manual: add charts explaining tunend and tunmap

Change-Id: Ia0674c97eb0d8b5caeae988aefe523c5eee7318b
---
M doc/manuals/chapters/overview.adoc
1 file changed, 26 insertions(+), 0 deletions(-)

diff --git a/doc/manuals/chapters/overview.adoc b/doc/manuals/chapters/overview.adoc
index a6dc345..32c3060 100644
--- a/doc/manuals/chapters/overview.adoc
+++ b/doc/manuals/chapters/overview.adoc
@@ -79,6 +79,19 @@
 OsmoUPF does not support the complete PFCP feature set. It detects exactly two
 use cases that will provide service of actual GTP tunnels:
 
+.tunend use case
+----
+Access                 osmo-upf              Core
+ PGW                      |              PDN/internet
+  |                PDR1:  > FAR1:             |
+  |                IP/GTP | IP                |
+  |        ------> F-TEID |            -----> |
+  |                       |                   |
+  |                FAR2:  < PDR2:             |
+  |                IP/GTP | IP                |
+  | F-TEID <------        | UE IP addr <----- |
+----
+
 * `tunend`: GTP tunnel encapsulation/decapsulation:
   - One Packet Detection Rule (PDR) accepts a GTP tunnel from the Access side
     with an Outer Header Removal.
@@ -86,6 +99,19 @@
   - Another PDR accepts plain IP on a specific IP address from Core.
   - The second PDR uses a FAR towards Access with Outer Header Creation for GTP.
 
+.tunmap use case
+----
+Access                 osmo-upf                 Core
+ PGW                      |                     PGW
+  |                PDR1:  > FAR1:                |
+  |                IP/GTP | IP/GTP               |
+  |        ------> F-TEID |        -----> F-TEID |
+  |                       |                      |
+  |                FAR2:  < PDR2:                |
+  |                IP/GTP | IP/GTP               |
+  | F-TEID <------        | F-TEID <-----        |
+----
+
 * `tunmap`: GTP tunnel forwarding:
   - One Packet Detection Rule (PDR) accepts a GTP tunnel from the Access side
     with an Outer Header Removal.

