Step 1 is the most difficult one and takes the most time. Several decisions are made about a packet to determine to which neighbor it should be sent. The decision process that takes place can be compared to filling in a tax form. It is fair to say that a router fills in a tax form for every packet it has to send through. The faster you make this process, the more packets a router can handle per second, the faster your network becomes.
Computer science is always about speeding up everything.
This makes life easier for students. Don't let it do work that does not influence the final decision. What they did at M.I.T. is take scissors and cut the tax form in pieces. On every strip of paper there is one question. In computer slang this means they have built modules containing a well-defined functionality.