... of, the physical address used by the frames that carry the packets between adjacent systems.Why should the systems need two addresses for the two layers? Why can’t they just both use either the ... 3, which forwards the data, is the destination reachable.)These forwarding decisions are made at the TCP/IP network layer. The Network Layer The network layer delivers data in the form of a packet ... where the packet came from (so the sender can reply)? The key concept at the network layer is the network address, which provides this information. In TCP/IP, the network address is the IP...