Re: [DMM] [Apn] Regarding APN Usecase in Mobile Core

Hi Sridhar,

Thanks for your explanation. It is much clearer for me as the following:

   UPF < ----- GTP-u tunnel [PDU session]------ > gNB

   PDU session contains multiple QoS flows [QFI marker->5QI]

   QFI marker in GTP-u extension header
5QI is not in GTP-u header directly but could be indicated by QFI. So the QoS requirements presented by 5QI can’t be used/seen by transport network in the existing in the current implementation (TEID is similar). And DSCP can act as a mediator between transport network and UPF/gNB.
Maybe the existing question becomes whether DSCP is sufficient for passing information from the mobile network to transport network? whether there is any simplification or omission of information in the mapping to the DSCP?

Best
Xuesong

From: Apn [mailto:apn-bounces@ietf.org] On Behalf Of Sridhar Bhaskaran
Sent: Friday, January 29, 2021 8:06 PM
To: Gengxuesong (Geng Xuesong) <gengxuesong@huawei.com>
Cc: apn@ietf.org; Uma Chunduri <umac.ietf@gmail.com>; Kaippallimalil John <john.kaippallimalil@futurewei.com>; dmm <dmm@ietf.org>; Lizhenbin <lizhenbin@huawei.com>
Subject: Re: [Apn] [DMM] Regarding APN Usecase in Mobile Core

Hi Gengxuesong,

QFI (mapped to 5QI) and TEID are to identify QoS flows and PDU sessions within UPF and gNB. They are not meant for transport network to look into. UPF and gNB map QFI to DSCP marking in the outer IP header which the transport network can use for differentiated services.

Regards
Sridhar

On Fri, Jan 29, 2021 at 3:37 PM Gengxuesong (Geng Xuesong) <gengxuesong@huawei.com<mailto:gengxuesong@huawei.com>> wrote:
Hi Sridhar,

Thank you for your additional information. Can I come to a conclusion that: both 5QI and TEID have the potential to provide additional information for differentiated services in transport network, although the two parameters act in different scopes?

Best
Xuesong

From: Sridhar Bhaskaran [mailto:sridhar.bhaskaran@gmail.com<mailto:sridhar.bhaskaran@gmail.com>]
Sent: Friday, January 22, 2021 12:39 PM
To: Kaippallimalil John <john.kaippallimalil@futurewei.com<mailto:john.kaippallimalil@futurewei.com>>
Cc: Gengxuesong (Geng Xuesong) <gengxuesong@huawei.com<mailto:gengxuesong@huawei.com>>; Uma Chunduri <umac.ietf@gmail.com<mailto:umac.ietf@gmail.com>>; Lizhenbin <lizhenbin@huawei.com<mailto:lizhenbin@huawei.com>>; apn@ietf.org<mailto:apn@ietf.org>; dmm <dmm@ietf.org<mailto:dmm@ietf.org>>
Subject: Re: [DMM] [Apn] Regarding APN Usecase in Mobile Core

Hi Xuesong,

In addition to what John said, in 3GPP networks there is one GTP-u tunnel per bearer (in case of 4G) and one GTP-u tunnel per PDU session (in case of 5G).

One UE (user equipment - i.e mobile device) may have multiple PDU sessions and hence in the network there may be more than one tunnel for a UE. The scope of GTP-u tunnel is from UPF to gNB only. GTP-u does not go all the way upto UE. The GTP-u header has a field called "TEID" (tunnel endpoint identifier). The TEID in the header identifies a context in UPF and gNB. The context gets established through signalling plane. The context provides information on the QoS to be provided for the bearer,  PDCP ciphering keys applicable for the bearer context etc.,. If there are a million UE that are getting connected to a UPF, there could be few million GTP-u tunnels (TEID).

In summary:
1. The 5QI / QFI marking in the GTP-u extension header provides a lookup for the general QoS characteristic applicable for that 5QI
2. TEID in the GTP-u header provides a lookup for UE and bearer specific contextual information for any differentiated treatment.

Regards
Sridhar

On Fri, Jan 22, 2021 at 2:55 AM Kaippallimalil John <john.kaippallimalil@futurewei.com<mailto:john.kaippallimalil@futurewei.com>> wrote:
Hi Xuesong,

Traffic policy for subscribers is managed per PDU session at the UPF (and gNB).
GTP-u does provide encapsulation between the end points, but its control fields are meant for conveying control semantics between the GTP endpoints: they were not intended for IP transport/ traffic underlays. 5QI/QCI etc are in the GTP extension header which may not be ideal to lookup to classify each packet in the transport network.

The entity that classifies data packets (upstream at gNB and downstream at UPF-PSA) also inserts the DSCP for that GTP packet. The classification is based on subscriber aspects but may also on be based on its content (e.g., using DPI).

Best Regards,
John

From: dmm <dmm-bounces@ietf.org<mailto:dmm-bounces@ietf.org>> On Behalf Of Gengxuesong (Geng Xuesong)
Sent: Wednesday, January 20, 2021 8:23 PM
To: Uma Chunduri <umac.ietf@gmail.com<mailto:umac.ietf@gmail.com>>; Lizhenbin <lizhenbin@huawei.com<mailto:lizhenbin@huawei.com>>
Cc: apn@ietf.org<mailto:apn@ietf.org>; dmm <dmm@ietf.org<mailto:dmm@ietf.org>>
Subject: Re: [DMM] [Apn] Regarding APN Usecase in Mobile Core

Hi Uma and all,

I have read the document and got a few questions:
In my understanding, in the UPF where traffic policy is enforced, the fine-granularity services are provided. Then what fields in the GTP-u encapsulation indicates the traffic's service requirements? When a GTP-u tunnel goes into a SRv6 policy, according to which fields in the GTP-u encapsulation the DSCP is generated? We know that there are parameters such as 5QI/QCI and QFI, whether they are associated with a GTP-u tunnel?

Best
Xuesong
From: Apn [mailto:apn-bounces@ietf.org] On Behalf Of Uma Chunduri
Sent: Tuesday, January 19, 2021 3:17 AM
To: Lizhenbin <lizhenbin@huawei.com<mailto:lizhenbin@huawei.com>>
Cc: apn@ietf.org<mailto:apn@ietf.org>; dmm <dmm@ietf.org<mailto:dmm@ietf.org>>
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 <lizhenbin@huawei.com<mailto:lizhenbin@huawei.com>> 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://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdatatracker.ietf.org%2Fdoc%2Fdraft-ietf-dmm-5g-uplane-analysis%2F&data=04%7C01%7Cjohn.kaippallimalil%40futurewei.com%7C77632db844b34a8e561108d8bdb38cb8%7C0fee8ff2a3b240189c753a1d5591fedc%7C1%7C0%7C637467926158632424%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C2000&sdata=5nVGUJhkHBn7FWHUCFPC4lGhwr6lBqtIWNyY1o0dxsg%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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--
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 _>  /__
(_) \(_)... Burn fat not fuel - Bike along to a healthier life and cleaner
world! :)

Sridhar Bhaskaran

--
 o__
 _>  /__
(_) \(_)... Burn fat not fuel - Bike along to a healthier life and cleaner
world! :)

Sridhar Bhaskaran