How to Determine the Right Fiber Optic Network Backup Switch For Your Application

1. Questions to Consider in the Design of Your Switch.

A. How many positions does your application require?

i. Two-position and three-position switches are very common. Complex multi-position switches are also required.

B. What type of connector or port preference? The selection of connectors include ST, SC, LC, ESCON and others.

i. ST connectors use a plug and socket that is locked in place with a half-twist bayonet lock.

ii. SC connectors feature a push-pull latching system providing speedy insertion and

removal along with a positive connection.

iii. LC connectors are smaller versions of the SC connectors.

iv. ESCON connectors have two 2.55 mm ceramic ferrules and a robust strain relief design.

C. Fiber Requirement: Simplex or Duplex?

i. In configuring your backup switch, a determination on the fiber type, simplex or duplex needs to be made.

1. Simplex fiber optic cable consists of a single fiber, and is primarily used in applications that only require one-way data transmission. Simplex fiber is available in both singlemode and multimode. Simplex means the cable has only one thread of fiber optic glass inside the single core and one single outer jacket.

2. Duplex cable consists of two fibers, usually in a zipcord (side-by-side) style. Duplex multimode or single mode fiber optic cables are used for applications that require simultaneous, bidirectional data transfer. Workstations, fiber switches and servers, fiber modems, and similar hardware usually require duplex cable. Duplex fiber is available in singlemode and multimode. Duplex fiber cable can be regarded as two simplex cables having their jackets joined by a jacket material. Some duplex fiber optic cables have clips on the two fiber optic connectors at each side of the cable to combine the two connectors together.

D. Mode: Multimode or Singlemode?

i. Multimode fiber optic cable has a large diameter core that is much larger than the wavelength of light transmitted, and therefore has multiple pathways of light. Several wavelengths of light may be used in the fiber core. Multimode optical cable is most commonly used for shorter distances, such as a building or a campus. Typical multimode links have data rates of 10 Mbit/s to 10 Gbit/s over link lengths of up to 600 meters.

ii. Singlemode fiber optic cable has a small core and only one pathway of light. With only a single wavelength of light passing through its core, singlemode realigns the light toward the center of the core instead of simply bouncing it off the edge of the core as with multimode. The glass fiber diameter is usually 8.3 to 10 microns. Single mode fiber provides a higher transmission rate and up to 50 times more distance than multimode.

E. Switch Specifications: Wavelength, Speed, Fiber Size, Simplex, Duplex, Interface Conversion will be unique to your network. Examples of two switches with very different specs follow.

F. Technology Preference: All Optic, Optic/Electronic/Optic, No Preference?

i. All-Optic (O-O-O) – Fiber optic network switches designed with scalable all-optical, O-O-O, MEMS (Micro-Electromechanical System) technology employ control mechanisms to tilt mirrors or direct prisms in multiple directions to manage light signals without converting the signals to electrical and back to optical. This increased level of control minimizes insertion loss and keeps the features of high data rate and protocol transparency.

ii. Optic/Electronic/Optic (O-E-O) Technology – Optic/Electronic/Optic technology is both economical and reliable, however such an architecture prevents the switch from performing with the same speed as an all-optical scheme and is not transparent to network protocols used.

G. Chassis Type: Rackmount or Desktop? – This table lists a variety of switches built to fit equipment racks and desktops.

H. Security Concerns can be addressed in a variety of ways.

i. Off-line positions.

1. External Off-line Position – The block diagram of the Model 4192 Fiber Optic SC Duplex A/B/C/D/Off-Line Switch illustrates a fiber optic switch with an external off-line position. This switch enables a fiber optic device connected to the SC Duplex COMMON connector of the unit to access any of the four fiber optic networks connected to the A, B, C, or D ports, or to disconnect completely from all output ports. The switch position can be changed via a pushbutton or via a device connected to the Remote port. Applying the appropriate voltage to the designated pins of the Remote connector will cause the switch to change position.

2. External Off-Line Position with Switch Position Memory – The Model 4196 4-Way All-Optic Fiber Switch, Multimode, 62.5/125 Microns with a Fully Decoupled Off-Line Capability allows a fiber optic device connected to the unit’s SC Duplex COMMON connector to access any of the four fiber optic networks connected to the A, B, C, or D ports, or to disconnect completely from all output ports. Switch position can be changed via front-panel pushbuttons or by a device connected to the rear panel Remote port. Applying appropriate voltage to designated pins of the Remote connector also changes the switch position. The Off-Line pushbutton uncouples all fiber ports from each other. The Model 4196 has Switch Position Memory. When power is lost, the Model 4196 automatically changes to the Off-Line position and decouples all fiber connection in and out of the unit. When power returns, the Model 4196 automatically reads the voltages on the Remote port and looks to the pushbutton activity to select its switch position.

3. Internal Off-Line Position with Options − The Model 6275 ST Duplex Fiber Optic 8-Position Switch with Off-Line Position and Remote Serial Control provides both an Off-Line position and a keylock to lock out the front panel pushbutton controls. The Model 6275 features both local and remote control. The Off-Line position is a valid state to preserve network and data isolation. The user can configure the switch to either maintain its position and data pathways on power failure or to revert to the Off-Line position during power failure. A key is provided to lockout the front-panel pushbutton controls.

ii. Front Panel Lockout – The Model 6293 Fiber Optic Mirror A/B/C Switch, Single Mode LC Duplex with Remote Serial Access allows sharing a fiber optic LC duplex pair connected to the COMMON port among three other sets of LC duplex pairs connected to the A, B, and C ports with local and remote access functionality. The front-panel pushbutton can be locked out using remote ASCII commands.

iii. PassWord Protection – Password protection is another method of providing network security. The Model 4185 Fiber Optic SC Duplex, Multimode Switch/Converter allows accessing two separate fiber optic 100 Base FX ports (ports A and B) from a 100 Base TX Fast Ethernet port (COMMON port). The fiber optic/twisted pair copper conversion is built in. This unit includes 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 lock out the front panel switching capability. A modem can also be connected to this port to remotely access the switch. Access to the Supervisory Remote Port feature is password protected.

I. Power Loss − How should your switch function during a power loss?

i. Should the switch continue to pass data?

ii. If passing data during a power loss, should data pass through the last selected switch position or go to the default position?

iii. Upon power up, should the switch remain in the last position or start up in default mode?

J. Number of Channels per Chassis – Electro Standards manufactures fiber optic backup switches ranging from Single-Channel to 16-Channel Switches.

K. Multiple channel switch control: Simultaneous or Individual.

Examples of how these switches function follow:

i. Simultaneous Channel Switching:

ii. Individual Channel Switching: All channels are switched individually with the

2. Putting the Switch All Together

3. Summary – Fiber optic switches of various functions are available to add versatility, improve efficiency, and enhance scalability of data networks. They may be operated locally by pushbutton or remotely via a variety of common communication interfaces. The agility that they add to network operational performance is limited only by the innovation of the user and the design expertise of the switch product provider.

Applications include switching to backup data lines, to test equipment, to monitoring equipment, or simply switching to off-line for security. Electro Standards Laboratories is available to provide an optimum switch solution for your application.

What Is an Ethernet Switch?

An Ethernet switch is a networking device that is used in almost all data networks to provide connectivity for our networking devices. Prior to the invention of the Ethernet switch, our Ethernet data networks used either Repeaters or Hubs to build Local Area Networks.

Before Ethernet Switches, a lot of networks used coaxial cable for local network connections, in a network topology that became known as a bus network. The most common bus networks used two early Ethernet cabling standards, which were the 10Base5 and 10Base2 coaxial cable standards. The 10Base5 networks were often referred to as Thicknet, while the 10Base2 networks were known as Thinnet. All network devices such as computers and servers were connected to a segment of cable in what was known as a “shared environment”, or more commonly a collision domain. This type of network relied on data being broadcast across the media to all connected devices.

The invention of the hub made it easier for devices to be added or removed from the network, but an Ethernet network using a Hub was still a collision domain, where collisions were way of life. Ethernet network interface cards were designed to use CSMA/CD and detect and deal with collisions. Unfortunately collisions do have an effect of slowing down a network and make that network less than efficient. A Hub is said to be a Layer-1 device as it has no real intelligence, and in fact it is really just a multi-port repeater, with data entering one port being duplicated when sent out the other ports. The reference to Layer 1 is to the bottom layer of the OSI 7 Layer reference model.

The Hub was eventually replaced by the Ethernet switch as the most common device in Local Area Networks. The switch, which is a much more efficient device, is said to be a more intelligent device than a Hub because it is able to interrogate the data within the Ethernet Frames, whereas a hub just retransmits the data. With Ethernet, we use 48-bit MAC Addresses when labelling specific physical network interfaces, and an Ethernet frame of data contains both the Source and Destination MAC Addresses to enable data to be routed and switched from one specific physical interface to another.

An Ethernet switch has 3 main functions, which are:

Address Learning

Forwarding and Filtering

Loop Avoidance.

Address Learning

When a data frame enters through a port on a switch, the Ethernet Switch reads the Source MAC Address and adds that address to a MAC Address Table. This table is often referred to as Content Addressable Memory (CAM). Within the table the MAC Address is associated with the physical port on the switch to which the network device is attached. The switch now knows which port to forward data to when an Ethernet frame arrives from elsewhere in the network, because it checks the destination MAC Address, and looks for a match in the table. The Destination MAC Address is therefore used by the Ethernet Switch to forward data out of the correct port to reach the correct physical interface.

Forwarding and Filtering

When a switch receives an Ethernet frame, it will read the Destination MAC Address in order to determine which port to forward the data out of. When a switch receives an Ethernet frame with a Destination MAC Address that is not referenced in the table, it floods that frame out of all ports in an attempt to reach the correct physical interface. If the correct device responds, then the switch will now know where that MAC Address resides, and is therefore able to add that address to the table for future reference.


Almost all modern switches run a protocol known as the Spanning-Tree Protocol, or STP. STP was originally a proprietary protocol developed by DEC, but is now an IEEE Standard known as IEEE 802.1d, which was later revised to IEEE 802.1w (Rapid Spanning-Tree Protocol). The role of Spanning Tree is to detect and manage loops in a network, which can be a big problem by allowing duplicate frames to be delivered, and cause the MAC Address Table to become unstable. In severe cases network loops will cause a network to be over subscribed and eventually be overwhelmed by the amount of data. Spanning-Tree allows network designers to build redundancy and resilience into a network, safe in the knowledge that any physical or logical loops created will be managed by the Spanning Tree Protocol.

You will hear the terms Layer 2 and Layer 3 Switch, what do they mean?

A Layer 2 Ethernet switch operates by performing like we described in the previous paragraphs. The Layer 2 name comes from the fact that it operates at Layer 2 of the OSI 7 Layer Reference Model. This Layer is often referred to as the Data-Link Layer, and it is the layer that Ethernet is described, and where MAC Addresses are used.

So what is a Layer 3 Ethernet Switch?

A Layer 3 Ethernet Switch combines the features and functions of a basic Layer 2 switch, with features normally associated with a Router. In fact, it is probably easy to describe a Layer 3 switch as a switch and a router combined. A Layer 3 switch will have either a number of fixed Ethernet ports that have layer 3 IP Addresses associated with them, or more commonly, configurable ports that can be Layer 2 or Layer 3 as desired. All but the smallest home consumer Layer 2 switches allow the configuration of VLANs (Virtual Local Area Networks), but are not able to directly route traffic between multiple VLANs. In order to do this, the addition of a Layer 3 device such as a Router would be needed. A Layer 3 switch can perform this function in addition to tradition Layer 2 switch functions.

When purchasing an Ethernet switch, you need to determine what its role will be in the network, and whether or not Layer 3 functions will be required. Normally a Layer 3 Ethernet switch will be more expensive than a comparable Layer 2 device, so it would be an unnecessary expense to employ a Layer 3 switch when a Layer 2 switch would suffice.

Ethernet switches have evolved since the first simple devices were introduced, and some have a lot of additional features and support a wide range of ever increasing network protocols. Some of these features and protocols will be discussed in future articles.

Network Switch Selection – How to Select a Network Switch


The network switch is the most common network device implemented with company infrastructure and as such the selection of any new switches or upgrading is a key part of most network design projects. The Cisco network switch components include Switch Chassis, Supervisor Engine, Switching Modules, IOS/CatOS software and Power Supplies. The decision to buy new switches or upgrade equipment will be decided after considering the network assessment and design features specified. Wireless designs, as an example, will have network switches interfacing with access points. That will have an affect on the switch such as increased utilization, assigned switch ports, access control lists, Trunking, Spanning Tree Protocol and increased wattage draw from Power over Ethernet (PoE).

Switch Chassis Features

The Switch Chassis features include – chassis dimensions, number of slots, processor slot assignments, switching fabric, engines types supported, power supplies, rack units needed.

Cisco Supervisor Engine (SE) Features

Cisco switches are implemented with an Engine (Switch Processor) for processing packets on a network segment. Routing is accomplished with an on-board Multi Layer Switch Feature Card (MSFC) or Route Processor running IOS code. The switch Engine running IOS code on the MSFC and the switch processor is in native mode, while those running CatOS on the processor are in hybrid mode. Some engines won’t support native and hybrid mode. The engine with no MSFC supports what is called CatOS mode. Select the engine that matches your design specifications. The MSFC module is integrated with the Engine or upgradeable. You must implement a PFC module with any MSFC. Some Engines have no MSFC module – the routing is integrated with the hardware and as such support native mode only.

The Cisco Supervisor Engine features include – supported chassis, uplink speed, processor memory, native IOS, CatOS, PFC, MSFC, slot assignment, failover.

These are some of the popular Cisco engines and their switching features.

720 – Cisco 6500 switches, 400 mpps, MSFC3, IOS, CatOS

32 – Cisco 6500 switches, 15 mpps, MSFC2A, IOS, CatOS

V – Cisco 4500 switches, 72 mpps, Integrated Routing, IOS

IV – Cisco 4500 switches, 48 mpps, Integrated Routing, IOS

Switching Module Features

The Switching Module features include – supported switch chassis, interface speed, number of ports, media, cabling, connectors, throughput (mpps), supervisor engines supported, protocol features, power over ethernet (Cisco prestandard or 802.3af).

– Media: Copper, Fiber

– Cabling: UTP Cat 5, CAT 5e, CAT 6, STP, MMF, SMF

– Connectors: RJ45, RJ21, SC, LC

– Transceivers: GBIC, SFP

Power Supply Features

The Power Supply features include – supported chassis, wattage ratings, failover, input/output amps, power cord type, IOS, CatOS.

IOS/CatOS Software

Cisco network switches can be deployed with IOS, IOS and CatOS or exclusive CatOS software. Design features will determine what mode and IOS or CatOS version is selected. The software running on the Route Processor must be IOS while the Engine Switch Processor will run IOS (native mode) or CatOS (hybrid mode). Some Cisco equipment such as the 4507R deploy the Supervisor Engine IV with no MSFC onboard. The Route Processor is integrated with the engine. With that design, the Engine IV doesn’t support CatOS.

Native IOS – deployed at the network edge where most routing occurs and some switching is needed

Hybrid – deployed at the network core where there is both routing and high speed switching

CatOS – deployed at the network access layer where there is switching and no routing

Switch Selection Process:

The following describes the 5 components of any network switch selection process:

1. Consider the network assessment and design features specified

2. Select switches that include all the design features

3. Select switches with proper scalability

4. Balance cost and equipment features while meeting budget guidelines

5. Select IOS and/or CatOS software version

The Network Assessment and design specifications should be considered before selecting any network switches. The network assessment examines the design, configuration and equipment that is implemented at the office where the selected devices will be deployed. The design specifications will determine performance, availability and scalability features needed. Selecting the IOS and/or CatOS version occur after deciding on the feature set. Companies will specify a budget and that is a key consideration with any equipment selection. It isn’t cost effective to select a Cisco 6509 switch for an office with 50 employees. It is important that you select equipment that meet the design specifications, has the scalability features needed while meeting budget guidelines.

Some typical switch features to consider:

1) Are there enough Chassis slots?

2) What Supervisor Engines are supported?

3) Does the Engine support failover?

4) Is Multi Layer Switching available?

5) What Switching Modules are available?

6) What Uplinks are available?

7) What Power Supply wattage is available?

8) How many Rack Units are needed?

Switch Selection Example:

The Network Assessment discovered the following at the company office.

· The Distribution Office has 300 employees

· Fast Ethernet (100BaseT) is implemented at the Desktop

· 6509 Cisco Switches with Gigabit Ethernet Trunking

· 3800 Cisco Router with dual T1 Circuits

· Power over Ethernet is implemented

· Multiple VLANS defined

· Local Unix and Windows Servers

· Some bandwidth intensive applications

· IP Telephony is implemented at all offices

· Wiring closets are 500 feet apart

· Several Rack Units are available in the Rack Cabinet

The design specifies that an additional 180 people will be employed soon. The company will have those employees working from a third floor where the nearest wiring closet is 500 feet from the Cisco 6509. The company will implement some Wireless, IP Telephony and define VLANS with each specific company department.

The following is a list of specific switching features needed:

1. 4 Chassis slots with Switching Modules of 48 Port – 10/100BaseT

2. Gigabit Ethernet Trunking between wiring closets

3. Supervisor Engines with failover

4. Multi Layer Switching

5. Power over Ethernet support

6. Dual Power Supplies with at least 2800W for IP Phones

7. Quality of Service for IP Telephony

8. Performance switching for converged telephony network

Selected Switch: Cisco 4507R

The Cisco 4507R switch has 7 slots and is a good selection with the additional 180 employees. The device will have 4 – 48 port modules with a slot available for any additional employees. The dual Engines IV will be assigned 2 slots with failover, Multi Layer Switching between VLANS and Gigabit Ethernet uplinks connecting the 6509 devices. Each of the switching modules are PoE capable with the new 802.3af standard. Dual power supplies provide enough wattage for implementing hundreds of Cisco IP Phones and Wireless Access Points. The engine performance is 75 mpps with wire speed switching. The Cisco 4507R is more cost effective than the nearest Cisco 6509 device. Several Engine models are available with additional performance features.

– 7 slot chassis with 2 Supervisor Engines and 4 Switching Modules with 48 Port – 10/100BaseT

– Engine IV with integrated Multi Layer Switching, failover, dual Gigabit uplinks

– Power over Ethernet (PoE) support with 802.3af standard

– Dual Power Supplies with 2800W or 4200W for Telephony, Wireless, Power over Ethernet

– Quality of Service features for voice traffic

– Fast performance with 75 mpps wire speed switching for converged networking

The 3750 series Cisco switch wasn’t as expensive however there were not enough slots, stacking technology is expensive and switches at 38.7 mpps compared with the 4507R device at 75 mpps. The company would have to buy 5 separate switches with 48 ports for 180 employees. The Cisco 2950 switch doesn’t have power supply failover and scalability. The 6509 switch was much more expensive, had 2 additional slots, more performance than was needed and the switching modules were expensive. Implementation is somewhat difficult with the 6500 Cisco devices.