Page 400 - From GMS to LTE

386 From GSM to LTE-Advanced Pro and 5G

HTTP, TLS and the Extensible Markup Language (XML) as part of the XCAP protocol,
which is also used for the VoLTE supplementary service configuration described earlier
in the chapter. The following list shows some of the parameters that are administered by
the MCPTT database for a group:

SIP group ID (e.g. 123456@example.com).
●
Name for the group call for display on users’ devices.
●
The list of users that are included in the call. The list includes a user’s SIP identity, a
●
display name that may describe the user’s role in the group and the user’s priority.
Whether users shall be invited when the group call is established.
●
Whether the group is pre‐arranged or whether the group is a chat group which allows
●
members to be invited.
Rules for joining and leaving and minimum number of participants.
●
Rules for automatic call take down (inactivity, minimum number of users, etc.).
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The overall priority of the group, which is important in case of network congestions.
●
Whether the group’s priority can be changed to ‘emergency’ status and whether
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‘emergency alerts’ and ‘imminent peril’ warnings can be sent with the group ID with-
out establishing the call itself.
Which services are supported in the group (typically voice).
●
In addition, the MCPTT system can also include an encryption key management
server to manage and distribute keys in case additional encryption for a group call is
required beyond the default encryption of unicast bearers between the LTE eNodeB
and individual user devices.
In some cases it might be required that a client is informed if a parameter is changed
in the group database for a group they are subscribed to. If required, a client can per-
form a SIP ‘Subscribe’ for the group in a way similar to that discussed earlier in the
chapter for requesting information about VoLTE registration changes.

5.7.10 eMBMS for MCPTT
As noted in the introduction section it is optionally possible to use a single IP multicast
bearer in a cell for the downlink audio channel of a group call instead of individual
transmissions to each recipient. If many participants are in the cell this significantly
reduces the amount of bandwidth required. This section describes how this can be
implemented in LTE with eMBMS (Multimedia Broadcast Multicast Service), which is
described in 3GPP TS 23.246 [37]. Originally, eMBMS was designed for distributing live
video content, such as TV programs, nationwide or locally, e.g. in a stadium during
football events. While broadcasting is defined as a multicast stream that can be received
by everyone without network interaction, multicasting is defined as a multicast stream
that individual devices have to first subscribe to and get permission to access. In prac-
tice eMBMS is not very widely used so far, mostly due to an unclear forecast of how the
service could be successfully monetized by network operators.
On the Internet and also in LTE networks, most IP data is sent in unicast mode. This
means that an IP packet is sent from one source to one destination, e.g. from a web
server to a web browser. For some applications, such as streaming live audio and live
video content that many people would like to receive at the same time, unicasting pro-
duces a lot of network traffic as the server must send a copy of each packet to each