osmocom Kernel GTPU module - Support for incoming DL packets for idle mode users in S-GW /SGSN

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Andreas Schultz aschultz at tpip.net
Sun Feb 19 14:38:11 UTC 2017


Hi Anoop, 

----- On Feb 18, 2017, at 1:03 AM, Anoop Singh Tomar <anooptomar at fb.com> wrote: 

> Hi ,

> Posting question related to capability to implement user plane (GTP tunnel) for
> S1-U and Iu-PS interface between S-GW & eNB and SGSN & RNC respectively via
> osmocom kernel GTP-U module.

> At present it seems if TE-ID is not valid packet is dropped in kernel GTP-U
> module. So in order to use this for S1-U/Iu-PS interface it is required to add
> support for following use-case:

> · Down link packet arrival in S-GW /SGSN for UE which is in idle mode – Buffer
> the packet and trigger paging to move the UE to connected.

> a. When UE moves to idle mode – S1-U or IuPS bearer is released. In this case IP
> address and TE-ID of eNB/RNC becomes invalid.

> b. DL Packet is received for the idle mode UE in S-GW/SGSN - In this case ,
> kernel GTP-U module should deliver packet to user-space application
> (SGW/osmoSGSN) so that these packets can be buffered in user space and paging
> can be initiated.

> Question – Is there any plan to support above in near-future in osmocom kernel
> GTP-U module or larger question would be to plan to enable usage of kernel
> GTP-U module in SGSN and SGW towards RAN ?

We (Travelping) have some ideas about implementing a S-GW based 
on the current ergw code [1]. This would also involve implementing kernel 
side support. 

The current idea for extending the kernel part is to change the PDP 
context logic from a 'GTP-U to network device' reeation to a 'GTP-U 
to something' relation. The 'something' then would be the existing network 
device, another GTP-U socket (including TEID's), a L2TP tunnel, a IPsec 
session, .... an so on. My current understanding is that the LWT infrastructure 
should be suitable for that. 

This implementation would support the S1-U use case. For Iu-PS, a user 
space only implementation would IMHO be more suitable. Anyhow, the 
current kernel implementation is passing all packets that it can't handle 
(has no PDP context for them) onto the user space process. 

But all that are only halve backed ideas, nothing concrete, yet. 

Regards 
Andreas 

[1]: https://github.com/travelping/ergw 

> Anoop
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