Page 313 - From GMS to LTE

Long Term Evolution (LTE) and LTE-Advanced Pro 299

UE Network
Attach (PDN Connectivity Request,
PDN Type IPv4v6 (or IPv6), DNS server IPv6 address request)

ESM Information Request
LTE Session Management
(ESM) ESM Information Response (APN, DNS Server IPv6 address request)
Signaling plane
Activate Default Bearer Context Request (temp. IPv6 interface id.,
IPv6 address of DNS server)
Activate Default Bearer Contest Accept

IPv6 address negotiation IPv6 Router Solicitation Message with Link Local IPv6 address
IPv6 Router Advertisement (IPv6 Prefix Information)
User plane
Global IPv6 address valid

Figure 4.29 IPv6 default bearer establishment.

To get an IPv6 prefix from the network the first action taken by a mobile device when
initially connecting to the network is to request an IPv6 or IPv4v6 default bearer, as
shown in Figure 4.29. In LTE this is done in the PDN Connectivity Request message that
is sent as part of the LTE attach process. In the message the following two information
elements are included:

PDN type: IPv4v6
[…]
Protocol or Container ID: DNS Server IPv6 Address Request (0x0003)

The first information element is the PDN type, which can be set to IPv4, IPv6 or to
IPv4v6 to get both an IPv4 address and an IPv6 prefix. In the example above the mobile
device requests both IPv4 and IPv6 connectivity. The second information element is
necessary to get an IPv6 DNS server address to be able to perform domain name resolution
later on.
In practice, most LTE devices and networks are configured in such a way that the
network asks the mobile device for the Access Point Name (APN) during the attach
process. This is done with an ESM (Session Management) Information Request mes-
sage sent from the network once the device has been authenticated and encryption has
been activated. The mobile responds with an ESM Information Response message that
contains, among other things, the APN name and once again the request to send an
IPv6 DNS server address. The network then assigns an IPv4 address and an IPv6 prefix
and instructs the mobile to establish an LTE ‘bearer’ with the Activate Default Bearer