You are tasked with implementing a 1000-phone remote access solution, where phone calls will traverse a WAN edge router. Assuming all of the following features are supported in a hardware- assisted ma

IPsec encryption requires every packet to undergo multiple rounds of cryptographic transformation - such as AES cipher rounds and HMAC integrity checks - adding processing latency that hardware acceleration reduces but cannot eliminate. For a 1000-phone VoIP deployment where end-to-end delay is a hard quality constraint, this per-packet cryptographic overhead is measurably larger than the simple header operations of GRE or MPLS encapsulation or the table-lookup cost of stateful firewall inspection. No other option in the list involves the same depth of per-packet computation.

A hardware-assisted stateful firewall performs fast connection-table lookups with minimal added latency, far less than the cryptographic rounds required by encryption.

MPLS encapsulation consists only of pushing or swapping a small label header, an operation hardware performs in negligible time with no meaningful delay impact.

GRE encapsulation prepends a fixed-size tunnel header to each packet, a simple operation that hardware executes with very low and predictable latency.