DCE/DTE

• DCE/DTE are two sides of a Serial connection.
  • The DCE (Data Circuit-terminating Equipment, Data Communications Equipment, or Data Carrier Equipment) transmits the clock signal and controls the clock rate
  • The DTE (Data Terminal Equipment) receives the clock signal
• In short:
  • DCE Transmits the clock signal and controls the clock rate
  • DTE Receives the clock signal

Clock rate only needs to be configured on the DCE
# sho controllers

R1(config-router)# do sho controllers s0/0/0
Interface Serial0/0/0
Hardware is PowerQUICC MPC860
DCE V.35, clock rate 128000
idb at 0x81081AC4, driver data structure at 0x81084AC0
SCC Registers:
General [GSMR]=0x2:0x00000000, Protocol-specific [PSMR]=0x8
Events [SCCE]=0x0000, Mask [SCCM]=0x0000, Status [SCCS]=0x00
Transmit on Demand [TODR]=0x0, Data Sync [DSR]=0x7E7E

The DCE V.35 indicates that R1 is the DCE in the pair, and controls the clockrate

HDLC

• High-Level Data Link Control (HDLC) is a Layer 2 WAN Encapsulation Protocol that is used on Synchronous data links
  • Serial connections use HDLC encapsulation by default
• It has a standard and a #Cisco-Proprietary version
• Cisco HDLC is the default WAN protocol on Cisco devices for point-to-point WAN links