Well the first question that you should ask yourself before connecting two sentences is 'How are the two sentences related?' The simplified versions of your sentences are:
x techniques are done at this phase.
x techniques do that.
It seems the relationship is of the purpose nature so an infinitive or structures similar to that are probably good enough to express the relationship:
'In anticipation of failure, protection techniques are done at the network design or planning phase in order to reserve backup lightpaths in advance.'
You could also use a relative clause to do that,
'In anticipation of failure, protection techniques which reserve backup lightpaths in advance are done at the network design or planning phase'