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.