Pablo, First of all, thank you for your thorough review on the draft, and concrete proposal to improve it. I think I agree almost on the three proposals. Let me comment on some of your points.
> [...snip...] > > I believe its straightforward to support IPv4 UE traffic by doing SRv6 with > T.Encaps behavior. Hence, I think this should be documented in the draft. Yes. > The encapsulation behavior should be the default one, both for IPv4 and IPv6 > UE traffic. However, a specific provider is allowed to do SRH insertion > within a controlled domain [draft-voyer-6man-extension-header-insertion-02] > for UE IPv6 traffic. > Also, in order to reduce overhead at the UPFs when using encapsulation, I > would replace the End.B6 function for a new End.MAP function. > For example, if we consider the following topology: > UE----gNB----UPF1----UPF2 > > Then the uplink packet flow for the basic mode would look like this: > UE_out: (A, Z) > gNB_out: (gNB, U1::1) (A, Z) -> T.Encaps <U1::1> > UPF1_out: (gNB, U2::1) (A, Z) -> End.MAP > UPF2_out: (A, Z) -> End.DT > > The End.MAP function is simply replacing the UPF1 SID for the UPF2 SID. So ‘End.MAP’ function you proposed looks that the dest address in outer header works as last SID in SRH but just one SID doesn’t require SRH in the packet over the wire. If it corrects, I think it’s a good idea. I’d appreciate if you can contribute text and pseudo code for End.MAP to the draft. I tend to replace basic mode with it. > > Notice that using encapsulation, if you compare it with today user-plane > using IPv6/GTP, the result is that SRv6 is just adding 40B of overhead (IPv6 > header), while GTP over IPv6 is using 56B (IPv6, UDP, GTP). That sounds make sense. I’ve studied and shared a comparison of total overhead size for various deployment cases. That study shows it as well. > > ======= > > With respect to the aggregation mode, aside from using the encapsulation mode > as described before, I would also like to add a note on the I-D on the fact > that we can support the aggregation mode without changes in the N2 interface: > The current I-D for aggregation mode assumes that the gNB (uplink) has > knowledge of an SR policy that contains all the SIDs belonging to TE, NFV and > so on. Even though the I-D does not describe how the gNB is retrieving this > information, I would like to make a statement on the fact that there are two > alternatives: > A. The N2 interface is modified in order to signal a SID list to the gNB. > B. The N2 interface is not modified. In this case, we signal through the N2 > interface an SRv6 BindingSID, that the gNB is going to resolve into a SID > list via an SDN controller either using PCEP, reverse DNS lookup or LISP. Maybe you have seen End.B6 defined as L2-anchor function in the section of aggregate mode. I think that the current draft doesn’t cover the case of N2 no-change. But I have to admit that the text need to be more clear to mention for that. Any text for it would be really welcome. > > I’m aware that the I-D focuses on the user-plane, however I believe it’s > important to state this alternatives since it simplifies the adoption and > reduces impact in the existing mobile architectures (without going into the > details on the mechanisms for each one of the alternatives of LISP, PCEP, > reverse DNS-lookup). I think that we are on the same page. Deploying srv6 for mobile user-plane provides programmability of data-path for not only existing style of mobility management, but also any other type of optimization logics from various aspects, such as ID-LOC, ETSUN for example. > > ======= > > On the other hand, the current I-D proposes a mechanism for stateless > interworking with legacy access networks that doesn’t support SRv6 (SGW > and/or eNB). This mechanism presented in the I-D is limited to IPv4/GTP > legacy networks. I would like to propose a mechanism to support interworking > with legacy gNBs that does not support SRv6 but do support IPv6/GTP. > The main benefit comes from the fact that we can leverage an SRv6 BindingSID > to have remote classification and steering of the UE traffic over an SR > policy [draft-filsfils-spring-segment-routing-policy]. Yes indeed. IPv6/GTP case should be supported in addition to the IPv4/GTP case. > > In this scenario, I propose that we add the notion of an SR GW -as the > current stateless interworking node in the I-D-. This SR GW can be either a > software based platform -e.g. VPP- or any existing router -the mechanism is > simple and can be supported in existing HW-. This SR GW receives through the > control plane the SR policies and installs the required Binding SIDs. > > Then, for any UE connecting to a gNB, the N2 interface is going to signal an > IPv6 address and a TEID. However, the difference is that with this new > mechanism the IPv6 address that we are going to signal is going to be an SRv6 > BindingSID instantiated at the SR GW. > > The overall workflow is the following: That looks good. Can you propose texts, pseudo code and diagram for that? > > Uplink > Note: S1, S2 represent service functions and C1 represents a node for TE > purposes > UE sends its packet (A, Z) on a specific wireless bearer to its gNB > gNB’s CP associates the session from the UE (A) with IPv6 address B and TEID > T (N2 interface unchanged) > gNB_out: (gNB, B) (GTP: TEID T) (A, Z) ;; Interface N3 > is unchanged > SR_GW_out: (SRGW, S1) (U2::1, C1; SL=2)(A, Z) ;; new End.GTP.UP > S1_out: (SRGW, C1) (U2::1, C1; SL=1)(A, Z) > C1_out: (SRGW, U2::1) (A, Z) ;; assuming > PSP > UPF2_out: (A, Z) ;; > End.DT > Don’t you need to care about TEID at SRGW in aggregate mode? I think it is okay for uplink in basic mode since it allocates SID per tunnel. > Downlink > UPF2_in: (Z, A) > ;; UPF2 maps the flow with SID list <C1, S1, SRGW::TEID, gNB> > UPF2_out: (U2::1, C1) (gNB, SRGW::TEID, S1, SL=3) (Z, A) ;; T.Encaps > C1_out: (U2::1, S1) (gNB, SRGW::T, S1, SL=2) (Z, A) > S1_out: (U2::1, SRGW::TEID) (gNB, SRGW::T, S1, SL=1) (Z, A) > SR_GW: (SRGW, gNB)(GTP: TEID=T)(Z, A) ;; > End.GTP.DN > gNB_out: (Z, A) That looks it works. > > The key points are: > - gNB is unchanged and encaps into GTP (N3 interface is not modified). gNB > only needs to support IPv6 which is currently common in existing deployments. > - 5G Control-Plane (N2 interface) is unchanged: 1! IPv6 address (i.e. a BSID > at the SR GW) > - SR GW removes GTP, finds SID list related to IPv6 DA (BSID), add SRH with > SID list > - Same TE, NFV and scale properties as Aggregation mode > - There is NO state for the downlink at the SR gateway > - There is simple state in the uplink at the SR gateway (notice that since we > are leveraging the aggregation mode, we expect few SR policies on this node. > SR policies are shared across UEs) > - As soon as the packet leaves the gNB (uplink), the traffic is SR-routed. > This simplifies considerably network slicing. > [draft-hegdeppsenak-isis-sr-flex-algo]. > - Traffic is already classified and steered into an SR policy when it arrives > to the SR GW. Yes, it enables legacy networks can be integrated into flexible/programmable platform. BTW do you think that it could also be applicable for basic mode? I think your intention that applying SRGW to such case might not motivate operators to do that since no additional value out there. But It would make user plane transition easy from GTP-U to SRv6. Even you can keep N2 as it is to support aggregate mode, N4 need to be aware for it. Keeping N4 or previous generation’s c-plane as it is makes the hurdle much lower for the transition. > > Finally, I believe that this mechanism is so simple, that it would be trivial > to implement it in VPP [https://wiki.fd.io/view/VPP/What_is_VPP%3F] . Hence > if the working group believes that this is interesting work and we add it to > the I-D, I will analyse how to implement it in this platform. BTW, do you have any ideas for naming of the functions? Some SRv6 guys suggest to reserve namespace of End.M** for mobile specific SRv6 functions. Cheers, --satoru _______________________________________________ dmm mailing list [email protected] https://www.ietf.org/mailman/listinfo/dmm
