Wireless roaming refers to that when an STA moves to a critical area covered by two aps, the STA associates with a new AP and disassociates from the original AP. In this process, the network connection is maintained uninterrupted.

Wireless roaming is equivalent to the mobile phone call function, mobile phone from the coverage of one base station to another base station coverage, can provide uninterrupted, seamless call ability.

Introduction to wireless roaming technology

In wireless networks, end users have mobile communication capabilities. However, the signal coverage of a single Access Point (AP) is limited. When terminal users move, they often cross from one AP service area to another. In order to avoid network communication interruption when mobile users switch between different aps, we introduce the concept of wireless roaming.

Wireless roaming means that when an STA (wireless Station) moves to a critical area covered by two aps, the STA associates with the new AP and disassociates from the original AP, and maintains uninterrupted network connection during this process. In simple terms, just like the mobile phone's mobile call function, the mobile phone can provide the ability to make continuous, seamless calls as it moves from the range of one base station to the range of another.

For users, roaming behavior is transparent and seamless roaming, that is, users will not perceive the occurrence of roaming in the process of roaming. This is similar to mobile phones, which may change base stations during a mobile call without us noticing or caring. The STA IP address remains unchanged during WLAN roaming.

Wireless roaming mode

Layer 2 roaming in the AC

1) A terminal uses AP1 to apply for association with the AC. The AC determines that the terminal is a first-time access user and creates and saves related user data for the terminal for future roaming.

2) The terminal moves from AP1 coverage area to AP2 coverage area; The terminal disconnects from AP1 and roams to AP2 connected to the same AC.

3) The terminal is re-associated with the AC through AP2, and the AC determines that the terminal is a roaming user. Since the roaming is in the same subnet (both belong to VLAN X), AC only needs to update the user database information and change the data path to be forwarded by AP2 to achieve the roaming purpose.

Layer 3 roaming in AC

1) A terminal uses AP1 (belonging to VLAN X) to apply for association with the AC. The AC determines that the terminal is a first-time access user and saves the user data for future roaming.

2) The terminal moves from the AP1 coverage area to the AP2 (belonging to VLAN Y) coverage area; The terminal disconnects from AP1 and roams to AP2 connected to the same AC.

3) The terminal is re-associated with the AC through AP2, and the AC determines that the terminal is a roaming user and updates the user database information; Although roaming is not in the same subnet, AC still treats terminals as if they were connected from the original subnet (VLAN X), allowing terminals to maintain their original IP addresses and support established IP communications.

Layer 2 roaming between AC's

 1) A terminal applies for association with AC1 (belonging to VLAN X) through AP1. The AC determines that the terminal is the first access user and saves the user data for future roaming.

2) The terminal moves from AP1 coverage area to AP2 coverage area; The terminal disconnects from AP1 and roams to AP2, which is connected to another wireless controller AC2 (belonging to VLAN X).

3) The terminal application is associated with the inbound AC (AC2), and the inbound AC (AC2) announces the terminal information to other ACs; After receiving a message, the outgoing AC (AC1) synchronizes the roaming user's information to the incoming AC (AC2).

4) Under the condition that the terminal IP address is unchanged, the final data of the cross-AC layer 2 roaming is still forwarded through the outgoing AC (AC1) :

A. The data sent from the end user is first sent to the inbound AC (AC2), then transmitted from the inbound AC (AC2) to the outgoing AC (AC1) through the tunnel, and finally forwarded by the outgoing AC (AC1);

B. Data packets sent to roaming users are first sent to the outgoing AC (AC1), and then transmitted from the outgoing AC (AC1) to the incoming AC (AC2) through the tunnel, and then forwarded to terminal users by the incoming AC (AC2).

AC layer 3 roaming

1) A terminal applies for association with AC1 (belonging to VLAN X) through AP1. The AC determines that the terminal is the first access user and saves the user data for future roaming.

2) The terminal moves from AP1 coverage area to AP2 coverage area; The terminal disconnects from AP1 and roams to AP2, which is connected to another wireless controller AC2 (belonging to VLAN Y).

3) The terminal application is associated with AC2, and AC2 determines that the terminal is a roaming user; AC1 synchronizes roaming end-user information to AC2.

4) Before and after roaming, in different subnets of different AC, the final data of three-layer roaming across AC is still forwarded by overspilling AC (AC1) while keeping the user IP address unchanged:

A. Data sent from the end user is first sent to the inbound AC (AC2), then transmitted from the inbound AC to the outgoing AC (AC1) through the tunnel, and finally forwarded by the outgoing AC (AC1);

B. Data packets sent to roaming users are first sent to the outgoing AC (AC1), and then transmitted from the outgoing AC (AC1) to the incoming AC (AC2) through the tunnel, and then forwarded to terminal users by the incoming AC (AC2).

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