spa112/cisco-lab/fax-passthrough-config-from-cisco-lab

Source screenshots

Field group	Source image
Line 1 general / NAT / Network / SIP / Call Feature / Proxy	`images/79511-spa112withCucm_04052013_page_15_img_2.png`
Subscriber / Supplementary Services / Audio Configuration	`images/79511-spa112withCucm_04052013_page_16_img_2.png`

Line 1 — top of page (page 15 screenshot) › Streaming Audio Server (SAS)

Field	Lab value
SAS Enable	no
SAS DLG Refresh Intvl	30
SAS Inbound RTP Sink	(blank)

Line 1 — top of page (page 15 screenshot) › NAT Settings

Field	Lab value
NAT Mapping Enable	no
NAT Keep Alive Enable	no
NAT Keep Alive Msg	`$NOTIFY`
NAT Keep Alive Dest	`$PROXY`

Line 1 — top of page (page 15 screenshot) › Network Settings

Field	Lab value
SIP ToS/DiffServ Value	`0x68`
SIP CoS Value	`3` (range 0–7)
RTP ToS/DiffServ Value	`0xb8`
RTP CoS Value	`6` (range 0–7)
Network Jitter Level	high
Jitter Buffer Adjustment	(blank)

Line 1 — top of page (page 15 screenshot) › SIP Settings

Field	Lab value	Note
SIP Transport	TCP	⭐ Critical — CUCM expects TCP; SPA112 default is UDP
SIP Port	5060
SIP 100REL Enable	no
EXT SIP Port	(blank)
Auth Resync-Reboot	yes
SIP Proxy-Require	(blank)
SIP Remote-Party-ID	yes
SIP GUID	no
SIP Debug Option	none
RTP Log Intvl	0
Restrict Source IP	no
Referor Bye Delay	4
Refer Target Bye Delay	0
Referee Bye Delay	0
Refer-To Target Contact	no
Sticky 183	no
Auth INVITE	no
Reply 182 On Call Waiting	no
Use Anonymous With RPID	yes
Use Local Addr In FROM	no

Line 1 — top of page (page 15 screenshot) › Call Feature Settings

Field	Lab value
Blind Attn-Xfer Enable	no
Xfer When Hangup Conf	yes
Conference Bridge URL	(blank)
Conference Bridge Ports	3
MOH Server	(blank)
Enable IP Dialing	no
Emergency Number	(blank)
Mailbox ID	(blank)

Line 1 — top of page (page 15 screenshot) › Proxy and Registration

Field	Lab value	Note
Proxy	`10.99.31.140`	⭐ Lab CUCM IP — Bingham would point at `cucm-pub.binghammemorial.org` (or its IP)
Outbound Proxy	(blank)
Use Outbound Proxy	no
Use OB Proxy In Dialog	yes
Register	yes
Make Call Without Reg	no
Register Expires	3600
Ans Call Without Reg	no

Line 1 — bottom of page (page 16 screenshot) › Proxy and Registration (continued)

Field	Lab value
Use DNS SRV	no
DNS SRV Auto Prefix	(unclear in screenshot)
Proxy Fallback Intvl	3600
Proxy Redundancy Method	Normal
Mailbox Subscribe URL	(blank)
Mailbox Subscribe Expires	2147483647

Line 1 — bottom of page (page 16 screenshot) › Subscriber Information

Field	Lab value	Note
Display Name	(blank)
User ID	`1022`	⭐ Matches the CUCM End User created earlier
Password	(masked — set to `1234` in lab)
Auth ID	`1022`
Use Auth ID	yes
Resident Online Number	(blank)
SIP URI	(blank)

Line 1 — bottom of page (page 16 screenshot) › Supplementary Service Subscription

All approximately 25 service-subscription checkboxes are set to yes in the lab config. Notable: Call Waiting Serv, Block CID Serv, Cfwd All/Busy/No Ans/Sel/Last Serv, Block/Accept Last Serv, DND Serv, Call Return/Redial Serv, Three Way Conf/Call Serv, Unattn/Attn Transfer Serv, VMWI/MWI Serv, Secure Call Serv, Referral Serv, Service Announcement Serv. (For a hospital fax-only ATA, most of these are irrelevant — fax doesn't need transfers, conferencing, or MWI.)

Line 1 — bottom of page (page 16 screenshot) › Audio Configuration ⭐ The HIPAA-relevant section

Field	Lab value	Note
Preferred Codec	G711u	μ-law — required for fax pass-through
Second Preferred Codec	Unspecified
Third Preferred Codec	Unspecified
Use Pref Codec Only	no
Use Remote Pref Codec	no
Codec Negotiation	Default
G729a Enable	yes	(Should be no for fax-only — G.729 mangles fax tones)
Silence Suppression Enable	no	⭐ Correct for fax — suppression breaks T.30 handshake
G726-32 Enable	yes
Echo Canc Enable	yes
FAX V21 Detect Enable	yes	Detects V.21 fax handshake tones
FAX CNG Detect Enable	yes	Detects "calling fax" tone
FAX Codec Symmetric	yes	Both legs use the same codec during fax
FAX Passthru Codec	G711u	μ-law pass-through path
FAX Passthru Method	NSE	Network Signal Event triggers codec switch
DTMF Process INFO	yes
DTMF Process AVT	yes

Line 1 — bottom of page (page 16 screenshot) › Audio Configuration — fields cropped from the lab screenshots

The Cisco PDF's screenshots end at DTMF Process AVT. The PDF's prose narrative does not enumerate the remaining FAX fields explicitly, but based on standard SPA112 firmware 1.3.1(003) defaults plus the prose-confirmed pass-through stance (FAX Enable T38: no), the remaining FAX fields would be:

Field	Standard pass-through default	Confidence
FAX Process NSE	yes	implied by `FAX Passthru Method: NSE`
FAX Disable ECAN	no	SPA112 firmware default
FAX Enable T38	no	confirmed in PDF prose — pass-through, not T.38
FAX T38 ECM Enable	yes	irrelevant when T.38 disabled
FAX Tone Detect Mode	caller or callee	SPA112 firmware default
FAX T38 Return to Voice	no	irrelevant when T.38 disabled

To verify any of the above against a real SPA112: log into the device's web UI as admin → Voice tab → Line 1 tab → scroll to Audio Configuration. Required as part of any Bingham fleet inventory exercise.

What this tells us about the Cisco lab's FAX strategy

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.

Open questions for Bingham fleet inventory

When capturing the actual SPA112 fleet:

[ ] SIP Transport: TCP confirmed on every device?
[ ] Proxy: pointing at the correct CUCM (PUB) IP / hostname?
[ ] Audio → Preferred Codec: G711u? (anything else breaks fax)
[ ] Audio → G729a Enable: should be no for fax-dedicated lines
[ ] Audio → Silence Suppression Enable: should be no (must be off for fax)
[ ] Audio → FAX Enable T38: what is it set to? (this is the strategic question)
[ ] Are all FXS ports terminating into fax machines / copiers, or any analog phones mixed in?
[ ] Firmware version on each device — anything older than 1.3.x is overdue for upgrade

Once captured, this data lives in the Bingham SPA112 fleet inventory page (separate doc, not in this asset bundle).

Change Log

Date	Note
2026-04-25	Manual transcription of pages 15–16 screenshots after `pdf_to_markdown` left them as image references. Six trailing FAX fields not visible in the available screenshots — listed with standard-default values and confidence levels