Nortel built a lot of cellular networks and owned a huge chunk if IP for it (that was surprisingly valuable during the bankruptcy auctions). They also had quite the large long-haul fiber optic install base (which they bet the farm on, that quickly became commodified, which is really what bankrupted them). They also had one of the first commercially available DSL modems.
Sure, they built “bad” edge routers and switches (they came out of the telco industry, so focused too much on managed services for them, which caused headaches for end-customers), but the company was an engineering powerhouse ruined by hubristic businessmen.