Der Netzbetreiber beginnt mit der Drosselung und drosselt die Geschwindigkeit.

German very often combines nouns into a single compound noun.
Here, Netz + Betreiber becomes Netzbetreiber.

• Netz = network
• Betreiber = operator

This is completely normal in German. English often writes similar ideas as two words, but German usually joins them into one.

Netzbetreiber is a masculine noun, so in the nominative singular it takes der.

A useful rule for compound nouns is that the last part decides the gender.
The last part here is Betreiber, and der Betreiber is masculine, so the whole word is also masculine:

• der Betreiber
• der Netzbetreiber

It is in the nominative case because it is the subject of the sentence, the one doing the actions:

• beginnt
• drosselt

So der Netzbetreiber is the thing that begins and throttles.

Because the verb pattern here is mit etwas beginnen = to begin with something / to start with something.

The preposition mit always takes the dative case.
That is why you get:

• die Drosselung in nominative
• der Drosselung after mit in dative

So:

• beginnt mit der Drosselung = begins with the throttling

They come from the same root, but they are different parts of speech:

• drosseln = the verb, meaning to throttle / reduce / limit
• die Drosselung = the noun, meaning throttling / reduction / limitation
• drosselt = the 3rd person singular present form of drosseln

So the sentence uses both:

• first a noun phrase: mit der Drosselung
• then a verb: drosselt die Geschwindigkeit

English can do something similar with the reduction and reduces, although German often uses this kind of noun/verb pairing more freely.

Geschwindigkeit is a feminine noun, so its basic article is die:

• die Geschwindigkeit

In this sentence it is the direct object of drosselt, so it is in the accusative case.
For feminine nouns, the definite article is still die in the accusative singular, so it does not change:

• nominative: die Geschwindigkeit
• accusative: die Geschwindigkeit

That is why it still looks the same.

German often omits the subject in a coordinated clause when it is the same as in the first clause.

Full version:

• Der Netzbetreiber beginnt mit der Drosselung und der Netzbetreiber drosselt die Geschwindigkeit.

But repeating der Netzbetreiber would sound unnecessary, so German normally leaves it out:

• Der Netzbetreiber beginnt mit der Drosselung und drosselt die Geschwindigkeit.

You can think of the second part as meaning:

• und er drosselt die Geschwindigkeit

Since the subject is omitted, the verb comes first in that second clause.

Because in German, all nouns are capitalized.

So:

• der Netzbetreiber
• die Drosselung
• die Geschwindigkeit

This is a standard spelling rule in German and one of the biggest visual differences from English.

It is understandable and grammatically correct, but it can sound a bit repetitive because both words come from the same root.

That said, in technical, legal, or telecommunications language, this kind of repetition is fairly common and acceptable.

A less repetitive version could be:

• Der Netzbetreiber beginnt mit der Drosselung und reduziert die Geschwindigkeit.
• Der Netzbetreiber beginnt, die Geschwindigkeit zu drosseln.

So the original is fine, but there are smoother alternatives.

German uses definite articles more often than English does. In a context like internet or network speed, die Geschwindigkeit can refer to the relevant speed in a general but still specific way.

So German naturally says:

• die Geschwindigkeit drosseln

where English might say simply reduce speed or throttle speed.

This is a common difference between the two languages: German often prefers an article where English may leave it out.

Both verbs are in the present tense:

• beginnt
• drosselt

In German, the present tense can describe:

• something happening now
• a general rule or process
• a scheduled or standard action

So this sentence could describe a current action or a general procedure, depending on the context.

Yes. A few common alternatives are:

• Der Netzbetreiber beginnt, die Geschwindigkeit zu drosseln.
• Der Netzbetreiber fängt an, die Geschwindigkeit zu drosseln.
• Der Netzbetreiber startet die Drosselung der Geschwindigkeit.

These are slightly different in style:

• beginnt is neutral
• fängt an is a bit more everyday
• startet die Drosselung sounds more formal or technical

So the original sentence is fine, but German offers several natural ways to say the same thing.