Nokia 7705 - 6.4.2 Line Timing Mode

Basic System Configuration Guide System Management
Edition: 01 3HE 11010 AAAC TQZZA 223
When configuring the priority order of the timing references with the ref-order
command for unfiltered BITS output (T4), all reference sources are valid options,
except the BITS input, which is excluded to avoid a timing loop. Because the same
priority order is used for the SETG output (T0), the BITS input option must be set as
the first (highest-priority) reference option.
Because both input and output clock pins are inside the physical RJ-45 port for each
BITS port, a custom cable is required to connect input and output ports to different
equipment. Refer to the 7705 SAR-18 Chassis Installation Guide, BITS Ports and
Pinouts.
6.4.2 Line Timing Mode
Line timing from a synchronous port, such as a T1/E1 port or synchronous Ethernet
port, provides the best synchronization performance through a synchronization
distribution network. Line timing mode derives an 8 kHz clock from the framing of T1/
E1, DS3/E3, and SONET/SDH signaling that can be used as an accurate reference
between nodes in a network. Line timing mode is immune to any packet delay
variation (PDV) occurring on Layer 2 or Layer 3 links.
On the 7705 SAR-M (variants with T1/E1 ports), line timing is supported on T1/E1
ports. Line timing is also supported on all RJ-45 Ethernet ports and SFP ports on the
7705 SAR-M (all variants).
On the 7705 SAR-X, line timing is supported on T1/E1 ports and Ethernet ports.
In addition, line timing is supported on the following modules when they are installed
in chassis variants with module slots:
• GPON module
• 8-port xDSL module (NTR over ADSL2, ADSL2+, or VDSL2)
• 6-port DSL Combination module (two references are available: NTR over
SHDSL and NTR over ADSL2, ADSL2+, or VDSL2)
• 2-port 10GigE (Ethernet) module
• 6-port SAR-M Ethernet module
On the 7705 SAR-H and 7705 SAR-Hc, line timing is supported on all Ethernet ports.
Line timing is also supported on the T1/E1 ports of the T1/E1 ASAP and RS-232
Combination module when it is installed in the 7705 SAR-H.