Re: [Apn] Regarding APN Usecase in Mobile Core

The APN provides the linkage between the application profile and the radio bearers.  GTP-u is manner by which the traffic is tunnelled to the anchor point and you MAY end up with different end points for each of the GTP bearers.

Traffic at both the UE and the PGW (in LTE - UPF in 5G) are directed to the correct APN by a Traffic Flow Template (TFT).  This is to ensure that traffic goes across both the correct radio bearer and is marked correctly in the IP network.

Users will often be unaware of multiple APNs on their UE; the most common hidden APN is one for VoLTE which, with the use of the TFT, will ensure that the VoIP frames (media) are put across the QCI 9 radio bearer and into the correct class on the IP network.  QCI 9 maps to a specific numerology on the Air Interface so that quality can be maintained for the voice call.

In theory, multiple APNs all with their own TFT rules and potentially multiple GTP-u tunnels could be used but this is very rarely done.

David

From: Apn <[email protected]> On Behalf Of Uma Chunduri
Sent: 18 January 2021 19:17
To: Lizhenbin <[email protected]>
Cc: [email protected]; dmm <[email protected]>
Subject: Re: [Apn] [DMM] Regarding APN Usecase in Mobile Core

Hi Robin,

In-line..

Cheers!
--
Uma C.

On Mon, Jan 18, 2021 at 5:25 AM Lizhenbin <[email protected]<mailto:[email protected]>> wrote:
Hi APNers and DMMers,
I remember that in the mobile core scenarios the GTP-u tunnel can be set up according to the user and application requirements, but I do not understand the details.

[Uma]: Obviously, the best reference for GTP-U is TS 29.281. However, uou should look into https://datatracker.ietf.org/doc/draft-ietf-dmm-5g-uplane-analysis/<https://eur02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdatatracker.ietf.org%2Fdoc%2Fdraft-ietf-dmm-5g-uplane-analysis%2F&data=04%7C01%7Cd.lake%40surrey.ac.uk%7C984c8fa55bbf4ea5b98908d8bbe5aa2d%7C6b902693107440aa9e21d89446a2ebb5%7C0%7C0%7C637465942368442430%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=namC6OofWdMQvTEjFwNkZT0ornR2gx1Q%2BV8SXxIHUis%3D&reserved=0> where lot more details and other references related this topic was analyzed (primarily started after/during REL-15, when  any other use plane other than GTP-U is worthwhile is debated for 5G N9 interface).

I think when the packet tunneled by GTP-u traverses the APN-based transport network, it may be mapped to the corresponding tunnel according to the user and application requirements to implement the uniform service. If you are familiar with the principle of GTP-u in the mobile core, please help provide some details.


Best Regards,
Zhenbin (Robin)


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