Mobile IPv6 and Proxy Mobile IPv6

Mobile IP (MIP) is a standard published by Internet Engineering Task Force (IETF) [7]

which defines a communication protocol that allow a mobile node (MN, or Mobile Station, MS) to retain its home address on moving from network to another. While MS uses MIP moving between networks, there is no need to modify the intermediate routing nodes.

In MIP, each MS has two network addresses – the permanent home address (HoA) and the Care-of-Address (CoA), which is calculated and reassigned while MS travels to another network. In MS’s home network, the Home Agent (HA) is responsible for keeping the information about MS’s permanent address. The HA also keeps being aware of which MNs are under the home network, and which MNs are visiting a foreign network.

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Normally when MS is under the home network, a node wanting to communicate with the MS, which is called Correspondent Node (CN), uses the permanent address of MS as the destination address in IP datagram to send packets to the MS. When MS travels to a foreign network, it tries to connect to internet through the local router, which is called access router (AR), and generally AR also works as Foreign Agent (FA). The AR advertises the address every time an MS moves into its network. And then the AR would assign a newly calculated CoA to MS. And afterwards, the MS would register this CoA information to the MS’s HA and CN. Now the packets from CN to MS are still routed by standard IP routing mechanisms, so the packets are forwarded to the HA. The HA would establish an IP tunnel to AR according to MS’s registered CoA, and redirect the packets through this tunnel.

While sending packets back to CN, the MS directly passes packets back to CN through the AR without sending them through the HA [8]. The two direction have different routing is called triangular routing, and it may causes lower efficiency. Figure 1.2 shows an overview of MIP.

Mobile Station(MS ) Home Agent (HA)

Correspondent Node (CN)

Access Router (AR)

Home Network Visited Network

Mobile Station(MS )

Movement

IP Tunnel

communication

Figure 1.2 Overview of Mobile IP

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Mobile IPv6 (MIPv6) is an enhancement of Mobile IPv4 and is developed to improve mobile communications in some circumstances. MIPv6 uses various methods to solve many problems in MIPv4, for example, the triangular routing, weaker security, and the limitation of address space [9]. There are some optimization steps which are triggered by the MS to improve the routing efficiency. In the route optimization process, after the MS switches to AR’s subnet, it registers this binding to the CN. By finishing this process, the CN can directly send packets to MS, instead of sending packets through HA continuously [10].

Although MIPv6 provide better solution than MIPv4, there still remain some problems, such as packet loss, handover latency, and signaling overhead. Furthermore, handover latency would seriously affect QoS but MIP does not offer any guarantee to it. As a result, another standard mentioned in following paragraph is developed to improve the performance of MIPv6.

Proxy Mobile IPv6 (PMIPv6, or PMIP) is designed as a network-based IP mobility management protocol and is also published by IETF. Just as MIP, PMIPv6 has the same mobile functions and there is no need to modify the host’s TCP/IP protocol stack. The main difference between them is that with PMIPv6, the MS can travel to another point-of-attachment (PoA) to the internet without MS participated in any mobility-related signaling. Unlike the MIP, the function that allows the MS to maintain the same IP address in different networks is implemented by the network but not triggered by MS. Therefore it is not necessary to modify MS’s mobility functions (It seems like remain in the same network on MS’s point of view) [11]. Other benefits of PMIPv6 include supporting both IPv4/IPv6, making better use of wireless resources, and improving handover performance [12].

In PMIPv6, there are two main network devices involved in the mobility

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management – Local Mobility Anchor (LMA) and the Mobile Access Gateway (MAG).

The LMA is similar to HA in MIP, and it maintains the MS’s address is reachable while MS moves around within a PMIPv6 domain. The LMA also includes a binding cache entry for each currently registered MS, which stores more information than those in MIPv6’s HA.

The additional information includes MS-Identifier, the MS’s home network prefix, a flag indicating a proxy registration, and the interface identifier of the bi-directional tunnel between the LMA and MAG. On the other hand, the MAG which usually runs on an AR, detects the movement of MNs and takes charge of managing mobility related signaling for MNs attached to MAG’s access link. In this thesis, when it comes to PMIPv6, we use the term AR to represent the MAG, and HA to represent LMA, so that we can unify the equipments’ names in different protocols.

The following is how PMIPv6 works (Figure 1.3). When a MS attaches to certain MAG, the MAG first performs the authentication procedure and obtains the profile of the MS. Then the MAG sends a proxy binding update (PBU) message include the MS-Identifier to the MS’s LMA on behalf of the MS. Once the LMA receives the PBU message, it allocates an appropriate home network prefix for the MS and encapsulates this prefix into proxy binding acknowledgment (PBA) message, and sends PBA back to MAG.

Now the LMA and MAG have enough information and create a bi-directional tunnel for enabling the MS to use an address from its home network prefix and the MAG emulates the MS’s home network on the access network for the MS. After the bi-directional tunnel is successfully established, all traffic sent by the MS would be routed to its LMA through the tunnel. And packets from CN to MS would send to the LMA in advance, and then the LMA forwards them to the MAG through the tunnel. Finally, the MAG removes the outer header of the packets and forwards them to the MS.

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Control message sent to establish a binding between MN-HoA and Proxy-CoA

MN Home Address (MN-HoA)

MN continues to use it as long as it roams within a same

From the above description, we can see that IEEE 802.16j is one of the latest WiMAX standards, which provides good coverage extension with low cost. In this standard, the MRS with moving RS mode is an efficient method to provide internet access for passengers aboard.

IEEE 802.16j defined the handover procedures in Data-Link layer (MAC layer, or layer 2);

however, when IEEE 802.16j combines the mobile mechanisms in network layer (IP layer, or layer 3) there are still some problems to be solved, including packet loss and long service disruption time (SDT). In many real time applications such as video streaming and VoIP (Voice over IP), these problems may seriously affect the performance and user’s experience.

As a result, achieving seamless handover in IEEE 802.16j with MRS mode has become the main purpose of this thesis.

The two main IP layer handover schemes mentioned above can be classified into two categories. One, MIPv6 belongs to the host based approach, which requires modification to the protocol stack of the mobile node MS. And the other one, PMIPv6 belongs to the