The Session Tracing
feature provides a 3GPP standards-based subscriber session-level trace function
for call debugging and testing new functions and access terminals in an LTE
In general, the
Session Trace capability records and forwards all control activity for the
monitored subscriber on the monitored interfaces. This is typically all the
signaling and authentication/subscriber services messages that flow when a UE
connects to the access network.
The EPC network
entities like MME, S-GW, P-GW support 3GPP standards based session-level trace
capabilities to monitor all call control events on the respective monitored
interfaces including S6a, S1-MME and S11 on MME, S5, S8, S11 at S-GW and S5 and
S8 on P-GW. The trace can be initiated using multiple methods:
Important: Once the trace is provisioned it can be provisioned through the
access cloud via various signaling interfaces.
initiation via direct CLI configuration
initiation at HSS with trace activation via authentication response messages
over S6a reference interface
activation through signaling from subscriber access terminal
The session level
trace function consists of trace activation followed by triggers. The time
between the two events is where the EPC network element buffers the trace
activation instructions for the provisioned subscriber in memory using camp-on
monitoring. Trace files for active calls are buffered as XML files using
non-volatile memory on the local dual redundant hard drives on the chassis. The
trace depth defines the granularity of data to be traced. Six levels are
defined including maximum, minimum and medium with ability to configure
additional levels based on vendor extensions.
Important: Only maximum trace depth is supported in the current release.
The following figure
shows a high-level overview of the session-trace functionality and deployment
Figure 1. Session
Trace Function and Interfaces
All call control
activity for active and recorded sessions is sent to an off-line Trace
Collection Entity (TCE) using a standards-based XML format over a FTP or secure
FTP (SFTP) connection.
Note: In the current
release the IPv4 interfaces are used to provide connectivity to the TCE. trace
activation is based on IMSI or IMEI.