human
This is a text : 
Input ports. An input port performs several key functions. It performs the physical layer function of
terminating an incoming physical link at a router; this is shown in the leftmost box of an input port
and the rightmost box of an output port in Figure 4.4. An input port also performs link-layer functions
needed to interoperate with the link layer at the other side of the incoming link; this is represented by
the middle boxes in the input and output ports. Perhaps most crucially, a lookup function is also
performed at the input port; this will occur in the rightmost box of the input port. It is here that the
forwarding table is consulted to determine the router output port to which an arriving packet will be
forwarded via the switching fabric. Control packets (for example, packets carrying routing protocol
information) are forwarded from an input port to the routing processor.
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gpt
--- Reasoning ---
1. Is the question multiple-choice question?
No
2. Is it implied multiple-choice question?
No
3. If two experts were independently asked the question, will the final answer be exactly the same?
No

--- Answer ---
open