zhège wǎngluò jīntiān zǒngshì diàoxiàn.

In standard Mandarin, 这 / 那 usually need a measure word (classifier) before a noun.

So the pattern is:

• 这 + 个 + 网络
• that + classifier + network

Here, 个 is the very common general classifier.

So 这个网络 is the normal, standard form.
You may sometimes hear 这网络 in very casual speech, but as a learner, 这个网络 is the safer choice.

网络 literally means network, and in everyday speech it often refers to an internet connection.

In this sentence, it most likely means something like:

• the internet connection
• the Wi-Fi/network
• the data/network service

The exact meaning depends on context. For example:

• at home: probably the Wi-Fi or home internet
• on a phone: possibly mobile data / network service
• in an office or school: the local network or internet connection

So 网络 is broader than just one English word.

This follows a very common Mandarin word order:

Subject + Time + Adverb + Verb

So here we get:

• 这个网络 = subject
• 今天 = time
• 总是 = adverb
• 掉线 = verb/result

That gives:

这个网络 今天 总是 掉线。

This is very natural Chinese word order.

A good rough rule is:
time words usually come before the main action, and adverbs usually come before the verb.

Yes, 总是 often means always, but in real use it can also mean keeps doing or does it again and again in this situation.

So in this sentence, 今天总是掉线 does not mean it has always disconnected forever. It means something more like:

• It keeps disconnecting today
• It’s always disconnecting today
• It keeps dropping out today

So 总是 is being understood within the time frame of today.

These words are similar, but not the same.

总是

• means always / keeps doing
• fairly neutral
• often used for repeated behavior

Example:
这个网络今天总是掉线。
This network keeps disconnecting today.

老是

• also means always / keeps doing
• more colloquial
• often sounds more annoyed or complaining

Example:
这个网络今天老是掉线。
This sounds a bit more like: This network keeps disconnecting today, and it’s really annoying.

一直

• means continuously / all along
• focuses more on duration than repeated separate events

Example:
今天网络一直不好。
The network has been bad all day.

So in this sentence, 总是 is a good choice because it suggests repeated disconnections.

Literally:

• 掉 = to fall / drop
• 线 = line

So 掉线 literally suggests something like the line drops.

In real usage, it means:

• to disconnect
• to lose connection
• to get dropped offline

It is commonly used for:

• internet connections
• phone calls
• online games
• livestreams or voice chats

Examples:

• 我刚才掉线了。 = I got disconnected just now.
• 游戏老掉线。 = The game keeps disconnecting.

So 掉线 is a very common modern tech-related expression.

Because this sentence is describing a repeated problem, not one single completed event.

总是掉线 means:

• it keeps disconnecting
• it repeatedly disconnects

If you say 掉线了, that usually points to a specific disconnection or a new situation:

• 又掉线了！ = It disconnected again!
• 刚刚掉线了。 = It disconnected just now.

So:

• 今天总是掉线 = repeated pattern today
• 掉线了 = one occurrence / a change of state

That is why 了 is not necessary here.

Yes, this sentence is natural.

Some other natural ways to say something similar are:

• 这个网络今天老是掉线。
• 今天这个网络总是掉线。
• 这个网络今天老掉线。
  (more colloquial)

Your original sentence is perfectly fine.
It sounds like a normal complaint about a bad connection.

In normal speech, 这个 is usually pronounced zhè ge, with 个 in a neutral tone.

So even if you see it written together as zhège, the important point is:

• 这 = fourth tone
• 个 = usually light / neutral here

So it sounds roughly like:

• zhè ge

This is very common after demonstratives:

• 这个
• 那个

The 个 is usually not stressed strongly.

It can be used both ways.

For devices/connections

• 网络掉线了 = the network disconnected
• 游戏掉线了 = the game connection dropped

For people

You can also say someone 掉线了 if their connection dropped:

• 我掉线了。 = I got disconnected.

In very informal speech, it can even be used figuratively to mean someone is mentally not keeping up, like their brain went offline, but that is a more playful extension.

In your sentence, though, it is being used in the normal technical sense.