Increased number of security threats, demand for greater efficiency, and requirement for cross-agency coordination all point to the need to modernize public safety communications networks toward IP and broadband. And, backhauling is at the forefront of this evolution.
The rationale for the evolution of public safety backhaul networks is twofold:
- In the short-term, existing voice-centric PMR/LMR networks need upgrading to support more data-centric applications.
- But they also need to get ready for upcoming deployment of wireless broadband 4G/LTE systems complementing existing narrowband PMR/LMR systems.
By deploying a converged MPLS-based backhaul network now, public safety organizations can address current and future requirements for public safety IP communications while controlling costs. And when properly designed, mission-critical public safety transport networks also feature more efficient and more resilient support of legacy TDM-based applications.
Employ backhauling as a strategic asset
For backhauling mission-critical voice and sensor traffic, traditional public safety communications networks use PDH and/or SDH/SONET-based TDM technologies. But times have changed. Many new applications are media-rich and computing-resource-intensive, so they require larger, fluctuating amounts of bandwidth.
Consequently, public safety agencies are swapping dedicated TDM-based backhaul networks with converged packet based backhaul to deliver broadband-based multimedia applications. These MPLS-based networks can transport first responder traffic coming, for instance, from:
- Project 25 (P25) systems
- Terrestrial trunked radio (TETRA and TETRAPOL) systems
- Any IP-based application
- Video surveillance
- And soon, 4G/long term evolution (LTE)
Further, this move to IP enables improved interoperability, superior performance, and economies of scale, as well as better integration with IT applications—much needed steps in the right direction.
Now let’s turn to some key considerations when building packet-based mobile backhaul for an upgraded LMR/PMR network.
Resiliency and fast recovery
Strong resiliency is indispensable for a public safety communications network carrying mission-critical voice, video, and data. High reliability and resiliency for uninterrupted operations is essential and platform protection is crucial.
Gone are the days of the 2-node architecture. State-of-the-art networks use fully redundant platform that supports hitless control/fabric protection—a dramatic improvement. Plus, the high-availability features provide for unparalleled availability and reliability—essential for aggregation sites, as they ensure that a control card failure has no service impact. All of this, combined with fast switching and fast fault detection, enable fault detection time to the very low 10s of milliseconds, and then the ability to reroute connections at SDH/SONET speeds.
The network should also support advanced topologies—multi-ring, necklace and hybrid— to improve robustness. In particular, when fully capitalized by dynamic IP/MPLS, multi-ring’s rich path diversity provides the highest redundancy protection even during a disaster.
Versatility and efficiency
A backhaul network often spans dense urban areas and remote environments. To do so efficiently, public safety organizations should be able to mix and match transmission media—microwave, fiber, copper, and even 3rd-party leased lines—when building a mission-critical network. Backhauling equipment that supports transmission layer integration is vital.
A consolidated and simplified network design and operations for all network sites is possible along with consistent commissioning and operations procedures—regardless of the medium.
The most common transmission medium is packet microwave complemented by optical fiber. For microwave, depending on geography and site constraints, either outdoor or indoor microwave radios can be deployed. And, to maximize bandwidth throughput of available microwave spectrum, the following advanced microwave capabilities are of utmost importance:
- Service-driven adaptive modulation
- Cross-polar interference cancelation
- Higher order modulation
- Multi-channel link aggregation
- MPLS-aware packet throughput boosters
When fiber is available, public safety operators should use it. Highly economical, coarse WDM (CWDM) allows up to 8 times 1 Gbps and/or 10 Gbps wavelengths to be carried on the same strand of fiber.
Advanced traffic management and quality of service
To deliver service guarantee and differentiation on a packet-based backhaul, a strong QoS mechanism with advanced traffic management capabilities is a must. The backhaul network should incorporate an extensive set of traffic management tools, such as advanced hierarchical scheduling and prioritization mechanisms.
These techniques optimize uplink utilization while maintaining maximum isolation and fairness among application traffic flows. This allows the network to always meet critical application performance parameters, such as bandwidth, delay, and jitter. In particular fragmentation and interleaving are key techniques to keep jitter under control on lower speed links.
To safeguard their critical infrastructure, networks must have extensive integrated security features. These defend against cybersecurity threats, ensure communications and data privacy, and help deliver uninterrupted services. Specifically, robust mechanisms are needed to protect the management, control, and data planes against security threats originating from outside or inside the agency.
For external threats, a host of security measures can be taken, such as access control lists, traffic rate controls, user authentication, authorization and accounting, encryption, or label switch paths.
But threats can also come from within the agency. Detailed event logging, and features such as user profiles that limit an employee’s scope of network access, can also mitigate risk.
Microwave links are inherently secure. However, for locations vulnerable to eavesdropping, layer 1 FIPS-197 compliant encryption can be applied.
IP/MPLS-based networks are ideal for multiservice backhauling, delivering superior performance and economies of scale. Multiservice backhaul networks can be deployed in various topology and connectivity configurations as required by public safety applications.
The challenge, though, is that legacy- and TDM-based traffic will continue to be used for the foreseeable future. Consequently, the resilience and performance of a new backhaul network should resemble that of a TDM-based network. This is achieved with pseudowire based circuit switched emulation that can be applied across a wide portfolio of legacy and T1/E1 TDM interfaces.
Support for these interfaces is required to migrate public safety applications gracefully. In addition, IP/MPLS based networks allow for improved interoperability and integration with IT applications.
Even now, a full range of MPLS-based VPN services have been deployed in numerous mission-critical networks and have been proven by commercial carriers in taxing environments.
Prepare for LTE
Future LTE deployments need to be built on a solid foundation—a network that is resilient, versatile, efficient, and that recovers rapidly.
IP/MPLS backhaul networks should scale seamlessly to accommodate different interface speeds and capacity requirements depending on the location in the network. They should also enable installation versatility for small enclosures and full outdoor environments.
At the same time, a single end-to-end network management platform—including the backhauling and the LTE radio and core access network—is needed. This simplifies operations (configuration, provisioning, supervision, fault detection, and management) and optimizes end-to-end network performance.
A service-aware network manager can maximize all these network management synergies while extending coverage to the microwave and optical transport domains, as well as the LTE domain.
The way forward
As cost-constraints take hold and demand and citizen expectations increase, public safety organizations will be drawn to evolutionary solutions that keep OPEX and CAPEX in check while meeting new performance requirements.
The way forward for these organizations is with IP/MPLS-based backhaul networks. This path allows public safety operators to modernize their mission-critical networks and paves the way for LTE.
Technical white paper: Mission-Critical Communications Networks for Public Safety News: Alcatel-Lucent strengthens the critical communications network of Dallas Solution: Alcatel-Lucent Communications for Public Safety Product: Alcatel-Lucent 7705 Service Aggregation Router (SAR) Product: Alcatel-Lucent 5620 Service Aware Manager (SAM) Product: Alcatel-Lucent 9500 Microwave Packet Radio (MPR)
-  Legacy interfaces include: E&M, FSX/FSO, V.24/V.35/X.21 serial
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