Use this small demo software to setup a localbreakout daemon on the node that terminates the LTE air interface. It has been tested with OAI and srsLTE.
Download a short demo video here.
In the video I followed the same naming conventions (IP addresses, interfaces) as in this guide.
To compile on ubuntu install first some required libraries and binaries on on the node that will run the software (and that runs the eNB):
sudo apt-get install libmnl-dev libnetfilter-queue-dev openvpn tshark
then run make.
- openvpn is needed to create the tunnel interface;
- tshark is used to sniff the GTP tunnel signalling ASN.1 traffic.
In the following description we assume the following topology:
-
a working LTE network (addresses in the ipLTE line), with ENB and SPGW/MME sharing a datalink segment (addresses in the ipLAN line);
-
an additional 'virtual' tun/tap network on the node running the eNB (address in the ipLB line).
ipLTE : 192.168.200.2 192.168.200.1
:
: UE ENB+lbo SPGW/MME
: o--> air <--USRP----o-------ethernet LAN---------o
: |
ipLAN : |10.20.13.91 10.20.13.92
: |
: |
: |
ipLB : 172.21.20.100
Additionally we consider the following names for the interfaces:
- UE: interface ppp0 (address 192.168.200.2);
- SPGW: interface gtp0 (address 192.168.200.1) and eth0 (address 10.20.13.92);
- eNB: interface enp0s31f6 (address 10.20.13.91) and tun10 (address 172.21.20.100).
On UE the route for SPGW is the default of the ppp0 and points to 10.64.64.64. UE traffic travels to/from SPGW embedded into GTP/UDP datagrams exchanged on the ethernet segment.
To set up the local break out daemon run in the following order:
-
Create a tun interface on the eNB:
We need to assign an address that is not used in this case 172.21.20.100.
We need to tell the eNB where is the UE (usually the eNB does not directly exchange traffic with the UE, it acts as a sort of "proxy") so that it can reach it through this new interface.
We have to intercept GTP traffic leaving the eNB and divert it to the localbreakout daemon with the help of netfilter/iptables. In this way the localbreakout daemon can decide which traffic should we forwarded to the SPGW/MME and which should be routed locally.
On the eNB execute
sudo openvpn --mktun --dev tun10
sudo ip link set tun10 up
sudo ip addr add 172.21.20.100/24 dev tun10
sudo iptables -A OUTPUT -p udp --dst 10.20.13.92 \
--dport 2152 -j NFQUEUE --queue-num 0
echo 1 | sudo tee /proc/sys/net/ipv4/ip_forward
sudo route add -net 192.168.200.0 netmask 255.255.255.0 tun10
- On the SPGW eth0 interface add 100ms artificial delay:
sudo tc qdisc add dev eth0 root netem delay 100ms
-
To test the delay, on the eNB try pinging the SPGW (you should see 100ms delay).
-
Start the localbreakout daemon on the eNB:
sudo ./localbreakout -p 2152 -a 10.20.13.90 -i tun10 \
-q 0 -g enp0s31f6
-
Start the EPC/SPGW stuff, start eNB, start UE.
-
After LTE network is started, check on the localbreakout daemon there is a like similar to this one:
Storing UE in table at row #0
0: 00000001 00000000 00000000 1
pkt from enodeb
Adding UE info in table at row #0
0: 00000001 CA6FE0DD 00000000 1
UE not found, dropping packet
learning new UE ip address
- Once network works try pinging the SPGW from the UE, you should observe high latency because of the artificial delay. Run in the UE:
ping 192.168.200.1
PING 192.168.200.1 (192.168.200.1) 56(84) bytes of data.
64 bytes from 192.168.200.1: icmp_seq=1 ttl=64 time=136 ms
- Now tell the UE where the "local" address on the eNB tun10 is:
sudo route add 172.21.20.100 gw 10.64.64.64`
- Try pinging the localbreakout from the UE, latency must be much smaller:
ping 172.21.20.100
PING 172.21.20.100 (172.21.20.100) 56(84) bytes of data.
64 bytes from 172.21.20.100: icmp_seq=1 ttl=64 time=30.1 ms