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This section is divided into two main parts - GPRS scenarios, and scenarios with the IP Multimedia Subsystem (IMS). The first part - GPRS scenarios - concentrates on scenarios with a User Equipment (UE) connecting to services in the Internet, e.g., mail, web. The second part - IMS scenarios - then describes how an IMS capable UE can connect to other SIP-capable nodes in the Internet using the IMS services.
1. GPRS Scenarios
This section describes the scenarios that might occur when a GPRS UE contacts services, or nodes outside the GPRS network, e.g., web- server in the Internet.
Transition scenarios of the GPRS internal interfaces are outside of the scope of this document. The following scenarios are described here. In all of the scenarios, the UE is part of a network where there is at least one router of the same IP version, i.e., GGSN, and it is connecting to a node in a different network.
The scenarios here apply also for PDP Context type Point-to-Point Protocol (PPP) where PPP is terminated at the GGSN. On the other hand, where the PPP PDP Context is terminated e.g., at an external ISP, the environment is the same as for general ISP cases.
1) Dual Stack UE connecting to IPv4 and IPv6 nodes
2) IPv6 UE connecting to an IPv6 node through an IPv4 network
3) IPv4 UE connecting to an IPv4 node through an IPv6 network
4) IPv6 UE connecting to an IPv4 node
5) IPv4 UE connecting to an IPv6 node
1) Dual Stack UE connecting to IPv4 and IPv6 nodes
The GPRS system has been designed in a manner that there is the possibility to have simultaneous IPv4, and IPv6 PDP Contexts open. Thus, in cases where the UE is dual stack capable, and in the network there is a GGSN (or separate GGSNs) that supports both connections to IPv4 and IPv6 networks, it is possible to connect to both at the same time. Figure 3 depicts this scenario.
+-------------+
| |
| UE | +------+
| | | IPv4 |
| | /| |
|------|------+ / +------+
| IPv6 | IPv4 | +--------+ /
+-------------+ IPv4 | | /
|/
| |------------------------|
| | |
| IPv6 | GGSN |\
|-------------------------------| | \
+-----------+ | | \ +------+
| GPRS Core | | | \ | IPv6 |
+-----------+ +--------+ \| |
+------+
Figure 3: Dual-Stack Case
However, the IPv4 addresses may be a scarce resource for the mobile operator or an ISP. In that case, it might not be possible for the UE to have a globally unique IPv4 address allocated all the time. Hence, the UE could either activate the IPv4 PDP Context only when needed, or be allocated an IPv4 address from a private address space.
2) IPv6 UE connecting to an IPv6 node through an IPv4 network
Especially in the initial stages of IPv6 deployment, there are cases where an IPv6 node would need to connect to the IPv6 Internet through a network that is IPv4. For instance, this can be seen in current fixed networks, where the access is provided via IPv4 only, but there is an IPv6 network deeper in the Internet. This scenario is shown in Figure 4.
+------+ +------+
| | | | +------+
| UE |------------------| |-----------------| |
+-----------+ | GGSN | +---------+ | IPv6 |
| |
| IPv6 | | GPRS Core | | | | IPv4 Net| | |
+-----------+ +------+ +---------+ +------+
+------+
Figure 4: IPv6 nodes communicating over IPv4
In this case, in the GPRS system, the UE would be IPv6 capable, and the GPRS network would provide an IPv6 capable GGSN in the network. However, there is an IPv4 network between the GGSN, and the peer node.
3) IPv4 UE connecting to an IPv4 node through an IPv6 network
Further in the future, there are cases where the legacy UEs are still IPv4 only, capable of connecting only to the legacy IPv4 Internet. However, the GPRS operator network has already been upgraded to IPv6. Figure 5 represents this scenario.
+------+ +------+
| | | | +------+
| UE |------------------| |-----------------| |
| | +-----------+ | GGSN | +---------+ | IPv4 |
| GPRS Core | | | | IPv6 Net| | |
| IPv4 |
+------+ +-----------+ +------+ +---------+ +------+
Figure 5: IPv4 nodes communicating over IPv6
In this case, the operator would still provide an IPv4 capable GGSN, and a connection through the IPv6 network to the IPv4 Internet.
4) IPv6 UE connecting to an IPv4 node
In this scenario, an IPv6 UE connects to an IPv4 node in the IPv4 Internet. As an example, an IPv6 UE connects to an IPv4 web server in the legacy Internet. In the figure 6, this kind of possible installation is described.
+------+
+------+
| | | | +---+ +------+
| UE |------------------| |-----| |----| |
| | +-----------+ | GGSN | | ? | | IPv4 |
| IPv6 | | GPRS Core | | | | | | |
+------+ +-----------+ +------+ +---+ +------+
Figure 6: IPv6 node communicating with IPv4 node
5) IPv4 UE connecting to an IPv6 node
This is similar to the case above, but in the opposite direction. Here an IPv4 UE connects to an IPv6 node in the IPv6 Internet. As an example, a legacy IPv4 UE is connected to an IPv6 server in the IPv6 Internet. Figure 7 depicts this configuration.
+------+ +------+
| | | | +---+ +------+
| UE |------------------| |-----| |----| |
| | +-----------+ | GGSN | | ? | | IPv6 |
| IPv4 | | GPRS Core | | | | | | |
+------+ +-----------+ +------+ +---+ +------+
Figure 7: IPv4 node communicating with IPv6 node
2. IMS Scenarios
As described in section 3.2, IMS is exclusively IPv6. Thus, the number of possible transition scenarios is reduced dramatically. In the following, the possible transition scenarios are listed.
1) UE connecting to a node in an IPv4 network through IMS
2) Two IPv6 IMS connected via an IPv4 network
1) UE connecting to a node in an IPv4 network through IMS
This scenario occurs when an IMS UE (IPv6) connects to a node in the IPv4 Internet through the IMS, or vice versa. This happens when the other node is a part of a different system than 3GPP, e.g., a fixed PC, with only IPv4 capabilities. This scenario is shown in the Figure 8.
+------+ +------+ +-----+
| | | | | | +---+ +------+
| UE |-...-| |-----| IMS |--| |--| |
| | | GGSN | | | | ? | | IPv4 |
| IPv6 | | | | | | | | |
+------+ +------+ +-----+ +---+ +------+
Figure 8: IMS UE connecting to an IPv4 node
2) Two IPv6 IMS connected via an IPv4 network
At the early stages of IMS deployment, there may be cases where two IMS islands are only connected via an IPv4 network such as the legacy Internet. See Figure 9 for illustration.
+------+ +------+ +-----+ +-----+
| | | | | | | |
| UE |-...-| |-----| IMS |----------| |
| | | GGSN | | | +------+ | IMS |
| IPv6 | | | | | | IPv4 | | |
+------+ +------+ +-----+ +------+ +-----+
Figure 9: Two IMS islands connected over IPv4 |
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