Re: OSPF-ISIS Operating Layers & Some TCP/IP Basics
I'll take a stab at a few of these.
OSPF just needs the IP protocol to function. It is given a specific IP Protocol Type for transport, in this case IP Prot 89. Other well known protocols like GRE (47) and ICMP (1) also use their own IP Protocol number. See RFC 1583 Section 1.3 for a history of the OSPF protocol.
The term routing protocol is pretty vague, but here is a good definition - http://en.wikipedia.org/wiki/Routing_protocol . As long as it shares routing (connectivity) information, it can be considered a routing protocol. This OSI layer which it operates is irrelevant.