User guide

August 2001 241
R2-CCITT - Central European Implementation
When the outgoing end terminates the call, it sends a Clear
Forward signal. When the incoming end detects the Clear
Forward, it transmits an intermediate signal called a Release
Guard before releasing the line. The Release Guard acts as an
intermediate signal to prevent bits A and B from both changing
at one time. An Answer Signal (01) followed by an Idle signal
(10) requires both bits A and B to change, called a double bit
change. By using a Release Guard (11), only one bit changes at
a time. Most implementations of R2-CCITT interpret a Release
Guard as a temporary Block signal on the line. Although this
transition is not necessary in other implementations, it does not
cause problems.