DataTAC 5000Network

Base stationBase station

ARLAN 640

ARLAN 690InfoTAC

Mobile workstation

ServerInfoTAC

Ethernet

Wireless LAN

SAHWW ArchitectureSAHWW Architecture

Mobile Workstation Server

Application Layer

handover initiationsignal

handover request /disconnect request

handover initiationsignal

handover request ;number of last packet received

System Agent -client

Handover Agent -client

Data Link Layer

Data Link Layer

WLANInterface

WANInterface

Application Layer

System Agent -server

Data Link Layer

Data Link Layer

WANInterface

WLANInterface

beaconclient

beaconserver

recovery request ;number of last packet received

buffer

Handover Agent -serverbeacon

no beacon / beacon detected signal signal

acknowledgment

Architecture of WLAN-WAN handoverArchitecture of WLAN-WAN handover

Handover from WLAN to WANHandover from WLAN to WAN

Beacons are continuously transmitted from beacon-server to Beacons are continuously transmitted from beacon-server to beacon-client through WLAN. The interval between two beacon-client through WLAN. The interval between two beacons it t ms.beacons it t ms.

When beacon-client cannot hear n consecutive beacons, the When beacon-client cannot hear n consecutive beacons, the wireless LAN connection is assumed to be broken.wireless LAN connection is assumed to be broken.

““No beacon” signal is sent to handover-agent-client (HA-No beacon” signal is sent to handover-agent-client (HA-client) which would send handover initiation signal to client) which would send handover initiation signal to application layer.application layer.

““Wireless LAN link failure” message would be displayed on Wireless LAN link failure” message would be displayed on the user screen and the handover to WAN decision is left to the user screen and the handover to WAN decision is left to the user.the user.

Two types of messages could be passed from the application Two types of messages could be passed from the application layer to HA-client:layer to HA-client: Handover requestHandover request Disconnect requestDisconnect request

Handover from WAN to WLANHandover from WAN to WLAN

Beacon-client and beacon-server would try to communicate through the WLAN. If n consecutive beacons are received by the beacon-client, WLAN link is assumed to be ready. Then the connection would be switched back to WLAN - reverse handover to WLAN.

‘Beacon detected’ signal would be sent to the HA-client which would send the signal to the SA-client.

SA-client would stop receiving data and send the handover signal together with the number of last packet received to SA-server. the message would pass through the WAN connection.

HA-client would switch the network connection from WAN to WLAN and listen to the WLAN link.

On the server side, after the SA-server has received the message, it would send the handover request to the HA-server. It would instruct the HA-server to switch to WLAN.

An acknowledgment would be sent back to the SA-client. SA-server would start to re-send the packets from the indicated

number. The process is resumed through WLAN connection.