In packet-switched networks such as the Internet, a router is a device or, in some cases, software in a computer, that determines the next network point to which a packet should be forwarded toward its destination.

Redundancy checking: http://searchnetworking.techtarget.com/definition/cyclic-redundancy-checking
Cyclic redundancy checking is a method of checking for errors in data that has been transmitted on a communications link. 

Hop: http://whatis.techtarget.com/definition/hop
In a packet-switching network, a hop is the trip a data packet takes from one router or intermediate point to another in the network. On the Internet (or a network that usesTCP/IP), the number of hops a packet has taken toward its destination (called the "hop count") is kept in the packet header.