Browse Prior Art Database

A Mechanism to Enable Continuous Network Switching Disclosure Number: IPCOM000166695D
Original Publication Date: 2008-Jan-21
Included in the Prior Art Database: 2008-Jan-21
Document File: 9 page(s) / 159K

Publishing Venue



A method to enable a computer or device roaming between different networks without dropping the existing connections: e.g. continuous network switching from a wired to a wireless or from one wireless to another wireless network. The method includes a network handler and a tunnel server to realize the seamless switching while maintaining the existing connections. The network handler creates a virtual network interface and handles the packets routing between the virtual network interface and the underlying physical network interfaces. The tunnel server maintains the Virtual IP (VIP) addresses pool (The VIP address pool should be its own subnet) and provide the tunnel service to forward the packets.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 33% of the total text.

Page 1 of 9

A Mechanism to Enable Continuous Network Switching


MVN: Moving Node, e.g laptop, PDA.
VIP: IP assigned to the virtual interface
RIP: IP assigned to the real interface

To accomplish continuous networks switching, we are faced with two mutually conflicting requirements:

To maintain the existing connections, the IP address cannot be changed. Changing

the IP address will cause the connection to be disrupted and lost.

The IP address has to be changed according to the subnets environment, so that the

packets can be routed out and in correctly.

Then, how to resolve the problem above?

A network handler is needed on the Moving Node (MVN) and it will Create a virtual

network interface and obtain a valid IP address from the tunnel server (see below) and this VIP will not be changed.
(Virtual network interface means not a real network card; Valid IP address means normal IP address.)

Applications always bind through the Virtual IP (VIP) to access remote networks or

accept remote access.

A tunnel server is also needed in the network environment, which maintains an IP

addresses pool of its own subnet and provides tunnel service.

The network handler will determine if a tunnel is needed and handle the packets

  routing between the virtual network interface and the underlying physical network interfaces (wired & wireless)
(Note: VIP is the same subnet with the IP of the tunnel server and will not be changed while roaming )

How the network handler works and why a tunnel server is needed? See below.

Here is how the network handler works:


Page 2 of 9

Open virtual interface

Apply an IP address from the tunnel server and assign it to the virtual interface


Is VIP the same subnet with RIP

Routing packets from VIP to RIP


Send request to tunnel server to setup a tunnel

Routing packets out and in with tunneling

FIG. 1 Flowchart of MVN network handler

How the tunnel server works.


Page 3 of 9

Open IP forward

Maintain IP addresses and ready for service


If assign an IP when requested



Find and assign an IP to the MVN

If setup tunnel when requested



Setup and maintain the tunnel for MVN

FIG. 2 Flowchart of tunnel server

The principle of this mechanism

From the startup, the network handler applies an IP (VIP) from the tunnel server for the virtual interface through the RIP route. The VIP may be in the same subnet with the RIP and also may be different. Also, the RIP may be changed when moving to other places or switch from wired to wireless or vice visa. Any way , whenever the MVN obtains a VIP from the startup or gets a new RIP while roaming, one of the following two situations will happen:

RIP in the same subnet with VIP;



Page 4 of 9

Telnet client
VIP: RIP: 9.125.66. 95 /24

Tunnel server

Telnet server