To add, any given make / model number of a modem's particular firmware load can and could be coded to make that indicator light blink continuously regardless of the presence of or the absence of any traffic.
thanks to oldTDNickell5
Definitions of terms: DHCP & ARP
DHCP: Dynamic Host Configuration Protocol. A protocol for assigning dynamic IP addresses to devices on a network.
ARP: Address Resolution Protocol. Its a protocol that allows the OS to associate an ip address (layer 3) with an ethernet MAC address (layer 2).
*This FAQ is based on user knowledge from a volunteer core of BroadbandReports' members. This FAQ in no way constitutes official information from Comcast or any of its affiliates.