Hi John, Please see zzh> below.
Juniper Business Use Only From: Kaippallimalil John <[email protected]> Sent: Tuesday, July 12, 2022 9:34 AM To: Jeffrey (Zhaohui) Zhang <[email protected]>; [email protected] Subject: RE: [DMM] Questions/comments on draft-zzhang-dmm-mup-evolution-00 [External Email. Be cautious of content] Hi Jeffrey, A few responses below: Zzh> Let me first describe two similar but not the same models – co-located AN and UPF vs. integrated AN and UPF. [John] co-located AN and UPF is what I referred to as “loosely coupled”. I’m fine with the co-located and integrated terminology as it is quite clear. Zzh> In 5G, UPFs can already be very much distributed – as much as co-locating UPF with gNB-CU. In this case, there is a local direct link between a gNB and UPF or even just an internal logical link if gNB and UPF are virtual functions running on the same compute server. With this, simplification of certain functionality can already happen. For example, we don’t need any special MEC procedures anymore (UL traffic getting off a distributed UPF is no different from getting off a central UPF – resources in local DN or central DN will be applied). If the UPF implementation is based on routing/switching, then we don’t need special procedures for 5G-LAN either – existing IP/E-VPN solution can be just used with wireless CE connections. [John] I share the same view. Zzh2> I am glad to hear that 😊 Zzh> Now, why do we bother further integrating AN and UPF together into a single NF in xG? Zzh> I realized that the draft does not talk about the following that I did talk about in the presentation in last IETF: (-- Optimized signaling and data plane / No need for separate N2 & N4 signaling / No need for AN-UPF connection) [John] This is where it gets tricky. For “optimized signaling” it implies a new interface that is composed of a minimum of (N2 + N4) interface (new interaction model at SMF <----> ANUP, and new interface) This is a moving target because 3GPP model (and parameters) are being extended /adapted/etc in every release. Zzh2> It is a moving target, and it is also theoretically possible in 6G (the architecture keeps evolving) – if the idea of integrating AN/UPF gets traction. For example, taking just QoS, Rel 18 work in XRM may end up adapting the QoS flow model to further include sub-flow aspects. This in turn affects the model/parameters at SMF, AN and UPF. (and similar updates to model/parameters may happen across other work items in 3GPP) My view is that this optimization cannot be done in IETF – its 3GPP work, and even disregarding that it’s a moving target (IETF will have to update this new optimized interface on a 3GPP release schedule) Zzh2> I had called out in the draft and in my presentation in IETF113 that it is *not* the plan to do the work in IETF. The reason I am socializing the integration idea in the DMM community is that if I bring this to 3GPP now it will get killed on the spot without any real discussion. On the other hand, with people familiar with both 3GPP/wireless technologies and IETF/wireline technologies, there is possibility to discuss the topic. If it gets enough sympathy in this community, especially from mobile operators, then we can bring this to 3GPP for further discussion and do the work there. If it can’t even get traction in this community, then there is no point going to 3GPP at all. Zzh> By “loosely integrated” do you mean the “co-locating” model? If so, is there any work needed at all? [John] I think there may be some work like best practices for various network aspects like optimized N3 connection, network domain security, perhaps routing/steering/mobility. Zzh2> With “loosely integrated/coupled” or “co-located” AN/UPF, N3 degrades to be over a local/direct/internal link – so it’s not clear to me what optimization can be done on IETF side for “optimized N3 connection, network domain security, perhaps routing/steering/mobility”? Even for documenting possible best practices, would that be in IETF? [John] For example, considering network sharing with multiple operators, optimal interconnection while providing necessary isolation of the functions may be useful to describe. There may be other aspects as well that we can think about if this is of value to explore further. Zzh2> When multiple operators are involved, will there be “loosely integrated/coupled” or co-located AN/UPF? It seems that they’ll be connected by N3 with “long” transit paths between them? Or is that outside the context of “loosely integrated/coupled” or co-located AN/UPF? Would be happy to discuss sometime during the upcoming meeting too. Zzh2> Yes, looking forward to that. Zzh2> Thanks. Zzh2> Jeffrey BR, John From: Jeffrey (Zhaohui) Zhang <[email protected]<mailto:[email protected]>> Sent: Monday, July 11, 2022 3:15 PM To: Kaippallimalil John <[email protected]<mailto:[email protected]>>; [email protected]<mailto:[email protected]> Subject: RE: [DMM] Questions/comments on draft-zzhang-dmm-mup-evolution-00 Hi John, Thank you very much for the comments. Please see zzh> below. Juniper Business Use Only From: Kaippallimalil John <[email protected]<mailto:[email protected]>> Sent: Sunday, July 10, 2022 7:19 PM To: [email protected]<mailto:[email protected]>; Jeffrey (Zhaohui) Zhang <[email protected]<mailto:[email protected]>> Subject: [DMM] Questions/comments on draft-zzhang-dmm-mup-evolution-00 [External Email. Be cautious of content] Hi Jeffrey, all, Thanks for putting together an interesting draft on mobile user plane evolution and related IP network related aspects. There are some important aspects that IETF/dmm could consider for xG without directly impacting 3GPP architecture/standards. This is partly described in comments under (3) below but would obviously need much more discussion in the group. Questions/comments for consideration: 1. Motivation for tightly integrating AN/UP functions in section 1.1 is not fully clear The point seems to be that with further virtualization and disaggregation, the functions could be combined. Sure, but the advantage of “combining” them is not clearly mentioned. - for simplification (as for multicast, mobility, etc), perhaps the draft can outline best practices to cut out unnecessary options, integrated management of AN + UP. - for performance, pseudo-wire as in 1.2 or some other dedicated high speed N3 connection should suffice (along with other recommendations in 3). Zzh> Let me first describe two similar but not the same models – co-located AN and UPF vs. integrated AN and UPF. Zzh> In 5G, UPFs can already be very much distributed – as much as co-locating UPF with gNB-CU. In this case, there is a local direct link between a gNB and UPF or even just an internal logical link if gNB and UPF are virtual functions running on the same compute server. With this, simplification of certain functionality can already happen. For example, we don’t need any special MEC procedures anymore (UL traffic getting off a distributed UPF is no different from getting off a central UPF – resources in local DN or central DN will be applied). If the UPF implementation is based on routing/switching, then we don’t need special procedures for 5G-LAN either – existing IP/E-VPN solution can be just used with wireless CE connections. Zzh> Now, why do we bother further integrating AN and UPF together into a single NF in xG? Zzh> I realized that the draft does not talk about the following that I did talk about in the presentation in last IETF: Optimized signaling and data plane • No need for separate N2 & N4 signaling • No need for AN-UPF connection Zzh> Instead of having AMF/SMF talk to gNB/UPF via N2/N4 separately, a single control plane entity can talk the single integrated user plane entity. Getting rid of AN-UPF connection is also good for latency besides reducing the complexity. Zzh> That’s in addition to the benefit of a simplified architecture where 3GPP/wireless technology is for establish the radio link (just like an ethernet cable or a WIFI connection connects a laptop to a router) and then leave the rest to IETF/IEEE/wireline technology (then all IETF/IEEE/wireline solutions can be applied w/o any work). Me being an engineer with IETF/wireline background that may be biased but I think it makes sense and part of this socializing in IETF is to see if it can get sympathy from the operators. 1. Concerns when combining AN, UP: While the draft points out advantages of combining, there are some risks as well. For example: a) QoS – the basic QoS aspects that are conveyed via N4 to UPF (filters, rules, etc) and other policies via NG-AP to RAN (and GTP-U /N3 in between) need to be considered in depth. Further, there are studies in 3GPP Rel 18 that are extending the QoS model, what’s handled on N4, policies to UPF or RAN and extensions to GTP-U. Just saying that its all at ANUP does not address the issues (and furthermore, this would be 3GPP work). Zzh> In the co-locating model, the above needs to be addressed anyway; whatever solution for that can be applied to the integration model, right? The only difference is that the simple N3 (of co-locating model) is reduced to nothing so no extensions to GTP-U is needed (actually it is not needed for co-locating model either). b) network sharing – in cases where, e.g., provider A operates AN and providers B, C operates UPs, tight integration into ANUP can be inflexible. (Reverse is also an issue, i.e., providers X, Y operate ANs and provider Z operates UP) zzh> Indeed – that’s why the draft does have section 1.2 about having PW/GTP between separate AN and UPF for three scenarios: a) MVNO b) Home-routed roaming c) for whatever reason one may want to have a single UPF to handle several ANs nearby. Zzh> Having that option does not mean we don’t need the integrated model. Basically, we integrate when it makes sense and separate when it is necessary. 1. Other aspects Consistent with the trend/direction to “softwarize” the different network components, i.e., AN and UP in this case, IETF may be able to complement 3GPP standards. For example, scenarios where AN, UP functions deployed in an infrastructure domain /data center and how security aspects, routing, QoS, mobility or management of these group of functions are handled optimally. (Note that in the above case, AN and UP are perhaps “loosely” integrated as opposed to the “tight” integration in ANUP) Zzh> By “loosely integrated” do you mean the “co-locating” model? If so, is there any work needed at all? Zzh> Thanks. Zzh> Jeffrey BR, John
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