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fax-passthrough-config-from-cisco-lab

15 chunks · spa112 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