In-theater connectivity - Flexibility is the key to matching local infrastructure

Story

September 14, 2010

Ian Colville

Aculab

Telecommunications infrastructure and connectivity underpin the effectiveness of military forces in the field. With multi-national force collaboration in theaters near and far becoming more common, the ability to quickly and easily interconnect communications equipment becomes a priority. The flexibility of DSP-based media gateways enables translation of disparate protocols and physical connections in the field through in-situ configuration and programming.

Whether in a rapid deployment scenario or a long-term, semi-permanent installation, military forces must have the ability to connect to diverse network types to facilitate operations. Telecommunications standards, networking protocols, and physical communications links have evolved over the past 75 years at different rates and in different dimensions across the world. In today’s world, a deployed military force must have the flexibility to connect to local military, law enforcement, government, and public communications infrastructures to ensure secure and reliable communications in-theater. Through the programmability of Digital Signal Processor (DSP)-based media gateways, military forces can quickly establish communications links with local infrastructure and other military branches (Figure 1).

Figure 1: DSP-based media gateways can join many disparate military and local-infrastructure networks in-theater.

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Communications – the third C in C4I

It is a well-established procedure for military units to deploy with self-contained communications network infrastructures. These highly sophisticated and secure communications networks underpin strategic and tactical communications, both in the field and upstream. The UK’s Skynet 5 is a current example of deployable nodes homed on a satellite network. This type of network provides a communications umbrella for transporting information from front-line locations to a rear command center. It should, therefore, be obvious that with a variety of military units from different countries deployed in various combat zones, the communications equipment will not always be directly compatible. To solve that problem, there is a need to translate signaling and data between these systems.

In the telecommunications world, the devices that carry out this type of interconnection are known as media gateways. And as a force arrives at a site, there are many logistical concerns that require reliable communications beyond the secure strategic network. Gateways become as important outside the core military communications network as they are within.

The basic problem that a media gateway is trying to solve is marrying together the disparity inherent in different telecommunications networks, whether they are based on PSTN/TDM technology or IP networks based on the SIP protocol. The key function of media gateways is protocol conversion of the telecommunications signaling (see Sidebar 1), which is used to set up and tear down a voice call and transcoding of the actual voice data (what the caller hears) between the data types the different networks are capable of carrying. Session Initiation Protocol (SIP) is the predominant protocol used for setting up and tearing down media sessions for voice calls in an IP network. The legacy Public Switched Telephone Network (PSTN) has relied on Time Division Multiplexing (TDM) encoding to transport voice and signaling for many years. Simply put, IP and TDM are incompatible at the physical and transport layers. SIP is the primary IP voice protocol, and there are numerous TDM voice protocols.

Sidebar 1: DSP-based media gateways’ protocol support is a complex process, often because of differing multinational protocols.

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The media gateway’s processing engine is based on DSPs, which perform algorithmic functions such as digitally encoding and decoding audio signals. DSP functions are firmware controlled, based on the specific application, and the firmware can be dynamically changed based on application needs. In the gateway, this dynamic configuration lends itself to managing the protocol and media stream conversion on a per-call basis.

In today’s world, those in command of military forces must have reliable connectivity with local military, law enforcement, emergency services providers, and friendly government officials. DSP media gateways reduce the burden on the strategic network and enable a level of separation between the secure communications network and networks not fully under the control of the military.

Flexibility – one conversation, many languages

Depending on the level of development and locale, in-theater telecommunications networks may employ a variety of commercial network protocols including Signaling System #7 (SS7), Session Initiation Protocol (SIP), Channel Associated Signaling (CAS), Integrated Services Digital Network (ISDN), Digital Private Network Signaling System (DPNSS), and others. While performing similar functions, each protocol is a uniquely separate language. Gateways are regularly employed in commercial telecommunications to translate the signaling between these different protocols.

With each of these protocols, another layer of complexity arrives in the physical layer connection. Two basic digital trunk standards are known as E1 (2,048 Mbps European standard) and T1 (1,544 Mbps North American standard.) This is the crux of the situation in which multi-national forces find themselves. U.S. troops will have equipment based on the T1 standard, and British and European troops will have equipment based on the E1 standard. When both are deployed in the same theater, a gateway is required for inter-unit communication because they are not directly compatible. This can be further compounded by the local infrastructure, which could be based on either of the standards.

To be effective, a gateway must have the flexibility to terminate both T1 and E1 connections and to communicate with multiple systems operating with different protocols and encoding methods. The real key to DSP-based gateway success lies in the efficiency with which the gateway transcodes between encoding schemes and translates between different protocols and physical connections.

Secure interconnection with other military forces’ communications systems may require different combinations of physical layer and protocol support. This is especially true for administrative communications, which are oftentimes provided by different PBX systems at each command post or encampment. ISDN is a common “uplink” connection for PBXs, but this connection can be any combination of commercial ISDN or Tactical ISDN, and T1 or E1 physical connections. The ISDN protocol was one of the first developed to carry both voice and data on the same multiplexed transport. As such, ISDN was adopted by many PBX manufacturers for digital trunk connections to telephone offices. Known as a Primary Rate Interface (PRI), the ISDN trunk provides 23 simultaneous voice connections (T1) – and 30 in E1.

Media processors and DSPs

Military communications system developers must consider the varied requirements for network connectivity and provisionable features. Most effective is a COTS device supporting strong gateway flexibility and programmable DSP resources. Aculab’s Prosody X media processing board addresses these needs with inherent support for most commercial and military protocols, selectable T1/E1 physical interfaces, and IP network connectivity. Many of these capabilities and functions have been tested and proven in the field by the UK military.

Ian Colville is a Product Manager at Aculab, where his key role includes support for the company’s global sales force and interfacing to engineering and R&D. His past experience comprises a variety of management roles by a major telecommunications manufacturer. He can be contacted at [email protected].

Aculab +44-1908-273-800 – UK 781-433-6000 – U.S. www.aculab.com