CSU/DSU connecting to Multiplexer

[SecureBlob]

I was reading about CSU/DSU and from what I understand it is used to connect a LAN to WAN.  DSU handles the interface with the DTE and CSU handles the interface with the telcom service. 

DTE can be a router or a multiplexer as per certain links. I have no confusion on Router being a DTE. What I don't understand is how a multiplexer can be a DTE. There are my basic questions.
1) In LAN, how is Multiplexer used? 
2) What problem does a Multiplexer solve in a LAN environment?
3) I always thought an edge router will be connected to a CSU/DSU and it would connect to a WAN Link. If that is true, why do certain internet links talk about connecting a Multiplexer to a CSU/DSU. If DTE is the Multiplexer what would be the role of the Edge Router in that enviroment? Can some of you show how these equipments are connected? 

When Router is DTE, the connection would be

Router -> CSU/DSU -> T1 Line.

Like how i represented above, Where does Multiplexer fit it? These are basic questions,hope some one will give a clear answer.

[Flavio Miranda]

Hi,

 By definition:

"In telecommunications and computer networks, multiplexing (sometimes contracted to muxing) is a method by which multiple analog or digital signals are combined into one signal over a shared medium. "

Which means, Multiplexer is a device usually installed before CSU/DSU to increase bandwidth. I don't think this kind of device is used anymore.

 It was useful when traffic was carried over serial lines with some kbps throughput.

[SecureBlob]

Thank you. I am still not able to visualize where in LAN a Multiplexer is connected. I always thought, computers would either be connected to Hub or Switch and then they will be connected to routers and routers will be connected to a CSU/DSU and then to WAN. So if a Multiplexer is connected before CSU/DSU, from where the inputs to MUX is coming? I know this is a very basic question, but I am just trying to understand the basics.

[Georg Pauwen · Accepted solution]

Hello,

on a side note, I have never seen a multiplexer in a LAN environment except for maybe multistation access units (MAUs) in Token Ring networks. In order to know what a MAU is, you have to look back at least 15 years. The only modern context I can think of for multiplexers are DSLAMs (Digital Subscriber Line Access Multiplexers), which are provider-operated.

I have attached a picture I found which maybe visualizes the position of a multiplexer. Fast forward to the present, and the multiplexer has become a switch...

[SecureBlob]

Thank you Georg. I also could find out a picture that shows a multiplexer and a router in a LAN with CSU/DSU.

[Georg Pauwen]

There is a massive amount of equipment out there. I happen to come across the device below at a customer site, which is a 2-port GigabitEthernet multiplexer:

http://www.lanode.com/multiplexers/fibre-optic/2-port-gigabit-ethernet-multiplexer.html

[Flavio Miranda · Accepted solution]

Multiplexer would be connected to router of course. Switches and hubs only speeks Ethernet basically.

 Router with serial links or multiples routers with multples serial links would be connected to a Multiplexer in order for increase capacity.

-If I helped you somehow, please, rate it as useful.-

[SecureBlob]

Thanks Flavio. I searched net again based on your answer and got a link that shows a connection that has Router, Multiplexer and Router. Thank you for your help. I really appreciate it. I am pasting the link in case it would be useful for someone else.

https://www.dcbnet.com/notes/9610ts.html