Cisco Systems AS5850 manual Clock Management

Chapter 1 Cisco AS5850 Product Overview

Cisco AS5850 Chassis

Table 1-2 Maximum Number of Trunk Cards For ERSC (continued)

	Non-Split Chassis					Split Chassis
	Total			Total	Total	Total		Total	Total
Chassis	Trunk		Total	DS0s	Ports	Trunk	Total	DS0s	Ports
Trunk	Cards Per		324-port	with	with	Cards Per	324-port	with	with
Type	Chassis		UPC	ERSC	ERSC	Chassis	UPC	ERSC	ERSC
24T1/T3	3	24T1	7	3072	2700	1	1	1248	1512
combination	2	T3
24E1/STM1	1 STM1		7	3330	3240	—	—	—	—
	2	24E1

Note Mixing CT1 or CT3 and CE1 or STM1 in the same chassis is not supported. If this configuration guideline is violated, an error message appears on the RSC and the disallowed card is shut down.

The universal gateway uses CT1, CE1, CT3, or STM1 trunk interfaces that terminate ISDN and modem calls and break out individual calls from the appropriate telco services. Digital calls are terminated on the trunk card high-level data link control (HDLC) controllers, and analog calls are terminated on the universal ports on the trunk card, if available, or universal ports on another feature card. As a result, any DS0 can be mapped to an onboard HDLC controller or any universal port. You can install multiple ingress interface cards, which enables you to configure your systems as fully operative, port redundant, or card redundant, depending on your specific needs.

Clock Management

The RSCs also provide clock and power control to the feature cards. Each RSC contains a block of logic, referred to as the common logic, and system clocks. This block of logic can use a variety of sources to generate the system timing, including a T1, E1,T3, STM1, or BITS input signal (accepts only T1 or E1) from the BNC connector on the RSC front panel.

Only one common logic circuit is active at any one time, which is identified by the CLK (clock) LED on the RSC front panel. The active common logic is user-selectable and is independent from each RSC. This ensures that if an RSC needs replacing or if the slave RSC becomes the master, clocking remains stable. The selected common logic should not be changed during normal operation unless related hardware failure is suspected or diagnosed.

The configuration commands for the master clock specify the various clock sources and a priority for each source. Together these commands define a list, ordered by priority, of the clock sources used to generate the master clock. The prioritized list, configured on the router shelves, is passed to and stored by the RSC providing the active clock. In the event of failure of the highest-priority clock source, the RSC switches to the source with the next-highest priority.

With a split backplane, the clock sources can be configured on either of the RSCs. Typically a router configures clock sources only from the slots that it owns; clock sources can be configured from other slots, but they are ignored. On the universal gateway, all valid clock source configurations need to be known to the RSC providing the clock, including the clock source configurations on the other RSC.

An error condition can arise if a clock input on one RSC is configured to have the same priority as a clock input configured on the other RSC. However, the command is not rejected, because the values configured on the other RSC may not be known. Warning messages are issued to both RSCs when this

	Cisco AS5850 Universal Gateway Hardware Installation Guide
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