Single-channel architecture

In computer networking, single-channel architecture (SCA) is the design of a wireless network in such a way that the wireless client sees a single point of access to the network. This design utilizes a centralized controller to decide which access point (AP) will be used to communicate with a client device. This method allows the network to maintain a higher level of control over the communication medium than does multiple-channel architecture, which allows client devices to determine which APs to communicate with.

Single-channel architecture is based on a principle of "virtual cells". All APs joined to a virtual cell use the same wireless channel and identify themselves with the same basic service set identifier (BSSID, i.e. a MAC address). The APs in a cell are managed by a centralized Wireless LAN controller (WLC) that coordinates the APs such that APs/transmissions do not interfere with one another. From a client's point of view, a virtual cell appears as a single AP.

Multiple virtual cells can co-exist, with each virtual cell having its own BSSID and channel. This topology effectively simulates a multiple-channel architecture and can be used to reduce channel congestion in environments with high AP density and overlapping signal range. For example, in a classroom with two cells, clients can be directed to associate with one or the other cell, leaving more bandwidth available to the clients on each channel.

The biggest advantage of a single-channel architecture is that there is a zero handoff time for roaming clients. In multiple-channel architecture, as a client device travels around the physical location of the network, it will change which AP it is associated with. Since each AP in a multiple-channel architecture has its own BSSID, a client needs to re-authenticate itself every time it associates with a new AP. In comparison, in a single-channel architecture, since the client only sees one AP, it is up to the central controller to decide when to communicate with the client using a different AP. This means that the handoff can occur behind the scenes and is completely invisible to the client. With a zero handoff time, there is no interruption to the client, which is ideal when a client is utilizing voice or video applications and does not have bandwidth in reserve to deal with the re-authentication process.

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