Cisco Signaling Controllers

Cisco Digital IP Telephony Gateway: DT-24+


Data Sheet

Cisco Digital IP Telephony Gateway: DT-24+

The Cisco DT-24+ digital gateway provides a connection path between the Cisco AVVID (Architecture for Voice, Video and Integrated Data) packet telephony network and the Public Switched Telephone Network (PSTN) or a PBX using digital (PRI ISDN) trunks. The DT-24+ supports 23 voice channels on a T1 interface. Gateways are managed, controlled, and administered through the required Cisco CallManager. The DT-24+ gateway consists of a single PCI bus-based card and mounts in any PCI bus PC (where it only draws power).

The digital gateways include the following features:

  • A single PCI-based card (PCI bus for power only) with the following components on board:

    • Integrated digital signal processors (DSPs)

    • T1 (RJ-48C female) interface

    • 10Base-T Ethernet network interface (RJ-45 female)

    • Control processor with communications software to connect to the Cisco CallManager (required) over TCP/IP/Ethernet link

    • Remote boot procedure with DHCP (for IP address) and TFTP software download (downloadable and upgradable)

  • T1 PRI ISDN Layer 3 protocols, including National ISDN-2 (NI-2), 5 Electronic Switching System (5ESS), 5ESS custom, DMS100, DMS250, and other protocol support

  • Both user-side and network-side ISDN signaling support to emulate either terminal equipment or switching equipment, respectively

  • Supports Skinny Gateway protocol communications with Cisco CallManager to provide supplementary services (hold, transfer, etc.) under control of IP telephone clients

Cisco DT-24+ Product Description

The Cisco access model DT-24+ (T1) allows customers to connect the Cisco AVVID packet telephony network to the PSTN or to a PBX. The physical circuit-switched interface is a single female RJ-48C interface. The circuit-switched signaling interface is T1 PRI ISDN. The DT-24+ gateway supports up to 23 simultaneous channels of voice over IP (VoIP) packet to circuit-switched adaption, G.711 encoding (A-law or m-law), dual tone multifrequency (DTMF) detection/generation, signaling, and line echo cancellation. A full 23 simultaneous channels of G.723.1 encode/decode are also supported.

The DT-24+ has been successfully connected to a wide variety of PBXs including:

  • Nortel Meridian (all options)

  • Lucent Definity (all G3 options)

  • Ericsson MD110

  • Siemens HiCom

  • Rolm 9XXX

  • Intecom E

  • InterTel (using T1 PRI)

  • Matra 6500

  • Many others

The DT-24+ has also been connected to many public switches including:

  • Lucent 4ESS and 5ESS

  • Nortel SL1, SL100, DMS-100, and DMS-250

  • DSC (Digital Switch DSC600E using T1 PRI)

Cisco DT-24+ Application Description

The Cisco AVVID telephony solution provides a full-featured telephony system running on an IP network. Various IP telephony devices including phones and gateways communicate seamlessly over IP infrastructures under the control of one or more Cisco CallManagers. This solution rewards users with greatly reduced cost of ownership and new IP-based feature capabilities. The DT-24+ digital gateways provide the ability to make and receive calls outside the IP network. These gateways provide the interface to the PSTN or existing PBX systems via ISDN PRI interfaces. They differ from the analog gateway products in that they support digital ISDN features including direct inward dial (DID, often called DDI) and caller ID. These features allow outside callers to dial directly to a particular user without going through an attendant (operator). In addition, digital interfaces usually provide a more economical interface choice when the number of trunks exceeds six to eight channels.

When deployed in a network, the DT-24+ Digital Gateways can be located in any convenient PCI bus-based PC. They simply draw power from the host PC and are completely managed via browser access through the Cisco CallManager. Because they only draw power, they do not affect the performance or operation of the host PC, nor do they require any special software or drivers. They may even be installed in the Cisco CallManager itself.

When more than one DT-24+ gateway is needed, it can be treated as a separate gateway or aggregated together with others as a common pool of channels. Any number of digital gateways can be installed in a network, and the number installed in a PC is only limited by the number of available slots.

The DT-24+ communicates with the Cisco CallManager, which allows the implementation of supplementary services such as hold, transfer, and forward on outside calls. Also, with proxy signaling provided by the Cisco CallManager, the DT-24+ is fully H.323 V.2 compatible.


  • Simple PCI bus installation

    • Installs in any PCI bus-based PC. The card only draws power, so no drivers or software need to be installed

    • Does not interfere with the performance or operation of the host PC

    • Can be mounted in the Cisco CallManager PC or any other convenient PC

    • For high-density applications, simply install more cards in the same PC up to the max number of slots

  • PRI ISDN (T1 rate) trunk interface through female RJ-48C interface

    • Both user-side and network-side Q.931 signaling (software selectable)

    • Support for National ISDN-II (NI-2), DMS, and 5ESS variants

  • Adds convenient call features to the IP telephony system

    • Caller ID (name and number, inbound and outbound)

    • Direct inward dialing

    • Supplementary services for outside calls (hold, transfer, forward, conference) under control of the Cisco CallManager

    • Per port management and backhaul of the signaling channel to the Cisco CallManager for complete control

    • Follows Cisco CallManager failover scenario—when Cisco CallManager switches to backup, the card registers with the new Cisco CallManager

  • Standard management features

    • Completely manageable from the browser-based Cisco CallManager

    • Ethernet device status LEDs (Ethernet link, Ethernet transmit/receive)

    • Trunk status LEDs

  • Network/application aware

    • H.323 compatible when used with Cisco CallManager

    • DHCP client—for IP address acquisition

    • Locates Cisco CallManager via DHCP or DNS

    • Automatic TFTP software and configuration download upon boot up if necessary

    • Automatic registration with Cisco CallManager

  • Framing format: D4 Superframe (SF) and Extended Superframe (ESF)

  • Input level: +1 dBo to -24 dBmo

  • Output level: 0, -7.5, or -15 dB

  • Diagnostic loopback support

Physical Specifications

  • Dimensions (H x W): 4.125 x 12.25 in. (10.48 x 31.12 cm)

  • Power: 1A from 5V PCI bus, (0A from 3.3V bus), for approximately 5W power

Environmental Conditions

  • Operating temperature: 32 to 104° F (0 to 40° C)

  • Storage temperature: -40 to 167° F (-40 to 75° C)

  • Relative humidity: 10 to 90 percent, noncondensing

  • Operating altitude: -60 to 4000m

  • Mean Time Between Failure (MTBF): seven years for system configuration


  • Simultaneous, 23-channel operation of the following functions

    • Circuit-switched to packet adaption

    • G.711 mu-law to A-law translation

    • G.711 A-law to mu-law translation

    • G.711 (A-law or mu-law) to G.723.1 transcoding

    • Line echo cancellation

    • DTMF detection and out-of-band signaling translation towards packet side

  • Out-of-band signaling conversion and DTMF generation towards circuit-switched side

  • Built-in CSU supports connections up to 100 feet from demarcation point.


  • T1—FCC Part 68 (CFR47), CS03, JATE Green Book E1—CTR13, TS016


  • UL1950, CSA C22.2 No. 950


  • FCC Part 15 (CFR47) Class A

  • VCCI Class A with UTP, B with FTP


The Cisco access model DT-24+ is certified (safety, emissions, and telco) for operation in the United States and Canada. Where safety, emissions, and telco certifications are held, the device can be directly connected to the PSTN (through an appropriate CSU device). Where only emissions and safety certifications are held, the device may not be connected to the PSTN, but can be connected to a customer premise-based PBX. Country specific certifications are continuing. For up-to-date, country-specific certification information, refer to the homologation/certification document (separately maintained on the Cisco Web site).

Ordering Information

Model Number

Cisco DT-24+

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