What Is SSID?
A Service Set Identifier (SSID) uniquely identifies a wireless local area network (WLAN). SSID is classified to the basic service set identifier (BSSID) and extended service set identifier (ESSID). Generally, an SSID refers to an ESSID, while BSSID is not perceived by users, and is used for management and maintenance. By configuring different SSIDs, the administrator divides a WLAN into many subnets for separate identification authentication. Users can then select the corresponding SSID to access the network. Therefore, configuring appropriate SSIDs effectively improves the Internet access experience and enhances the WLAN flexibility and security.
Why Do We Need SSIDs?
An SSID uniquely identifies a WLAN.
- Appropriate SSIDs will improve the Internet access experience for terminal users:
- In the SSID list, an easy-to-understand SSID helps users to easily find the wireless network to access.
- The same SSID can be configured for different APs in a WLAN to implement the roaming function, which enables users to move freely in the area covered by these APs without interrupting network services.
- The administrator can divide a WLAN into subnets with different SSIDs and configurations to allow users of different identities to access corresponding networks based on the SSIDs. This distinguishes between access permissions and network functions of different users and enhances the WLAN flexibility and security. For example, in an enterprise network, the administrator can configure the SSID employee for employees and the SSID guest for guests to provide different services for enterprise employees and guests.
BSSID and ESSID
SSID is classified into BSSID and ESSID, which identify the basic service set (BSS) and extended service set (ESS), respectively.
Generally, the so-called SSID refers to an ESSID, which is a wireless network name in the SSID list. BSSID is not perceived by users, and is used for managing and maintaining wireless networks, and locating problems.
BSS and BSSID
As specified in IEEE 802.11, the BSS is a minimum element of a WLAN and indicates the area an AP covers. STAs in a BSS can communicate with each other.
As shown in the following figure, AP1, STA1, and STA2 form a BSS, while AP2 and STA3 form the other BSS. STA1 and STA2 can communicate with each other. To implement communication between STA1 and STA3, packets need to pass through AP1, AP2, and the intermediate network, and AP1 and AP2 need to be able to communicate with each other.
BSS and ESS
Each BSS has a BSSID. A BSSID is actually the MAC address (48 bits) of an AP's radio.
In a multi-SSID scenario, multiple VAPs can be created on an AP to provide access services of wireless networks with different SSIDs. At this time, a BSSID is actually the MAC address of each VAP on the AP. Each BSSID has a one-to-one mapping with a VAP, and you can quickly locate a VAP based on a BSSID.
Relationships between BSSIDs and VAPs
ESS and ESSID
An ESSID identifies a single wireless network or a group of wireless networks. ESSIDs are SSIDs displayed in the SSID list after network scanning.
If multiple BSSs use the same ESSID, they form an ESS. For example, when two BSSs use employee as an ESSID, these two BSSs form an ESS. Generally, an ESS is a collection of several APs and related STAs, with these APs being connected through a distributed system.
Application of SSID
Dividing a Network into Subnets Based on Multiple SSIDs
Early 802.11 chips in APs support only a single SSID, providing only one WLAN for users. With the growth of WLAN users, a single network cannot meet the requirements of users with different identities.
Currently, APs support the multi-SSID function. With this function, multiple VAPs can be created on an AP. Each VAP targets at a specified user group, and has a unique SSID as well as customized configurations of security policies, access authentication, rate limiting, access control, multi-user multiple-input multiple-output (MU-MIMO), and orthogonal frequency division multiple access (OFDMA). That is, a WLAN can be divided into many subnets with different SSIDs, and each subnet provides customized services for its user group.
For example, an enterprise network is divided into two subnets for employees and guests:
- SSID employee: SSID hiding is enabled for this SSID, and only users who know the SSID can join the network employee after being authenticated.
- SSID guest: This SSID is not hidden, and authentication is not needed when accessing this network.
Roaming Capability Based on an SSID
A single AP has a limited coverage area. To enable users to roam between multiple APs, an enterprise can configure the same SSID for APs. The signal coverage areas of these APs overlap to ensure uninterrupted communication. The following uses the mobile phone roaming process of an enterprise employee as an example.
- The employee finds a wireless network named employee at the lobby on a mobile phone, and accesses the wireless network. The ESSID is employee, and the BSSID is the MAC address of the VAP on the AP in the lobby.
- When the employee moves towards the office, the mobile phone enters the coverage of the office AP.
- When the signal strength meets the requirement, the mobile phone automatically roams to the network employee of the office AP based on the SSID, implementing smooth service switchover. The ESSID is still employee, but the BSSID changes to the MAC address of the VAP on the AP in the office.
Example for the roaming process
- Author： Liu Jiayu
- Updated on： 2022-04-02
- Views： 4928
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