Connect a Cisco ATA to a NumberGroup SIP trunk
Put an existing analogue phone, fax machine or cordless base on a NumberGroup SIP trunk with a Cisco ATA 191 or ATA 192 (multiplatform firmware). Real Voice > Line config: sip.numbergroup.com Proxy, T-AAAAAA-NNN User ID and Auth ID, Use Auth ID, codecs, T.38 fax and the registration pitfalls.
A Cisco ATA 191 or ATA 192 (multiplatform firmware) lets you keep an existing analogue phone, fax machine or cordless baseand put it on a NumberGroup SIP trunk — the analogue device plugs into the PHONE port, the ATA registers to us over the internet. It's the standard way to carry an old analogue line across the PSTN / ISDN switch-off without replacing the handset. The ATA 191 has two FXS ports, the ATA 192 two plus a built-in router; each port is configured on its own Line tab.
For a desk phone or fax where a human reads the Caller ID, ask us to set Send Numbers As to "United Kingdom" so it lands in the familiar 01214001262 format.
Firmware note: this guide is for the multiplatform (MPP)firmware — the open-SIP build. If your ATA was shipped locked to Cisco Unified Communications Manager, it needs converting to MPP first (Cisco's admin guide covers the migration).
The credentials and settings your device needs to register against the NumberGroup SIP trunk are:
- Domain / registrar:
sip.numbergroup.com - Authorisation ID (also called SIP username): looks like
T-AAAAAA-NNNe.g.T-102377-001 - Password: a random string we generate per trunk
- User-Agent Type: we set this our side to match your device (e.g. 3CX Phonesystem, DDI in R-URI (Asterisk), RFC3261 Standard Trunk) so DDIs present in the format your equipment expects
- Send Numbers As: also set our side — pick the format that works best for your platform:
- International (+xx) — true E.164 (
+441214001262) for 3CX, Cisco, Yealink and most modern PBXs - International (xx) — bare digits (
441214001262) for Asterisk / FreeSWITCH dialplan regex - United Kingdom — UK format (
01214001262) for direct-register desk phones / softphones where humans read the Caller ID
- International (+xx) — true E.164 (
- Allowed IPs (optional): for an extra security layer we can lock the trunk to only register from your office IPs — tell us which when you ask
Once you have the credentials, the rest of this guide walks through the device-side config. If you'd rather skip the config altogether, ask us — we'll do it for you on most common PBXs and phones.
Field mapping
Browse to the ATA's web UI, open the Voice → Line 1 tab (and Line 2 for the second port), and work through the Proxy and Registration and Subscriber Informationsections. Cisco owns the click-path and keeps it current — the table is the part that's specific to your NumberGroup trunk.
Find the ATA's IP address (lift the attached phone and dial **** then 110# to hear it), browse to it from a computer on the same network, log in as admin, then open Voice → Line 1.
Full navigation is in the manufacturer's own guide: Cisco ATA 191/192 Administration Guide — Voice Settings (cisco.com). We keep the click-path with them so it stays current — the table below is the part that's specific to your NumberGroup trunk.
| NumberGroup value | Cisco ATA 191 / ATA 192 (multiplatform) field |
|---|---|
| sip.numbergroup.com | Proxy (Proxy and Registration) |
| UDP | SIP Transport (Proxy and Registration) |
| Yes | Register (Proxy and Registration) |
| T-AAAAAA-NNN | User ID (Subscriber Information) |
| Yes | Use Auth ID (Subscriber Information) |
| T-AAAAAA-NNN | Auth ID (Subscriber Information) |
| your trunk password | Password (Subscriber Information) |
| PCMU / PCMA | Preferred Codec (Audio Configuration) |
Split-field note: set Use Auth ID to Yes, then put your T-AAAAAA-NNN in both User ID and Auth ID. On a NumberGroup trunk they're always the same value. (Leave Use Outbound Proxy set to No.)
Verify
- On Voice → Information, the Line shows Registration State: Registered
- Lift the attached handset — you should hear dial tone
- Dial your mobile to confirm Caller ID; ring your DDI from a mobile to confirm inbound
- We can confirm the trunk has registered our side — ring us or check the trunk-live email
If it won't register
- Wrong User ID / Auth ID / Password — re-check against the trunk email (a stray trailing space in the password is a common culprit)
- Make sure Use Auth ID is set to Yes — leave it No and the ATA authenticates with the wrong identity
- Proxy must be
sip.numbergroup.comexactly - Outbound UDP 5060 blocked on your network firewall
- One-way audio: disable SIP ALG on the router
- Outbound rejected with 403: your Default CLI on the trunk isn't one of your DDIs — fix on the trunk
Sending faxes
For a fax machine, set the codec to PCMU/PCMA only and enable T.38 faxin the Line's audio settings. Fax over IP is sensitive to packet loss — for high fax volumes ask us about a dedicated fax option.
Set fraud caps before going live
A single analogue line should never place more than 1–2 simultaneous calls. Ask us to set Fraud Detection Simultaneous Calls to 2 and a sensible Daily Spend ceiling. See our telecom fraud guide.
Keep your analogue kit, lose the old line
Members move existing analogue phones, fax machines and cordless bases onto a NumberGroup SIP trunk via an ATA — we'll provision one you already own at no extra charge, or supply one at distributor cost.