The best replacement for nortel is cisco.

The best alternatives to nortel are rated as following:
★★★★★  cisco
★★★★  avaya
★★★  cisco voip
★★  shoretel
★  mitel
★  nec
★  alcatel
★  lucent
  norstar
  necon
  3com

Your alternative for nortel is not listed? Suggest!
Speaking about nortel, one probably shouldn't forget about avaya.

Other search terms related to nortel and their ratings are:
★★★★★ avaya
★★ cisco qsig
You have in mind a companion for nortel and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of nortel in all years. Click on graph for more.
nortel
cisco
avaya