Cisco 4000 Series Integrated Services Router Gigabit Ethernet WAN Modules Data Sheet - Cisco
Cisco 4000 Family Integrated Services Router Data Sheet - Cisco
Cisco 2- and 4-Port ISDN BRI S/T Network Interface Modules Data Sheet - Cisco
ISR4331/K9 Datasheet Overview
Hardware Installation Guide for Cisco 4000 Series Integrated Services Routers - Overview of the Cisco 4000 Series ISRs [Cisco 4000 Series Integrated Services Routers] - Cisco