Radio communication networks have long relied on copper lines for infrastructure, but as the copper degrades over time, the lines become increasingly difficult to maintain. Emergency networks are being forced to look for alternatives.
Finding the proper alternative to aged leased copper lines is essential to keeping networks operating at peak performance. Some operators have opted for a network overhaul moving to an entirely digital system, while others prefer updating only the necessary pieces of the system. A system overhaul can be costly and unnecessary, while risk of downtime and finding compatible equipment can cause project delays.
Many radio network operators are choosing to transition the fixed line parts of their network to Ethernet or E1, while keeping their analogue radios. Common concerns are dropped packets or speech, change in audio quality, and compatibility issues which all have to be addressed.
In the network upgrade, many moving parts must align. Emergency networks can manage complications by choosing an upgrade that involves one piece instead of the whole network.
In the UK, BT has already ceased taking orders for new TDM-based private circuits or requests to re-site existing services. Without a proper alternative in place, networks are at risk of downtime should equipment fail. Of course, BT has publicised its intent to remove such services well in advance, giving users until 31st of March 2020 before its legacy services are switched off.
Choosing a network
The first thing to figure out is what the new network will be. The most common alternatives are Ethernet or E1 from the Telco through fibre, Multiprotocol Label Switching (MPLS), or a microwave network.
Everyone dreams of monitoring their emergency network from their home couch. They want to sleep peacefully at night knowing there is redundancy in the network and that they will be notified of any emergencies in a timely manner. Such is the beauty of an Ethernet network.
However, many remote locations do not have Ethernet available as an option. In these cases, an E1 network might be the better alternative. In addition to the TDM nature of E1, making it an easy conversion from 4-wire analogue to E1, many Ethernet microwaves and MPLS networks have built in prioritization for E1 handoffs.
What is Radio over IP (RoIP)?
At the very basic level, the 4-wire or 2-wire analogue radio signal is converted to a digital packet to transport over an IP network, then converted back to an analogue radio signal on the other end. Typical large radio networks of a certain age, include radio receivers, repeaters, alarm relays, and analogue trunked systems at central sites. Signals such as Push-to-Talk (PTT) and Carrier Operated Relay (COR), guard tone and pilot tone operation should also be supported.
More than Voice over IP (VoIP)
VoIP technology can be used for basic audio communications, but does not meet the more stringent needs of RoIP. Many Voice over IP (VoIP) devices claim to work for public safety applications. It is important to consider the requirements above basic voice when assessing analogue-to-IP conversion products. For example, VoIP is often based on Session Initiation Protocol (SIP) which compresses the audio. This leads to unclear communications – something that cannot be tolerated in real-time mission critical networks.
Time Division Multiplexing (TDM) over IP: Connecting the old to the new
Radio over IP in TC Communications’JumboSwitch uses Time-Division Multiplexing (TDM) to IP to ensure the integrity of the radio signal. This maximises compatibility with the existing devices in the network. Latency is a few milliseconds or less and Packet Delay Variation (PDV) can be adjusted to account for jitter. Latency and PDV are extremely important factors in emergency radio communication and this kind of performance can only be accomplished using TDM over IP.
JumboSwitch TC3846-6
Industrial grade radio communication network products from TC Communications for linking or extending 2- or 4-wire analogue, audio and intercom devices, deliver high quality voice communications combined with maximum system reliability between emergency dispatch centres and remote radio transmitters and receivers.
The TC3846-6 is a 600ohm analogue over IP gateway that links or extends up to four channels each of 2- or 4-wire analogue and dry contacts over layer 2 or 3 networks. The TC3846-6 delivers high quality voice communications combined with maximum system reliability between emergency dispatch centres and remote radio transmitters and receivers. With a direct conversion from 2- or 4-wire analogue to IP, it features low (1-3ms) latency, meeting the needs of critical communications applications, while uncompressed 64K channels provide clear audio.
Mini Channel Bank TC8614
The TC8614 is the E1 based counterpart. The device links up to four channels each of 2- or 4-wire analogue and dry contacts over an E1 connection. Similar to the JumboSwitch, the TC8614 also delivers high quality voice with minimal latency.
Important considerations
There is no question that companies are moving away from copper lines whether by choice or obsolescence. However, there are many directions to go and many things to consider – deciding which network to choose, what equipment to upgrade, technical and compatibility requirements.
Preserve or replace equipment?
Many network managers do not know they have the option to keep their analogue radios while still upgrading their network. A complete overhaul of infrastructure, receivers, and radios is often not practical. Maintenance contracts might still be in place on the current equipment. In these situations, preserving the analogue radios makes sense.
The second factor to consider when making this decision is the impact on the users. There are many things to consider in addition to the network backbone – the radios and receivers, MPT-1327 trunking systems, downtime during repairs and learning curve for the maintenance crew. Choosing equipment that is not compatible, does not integrate with existing networks or is difficult to use can cause unforeseen delays during an upgrade.
Technical requirements
The TC3846-6 meets the needs of RoIP for emergency services applications. Its “analogue direct to IP” functionality means users can preserve existing analogue equipment, migrating 2-wire and 4-wire analogue signals to IP/Ethernet networks. These RoIP products eliminate leased line dependency, use existing network infrastructure and increase network transparency. The extremely low latency of 1-3ms enables these products to meet the needs of critical communications applications, while the uncompressed 64K channels means no lost or dropped syllables and more clarity for voting.
The TC3846-6 is an analogue and dry contact Ethernet gateway that can link or extend up to four channels of 600Ω 2/4 wire analogue and dry contacts across Layer 2/3 Ethernet networks. It is simple to configure and supports both point-to-point and point-to-multipoint topologies. The ability of the TC3846-6 to broadcast 4-wire analogue signals over MPLS means it is the only communications device in its class that is viable for use in public network solutions.
Lessons learned
In one case, the customer implemented a network overhaul without proper testing. They experienced packet delays and poor audio quality, and intermittent system failures. Fire and emergency departments experienced loss of communications for up to ten minutes during these system failures. The fire departments missed calls and had communication difficulties.
Network managers found that the analogue conversion product used at the time would often lock up, cutting communications and required a cold reboot or physical pulling out of the power cord. Attempts to warm bootup or reset the Ethernet ports often failed.
Upon installation of the TC3846-6 and without any adjustments, the voice channel worked right away. Operators of the public safety network noticed an immediate improvement in audio quality. There were no more equipment lockups, failures, or downtime. Audio quality increased greatly – an unexpected benefit. Channels are now uncompressed 64K with no loss of packets or speech and pass all status tones. In a nut shell, the TC3846-6 works.
By keeping the radios in place, they ensured minimal downtime and training needed in the switchover. Most importantly, lock-ups, cold boots, and ten-minute communications downtimes are no longer a concern for emergency personnel. There are plans to expand operations to five more cities requiring four more radio receiver sites.
Two months after the initial call to TC Communications, the JumboSwitch TC3846-6 solution was fully integrated into the OSPF microwave network. After just a few programming adjustments for PDV on the longer paths, everything worked. A few locations traverse up to five hops to the dispatch center; all without loss of quality or issues. The Public Safety JumboSwitch Network consists of 12 standalone units at the towers and two rackmount units, a 1U and 4U, at Central Dispatch with a mix of 4-wire and 2-wire interface cards (TC3846-6 Analogue Radio over IP).
While the challenges created by the migration from copper for radio network operators seeking to make the most of their existing analogue radio infrastructure are significant, they are by no means insurmountable. The technology to provide crystal clear audio quality via TDM over IP is here and is being relied upon by public safety users today. If you are facing similar problems to the customer discussed above, TC Communications is just a call away.
