GDC DataComm VF 28.8/33.6 modem 

General DataComm Lease Line (2/4 wire) and Dial - Synchronous and Asynchronous

High Speed V.34 Data Modem


Technically Advanced The DataComm VF 28.8 / 33.6 is an excellent choice for central office locations requiring high speed, dial-up access to off-premise LANs, particularly in Windows and Graphical User Interface (GUI) environments. The VF 28.8/33.6 modems transmit synchronous and asynchronous data at speeds up to 33.6 Kbps, including dial-up and leased line connectivity with automatic dial backup, as well as dial only modems. With advanced compression techniques, the DataComm V F 28.8 / 33.6 can achieve an effective throughput of up to 64 Kbps in synchronous and 128 Kbps in asynchronous applications. Using V34 modulation along with powerful V 42/V 42 his error correction and compression features ensures superior error-free performance.

Effortless Upgrades The DataComm VF 28.8 / 33.6 incorporates a powerful technological platform that is completely defined by Flash Memory. As your future needs and technological developments dictate, software upgrades to add new features and capabilities may be done in­ place.

Superior Performance The DataComm V F 28.8 / 33.6 provides V34 and supports slower standard speeds through General Data Comm's powerful Digital Signal Processor (DSP) based platform, including custom VLSI. Using Auto-Rate Renegotiation, the V F Series dynamically adjusts operating rates to compensate for switched network line impairments. The V F Series provides superior performance, even over public network circuits that may vary in quality. This means the public network can be utilized to support high speed applications like remote LAN access, which in the past would have required dedicated links (and therefore may not have been economically feasible).

Flexible Packaging Design The DataComm V F 28.8 / 33.6 follows GDC's extremely flexible DataCommonality packaging design. It is available in high density rackmount units - up to 16 can be installed in a 19 inch or 23 inch shelf - or in an attractive, desktop enclosure.

The DataComm V F 28.8 / 33.6 also supports network monitoring through a full LED array, 4­character Electronic Display Window (EDW), and front-panel pushbutton controls for modem option selection and other menu choices.

All models offer V35 and EIA/TIA-530A interfaces, eliminating the need for external interface converters in migrating to high speed data applications.

Powerful Diagnostics A comprehensive array of diagnostic tests provides accurate detection of system faults and allows service to be restored quickly. these include ANALOOP® (Analog Loopback/V54 Loop3), DATALOOP® (Digital Loopback V54 Loop2), Remote Digital Loopback (V54 Remote Loop2), and Self-Test. All tests can be initiated with front panel switches and monitored through easy-to-read LED displays. AN ALOOP and RDL may also be initiated through the terminal equipment (DTE) interface under the control of communications software.

Security GDC's Steadfast Security' protects critical financial, governmental, or company­ sensitive applications via a password embedded within the handshake sequence and mandatory callback feature.

Setting The Standard The DataComm VF 28.8 / 33.6 sets the standard for quality design that meets current and future communications requirements. All VF Series Modems support V34, V32 bis, V32, V22 bis, V22, V21, Bell 212A and Bell 103, providing for maximum connectivity and operational flexibility.



Data Modes 
33.6 Kbps
V32 bis - 1.4.4 Kbps
V32 -9.6 Kbps
V22 bis - 2.4 Kbps
V22 - 1.2 Kbps
Bell 212A- 1.2 Kbps
Bell 103 -300 bps
Factory option available for 
"POS" Point of Sale handshake


Automatic, adaptive

Operating Format:

Synchronous and Asynchronous

Operating Mode:

Two-wire dial-up (PSTN) or two-wire/four-wire PL (ADR in V34, V32 bis and V32) 

Async Character  Codes:

8, 9, 10 or 11-bit characters, V14 compliant

Carrier Detect Acquisition:

Assured with a receive level at or above -43 dBm*  Leased line level: -33 dBm * 2-wire

Carrier Detect Release: 

Assured with a receive level at or below -48 dBm*

Leased line level:

-38 dBm* 2-wire

Error Correction:

CCITT V42 and MNP4

Data Compression:

CCITT V42 bis and MNP5 giving a throughput of 128 Kbps asynchronous and 64 Kbps in synchronous mode

Config. & Control  Protocols:

Extended "AT" command set, V25 bis, front panel switches


Online password, dial back -fixed and roving, proprietary SteadFastTM Security with embedded password for synchronous and asynchronous operations, mandatory callback feature

Flow Control: 

In-band XON/XOFF or external EIA-232 signaling using CTS or RTS/CTS control lines

LED Indicators:

Clear to Send, Transmit Data, Receive Data, Off Hook, Power On Indicator, Request to Send, Signal Quality, Test Mode Indicator

Call Monitoring:

"AT", V25 bis

Line Interface:

RJ45 Switched Network, RJl1 Phone, RJ45 Private Line

Output Level:

Permissive (-9 dBm*) or Adjustable (0 to -15 dBm in Private Line)

Digital Interface            Standard:

EIA/TIA-232-E/CCITT V.24/V.28/ISO 2110


CCITT V35, V36 compatible; EIA/TIA-530-A/V.24/V. 10/V.1 UISO 2110 AMD1 RTS/CTS Delay:            "AT": 10 to 250 ms, in 10 ms steps; V13 compliant

Test Modes:

V.54-compliant test modes for Analog Loop, Digital Loop, Remote Digital Loop and Self Test

Physical Characteristics



 Card Size


 267 mm (10.5")

99 mm (3.9")

 254 mm (10")


 483 mm (19.0")

277 mm (10.9")

22.86 mm (.9")


 343 mm (13.5")

318 mm (12.5") 

292.1 mm (11.5")


 18.3 kg (40.25 lbs.)

3.22 kg (7.1 lbs.)

Shipping Weight:

19.1 kg (42 lbs.)

 3.6 kg (8.1 lbs.)

Operating Temperature:

0° to 50°C (32° to 122°F)


Up to 95% (non-condensing)

Interference Protection: 

Verified to comply with FCC Part 15, Subpart J (Class A requirements) and Part 68

Power Consumption:

7 card-edge watts DC maximum

Safety Protection:

UL listed and CSA approved; complies with UL 1459 and 1012°

Related pages

301-924-7400 EXT 25

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