Voice Gateway Platform Picker

Cisco is transitioning from ISR 4000 to Catalyst 8000 for voice gateways. ISR 4431/4461 are still sold but End-of-Sale dates are approaching. Catalyst 8200L is the spiritual successor to ISR 4321 for SMB voice; CAT 8300 replaces ISR 4431/4461; CAT 8500/8500L picks up where ISR 4461 tops out. All modern IOS-XE (17.12 LTS) supports both chassis families. Pricing: CAT 8000 comes with SD-WAN + security features that inflate the list price 20-30% over equivalent ISR. If you only need CUBE, ISR 4461 is still a valid choice while it's in the catalog.

NIM port density: NIM-2FXS, NIM-4FXS, NIM-2FXO, NIM-4FXO, NIM-8FXS, NIM-PRI (1/2/4/8 PRI). CAT 8300 has 3 NIM slots; CAT 8500L has 4 NIM slots plus SM-X slots for higher density. Analog-only gateways max out around 72 FXS with SM-X-24FXS modules. Don't mix NIMs on the same ISR-series chassis except as documented — some combinations underperform due to DSP channel sharing.

vCUBE (C8000v) for cloud deployments: runs in VMware, KVM, AWS, Azure. Max ~2000 CCS per VM. No DSP (virtual platforms don't have PVDM) — transcoding is software via IP-IP-GW, much slower and CPU-hungry. Use vCUBE when you're terminating SIP trunks in cloud and don't need analog/PRI. For on-prem voice, always go hardware — DSP density and cost-per-port are much better.