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FAQ-How to Set the Clock Correctly When Connecting a Datacom Device with Transmission Equipment

Publication Date:  2012-07-27 Views:  37 Downloads:  0
Issue Description
Q:
The clock track settings are quite complex when you connect a datacom device with transmission equipment. This document is written by both datacom and R&D experts and is used as a reference for project deployment and maintenance. 
 
Alarm Information
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Handling Process
A:
During the project deployment and maintenance, you may not pay attention to the clock settings; however, the inconsistent clock settings cause problems and decrease the maintenance efficiency.
Generally, inconsistent clock settings on the peer devices cause packet loss and unstable communication. The symptoms are as follows:
(1) Irregular packet loss. The packet loss frequency, and the size and type of packets discarded are irregular.
(2) Interfaces are Up or Down irregularly.
(3) When the devices are far from each other or the link quality is poor, the preceding symptoms are more severe.
The following parts describe how to correctly set the clock when you connect a datacom device with transmission equipment:
1. Scenario 1: PDH
Network topology:
Router-A���PDH transmission equipment side A�����PDH transmission equipment side���Router-B
Networking description:
The two routers are connected with the PDH transmission equipment through interface boards E1/T1, and E3/T3.
The functionality of tributary boards E1/T1, and E3/T3 used for SDH transfer is similar to that of the PDH transmission equipment. Therefore, in such a network topology, you can use traditional PDH transmission equipment or tributary boards E1/T1 and E3/T3 used for SDH transfer.
Interface type: E1/T1, and E3/T3
Configuration guide:
In this networking, the PDH transmission equipment only transparently transmits the clock signal rather than providing the clock; therefore, you are recommended to set the master clock on the interconnecting interfaces of one router and the slave clock on the interconnecting interface of the other router.
In addition, you are not recommended to set the clocks of both routers to the DTE mode (that is, each router uses its internal clock source), though the routers can still communicate with each other. The reason is that if the clock signals of the routers cannot be coupled well, packet loss or unstable communication may occur.
2. Scenario 2: SDH
Network topology:
Router-A���SDH transmission equipment side A�����SDH transmission equipment side���Router-B
Networking description:
The two routers are connected with the SDH transmission equipment through ATM or POS interfaces.
Interface type: ATM and POS. The interface type is irrelevant to the specific rate such as 155 Mbit/s, 622 Mbit/s, 2.5 Gbit/s, and 10 Gbit/s.
Configuration guide:
Because the clock of a SONET or SDH transmission equipment is more accurate than that of a datacom device, you are recommended to set the datacom device to work in slave clock mode, that is, to obtain the clock signal through lines.
Note that the SDH transmission equipment uses the overhead bits including J0, J1, and C2 for monitoring. Therefore, configurations for these overhead bits on both routers must be consistent; otherwise, an alarm will be generated and the connection between the SDH and routers may fail. Configurations for the overhead bits, however, are irrelevant to the clock settings.
3. Scenario 3: CPOS
Network topology:
Router-A (CPOS)��SDH transmission equipment����PDH transmission equipment��(E1/T1/E3/T3) Router-B
Networking description:
The central router (Router-A) is connected with the SDH transmission equipment through the CPOS interface. The remote router (Router-B) is connected with the PDH transmission equipment through interface boards E1/T1 and E3/T3.
The functionality of tributary boards E1/T1 and E3/T3 used for SDH transfer is similar to that of the PDH transmission equipment. Therefore, in such a network topology, you can use traditional PDH transmission equipment or tributary boards E1/T1 and E3/T3 used for SDH transfer.
Interface type: channelized CPOS, E1/T1, and E3/T3.
Configuration guide:
Because SDH transmission equipment provides the clock for the CPOS father interface of Router-A, you are recommended to set this CPOS father interface to work in slave clock mode, that is, to obtain the clock signal through lines.
Because the transmission equipment do not provide clocks for Router-B and the channelized CPOS subinterface of Router-A, you need to configure one router to work in master clock mode and the other one in slave clock mode. You are recommended to set the channelized CPOS subinterface of Router-A to work in master clock mode, and set Router-B to work in slave clock mode. 
 
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