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Feature #5153

support hnbgw co-located GTP-U proxy

Added by laforge 6 months ago. Updated 2 days ago.

Status:
New
Priority:
Normal
Assignee:
sysmocom
Target version:
-
Start date:
05/13/2021
Due date:
% Done:

0%

Spec Reference:

Description

In the current osmo-hnbgw implementation, we simply configure the hNB GTP-U data to go directly to the SGSN. This requires IP-level routing between the RAN and the CN, which is possible in most lab situations, but not possible in real operator networks.

So we'd need to add support for a GTP-U proxy to control a co-located osmo-mgw. That proxy would translate GTP flows on the RAN side to GTP flows on the CN side (each with their own IPs/TEIDs).

The problem faced here is a 1:1 identical situation to what we're facing in OsmoSGSN in #5154. So both should then be able to use that same GTP-U proxy component.

Further brainstorming about this problem revealed that we're actualy talking about the same as the "SGW-U" network element described in 3GPP TS 23.214, which is what 3GPP invented when they introduced the control/user plane separation into the 4G EPC.

The SGW-U is exactly a GTP-U proxy between the RAN and the CN side, and it even includes functions for buffering GTP-U packets during mobility related GTP-U tunnel modification. It also includes functions for notifying the control plane entity of the first downlink packet received (so it can trigger paging). The SGW-U is controlled by the PFCP protocol. Only very few features of PFCP are required (PFCP is also used for he PGW-U which is much more complex).

So in fact, what we'd have to implement is
  • a minimalistic SGW-U with PFCP suport
  • functionality in osmo-hnbgw to control that SGW-U via PFCP

Related issues

Related to OsmoSGSN - Bug #5154: OsmoSGSN doesn't trigger 3G paging if downlink GTP traffic arrives after long breakNew05/13/2021

History

#1 Updated by laforge 6 months ago

SGW-U PFCP features needed (TS 23.214)

  • traffic detection based on local F-TEIDu (access and core side)
  • usage reporting to the CP function (in theory, can probably be skipped
  • F-TEIDu allocation in UP
  • control of forwarding
    • FTP-U encapsulation with new F-TEID
  • generation of "end marker" from SGW-U to NodeB
  • idle state packet bufering in SGW-U
    • buffer without reporting the arrival of first packet
    • buffer with reporting the arrival of first DL packet
    • drop packets

#2 Updated by laforge 6 months ago

  • Related to Bug #4886: UE does not connect data when moving from 2G->3G added

#3 Updated by laforge 6 months ago

  • Related to deleted (Bug #4886: UE does not connect data when moving from 2G->3G)

#4 Updated by laforge 6 months ago

  • Related to Bug #5154: OsmoSGSN doesn't trigger 3G paging if downlink GTP traffic arrives after long break added

#5 Updated by laforge 6 months ago

  • Description updated (diff)

#6 Updated by laforge 2 days ago

  • Assignee set to sysmocom

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