Connectivity Solutions for Parallel to Duplex Optics

Since we have discussed connectivity solutions for two duplex optics or two parallel optics in the last post (see previous post: Connectivity Solutions for Duplex and Parallel Optics), the connectivity solutions for parallel to duplex optics will be discussed in this article, including 8-fiber to 2-fiber, and 20-fiber to 2-fiber.

Parallel to Duplex Direct Connectivity

When directly connecting one 8-fiber transceiver to four duplex transceivers, an 8-fiber MTP to duplex LC harness cable is needed. The harness will have four LC duplex connectors and the fibers will be paired in a specific way, assuring the proper polarity is maintained. This solution is suggested only for short distance within a given row or in the same rack/cabinet.

8-fiber to 2-fiber direct connectivity

Figure 1: 8-fiber to 2-fiber direct connectivity

Parallel to Duplex Interconnect

This is an 8-fiber to 2-fiber interconnect. The solution in figure 2 allows for patching on both ends of the fiber optic link. The devices used in this link are recorded in the table below figure 2.

8-fiber to 2-fiber interconnect

Figure 2: 8-fiber to 2-fiber interconnect

Item Description
1 8 fibers MTP trunk cable (not pinned to pinned)
2 96 fibers MTP adapter panel (8 ports)
3 8 fibers MTP trunk cable (not pinned)
4 MTP-8 to duplex LC breakout module (pinned)
5 LC to LC duplex patch cable (SMF/MMF)

Figure 3 is also an interconnect for 8-fiber parallel QSFP+ to 2-fiber SFP+. This solution is an easy way for migration from 2-fiber to 8-fiber, but it has disadvantage that the flexibility of the SFP+ end is lacked because the SFP+ ports have to be located on the same chassis.

8-fiber to 2-fiber interconnect

Figure 3: 8-fiber to 2-fiber interconnect

Item Description
1 8 fibers MTP trunk cable (not pinned to pinned)
2 96 fibers MTP adapter panel (8 ports)
3 8 fibers MTP trunk cable (not pinned)
4 8 fibers MTP (pinned) to duplex 4 x LC harness cable

Figure 4 shows how to take a 20-fiber CFP and break it out to ten 2-fiber SFP+ transceivers. The breakout modules divide the twenty fibers into three groups, and ten LC duplex cables are used to accomplish the connectivity to SFP+ modules.

20-fiber to 2-fiber interconnect

Figure 4: 20-fiber to 2-fiber interconnect

Item Description
1 1×3 MTP breakout harness cable(24-fiber MTP to three 8-fiber MTP) (not pinned)
2 MTP-8 to duplex LC breakout module (pinned)
3 LC to LC duplex cable (SMF/MMF)
Parallel to Duplex Cross-Connect

There are two cross-connect solutions for 8-fiber parallel to 2-fiber duplex. The main difference for figure 5 and 6 is on the QSFP+ side. The second cross-connect is better for a greater distance between distribution areas where the trunk cables need to be protected from damage in a tray.

8-fiber to 2-fiber cross-connect (1)

Figure 5: 8-fiber to 2-fiber cross-connect (1)

Item Description
1 8 fibers MTP trunk cable (not pinned)
2 MTP-8 to duplex LC breakout module (pinned)
3 LC to LC duplex cable (SMF/MMF)

8-fiber to 2-fiber cross-connect (2)

Figure 6: 8-fiber to 2-fiber cross-connect (2)

Item Description
1 8 fibers MTP trunk cable (not pinned to pinned)
2 96 fibers MTP adapter panel (8 ports)
3 8 fiber MTP trunk cable (not pinned)
4 MTP-8 to duplex LC breakout module (pinned)
5 LC to LC duplex cable (SMF/MMF)
Conclusion

These solutions are simple explanations to duplex and parallel optical links. It seems that the difference between each solution is not that significant in plain drawing, but actually the requirements for components are essential to an efficient fiber optic network infrastructure in different situations. Whether it is a narrow-space data center or a long-haul distribution network that will mostly determine the cabling structure and the products used.

Which Fiber Loopback Should I Use for My Transceiver?

In telecommunication, fiber loopback is a hardware designed to provide a media of return patch for a fiber optic signal, which is typically used for fiber optic testing or network restorations. When we need to know whether our fiber optic transceiver is working perfectly, we can use a fiber loopback cable as an economic way to check and ensure it. Basically, the loopback aids in debugging the physical connection problem of the transceiver by directly routing the laser signal from the transmitter port back to the receiver port. Since fiber optic transceivers have different interface types and connect different types of cables, it is not that simple to choose a right loopback for our transceiver. This post will be a guide on how to choose a right loopback cable for specific transceiver module.

Fiber Loopback Types and Configurations

Before deciding which loopback cable to use, we should firstly know the structure and classification of fiber loopback cable. Generally, a fiber loopback is a simplex fiber optic cable terminated with two connectors on each end, forming a loop. Some vendors provide improved structure with a black enclosure to protect the optical cable. This designing is more compact in size and stronger in use. Based on the fiber type used, there is single-mode loopback and multimode loopback, available for different polishing types. According to the optical connector type of the loopback, fiber loopback cables can be divided to LC, SC, FC, ST, MTP/MPO, E2000, etc. In testing fiber optic transceiver modules, the most commonly used are LC, SC and MTP/MPO loopback cables.

lc&sc loopback cable
Figure 1: LC & SC Loopback Cable

The LC and SC loopbacks are made with simplex fiber cable and common connectors; it’s not difficult to understand their configurations. As for the MTP/MPO loopback, it is mainly used for testing parallel optics, such as 40G and 100G transceivers. Its configuration varies since the fiber count is not always the same in different applications.

8 Fibers MTP/MPO Loopback Cable Configuration

In a 8 fibers MTP/MPO loopback, eight fibers are aligned on two sides of the connector, leaving the central four channels empty. And the fibers adopt a straight configuration of 1-12, 2-11, 5-8, 6-7. The polarity channel alignment is illustrated in the following figure.

8 Fibers Loopback Polarity Channel Alignment
Figure 2: 8 Fibers Loopback Polarity Channel Alignment
12 Fibers MTP/MPO Loopback Cable Configuration

The only difference between the 12-fiber MTP loopback and the 8-fiber loopback is that the central four channels are not empty. Its alignment is 1-12, 2-11, 3-10, 4-9, 5-8, 6-7.

12 Fibers Loopback Polarity Channel Alignment
Figure 3: 12 Fibers Loopback Polarity Channel Alignment
24 Fibers MTP/MPO Loopback Cable Configuration

The 24 fibers MTP loopback also adopts type 1 polarity. Its alignment design is shown below.

24 Fibers Loopback Polarity Channel Alignment
Figure 4: 24 Fibers Loopback Polarity Channel Alignment
Which to Choose for a Specific Transceiver?

Considering the common features of the transceiver and the loopback, we should think about the connector type, polish type, and cable type when selecting a loopback for the transceiver. The selection guide for some mostly used transceiver modules is summarized in the following tables.

Table 1: Loopback choices for 10G SFP+ transceivers

Model Interface type Cable Type Suited Loopback
10GBASE-USR LC Duplex (PC) MMF

LC/UPC Duplex Multimode Fiber Loopback

10GBASE-SR LC Duplex (UPC) MMF
10GBASE-LR LC Duplex (UPC) MMF
10GBASE-ER LC Duplex (UPC) SMF

LC/UPC Duplex Single-mode Fiber Loopback

10GBASE-ZR LC Duplex (PC) SMF

Table 2: Loopback choices for 40G QSFP+ transceivers

Model Interface type Cable Type Suited Loopback
40GBASE-CSR4 MTP/MPO (UPC) MMF

8/12 Fibers MTP/UPC Multimode Fiber Loopback

40GBASE-SR4 MTP/MPO (UPC) MMF
40GBASE-PLRL4 MTP/MPO (APC) SMF

8/12 Fibers MTP/APC Single-mode Fiber Loopback

40GBASE-PLR4 MTP/MPO (APC) SMF
40GBASE-LR4 LC Duplex (PC) SMF

LC/UPC Duplex Single-mode Fiber Loopback

40GBASE-LR4L LC Duplex (UPC) SMF
40GBASE-ER4 LC Duplex (UPC) SMF
40GBASE-LX4 LC Duplex (UPC) MMF/SMF

LC/UPC Duplex Multimode/Single-mode Fiber Loopback

Table 3: Loopback choices for 100G QSFP28 transceivers

Model Interface type Cable Type Suited Loopback
100GBASE-SR4 MTP/MPO (UPC) MMF

8/12 Fibers MTP/UPC Multimode Fiber Loopback

100GBASE-PSM4 MTP/MPO (APC) SMF

8/12 Fibers MTP/APC Single-mode Fiber Loopback

100GBASE-LR4 LC Duplex (UPC) SMF

LC/UPC Duplex Single-mode Fiber Loopback

Table 4: Loopback choices for CFP transceivers

Model Interface type Cable Type Suited Loopback
40GBASE-SR4 CFP MPO/MTP (UPC) MMF

8/12 Fibers MTP/UPC Multimode Fiber Loopback

40GBASE-LR4 CFP SC Duplex (UPC) SMF

SC/UPC Duplex Single-mode Fiber Loopback

40GBASE-FR CFP SC Duplex (UPC) SMF
100GBASE-LR4 CFP SC Duplex(PC/UPC) SMF
100GBASE-ER4 CFP SC Duplex(PC/UPC) SMF
100GBASE-SR4 CFP MPO/MTP (UPC) MMF

24 Fibers MTP/UPC Multimode Fiber Loopback

Conclusion

This post discusses specific fiber loopback choices for some most commonly used fiber optic transceivers. For other transceiver modules that are not mentioned in this post, we can also know how to choose a suitable loopback for it by getting details about its interface type, physical contact and cable type.

MTP Specifications and Deployment for 40GBASE-PLRL4 QSFP+

Commonly, QSFP+ transceiver designed with LC interface works with single-mode fiber for long distance application, while QSFP+ transceiver with MTP/MPO interface is used over multimode fiber for short distance transmission. For instance, 40GBASE-ER4 QSFP+ is designed with LC duplex interface, and it supports maximum transmission length of 40 km over single-mode LC duplex fiber; 40GBASE-SR4 QSFP+ with MTP/MPO interface supports a transmission distance no more than 150m over multimode fiber. However, in order to meet user’s diverse needs in real applications, some 40G transceivers are designed not following this rule, like 40GBASE-PLRL4 (parallel LR4 Lite). This transceiver is with MTP/MPO interface design but is used over single-mode fiber for long distance transmission. This article will introduce the MTP/MPO specifications for this transceiver and its deployment cases.

40GBASE-PLRL4 transceiver

MTP Specifications for 40GBASE-PLRL4 QSFP+

QSFP-40G-PLRL4 transceiver uses MTP-12 interface to achieve parallel transmission, supporting maximum data links up to 1.4 km. The cable type required for 40GBASE-PLRL4 is an APC (angle polished connector) single-mode MTP-12 cable. The cable is similar to the 40G-SR MTP or MPO, with the only change being the use of single-mode fiber. UPC (ultra polished connector) is another type of connector for MTP-12 cables, but it is not suited for single-mode fiber in market. APC is the only available type for single-mode MTP-12 fiber. The MTP-12 connector plugged into the QSFP-40G-PLRL4 transceiver carries the 40G signal over only 8 of the 12 fibers, remaining four fibers unused, and these four can optionally be not presented in the cable for economic reason. The used 8 fibers are mapped as 4x10G Tx and Rx pairs. In addition, the MTP cables connected to QSFP-40G-PLRL4 transceiver can be either MTP trunk cables or MTP splitter cables.

Deployment of 40GBASE-PLRL4 QSFP+

The QSFP-40G-PLRL4 is optimized to guarantee interoperability with any IEEE 40GBASE-LR4 and 10GBASE-LR. So when the link for 40G network and 10G to 40G migration is less than 1.4 km, it will be very appropriate to use 40GBASE-PLRL4 QSFP+ transceiver with single-mode MTP cables.

In the first case, you can choose a MTP trunk cable together with the 40GBASE-PLRL4 QSFP+ module for direct 40G connection. The following picture shows two 40GBASE-PLRL4 QSFP+ transceivers connected by a single-mode 12-fiber MTP trunk cable.

40GBASE-PLRL4 QSFP+ for 40G connection

In the second case, you can simply use an 8-fiber MTP to 4xLC duplex harness cable with one 40GBASE-PLRL4 QSFP+ and four 10GBASE-LR SFP+ to achieve 10G to 40G.

40GBASE-PLRL4 QSFP+ for 10G to 40G migration

You can see in the above two cases, MTP cable plays an important role and due to the special requirements of 40GBASE-PLRL4 for single-mode MTP APC fiber, it is necessary to choose the right MTP products connected to this 40G QSFP+.

Conclusion

40GBASE-PLRL4 QSFP+ module has special interface design which can be only compatible with single-mode MTP connector. During the deployment of 40GBASE-PLRL4 QSFP+ module, selecting proper MTP assemblies are essential to successfully accomplish the link. FS.COM is a professional fiber optic transceiver vendor and MTP product manufacturer, supplying compatible 40GBASE-PLRL4 QSFP+ transceiver of different brands, such as Cisco, Arista, Brocade, Huawei, etc. Also other customized compatible brands are available for your requirements. MTP cables and assemblies are available for same-day shipping at low prices, including customized 8 fibers MTP/MPO trunk cable. You will be surprised to see how many kinds of network devices FS.COM can offer and you will get more than cost-effective products but also impressive service.

Choose the Right Patch Cable for Your Transceiver Module

To a large extent, a fluent data transmission relies on the seamless transition between patch cables and fiber optic transceivers. As high bandwidth gradually dominates the market, patch cables and transceivers become much more essential to data transmission, especially for data transmission between the switches and equipment. But when you try to find the right patch cable for your transceiver, you may feel dazzling about the great variety of products. Don’t worry, this article will help you find the quickest way to choose the suitable product. But first, let’s have a look at the basic knowledge about patch cables and transceiver modules.

Overview of Patch Cables and Transceiver Modules

A patch cable or patch cord is an electrical or optical cable used to connect one electronic or optical device to another for signal routing. It is composed of an electrical or optic cable terminated with connectors on the ends. Optical patch cables are now widely used in data centers for data transmission. They have different fiber connectors including LC, SC, ST, FC, MTRJ, E2000, MU, MPO/MTP, etc. As for fiber types, there are also single-mode patch cables and multimode patch cables. Single-mode patch cables can further be classified into OS1 and OS2. While the multimode can be further divided into OM1, OM2, OM3 and OM4.

fiber-vs.-copper

Transceiver is a self-contained component that can both transmit and receive. It is often inserted in devices such as switches, routers or network interface cards which provide one or more transceiver module slot. Many transceivers types, such as SFP, X2, XENPAK, XFP, SFP+, QSFP+, CFP, etc. are used for various applications. The transceiver accepts digital signals from the Ethernet device and converts them to optical signals for transmission over the fiber.

Several Aspects to Consider
Transmission Media

Two kinds of transmission media can be found in the network. They are optic fiber cable and copper cable. Therefore, transceivers also have two types based on transmission media — copper based transceivers and fiber optic based transceivers. Copper based transceivers like 100BASE-T SFP, 1000BASE-T SFP are the commonly used types. They have a RJ45 interface to connect with the copper cables. Generally, cat 5, cat 6 and cat 7 cables attached with RJ45 connectors are typically linked to the copper based transceivers.

Compared with copper based transceivers, fiber optic transceivers support higher data rates for over 100 Gbps. The supported fiber patch cables are more complicated for selection. Usually single-mode and multimode fiber patch cables are used. But according to different transmission rates and transmission distance, further choices should be made.

Transmission Rate and Distance

It is known that data rate decreases as the transmission distance increases in fiber optic cables. Multimode fiber optic cables are often used for short distances due to the high cost of single-mode optical cables. But single-mode patch cables have better performance for different data rates in both long and short distances. Thus, if your transceiver supports high data rate over long distance, single-mode should be a better choice, and vice versa.

Transceiver Interface

Interfaces are also important to the selection of patch cables that match with transceivers. Optical transceivers usually use one port for transmitting and one port for receiving. Cables with duplex SC or LC connectors are typically employed to connect with this type of fiber optic transceivers. However, for BiDi transceivers only one port is used for both transmitting and receiving. Thus, simplex patch cables are used with BiDi transceivers.

Other high data rate transceivers like 40G/100GBASE QSFP+ often use MTP/MPO interfaces. They should be connected to the network with multi-fiber patch cords attached with MTP/MPO connectors. If these ports are used for 40 G to 10 G or 100 G to 10 G connections, fanout patch cables should be used.

transceiver-and-patch-cords

Conclusion

Knowing the transmission media, transmission data rate and distance, transceiver interfaces can give you a general direction of which type of patch cables should be chosen. Only matched patch cables and transceiver modules can provide better performance.

100G Optical Transceiver Solutions

Network has been rapidly developed over the years. People are always dreaming of entering into the world of higher bandwidth. And now the dream has come true since we already reach the 100 gigabit Ethernet (100 GbE) networking. This technology enables the transmission at rates of 100 gigabits per second (100 Gbit/s). The standard was first defined by the IEEE 802.3ba in 2010. To accommodate the trend, different types of 100G optical transceiver emerge as a reflection of the development. QSFP28 (quad small form-factor pluggable 28), CFP (centum form-factor pluggable) and CXP (centum extended-capability form-factor pluggable) are most commonly used optical transceiver solutions for 100G active equipment. Today, the article will mainly introduce these three solutions.

100G Transceiver Solutions
CFP

Specified by a multi-source agreement (MSA) between competing manufacturers, CFP was designed to replace many former transceivers like SFP+, SFP, XFP with a significantly larger support of 100 Gbps. The electrical connection of a CFP uses 10 x 10Gbps lanes in each direction (RX, TX). The optical connection can support both 10 x 10Gbps and 4 x 25Gbps variants. In addition, there are another two CFP next-generation 100G form factors — CFP2 and CFP4. Compared to the existing CFP, CFP2 and CFP4 are respectively double and quadruple front panel port density. All of them are now available on the market.

CFP

QSFP28

QSFP28 transceiver is designed for 100G Ethernet which uses the 4 x 25 wiring specification. It has the same size as 40G QSFP+ but with a higher performance. The 100G QSFP28 is implemented with four 25Gbps lanes. “28” stands for the highest possible rate of 4x28Gbps in transmission. Two basic versions of QSFP28 transceivers are 100GBASE-SR4 QSFP28 transceiver and 100GBASE-LR4 QSFP28 transceiver, which are respectively used for multimode fiber (MMF) and single-mode fiber (SMF) 100G applications. 100GBASE-SR4 QSFP28 operates at multimode fiber for a distance of 100 m. 100GBASE-LR4 QSFP28 can support a much longer distance of 10 km.

qsfp28
100GBASE-LR4 QSFP28
CXP

As a complement to CFP, CXP is also specified by MSA aiming at the clustering and high-speed computing markets. CXP has a higher density network interface with 45 mm in length and 27 mm in width, making it slightly larger than an XFP or 1/4 size of a CFP transceiver. It has a form-factor pluggable active device interface with 12 transmit and 12 receive lanes, capable of supporting bit-rates in excess of 10 Gbps per lane on a variety of optical transmission technologies.

cxp

Future Trend of Optical Transceivers in Data Centers

In the future, higher bit rates over 100G are the inevitable trend in data centers. The next data center developments will be following the 4x trend set by 40G and 100G, such as 200G, 400G, etc. Accordingly, optical transceivers should keep up with the steps and satisfy higher demands.

In 200G applications, next generation switching ASICs (Application Specific Integrated Circuits) are expected to have native port speeds of 50G and 128 ports, which correspond to a net throughput of 6.4 Tbps. This means that 200G QSFP modules (QSFP56, 4 x 50 Gbps) would result in a front panel bandwidth of 6.4 Tbps (32 x 200 Gbps).

For 400G applications, the module must accommodate either 16 x 25G or 8 x 50G electrical input lanes, which exceeds the 4 lanes defined for the QSFP. 400G transceivers will have larger size than QSFP. However, meeting the 3.5W power limit of QSFP modules appears infeasible for some 400G implementations. Thus, proposals for larger form factors for 400G can be anticipated from CFP MSA, which has had large success in 100G with CFP, CFP2, and CFP4. In this case, a key requirement will be that the size allows for at least 16 ports on the front panel in order to satisfy a net throughput of 6.4 Tbps (16 x 400 Gbps, and possibly more).

Conclusion

The market of 100G optical transceivers is accelerating. It is no doubt that more 100G transceivers and other assemblies will be deployed in data centers. QSFP28, CFP series and CXP are presently the most suitable solutions for 100G applications. Definitely one of them can solve your project needs.