Handoff in Hybrid Mobile Data Networks

Vijay Dadlani.

Types of Handoffs

Handoff in Cellular Telephony.

Handoff in Wireless Networks.

Handoff in Hybrid Networks.

The Ping-Pong Effect

Takes a severe toll on the user’s quality reception and the network load.

Persist with a BS for as long as possible.

Important Issues involved in Handoff mechanism.

The GPRS routing update procedure

Handoff procedures in an IEEE 802.11 WLAN

Active scanning Vs Passive scanning

Passive scanning – mobile host simply listens to available beacons.

Active scanning – mobile host sends a probe request to a targeted set of APs that are capable of receiving its probe.

Comparison of handoff procedures in voice and data mobile networks.

IEEE 802.11 GPRS CDPD

Beacon is on the same physical channel as data.

Beacon is on separate physical channel from data traffic.

Beacon is on separate physical channel from data traffic.

Decision on Handoff is made at the mobile terminal.

Decision on Handoff is made at the base station controller or mobile host.

Decision on Handoff is made at the mobile terminal.

IAPP protocol to inform old AP about handoff.

SGSN updates GGSN in GPRS.

Flush/redirect packet message from MHF to MSF of the old BS.

The multiple access is CSMA.

The multiple access is TDMA.

Multiple access is DSMA/CD.

Horizontal Vs Vertical Handoff.

Upward vertical Vs Downward vertical handoff.

Design Considerations

The objective is to reduce major changes to existing networks esp. at lower levels.

This will ensure that existing networks will continue to function as before without requiring current users to change to the new approach.

Mobile-IP Based Architecture

Conclusions

Traditional Handoff algorithms have poor performance and are being replaced by emerging advanced Handoff algorithms.

No one technology can provide ubiquitous coverage, resulting in the need for HO in a Hybrid network.