission is independent of cables, enabling the WLAN to get rid of wired medium restrictions. The advantages are described as follows:

• Mobility

  Users can move freely, without service interruption.

• Easy deployment

  In some scenarios where wall damage is not allowed, wired networks cannot be deployed. Only wireless networks can be deployed.

• High scalability

  The network scale can be expanded just by expanding the coverage area of wireless signals instead of laying out cables.

• Low costs

  Deploying wireless networks can save a lot of cabling costs.

On the WLAN, air interfaces share the transmission medium, which may easily cause problems in air interface security and performance.

• Air interface security

  As air interfaces share the transmission medium, attackers may listen to or forge communication contents of others or maliciously send a large amount of data to air interfaces, occupying air interface bandwidth. Such problems can be resolved by air interface packet encryption, access authentication, wireless intrusion detection system (WIDS), and wireless intrusion prevention system (WIPS).

• Air interface performance

  Air interface performance may be affected by various factors, such as:

  • When multiple users on an air interface attempt to send packets simultaneously, signals conflict on the air interface, leading to packet sending failures for all users.

  • Burst signal interference on air interfaces causes a communication failure between users and APs.

  • When a user is far away from an AP, the weak signal strength causes a dramatic drop in the throughput, and the long-time air interface occupation by this user affects other users.

• Good air interface performance can be ensured by a series of complex measures. The following lists some examples:

  • The collision avoidance and random backoff mechanisms lower the probability of simultaneous packet sending by users, reducing collisions and enabling users to fairly preempt an air interface.

  • Dynamic channel adjustment for APs reduces interference.

  • Air interface rate adaptation prevents interference and packet sending failures.

  • Smart roaming ensures that STAs are always connected to APs with the strongest signals.

  • Load balancing enables users to be evenly distributed on different channels.