SubscribeSecure Telephony Issues in the Tactical Communications Environment Today
In order to provide compatibility across the wide-range of government communication devices, offer toll quality secure voice, improve secure data rates, and enhance ease of use, the unifying Future Narrowband Digital Terminal (FNBDT) architecture was designed in 2002. These devices serve as telephone line adapters and provide toll quality secure voice, high data rates, and add Type-1 security to any standard commercial analog telephone or personal computer.
A key benefit of this new FNBDT technology is the wide range of interoperability between existing STE devices in the field and the newer FNBDT-based wireline and wireless GSM-type cell phones, thus providing a nice migration path for users moving towards the Network Centric vision
Lack of Adequate Bandwidth
In a tactical environment bandwidth is scarce and the extensive use of secure voice communications along with the growing amount of secure data and video traffic presents unique challenges.
At the access points in the network, tactical users typically experience a concept that commercial world users often call the "last mile" bottleneck. There is plenty of bandwidth at the core of the network (GIG-BE), and usually a sufficient amount of bandwidth at the edge of the network (STEP), however the bandwidth available for this last mile can vary anywhere from 64Kbps on a Navy small ship to possibly 2 Mbps for a ground battalion.
In the normal clear voice communications environment, PSTN type phone lines support 30 - 4000Hz analog signals that can be represented in a 64 Kbps digital stream (Figure 1). In order to preserve the limited available bandwidth, these clear voice calls are compressed to either 16 Kbps or 32 Kbps. Devices like STU-III, STE, and FNBDT rely on the availability of this spectrum of bandwidth when making a call secure as the call is switched over a modem when in secure mode.
Secure telephones code the analog voice into a pulse code modulation (PCM) digital format and advanced encryption techniques are implemented in the telephone. The benefit of this approach is the network does not need to have any knowledge of the encryption techniques, and only sees the call as a modem call carrying data.
The drawback is that tactical networks often deploy speech compression that will degrade or disrupt modem performance. Thus, planners of secure voice networks must choose between foregoing the use of voice processing equipment and restricting the number of simultaneous secure voice calls or implementing more sophisticated voice processing equipment that will permit secure voice transmission with greatly reduced bandwidth requirements.
Figure 1 - Bandwidth Utilization of Analog Transmission
The inadequate availability of network bandwidth in the tactical environment and the rising volume of new, IP-based applications will require special steps be taken by network planners to reduce the bandwidth requirement for voice networks across a transport network that is sharing data traffic.
The final challenge for tactical users is combining all of this voice, data, and even video traffic on the narrow pipes and trying to maintain an adequate level of service for all traffic types. Today this traffic is managed efficiently using TDM designed voice compressions schemes and point-to-point, dedicated TDM-based circuits. Maintaining this same level of service for multiple traffic types on the newer IP-based networking environment that is using connectionless technology will be a great challenge in tactical networks.
Support for Backward Compatibility and Future Growth
Backward compatibility is a large issue for tactical users as they are often forced to make use of a combination of older, legacy devices and newer devices within their tactical environment. The STU-III was released in late 1987, and is no longer manufactured. Users purchase the newer STE, which was designed in the late 1990's; however many tactical users have been forced to fall back to earlier software versions on the STE to help insure the maximum performance possible for secure calls in a tactical environment. Users are therefore not able take advantage of newer STE features such as forward connectivity to wide variety of wireline and wireless FNBDT devices.
As DoD users continue forward with the transition to the Network Centric Warfare vision, it will be critical for tactical end users be able to maximize investments made on communication networking and secure phone platforms. All types of equipment will have to be both backward compatible with the legacy equipment used in the field and easily incorporate new features and functions through remote software upgrades rather than being forced to forklift hardware upgrades or replacements.
Logistical Considerations
With the older STU-III and STE devices, users had to physically carry around keys or cards that allowed them access to the secure functionality of the device. This causes logistical strain as network operators are required to keep track of the keys. In addition, rekeying is a standard procedure for updating the keys used to access the secure capabilities of the secure unit. This, too, adds to the logistical requirements of supporting the rekeying effort for all keys used in that environment.
TDM-based communications equipment and the older secure phone devices are bulky and heavy, making it hard to pack up and move around easily. This creates a challenge for packaging into transit cases, storage, and transport.
Achieving Efficient Secure Telephony
All DoD networks must continue support for secure communications from the warfighter at the tactical level up to the GIG-BE backbone. There are specific steps that can be taken to help overcome their limitations and insure operational success. While this document will present these steps in a logical order, it is imperative that tactical network managers implement all of these steps to insure an optimum communications environment.
Maximize Use of Limited Bandwidth
The first component for improved performance across the tactical network is implementation of the newer FNBDT devices with their modern vocoders. They will provide superior voice quality across low bandwidth connections such as 2.4 Kbps and higher data rates such as V.90 (56 Kbps), which will insure the tactical user receives optimum performance from their secure voice devices in their narrowband environment.
The deployment of networking equipment that will assure an efficient modem call between secure devices, with far less than the typical 64 Kbps connection requirements, is critical. This equipment should provide to accommodate a low bit-rate voice compression algorithm for handling modem calls across a network (Figure 2). Migrating from TDM-based technology to cell/packet-based systems that dynamically allocate bandwidth to network applications will provide tactical end users the Quality of Service (QoS) needed in the trenches to support decisions based on real-time data - whether that be a video, a satellite image, or a secure telephone call.
Figure 2 - Secure Bypass or Call Relay
Modem bypass handles the modem call by either relaxing or disabling the voice compression algorithm while the call is in secure mode. Although this feature will allow the signal to pass and maintains interoperability, it requires true dynamic bandwidth to overcome this inefficiency (Figure 3). Secure Call Relay involves demodulation/ modulation technology of secure calls across a network.
In this solution, the analog modem signal will be demodulated at the network ingress side, with the recovered digital data transferred through the network. By using this demodulation technique, secure calls will consume only 14.4, 9.6, 4.8, or 2.4 Kbps of bandwidth when crossing the network (Figure 4). The data is modulated to its original form at the remote network egress side. By utilizing this Secure Call Relay technology the bandwidth savings could potentially allow as many as eleven 2.4 Kbps secure voice connections across a single 64 Kbps network connection.
Figure 3 - Bandwidth Utilization using Modem Bypass
Figure 4 - Bandwidth Utilization using Modem Relay
Deploy Platforms that Support Backward Compatibility and Future Growth
The first component of this step involves deployment of FNBDT secure phone devices in the tactical environment. This will provide compatibility for Joint and Coalition forces during secure communications. Figure 5 shows the wide range of interoperability an FNBDT device has with other types of secure phone devices. FNBDT users will now be able to take advantage of the latest FNBDT wired and wireless devices and the increased functionality and performance each new release brings.
Deployment of networking equipment that provides the flexibility to support older legacy devices, yet also accommodates new features and functions by simple software upgrades is necessary. This networking equipment should also provide interconnectivity for older serial stream traffic, satellite modems and older cryptographic equipment, as well as forward-looking flexibility to accommodate the increasing amount of new traffic like, IP-based voice or video, with guaranteed levels of service. Using these features of communications equipment, tactical users can be guaranteed of a smooth migration path towards the desired IP-based networks without having to incur significant overhaul costs.
Figure 5 - FNBDT Interoperability
Simplify Logistical Requirements
Rather than handling older physical secure keys or forcing users of some types of secure phone devices to physically move the secure phone device to another line for rekeying, the FNBDT secure phones provide embedded Type I cryptography with a secure access control system that includes controlled access to the units' secure functions and flexible key management. Both the secure phone device being used and the networking equipment deployed should support Over-the-Air Rekeying (OTA), which would greatly reduce the amount of logistical support required.
Today's deployed networking equipment comes in a space efficient form factor, is light in weight, provides easy setup, allowing flexible configuration options that support mobile deployments and greater equipment densities. The newer FNBDT devices fit nicely into the tactical environment with greater portability through their smaller size and lighter weight. Finally, new communications equipment and secure phone devices should provide easy methods for field upgradeability via remote software downloads. Tactical equipment that meets all of these requirements will help to reduce the amount of logistics required with the transport, sparing, and storage of existing equipment extensively.
Summary
As new technology is assimilated into the DoD network, access technologies at the tactical level will improve over time by offering increased bandwidth resources. However, during the interim period, tactical network planners and managers will need to provide solutions that will optimize bandwidth bottlenecks, allow the mix of legacy and new technology, while still providing the highest levels of quality possible for secure communications.
