[MRIC] I want to learn

Sun Oct 24 19:59:58 EDT 2010

Hi Bob,

In order to employ fiber, rather than copper, from the tower shelter to your EOC building, I suggest using a radio that is capable of remote operation via Ethernet. These radios allow you to install the radio in one location, and operate it remotely from a PC anywhere you can get an Ethernet connection on the same internetwork. Typically, the PC will display a graphical interface that looks like the radio front panel and give you the ability to perform all front panel operations remotely from the PC. Audio is passed from the PC to the radio via a headset plugged into the PC mic and headphone jacks. The audio is encoded into Ethernet packets and sent to/from the radio over Ethernet, along with the radio front panel commands, and programming information. I believe our MRIC Winlink equipment list mentions several such radios and generic remote radio control software, but there is more on the market every year, and others with more experience with these can recommend some specific equipment.

I can share with you how radio audio and control information is typically sent over fiber in Maryland for public safety organizations, so when you select your radio (or remote control software) you can proceed. A little background first, so you know the players:

Infrastructure Committee
------------------------

In Maryland, state agencies that use state-owned towers are members of the Public Safety Communications Infrastructure committee. This Infrastructure committee decides how the state public safety communications infrastructure can be used. Anyone that wants to put anything on a state-owned tower, or in a state-owned tower shelter, must fill out an "Application for Tower and Shelter Co-location" form and submit it to the infrastructure committee for approval (after getting local approval). Although I sometimes attend these meetings, Hank Black of MEMA is a member of the committee and can provide more specific details and assist you in the process of getting permission to install equipment in a state-owned tower shelter. Please contact him directly for procedural details.

Equipment mounted on the tower, or in the state-owned tower shelter buildings, must be installed according to Public Safety radio industry standard practices, or it will be disconnected. For example, if Motorola or M/A-COM commercial radio equipment is in the shelter, you cannot violate Motorola R56 or M/A-COM grounding specifications. I am intimately familiar with these, and can assist you. For example, any equipment you install in a rack must be properly grounded with a 6 AWG green jacketed copper stranded wire, to a 2 AWG rack ground cable to the Master Ground Bus (MGB). All coax entering the building must be protected with a lightening arrester (polyphaser) within 18 inches of the entry port. etc., etc. These standards are about 100 pages or so in length and can get complicated. Once you come up with a plan, I would be happy to review it for you to ensure it does not get rejected for not meeting standard practices.

Public Safety radio equipment must continue to operate during thunderstorms, and these standards were developed to ensure a lightening hit to the tower does not take out equipment on the tower or in the shelter (or at least minimizes its affect). To this end, many 911 Centers (Public Safety Answering Point - PSAP) and EOCs now restrict the amount of copper entering their building in order to keep any lightening that does enter the shelter, from damaging computers in their EOC. In lieu of copper, the standard practice is to now run fiber from the tower shelter into the PSAP or EOC building, and all the radios are physically located in the tower shelter building, hence, your predicament. There are several ways the audio and control signals from your EOC operator position PC can be carried over fiber to your radio.

T1 Multiplexers and Optimuxes Over Fiber
----------------------------------------

Historically, T1 multiplexers (mux) are used to convert up to 24  4-wire audio circuits for radios into a T1. The T1 is then run into an Optimux, or some other device that converts 12 or so T1s into a single pair of fibers (or two pair for redundancy). The signal then travels over fiber between buildings and is decoded back down into 4-wire audio using the same equipment in the tower shelter, as was used on the EOC end of the fiber (a T1 mux and an Optimux). The 4-wire audio copper is then directly connected from the mux to the radio equipped with a 4-wire interface. Typically multi-mode fiber is installed if the distance is under 1000 meters, otherwise single-mode fiber is installed. You need to use equipment with optical interfaces that matches the fiber type. The fiber bundle may contain anywhere from 6 to 50 or so fiber pair. Typically it is 6, 12 or 24 fiber pairs at most tower sites in Maryland.

Many muxes also have RS-232 serial interface cards, 64 kbps Ethernet cards, and other types of interface cards that can be inserted into the mux to carry different types of traffic, other than 4-wire audio, over a T1. So the first way to get your audio/control info over fiber is to find out if a mux and Optimux is installed at each end, and get permission from whoever owns the mux to install an Ethernet card in both muxes to carry your audio/control data between buildings. You will need to make sure you install mux Ethernet cards that have enough bandwidth to carry all your traffic (e.g. 64kbps, 128kbps, etc.). Alternatively, if you are using commercial radios that are equipped with 4-wire interfaces, you can just use a 4-wire interface for each radio. This is not the simplest solution, so I do not recommend it, but it is a possibility.

Ethernet Over Fiber
-------------------

The newer way to carry audio and control information over fiber is to use straight Ethernet over fiber. Most new commercial radios are now equipped with Ethernet interfaces.

All the state tower sites in Maryland are interconnected with microwave links. Most tower sites have T3 microwave links to more than one other tower site, in order to provide redundant paths through the system for critical public safety communications so the communications gets through even if one microwave link goes down. The agency I work for--the Maryland Institute for EMS Systems (MIEMSS)—maintains the state microwave equipment, although most decisions regarding its use is made by the Infrastructure committee mentioned above. The state microwave system is used by all jurisdictions in Maryland to interconnect their public safety radio system tower sites via T1s over microwave. There is also a state-wide IP network that operates over the same microwave system, called the Public Safety Interoperability Network (PSInet).

PSInet employs routers at most tower sites to route IP network traffic between tower sites, via T1s on the microwave system, to get anywhere in the state. The T1s are directly connected from the microwaves to the PSInet network routers. My boss and I are building out this network and are responsible for maintaining it. We are in the process of extending the PSInet into all PSAPs and EOCs in Maryland. Most sites are already done. In those sites that have fiber run between the tower shelter and the EOC/PSAP, we employ routers and switches with fiber interfaces to carry the network into the EOC/PSAP. This eliminates the use of T1 muxes, and Optimuxes. The microwave T1s are directly connected to the router, which may be directly connected to the fiber to the EOC. The fiber on the EOC end is directly connected to another network router or switch.

Therefore, the second way to get your audio from your EOC to your radio located in the tower shelter building, would be to request a separate VLAN over the existing PSInet. You will need to know how much bandwidth you require when you make the request. Then, if approved, all you have to do is plug your Ethernet interface on your radio in the shelter, into our switch located in the shelter; and plug your computer operator position PC in the EOC, into our switch in the EOC. This is the simplest solution for you because someone else is responsible for maintaining all the equipment between the tower and your EOC.

Alternatively, your county might already have extended their IP network from their EOC into the tower shelter via fiber, and may be willing to provide a network connection for you at both locations (EOC and shelter).

Media Converters
----------------

The last way typically used to get your audio and control information between your EOC and tower shelter over fiber is by using media converters. These are inexpensive, dumb devices that directly convert an Ethernet electrical signal into an optical signal for fiber. Put one of these on either end of a pair of fibers, and you can directly connect the Ethernet interface on your radio in the shelter, to the Ethernet interface of your operator position PC in the EOC. The media converters are transparent to the IP network. The biggest drawback to this solution, is that you are using a pair of fibers that is capable of carrying gigabits of information, for just a few kilobits of traffic, so it is a very inefficient use of the fiber infrastructure, and might be hard to convince whoever owns the fiber (county or state) to let you do that.

I hope this helps. Hopefully others will provide some details on some remote controllable radios (via Ethernet) and some generic remote control software that can be used to control almost any radio over Ethernet.

Brett Hammond
Talbot County RO

On Sun Oct 24 17:07:54 2010, <rjlong61 at myactv.net> wrote:
> Yesterday I discussed with several of you about the necessity of 
> establishing a fiber link from the EOC to the equipment building at the 
> base of the tower.
> 
> Where can I learn more about how this can be accomplished, what the 
> interfaces are like and how this "magic" is really works?
> 
> I am pulling together the list of what we need in the EOC radio room and 
> do want to talk from some intelligence rather than ignorance.
> 
> Bob KD3JK
> 
> 
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