10.2 Packet Data Services Description
10.2.1 Simple IP
The main characteristic of simple IP is that it does not provide mobility beyond the serving PDSN. The network only provides IP routing service to the current point of attachment in the network (i.e., PDSN). This is equivalent to the dial-up Internet service provider (ISP) service. An MS can roam from one RN to another using the location update procedure, but once a session is established with a PDSN, the MS can't hand over the session to another PDSN. PPP is used to provide the data link protocol between a user and the PDSN. The PDSN
The user authentication is provided by the Password Authentication Protocol (PAP) and the Challenge Handshake Authentication Protocol (CHAP) procedures. The PDSN, acting as an AAA (RADIUS) client, communicates user CHAP or PAP authentication information to the AAA server. PAP is the most basic form of authentication, in which a user's name and password are sent by the user and compared to a table of
Simple IP supports header and payload compression as defined in the TIA/EIA/IS-835 specification. The Van Jacobson's TCP/IP header compression is supported as specified in RFC 1144. The PPP Compression Control Protocol is also
10.2.2 Mobile IP
The mobile IP service (RFC 2002)
provides complete mobility to a user. The PDSN has the functionality of an FA. A user is assigned an HA in its home IP network. The MS is assigned an IP address, called home address, which is in the same subnet as the HA. The MS uses CoA (IP address of the FA) to register with the HA. Registration causes the HA to perform proxy ARP on the home subnet and begins intercepting all packets destined to the MN's home address. The HA also creates a binding between the home address of the MN and the care-of address specified in the Registration request. When the HA receives data for an MS, it forwards the data to the FA using CoA and the FA forwards the data to the MS. Packets destined for the MN are tunnelled using IP-in-IP tunnelling to the care-of address. IP-in-IP tunnelling is specified in RFC 2003. Mobile IP allows an MS to be
As in simple IP, the data link protocol between MS and PDSN is provided by PPP. If the PDSN receives a packet for an MS with no established PPP session, the PDSN discards the packet and sends an ICMP destination unreachable packet to the source. A single PPP session can support multiple IP home addresses, thus allowing different applications per MS.
Mobile IP signaling is exchanged on the traffic channels over the air interface, which is an inefficient usage of the expensive radio resource. There are some improvements with respect to the base mobile IP protocol to make the signaling more RR efficient. One such improvement is that the agent advertisement messages are not broadcast continuously and periodically by the PDSN to all the MS. Instead, they are sent to an MS after establishing PPP connection. Another improvement is that the PDSN can only repeat the advertisements a configurable number of times for an MS. Also, the PDSN stops sending the advertisements to an MS once it receives a registration request from the same MS. As mobile IP runs over the PPP connection, the mobile IP registration lifetime should be smaller than the PPP inactivity timer.
Mobile IP provides its own set of security procedures between mobile client (MS) and mobile agents, and also between the mobile
The MS-FA security procedure is provided by using MS-FA challenge/response mechanism as described in RFC 3012. It is initiated by the PDSN to authenticate a user in a visited domain upon user registration. The PDSN includes an MS-FA challenge extension in the agent advertisement. Since the advertisements are rarely sent, the PDSN includes the next challenge in the registration reply. The MS uses this next challenge in the