System Management
7750 SR OS Basic System Configuration Guide Page 239
Network Timing
In Time Domain Multiplexed (TDM)-based networks (for example, SONET or SDH circuit-
switched networks), the concept of network timing is used to prevent over-run or under-run issues
where circuits are groomed (rebundled) and switched. Hardware exists in each node that takes a
common clock derived from an internal oscillator, a specific receive interface or special BITS
interface and provides it to each synchronous interface in the system. Usually, each synchronous
interface is allowed to choose between using the chassis-provided clock or the clocking recovered
from the received signal on the interface. The clocking is used to drive the transmit side of the
interface. The appropriate configuration at each node which defines how interface clocking is
handled must be considered when designing a network that has a centralized timing source so each
interface is operating in a synchronous manner.
The effect of timing on a network is dependent on the nature of the type of traffic carried on the
network. With bit-wise synchronous traffic (traditional circuit-based voice or video), non-
synchronous transmissions cause a loss of information in the streams affecting performance. With
packet-based traffic, the applications expect and handle jitter and latency inherent to packet-based
networks. When a packet-based network is used to carry voice or video traffic, the applications
use data compression and elasticity buffering to compensate for jitter and latency. The network
itself relies on appropriate Quality of Service (QoS) definitions and network provisioning to
further minimize the jitter and latency the application may experience.
Power Supplies
7750 SR OS supports a power-supply command to configure the type and number of power
supplies present in the chassis. The operational status of a power source is always displayed by the
LEDs on the Control Processor/Switch Fabric Module (CP/SFM) front panel, but the power
supply information must be explicitly configured in order for a power supply alarm to be
generated if a power source becomes operationally disabled.
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