Many thanks to Sridhar and John 's insightful description of GTP-u tunnel for
both 4G and 5G.
IMHO, APN should focus on the 5G case, i.e. potentially hundreds of thousands
(or even millions) of GTP-u tunnels between a pair of one gNB and one UPF.
I think two scenarios worth exploring further separately:
1. 5G core can exchange signal with the IP network (the N6 interface), more
likely the 5G Core and N6 network are administrated by the same network
operator.
* 5G core can tag the packets before handing off to the N6 interface
(i.e. the IP network), such as inserting a metadata to the data packets
* inform the IP network of the meaning of the inserted Metadata.
* The IP network needs to remove the metadata before handing the packets
to their destinations
1. There is no communication between the 5G core and the IP network, then
the IP network can only depend on the priority bits added by the UE, which can
be very unpredictable.
The Section 4 (Mobility Packet Transition in the Data Network) and the Section
5 (Transport Network characteristics Mapping to SR-TE Paths) have good
description on how to extend 5G core's TN aware mobility information for
various TE paths within IP networks.
https://datatracker.ietf.org/doc/draft-mcd-rtgwg-extension-tn-aware-mobility/
Linda Dunbar
From: Apn <[email protected]> On Behalf Of Sridhar Bhaskaran
Sent: Thursday, January 21, 2021 10:39 PM
To: Kaippallimalil John <[email protected]>
Cc: [email protected]; Gengxuesong (Geng Xuesong) <[email protected]>; Uma
Chunduri <[email protected]>; Lizhenbin <[email protected]>; dmm
<[email protected]>
Subject: Re: [Apn] [DMM] 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
<[email protected]<mailto:[email protected]>>
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 <[email protected]<mailto:[email protected]>> On Behalf Of
Gengxuesong (Geng Xuesong)
Sent: Wednesday, January 20, 2021 8:23 PM
To: Uma Chunduri <[email protected]<mailto:[email protected]>>; Lizhenbin
<[email protected]<mailto:[email protected]>>
Cc: [email protected]<mailto:[email protected]>; dmm <[email protected]<mailto:[email protected]>>
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:[email protected]] On Behalf Of Uma Chunduri
Sent: Tuesday, January 19, 2021 3:17 AM
To: Lizhenbin <[email protected]<mailto:[email protected]>>
Cc: [email protected]<mailto:[email protected]>; dmm <[email protected]<mailto:[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://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdatatracker.ietf.org%2Fdoc%2Fdraft-ietf-dmm-5g-uplane-analysis%2F&data=04%7C01%7Clinda.dunbar%40futurewei.com%7C5985b13c46f440f9c3af08d8be8fc90e%7C0fee8ff2a3b240189c753a1d5591fedc%7C1%7C0%7C637468872069926165%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C2000&sdata=x4dOKXMZutPMV2%2BXZltRgnXKhVzJOktjqWAt%2FuDswHs%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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--
o__
_> /__
(_) \(_)... Burn fat not fuel - Bike along to a healthier life and cleaner
world! :)
Sridhar Bhaskaran
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