Start simple: if it was a term server and a router (via console), the octal serial cable goes directly into the console port of 2500, 2600 ... anything with an RJ45-style port..

If the console is something like a 6500 or 7500, then you'd need an adapter to a db25 connector.

If you were going directly from a PC (db9f)to an RJ45-style console, it's via a "rolled" cable (reverse the pin order, 1-8, 2-7,3-6, etc) which is most often a powder blue flat cable.

Now, if you need to extend those connections, anything that ultimately results in a "straight through" extension should work, if it's not too long.

So, whatever cable you'd normally use, with whatever "straight-through" assemblies you use to create an extension.

Good Luck

Scott