Central Control (English)

by Sasha Shkrebets — last modified Feb 04, 2025 10:14 AM

Today we're going to be talking about the history of software defined networking. We'll start by discussing the timeline of software defined networking from the 1980s to present. And in doing so, you should gain some awareness about where the ideas and principles of software defined networking came from. And hopefully, you'll recognize that some of the architectural themes that we see in packet switch computer networks today actually originated from quite some time ago and actually have their roots in the telephone network.

Welcome back.

Today we're going to be talking about the history of software defined networking.

We'll start by discussing the timeline of

software defined networking from the 1980s to present.

And in doing so, you should gain some awareness about

where the ideas and principles of software defined networking came from.

And hopefully, you'll recognize that some of the

architectural themes that we see in packet switch computer

networks today actually originated from quite some time ago

and actually have their roots in the telephone network.

There are four chapter in SDN history that that we'll discuss throughout this module.

The first is the evolution of supporting technologies.

In particular, we'll talk about how programmable data

planes, things like control data plane separation took shape.

We'll speak about the control data plane separation details as well as its history.

Where, where it came from.

We'll also talk about how different specific control channels for

certain data planes like communication

or routing information between independently operating

networks evolved and we'll talk about how after the proliferation of

these different control channels in data planes, there's been some convergence.

In particular, the emerging open-flow standards is an example of

convergence of a control data plane around a specific standard.

Let's first start by talking about the evolution of supporting technologies.

So, we'll, we'll break this up into three different lessons.

First, we'll talk about the origins of central network

control which dates back at least to the early

1980s in the form of AT&T's network control point

which is, by the way, still in use today.

Next we'll talk about the history of programmability in networks,

which can be traced back to active networks in the 1990s.

And then we'll talk about as network virtualization,

which some, in fact, described as the killer

app for SDN, which also has its roots

back in the, in various technologies in the 1990s.

So, let's start by talking about the origins of central network control.

So, it wasn't always the case that

networks had central network control, particularly in

the early days, control and data planes op, operated together in the same channel.

This is a technology or a paradigm known

as in-band signaling, where data and control, or

in the case of the phone network, voice

and control, were sent over the same channel.

Certain frequencies in this channel, for example, 2,600

hertz, could do things like reset phone trunk lines.

And other types of things, like pulses on the line, could

be used to route calls and set, set up circuits for calls.

well, this offered some advantages in terms of simplicity.

The resulting network turned out to be fairly brittle, insecure, and so forth.

In particular, here, here's an example or a, a picture of Steve Wozniak's blue box.

A blue box was something that various people, hobbyists, developed to send

signals, pulses frequencies over the phone

network's channel to essentially take control of

it, and this particular box was able to do things like reset a phone trunk

line, route phone calls to a particular place, and so forth.

In the early 1980s, AT&T took a particular turn towards separating

the data and control planes in something called the network control point.

So, this was developed for the telephone network.

And the idea was that in separating the control from, or the signalling

from the voice and data that this could enable a number of new services.

In particular, it was used to develop

the 800 service and several other phone services.

The idea was that all signalling would go

to the network control point or the NCP, which

could also talk to a back end data

base which could have additional auxiliary information about customers.

So, benefits of this particular technology were the ability to

deploy specific services on demand and also, more importantly, rapidly

introduce new services was in, in the past it might

have taken quite a bit longer to deploy a new service.

So, in particular the, the technical reports described

the NCP, talk about a number of different advantages.

One is that elimination in-band signaling reduced expenditures.

Because they had a better view of what was going on inside the network,

they were able to shorten the amount

of time that particular circuits were held up.

And more specifically, the ability to determine the

busy or idle status of a circuit or

a trunk line before requesting that circuit allowed

for more efficient and quicker allocation of resources.

Secondly the technical reports cite the potential for rapidly

introducing new services, in particular, quoting from the article

it says, in the area of new services that

can be supported, the possibilities are only limited by imagination.

So, the idea was that the NCP architecture

would expose various basic primitive such as collecting

N digits from a number, sending and receiving

messages, making a billing record and so forth.

And more complicated applications could be build on top of those primitives.

One example of an envisioned service that the,

that the early reports described something called a

person locator; where, a user would register their

specific location at any time with the NCP database.

And the NCP would then route a call which would be made to a more generic

number, would route that specifically to where the

user happened to be at that particular time.

So, NCPs today are currently used to route 800 calls in a very similar fashion.

So, to summarize the benefits of central control

for something like the NCP and the phone network.

Was that a single network wide vantage point

could allow operators to directly observe rather than

infer network wide behavior, and importantly, evolve the

infrastructure data and services independently from one another.

So, that's a summary of some history of

where central network control came from and next

we'll look at the history of programmability in

networks as well as a history of network virtualization.