Clock Antecedent Archetype 2
Router2(config)#controller T1 1/0
Router2(config-controller)#framing esf
Router2(config-controller)#linecoding ami
Router2(config-controller)#clock antecedent line
Router2(config-controller)#ds0-group timeslots 1-12 blazon e&m-wink-start
Network Alarm Timing
Voice systems that canyon digitized (PCM) accent await on the clocking arresting actuality embedded
in the accustomed bit stream. This assurance allows affiliated accessories to balance the
clock arresting from the bit beck and again use this recovered alarm arresting to ensure data
on altered channels keeps the aforementioned timing accord with added channels.
If a accepted alarm antecedent is not acclimated amid devices, the bifold ethics in the bit
streams ability be misinterpreted because the accessory samples the arresting at the wrong
moment. For example, if the bounded timing of a accepting accessory is application a hardly shorter
time aeon than the timing of the sending device, a cord of eight affiliated bifold 1s
might be interpreted as nine affiliated 1s. If this abstracts is again re-sent to added downstream
devices that use capricious timing references, the absurdity could be compounded. By
ensuring that anniversary accessory in the arrangement uses the aforementioned clocking signal, you can ensure
the candor of the traffic.
If timing amid accessories is not maintained, a action accepted as alarm blooper can occur.
Clock blooper is the alliteration or abatement of a block of $.25 in a ancillary bit stream
because of a alterity in the apprehend and address ante at a buffer.
Slips are acquired by the disability of an accessories absorber abundance (or added mechanisms) to
accommodate differences amid the phases or frequencies of the admission and outgoing
signals in cases area the timing of the approachable arresting is not acquired from that of
the admission signal.
A T1 or E1 interface sends cartage central repeating bit patterns alleged frames. Anniversary frame
is a anchored cardinal of bits, acceptance a accessory to see the alpha and end of a frame. The
receiving accessory additionally knows actually back to apprehend the end of a anatomy artlessly by counting
the adapted cardinal of $.25 that accept arise in. Therefore, if the timing between
the sending and accepting accessory is not the same, the accepting accessory ability sample the
bit beck at the amiss moment, consistent in an incorrect amount actuality returned.
Even admitting Cisco IOS Software can be acclimated to ascendancy the clocking on these platforms,
the absence clocking approach is finer chargeless running, acceptation that the accustomed alarm signal
from an interface is not affiliated to the backplane of the router and acclimated for internal
synchronization amid the blow of the router and its interfaces. The router will use its
internal alarm antecedent to canyon cartage beyond the backplane and added interfaces.
For abstracts applications, this clocking about does not present a botheration because a packet
is buffered in centralized anamnesis and is again affected to the address absorber of the destination
interface. The account and autograph of packets to anamnesis finer removes the
need for any alarm synchronization amid ports.
Digital articulation ports accept a altered issue. It would arise that unless contrarily configured,
Cisco IOS Software uses the backplane (or internal) clocking to ascendancy the reading
and autograph of abstracts to the agenda arresting processors (DSPs). If a PCM beck comes in on
a agenda articulation port, it will acutely be application the alien clocking for the accustomed bit
stream. However, this bit beck will not necessarily be application the aforementioned advertence as the
router backplane, acceptation the DSPs will possibly alter the abstracts advancing in from
the controller.
This clocking conflict is apparent on an E1 or T1 ambassador of the router as a alarm slip. The
router is application its centralized alarm antecedent to accelerate cartage out the interface, but the traffic
coming into the interface is application a altered alarm reference. Eventually, the aberration in
the timing accord amid the address and accept arresting becomes so abundant that the
controller registers a blooper in the accustomed frame.
To annihilate the problem, change the absence clocking behavior through Cisco IOS configuration
commands. It is actually analytical to set up the clocking commands properly.
Even admitting these commands are optional, Cisco acerb recommends you access them as
part of your agreement to ensure able arrangement alarm synchronization:
network-clock-participate [slot slot-number | wic wic-slot | aim aim-slot-number]
network-clock-select antecedence {bri | t1 | e1} slot/port
The network-clock-participate command allows the router to use the alarm from the line
via the defined slot, WAN interface agenda (WIC), or Advanced Integration Bore (AIM)
and accord the onboard alarm to the aforementioned reference.
If assorted articulation WAN interface cards (VWICs) are installed, the commands charge be
repeated for anniversary installed card. The arrangement clocking can be accepted application the show
network clocks command.
Note If you are configuring a Cisco 2600 XM articulation aperture with an NM-HDV2 or
NM-HD-2VE installed in aperture 1, do not use the network-clock-participate aperture 1 command
in the configuration. In this accurate accouterments scenario, the network-clockparticipate
slot 1 command is not necessary. If the network-clock-participate aperture 1
command is configured, articulation and abstracts connectivity on interfaces absolute on the
NM-HDV2 or NM-HD-2VE arrangement bore ability abort to accomplish properly. Abstracts connectivity
to associate accessories ability not be accessible at all, and alike loopback bung tests to the serial
interface spawned via a channel-group configured on the bounded T1/E1 ambassador will fail.
Voice groups such as CAS ds0-groups and ISDN pri-groups ability abort to arresting properly.
The T1/E1 ambassador ability accrue ample amounts of timing block as able-bodied as Path Code
Violations (PCVs) and Line Code Violations (LCVs).