Learn how to ensure service quality, reliability, availability and resilience in 911, E-911 and NG-911 networks
Access to emergency services like police, fire and ambulance are the backbone of a civilized society. In the U.S., first responders are reached through a single number–911. In other countries, there may be a different unique number or several numbers. In the European Union, the number is 112, in other countries 999, for example. Once a call is placed, a governmental agency or other service representative at a Public Service Access Point, or PSAP, close to the location of the emergency answers the call and dispatches the required first responders. PSTN, VoIP and wireless carriers have developed methods for voice connection to the right PSAP to provide accurate location data that enables first responders to reach emergencies quickly and efficiently.
Such mission-critical public safety networks are undergoing a tremendous evolution from simply delivering traditional voice services to supporting high-volumes of voice, data and video, as well as inter-connectivity between different public organizations for a reliable communication during emergency situations. These trends are resulting in the adoption of newer technologies such as LTE, all-IP networking, and standards being developed to define the ways the network and devices can be tailored for mission-critical communications.
The diagram below shows a simplified architecture of the current 911 and E-911 networks. Typically, a call flow starts with the carrier network routing the voice call to a 911 Selective Router, which in turn routes the call to the responsible PSAP. Routing is based on an eight, 10 or 20-digit number, or an equivalent key provided by the carrier network to the 911 Selective Router. The PSAP attendant, in addition to answering the emergency call, also uses the number routing number or key to access many location databases – Selective Router (SR), Master Street Address Guide (MSAG), or the Automatic Location Identifier (ALI)–that provide the specific location of the caller including street address, building floor, suite, latitude/longitude, and the like.
911 and E-911 network architecture
In all networks, the SR determines the correct PSAP to connect to by interrogating databases, and completes the voice connection to the PSAP attendant. The caller’s numerical code or identification key are termed the Automatic Number Identification (ANI), Pseudo Automatic Number Identification (PANI), or Enhanced Services Routing Key (ESRK/ESQK), depending on if the call is from a PSTN, VoIP, or wireless carrier, respectively.
These numbers are transmitted in-band to the PSAP via multi frequency (MF) digits, or Enhanced MF if more than 10 digits are required. In the T1/PRI or SS7 connectivity case, these numbers or keys are transmitted via ISDN or ISUP messaging fields. In a wireless LTE/UMTS network, this information is carried through similar messaging fields with MSISDN (the Mobile Subscriber Integrated Services Digital Network), cell site number, and location based services.
Other essential features served by traditional land mobile radio networks include push-to-talk, and direct communication mode between devices, called “Device-to-Device” (D2D) communications, which provides the ability to communicate even in the absence of network coverage. This feature is also being adopted in newer wireless devices, although D2D it is not yet ubiquitous.
To ensure quality, reliability, availability and resiliency, testing and monitoring systems for public safety networks must be multi-functional, device-independent, compatible with hybrid-networks, and capable of end-to-end testing on devices both indoors/outdoors.
Consider: a normal analog call that is routed based on the destination (called party) phone number; however, 911 calls are routed based on the calling party number. This type of signaling, called centralized automated message accounting, or CAMA, is used for sending the calling party’s Automatic Number Identification (ANI) to the 911 selective router. GL Communication’s tProbe™ FXO can be tapped into CAMA-type circuits for non-intrusive monitoring of 911 service, including measures of seizure and wink start detection, onhook and off-hook detection and MF digit (calling party ANI) detection.
Similarly, GL’s simulation test tools such as the MAPS™ CAS Emulator, MAPS™ ISDN Emulator, MAPS™ SS7 Emulator and MAPS SIP Emulator can be configured to simulate real world 911 services and users in lab environment. The networks can be put under load and stress testing by simulating high volumes of callers, which is often the case during a disaster or emergency. All these tools can be accompanied by protocol analyzers and call capture applications, to record network behavior and replay the captured traffic for later analysis and troubleshooting.
For 911 services deployed over next-generation networks, application developers need to test their applications with realistic network conditions prior to live deployment. Conducting tests on real WAN links is expensive and, in some cases, simply not feasible. IP WAN Link Emulators help test the performance of such WAN network-dependent applications by easily and cost effectively emulating wide area network conditions in a local setup. Congestion in the network can be simulated by generating background traffic in addition to traffic of interest. Latency can be used to recreate the constant or varying delay caused by various factors in the network.
To perform complete end-to-end testing with real devices, GL Communication’s VQuad™ Probe offers voice, video and data quality testing in a portable single-box system, and works with wireless PTT, Bluetooth, Wi-Fi, VoLTE, LTE and 3G networks, and VoIP, analog and TDM networks, for testing at practically any endpoint interface. Drive testing can be accomplished with any wireless device using real-time GPS mapping and automation for unattended, 24/7 testing. This end-to-end approach to testing public safety networks means a wireless device in a pocket, in a car, on a train, or virtually anywhere else is constantly executing the functions that ensure when a call is placed to 911, first responders can locate emergencies and respond appropriately.
Contact experts at GL Communications Inc for further details.
