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MPX over IP

In the progression from Circuit Switched Data to Packet Switched Data, I can think of many different applications for something like this:

FMC01 MPX to IP CODEC

FMC01 MPX to IP CODEC

The FMC01 MPX to IP encoder can be used for multi-point distribution (multi frequency or same frequency network) of FM Composite audio, or as a backup solution over a LAN bridge, LAN extension, or public network.  I can think of several advantages of using this for a backup when composite analog STL’s are in use.  There are many compelling reasons to extend the LAN to the transmitter site these days; Transmitter control and monitoring, security cameras, office phone system extensions, internet access, backup audio, etc.  I would think, any type of critical infrastructure (e.g. STL) over a wireless IP LAN extension should be over a licensed system.  In the United States, the 3.6 GHz WLAN (802.11y) requires coordination and licensing, however, the way the rules are set up, the license process is greatly simplified over FCC Part 74 or 101 applications.

Another similar CODEC is the Sigmacom Broadcast EtherMPX.

Sigmacom Broadcast EtherMPX CODEC

Sigmacom Broadcast EtherMPX CODEC

Features include:
• Transparent Analog or Digital MPX (MPX over AES), or two discrete L/R channels (analog or AES).
• Built-in MPX SFN support with PTP sync (up to 6.000km in basic version). No GPS receivers!
• Unicast or Multicast operation to feed unlimited number of FM transmitters with MPX from one encoder.
• Linear uncompressed PCM 24-bit audio.
• Very low audio latency: 2,5mS in MPX mode.
• Perfect match with Sigmacom DDS-30 Exciter with Digital MPX input.
• Can be used with high quality 802.11a/n Ethernet links.
• DC coupled, balanced Analog inputs & outputs with -130dBc noise floor.
• No modulation overshoots due compression or AC capacitor coupling.
• Decoder provides simultaneously Analog & Digital output for transmitter redundancy.
• Aux RS232 serial transparent link, Studio to Transmitter.
• Auto switchover to Analog input when Digital signal is lost.
• Centralized remote control & management software

One last thought; separating the CODEC from the radio seems to be a good idea. It allows for greater flexibility and redundancy. Using an MPX type STL allows sensitive air chain processing equipment to be installed at the studio instead of the transmitter site.

Fifth Generation WLAN

Like all data carrying technology, WLAN, or WiFi, continues to evolve into a better, faster and more robust platform.  The IEEE wireless ethernet specification 802.11ac combines all of the past developments, plus some added features, into one specification.  Here are some of the highlights:

  • Operation on 5 GHz only.  Many more available channels in this spectrum than in 2.4 GHz
  • Increased channel bonding making wider channels carrying more data.  In the 5 GHz spectrum channels are 20 MHz wide and do not overlap.  802.11ac allows for 40, 60, 80 or even 160 MHz channels.  This is great for short distances, longer distances will be prone to greater interference over wider channels
  • Modulation schemes that allow up to 256 QAM.  A 256 QAM constellation is going to look pretty crowded unless it is on a wide channel.  Again, this would be good for short distances.
  • Increased MIMO.  Up to 8×8 MIMO (Multi In Multi Out) which can greatly improve throughput.  MIMO means multiple transmitters and antennas in the same unit.  The first number is the transmitter count the second number is the antenna count.  Thus an 8X8 system will have eight transmitters and eight antennas.  This allowed beam forming by use of phased antenna arrays, which can greatly reduce multi-path
  • MU-MIMO (Multi-User MIMO).  Basically, the access point sends the data frame only to the desired host, thus instead of acting like an ethernet hub sending the frame to every connected host, the AP is acting more like an ethernet switch.
Comparison of 802.11n to 802.11ac

Comparison of 802.11n to 802.11ac

The goal of all of these modifications is to get gigabit transfer rates over WLAN.

What does all of this have to do with radio broadcast, one might ask.  That is a good question.

There are several applications that have to do with remote broadcasting.  Many sports areas, night clubs, or other likely places to be broadcasting from have WIFI installed.  Using a laptop with an AoIP client installed not only can connect to the studio for audio delivery, the same laptop can use RDP or VNC to control the station’s automation computer as well.  This means easier integration of the remote into voice tracked or syndicated programming.

Secondly, wireless LAN bridges between studio and transmitter site can act as a STL, a backup STL, a remote control return link, bridge for a network connected transmitter,  VoIP phone link, IP security camera back haul or almost anything else that can send ethernet data.  I have found it useful to simply have a computer available at the transmitter site, even if it is only to download manuals and what not.  We have taken several old Windows XP machines and reloaded them with a Linux variant and installed them at various transmitter sites.  It saves the trouble of having to download a manual on the smart phone then page back and forth across a really small screen to read it.  As for using unlicensed WiFi to link to a transmitter site; the link between the WICC studio and transmitter site runs a 78 Mbps most days.  This is a two mile link over mostly water.  I will say, when there is fog, the link rate drops to 32 Mbps, which is still pretty good, all things considered.

Of course, office network applications; laptop, tablet, smartphone and other personal devices.

Finally, Broadcast Engineers really need to keep abreast of networking technology.  There are many, many applications for WiFi units in the broadcast industry.

Cable Porn

On occasion, the company I currently work for does installation work. Thus, I am always keeping my eyes open for new equipment and tools to make that job easier. The cable comb seems like it is just such a thing:

ACOM tools cable comb

ACOM tools cable comb

Instructional video from youtube:

Then there is this:

Which is simply amazing. It is described as “1320 Category 6 cables, dressed and terminated.”

Incidentally, there is an entire sub-reddit: reddit.com/r/cableporn for all those cable geeks that like to look at neat cabling work.

Network Data Flow Analysis

PRTG network sun

PRTG network sun

As more and more broadcast facilities are moving toward IP data for all types of data transfer including digitized audio, video, telephony, documents, email, applications and programs.  Managing an IP network is becoming more and more important.  In most broadcast facilities, Ethernet based IP networks have been the normal operating infrastructure for email, printing, file sharing, common programs, file storage and other office functions for many years.  Either directly or indirectly, most broadcast engineers have some degree of experience with networking.

With many more IP based audio consoles, routing systems, STL’s and other equipment coming online, understanding IP networking is becoming a critical skill set.  Eventually, all distribution of content will transition to IP based systems and the current network of terrestrial broadcast transmitters will be switched off.

The difference between an ordinary office network and an AoIP (Audio over IP) or VoIP network is the transfer consistency.  In an office network, data transfer is generally bursty; somebody moves a file or requests an HTTP page, etc.  Data is transferred quickly from point A to point B, then the network goes back to its mostly quiescent state. In the AoIP environment, the data transfer is steady state and the data volume is high.  That is to say, once a session is started, it is expected to say active 24/7 for the foreseeable future. In this situation, any small error or design flaw, which may not be noticed on an office network can cause great problems on an AoIP network.  The absolute worst kind of problem is the intermittent failure.

Monitoring and analyzing data flow on a network can be a critical part of troubleshooting and network system administration.  Data flow analysis can discover and pinpoint problems such as:

  • Design flaws, infrastructure bottle necks and data choke points
  • Worms, viruses and other malware
  • Abusive or unauthorized use
  • Quality of Service (QoS) issues

Cisco defines flow as the following:

A unidirectional stream of packets between a given source and destination—both defined by a network-layer IP address and transport-layer source and destination port numbers. Specifically, a flow is identified as the combination of the following seven key fields:

  • Source IP address
  • Destination IP address
  • Source port number
  • Destination port number
  • Layer 3 protocol type
  • ToS byte
  • Input logical interface

Packet sniffers such as Wire Shark can do this, but there are far better and easier ways to look at data flow.  Network monitoring tools such as Paessler PRTG can give great insight as to what is going on with a network.  PRTG uses SNMP (Simple Network Management Protocol) on a host machine to run the server core and at least one other host to be used as a sensor.  There are instruction on how to run it as a virtual machine on a windows server, which would be the proper way to implement the server, in my opinion.

For small to medium installations, the freeware version may be all that is needed.  For larger network and major market installation, one of the lower cost paid versions may be required.

Goodbye, ISDN

The imminent demise of ISDN has been talked about for some time.  There now appears to be a date attached which makes it semi-sort of official.  As of May 18, 2013, Verizon will no longer accept orders for new ISDN lines.  They will also not make any changes to existing lines and will start charging more for the service.

Taking the place of ISDN will be a variety of Ethernet/IP based audio transmission methods.  As technology evolves, this makes sense.  The quality of ISDN and the bidirectional nature was a vast improvement over the old system  5/7/10/15 KHz point to point analog lines.  The one downside, ISDN equipment was expensive and the service was expensive to install and operate.

High speed internet is available in almost every business and venue.  Many times, there is no cost to access it and equipment is relatively inexpensive.  Depending on the equipment, CODEC, and speed, it can sound almost as good as ISDN.  For those opposed to using the public network due to reliability issues, there is always frame relay.

Time moves on, so buy your IP CODECS now.

Undersea Cable Map

With the advent of fiber optic cables starting in the 1980’s,  the majority (one estimate says 99%) of this country’s overseas communications are carried by undersea cables.  These are interesting system constructions, being first redundant and second, self healing.  Glass fiber stands themselves are fairly fragile.  Bundling several together then sinking them in the ocean can create mixed results.  Deep ocean bottoms are often very rugged, containing mountains, canyons and fault lines.  Thus the submarine cables used have to be pretty rugged.

There is a common misconception that fiber optic cables do not need repeaters.  That is not true, while they do not need as many repeaters as copper cable, repeaters are still required approximately every 40-90 miles (70-150 km) depending on the cable type.  These active devices are another failure point.  Overall, it is a complex system.

Submarine Fiber Optic Cable cross section

Submarine Fiber Optic Cable cross section, courtesy of Wikipedia

Cross-section of a submarine fiber optic communications cable:

1. Polyethylene
2. Mylar tape
3. Stranded metal (steel) wires
4. Aluminum water barrier
5. Polycarbonate
6. Copper or aluminum tube
7. Petroleum jelly
8. Optical fibers

It weights about 7 pounds per foot, which is pretty hefty.

There are a couple of interactive maps on line that have detailed information about where these cables go, date in service and data capacity.  My favorite is Greg’s Cable Map which is a google map with cable data over layed with a downloadable KML file:

Undersea cable map

Undersea cable map

This shows a new cable called the “Emerald Express” which is going into service in 2013. Throughput is reported as 60 Tbps, which is moving right along.  As noted on the map, this is more of a schematic diagram connecting two shore side points.  The path the cable takes is an estimate and the actual geographical location may (is likely to) be different.  Click on any line on the map for cable information.  Most cables have their own web page and Wikipedia article.

Another undersea cable map is the Telegeography Submarine Cable Map, which has many of the same features noted above:

China US submarine Cable network diagram

China US submarine Cable network diagram

Just in case you were wondering, as I often do, how a TCP/IP connection is being routed to any given place.  For fun, I tried a trace route to a known server on Guam and found the results interesting:

Trace Route, Guam

Trace Route, Guam

Approximately 231 ms round trip route from NYC to LA to Guam and back, which is over 8,000 miles (12,850 km). A few of the intermediate routers did not answer and I tried this several different times; the same routers time out.   This missing information looks to be small steps, not large ones.  So, which cable goes directly from LA to Guam?  Possibly the China-US Cable Network (CHUS) (picture above).  At 2.2 Tbps and landing at San Luis Obispo, that is the likely candidate for the cable that carried my data.

As a general exercise, it is kind of fun, although it may be harder to figure out a particular route to say London or Berlin because there are many more different possibilities.

Route latency is something to keep in mind when planing out AOIP connections for remotes and other interactive type connections between studio and remote location.  Almost nothing is worse than that half second delay when trying to take phone calls or banter back and forth with the traffic reporter.

h/t: jf

Subnetting 101

More information on IP networking:

Most radio station networks that I have seen are divided along several different lines based on functions.  These functions are:

  • Office network; E-mail, document storage and retrieval, printing, applications like traffic and billing, promotions, music scheduling and so on
  • Automation network; automation servers, workstations and audio editing machines used in production
  • Audio over IP (AOIP) network; any AOIP consoles, devices or STL equipment
  • Voice over IP (VOIP); telephone system
  • Wireless LAN; WLAN or WIFI

It is helpful, then, to segment the network into different broadcast domains to reduce the congestion on any one network.  That is where a good subnetting scheme can be beneficial.  Subnets segment the network into smaller parts, reducing the amount of broadcast traffic and increasing network speeds by reducing MAC table sizes, and thus switching and lookup times.  They also can secure certain areas of the network from the outside or other subnets, adding a level of security.  For example, it may not be a good idea for the automation computers or the AOIP consoles to have access to the internet.  Certain functions in routers and switches can be enabled for that added security.

It is also important to efficiently use IP addresses in a large organization where WANs are used.  The better the subnetting scheme, the easier it is to understand and the better it performs.   Avoiding or reducing discontiguous networks is key to efficient and speedy routing.   That is an important consideration where applications like AOIP and VOIP are concerned

To really understand subnetting, it must be broken down into the fundamental parts.  This pertains to IPv4, which will likely remain in use for quite some time.  The big chart, class B networks:

3nd  octet 4th octet CIDR Decimal Wild card Hosts 3rd Up by Subnets
00000000 00000000 /16 255.255.0.0 0.0.255.255 65,534 255 0
10000000 00000000 /17 255.255.128.0 0.0.127.255 32,766 128 2
11000000 00000000 /18 255.255.192.0 0.0.63.255 16,382 64 4
11100000 00000000 /19 255.255.224.0 0.0.31.255 8,190 32 8
11110000 00000000 /20 255.255.240.0 0.0.15.255 4,094 16 16
11111000 00000000 /21 255.255.248.0 0.0.7.255 2,046 8 32
11111100 00000000 /22 255.255.252.0 0.0.3.255 1,022 4 64
11111110 00000000 /23 255.255.254.0 0.0.1.255 510 2 128
11111111 00000000 /24 255.255.255.0 0.0.0.255 254 1 256

Class C networks

3rd octet 4th octet CIDR Decimal Wild card Hosts 4th Up by SubnetsB SubnetsC
11111111 00000000 /24 255.255.255.0 0.0.0.255 254 255 256 0
11111111 10000000 /25 255.255.255.128 0.0.0.127 126 128 512 2
11111111 11000000 /26 255.255.255.192 0.0.0.63 62 64 1024 4
11111111 11100000 /27 255.255.255.224 0.0.0.31 30 32 2048 8
11111111 11110000 /28 255.255.255.240 0.0.0.15 14 16 4096 16
11111111 11111000 /29 255.255.255.248 0.0.0.7 6 8 8192 32
11111111 11111100 /30 255.255.255.252 0.0.0.3 2 4 16384 64
11111111 11111110 /31 255.255.255.254 0.0.0.1 0 2 N/A
11111111 11111111 /32 255.255.255.255 0.0.0.0 0 1 N/A

The terms “Class B” and “Class C” networks are outdated.  Basically, I broke the chart up along a classful boundary to make it easier to read.

An IP v4 address consists of four octets of binary data. A common example is 192.168.1.154, which in binary numbers looks like this: 11000000.10101000.00000001.11111110. It is converted to base ten numbers (dotted decimal) so that we humans can deal with it. A typical subnet mask seen in many office networks is 255.255.255.0, which in binary looks like this: 11111111.11111111.11111111.00000000.  When a router receives a packet, it does something called an “ANDing process.”  When a router ANDs, it overlays the subnet mask on the network address and uses the following function: 1+1 = 1, 1+0 = 0 and 0+0 = 0.  Thus, in the above example, a router AND would look like this:

Dotted Decimal Binary Octets
192 168 1 254
255 255 255 0
192 168 1 0
11000000 10101000 00000001 11111110
11111111 11111111 11111111 00000000
11000000 10101000 00000001 00000000

The subnet mask is telling the router to ignore the last octet, thus saving a bit of time and processing power.  It may seem very small and insignificant.  When considering that routers make sometimes hundreds or thousands of routing decisions in a second, even a small bit of work reduction adds up quickly.  Subnet masks allow routers to look at only the layer three network address, ignoring the host portion.  This takes advantage of IPs inherent hierarchical addressing system and speeds the process of routing to the proper destination.

Another way to look at it:

IPv4 subnet chart

IPv4 subnet chart, click for .pdf version

There are three IPv4 address ranges set aside for private (internal) use:

  • 192.168.0.0 to 192.168.255.255 /16
  • 172.16.0.0 to 172.31.255.255 /12
  • 10.0.0.0 to 10.255.255.255 /8

Thus, very large networks can use an internal IP address scheme in the 10.0.0.0 range and have up to 16,777,216 hosts, or 224 addresses minus two, one for the network line address and one for the broadcast address.  That would be one giant network clogged with ARP requests, ICMP packets and other miscellaneous multicast messages. A notation of /16 means that 16 bits are used for the network address, the remaining address bits are host bits.  A /24 network has 24 network bits and 8 host bits making the available hosts 254.

An example of an efficient network would be a medium market operation with six radio station under one roof.  This facility has ten studios and a news room using AOIP consoles, a VOIP phone system, an automation system, an office network with an internal file server and exchange server.  The number of required hosts on each subnetwork is

  • Office network, servers and wireless hosts: 78
  • VOIP phone system: 70
  • AOIP consoles and nodes: 30
  • Broadcast automation system: 22

Given IP address: 172.19.0.0 /22

In most instances, office networks are usually installed on one class C segment, that is to say, the network mask is 255.255.255.0.  However, in the example above, 254 hosts are not needed on the office network, thus it can be divided in half using the subnet mask of 255.255.255.128, leaving the other half for the VOIP phone system.  This subnetting scheme would leave 126 hosts on the office network and 126 hosts on the VOIP network.  The AOIP console and broadcast automation system can be placed on another class C segment, using the subnet mask of 255.255.255.192, which would give each subnet 62 hosts.  All subnets would have room to expand.  Each subnet is isolated from the others by a router.  The office subnet contains the gateway to the internet, usually .1 or .126 (first or last) IP address.

That would look something like this:

Office network
Line address First available Last available Broadcast Subnet mask
172.19.0.0 172.19.0.1 172.19.0.126 172.19.0.127 255.255.255.128
VOIP phone system
Line address First available Last available Broadcast Subnet mask
172.19.0.128 172.19.0.129 172.19.0.254 172.19.0.255 255.255.255.128
AOIP consoles and nodes
Line address First available Last available Broadcast Subnet mask
172.19.1.0 172.19.1.1 172.19.1.62 172.19.1.63 255.255.255.192
Broadcast Automation system
Line address First available Last available Broadcast Subnet mask
172.19.1.64 172.19.1.65 172.19.1.126 172.19.1.127 255.255.255.192

That keeps the network segments small but has room to grow.  This is a diagram of a converged network:

Radio Broadcast Facility converged network

Radio Broadcast Facility converged network

With a setup like this, reliability is the key to a happy life. The router should be a good Cisco product with four or more Fast Ethernet ports. A second way to do this would be to have four routers plugged into a distribution switch and use OSPF to route between subnetworks. The switches should also be a good Cisco product, which can take advantage of port security options and QoS on the VOIP and AOIP segments.  VOIP systems usually require Power over Ethernet (POE) ports, thus that switch can be specialized for that purpose.

Many AOIP systems want to see Gigabit switches or at least Fast Ethernet switches with Gigabit or better back planes.  Any AOIP STL system can be connected to the AOIP network along with other things like AOIP remote broadcast and studio telephone solutions.

Many WLAN access points can be configured as a network router and DHCP server for wireless hosts.

The largest users of the public (i.e. internet) network would be the VOIP phone system and office network.  The broadcast automation network may also be a if voice tracking or other program delivery over WAN is used.

Nanobridge M5 wireless LAN link, Part II

After a bit of delay, we were able to return to the WICC transmitter site to install the Wireless LAN link.  The installation was pretty straight forward.  The studio unit was mounted on an existing STL tower on the top of the elevator room, the transmitter unit was mounted on an existing pipe on the roof of the transmitter building.

M5 Nanobridge mounted on transmitter building with radome

M5 Nanobridge mounted on transmitter building with RADOME

I included RADOMEs for a couple of reasons; first, there is a lot of critters around of the two legged and winged kind. The upright two legged critters may be attracted to the signal strength lights at night. This unwanted attention could invite the juvenile delinquents bored teenagers to throw various objects found laying around on the ground at the antenna, damaging it.  The winged type critter may be inclined to view the feed horn as a good nesting location. The other reason is this site gets a lot of rain, wind, ice and snow, therefore the RADOMEs afford some protection against the weather.

Aiming the antennas was pretty straight forward, but requires at least two people.  Using landmarks, we aligned the dishes in the general direction of each other.  Both ends of the system were turned on and we had a -89 dBm signal path, and somewhat surprisingly, the radios linked up and my laptop grabbed an IP address via DHCP.  Using the signal strength meter on the side of the antenna, each dish was peaked in turn:

M5 Nanobridge Antenna signal strength meter

M5 Nanobridge Antenna signal strength meter

Then, somebody on either end went below and looked at the signal strength screen on the web interface while the other end was peaked.  In the end, we had about -65 dBm signal strength, which is somewhat less than the -58 dBm predicted.  I think we can do better, so on the next clear day, I am going to peak the signal again.

The data rate initially reported was over 100 MBPS, however, once I started transferring files back and forth, that dropped to about 50 MBPS.  If it is raining, that rate drops to about 35 MBPS, which is still far above what we need this link to do.  As a test, I streamed a youtube video, downloaded a windows update, loaded several web pages and checked my email simultaneously.  There where no issues with the data rate while those tasks were being preformed.

It is quite amazing to me that these little inexpensive radios can work so well.  My boss thinks that they will be blown up by lightning during the first thunderstorm of the season.  I don’t know.  There are several of these units that have been installed at mountain top tower sites and have been working for several years without issue.

Next step, installing the IP cameras and warning signs on the fence, setting up the monitoring software, etc.

Transmitter site security cameras

Transmitter site security cameras

Cameras mounted on old chimney platform.  This is the first set of cameras covering the south, north and west approaches.  A fourth camera will be mounted on the back of the building covering the east approach.  Then, under the eves cameras will be mounted on all four corners of the building and the generator shed.  If anything moves, it will be recorded.

Ubiquiti Nanobridge M5 IP radio

I am in the process of installing a pair of the Nanobridge M5 units as an IP network link between a transmitter site and the studio location. The path is relatively short, about 1.5 miles over mostly water.  The main reason for this is to replace the analog phone lines used for remote control data and backup programming delivery to the transmitter site.  One added benefit, we are also installing several  IP cameras to keep an eye on the place.  We purchased the Nanobridge system for $80.00 per side.  The price is pretty good, but the configuration and testing is a bit intensive.

Network diagram

Network Diagram

There are many versions of these spread spectrum radios, some are licensed, some are license free.  These are inexpensive, license free links that I would count on for short paths or use in non-congested areas.  In congested areas, licensed (Part 101) links should be used, especially for critical infrastructure like STLs.

Since I dreamed up this idea, I figured I should make sure it is going to work before recommending it to the powers that be.  I have learned the hard way, almost nothing is worse than a failed project with your name on it.  Better to over study something than to go off half cocked, spend a bunch of money, then realize the idea was flawed from the start.  See also: Success has a thousand mothers but failure is an orphan.

Nanobrige path study, 5.8 GHz

Nanobrige path study, 5.8 GHz, moderate noise floor, 1.5 miles

Looks pretty good.  300 MB/s bi-directional which is faster than the Ethernet port on the unit.  This will be set up in bridge mode with pretty robust encryption.  The transmitter site side is configured in the router mode, creating a second class A network at the remote site.

Nanobridge M5 22 dBi antenna

Nanobridge M5 22 dBi antenna

Next step, configuring the units.  The Nanobridge units were set up in a back to back configuration in the engineering room.  Each end comes with a default IP address of 192.168.1.20.  The units were several steps behind the latest firmware version, therefore the firmware was upgraded first.  The default admin user, password, and IP addresses were changed.  There is no greater security risk than default user and password.  The wireless security feature is enabled using WPA2-AES PSK and a greater than 192 bit access code.  The unit allows for any access code length up to 256 bits.  With a key of between 192 and 256 bits, the number of possible solutions is between 6.2771 E 57 and 1.1579 E 77, which should be pretty hard to crack.  By way of reference, a 192 bit password has 24 ASCII characters and a 256 bit password has 32 ACSII characters.

Air OS main screen

Air OS main screen

The system requires an access point, which is configured for the studio side making the transmitter site stub network the station side.  The access point is configured not to advertize its SSID, thus it should be transparent to anyone sniffing around.  The WLAN is configured as a layer two bridge, which will cut down on the data overhead, as layer three framing will not need to be opened between the two units.  The transmitter site network is set up with SOHO router function built into the Nanobridge.  One static route is needed to get to the main network.  Once the security cameras are installed, PAT may need to be used to access individual camera units via the public network.

Ubiquity air os signal strength screen

Ubiquity air os signal strength screen

Next step, deploy the units and aligning antennas.  These are 22 dBi gain antennas, which have a pretty tight beam width.  Maximum transmit power is 23 dBm, or 200 mW.  The transceiver/antenna unit has a handy signal strength meter on the side of the unit, which is good for rough in.  The web interface has a more precise meter.  In addition to that, there is a java based spectrum analyzer, which is very handy for finding open channels in congested areas.  These units can also be used on UNii frequencies with special requirements.

According to the manufacture, UV resistant shielded Category 5e cable should be used for outdoor installations.  We have several spools of Belden 1300A, which fits the bill.  The shielded Cat 5 is necessary for lightning protection as the cable shield offers a ground path for the antenna unit.  The antenna mounting structure is also grounded.  I did not take the equipment apart to examine, but I believe the POE injector and antenna have 15KV TVSS diodes across all conductors.  It will be interesting to see how these units do at the transmitter site, where there are two 300 foot towers which likely get struck by lightning often.

More pictures of the installation when it is completed.

Next step, put the system into service and monitor the link.  At the transmitter site, a re-purposed 10/100 Ethernet switch will be installed for the cameras, computer, IP-RS232 converter and anything else that may need to be added in the future.  One thing we may try is an Audio of IP (AoIP) bridge like a Barix or Tieline for program audio and room audio.

AES X192

There is a lot of buzz about converged technologies and what not.  I have always been a wee bit leery of bleeding edge technology, lots of money and time can be wasted there.  Incompatibility between different manufactures equipment and protocols can cause major heartburn in all equipment life stages.  See also: VHS vs Betamax.  Thus, when many disparate standards are homogenized into one acceptable system for everyone, we all benefit and technology moves forward.

Binary

Binary Data

Audio over IP (AOIP) is moving into the general acceptance of broadcasters as a reliable system for studio construction.  As with anything, there are pluses and minus to this development:  First of all, packet switched data is more efficient and flexible than circuit switched data.  For the purposes of clarity, an AES3 signal within a broadcast facility going from one piece of equipment to another can be defined as circuit switched data.  Once the data is segmented, packetized and framed, it can be sent anywhere, over any LAN or WAN.  This allows for greater connectivity between facilities and greatly increased delivery methods and redundancy.

The downsides are increased complexity in transmission, greater reliance software and delicate operating systems to process audio into data and deliver it, and Quality of Service (QoS) issues.  Additionally, there are many different AOIP protocols and applications currently in use.  To date, this is the current list AOIP standards that are used by various manufactures:

  • Wheatnet – Wheatstone, inc
  • Livewire – Telos
  • Ravenna – ALC Networkx (Open source)
  • Dante – Audinate
  • CobraNet – Peak Audio
  • EtherSound – Digigram
  • N/ACIP – EBU
  • Q LAN – QSC Audio Products
  • AVB – IEEE, AVnu

Each system has different characteristics.  A Livewire system will not talk with a Wheatnet system and so forth.  This is because of differences in the transport layer encoding schemes.  Some use UDP, some use RTP, some use a propriety transport protocol, and some may even use TCP (remember the 7 layer OSI model).  It would be similar to having an analog Wheatstone console unable to send audio to an analog Optimod which would be unable to modulate a BE transmitter.

AES X192 is an effort by the Audio Engineering Society to set an Audio over IP interoperability standard.  This is the direction that studio audio equipment is moving and indeed, broadcasting in general.

The X192 project endeavors to identify the region of intersection between these technologies and to define an interoperability mode within that region. The initiative will focus on defining how existing protocols may be used to create an interoperable system. No new protocols will be developed to achieve this. Developing interoperability is therefore a relatively small investment with potentially huge return for users, audio equipment manufacturers and network equipment providers.

More here.

Eventually, broadcast audio consoles will plug into a WAN and be able to source audio from all over the place, not just the local physical studio structure.  This lends itself to the evolving wired or wireless IP delivery method in place of the current terrestrial radio broadcasting currently used.  As such, I will be diving into the fascinating world of AOIP more in future posts.

Axiom


A pessimist sees the glass as half empty. An optimist sees the glass as half full. The engineer sees the glass as twice the size it needs to be.

Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances.
~1st amendment to the United States Constitution

Any society that would give up a little liberty to gain a little security will deserve neither and lose both.
~Benjamin Franklin

The individual has always had to struggle to keep from being overwhelmed by the tribe. To be your own man is hard business. If you try it, you will be lonely often, and sometimes frightened. But no price is too high to pay for the privilege of owning yourself.
~Rudyard Kipling

Everyone has the right to freedom of opinion and expression; this right includes the freedom to hold opinions without interference and to seek, receive and impart information and ideas through any media and regardless of frontiers
~Universal Declaration Of Human Rights, Article 19

...radio was discovered, and not invented, and that these frequencies and principles were always in existence long before man was aware of them. Therefore, no one owns them. They are there as free as sunlight, which is a higher frequency form of the same energy.
~Alan Weiner

Free counters!