An Easy Guide to MPO/MTP Polarity

Nowadays, many data centers are migrating into the 40G and 100G transmission. To prepare for this change, MPO/MTP technology is applied to meet the requirements of high density patching. Typically, a fiber optic link needs two fibers for full duplex communications. Thus the equipment on the link should be connected properly at each end. However, high density connectivity usually requires more than two fibers in a link, which makes it more complex to maintain the correct polarity across a fiber network, especially when using multi-fiber MPO/MTP components for high data rate transmission. Therefore, many technicians would prefer to use pre-terminated MPO/MTP components designed with polarity maintenance for easier installation. This article will specifically guide you to understand the polarity of MPO/MTP products and the common polarization connectivity solutions.

What Is Polarity?

Keeping the right polarity is essential to the network. A transmit signal from any type of active equipment will be directed to the receive port of a second piece of active equipment and vice versa. Polarity is the term used in the TIA-568 standard to explain how to make sure each transmitter is correctly connected to a receiver on the other end of a multi-fiber cable. Once the component is connected to the wrong polarity, the transmission process will be unable to go on.

Structure of MPO/MTP Connector

When discussing about the polarity, MPO/MTP connector is an important component for you to know. An MPO/MTP connector has a key on one side of the connector body. There are two positions of the key – key up or key down. Key up position means that the key sits on top. When the key sits on the bottom, it is the key down position. Moreover, the fiber holes in the connector are numbered in sequence from left to right named as P1 (position 1), P2, etc. Each connector is additionally marked with a white dot on the connector body to designate the P1 side of the connector when it is plugged in. The MPO/MTP connector can be further divided into female connector and male connector. The former has no pins while the latter has two pins on the connector. The following picture shows the basic structure of MPO/MTP connector.

structure-of-mpo-connector

Connecting Methods of A, B, C

The TIA standard defines two types of duplex fiber patch cables terminated with LC or SC connectors to complete an end-to-end fiber duplex connection: A-to-A type patch cable is a cross version and A-to-B type patch cable is a straight-through version. Based on this, there are three polarity connecting methods for MPO/MTP products. Here will introduce them in details.

duplex-patch-cable

Method A is the most straight-forward method. It uses straight-through patch cords (A-to-B) on one end that connect through a cassette (LC-to-MPO or SC-to-MPO depends on what the equipment connector is), a straight-through MPO/MTP key up to key down backbone cable and a “cross-over” patch cord (A-to-A) at the other end.

method-a

Method B is the “cross-over” occurred in the cassette. The keys on the MPO cable connectors are in an up position at both ends, but the fiber that is at connector P1 in one end is in P12 at the opposite end, and the fiber that is in P12 at the originating end is in P1 at the opposing end. Only A-to-B type patch cord is needed for this method.

method-b

Method C is the most complicated. There is pair-wise “cross-over” in the backbone cable. A-to-B patch cords are used on both ends. The cassette uses MPO/MTP key up to key down and the backbone cable is pair-wise flipped so P1, P2 connects to P2, P1 and P3, P4 connects to P4, P3, etc.

method-c

Conclusion

Knowing the polarity of MPO/MTP system helps you better upgrade the 40G and 100G networks. According to different polarity methods, choosing the right MPO/MTP patch cables , connectors and cassettes will provide greater flexibility and reliability for your high density network.

What's the best way to terminate fiber optic cable?

What's the best way to terminate fiber optic cable? That depends on the application, cost considerations and your own personal preferences. The following connector comparisons can make the decision easier.

Epoxy & Polish

Epoxy & polish style connectors were the original fiber optic connectors. They still represent the largest segment of connectors, in both quantity used and variety available. Practically every style of connector is available including ST, SC, FC, LC, D4, SMA, MU, and MTRJ. Advantages include:

• Very robust. This connector style is based on tried and true technology, and can withstand the greatest environmental and mechanical stress when compared to the other connector technologies.

• This style of connector accepts the widest assortment of cable jacket diameters. Most connectors of this group have versions to fit onto 900um buffered fiber, and up to 3.0mm jacketed fiber.

• Versions are. available that hold from 1 to 24 fibers in a single connector.

Installation Time: There is an initial setup time for the field technician who must prepare a workstation with polishing equipment and an epoxy-curing oven. The termination time for one connector is about 25 minutes due to the time needed to heat cure the epoxy. Average time per connector in a large batch can be as low as 5 or 6 minutes. Faster curing epoxies such as anaerobic epoxy can reduce the installation time, but fast cure epoxies are not suitable for all connectors.

Skill Level: These connectors, while not difficult to install, do require the most supervised skills training, especially for polishing. They are best suited for the high-volume installer or assembly house with a trained and stable work force.

Costs: Least expensive connectors to purchase, in many cases being 30 to 50 percent cheaper than other termination style connectors. However, factor in the cost of epoxy curing and ferrule polishing equipment, and their associated consumables.

Pre-Loaded Epoxy or No-Epoxy & Polish

There are two main categories of no-epoxy & polish connectors. The first are connectors that are pre-loaded with a measured amount of epoxy. These connectors reduce the skill level needed to install a connector but they don't significantly reduce the time or equipment need-ed. The second category of connectors uses no epoxy at all. Usually they use an internal crimp mechanism to stabilize the fiber. These connectors reduce both the skill level needed and installation time. ST, SC, and FC connector styles are available. Advantages include:

• Epoxy injection is not required.
• No scraped connectors due to epoxy over-fill.
• Reduced equipment requirements for some versions.

Installation Time: Both versions have short setup time, with pre-loaded epoxy connectors having a slightly longer setup. Due to curing time, the pre-loaded epoxy connectors require the same amount of installation time as standard connectors, 25 minutes for 1 connector, 5-6 minutes average for a batch. Connectors that use the internal crimp method install in 2 minutes or less.

Skill Level: Skill requirements are reduced because the crimp mechanism is easier to master than using epoxy. They provide maximum flexibility with one technology and a balance between skill and cost.

Costs: Moderately more expensive to purchase than a standard connector. Equipment cost is equal to or less than that of standard con¬nectors. Consumable cost is reduced to polish film and cleaning sup-plies. Cost benefits derive from reduced training requirements and fast installation time.

No-Epoxy & No-Polish

Easiest and fastest connectors to install; well suited for contractors who cannot cost-justify the training and supervision required for standard connectors. Good solution for fast field restorations. ST, SC, FC, LC, and MTRJ connector styles are available. Advantages include:
• No setup time required.
• Lowest installation time per connector.
• Limited training required.
• Little or no consumables costs.

Installation Time: Almost zero. Its less than 1 minute regardless of number of connectors.

Skill level: Requires minimal training, making this type of connector ideal for installation companies with a high turnover rate of installers and/or that do limited amounts of optical-fiber terminations.

Costs: Generally the most expensive style connector to purchase, since some of the labor (polishing) is done in the factory. Also, one or two fairly expensive installation tools may be required. However, it may still be less expensive on a cost-per-installed-connector basis due to lower labor cost.

The Ports On CWDM and DWDM MUX/DEMUX

It is quite common to use CWDM or DWDM to increase the existing fiber optic network without adding any fibers. Using WDM MUX/DEMUX is necessary to build a CWDM or DWDM network. Now there are different ports installed on the CWDM and DWDM MUX/DEMUXs to add more beneficial to the fiber optic network. This post will offer details about the ports on CWDM and DWDM MUX/DEMUX.

 

DWDM MUX/DEMUX Port

The basic function of the CWDM and DWDM MUX/DEMUX is combining data rate of different wavelengths over the same fiber cable to increase the network capacity. Thus, channel ports supporting different wavelengths and Line port used to connect the WDM MUX/DEMUX are the must-have ports for these devices.

CWDM uses 18 wavelengths ranging from 1270nm to 1610nm with a channel space of 20nm. Channel port count on CWDM MUX/DEMUX is usually ranging from 2 to 18. The following picture shows a full-channel CWDM MUX/DEMUX with all the 18 CWDM wavelengths: 1270nm, 1290nm, 1310nm, 1330nm, 1350nm, 1370nm, 1390nm, 1410nm, 1430nm, 1450nm, 1470nm, 1490nm, 1510nm, 1530nm, 1550nm, 1570nm, 1590nm, 1610nm.

18CH CWDM MUX/DEMUX

 

DWDM uses the wavelength ranging from 1470nm to 1625nm usually with channel space of 0.8nm (100GHz) or 0.4nm (50GHz). DWDM MUX/DEMUX can support much more wavelengths that of CWDM MUX/DEMUX. The channel port of a DWDM MUX/DEMUX is usually ranging from 4 to 96.

Line Port

 

There are two types of line port available for CWDM and DWDM MUX/DEMUX. One is dual fiber line port, and the other is single fiber line port. The selection of the line port depends on applications. The WDM MUX/DEMUX with a single fiber line port is very different from the WDM MUX/DEMUX with a dual fiber line port on the using of wavelengths.

 

Dual-fiber MUX/DEMUX uses the same wavelength for dual-way transmission, which means the TX port and RX port of every duplex channel port supporting the same wavelength. The WDM MUX/DEMUXs with dual fiber line ports installed on the two ends of the network could be the same.

 

signle-fiber DWDM MUX/DEMUX

 

For single-fiber WDM MUX/DEMUX, all the wavelengths just flow in one direction. And the TX port and RX port of every duplex channel port supporting two different wavelengths. The above picture shows the front panel of an 8-channel DWDM MUX/DEMUX with single-fiber line port. As it is clearly marked the TX port and RX port use different wavelengths. If you choose a single-fiber WDM MUX/DEMUX on one side of the network, there should be a single-fiber WDM MUX/DEMUX which supports the same wavelengths but has the reverse order on the TX port and RX port of every duplex channel port. Please note, the line port of some  single-fiber CWDM MUX/DEMUXs is made into a duplex port, but one one port is function. Here takes the example of fiber-mart.COM FMU CWDM MUX/DEMUX as an example, as shown in the following picture, the single-fiber CWDM MUX/DEMUX has a duplex port, but one of the port marked as “N/A” is not in use.

 

single-fiber CWDM line-port

 

The Functioning Ports on CWDM and DWDM MUX/DEMUX

Except the above mentioned must-have channel ports and line port, WDM MUX/DEMUX can also be added with other ports which bring more profits to the existing WDM network. The following will introduce these special ports that are often added on CWDM and DWDM MUX/DEMUX.

Expansion Port

 

Expansion port added on WDM MUX/DEMUX is really useful. If you installed a CWDM network which just using several of the CWDM wavelengths, you can use this expansion port to increase the network capacity by connecting the expansion port with the line port of another CWDM MUX/DEMUX supporting different wavelengths. Then the network of this CWDM network can be increased easily. Both CWDM MUX/DEMUX and DWDM MUX/DEMUX support this expansion port. Kindly click the following picture for details of how to use expansion port.

WDM Expansion Solution

 

1310nm Port and 1550nm Port

The 1310nm and 1550nm are actually WDM wavelengths. How could these two wavelengths become special? It can be recognized that many fiber optic signals for are transmitted over 1310nm and 1550nm. Many fiber optic transceivers support long distances use these two wavelengths. However, the standard channel port on WDM MUX/DEMUX can only be connected to color coded fiber optic transceiver like CWDM SFP/SFP+ and DWDM SFP/SFP+. With these special designed 1310nm port and 1550nm port, the signal running through ordinary fiber optic transceivers can be combined together with other CWDM wavelengths.

 

Please note that DWDM MUX/DEMUX can only add special 1310nm port. For CWDM MUX/DEMUX, not all the wavelengths can be added, if you add special 1310nm or 1550nm port on the device. There is a simple rule for how to add the special ports and other standard channel ports on CWDM MUX/DEMUX. If you want to add 1310nm or 1550nm ports on your CWDM MUX/DEMUX, wavelengths which are 0-40nm higher or lower than 1310nm or 1550nm cannot be added to the MUX. The following table shows the specific details.

 

Monitor Port

Many technicians will add a monitor port on CWDM or DWDM MUX/DEMUX for better network monitoring and management. If you choose a single-fiber WDM MUX/DEMUX, the monitor port should be a simplex fiber optic port. For dual-fiber WDM MUX/DEMUX, you can add a duplex monitor port for the whole network monitoring, or just add a simplex port for MUX or DEMUX monitoring.

MUX/DEMUX monitor port

 

fiber-mart.COM WDM CWDM and DWDM Solution

The above mentioned ports are the most commonly used in WDM MUX/DEMUX. All these ports can be customized in fiber-mart.COM where affordable complete solutions for CWDM, DWDM and DWDM over CWDM network are available. Kindly contact sales@fiber-mart.com for more details if you are interested.

Popular ToR and ToR Switch in Data Center Architectures

Top of rack (ToR) is one common architecture of switch-to-server connections. According to a survey result in 2015, ToR was the most popularly used architecture both in colocation data centers and enterprise data centers. Seen from current trend, it will be widely deployed in the present and in the future as well.

 

“But, wait, what does a ToR look like? Is a top-of-rack switch placed at the top of the rack?”

 

Thanks for your questions. A ToR switch could be at the top of the rack, but the actual physical location does not necessarily need to be at the top of the rack. It can also be at bottom or middle of the rack. After practical installation, however, engineers found that top of the rack is better due to easier accessibility and cleaner cable management.

 

Benefits of ToR are many and in brief they are:

Copper stays “In Rack”.

Lower cabling costs.

Modular and flexible “per rack” architecture.

Future-proofing for higher speeds.

In a ToR design, at least one switch is placed in each rack and servers within the rack are connected to the switch typically via copper cable. Then switches in each rack are connected to top-tier switches.

 

In today’s leaf-spine topology, the ToR switches are the leaf switches and they are attached to the spine switches. For example, 10G servers are connected to a 10G ToR/leaf switch (it has 40G ports as well) via 10G SFP+ DAC (direct attach copper cable), or via Cat6a/Cat7 cable and . Then the 10G switch is connected to a 40G spine switch.

 

The combination of ToR and leaf-spine has solved some problems that existed in traditional three-tier (access-aggregation-core) topology, such as the “traffic jam” in top-tier switch. In a three-tier network topology, the data traffic will all take a single “best path” that is chosen from a set of alternative paths, until the point that it gets congested then packets are dropped.

 

In leaf-spine topology, to prevent any one uplink path from being chosen, the path is randomly chosen so that the traffic load is evenly distributed between the top-tier switches. If one of the top-tier switches were to fail, it only slightly degrades performance through the data center.

 

Since ToR is the most popular design of data center architecture, ToR switches naturally become popular as well. Here are some high performance ToR switches of different switch-to-server data rates, ranging from 1G to 100G.

 

All these ToR switches support L2/L3 features, IPv4/IPv6 dual stack, data center bridging and FCoE. ToR switches are often required to be multiport and the low-latency since they have to deal with different layers’ traffic.

 

In present, the 1G and 10G data rates still contribute to the largest portion of all switch-to-server connections, 40G and 100G ToR switches that can support multiple data rates are still not many. The 40G example and the 100G example I listed above are one the few multiport high speed ToR switches that are with low latency and high performance.