Subject: [Mip4] Suggestion for Multiple-Interface MNs

From: "Alexandre Tian" <[email-masked]>
Date: Mon, 22 Mar 2004 17:23:47 +0800

I think this words found in “Appendix B - Low Latency Handoffs for Multiple-Interface MNs”:“The MN activates the interface to RN2 but continues communicating through RN1.  The MN may solicit advertisements from nFA through the  interface connected to RN1 to speed up the handoff process, provided there is no TTL restriction, or it can solicit advertisements through the interface connected to RN2 if it has been configured for IP traffic.” maybe inaccurate. These couldn't provide "seamless handoff" as said in the following.
I have realized a Mobile IP implementation in Windows 2000 platform one year ago. In a Multiple Physical Interface situation, there should only be one IP interface for Mn. if we want seamless handoff. For example, assume we have two physical interfaces( PI1 and PI2) and both have their own IP interface. When there is a handoff from PI1 to PI2, we must first unbind mobile ip address from PI1 and then bind it to PI2. During the break (even only several milliseconds), the IP route table would be empty and unusable, that would surely break most stream applications like online movie or VoIP phone.
Still the example, my implementation cancels the original IP bindings of both PI1 and PI2. Instead, I use unique system virtual IP device and configure the mobile ip address to it. All physical interfaces are only Layer 2 devices and managed by the virtual layer 3 IP device(VIPD). IP packets are transmitted by the VIPD. Of cause , VIPD select which device to send a specific IP packet. When handoff from PI1 link to PI2 link, VIPD keep IP traffic through PI1, and send solicit advertisements through PI2.
Thus, during the handoff, there is no IP address unbinding and binding need more. This is real seamless handoff.