[PATCH] Documentation: networking: add UPF (User Plane Function in 5GC) description

[Ian Chen <yi.chen@saviah.com>]

Add the content of User Plane Function (UPF),
which was defined in 3GPP specifications since release 15.

Signed-off-by: Ian Chen <yi.chen@saviah.com>
---
 Documentation/networking/gtp.rst | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/Documentation/networking/gtp.rst b/Documentation/networking/gtp.rst
index 9a7835cc1..c02aa34c4 100644
--- a/Documentation/networking/gtp.rst
+++ b/Documentation/networking/gtp.rst
@@ -31,12 +31,12 @@ payload, such as LLC/SNDCP/RLC/MAC.
 
 At some network element inside the cellular operator infrastructure
 (SGSN in case of GPRS/EGPRS or classic UMTS, hNodeB in case of a 3G
-femtocell, eNodeB in case of 4G/LTE), the cellular protocol stacking
+femtocell, eNodeB in case of 4G/LTE, gNobeB in case of 5G), the cellular protocol stacking
 is translated into GTP *without breaking the end-to-end tunnel*.  So
 intermediate nodes just perform some specific relay function.
 
-At some point the GTP packet ends up on the so-called GGSN (GSM/UMTS)
-or P-GW (LTE), which terminates the tunnel, decapsulates the packet
+At some point the GTP packet ends up on the so-called GGSN (GSM/UMTS),
+P-GW (LTE), or UPF (5G), which terminates the tunnel, decapsulates the packet
 and forwards it onto an external packet data network.  This can be
 public internet, but can also be any private IP network (or even
 theoretically some non-IP network like X.25).
@@ -60,7 +60,7 @@ payload, called GTP-U.  It does not implement the 'control plane',
 which is a signaling protocol used for establishment and teardown of
 GTP tunnels (GTP-C).
 
-So in order to have a working GGSN/P-GW setup, you will need a
+So in order to have a working GGSN/P-GW/UPF setup, you will need a
 userspace program that implements the GTP-C protocol and which then
 uses the netlink interface provided by the GTP-U module in the kernel
 to configure the kernel module.
@@ -162,7 +162,7 @@ Local GTP-U entity and tunnel identification
 GTP-U uses UDP for transporting PDU's. The receiving UDP port is 2152
 for GTPv1-U and 3386 for GTPv0-U.
 
-There is only one GTP-U entity (and therefore SGSN/GGSN/S-GW/PDN-GW
+There is only one GTP-U entity (and therefore SGSN/GGSN/S-GW/PDN-GW/UPF
 instance) per IP address. Tunnel Endpoint Identifier (TEID) are unique
 per GTP-U entity.
 
-- 
2.38.1