The first of a series breaking down the compatibility journey starting with legacy GE x710B analog serial networks onto MDS x710A, SD, ORBIT digital serial / Transparent-serial operations.
The objective is a general framework to help navigate the 25 years of backward compatibility between the MDS x710, SD, ORBIT series remotes and x790 and MPRS Redundant Master Stations.
Future post will elaborate more on Transparent / IP Payload and Packet-with-MAC operations. I recommend you use your local GE Grid Solutions (MDS) Distributor if you need local support with legacy, ethernet, or hybrid 4G / 5G systems.
Find a Channel Parter: https://www.gegridsolutions.com/communications/contactus.htm
Please help me improve my post by sharing, offering constructive feedback, corrections and questions you may have. Thank you for visiting.
Written by: Phillip A. Yancey - BCI Technologies Sales and Support Manager.
Topics Covered:
Migration Planning Checklist
How is remote data being polled?
What age and model PLC(s) / RTU(s) are being used?
What are current serial device parameters, cable types, and pinouts?
Locate a network segment ideal for upgrade
Collect configurations
Locate bad or spare radios to be repaired for spares.
Determine how urgent your need for ethernet is.
Skipping this phase altogether.
Serial Devices and Serial Modems.
The x710 remotes and x790 Masters are serial data modems. Depending on the model x710A you have a digital Modem, or x710B you an Analog modem. We can only use A-code radios in backwards compatibility operation. B-code is no longer supported as it once was back around firmware version 4.3.8.
Hardware handshaking also known as hardware flow control. This started being phased out in the late 90's and today isn't required or likely included on most modern hardware. Legacy B-code systems require hardware handshaking specifically using clear-to-send (CTS), request-to-send (RTS) to control the device and modem.
Our first step in a migration is to confirm our PLC or RTU devices do not require hardware handshaking as our migration will be using software flow control which only requires TX, RX, GND. If your devices do not require hardware handshaking, then nothing needs to happen.
Once we migrate onto X710 mode these pins, RTS, CTS and others will simply be ignored.
Devices that require hardware handshaking will need to be looped to trick the device into permitting its own transmission. Best to check with the device MFG. to see if they can confirm first, but this is really mostly applicable on older devices and is becoming less common.
Here are some ways we can fool legacy hardware
Looping CTS/RTS in pinout
Insert DCD on SD series
Master Stations and System Operations.
Most migrations start at the master station because these are the most critical points of failure and it's when these legacy x790 masters fail we are thrust into migrations.
The replacement for X790 Masters is the MDS Master Station which I presume and hope most people are using by now.
There are some of you out there with the transition SDXP or SD Protected Masters and I won't be covering these, but you can and should use the MDS Master station.
Data Keying Mode
In data keying mode the radio will key upon receipt of payload data and is our primary goal of our migration. Key on Data is required to move into Transparent and packet with mac radio mode operation.
RTS Keying Mode
In RTS signal keying mode the radio is keyed on receipt of RTS signal on the serial port. RTS Keying mode is only supported in x710 Mode. This should only be used if legacy serial devices require CTS / RTS are being used, while SD can be looped or faked out.
Continuously-Keyed Operation (C-KEY)
This is a full-duplex master station transmitter that is always keyed with RF carrier that is always present, even when there is no data to send. The C-KEY master station is always simultaneously transmitting and listening. This operation requires different frequencies to transmit and receive. C-KEY operation does not apply to legacy-packet or packet with MAC modes and is most commonly found on streaming repeater networks.
In the Figure 2. example we are streaming raw serial bits, and when a poll is sent from the host it's immediately transmitted to all remotes on the network at once. The RTU who the message is intended for replies and all RTUs including the host hear this response.
Continuous-key operation is supported on the Master Station using SD modules (MPRS) operating in x710 mode or transparent mode when operating as a repeater. C-KEY is not associated with modulation but is used for devices that require "constant carrier" RTS, CDT are signs of a C-KEY system.
Our goal if requiring Ethernet Operation will be to eventually remove continuous-key operation onto key-on-data. If a streaming repeater is involved check the manuals as suggested serial timings are provided along with more on the repeater operations.
Switched-Carrier Operation (SWC)
This is a half-duplex mode where the master station transmitter is keyed to send data and unkeyed to receive. The transceiver uses different frequencies for transmit and receive. This prevents different remotes from interfering with each other. This mode results in slower polling times than a Continuous-Keyed master due to the keying time for the master
and squelch opening time for the remote.
x710B remotes always operate in switched-carrier mode. SD Remote may have SWC enabled to support legacy b-code operation only. x710B SWC remotes can receive data from a master that operates in either switched-carrier or continuously keyed.
Imagine a host computer polling the serial network. All remotes are actively listing since none are keyed. The host polls the network and Master is keyed first adding delay before sending to all listening remotes. When the polled remote responds, it is keyed while the Host is de-keyed to listen.
Review of MPRS Setup Parameters
The MDS Master Stations, built upon our modular communications platform, are used with SD Series and x710 series remote radios. The MDS Master Stations support full duplex communication in a protected 1+1 warm standby transceiver configuration to provide reliability for continuous use, high duty cycle applications associated with licensed narrowband Base Station and Repeater applications.
The below screen shots we're taken from an MPRS build using firmware 4.8.1. These original builds were able to support legacy B-code switch-carrier operation. Ge is no longer able to support this, and it has since been deprecated. If you are running a first edition MPRS build with legacy firmware, it's important you do not update the platform firmware until you are off switch-carrier operation.
SDMS Interface - Basic Config
These settings must match on all SD & LN remotes.
Radio Mode:
x710 - This is the generic name for GE MDS Legacy transceiver-family products including (9710, 4710, 2710, 1710) Products. When using this mode, the Master Station is in a legacy x710 network. SCD is applicable for this mode and VRC is not supported.
Transparent - Over the air compatible with x710 while supporting payload data encapsulated in IP at ethernet port. Data is unchanged from its original format when sent over the air. This mode is "transparent" to the connected equipment at each end of link. Does not support ethernet bridging but works with and without AES Encryption 128-bit, which requires all SD radios. SCD is applicable for this mode, but VRC is not supported.
Packet with MAC - Packet radio uses a transmission scheme in which data elements are assembled into units, that are consecutively numbered and error-checked at the time of transmittal. Errored packets result in retry request from the receiving station. Supports Ethernet Bridging, peer-to-peer, store-and-forward and works with and without AES Encryption 128-bit and SCD should be left to 0 when operating in this mode. This helps to avoid delayed key downs on packetize data. Supports up to 3 Virtual Radio Channels (VRC) in all SD network.
Modem Type: This setting determines the over-the-air speed and bandwidth of the radios transmitted signal. All radios must use the same modem type. Note: 4800B users must move to 9600 baud as 4800 is not valid for U.S operation.
Keying Mode: This setting determines the over-the-air speed and bandwidth of the radios transmitted signal.
Data or RTS – Radio will key upon receipt of either payload data or an RTS (request
to send) signal on the serial port.
Continuous – Radio will be continuously keyed. This is primarily used in a transparent
streaming repeater configuration.
Soft Carrier Dekey: Specifies how long to wait after the removal of the keying signal before actually dropping the transmitter's carrier. In most cases this is not required but may be required for legacy x710 radio equipment.
Clear to Send Dekey: Specifies a brief time delay between when an RTS (ready-to-send)
signal is received and when the CTS (clear-to-send) signal is returned. In most cases this is not required but may be required for legacy x710 radio equipment.
Switch Carrier B Modems: Depreciated.
Data Key Hold Time Out: When operating in data key mode, this parameter specifies
the number of character-times the transmitter will remain keyed for after the last character
it receives. For networks with the demand for a higher modem speed than the baud rate of
the serial port, this parameter can be adjusted from 1 to 10 characters. This parameter
gives the overall network better performance by preventing frequent key-up and key-down
sequences between characters. This only applies to networks with all SD radios.
Simplex Mode: This controls whether or not the Master Station will be running in
simplex (switched carrier) or full duplex mode. When simplex is enabled, TX and RX are
switched onto a single RF interface. A Master Station without an internal duplexer with a
single antenna output must have simplex mode enabled.
Data Device Mode: (x710 mode only) – This value controls the device behavior of the radio when operating in x710 mode. DCE mode, CTS will go high following RTS, subject to the CTS programmable delay time.
Remote Broadcasting and Rollout planning.
The MPRS has the following SD Broadcast that can help in your migration roll-out but be warned not all remotes will receive it, it will happen.
Consider performing twice before proceeding into making MPRS operation changes. Once a broadcasted change is sent all remotes modified will lose connectivity until the MPRS is modified to match the new settings. Here are the broadcast changes you'll want to make.
In the case of legacy Switched Carrier Detect systems you do not need to broadcast this change when converting from B code to A code operation. Since SCD is not available in x710 radio mode by making this change it will ignore / disable SCD automatically. If only SDs are on the network, consider skipping x710 and using Transparent. When performing a remote broadcast send modem mode changes first and Radio mode second.
Remote Management broadcast commands for SD radios.
Set Modem Type:
Set Radio Mode:
Set Switch-Carrier-Detect (SCD):
x710B to X710A Firmware vs replacement.
In some cases where x710B modems may still be in operation but a migration must happen you may attempt to update their firmware manually. Manually updating each 4710B modem to use 4710A firmware will be a labor intense effort.
It will require planning and ideally off-line staging before attempting a migration and roll-out. The challenge is, by updating these devices we are essentially making them unusable on the current operating analog or x710B code network. Only until we change our Master off B-code will these units start working again. Because of this challenge you can see why it's the least preferred. If you require this path, you'll need to use the GE MDS Element Manager software.
Putting it all together.
Serial systems stream raw bits of data and this diagram on the right shows a visual of what the bit level migration path looks like as we move forward in our serial to ethernet migration. As we migrate off serial-based systems we are adding layers of overhead. While there's benefits to doing this, it should be known, narrow band ethernet telemetry isn't going to be faster than serial.
As we migrate onto ethernet native devices our bits are framed, our frames can become packetized, and those packets routed.
The biggest hurdle of a migration is really getting off of the Analog hardware and operation. If your able to replace all the x710 with SDs, then it's not all that bad.
Removing Switch carrier operation is critical as this is only supported on B-code. The hurtle is, when we have to make field changes to remotes which translates to a lot of time driving to each remote while the system is down.
We want to avoid this because no one wants to start a migration at 7am to have to undo it at 5pm. Leverage pre-configured radios and spares, use the MPRS broadcasting and minimize as much of this as possible. Depending on your urgency once you are on A-code operation the other changes can be done over time and are not as urgent.
If you have all SD consider skipping x710 and go to transparent instead, this will give you the option to add encryption and similar to UDP operation allowing for IP payload as well. Change from continuous to key-on-data in many cases is as simple as just making the change at the master and seeing if the system continues working. Remember, if it doesn't the devices may need to be looped to be tricked into thinking DCD is available.
Before considering Packet with MAC we should let the system stabilize for a week or more. At this for the 4.8.1 customers we can upgrade our firmware and reset knowing that replacement modules and chassis will be supported. I hope this has been helpful and check back for updates and please feel free to comment and make any corrections or suggestions.
Supporting Links:
GE Grid Solutions Webstore:
GE RMA / Repairs:
MDS Master Station Configurator:
MDS Master Station Resources:
MDS SD Seres Configurator:
MDS SD Series Resources:
Check out Top GE MDS Links for Legacy System Migrations on a previous blog post here: https://www.bcitech.com/post/topgemdslinksforlegacysystemmigrations