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Intoduction:

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Le but de ce cours est de vous familiariser avec l’équipement SDH Loop Telecom 9100 à savoir connaître ses differents composants et leur fonctionnalités ainsi que de pouvoir configurer les différents paramètres de celui-ci et interpréter les alarmes qui peuvent être générées lors d’incidents sur le réseau SDH. Un rappel des bases du protocole SDH sera également donné afin d’optimiser la compréhension du fonctionnement de l’équipement.

SDH: Clocking: Because of the speed at which they operate,all SONET networks require timing signals that are Stratum 3 or better.Otherwise,pointer justification and other functions that were discussed earlier will not take place with appropriate levels of accuracy.

The devices in a SONET network have the luxury of choosing from any of five timing schemes to ensure accuracy of the network. As long as the schemes have Stratum 3 accuracy or better, they are perfectly acceptable timing sources.The five are discussed below. ■ Line timing: Devices in the network derive their timing signal from the arriving input signal from another SONET device. For example, an add-drop multiplexer that sits out on a customer’s premises derives its synchronization pulse from the incoming bit stream and might provide further timing to a piece of E that is out beyond the . ■ Loop timing: Loop timing is somewhat similar to line timing;in loop timing,the device at the end of the loop is most likely a terminal multiplexer. ■ External timing: The device has the luxury of deriving its timing signal directly from a Stratum 1 clock source. 77SONET Basics ■ Through timing: Similar to line timing,a device that is through timed receives its synchronization signal from the incoming bit stream,but then forwards that timing signal to other devices in the network.The timing signal then es through the intermediate device. ■ Free running: In free-running timing systems, the SONET equipment in question does not have access to an external timing signal and must derive its timing from internal sources only.

Path overhead:

Path Overhead As shown in Figure 3-12, the SDH Path Overhead comprises nine bytes, just as it does in SONET networks.These bytes include J1,B3,C2,G1,F2, H4,F3,K3,and N1.Each is described in the following section. J1:The path trace byte is used by a receiving device to ensure that it is connected to the proper transmitting device.The field is used to generate a 64-byte repeating string that identifies the source of the received signal. The field can be programmed by the any way he or she likes and often Chapter 394 Figure 3-12 Path Overhead. J1 B3 C2 G1 F2 H4 F3 K3 N1 contains an IP address,a Common Language Location Code(CLLC,or click code), a Common Language Location Indicator (CLLI, or silly code), or a telephone number that identifies the transmitting device.In SDH systems, the J1 byte often contains an E-164 because that is the only address format that is allowed at international handoff points. If for some reason neither party uses the field,it is filled with null characters. B3:The Path BIP-8 is used to error-check the content of the previous payload before being scrambled. C2:The signal label byte is used to tell a receiving device what is actually contained in the payload that is arriving in of the actual construction of the payload. This permits the simultaneous transport of multiple traffic types. This byte is one of the most important in the SDH domain, particularly for SDHSONET system handoffs. Figure 3-13 illustrates the differences that exist in payload mappings between SONET and SDH systems. 95SDH Basics Figure 3-13 Payload mappings in SDH and SONET. Hex SDH Payload SONET Payload Code Mapping (C2) Mapping (C2) 00 Unequipped or supervisory Unequipped;not available for live traffic

G1:As its name implies,the path status byte is used to communicate the overall transmission status of the duplex circuit to the originating device.In practice,it transports two indicators:the Path Remote Error Indicator(REIP) in bits one through four,and the Path Remote Defect Indicator(RDI-P) in bits five through seven,leaving a single unused bit. F2/3:The network service provider can use these bytes to transport communications information such as network management data. H4:This multiframe indicator byte is used to indicate the relative position

of payload within a container and is often specific to the payload being transported.It is used when payloads are configured as virtual containers and four of them are grouped into a superframe or multiframe. K3:Formerly known as the Z4 growth byte, the F3 byte has been reassigned for future use. N1:Formerly known as the Z5 growth byte,N1 is used for the transport of network maintenance and management information. This concludes our discussion of the SDH overhead bytes.We now turn our attention to the SDH tributary units designed to transport sub-rate payloads.