Grandstream GXW4504 E1/T1/J1 Digital VoIP Gateway

The Grandstream GXW4504 is the largest of the GXW4500 digital gateways: four software-configurable E1/T1/J1 spans, converting up to 120 concurrent calls between digital ISDN trunks and SIP.

This is bridge equipment for a migration in progress — the same job as the single-span GXW4501, at campus scale. A large legacy PBX with multiple ISDN30 circuits plugs its spans into one side; SIP comes out the other. The two systems carry each other's calls while the migration finishes on your schedule rather than a cutover weekend.

Four spans is the size for head offices, hospitals, campuses and call centres — anywhere that ran more than one E1. It also speaks SS7 and MFC R2 alongside PRI, which matters to carriers and to equipment older than ISDN etiquette; the smaller sites that only ever had PRI rarely need that.

Key features

• 4 × E1/T1/J1 spans, software configurable — no hardware change between standards
• Up to 120 concurrent calls — four full E1s' worth of channels
• PRI, SS7 and MFC R2 signalling — beyond PRI where the old equipment demands it
• Digital-to-SIP in both directions — old PBX to new trunks, or new platform to old PBX
• Dual Gigabit ports with integrated NAT router — sits inline where needed
• Wide codec support — Opus, G.722, G.711, G.729, G.723, iLBC, G.726, GSM-FR
• T.38 fax relay — fax survives the crossing
• TLS and SRTP — the SIP side is encrypted even though the ISDN side never was
• Remote provisioning and management — administered without a site visit

Works with

• Grandstream GXW4501 — one span, 30 calls
• Grandstream GXW4502 — two spans, 60 calls
• Grandstream UCM6308 — a SIP platform sized for the same building
• Grandstream GXW4248 V2 — the analogue equivalent at scale, for FXS rather than ISDN
• All Grandstream gateways

Frequently asked questions

Which direction does it convert?

Both. It presents SIP to the IP side and E1/T1/J1 to the digital side, so it serves an old PBX using new SIP trunks just as well as a new platform reaching an old PBX.

How do I know I need four spans?

Count the circuits, not the sites. Each E1 is 30 channels — if the old PBX terminates three or four ISDN30s, this is the unit. One circuit, the GXW4501; two, the GXW4502. Spans you do not connect are simply spare capacity.

E1, T1 or J1 — which do I have?

In the UK, E1 — 30 channels per span, which is where the 120-call figure comes from. The spans are software configurable, so the same box covers all three standards.

What are SS7 and MFC R2 for?

Carrier-grade and legacy international signalling. Most UK business PBXs use PRI and can ignore this; it matters for interconnects and for older switches that predate PRI. If you are not sure, you almost certainly use PRI.

Is this a long-term or interim purchase?

Usually interim — it decouples the PBX replacement from the trunk migration so neither forces the other's timetable. Interim in telecoms often means years, and the box is built accordingly.

Does it work with non-Grandstream PBXs?

Yes — both sides are standards-based. The digital side speaks E1/T1/J1 signalling and the IP side speaks SIP, so the vendor on either end is not a constraint in most installs. Tell us what you have and we will confirm.

Migrating a multi-span site? Call 0333 242 1314 or email sales@clisecure.com and we will map the migration so nothing gets cut off before its replacement works.