Re: [DMM] questions and comments to draft-ietf-dmm-tn-aware-mobility-07

[Sridhar Bhaskaran <[e-mail]>]

Hi Linda,

Thank you for the comments and questions. I am providing below my answers
inline with tag [SB] as a co-author


On Sat, Sep 2, 2023 at 8:07 AM Linda Dunbar <[e-mail]>
wrote:

> Uma, John, Sridhar, Jeff, and Praveen,
>
>
>
> draft-ietf-dmm-tn-aware-mobility-07 has very good description of 5G system
> and 5G slices mapping to transport network VPNs.
>
>
>
> I have some questions and comments:
>
>    - Section 3.1:
>
> There are data plane traffic (i.e. UE<-> service instance in DC) and
> Control Plane traffic (UE<->gNB<-> 5G functions). Is the 5G End-to-End
> network slicing for the control plane and data plane?
>
[SB] It is for both. In the control plane, slice specific isolated control
functions (SMF, PCF, NRF, NSSF etc) are selected during UE registration
procedure as specified in 3GPP TS 23.501. The AMF remains common for a set
of slices. In view of the ability to select separate and distinct instances
for these control plane functions, it is possible to assign control plane
interface IPs to these functions from different IP pools. It is possible to
engineer the IP transport networks for different slice requirements based
on these IP pool differentiations.

In the user plane, entropy is built into each packet to identify the slice
it belongs. One of the suggested methods in this draft is to use the UDP
source port.


For the data plane traffic, the End-to-End network sliding should continue
> from UPFs to the service destination (which could be VMs in data center).
>
[SB] UPF to service destination path is outside the scope of 3GPP. Any IETF
based mechanism can be used here for slicing (e.g. Service function
chaining, SRv6, SR-MPLS etc)

>
>    - Section3.2:
>
> Fronthaul network is very time sensitive. So must have very few links
> (hops) from IP perspective. Do you see applicability of TE in the Fronthaul
> network?
>

[SB] This section also talks about L2 network for fronthaul. In fact for
the fronthaul eCPRI over Ethernet is more common than eCPRI over IP.  The
following statement clearly mentions that the provisioned capabilities
shall take into account overall delay budget



“The provisioned slice

   capabilities in the fronthaul transport network MUST take care of the

   latency and jitter budgets of the specific slice for the fronthaul
interface”



So this could imply reducing the number of hops. Actually IETF need not be
prescriptive here. The key thing is the overall delay budget shall be met
(for e.g. if the fronthaul delay budget is 100 microseconds then
irrespective of number of hops this budget shall be met).

>
>    - Section 4: it would be clearer to emphasize that the transport
>    network is really among 5G functions. So, from data plane perspective, the
>    End-to-End transport has to traverse the IP network between the UPFs and
>    the service destinations.
>
>
>
 [SB] This is a good comment. We can consider revising the text to
emphasize this in the next revision.

Thank you.
>
> Linda Dunbar
>
>
>
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Sridhar Bhaskaran