Circuit Emulation (Cpipe) Services
Page 134 7210 SAS M Services Guide
Control Word
The structure of the control word is mandatory for SAToP and is shown in Figure 19.
Figure 19: Control Word Bit Structure
The control word descriptions are listed in the Table 11:
Table 11: Control Word Bit Description
Bit(s) Description
Bits 0 to 3 The use of bits 0 to 3 is described in RFC 4385. These bits are set to
‘0’ unless they are being used to indicate the start of an Associated
Channel Header (ACH) for the purposes of VCCV.
L (Local TDM Failure) The L bit is set to 1 if an abnormal condition of the attachment
circuit such as LOS, LOF, or AIS has been detected and the TDM
data carried in the payload is invalid. The L bit is cleared (set back
to 0) when fault is rectified.
R (Remote Loss of
Frames indication)
The R bit is set to 1 if the local CE-bound inter-working function
(IWF) is in the packet loss state and cleared (reset to 0) after the
local CE-bound IWF is no longer in the packet loss state.
M (Modifier) The M bits are a 2-bit modifier field. For SAToP, M is set to 00 as
per RFC 4553.
Sequence number The sequence number is used to provide the common pseudowire
sequencing function as well as detection of lost packets.
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