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Browse Prior Art Database

Seamless Mobility using Multiple Interfaces

IP.com Disclosure Number: IPCOM000009459D
Original Publication Date: 2002-Aug-26
Included in the Prior Art Database: 2002-Aug-26
Document File: 2 page(s) / 43K

Publishing Venue

Motorola

Related People

Narayanan Venkitaraman: AUTHOR

Abstract

The handoff latency of many new access technologies such as wireless LAN devices is very large, on the order of hundreds of milliseconds. This results in significant performance degradation during handoff. In this document we propose an approach that uses multiple transceivers of the same access type to enable make-before-break handoffs. This approach eliminates latencies and packet loss during handoffs.

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Seamless Mobility using Multiple Interfaces

Narayanan Venkitaraman

Abstract

The handoff latency of many new access technologies such as wireless LAN devices is very large, on the order of hundreds of milliseconds. This results in significant performance degradation during handoff. In this document we propose an approach that uses multiple transceivers of the same access type to enable make-before-break handoffs. This approach eliminates latencies and packet loss during handoffs.

1.                 Problem Statement

The handoff latency of many new access technologies such as wireless LAN devices is very large, on the order of hundreds of milliseconds. During this period mobile nodes cannot receive or transmit packets. This results in significant performance degradation during handoff. Furthermore, while handing off across subnets, network layer handoff can be initiated only after link layer handoff is complete. This increases the latency even further. Current cellular systems designed to handle mobility well solve the latency issue by adding intelligence to the network and the interfaces (e.g. RNCs which strictly coordinate handoffs, interfaces that can do neighbor cell discovery). RNCs are complex and expensive devices specific to the link layer being used. In the IP world the key focus is KISS (Keep it simple stupid) and inexpensive, flexible devices. So in IP-based architectures the access technologies do not support the level of handoff coordination that cellular systems provide.  Though packets can be buffered in a local mobility agent and then retransmitted to eliminate packet losses during handoffs, the high level of latency still exists.

2.                 Proposed Solution

Figure 1

A well-known approach to improve handoff performance is to do make-before-break handoffs. However, WLAN technologies like 802.11b and 802.11a do not provide make-before-break handoffs. Their interface cards cannot simultaneously listen to different APs transmitting at different frequencies. The solution is the following: For a given link access type, the mobile node should have at least 2 transceivers. In the above figure the mobile node has 2 transceivers, i1 and i2. When one of the interfaces, say i1, is in what we term as “transmit mode” (i.e. connected to one access point and is being used to transmit and receive packets) the other interface, i2,  is in “search mode” (i.e. it is used to connect t...