SDH networks are usually deployed in protected rings. This has the advantage of giving protection to the data, by providing an alternate route for it to travel over in the event of equipment or network failure.
Each side of the ring (known as A and B, or sometimes, East and West), consists of an individual transmit and receive fibre. These fibres will take diverse physical paths to the distant end equipment to minimise the risk of both routes failing at the same time.
The SDH equipment’s have the ability to detect the problem and will automatically switch to the alternate route.
SDH multiplexers transmit on both sides of the ring simultaneously, But to speed up switching times, they only receive on one side at any time. This means that only the receiving end needs to switch, thus reducing the impact of a fault on the customers' data.
In previous post we have seen the limitations of PDH. Now let us see the advantages of SDH.
· SDH permits the mixing of the existing European and North American PDH bit rates.
· All SDH equipment is based on the use of a single master reference clock source & hence SDH is synchronous.
· Compatible with the majority of existing PDH bit rates
· SDH provides for extraction/insertion, of a lower order bit rate from a higher order aggregate stream, without the need to de-multiplex in stages.
· SDH allows for integrated management using a centralised network control.
· SDH provides for a standard optical interface thus allowing the inter-working of different manufacturers equipment.
· Increase in network reliability due to reduction of necessary equipment/jumpering.