Cell Traffic
Trace
The Cell Traffic Trace feature for subscriber and equipment tracing
provides detailed information at the call level on one or more UEs and serves
as an additional source of information (along with Performance Measurements)
for monitoring and optimization operations.
This section describes MME support for Cell Traffic Trace.
Feature
Description
The Cell Traffic Trace feature, for subscriber and equipment tracing,
provides detailed information at the call-level on one or more UEs and serves
as an additional source of information (along with Performance Measurements)
for monitoring and optimizing operations.
The Cell Traffic
Trace feature provides a 3GPP standard-based cell trace function for tracing
all calls in a single cell or multiple cells. Cell Tracing provides the
capability to log on to data on any interface at a call level for a specific
user or mobile type or a service initiated by a user. In addition, Cell Tracing
provides instantaneous values for a specific event.
Trace
activation/deactivation is administered by an entity called an Element Manager
(EM) on the Network Elements (NE) that comprise the network. The NE generate
the trace data or results and transfers the information to a Trace Collection
entity (TCE). Trace activation/deactivation can be of two types:
- Management Activation/Deactivation -
Trace activated/deactivated in different NEs directly by using the management
EM.
- Signaling based
Activation/Deactivation - Trace activated/deactivated in different NEs using
signaling interfaces between them. The NEs forward the activation/deactivation
originating from EM.
In an EPS network,
trace is enabled on the following NE: eNodeB, MME, SGW, PGW, HSS, EIR and so
on. Cell Traffic Trace enables tracing of all active at one or more Cells in
eNodeBs.
A valid license key
is required to enable Cell Traffic Trace. Contact your Cisco Account or Support
representative for information on how to obtain a license.
How It Works
When Cell Traffic Trace
is activated in the monitored cell(s) of E-UTRAN, the
eNodeB starts a Trace Recording Session for new calls/session
and also for existing active calls/session. A
Trace Recording Session Reference (TRSR) is allocated
by eNodeB for each of the monitored call/session. The
TRSR includes the TRSR reference along with the Trace Reference
and TCE address in the CELL TRAFFIC TRACE message to the MME over
S1 connection.
Cell Traffic Trace
Procedures are used at the MME to assist the TCE Server in correlating the
Trace Reference (generated by EM) and Trace Recording
Session Reference (generated by the eNodeB) with
the IMSI, IMEI (SV) corresponding to
the traced session as the eNodeBs only have access to temporary
UE identities and not permanent identities (IMSI, IMEI (SV)).
Cell Traffic Trace
involves the following nodes:
- Network Element (NE): Network
elements are the functional component to facilitate subscriber session
trace in mobile network. The term network element refers
to a functional component that has standard interfaces in and out
of it. It is typically shown as a stand-alone
AGW. Examples of NEs are the MME, S-GW, and
P-GW.
- Element Manager (EM): The
Element Manager (EM) forwards the globally unique
Trace Reference to each eNodeB.
- eNodeB
- MME and
- Trace Collection Entity (TCE) server
The Cell Traffic Trace
feature operates sequentially and is classified into two stages:
- Trace Files management - Creation
of Trace files, renaming and moving trace files to respective
directories, compression and archiving of trace files. The
configuration for this process is discussed in the Configuring Cell
Traffic Trace section.
- Decompression - This
process is executed to extract compressed and archived files. The
files are named by a .gz extension. It
is highly recommended to use tar for the decompression process. The
command syntax to decompress the trace files is as follows: Syntax: tar -zxf
<file_name>.gz
Architecture
MME supports the
following in Cell Traffic Trace:
- When MME receives a Cell Traffic Trace
message from eNodeB, it extracts the Trace Reference and Trace Recording
Session Reference, and checks for the IMSI and IMEI if present, from the S1 AP
ID.
- The MME send the IMSI, IMEI if
present, and the Trace References received in a Cell Traffic Trace to the TCE.
The TCE address is received in the Cell Traffic Trace signal from eNodeB.
- The MME complies with data formats of
Trace Reference, Trace recording Session Reference and TCE Address.
The Cell Traffic
Trace operation takes place in the following stages:
Stage 1: Creation of trace files on
expiry of Collection Timer
- A list is initialized at the session
manager to store relevant information of all the incoming cell trace messages.
- Once the collection timer expires, the
session manager gathers all the cell traces into a file, which has a temporary
name, and writes it to the hard-disk.
Stage 2: Renaming and moving the files to archive directories by
session trace
- The session trace
renames these temporary filenames to C Type filenames. The C Type file name is
a modified version of the 3gpp specification. A suffix is added to every C type
file. Thus starting from 1 the suffix ends at 4294967295. After reaching the
maximum limit, then the suffix restarts from 1. The files are then moved to the
directories.
For example,
refer to the file name given below:
C20150520.0137-0400-MME.RTPBNGASR5KCH78.21436500008D-1C20150529.0231-0400-MME.RTPBNGASR5KCH78.3143650000FF-4294967295
The C Type file
format is modified to provide additional trace information with a trace
extension, which has three additional fields such as eNodeB ID, UE S1 AP
identity and the MME UE S1 AP identity.
- A new archive
directory is created by the session trace when the previous directory is full.
The syntax for the new directory is as follows: Syntax:
<nodename>.<time-stamp in
seconds>.<tce_index>.<file-counter>. For example:
RTPBNGASR5KCH78.555ac613.1.1
- If the cell trace
messages are meant to be for two different TCE's, then a second directory would
be created and the files are moved to their directories respectively.
Stage 3: Compression and Archiving files to directories by session
trace
- Session trace waits for a configured file count or timer expiry or
directory size to be reached before archiving the directories.
- Once the archive directories are full, the session trace archives
or compresses these directories and moves them to the final directories.
The above mentioned
files and are monitored and processed to their final directories based on the
following timers:
- Collection timer: This
timer is configurable, and the timer ranges from 0 - 255 seconds. The
collection timer is triggered by the session manager. Once the timer expires,
the session manager writes the files to the staging location in the hard disk.
After all files are written, a messenger call is sent from session manager to
session trace indicating the details of the new file.
- Archive trigger timer:
This timer is configurable, and the timer ranges from 1 to 3600 seconds. The
Archive timer is triggered by the session trace. This timer is a safety
mechanism to make sure archive directories are closed and sent for compression
and archiving.
Limitations
Decompression of the
trace files using gzip or gunzip may cause file corruption depending
on the system platform used, for example: Linux. Mac
and so on
Standards Compliance
The Cell Traffic
Trace feature complies with the following standards:
- 3GPP TS 36.413
Release 10, S1 Application Protocol (S1AP)
- 3GPP TS 32.422
Release 10, Trace control and configuration management
- 3GPP TS 32.423
Release 10, Trace data definition and management
Configuring Cell
Traffic Trace
This section
documents configuration of Cell Traffic Trace and its related functionality.
Configuring Trace
Files Storage
The configuration
provided in the below section is used to store the cell traffic trace files
locally or on a TCE server.
The commands
illustrated below configure the Cell Traffic Trace. In support of the Cell
Trace feature, the
enb keyword has
been added, which monitors the traffic from the eNodeB network element. The
configuration also includes archiving and compression parameters to archive and
compress trace files into their directories.
Local
Storage
To store the trace
files locally, use the following configuration:
configure
session trace network-element enb tce-mode none collection-timer timer_value
[ no ] session trace network-element enb
end
Notes:
All parameters are
new to the Cell Traffic Trace feature. For information on these parameters
refer to the
session trace
command in the
Command Line
Interface Reference.
TCE Server
Storage
To store the trace
file on a TCE server, use the following configuration:
configure
session trace network-element enb tce-mode push transport sftp path server_path_name username user_name [ encrypted ] password user_password collection-timer timer_value
[ no ] session trace network-element enb
end
Notes:
All parameters are
new to the Cell Traffic Trace feature. For information on these parameters
refer to the
session trace
command in the
Command Line
Interface Reference.
Configuring Cell
Traffic Trace Template - Archiving and Compressing Trace Files
The configuration
provided in this section is used to archive and compress trace files into their
directories.
This command creates
a template with parameters that configure archiving and/or compression for the
files generated by Cell Traffic Trace. Defining this template and archiving
and/or compression of files is optional when setting up Cell Traffic Trace. The
enb keyword
processes Cell Traffic Trace in the MME.
configure
template-session-trace network-element enb template-name cell-trace
[ no ] disk-limit disk_size
[ no ] archive files number_of_files size size timer timer_value
[ no ] trace-extension enb-id ue-s1ap-id
end
Notes:
- cell-trace indicates the template name
'cell-trace' for storage of the eNodeB cell trace storage parameters. Note that
you cannot define a template name - there is only one template and its name is
'cell-trace'.
- disk-limit
disk_size is
measured in megabytes (MB). This keyword defines the total space to be reserved
on the hard disk. If disk-limit alone is configured then compression is not
considered. The disk-limit size ranges from 1 MB to 20480 MB. If disk-limit is
not configured, a default size of 200 MB is allocated in the hard disk for
storing Cell Trace files.
- archive allows you to define the archive directory
and the archive parameters.
- files
number_of_files
defines the maximum number of files that can be archived in the directory. When
the limit is reached, the archive closes. The range is an integer from 1 to
10000.
- size
size defines
the directory limit in MB. The range is an integer from 1 to 10
- timer
timer_value
defines the total time in seconds before the pending directories are archived.
The range is an integer from 1 through 3600.
- The
trace-extension
keyword defines the UE or eNodeB identity extension parameters for the C Type
files.
- The
enb-id keyword
is an additional field in the C Type file that identifies the global eNodeB
entry.
- The
ue-s1ap-id
keyword is an additional field in the C Type file that identifies the eNodeB
ID, UE S1 AP identity and the MME UE S1 AP identity.
Verifying the Cell
Traffic Trace Configuration
The following command
is used to display/verify the parameters for Cell Traffic
Trace from the eNodeB network element.
show session trace template network-element enb template-name cell-trace
On running the above
mentioned show command the following statistics are displayed:
Template name: cell-trace
NE Type: ENB
Cell Trace file Extension entries: GLOBAL-ENB-ID ENB-UE-S1AP-ID MME-UE-S1AP-ID
Storage Parameters for Archiving Cell trace files:
Disk Storage Limit: 200 MB
Files per Archive Directory: 4000
Total size per Archive directory: 3 MB
Archive directory timeout: 300 seconds
Monitoring and
Troubleshooting the Cell Traffic Trace
The following
section describes commands available to monitor Cell Traffic Trace
on the MME.
Cell Traffic Trace
Show Command(s) and/or Outputs
show session trace
statistics
On running the above
mentioned show command, statistics similar to the following
are displayed:
Interface not traced: 0
Total number of file generated: 25541
Number of Cell Traffic Trace files generated: 25541
Total archive files: 7
Avg Time in secs, for archiving one directory: 2.247592
Avg Time in secs, for Moving one C type file: 0.0200471
Avg files per archive directory: 3648
Frequency of Archiving Triggers:
Files: 5
Size: 1
Time-out: 1
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