Mobile IP

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Mobile IP

a.k.a. MIP, MIPv4 (MIP for IPv4), MIPv6 (MIP for IPv6)

Defined by IETF RFC 3344, Mobile IP is an architecture that allows a mobile device to move from one network to another while maintaining the same IP address. Use of Mobile IP in cdma2000 wireless IP networks is defined in IS-835 (3GPP2 X.S0011).

Mobile IP is supported by two network elements:

  • Home Agent (HA) – The HA is located in a user’s home network. Mobile IP Mobile Node (MN) must register with their HA to obtain an IP address when establishing a packet data session. This IP address is known as the home address and does not change during the packet data session, even if the mobile roams into a new area. Other functions provided by the HA include:
  • authenticates Mobile IP registrations
  • redirects packets to the serving foreign agent (FA)
  • may receive and route reverse packets from the FA
  • receives provisioning information from the H-AAA

An operator must have a HA to support Mobile IP for their own subscribers. If an operator only needs to support Mobile IP for inbound roamers (i.e., subscribers from other networks), a HA is not required since these inbound roamers will register with the HA in their own home network.

  • Foreign Agent (FA) – Each serving network that supports Mobile IP must provide a FA. FA capability is typically a software upgrade to the PDSN; as such, the FA is often referred to as the PDSN/FA. The FA is a Mobile IP device’s “Point of Attachment” to the data network and provides a Care-of-Address (CoA) for the mobile device in the serving network. The FA is required to support Mobile IP for both inbound and outbound roamers.

Mobile IP works by using two IP addresses for each Mobile IP device:

  • Home address – The home address is the IP address assigned to a MN by its HA when it registers for a new packet data session. This address is topologically associated with the home network and does not change for the duration of the packet data session. The home address is the IP address used by anyone attempting to reach the MN.
  • Care-of-Address (CoA) – The CoA is the IP address of the FA currently serving the MN. When traffic addressed to a MN’s home address is received at the HA, the HA forwards this traffic to the CoA for delivery to the MN. If the MN roams into a network served by different FA, the new serving FA will provide a new CoA for the MN; however, the MN’s home address remains unchanged. Thus, roaming from one FA area to another is transparent to transport and higher-layer protocols and applications.

In the Mobile IP roaming architecture, traffic sent from the MN is typically tunneled from the serving FA to the HA using a reverse tunnel with either IP-in-IP or GRE encapsulation. Traffic sent to the MN’s home address is received by the HA and forwarded to the FA via the CoA.

In CDG Executive Board Resolution 20060725, Mobile IP was identified as an architecture to be provided by all operators for supporting CDMA packet data international roaming.

For information on using Mobile IPfor packet data roaming, see CDG Reference Document #136.


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