Nokia PDH and Marconi SDH

The original Mediahub project 2MB/s leased lines were presented from a Nokia 34MB/s PDH “box” on the wall. When we moved site, Telewest provisioned these with a rack mount version, and on the day of the move, cut over in their network the optical fibre to each. In due course, we added more sites and Telewest needed to add more leased lines to service them. This time we were provided with an SDH rack mount Add Drop Multiplexer.

Left hand shows both units mounted in our rack, PDH on top, SDH bottom, right hand picture show a similar Nokia frame in an external Telewest cabinet they kindly left unlocked for me.

This ADM is made by Marconi, but why they don't advertise it with any sort of logo is a mystery.

It was connected back to Telewest's network via a dual SDH ring operating at stm1 or oc3 or 155MB/s. These rings were presented over single mode fibre (blue) with F type optical fible connectors, four fibres in total, tx and rx for each ring

We had a breakout of 2Mb/s circuits to feed our networking equipment presented on BNC coax connectors. The inner workings of this are a mystery, as it was part of Telewest's network, they managed it.

The power supply to this was 48v DC, with a stack of batteries as a battery backup. As it would have carried other traffic for other users in the ring, if we had a power failure, it could have caused distruption to them.

This kit was manufactured by Nokia, the differnce in physical construction is quite marked. The SDH Marconi node looks better made, but the Nokia PDH kit seems to have been engineered to reduce cost as much as possible, eg. using plastic parts in many places with a thin screen of metal where required.

The feed for this is a 34Mb/s single mode fibre pair on the left hand side (blue again). There is no redundancy on this link, it is just a single circuit. Power is 48V DC fed from the same PSU as the SDH node.

Note the antistatic press stud connector on the LHS rack mount bracket.

The tributary inputs to this are 16 x 2Mb/s, these are the gold (SMB) connectors on the lower part of the circuit boards, they seem to be multiplexed in groups of 4 to 8Mb/s and seem to come out of the top pair of gold connectors (DM8.1, i.e. 4x 2Mb/s) and then these 4 x 8Mb/s circuits multiplexed up to 34Mb/s (DM34), this is on the LHS card next to the blue optical fibre. The 34Mb/s copper output is then converted to a single mode optical fibre to give greater range (DF34) in the card on the extreme left.

This seems an identical method to Digital Microwave 16x2Mb/s to 34MB/s multiplexer and is shown in the diagram to the right.

In the diagram, only the first 2 8Mb/s groups are used.