Getting Started

To get started with srsEPC you will require a PC with a GNU/Linux based operating system. This can be a distribution of your preference, such as Ubuntu, Debian, Fedora, etc.

If you are using Ubuntu, you can install from the binary packages provided:

sudo add-apt-repository ppa:srslte/releases
sudo apt-get update
sudo apt-get install srsepc

If you are using a different distribution, you can install from source using the guide provided in the project’s GitHub page.

After installing the software you can install the configuration files into the default location (~/.config/srslte), by running:

srslte_install_configs.sh user

Running the software

To run srsEPC with default parameters, run sudo srsepc on the command line. srsEPC needs to run with sudo admin privileges in order to create a TUN device. This will start the EPC and it will wait for eNBs and UEs to connect to it.

srsEPC will start a TUN interface srs_spgw_sgi that will allow user-plane packets to reach the UEs.

Configuration

The EPC can be configured through two configuration files: epc.conf and user_db.csv. The epc.conf will hold general configuration parameters of the MME, SPGW and the HSS. This includes PLMN value, integrity/ciphering algorithms, APN, SGi IP address, GTP-U bind address, etc.

The user_db.csv is used to keep UE specific parameters for the HSS. This will include IMSI, authentication algorithms, K, OP or OPc, etc.

In the following subsections, we will cover a few common configuration cases with srsEPC: adding a new UE to the HSS database, running the eNB and EPC on separate machines, and setting up network routing to enable UEs to connect to the Internet.

Adding an UE to HSS database

When adding a UE to be able to the user_db.csv database that the HSS will use, you must make sure that that parameters in that file match the parameters stored in the UE’s USIM card.

Of particular relevance are the IMSI, authentication algorithm, K and OP or OPc (if using the MILENAGE algorithm). The IMSI is the unique identifier of the SIM card, the K the secret key that the HSS and the UE use to authenticate each other.

The usual authentication algorithm used by SIM cards is MILENAGE, but there are also test SIMs that use XOR authentication. If you are using the MILENAGE algorithm, you must also know whether you are using OP or OPc and the corresponding value of this parameter.

Once you know these parameters you can replace then in the user_db.csv which has the following format:

(ue_name),(algo),(imsi),(K),(OP/OPc_type),(OP/OPc_value),(AMF),(SQN),(QCI),(IP_alloc)

So, if you have a SIM card with the following parameters:

  • MILENAGE algorithm
  • IMSI = 901700000000001
  • K = 00112233445566778899aabbccddeeff
  • Using OPc
  • OPc = 63bfa50ee6523365ff14c1f45f88737d

You can configure the user_db.csv like this:

ue1,mil,901700000000001,00112233445566778899aabbccddeeff,opc,63bfa50ee6523365ff14c1f45f88737d,9000,000000000000,9,dynamic

eNBs and srsEPC on separate machines

By default, srsEPC is configured to run with srsENB on the same machine. When running srsEPC with an eNB on a separate machine, all that is necessary to configure is the mme_bind_addr and the gtpu_bind_addr.

The MME bind address will specify where the MME will listen for eNB S1AP connections. The GTP-U bind address should be the same as the MME bind address, unless you want to run the user-plane on a different sub-net then the S1AP connection.

So if you want to listen to eNB on the interface with IP 10.0.1.10, you can do:

sudo srsepc --mme.mme_bind_addr 10.0.1.10 --spgw.gtpu_bind_addr 10.0.1.10

Connecting UEs to the Internet

To allow UEs to connect to the Internet, it is necessary to perform IP masquerading. Without masquerading, the Linux kernel will not do packet forwarding from one subnet to another.

To enable this, you can run a convenience script sudo srsepc_if_masq <out_interface>, where out_interface is the interface that connects the PC to the Internet.

Warning

out_interface is NOT the srs_spgw_sgi interface, but the Ethernet or WiFi ethernet that connects the PC to the Internet.

Observing results

By default, log files are stored in /tmp/epc.log. This file can be inspected to troubleshoot any issues related to srsEPC. Log files can have multiple verbosity levels, which can be configured in the epc.conf or through the command line. They can also be enabled on a per-layer capacity, which is useful when troubleshooting a specific layer.

The srsEPC application supports packet capture (pcap) of S1AP messages between the MME and eNodeBs. Enable packet captures in epc.conf or on the command line, by setting the pcap.enable value to true. Capture files are created by default at /tmp/epc.pcap and can be viewed using Wireshark (www.wireshark.org). To view in wireshark, edit the preferences of the DLT_USER dissector (add an entry with DLT=150, Payload Protocol=s1ap).