Path  Overhead

It is part  of SPE  and contain followings  information: Performance monitor of synchronous transport , signal , path , track ,parity ,checks,  and path  status.

                                                                                     Figure  Path Overhead

a.Path  trace byte : The JI bytes in consecutive frames form a 64 kbps channel used for  tracking the path . the JI byte send a continuous 64 bits string to verify  the connection. The choice  of the  string  is left to the application  programs.

b.Path parity byte : Byte B3 is for  bit interleaved parity  like byte B1 and B2. But calculated for the path header.

c.Path signal  label byte > Byte  C2 is the  path  identification byte. It is used to  identify different protocols  used at higher levels .

d.Path status byte > Byte  G1 is sent by the receiver to communicate  its status to the  sender.

e.Path  user channel byte : The byte 2 bytes in consecutive frames like the F1 bytes form a 64 kbps channel is reserved for user needs,, but  at the path  level.

f.Virtual tributary indicate byte H4 is the multi frame indicator. It  indicates payloads that cannot  fit in single frame. Virtual tributaries are discussed in the  next section.