Questions on draft-matsushima-stateless-uplane-vepc-02
After viewing your slides from the presentation you did overnight (sorry I couldn't
be on the call) I went back and re-read the draft-matushima-stateless-uplane-vepc-02
draft. I am still confused about a number of things:
You show in Figure 4, step 15 a Route Update (is this a BGP UPDATE?) going from the
EPC-E to the core network RTR, containing a Destination of UE-prefix and a Next-Hop
of EPC-E address. However, in Section 3.4, you describe the RTR as knowing only the
PDN prefix, which is the same for all EPC-E, and the use of "hot-potato" routing to
deliver the packets to the nearest EPC-E no matter the UE destination IP address.
Which one is it? Are the UE prefixes advertised into the core or not?
Assuming for now that the UE prefixes are not advertised into the core, but only the
PDN prefixes are advertised, then that means that every EPC-E must know about every
UE session, including the eNB F-TEID for every UE in the network, correct? That's
because any one of them at any time could receive a packet for the UE from the core.
This doesn't seem scalable to me.
You seem to attempt to address this issue in Section 4.1 when you talk about multiple
"sets" of EPC-E devices, each one dedicated to a given geographic region. It seems
to me that each "set" of EPC-E could cover no more than the scope covered by a single
SGW today, because they each have the same amount of state as an SGW. Essentially
you have described how to build a replicated SGW with failover to different nodes
based on the re-convergence of BGP after a failure (presumably you could get the
core network to react to the closure of a BGP TCP session). So I think this addresses
the problem of fault-tolerance that has been identified with the tunnel-based solutions,
but not really the scalability bottleneck problem.
In fact, if you consider mobility from one "set" to another, if you want to keep the
UE's IP address, you would need to broadcast the same set of PDN prefixes from all
sets of EPC-E. In fact this would mean that all EPC-E throughout the network, even
if they are in different "sets", need to be prepared to handle packets for any UE
and so they ALL would need the eNB F-TEIDs for ALL UEs. Please tell me where I have
made a mistake.
Peter J. McCann
Huawei Technologies (USA)
+1 908 541 3563
Rm. C-0105, 400 Crossings Blvd. (2nd floor), Bridgewater, NJ 08807-2863 USA