For the combination of an OpenScape 4000 with SDH transmission equipment the following must be considered other than with PDH equipment:

Transmission within the SDH (Synchronous Digital Hierarchy) is synchronous with the SDH network clock on the levels STM - n. Data rates below 155.52 Mbps are mended but differently than with PDH (Plesiochronous Digital Hierarchy). Data streams from the SDH< 155.52 Mbps can or could be supplied with the SDH network clock. This is called "retiming". "Retiming" can be performed both in the SDH multiplexer or in the OpenScape 4000 system. For retiming in the OpenScape 4000 system, a clock connection from the SDH multiplexer (port T4) to the OpenScape 4000 front reference port must be established (special cable). The front reference is then set using the AMO REFTA and its priority adjusted correspondingly for the OpenScape 4000 system to synchronize onto this front reference. "Retiming" is then automatically executed in the OpenScape system. The advantage only exists as long as an overflow of the "retiming" buffer leads to a bit slip and not to a total loss of frame synchronization with a complete disconnection of all B channels as the SDH multiplexer has only 40 µsec buffer depth for retiming, while the OpenScape 4000 PMA interfaces have a buffer of +/- 125 µsec.

SDH equipment without "retiming" behave identically to PDH equipment in the case of 2-Mbps interfaces, i.e. the connections must be treated as clock-transparent (PDH). Priorities for the OpenScape 4000 reference clock table remain the same.

The fact that the SDH network should be operated synchronously to the Telecom/carrier clock at this point should be considered when planning the network. If an SASE (tracking oscillator) is connected, further T4 ports with 2.048 MHz for the T3 clock ports of the PABX equipment are used in addition to the clock for the front reference.

As soon as "retiming" is used, clock distribution in the network must be redesigned since the SDH network is important for clock distribution.

In case of "retiming", the SDH network must be able to receive the master clock (PTT or SASE) from two independent ports. Thus the SDH network has the same clock supply as an OpenScape 4000/HiPath 4000 network with clock-transparent (PDH) connections and minimum meshing. The clock is then distributed in the SDH with the STM-n level. Reconfigurations during interruptions etc. are automatically performed in the SDH network (comparable to the OpenScape 4000/HiPath 4000 network planning with the AMO REFTA). The 2-Mbps connections between the OpenScape 4000 systems in the network cease to be clock-transparent. All OpenScape 4000 systems connected to the SDH network are operated as clock slaves on the SDH network. OpenScape 4000 tie trunks on the same clock hierarchy level can no longer be used as substitute routes but are allocated a priority unequal zero on both sides. This puts these ports on the OpenScape 4000 systems on one level with the direct clock paths.

Normal transmission jitter is not greater with SDH than with PDH. During reconfigurations in the network or with plesiochronous connections between various SDH islands the so-called "pointer adjustment" jitter with an amplitude of up to 5 µsec can appear in addition to the normal jitter. Both the OpenScape 4000 interfaces and the clock generator can handle and accept this additional jitter and drift caused by SDH.

Network synchronization and SDH equipment planning should be performed in conjunction with personnel representing the relevant transmission systems.