Transmission network protection using loop topology
Introduction
Nokia Loop Protection is considered the most efficient way to protect traffic in a
transmission network such as a GSM base station subsystem. In a live
telecommunications network it is important to secure the network
synchronisation and the centralised network management, in addition to the
actual payload traffic, during any period of abnormal circumstances.
For these reasons, Nokia Loop Protection protects
. payload traffic
. network synchronisation
. network management connections.
A transmission loop formed with Nokia elements consists of one loop master and
several loop slaves. Usually the loop master is a transmission node whereas the
loop slaves can be either transmission nodes, BTSs or a combination of both
inside one loop.
The loop principle is that the transmitted signal is always sent in both directions
but the received signal must be chosen from only one direction. The loop master
sends pilot bits on the basis of which the switching decision is made. Each
individually protected slave station needs one pilot bit.
Network synchronisation must also be ensured in a loop network and it follows
the loop principle in a similar way. The synchronisation switching takes place
independently from the pilot bits by having a master clock bit (MCB) and a loop
control bit (LCB).
Each network element decides individually from which direction the signal and
the synchronisation will be received, and so it does not require any external or
additional supervision for its decision.
Nokia’s way of implementing loop protection is ultimately secure, providing very
fast route switching that recovers the transmission connections instantly. Nokia
loop protection is embedded and thus very fast. Nokia loop protection protects
against failures, such as cable-cut, equipment failure, heavy rain and multipath
fading, and against obstacles in the line-of-sight, such as cranes and growing
trees.
Compared to an unprotected wireless network, Nokia loop protection increases
site availability at least tenfold and prevents end-of-chain availability
degradation. Further, it enables significant hop length increases without site
availability sacrifices and helps minimise radio link antenna sizes.