Table 19: Differences Between Sonet And Sdh Standards - Alcatel-Lucent 7750 SR OS Interface Configuration Manual

Differences in SONET/SDH Standards for K Bytes
SONET and SDH standards are slightly different with respect to the behavior of K1 and K2 Bytes.
Table 19

Table 19: Differences Between SONET and SDH Standards

SONET/SDH standards
use different codes in the
transmitted K1 byte (bits 1-
4) to notify the far-end of a
signal fail/signal degrade
detection.
SONET systems signal the
switching mode in bits 5-8
of the K2 byte whereas
SDH systems do not signal
at all.
Failures Indicated by K Bytes
The following sections describe failures indicated by K bytes.
APS Protection Switching Byte Failure
An APS Protection Switching Byte (APS-PSB) failure indicates that the received K1 byte is either
invalid or inconsistent. An invalid code defect occurs if the same K1 value is received for 3
consecutive frames (depending on the interface type (framer) used, the 7750 SR may not be able
to strictly enforce the 3 frame check per GR-253 and G.783/G.841) and it is either an unused code
or irrelevant for the specific switching operation. An inconsistent APS byte defect occurs when no
three consecutive received K1 bytes of the last 12 frames are the same.
If the failure detected persists for 2.5 seconds, a Protection Switching Byte alarm is raised. When
the failure is absent for 10 seconds, the alarm is cleared. This alarm can only be raised by the
active port operating in bi-directional mode.
7750 SR OS Interface Configuration Guide
depicts the differences between the two standards.
SONET
1100 for signal fail
1010 for signal
degrade
1101 unused
1011 unused
101 for bi-dir
100 for uni-dir
SDH
1101 for signal fail
1011 for signal degrade
1100 unused
1010 unused
Not used. 000 is signaled
in bits 5 to 8 of K2 byte
for both bi-directional as
well as uni-directional
switching.
Interface Configuration
Comments
None
SONET systems raise a mode
mismatch alarm as soon as a
mismatch in the TX and RX
K2 byte (bits 5 to 8) is
detected.
SDH systems do not raise the
mode mismatch alarm.
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