Packet Data Transport Process Flow

CDMA2000 data services fall within two distinct categories: circuitswitched
and packet. Circuit-switched data is handled effectively the same
as a voice call. But for all packet data calls, a PDSN is used as the interface
between the air interface data transport and the fixed network transport.
The PDSN interfaces to the base station (BS) through a Packet Control
Function (PCF), which can be colocated with the BS.
The CDMA2000 has three packet data service states that need to be
understood in the process:
■ Active/connected Here a physical traffic channel exists between
the subscriber unit and the BS, with packet data being sent and
received in a bidirectional fashion.
■ Dormant No physical traffic channel exists, but a PPP link between
the subscriber unit and the PDSN is maintained.
■ Null/inactive Neither a traffic channel nor a PPP link is maintained
or established.
The relationship between the three packet data states is best shown in
the simplified state diagram in Figure 7-7.
CDMA2000 introduces to the mobility environment real packet data
transport and treatment at speeds that meet or exceed the IMT-2000 system
requirements. The voice call processing that is implemented by
CDMA2000 is functionally the same as that of existing cdmaOne networks,
with the exception that a vocoder change exists in the subscriber units.
However, the key difference is that packet data can now be handled by the
network.
The mobile initiates the decision as to whether the session will be a
packet data session, voice session, or concurrent session, meaning voice and
data. The network at this time cannot initiate a packet data session with
the subscriber unit, with the exception of the Standard Management System
(SMS), which does require a packet data session.
For call processing, the voice and data networks are segregated in general
once the information, whether it is voice or data, leaves the radio environment
at the BSC itself. Therefore, for packet data, the PDSN is central
to all decisions. Figure 7-8 depicts a generalized network architecture.

The PDSN does not communicate directly with the voice network nodes
like the HLR and VLR; instead it is done via the AAA. As discussed previously,
the voice and data networks normally are segregated once they leave
the radio environment at the BSC. Additionally, in a CDMA2000 network,
the system utilizes PPP between the mobile and the PDSN for every type
of packet data session that is transported and/or treated.
The PDSN is meant to provide several key packet data services, including
Simple IP and Mobile IP. Also, several variants, to be discussed shortly,
are relative to each of these services. However, the concepts behind Simple
IP and Mobile IP need to be explored first.

Simple IP is a packet data service relative to CDMA2000 1xRTT and is
where the subscriber is assigned a Dynamic Host Configuration Protocol
(DHCP) address from the serving PDSN with its routing service provided
by the local network. The specific IP address that the subscriber is assigned
remains with the subscriber as long as it is served by the same radio network
that maintains connectivity with the PDSN that issued the IP
address. It is important to note that Simple IP does not provide for mobile
terminations and therefore is an origination-based service only, that is, a
PPP service using DHCP.

In Mobile IP, the public IP network provides the mobile’s IP routing service.
In this functionality, the mobile is assigned a static IP address that
resides with the HA. A key advantage of Mobile IP over simple IP is that
the mobile, due to the static IP address, can handoff between different radio networks that are served via different PDSNs, which resolves the ROAMing
issues that are part of Simple IP. Mobile IP, due to the static IP, also
enables the possibility for mobile terminations.
Now with mobility, whether the packet service is Simple or Mobile IP, the
notion of mobility is fundamental to the concept of CDMA2000. Figure 7-9
illustrates some of the internetwork communication that needs to take
place for establishing a packet data session.
It is important to note that the transport of the packets is not depicted in
Figure 7-9. It shows just the elements in the network that need to communicate
in order to establish which services the subscriber is allowed to have
and how the network is going to meet the Service-Level Agreement (SLA)
that is expected for the packet session.
The VLR, is normally colocated with the MSC, as shown in Figure 7-9.
When a subscriber initiates a packet data session the BSC via the
MSC/VLR to check the subscriber subscription information prior to the system
granting the service request to the mobile subscriber. This will take
place prior to the PDSN being involved with the packet session.
Elaborating on the various packet sessions available for use within a
CDMA2000 network are, of course, Simple IP and Mobile IP. However,
along with each of these packet session types are two variants where one
uses a VPN and the other does not:
■ Simple IP
■ Simple IP with VPN
■ Mobile IP
■ Mobile IP with VPN
A more specific discussion of Simple IP and Mobile IP is covered in the
next section.