Node Timing

The 7705 SAR supports a centralized synchronization system with an SSU in each CSM. The SSU can be synchronized to a traceable primary reference clock through an external timing port, line interface, or timing-over-packet technology. The transmit clock of each T1/E1, DS3/E3, SONET/SDH port or synchronous Ethernet-capable port (referred to as a synchronous Ethernet port in this guide) can then be configured to use the node clock or alternatives.

The 7705 SAR supports three timing references — one external and two internal. The timing references can be configured as an ordered list of highest to lowest priority. The system uses an available valid timing reference with the highest priority. If a failure on the current timing reference occurs, the next highest timing reference takes over. The reference switching can be configured to operate in a revertive or non-revertive manner with the sync-if-timing revert command. Revertive switching always selects the highest-priority valid timing reference as the current source. If a reference with a higher priority becomes valid, the system automatically switches to that timing reference. Non-revertive switching means that the active timing reference remains selected while it is valid, even if a higher-priority timing reference becomes available. If the current timing reference becomes invalid, then a switch to the highest-priority available timing reference is initiated. If all the timing references fail or have not been configured, the SSU enters holdover mode of its Stratum 3 oscillator (if it was previously synchronized) or free-run mode.

The external timing reference input with a 2.048 MHz G.703 signal, 5 MHz sine wave, or 10 MHz sine wave, is available directly on the following:

The CSMv2 on the 7705 SAR-8 Shelf V2 does not support a 5 MHz signal. On the 7705 SAR-18, the external timing reference input with a 2.048 MHz G.703, T1 (100 Ω), or E1 (120 Ω), is supported by the BITS ports 1 and 2 located on the Alarm module.

The two internal timing references originate from timing extracted from interface ports. This timing can be recovered directly from physical layer framing on a T1/E1 port, from adaptive timing recovery for TDM pseudowires, or from a synchronous Ethernet port.

On the 7705 SAR-M, all RJ-45 Ethernet ports and SFP ports support synchronous Ethernet and can supply a timing reference to be used as a source of node synchronization. On the 7705 SAR-M variants with T1/E1 ports, two T1/E1 ports can supply a timing reference. The 2-port 10GigE (Ethernet) module or 6-port SAR-M Ethernet module can supply two timing references.

On the 7705 SAR-H and 7705 SAR-Hc, all RJ-45 Ethernet ports and SFP ports support synchronous Ethernet and can supply a timing reference to be used as a source of node synchronization. When the 4-port T1/E1 and RS-232 Combination module is installed in the 7705 SAR-H, a single T1/E1 port on the module can supply a timing reference; it can be independently configured for loop-timing or node-timing. When the GPS Receiver module is installed in the 7705 SAR-H, the GPS RF port can be used as a source of node synchronization.

On the 7705 SAR-A, all synchronous Ethernet ports can supply a timing reference to be used as a source of node synchronization. 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 (except when 10/100/1000BaseT copper SFP is used) and, therefore, cannot be used as a timing reference. On the 7705 SAR-A variant with T1/E1 ports, two T1/E1 ports can also supply a timing reference.

On the 7705 SAR-Ax, all Ethernet ports support synchronous Ethernet and IEEE 1588v2 PTP and can supply a timing reference to be used as a source of node synchronization. The 7705 SAR-Ax can also derive its timing from a GPS antenna signal using the GNSS RF port.

On the 7705 SAR-Wx, all RJ-45 Ethernet ports and SFP ports support synchronous Ethernet and IEEE 1588v2 PTP, and can supply a timing reference to be used as a source of node synchronization. For 7705 SAR-Wx variants with a GPS RF port, the GPS RF port can be used as a source of node synchronization.

On the 7705 SAR-X, all Ethernet ports support synchronous Ethernet and IEEE 1588v2 PTP. Ethernet ports and T1/E1 ports can supply two timing references to be used as a source of node synchronization. In addition, each T1/E1 port can be independently configured for loop timing.

The 7705 SAR-8 Shelf V2 and 7705 SAR-18 can receive one or two timing references depending on the port and card type supplying the reference. A timing reference can come from:

The 7705 SAR-8 Shelf V2 and 7705 SAR-18 can also use IEEE 1588v2 PTP as a source of node synchronization.

Each T1/E1 port can be independently configured for loop-timing (recovered from an Rx line) or node-timing (recovered from the SSU in the active CSM).

In addition, T1/E1 CES circuits on the following can be independently configured for adaptive timing (clocking is derived from incoming TDM pseudowire packets):

T1/E1 CES circuits on the following can be independently configured for differential timing (recovered from RTP in TDM pseudowire packets):

Adaptive timing and differential timing are not supported on DS1 or E1 channels that have CAS signaling enabled.

A T1/E1 port can be configured to be a timing source for the node.

Each SONET/SDH port and each T1/E1 CES circuit on a 2-port OC3/STM1 Channelized Adapter card can be independently configured to be loop-timed or node-timed; each DS3 circuit can be independently configured to be loop-timed or free-run. A SONET/SDH port can be configured to be a timing source for the node.

Each SONET/SDH port on a 4-port OC3/STM1 Clear Channel Adapter card can be independently configured to be loop-timed or node-timed. A SONET/SDH port can be configured to be a timing source for the node.

Each SONET/SDH port on a 4-port OC3/STM1 / 1-port OC12/STM4 Adapter card can be independently configured to be node-timed; each T1/E1 CES circuit can be independently configured to be node-timed, loop-timed, or differential-timed. A SONET/SDH port can be configured to be a timing source for the node.

Each clear channel DS3/E3 port on a 4-port DS3/E3 Adapter card can be independently configured to be loop-timed, node-timed, or differential-timed. When a DS3 port is channelized, each DS1 or E1 channel can be independently configured to be loop-timed, node-timed, or differential-timed (differential timing on DS1/E1 channels is supported only on the first three ports of the card). When not configured for differential timing, a DS3/E3 port can be configured to be a timing source for the node.

Parent topic: System Management