Signaleers make high-speed dismounted extension switch work for infantry

by SFC Darrell Krumme

As the Army continues to deploy more and more automated systems to the tactical environment, the need for high-capacity data circuits continues to increase. In a light-infantry division, the commander requires both voice and data communications while keeping the size of the communications package as small as possible. The 25th Infantry Division (Light)’s solution was to increase the AN/TTC-51 dismounted extension switch’s capabilities by adding a high-capacity data network.

Standard DES

DES is a portable automatic communications-switching system. It provides automatic switching for up to 16 local subscribers, two commercial office-access circuits and 10 digital encrypted trunks. DES also provides operator position, combat-net radio and input/output computer interfaces. DES connects to the forced-entry switch (communications central) or other mobile-subscriber equipment parent nodes via line-of-sight radio links, or by direct cable to FES.

DES consists of:

One SB-4303, to provide subscriber, commercial and trunk interface;
One MD-1270 communications modem, to provide multiplexing of the 10 trunks and orderwire to one digital trunk group, and modulation to pulse-coded modulation to be transmitted and received via cable;
One KG-194A, to provide trunk encryption of DTG;
One KY-57, to provide encryption of orderwire communications;
MSE power supply, to convert alternating-current power to direct-current prime power for the KG-194A, KY-57 and MD-1270; and
Associated interface cables and transit case for transport.

DES is a small package-switching system that can be employed in most environments. DES is normally transported in a specially configured tactical vehicle and can easily be palletized for a deployment’s limited-space requirements.

DES interconnection diagram DES interconnection diagram.

Data in the field

Initial design criteria for DES never included the capability to extend the packet-switch network to the supported unit. Other MSE systems allowed users to send and receive data via the MSE network at low data rates. Small-extension-node subscribers were limited to throughputs of 16 kilobytes per second, and the large parent switch (node center, FES and large extension node) subscribers were limited to 64 kbs maximum throughput. When MSE was introduced, the use of computers in the field was limited to certain commands. Therefore, packet-switch equipment was excluded from the DES package.

However, the use of computers in the field for tactical operations has dramatically increased. Today we find users requiring higher rates of data throughput to effectively perform and accomplish their assigned missions. Graphical images and documents are required to keep key leaders informed of the battlefield’s situational aspects. These images and documents are extremely large in file size and would easily bog down the normal PSN. These trends required MSE units to redesign their network to accommodate the higher levels of data.

The "super SEN" was the first attempt to accommodate the subscribers’ requirement for more data capability. This modification increased PSN data rates of the SEN from 16 kbs to 64 kbs. However, complications occurred continually, causing loss of data capabilities.

Soldiers in 124th Signal Battalion at Fort Hood, Texas, then decided to employ another modification to increase a portion of the MSE network’s overall throughput. The 124th Signal Battalion successfully employed Cisco routers and high-speed-multiplexing circuit cards in NCs and small extension switches to provide data throughput within the network at a maximum rate of 256 kbs. The 125th Signal Battalion at Schofield Barracks, Hawaii – as well as other MSE units in the Army – mirrored these modifications to increase data throughput for their own MSE networks. Units with FESs adapted the technology to increase FES’s data throughput. DES never had data capabilities and was overlooked for its possibilities … until now.


The 125th Signal Battalion’s electronic-maintenance facility adapted the HSMUX technology to DES. For the first time, subscribers connected to DES may communicate via the MSE HSMUX network to other data users within the MSE network. Also, 125th Signal Battalion now can deploy a complete contingency package with voice and data communications anywhere in the world on short notice and with minimal number of vehicles.

DES with HSMUX DES with HSMUX additions.
Interface cable alteration diagram To adapt DES to mission requirements, the interface cable was altered (diagrammed left).
HSDES with Cisco router HSDES with Cisco 2514 router, top left of diagram.

We did this by adding another transit case to the DES package. The transit case houses a Cisco 2514 router and CHS-2 uninterrupted power supply. The only physical alteration to existing equipment was to the interface cable (SB-4304 to MD-1270). This modification called for removing the P3 connector (J5 on the CM, diagrammed in third diagram above) and replacing it with a new connector and more wiring to interface the Cisco router to the CM as well as to the switchboard. (If you have access to this restricted site, see the warfighter’s lessons-learned website for the cable pin-outs at under the lessons-learned for March.)

Also, a high-speed balanced-interface card was populated into the CM’s A4 slot, and the multiplexing/demultiplexing circuit-card assembly was replaced with a HSMUX CCA. The next step in this process was to install an internal cable from Port 1 on the HSMUX CCA to Port 3 on the HSBIC CCA. The byte CCA in the CM’s A12 slot must be set to seven. The final step is to close the CM and set the group-rate thumbwheel to six (for 512 kbs).

These modifications now make it possible for subscribers attached to DES to interface with any other data subscribers within the MSE network at a data rate of 256 kbs. (See the Warfighter Lessons Learned website for the cost breakdowns for the DES upgrade.) Also, these modifications make DES a total communications platform for almost any conceivable operation within the world. DES can be deployed with minimum additional equipment to provide voice and data access to most military switching networks.

SFC Krumme, a 15-year Army veteran, is 125th Signal Battalion’s electronic-maintenance section’s noncommissioned officer in charge. Krumme has served in a variety of duty positions in the electronic-maintenance field, including with 782d Maintenance Battalion, 82d Infantry Division (Airborne), 73d Signal Battalion, 327th Signal Battalion, 50th Signal Battalion, 304th Signal Battalion and 3d Group Special Forces’ General Support Company. He is working on his bachelor’s degree in information technologies/networks and telecommunications from the University of Phoenix. Krumme is scheduled for reassignment to 82d Infantry Division (Airborne) for another tour of duty.

Acronym QuickScan
CCA – circuit-card assembly
CM – communications modem
DES – dismounted extension switch
DTG – digital trunk group
FES – forced-entry switch
HSBIC – high-speed balanced-interface card
HSMUX – high-speed multiplexing
Kbs – kilobytes per second
MSE – mobile-subscriber equipment
NC – node center
PSN – packet-switch network
SEN – small extension node

dividing rule

Back issues on-line | "Most requested" articles | Article search | Subscriptions | Writer's guide

Army Communicator is part of Regimental Division, a division of Office Chief of Signal.

This is an offical U.S. Army Site |
This is an offical U.S. Army Site |