Huawei WLAN Roaming Feature Presentation

HUAWEI TECHNOLOGIES CO., LTD.

www.huawei.com/enterprise

Huawei WLAN Roaming

Feature Presentation

HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential

Huawei Enterprise A Better Way

WIFI Roaming Concept

Roaming is the process that the wireless client STA moves from one BSS

to another BSS. Roaming has the following key features.

An STA can move to any position covered by a WIFI network in an ESS.

For example, an STA can move to any position in the campus whose SSID is

UNIVERSE.

Services are not interrupted.

During roaming, services of the roaming STA are not interrupted.

User IDs (IP addresses) do not change.

An STA obtains an IP address when connecting to the network, and the IP

address does not change during roaming.


WIFI Roaming Driver and Determination

Wireless STAs drive WIFI roaming.

A wireless STA determines whether to enable roaming based on various

conditions, for example, signal strength and quality, number of missed

beacons, and errors caused by conflict or interruption.

1. As shown in the figure on the left, when an STA

is at A, the STA uses AP1 to connect to the

Internet.

2. When the STA moves to B, the STA sends an

802.11 probe request frame through various

channels. After receiving the probe request

frame through channel 6, the AP2 uses channel

6 to send a probe response frame. After

receiving the response frame, the STA

determines whether to associate with AP2 and

whether to roam.

3. The STA determines to roam and uses AP2 to

connect to the Internet at C.



WIFI Roaming Scenarios and Classification

AC6605

PoE switch

Wired and wireless

networks cover

classrooms and offices.

Wireless networks cover the

campus and playground.

eSight unified network

management system

PoE switch

Access

switch

Convergence switch

AP6010

SN/DN

When a wireless station (STA) moves (for

example, in the figure on the left, the STA

moves from A to B in the library, or moves to

another area ( to C on the playground), WIFI

products must support roaming to ensure that

real-time services (for example, video and

voice services) are not interrupted.

WIFI Roaming Scenarios

AP 6610DN

A B C

VLAN1 VLAN2

Campus

Network

Layer2 Roaming: If an STA moves from A to

B, within the same VLAN. That is layer2

roaming. layer2 roaming applies to small

enterprises that are covered only by layer2

network.

Layer3 Roaming: If an STA moves from B to

C on different layer3 subnets (different VLAN),

that is layer3 roaming.Layer3 roaming applies

to medium- or large-size enterprises that are

covered by Layer3 network.

WIFI Roaming Classification

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Roaming Key Performance

The most important performance indicator is roaming delay. When an STA roams from

an AP to another AP, the STA disconnects from the original AP. Before the STA

connects to a new AP, all data sent to or from the STA will be discarded. Roaming

delay indicates the interval from the time when the STA disconnects from the original

AP to the time when the STA connects to a new AP.

In Huawei WLAN solution, services can be smoothly migrated by using the following

rapid roaming technologies:

PMK caching：PMK caching technology is used in the 802.1X authentication scenario. In this case, both STA and

AC will cache the PMK and PMK-ID when an STA communicated with the original AP. When roaming to a new AP,

the STA will send the cached PMK-ID to the AC. The AC will search PMK information according to the received

PMK-ID. if found, the AC will think the STA has passed 802.1X authentication. They will skip the 802.1X

authentication process, and directly negotiate the encryption KEY with cached PMK information. Thereby

shortening the 802.1X users roaming delay. If not found, the STA need the 802.1X authentication process again.

Lower-level key negotiation technology： This technology is used for the data encryption users including

WPA/WPA2 PSK and 802.1X user. This feature is not enabled, STA does the keys negotiation with the AC. When

this feature is enabled, STA does the keys negotiation directly with the associated AP. When roaming to the new AP,

the user roaming delay will be shortened by reducing the keys negotiation time.

Notes: Some STA s can’t support RSN key-cache. When they roaming to a new AP, 802.1X authentication process also

need be performed and PMK information is generated again.


Rapid Roaming in 802.1X Mode

For users authenticated

in the 802.1x mode,

besides the lower-level

key negotiation

technology, the PMK

caching technology is

used so that the complex

802.1x authentication is

not required after the

STA switches APs, which

accelerates the

switchover. The following

figure shows the service

process of 802.1x

authentication.

Radius Server

New AP

AC

STA STA generates

PMK/

PMK ID

Old AP 漫游切换到新AP

AC generates

PMK/

PMK ID

7. AC will check

whether the PMK ID

existing. if existing,

fast roaming allowed.

PMK Caching



Services Switching Process (Layer2 Roaming)

Campus network

Switchover

Roaming switchover

Roaming process

The process of switching to AP2 when the STA has associated

with AP1 is as follows:

1) The STA cancels the association relationship with AP1, as shown in area 1 in the figure on the left.

2) The STA sends a re-association request with the AC through AP2, as shown in area 2 in the figure on the left. After the STA is associated with the AC, AC updates the user information(including VLAN information) to AP2.

3) At step3, different users have the different mechanisms :

• For Open users, directly communicate the data services;

• For WPA2/WPA PSK users, directly negotiate encryption keys with AP;

• For 802.1X users, AC will check whether the PMK information existing according to the received PMK ID from STA. if existing, fast roaming is allowed and 802.1X authentication process is omitted. The STA directly negotiates encryption keys with AP. If not existing, 802.1X authentication process must be performed and PMK information is generated again;

AC devices

AP2 AP1

1 2

SSID: HUAWEI SSID: HUAWEI

Pre-authentication

domain/Isolated domain/Post-

authentication domain

Server area

VLAN

1 VLAN

1

3


Huawei Enterprise A Better Way Cross-VLAN Services Switching

Process (Layer3 Roaming)

Campus network

Switchover

Roaming switchover

Roaming process

The process of switching to AP2 when the STA has

associated with AP1 is as follows:

1) The STA cancels the association relationship with AP1, as shown in area 1 in the figure on the left.

2) The STA sends a re-association request with the AC through AP2, as shown in area 2 in the figure on the left. After the STA is associated with the AC, AC updates the user information(including VLAN information) to AP2.

3) At step3, different users have the different mechanisms :

• For Open users, directly communicate the data services;

• For WPA2/WPA PSK users, directly negotiate encryption keys with AP;

• For 802.1X users, AC will check whether the PMK information existing according to the received PMK ID from STA. if existing, fast roaming is allowed and 802.1X authentication process is omitted. The STA directly negotiates encryption keys with AP. If not existing, 802.1X authentication process must be performed and PMK information is generated again;

4) While roaming is not on the same subnet, AC still regards

the STA as from the original subnet (VLAN1). Ensuring the STA

maintains its original IP and supports IP communication

established， In the centralized forwarding scenarios specified

by area 4 in the figure on the left, the AC must mark roaming

user messages as from pre-roaming VLAN1.

AC devices

AP2 AP1

1

2

SSID: HUAWEI SSID: HUAWEI

Pre-authentication

domain/Isolated domain/Post-

authentication domain

Server area

VLAN1 VLAN2

In channel forwarding mode:

The AC must mark roaming

user messages

as from pre-roaming VLAN1.

3

4

Thank you www.huawei.com

Huawei WLAN Roaming Feature Presentation

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