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