Low latency mobile initiated tunneling handoff

Details Low latency mobile initiated tunneling handoff Low latency mobile initiated tunneling handoff

2002-06-28

2004-12-14

Vuong, Quochien B. (Department: 2682)

Telecommunications

Radiotelephone system

Zoned or cellular telephone system

C370S331000

Reexamination Certificate

active

06832087

ABSTRACT:

FIELD OF THE INVENTION
This invention relates generally to the communication of digital data in digital data networks and more specifically to communication of digital data in wireless, mobile-access, Internet protocol-based data networks. This invention is particularly relevant to handoff operations performed by mobile nodes roaming in wireless, mobile-access, Internet protocol-based data networks.
BACKGROUND OF THE INVENTION
Throughout evolution of wireless communications systems, technical challenges associated with implementing wireless communication have always been posed by a mobile node (MN), as traveling from one area to another, irregularly changing its point of attachment to terrestrial radio access point (AP) with which it is communicating wirelessly. Indeed, the most critical factor in achieving good performance for mobility protocols is the design of handoff. A handoff occurs when a MN moves from one radio AP to another. A mere change of radio AP is called a “Layer
2
(L
2
) handoff,” which does not involve any Layer
3
(L
3
) signaling at the IP level. If the new radio access point is associated with a new subnet, i.e., if the MN moves from one subnet to another, a changing in routing reachability occurs and requires Layer
3
(L
3
) protocol action. This L
3
protocol action is called a “L
3
handoff” and usually involves exchange of a series of IP messages that are used to update routing information for the MN to make sure that data destined to the MN is routed through the new subnet to the MN.
The Internet Engineering Task Force (IETF) has proposed several standards to deal with the handoff operations. For instance, IETF RFC 2002 titled “IP Mobility Support,” which is usually referred to as Mobile IP Version 4 (IPv4), and draft working document <draft-ietf-mobileip-ipv6-17> entitled “Mobility Support in IPv6,” also referred to as Mobile IP Version 6, both of which are incorporated herein by reference, describe how a MN can perform L
3
handoffs between subnets served by different agents. Under Mobile IPv4, a MN is given a long-term home address by its home agent (HA) and uses the home address as the source address of all IP data that it sends. When located on a foreign subnet away from its home subnet, a “care-of address” (CoA) is associated with the MN and reflects the MN's current point of attachment. Through an L
3
handoff, the CoA is registered in the MN's home agent to enable the HA to update its binding or data-routing information for the MN. A similar protocol is implemented under Mobile IPv6.
The L
3
handoff process pursuant to RFC 2002 requires mobility agents, i.e., foreign agents and home agents, to advertise their presence via Agent Advertisement messages. A MN that receives these Agent Advertisements determines whether it is operating on its home subnet or a foreign subnet. When the MN detects that it has entered a new subnet, it obtains a CoA from Agents Advertisements sent from the foreign agent serving the foreign network. The MN then registers the new CoA by sending a registration request including the CoA to its home agent (HA). The L
3
handoff completes when the HA receiving the registration request updates its internal binding information for the MN and returns a registration reply to the MN. After the registration, data sent to the MN's home address are intercepted by the HA, tunneled by the same to the MN's CoA, received at the tunnel endpoint (either at a FA or at the MN itself), and finally delivered to the MN. In the reverse direction, data sent by the MN is generally delivered to its destination using standard IP routing mechanisms, not necessarily passing through the HA.
Mobile IP was originally designed without any assumptions about the underlying link layers over which it would operate so that it could have the widest possible applicability. This approach has the advantage of facilitating a clean separation between L
2
and L
3
of the protocol stack, but it has negative consequences. Because of the strict separation between L
2
and L
3
, a MN may only communicate with a directly connected FA. This implies that a MN may not begin the registration process until it obtains L
2
connectivity to a new FA after having lost L
2
connectivity to the old or previous FA. In addition, the registration process itself takes some time to complete as the registration request and reply messages propagate through networks between the MN to its HA. The time from the last L
3
connectivity between the MN and the old FA, to the time when the L
3
connectivity to a new FA has been established manifests itself as handoff latency. During this time period, the MN is not able to send or receive any data. The handoff latency resulting from standard Mobile IP handoff procedures could be greater than what is acceptable to support real-time or delay sensitive traffic.
Several protocol designs have been proposed for both Mobile IPv4 and IPv6 that seek to reduce the amount of handoff latency. For instance, Internet Draft “Low Latency Handoffs in Mobile IPv4” < draft-ietf-mobileip-lowlatency-handoffs-v4-03.txt>, which is incorporated herein by reference, proposes two techniques for minimizing the period of time when a MN is unable to send or receive data due to the delay in the Mobile IP registration process. One such technique is “pre-registration handoff” which allows the MN to communicate with a new FA while still connected to the old FA. The other is called “post-registration handoff” which provides for data delivery to the MN at the new FA even before the formal registration process has completed. More specifically, under the pre-registration handoff method, the old FA, initiated by an L
2
trigger, notifies the MN of a new FA. The MN then begins an L
3
handoff with the new FA while still in communication with the old FA, i.e., while receiving and sending data through the old FA. In other words, the pre-registration handoff method allows the L
3
handoff to begin even before the L
2
handoff begins and thus helps achieve seamless handoffs between old and new FAs. The new FA may initiate the pre-registration handoff by sending its presence through the old FA to the MN. Also, the MN may become an initiator of the pre-registration handoff by sending a Proxy Router Solicitation to the old FA, which in return advises the MN of the new FA. In any event, a prompt and timely L
2
trigger is necessary to implement the pre-registration handoff.
The post-registration handoff method allows the old FA and new FA to utilize L
2
triggers to set up a bi-directional tunnel (BDT) between the old FA and new FA that allows the MN to continue using the old FA while on the new FA's subnet. The post-registration handoff is likewise initiated by an L
2
trigger that is provided to either the old FA or the new FA. Following a successful Mobile IP Registration between the MN and the old FA, the old FA becomes the mobility anchor point for the MN. Either the old FA or the new FA then receives an L
2
trigger informing that the MN is about to move from the old FA to the new FA. The FA (old or new FA) receiving the trigger sends a Handoff Request to the other FA (new or old FA), which returns a Handoff Reply, thereby creating a bi-directional tunnel between the FAs. When the link between old FA and MN is disconnected, the old FA begins forwarding MN-bound data through the tunnel to the new FA. When a new link is established between new FA and MN, the new FA begins delivering the data tunneled from the old FA to the MN and forwards any data from the MN through the reverse tunnel to the old FA. After the L
2
handoff is completed, the MN may, while sending and receiving data through the tunnel from the new FA, perform a formal Mobile IP registration with the new FA. The initiation of this formal registration may be delayed. Thus, the post-registration handoff enables a rapid establishment of service at the new FA.
Internet Draft “Fast Handovers for Mobile Ipv6” <draft-ietf-mobileip-fast-mipv6-03.txt>, which is incorporated herein by ref

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