Circuit switch versus Packet switch mechanism

Circuit switching
* Middle routers must presetup the link to transmit the data between two different DTEs
* Circuit-switched networks require dedicated point-to-point connections during calls.
* Data will arrive with constant bandwidth and at constant delay.
* example include Public Switch Telephone Network (PSTN)


Packet switching
* No need to presetup the link to transmit the data between two different DTEs. Data will go ahead from the source DTE to the destination DTE by using the store-and-forward mechanism in all the middle routers
* Pakcet-switched networks don't require dedicated point-to-point connections during calls.
* No predetermined path
* Data will not guarantee with constant bandwidth and constant delay. The communication may suffer from variable bit rate and delay, due to varying traffic load and packet queue lengths
* Include connection-oriented (known as virtual-circuit, described as stateful.) and connectionless (described as stateless)
* examples include TCP, X.25, Frame Relay, GPRS
* Virtual circuit switching technologies include ATM (use VCI/VPI in the cell header), MPLS

DTE vs DCE

(Refer from the http://www.infocellar.com/cable-dsl/dte-vs-dce.htm)

Actually, DTE and DCE are different for the pin definitions of the connecting-interface. For the case of Ethernet scenario. In the DTE, port 1,2 are transmitted port, port 3,6 are received port. In the DCE, port 1,2 are received port, port 3,6 are transmitted port.
Cardinal Rule

DTE-DCE or DCE-DTE connections use Standard Ethernet Cable (straight-thru)
DTE-DTE or DCE-DCE connections use crossover Ethernet Cable (send/receive "cross over")
DCE/DTE refer to interfaces - not the actual device. A device can have both DCE and DTE ports. However, in general:

PC LAN cards (NIC - Network Interface Card) are DTE
Hub LAN ports are DCE
Hub Uplink Ports are DTE - it is a shared port with the last LAN port, but has the pinouts crossed
Cable Modem LAN port is DCE
Router LAN ports are DCE
Home Router WAN Ethernet ports are DTE

Almost all the WAN ports of CPE (Customer-premises equipment) device are DTE. All the LAN port of CPE devices are DCE.