About DCE Devices

[sawquecisco]

Sorry about this question but I am confused about DCE Devices locations.

Do DCE Devices locate in our office or is it indicated the devices that are used by Service Provider?

Thanks..

[Peter Paluch]

Hello,

Both DTE and DCE devices are located at your office, in customer premises, because the cable between DTE and DCE can be at most a couple of meters long.

Best regards,

Peter

[sawquecisco]

But some documents or books represent DCEs as  ISP's devices.

For example I'm reading CCNA Certification All-in-One For Dummies book nowadays and on page 856 it says:

All sites connect to the carrier provider’s Frame Relay network infrastructure, or cloud, which is established by interconnecting numerous carrier-owned DCE network devices. The customer has no control over these devices, only
their own DTEs. For proper communication to occur between the data terminal equipment located at multiple customer sites, virtual circuits must be established between them.
The clock rate assignment for data transmission is determined by the service provider’s DCE device, or channel service unit/data service unit (CSU/DSU). The customer’s DTE or customer premises equipment (CPE) has no authority to ignore, dismiss, or invalidate the clock rate specified by the DCE device, and must agree with the chosen settings.

[Peter Paluch · Accepted solution]

Hello,

But some documents or books represent DCEs as  ISP's devices.

By ownership - yes, that is quite often the case. But not by their position: they are always co-located with the DTE at customer premises.

All sites connect to the carrier provider’s Frame Relay network  infrastructure, or cloud, which is established by interconnecting  numerous carrier-owned DCE network devices. The customer has no control  over these devices, only their own DTEs.

In my understanding, this statement talks about who owns the DCE but not where the DCE is placed. Also note the context of this statement: nobody doubts that the devices forming the service provider's network and located at the provider's premises are under his ownership and control. Why would then this book specifically stress that DCE devices belong to the provider? Obviously, pointing out this fact would be necessary if the DCE devices were located at customer's premises - which is what I originally stated.

There is a small but important fact to consider: the DCE behaves essentially like a modem (in fact, a modem is one of more types of DCE devices), converting digital data coming from attached DTE devices into a form that is capable of being carried over long distance media, and at the other end of this long connection, reconvert the signals into original digital data and allow the remote DTE device to process it. Note, however, that in Frame Relay, the nearest device that needs to process the data sent by customer's router is the nearest Frame Relay switch. Therefore, the Frame Relay switch itself must have a built-in DCE device that talks to the device at the customer's premises. If the Frame Relay connection between two routers went through two Frame Relay switches, the sequence of devices would be:

Router (DTE) --- Modem (DCE) --- (DCE) Frame Relay switch 1 (DCE) --- (DCE) Frame Relay switch 2 (DCE) --- (DCE) Modem --- (DTE) Router

In other words, between every two connected devices that process data, there must be a pair of DCE devices, one at each data device's location, that adapts the digital signal for the transmission over the cable. So the DCE devices are actually both at customer's premises and in provider's network. However, the original picture you have included talks about a device that would definitely be located at the customer's premises along with the router.

Best regards,

Peter