Average internet router, let's take a guesstimate - 10 OC192s. 10x2.4 Mbs = 24 Gbs for all interfaces, assume 50% utilization = 12 Gbs.
3.15*7 seconds/yr
Average lifespan of 7 years before replacement
2.2 *10^7 seconds lifetime
12 * 10^9 bits/sec (12 Gbs)
=2.64 * 10^17 bits in 7 years for TX, same number for RX.