[e2e] j'accuse NFV

Detlef Bosau detlef.bosau at web.de
Thu Apr 30 08:32:48 PDT 2015

Perhaps my comment is a typical "Detlef" comment, but again I look at

Section 2: Modern Mobile Networks.

Followed by the (both fundamental and brand new) insight, that these
differ from other networks in fundamental ways.

Afterwars, I see table 1 with a lot of acronyms, which are always
pleasant look at and memorizing them has its benefit in prevention of
Alzheimer disease,

And I see these funny things like:
> 2.1.1 The Control Plane:
> The control plane logically consists of two compo-
> nents:
> Radio network.
> The handset connects to the base sta-
> tion (Node B in 3G networks), which in turn is con-
> trolled by the Radio Network Controller (RNC). In
> 4G LTE networks, the RNC and Node Bs combine
> into an enhanced Node B (eNB); this has the advan-
> tage of reducing latency to the handset. The RNC is
> primarily responsible for managing spectrum and bat-
> tery usage of handsets.
> Support nodes.
> The Serving GPRS Support Node,
> or SGSN (S-GW in LTE), is responsible for billing,
> authentication, mobility management, and relaying
> packets between the base stations under its control
> and the gateway (Gateway GSN, or GGSN, in 3G;
> Packet Gateway, or P-GW, in LTE). It also intercon-
> nects decoupled 2G, 3G, and 4G deployments for a
> given mobile operator. The GGSN serves as the gate-
> way for handsets to access the Internet

Excuse me for being nasty here. But I read literally several hundred of
texts like these and except from filling my mind with useless acronyms,
all these things hide the forest for the trees:

The major characteristic for any wireless link ("a connection from one
IP hop to an adjacent one") is:

First: We don't know in advance how long it takes to deliver the datagram.
Second: We don't know in advance, whether the datagram can be
successfully delivered at all.
(Of course in bounded time or a bounded number of transmission attempts,
but one of these has to be bounded, otherwise we would face the risk of
an infinite head of line blocking, when there is only a milk can in the
way in "optimum unfortunate position").

These are the most prominent properties of  wireless networks - and
these are the important ones.

Whether a packet passes a GGSN or a GGR2D2SN or a GGC3POSN or however
these funny boxes are called, simply doesn't matter. The aforementioned
two issues are ehough to drive the mechanisms in upper layers crazy.

And I'm a bit frustrated that many researches try to work around this
gap, which can hardly be closed, by digging in a whole Encyclopaedia
Britannica of complex and impressive details, which are more or less
meaningless for the outside world.

I know, that this sounds very upset.

But it reflects my experience from the fast fifteen years.

A packet switching link is a black box, where a packet is submitted by a
sender and which delivers the packet at the receiver after some time or
discards it. No more, no less. And from the basic idea of
internetworking - or packet switching (in the sense auf Baran's work) it
MUST NOT matter, whether we
- Ethernet
- Avian Carriers
- message in a bottle.

This sounds harsh, this is harsh. But from my perspective, I see us
running into the same trouble again and again for more than twenty years

There are literally hundreds of models for mobile networks around, all
of them providing a huge number of gory details of implementation, but
hardly any of them providing new insight.

The reason is stated above: The insight into the dominant properties of
mobile networks is as simple - as frustrating.
And the situation will not ameliorate only because we consider 200
parameters instead of 20. Or fifty kinds of middle boxes instead of
thirty.  Or because we introduce the ultimate well thought out virtual
abstraction and management tool - perhaps enhanced by a "software
defined networks management plane federation".

Or, as a former employer of me used to say: What cannot be achieved in a
simple manner, will neither be achieved in a complicated one.

We are used to model links by a link specific quadruple
(queueing delay, MAC delay, serialization delay, propagation delay)
and we insist in  this model from the earliest days of network
simulation (as I remember from this list) in FORTRAN IV programs in the
1960ies for about fifty years now.

This model is oversimplified - and we cannot escape this insight by
making our simulators or algorithms more complex.

Sorry for the rant, but during the last years, I got crazy on these things.


Detlef Bosau
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