Each clear channel DS3/E3 port on a 4-port DS3/E3 Adapter card can be independently configured to be loop-timed (recovered from an Rx line), node-timed (recovered from the SSU in the active CSM), or differential-timed (derived from the comparison of a common clock to the received RTP timestamp in TDM pseudowire packets). When a DS3 port is channelized, each DS1 or E1 channel can be independently configured to be loop-timed, node-timed, or differential-timed (differential timing on DS1/E1 channels is supported only on the first three ports of the card). When not configured for differential timing, a DS3/E3 port can be configured to be a timing source for the node.