[[osmoepdg]]
== osmo-epdg/erlang

The core component of the osmo-epdg is the osmo-epdg/erlang daemon.
It holds the state of the UE and communicates with the relevant core components.

[[fig-osmo-epdg-erlang]]
.osmo-epdg/erlang structure
[graphviz]
----
include::{srcdir}/osmo-epdg-erlang.dot[]
----

=== Debian packages

For Debian based distributions, Osmocom provides package repositories:

- https://osmocom.org/projects/cellular-infrastructure/wiki/Latest_Builds
- https://osmocom.org/projects/cellular-infrastructure/wiki/Nightly_Builds

The osmo-epdg package contains a systemd.service file and a default example configuration.

=== Configuration

The osmo-epdg/erlang is configured via Erlang configuration (https://www.erlang.org/doc/man/config.html).
When using the osmo-epdg debian package, the default location for the configuration is
*/etc/osmocom/osmo-epdg.config*.

===== CEIA: Connection for strongSwan

The CEIA is the internal protocol between strongSwan and osmo-epdg/erlang.
See [CEIA]

[format="csv",options="header"]
|===
key, default, description
gsup_local_ip, 127.0.0.1, bind IP of the GSUP server (TCP). strongSwan connects to this IP.
gsup_local_port, 4222, bind TCP server port
|===

===== SWx (diameter)

SWx (<<3gpp-ts-29-273>>): Interface between AAA and HSS.
The AAA will retrieve authentication, authorize the UE and
update the location (AAA, PGW address) in the HSS.

See Erlang diameter specific behaviour on https://www.erlang.org/doc/man/diameter.html

[format="csv",options="header"]
|===
key,default,description
dia_swx_remote_ip, 127.0.0.1, Remote IP of the HSS
dia_swx_remote_port, 3868, SCTP port of the HSS
dia_swx_proto, sctp, Protocol. sctp or tcp
dia_swx_connect_timer, 30000, Watchdog Connect timer in ms. RFC 6733.dia_swx_watchdog_timer, 30000, Watchdog TwInit. RFC 3539.
dia_swx_watchdog_config, "[ok, suspect]", See https://www.erlang.org/doc/man/diameter.html
dia_swx_transmit_timer, 10000, SWx Transmit Timeout (ms)
dia_swx_vendor_id, 0, Diameter Vendor Id
dia_swx_origin_host, epdg.localdomain, Diameter Origin Host
dia_swx_origin_realm, localdomain, Diameter Origin Realm
|===

===== S6b (diameter)

S6b (<<3gpp-ts-29-273>>): Interface between AAA and PGW.
Authorize the GTP session of the ePDG.

See Erlang diameter specific behaviour on https://www.erlang.org/doc/man/diameter.html

[format="csv",options="header"]
|===
key,default,description
dia_s6b_local_ip, 127.0.0.10, local bind IP
dia_s6b_local_port, 3868, local bind Port
dia_s6b_proto, sctp, Protocol. sctp or tcp
dia_s6b_connect_timer, 30000, Watchdog Connect timer in ms. RFC 6733.
dia_s6b_watchdog_timer, 30000, Watchdog TwInit. RFC 3539.
dia_s6b_watchdog_config, "[ok, suspect]", See https://www.erlang.org/doc/man/diameter.html
dia_s6b_vendor_id, 0, Diameter Vendor Id
dia_s6b_origin_host, aaa.localdomain, Diameter Origin Host
dia_s6b_origin_realm, localdomain, Diameter Origin Realm
|===

===== S2b (GTPv2)

S2b (<<3gpp-ts-29-273>>): Interface between ePDG and PGW.
GTP control plane for the UE traffic.

[format="csv",options="header"]
|===
key,default,description
gtpc_local_ip, 127.0.0.2, local bind IP
gtpc_local_port, 2123, local bind Port
gtpc_remote_ip, 127.0.0.1, remote IP of the PGW
gtpc_remote_port, 2123, remote port of the PGW
|===