Line timing mode provides physical layer timing (Layer 1) that can be used as an accurate reference for nodes in the network. This mode is immune to any packet delay variation (PDV) occurring on a Layer 2 or Layer 3 link. Physical layer timing provides the best synchronization performance through a synchronization distribution network.
On the 7705 SAR-A variant with T1/E1 ports, line timing is supported on T1/E1 ports. Line timing is also supported on all synchronous Ethernet ports on both 7705 SAR-A variants. Synchronous Ethernet is supported on the XOR ports (1 to 4), configured as either RJ-45 ports or SFP ports. Synchronous Ethernet is also supported on SFP ports 5 to 8. Ports 9 to 12 do not support synchronous Ethernet and therefore do not support line timing.
On the 7705 SAR-Ax, line timing is supported on all Ethernet ports.
On the 7705 SAR-H, line timing is supported on:
all Ethernet ports
T1/E1 ports on a chassis equipped with a 4-port T1/E1 and RS-232 Combination module
On the 7705 SAR-Hc, line timing is supported on all Ethernet ports.
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 all 7705 SAR-M variants.
In addition, line timing is supported on the following 7705 SAR-M modules:
2-port 10GigE (Ethernet) module
6-port SAR-M Ethernet module
On the 7705 SAR-Wx, line timing is supported on:
RJ-45 Ethernet ports and optical SFP ports (these ports support synchronous Ethernet and IEEE 1588v2 PTP)
On the 7705 SAR-X, line timing is supported on T1/E1 ports and Ethernet ports.
On the 7705 SAR-8 Shelf V2 and 7705 SAR-18, line timing is supported on:
16-port T1/E1 ASAP Adapter card
32-port T1/E1 ASAP Adapter card
6-port Ethernet 10Gbps Adapter card
8-port Gigabit Ethernet Adapter card (dual-rate and copper SFPs do not support synchronous Ethernet)
2-port 10GigE (Ethernet) Adapter card
10-port 1GigE/1-port 10GigE X-Adapter card (supported on the 7705 SAR-18 only)
4-port DS3/E3 Adapter card
2-port OC3/STM1 Channelized Adapter card
4-port OC3/STM1 / 1-port OC12/STM4 Adapter card
4-port OC3/STM1 Clear Channel Adapter card
Packet Microwave Adapter card on ports that support synchronous Ethernet and on ports that support PCR
Synchronous Ethernet is a variant of line timing and is automatically enabled on ports and SFPs that support it. The operator can select a synchronous Ethernet port as a candidate for the timing reference. The recovered timing from this port is then used to time the system. This ensures that any of the system outputs are locked to a stable, traceable frequency source.