== LTE Traffic Trace Collection ==
This wiki page contains the tutorial to collect traffic traces for realtime application such as video, web, mail etc. at RLC, MAC and PDCP layer of LTE protocol stack in ORBIT testbed using OpenAirInterface (OAI).Users were connected over the air using b210 USRPs and data/logs recorded at eNodeB were extraced using standard linux tools. A high level system diagram is given below.

||||||Figure 1: System Diagram - Trace Collection||
 || [[Image(Intro.jpg, 325px)]] || 

=== Description ===
For this experiments we need UEs, eNB having b210s USRP, two other nodes for EPC and Server are also needed. We have used grid sandbox with node8-7 as eNB; node13-7, node13-14 and node8-14 as UEs; node2-2 as EPC; node3-2 as server. More UEs can be added but we have tested with just 3 users in this experiment. A detailed system diagram with list of all the interfaces is given below. This tutorial will cover following sections:
* Setup OAI emulation framework
* Connecting UE to LTE network
* Connecting Multiple UEs
* Running OAI logging Module
* Application Design
* Trace collection and Evaluation
* OAI script

||||||Figure 2: GRID OAI System Design Implementaion - Trace Collection||
 || [[Image(topology.jpg, 650px)]] || 

=== Setup OAI emulation framework ===
1) Loading an image into ORBIT node

* Loading UE image: \\
  UE1: {{{omf load -i ue1.ndz -t node13-14}}}\\
  UE2: {{{omf load -i ue2.ndz -t node13-7}}}\\
  UE3: {{{omf load -i ue3.ndz -t node8-14}}}

* Loading eNB image: \\
  eNB: {{{omf load -i enb.ndz -t node8-7}}}

* Loading EPC image: \\
  EPC: {{{omf load -i epc.ndz -t node2-2}}}

* Loading Server image: \\
  Server: {{{omf load -i baseline.ndz -t node3-2}}}

After loading the image turnon the nodes using command: {{{omf tell -a on -t node13-14,node13-7,node8-14,node8-7,node3-2,node2-2}}}

2) Starting EPC : Run the following commands to enable eth0 interface and to start EPC components - HSS, MME and SPGW:
{{{
ssh root@node2-2
cd /root/openair-cn/SCRIPTS 
ifconfig eth0 192.168.3.1/24 up 
./run_hss 
./run_mme 
./run_spgw
}}}

3) Configuring Server
{{{
ssh root@node3-2
ifconfig eth0 192.168.3.2/24 up
ip route add 172.16.0.2 via 192.168.3.1
}}}

4) Starting eNodeB
{{{
ssh root@node8-7
ifconfig eth1 mtu 1440
cd /root/openairinterface5g/cmake_targets/lte_build_oai/build
sudo -E ./lte-softmodem -P /tmp/oai_enb.pcap -O /root/openairinterface5g/targets/PROJECTS/GENERIC-LTE-EPC/CONF/enb.band7.tm1.25PRB.usrpb210.conf --T_nowait
}}}

=== Connecting UE to LTE network ===
Considering UE1
{{{
ssh root@node13-14
cd /root/openairinterface5g/cmake_targets/tools/
source ./init_nas_s1 UE
cd /root/openairinterface5g/targets/bin
sudo -E ./lte-softmodem.Rel14 -U -C2685000000 -r25 --ue-scan-carrier --ue-txgain 70 --ue-rxgain 80 -W
}}}

In a separate terminal 
{{{
ssh root@node13-14
sudo ifconfig oip1 up
ifconfig oip1 mtu 1440
route add default gw 172.16.0.2
}}}

The Tx and Rx gain have to adjusted based on physical distance between UE and eNB. Same procedure is repeated if you want to add UE2 and UE3 but the IP address will be different. IP address assignment by MME depends on when the UE is attached to network. If UE1, UE2 and UE3 are attached sequentially then their IP address will be {{{172.16.0.2, 172.16.0.4 and 172.16.0.6}}} respectively.

=== Connecting Multiple UEs ===
More users can also be connected for a realistic LTE scenarnio. Apart from the nodes used above {{{node18-2, node18-19 and node3-19}}} has USRPb210s and can be used to emulate UEs. The same UE image can be used but we have to change IMSI and MSISDN for newly added UEs. The following procedure has to be followed to add multiple UE -
* IMEI should be different for different users. Take the same IMEI from HSS database, add it to config of UE but while adding in database (DB) again, make it null (IMP).
* Remove any existing UE with same imsi from DB
* Add in DB using the command below with IMSI, MSISDN
{{{
ssh root@node2-2 (EPC)
mysql -u root -p
linux
INSERT INTO users (`imsi`, `msisdn`, `imei`, `imei_sv`, `ms_ps_status`, `rau_tau_timer`, `ue_ambr_ul`, `ue_ambr_dl`, `access_restriction`, `mme_cap`, `mmeidentity_idmmeidentity`, `key`, `RFSP-Index`, `urrp_mme`, `sqn`, `rand`, `OPc`) VALUES ('To be changed', 'To be changed', NULL, NULL, 'NOT_PURGED', '120', '50000000', '100000000', '47', '0000000000', '7', 0x8BAF473F2F8FD09487CCCBD7097C6862, '1', '0', '', 0x00000000000000000000000000000000, '');
}}}
* At UE change and build the config file as below:
{{{ 
./conf2uedata -c ~/openairinterface5g/openair3/NAS/TOOLS/ue_eurecom_test_sfr.conf -o ~/openairinterface5g/targets/bin
}}}
* Build the UE again using: 
{{{
source ./init_nas_s1 UE
}}}

=== Running OAI logging Module ===
To collect the trace we need to enable T tracer present in OAI before starting the application and eNB. The following command is used to obtain the trace at eNB: 
In a different terminal-
{{{
cd /root/openairinterface5g/common/utils/T/tracer;./textlog -d ../T_messages.txt -ip 0.0.0.0  -on MAC -on RLC -on PDCP -on RRC -no-gui >  /var/log/enbtracer.log 2> /var/log/enbtracer.log &
}}}