What this tells us about the Cisco lab's FAX strategy — fax-passthrough-config-from-cisco-lab

breadcrumb: What this tells us about the Cisco lab's FAX strategy
source: spa112/cisco-lab/fax-passthrough-config-from-cisco-lab.md
chunk_id: spa112::cisco-lab::fax-passthrough-config-from-cisco-lab::fax-passthrough-config-from-cisco-lab::What-this-tells-us-about-the-Cisco-lab-s-FAX-strategy::12

Cisco's lab uses G.711µ pass-through fax, not T.38:

FAX Enable T38: no (pass-through path active)
FAX Passthru Method: NSE (codec-switch signaled via Network Signal Events)
FAX Codec Symmetric: yes (both legs negotiate to G.711µ during fax)
Detection of fax tones via FAX V21 Detect: yes + FAX CNG Detect: yes

Pass-through (this config) vs. T.38 (alternative):

	G.711µ pass-through	T.38
Bandwidth	~87 kbps per fax (full G.711)	~14–28 kbps
Resilience to packet loss	Poor — page corruption, no retransmission	Good — protocol-level page retry
End-to-end requirement	All hops must support G.711 + NSE	All hops must support T.38
Carrier support	Universal	Spotty — verify with SparkLight
Hospital risk profile	Higher — silent partial-page corruption	Lower — corruption gets retried

Question to answer for Bingham: does SparkLight support T.38 end-to-end on the SIP trunk? If yes, T.38 is the better choice for HIPAA-relevant fax. If no, pass-through is the only option and the network path between SPA112 → CUBE → SparkLight needs careful QoS to keep page corruption rates acceptable.