Technically Advanced Data Network Backup Switches
Abstract: Backup switches allow the users the capability of sharing devices or networks connected to the COMMON port/s among devices or networks connected to the (A, B, C, etc.) lettered or (1, 2, 3, etc.) numbered ports. Network switch designs and capabilities have changed significantly since the dawn of the computer age. This white paper delineates and clarifies some of the capabilities of the network switches on the market today.
Introduction: Network switches have come a long way since they were simply used to select either printer A or B for that report coming from a particular computer. Today's switches can still have simple designs and functions; however, new demands for high-speed capability, high reliability factors, and sophisticated control methods have developed a market for technically advanced network backup switches.
1. Today's Switch Requirements
Let's start at the beginning. The significant number of choices that need to be made to determine the exact switch to meet the user's requirements is an indication of the growing complexity of today's data network backup switches.
Switches are available with any number of positions, including secure off-line positions. The switches can have letters, A, B, C, etc., or numbered positions. Connect and Disconnect, On-Line and Off-Line, Normal and Loopback, and Normal and Crossover positions are also offered.
Switches can be designed to meet space requirements. As an example, a particular switch was developed with a small size and with mounting ears to fit a mobile/motion application. Another switch was designed to be built into a wall for a secure and handy application. Multiple modular units can fit into a rack and can be expandable as required.
Most Rackmount configured switches are designed to fit standard 19" racks. A 1U rackmount switch dimensions are 19" W x 1.75" H x 8.0" D (48.3 x 4.4 x 20.3 cm). A 2U rackmount switch dimensions are 19" W x 3.5" H x 8" D (48.3 x 8.9 x 20.3 cm).
Racks are available to house modular switches. A 19" W x 5.25" H x 7" D (48.3 x 13.3 x 17.8 cm) rack can accommodate multiple switch module chassis of various widths. Filler panels are available to cover empty slots and provide the data center with a neat appearance. Modular switches are ideal for networks that plan expansion over a period of time.
Switches can be built with any connector and with combinations of connectors. An example is a tri-channel A/B switch with both RJ45 and BNC interfaces. Channel 1 allows access to RJ45 devices 1-A or 1-B. Channel 2 allows access to BNC devices 2-A or 2-B. Channel 3 allows access to BNC devices 3-A or 3-B. Fiber optic connectors include ST, SC, LC, ESCON, FC, and others.
Switches can be selected that operate at various speeds. If the switch has RJ45 ports, CAT5, CAT5e, CAT6, CAT6a are options. CAT5 switches allow access to networks rated for 10/100Base-T (up to CAT5). CAT5e switches allow access to networks rated for 1000Base-T Gigabit Networks. CAT6 switches allow access to networks rated for Gigabit Ethernet. CAT6a switches allow access to networks rated for 10/100/1000Base-T.
Switches can be controlled via a push-button or remotely via a number of methods. Switches can switch automatically when they sense a loss of data or receive a trigger signal. Remote control types include RS232 serial, contact closure, IP addressable, and Graphical User Interface (GUI) and any combination of these controls. Automatic control is also available.
Offline switching can be accomplished where the switch can automatically switch to an offline position before switching between ports A and B. A switch can have a secure off-line position where absolutely no data passes through the switch when in the off-line position. This is the ultimate firewall.
The point is that both copper and fiber optic switches can be complex. Let's try to demystify some of the sticking points with further explanations and examples.
2. Flexibility in Switch Controls
Push-button - Many switches offer front-panel push-button for local control. Any person with access to the switch can easily change the switch position. If that's all you need, push-button control is the way to go.
Keylock - A Pass Key can ensures proper authorized usage. The advantage of the keylock is the security of knowing that only the person with the key can change the switch position. The keylock mechanism can be located on the front panel. Removing the key ensures that the switch will remain in the exact position that it was in when it was locked. Pocket the key and rest assured that the switch will continue operating exactly as it was intended.
Remote Control - Now the switching choices are a little more complex, but there are definite advantages. The switch can be controlled remotely in a number of fashions:
RS232 Serial Control - With RS232 serial control, the REMOTE connector accepts RS232 serial data ASCII commands. The remote port may be connected to any standard RS232 port on a computer. The computer, once connected to the remote port, may use any common terminal emulation software to generate RS232 serial data ASCII commands.
Contact Closure - The REMOTE connector accepts Contact Closure signaling for remote control operation. An example of the methodology for contact closure is when the switch detects a transition from open to close and remains closed across pins 2 and 3, the unit will switch to the B position. If the switch detects a transition from closed to open and remains open across pins 2 and 3, the unit will switch to the A position.
IP Addressable - An IP Addressable feature is ideal for critical network alternate-path switching. Remote control and monitoring of the switch position can be from a 10/100 Base-T LAN Ethernet environment. Users can communicate with the switch via TELNET session. The user setup can allow assignment of an IP address for the switch unit.
Graphical User Interface (GUI) - The remote GUI interface allows the user to control the switch remotely with simple point and click operation. Many switches today offer extensive GUI features. To utilize the user-friendly software, the users may simply connect to the switch from a computer with access to the LAN to which the switch port is connected. Simply launch a standard Web browser and type in the appropriate IP address.
Code-Operated - The switch position and lockout can be changed through the data stream on the COMMON port. The switch monitors its COMMON port and its A port for a specified trigger character sequence.
Auto Sensing - With automatic sensing the switch can switch itself based on sensing a loss of carrier (DCD). Some switches have multiple control methods and can also be controlled locally via a front-panel push-button, or the switch can be managed off-site with the Remote option. An Automatic Fallback A/B Switch with Optional Remote Management Port allows a device connected to the COMMON port to connect through to the A port. The unit monitors carrier presence (DCD) signal on the primary line, port A. If carrier is lost, the unit automatically switches to port B. The switch will maintain its connection to port B until carrier presence is again detected on port A. When carrier is detected on port A, the unit will automatically return to the A position. With some switches, the user can override the automatic fallback operation from the front panel and force the unit to operate as an A/B switch.
To sum up flexibility in switch control, today's switches are available with automatic, manual, and remote control systems and with any number of combinations.
3. Redundancy in Network Switches
Redundancy in network switches can mean added reliability. In the first example, the switch uses a redundant system to back itself up. In the second example the switch uses an extra remote port as an additional means of communicating with the switch and an additional power supply port to ensure power is always available to the unit.
Redundant Backup - A particular switch design of interest is a normal/redundant fallback switch that self-configures connectivity based on the devices connected to it. This type switch allows data broadcast, TD of the RS232 interface, from two data origination devices to be channeled to two devices designated as destination devices. The switch will self-configure its connectivity based on the devices connected to it, or the user can override its connection status from a front panel push-button.
This is how the Normal/Redundant switch works. During the Normal mode, the origin device connected to port D1 is connected to port COM1. The device connected to port D2 is connected to port COM2. If the RTS signal is lost from the device connected to D1, the switch changes to Redundant Fallback mode and automatically broadcasts the data from D2 device to both destination devices, COM1 and COM2. Likewise, if the RTS signal is lost from the device connected to the D2, the switch automatically broadcasts the data from the D1 device to both the devices COM1 and COM2. One of the status LED's will be lit steady ON to reflect the connectivity status and signify that the unit is in Automatic operation. To override the Automatic operation, the user simply depresses the front panel push-button and holds it down for 5 seconds and then releases.
Redundant Remote Port/Power Supplies - Redundancy can also refer to achieving reliability through using duplicate physical methods. A switch can incorporate dual serial remote control ports and dual power supply ports to achieve high reliability via redundancy. Remote access can be accomplished by RS232 commands sent via the remote serial ports. Users can remotely monitor status and control switch functions. The dual power supply ports allow each of two separate external power supplies to be connected to the unit for redundancy. Internal circuitry will automatically regulate which supply source powers the unit. If a supply is removed, the supply remaining will power the switch.
The point is that your network is critical to the operation of your enterprise and your data switch can play an important role in the reliability of your network. Innovative switch designs that incorporate redundancy or other reliability enhancements can be built right into your switch.
4. Data Transmission and Power Loss
Rolling blackouts, wind storms, hurricanes, automobile accidents can all cause power loss. The lights flicker and everyone groans. Will your network hiccup?
Pass Data in Event of Power Loss - One solution to avoid a disruption in the data stream during a power loss is using a network switch that utilizes latching relays and maintains the last set position upon a power loss and continues to pass data. The ability to continue to pass data in the event of a power loss is a feature that is in demand today.
Switch Position Memory - If you do not want your switch to pass data during a power loss, you may want to select a switch with Switch Position Memory. In the event of a temporary power failure, the switch will return to the last ordered position when power is restored. Data will not pass through the unit during a power loss.
Smart Switch Checks Settings - A newly developed A/B switch includes Fallback and a Remote Port. The switch can sense RD activity or DCD presence on the ports and switch accordingly. This switch can be controlled manually via push-button or remotely via contact closure. All switched signals are passed via latching copper contact relays that maintain their position and continuity in the event of a power loss. When power is restored, the smart switch loads the previous position and mode of operation and checks DIP switch settings and the remote port to determine the correct start-up configuration.
Switch Retains Last Switch Position - A Fiber Optic A/B/Cut-off switch/converter with switch position memory is now available in the marketplace. The switch position, password, and configuration data is written to memory. In the event of a power loss, all information is retained. The switch retains the last switch position in the event of a power loss and continues to pass data.
Contact Command Determines Switch Position - A new A/B switch with contact remote control port retains the last switch position and continues to pass data upon power loss. When power is restored, the switch position will be determined by the state of contact command on the Remote port.
The conclusion is that you can have it your way. If you want the data to continue streaming during a power loss, a switch can be designed to do just that. The switch can stop passing data during a power outage if that works for you. The switch can handle power loss and restarts in any way that works best for your network application.
5. Switch Monitoring
Front Panel Indicators - Monitoring your switch can be as simple as looking at the front panel. Front panel LED's are frequently used to display the current position of the connected devices and the power status. Or the rotary knob is simply pointed to A, B, C or D.
RS232 Remote Port - Many copper and fiber optic network switches include an RS232 serial security enhanced Supervisory Remote Port. Upon proper authentication, a terminal or computer in terminal mode connected to this port can communicate with the unit, determine its status, change the switch position as desired, and/or lockout the front panel switching capability. A modem can also be connected to this port for remote access to the switch.
Graphical User Interface (GUI) - GUI software is also available to control and monitor your data switch. Utilizing user-friendly remote GUI software enables users across the LAN or over the Internet access to control and monitor the switch with simple point-and-click operation.
Telnet and GUI - Modern switches can incorporate both Telnet and a GUI. With this software program, the user can easily check to see if the front panel push-button capability is locked or unlocked and to see which channel is active. The user can change the lock status of the front panel push-button by clicking the virtual control labeled "Front Panel."
Voltage Signaling - Voltage signaling is another method of remote monitoring. An example is an A/B/C/D/Offline Switch with remote port that offers a fully decoupled off-line capability. The switch position can be changed either by depressing the desired front panel A, B, C, D, or Off-line push-buttons, or by a device connected to the Remote port located on the rear panel. Applying the appropriate voltage to the designated pins of the Remote connector will cause the switch to change position. The Remote control port allows off-site monitoring and switch management via 24 VDC signaling.
Supervisory Remote Port and Telnet - Switches that feature a Supervisory Remote Port and Telnet provide control through Telnet commands and allows the user to control the switch position, lockout the front panel operations and obtain the switch position remotely.
To sum up the discussion on switch monitoring, the switch front panel LED's, the remote serial port, your computer, your Internet connection, a user-friendly GUI, or a voltage signaling method can provide switch status information.
6. Special Purpose Switches
Video Feed Controller Switch: Switches can be developed to meet specific requirements such as a Video Feed Controller switch with contact control remote port. A new switch on the market allows three video sources to be switched among two video monitors with the option of all sources being put in a cutoff position.
Sleep Lab Switch: A switch was recently designed specifically for a sleep lab. The switch is multi-peripheral with RJ45 CAT5, XLR 3-Pin and BNC connectors. The unit switches data, audio and video channels to either of two locations. This switch allows quick and easy connection of PC Data, Microphone Audio and Video channels to either of two remote locations. The data channel utilizes RJ45 Cat5 connectors and cabling. The audio channel utilizes XLR 3-pin microphone connectors and cabling. The video channel utilizes BNC connectors and cabling.
Switch Designed to Withstand Temperature Extremes - If it gets extremely hot or cold in the area where your switch is located, you may require a special switch with enhanced operating temperature. An enhanced temperature range A/B switch with built-in conversion on Port A to RS422/485 is on the market today. This particular A/B switch connects the COMMON port to either Port B as a pass through connection, or to Port A which accepts RS232 signals in from the COM port and converts them to RS422/485. This switch has an enhanced operating temperature range of -17º C to 75º C (1.4º F to 167º F).
Switch for Nuclear Power Plant - A Seismic-proof DB9 A/B switch was designed to withstand an environment subject to vibrations. This switch and its feed-through connector successfully passed the rigorous seismic testing of the EPRI "SQURTS" Program, qualifying it for use in nuclear power plants.
7. Summary
Of course switches today have much more capability than the A/B switch that sat on my desk so many years ago. Network switches can be designed to fit anywhere: desktop, computer room rack, process control system, nuclear power plant and other rough environments, ships and other mobile/motion applications and even built into a wall. Switches can be built as boards to be incorporated into other products. Switches can be built with the ruggedness necessary to function in areas subject to noise, vibrations and extreme temperatures.
Copper and fiber optic switches can handle any number of channels and positions. Switches can handle data at high speeds. A number of fiber optic switches support Gigabit data rates. Fiber switch technology includes MEMS-based mirror technology.
Security issues are addressed with passwords, passwords with limited privileges, secure offline positions, key-locks, and the ability to lockout the front panel controls remotely. Switches are smart and can switch channels either independently or simultaneously. They can switch via RS232 serial data ASCII commands sent by the user, via Contact Closure signaling, via a trigger character sequence, or via a GUI point & click. They can switch automatically by sensing a loss of data. Network switch designs are always adapting to the needs of IT Managers worldwide.
