Category: Fiber Transceivers

Optical transceivers, Active Optic Cables, data center switches, and cable management in data centers.

Compatible Test of Cisco QSFP-40G-SR4 Optics

When purchasing the third party optics, customers usually suffer from the poor quality and compatibility issue, which is the major obstacle of OEM market. Just as a saying goes, what is good is not cheap. However, this article will prove that the cost-effective OEM optics from fiber-mart.COM are well worth the penny.
fiber-mart.COM, as a professional and reliable manufacturer and supplier of compatible optical transceiver, provides a series of self-developed products which can be highly compatible with many major brands, such as Cisco, HPE, Juniper, Brocade, Arista, etc. In this blog, we are going to present a compatibility testing of our hot-selling Cisco compatible QSFP-40G-SR4 optics on Cisco Nexus 9396PX.
Before we come to the major part, let’s have a brief overview of the 40G QSFP-40G-SR4 and the Cisco Nexus 9396PX switch. Cisco QSFP-40G-SR4 Compatible 40GBASE-SR4 QSFP+ transceiver is a short-range transceiver for 40 Gigabit Ethernet. It supports link lengths of 100m and 150m on laser-optimized OM3 and OM4 multimode fiber, respectively. Cisco QSFP-40G-SR4 enables high bandwidth 40G optical links over 12-fiber parallel fiber terminated with MPO/MTP multifiber connectors, which is also optimized to guarantee interoperability with any IEEE 40GBase-SR4 and 10GBase-SR.
Our Cisco compatible QSFP-40G-SR4 optics is fully tested with most Cisco platforms to ensure compatibility and compliance. Thus, it can be supported on a wide range of Cisco equipment, such as Cisco ASR 9000 series, Nexus 9000 series, Nexus 6000 series, and so on.
Cisco Nexus 9396PX Switch
Cisco Nexus 9396PX belongs to the Cisco Nexus 9000 series. It delivers a comprehensive line-rate layer 2 and layer 3 featuring in a two-rack-unit form factor. It can support 1/10/40 Gbps of switching capacity with forty-eight 1/10 Gigabit Ethernet SFP+ port and twelve 40 GE QSFP+ nonblocking ports. The main advantage of this switch is that you can reuse the existing 10 Gigabit Ethernet multimode cabling for 40 Gigabit Ethernet by connecting the 40Gb bidirectional transceiver. Figure 1 shows the Cisco Nexus 9396PX switch.
The Testing Procedure of the Cisco QSFP-40G-SR4 on Cisco Nexus 9396PX Switch
In fiber-mart.COM’s test center, we care of every detail from staff to facilities to ensure our customers to receive the optics with superior quality. Just take our hot-selling Cisco QSFP-40G-SR4 optics as an example, the procedure can be quite simple that can be concluded in three steps:
1. Plug the Cisco QSFP-40G-SR4 compatible QSFP+ into the 40-Gbps ports of the Nexus 9396PX
2. Plug the cleaned MTP patch cord into the optical ports of the transceivers
3. View the state of LED light and more information in the CLI.
Besides the above procedures, we also have a testing demo of QSFP-40G-SR4 Cisco compatible module testing on Nexus 9396PX.
Conclusion
At the end of the article, you must know the reason why fiber-mart.COM is the number one choice of compatible optical transceivers. Not only the Cisco QSFP-40G-SR4 optics, but other reliable compatible fiber optic transceivers from fiber-mart.COM are the best-seller products over the past years. If you are the major brand user like Cisco, HPE or Juniper, and want to cut down your budget this time, you might want to have a look at our cost-effective compatible fiber optic transceiver.

100G QSFP28 PSM4 to Address 500m Links in Data Center

100G QSFP28 PSM4 optics is a type of 100G optical transceiver that provides a low-cost solution to long-reach data center optical interconnects. 100G PSM4 (parallel single-mode 4 lane) standard is mainly targeted to data centers that based on a parallel single-mode infrastructure for a link length of 500 m. Compared with the hot-selling 100GBASE-SR4 and 100GBASE-LR4 optics, 100G QSFP28 PSM4 recently wins the popularity among the overall users. This article will provide a complete specification of the 100G QSFP28 PSM4 transceiver and explain the reason why people would need QSFP28 PSM4.
QSFP28 PSM4—A Low-Cost but Long-Reach Solution
100G QSFP28 PSM4 is compliant with 100G PSM4 MSA standard, which defines a point-to-point 100 Gb/s link over eight parallel single-mode fibers (4 transmit and 4 receive) up to at least 500 m. PSM4 uses four identical lanes per direction. Each lane carries a 25G optical transmission. The 100G PSM4 standard is now available in QSFP28 and CFP4 form factor. Table 2 shows the diagram of the 100G QSFP28 PSM4 Specification. 100G PSM4 is a low-cost solution. Its cost structure is driven by the cost of the fiber and the high component count. fiber-mart.COM offers the Cisco compatible 100G QSFP28 PSM4 at US$750.00.
As you can see in the above image, 100G QSFP28 PSM4 transceiver uses four parallel fibers (lanes) operating in each direction, with transmission distance up to 500 meters. The source of the QSFP28 PSM4 module is a single uncooled distributed feedback (DFB) laser operating at 1310 nm. It needs either a directly modulated DFB laser (DML) or an external modulator for each fiber. The 100GBASE-PSM4 transceiver usually needs the single-mode ribbon cable with an MTP/MPO connector.
Why Do We Need 100G QSFP28 PSM4?
100G PSM4 is the 100G standard that has been launched by multi-source agreement (MSA) to enable 500m links in data center optical interconnects. But as we all know, there are several popular 100G interfaces out there on the market, such as QSFP28 100GBASE-SR4, QSFP28 100GBASE-LR4, QSFP28 100GBASE-CWDM4, and CFP 100GBASE-LR4, etc. So with so many options, why do we still need 100G QSFP28 PSM4?
To better help you make up your mind, you need to figure out the following questions:
Q1: What are the net link budget differences between PSM4, SR4, LR4 and CWDM?
Table 3 displays the detailed information about these 100G standards.
Note: the above diagram excludes the actual loss of each link (it is the ideal situation). In fact, WDM solution are at least 7 db worse link budget than PSM4. For a 2 km connectivity, a CWDM module will have to overcome about 10 db additional losses compared to PSM4. And the 100G LR4 optics at 10 km is 12 db higher total loss than PSM4.
Q2: What power targets are achievable for each, and by extension what form factors?
According to the IEEE data sheet, the WDM solutions cannot reasonably fit inside QSFP thermal envelop, while PSM4 can fit inside the QSFP thermal envelope. That means you would need the extra power for the WDM solution of your network. But if you use the QSFP PSM4, this won’t be a problem.
All in all, a 100G QSFP28 PSM4 transceiver with 500m max reach is a optional choice for customers. Because other 100G optics are either too short for practical application in data center or too long and costly. QSFP28 PSM4 modules are much less expensive than the 10 km, 100GBASE-LR4 module, and support longer distance than 100GBASE-SR4 QSFP28.
Summary
QSFP28 PSM4 is the lowest cost solution at under one forth the cost of either WDM alternatives. 100G QSFP28 PSM4 can support a link length of 500 m, which is sufficient for data center interconnect applications. 100G QSFP28 PSM4 also offers the simplest architecture, the most streamlined data path, higher reliability, an easy upgrade path to 100G Ethernet.

100G Direct and Breakout Cabling Solutions

With the emerging high-speed network standards and rapidly advancing technology, fiber optic network is driven to meet the growing demand for faster access to larger volumes of data. Although 10G/40G Ethernet becomes the mainstream of telecommunication market nowadays, organizations of all sizes still need to be prepared to integrate speeds of 100G and beyond. For data center networking, users can choose different solutions based on the different transmission distance need. In general, there are two kinds of 100G fiber optic solutions: direct cabling and breakout cabling. It is essential for users to understand the detailed information of each type of solution in order to select the one that meets their current and future connectivity needs.
How 100G Optics Develop
After the IEEE completing the certification of the first 100G standard for Ethernet networks, the transceiver industry launched a new type of form factors for 100G connectivity—CFP (“C” for 100, and FP for Form factor Pluggable). Compared to the most popular 40G QSFP, the size of CFP transceiver is huge. And most CFP implementations doubled the power consumption per bit. Furthermore, the price per bit increased by a factor of ten. These disadvantages becomes the main obstacles of the popularity of 100G CFP transceivers.
The next version of 100G form factors is the CFP2, CFP4, and the CPAK that are improved upon the CFP. But when compared to the popular 10G SFP+ and 40G QSFP+, none of these new members of the CFP family improved density, power consumption, or cost. Fugure 1 shows the size comparison between CFP2, CFP4 and QSFP28 modules.
Then here came the 100G QSFP28. The QSFP28 is the exact same footprint as the 40G QSFP+. The 100G QSFP28 is implemented with four 25-Gbps lanes, Just as the 40G QSFP+ is implemented using four 10-Gbps lanes. In all QSFP versions, both the electrical lanes and the optical lanes operate at the same speed, eliminating the costly gearbox found in CFP, CFP2, and the CPAK. The 100G QSFP28 makes it as easy to deploy 100G networks as 10G networks. When compared to any of the other alternatives, 100G QSFP28 increases density and decreases power and price per bit. That’s why it is fast becoming the universal data center form factor. The following part will move on to talk about the 100G optic cabling solutions.
100G Direct Cabling Solutions
QSFP28 transceiver utilizes either fiber or copper media to achieve 100GbE communication in each direction. This transceiver has 4 individual 25GbE lanes which can be used together to achieve 100GbE throughput or separately as 4 individual 25GbE connections (using 4 SFP28 modules).
For 100G short-reach direct cabling within 100m, 100GBASE-SR4 QSFP28 optical module and 100G QSFP28 cable are good choice. Just from the table list of fiber-mart.COM 100G optical modules and cables, we know that 100GBASE-SR4 QSFP28 modules can support up to 100 m on OM4 12 fiber multimode MTP cable. And 100G QSFP28 to QSFP28 direct attach copper cable can support up to 5m and 100G QSFP28 to QSFP28 active optical cable can support up to 10m. Figure 2 describes a 100G direct cabling with the use of QSFP28 to QSFP28 DAC and AOC cables.
For 100G long-haul direct cabling, like 10km, both 100GBASE-LR4 QSFP28 optical module and 100GBASE-LR4 CFP4 transceiver can support up to 10km on single-mode LC patch cables. For longer 100G direct cabling above 10km, the 100GBASE-ER4 CFP is the ideal choice as their transmission distances support up to 40 km.
100G Breakout Cabling Solutions
A breakout cable is a multi-strand cable, typically custom-made, which is divided into multiple duplex cables. For instance, a 40G breakout cable has four individual 10G duplex cables totaling eight strands, while a 100G breakout cable has 10 duplex cables and 20 strands. Figure 3 displays a simple 100G connectivity with 100GBASE-SR4 QSFP28 and QSFP28 to 4SFP28 breakout cables.
Between the 100G optical module and 25G optical modules, there always uses the breakout cables connected the two kinds of optical modules, and the common cable solutions are 100G QSFP28 to 4SFP28 Breakout AOC cables or 100G QSFP28 to 4x 25G SFP28 Breakout Direct Attach Passive Copper Cables.
The commonly used 100G breakout cabling solutions is 100G QSFP28 to 4SFP28 DAC. It’s easy to understand how this type of cable function. Just as the QSFP+ breakout cable, the 40GBASE-SR4 QSFP+ optical module at the one end can be connected to 4x10GBASE-SR SFP+ optical modules at the other end.
Conclusion
As IT infrastructures are planning to migrate to 100G data rate, network designers must carefully weigh alternative implementations of such links. With a variety of fibers already deployed, it is important to understand the interoperability of new optics with existing fibers. And for 100G deployment, you are supposed to understand the benefits and challenges of each type of the fiber optic solutions before taking an action. fiber-mart.COM’s 100G FHD series covers a full range of 100G optical transceivers and cables, like CFP, CFP2, CFP4, QSFP28, as well as 100G QSFP28 to QSFP28 DAC, 100G QSFP28 to 4SFP28 DAC. Besides the above products, 100G FHD Fiber Enclosures, 100G FHD MTP Modular Cassettes, 100G 160 Fiber 2U Panels and 100G CFP SR10 Cables are also provided. If you want to know more about our products, please contact us directly.

Guide to Several Materials in Fiber Optic Cable Construction

Fiber optic cable is considered as one of the most effective transmission medium today for safe, and long-reach communications, and it also offers a number of advantages over copper. In general, fiber optic cable consists of a core, cladding, coating, strengthening fibers, and a cable jacket, which has been clearly introduced in the previous article. Today’s article will focus on the several materials in fiber optic cable construction, as well as their features and applications.
PVC (Polyvinyl Chloride)
Polyvinyl Chloride (PVC) is one of the most commonly used thermoplastic polymers in the world. The PVC cable is typically used for patch connections in the data center, wiring closet, and at the desktop. PVC is produced in two general forms, first as a rigid or unplasticized polymer (RPVC or uPVC). The following image shows a ST single-mode pre-Terminated cable (0.9mm PVC Jacket).
Features:
Good resistance to environmental effects. Some formulations are rated for -55 to +55.
Good flame retardant properties. Can be used for both outdoor and indoor fiber optic cables.
PVC is less flexible than PE (Polyethylene).
PE (Polyethylene)
Polyethylene is a kind of polymer that commonly categorized into one of several major compounds of which the most common include LDPE, LLDPE, HDPE, and Ultrahigh Molecular Weight Polypropylene. Polyethylene fiber has a round cross section and has a smooth surface. Fibers made from low molecular weight polyethylene have a grease like handle.
Features:
Popular cable jacket material for outdoor fiber cables
Very good moisture and weather resistance properties
Very good insulator
Can be very stiff in colder temperatures
If treated with proper chemicals, PE can be flame retardant.
Kevlar (Aramid Yarn)
The word Aramid is a generic term for a manufactured fiber in which the fiber forming substance is a long chain synthetic polyamide in which at least 85% of the amide linkages are attached directly to the two aromatic rings as defined by the U.S. federal trade commission. Kevlar fiber is based on poly (P-phenylene terephthalamide). Aramid yarn is the yellow fiber type material found inside cable jacket surrounding the fibers. It can also be used as central strength members.
Features:
Aramid yarn is very strong and is used in bundle to protect the fibers.
Kevlar is a brand of aramid yarn. Kevlar is often used as the central strength member on fiber cables which must withstand high pulling tension during installation.
When Kevlar is placed surrounding the entire cable interior, it provides additional protection for the fibers from the environment.
Steel Armor
The steel armored fiber cable, using light-steel tube, can provide maximum bend radius, strong protection and flexible cabling. Steel armor jacket is often used on direct burial outdoor cables and it provides excellent crush resistance and is truly rodent-proof. Since steel is a conductor, steel armored cables have to be properly grounded and loss fiber optic cable’s dielectric advantage. Armored fiber optic cable are often used in the outdoor direct burial cables and for the industrial environment where cables are installed without conduits or cable tray protection. The following image shows a single-mode armored fiber optic cable.
Various types of these light-steel armored fiber cables are in stock in fiber-mart.COM, including pre-terminated armored fiber patch cables, armored fiber trunk cables and field-terminated armored fiber cables for both indoor and outdoor applications.
Features:
Provides excellent crush resistance for outdoor direct burial cables
Protects cables from rodent biting
Decreases water ingress into the fiber which prolongs the fiber cable’s life expectancy
Central Strength Member
Strength member is used to increase the tensile force that will be applied on the cable during installation. Strength member will take the pulling force and will keep the fibers safe during installation. For large fiber count cables, a central strength member is often used.
The central strength member provides strength and support to the cable. During fiber optic cable installation, pulling eyes should always be attached to the central strength member and never to the fibers. On fiber splice enclosure and patch panel installations, the cable central strength member should be attached to the strength member anchor on the enclosure or patch panel.
Conclusion
When you choose to use which type of the fiber optic cables, the fiber optic cable construction, along with the mechanical and environment requirements should all be taken into account. All the above materials in the fiber optic cable construction are specifically required to meet the network infrastructure. fiber-mart.COM fiber optic cables come in various types with detailed specifications displayed for your convenient. These quality cables are designed with best-in-class performance. For more information about fiber optic cables or patch cords, you can visit fiber-mart.com.

Whether to Choose 40G DAC or AOC Cables

With the top trend for data center and enterprises to move to higher data rate like 40G, relevant products and technologies are developed to back this new speed (e.g. the 40G optical transceivers and cables). However, there are so many options out there on the market. Network users usually don’t know how to make a choice. Take the 40G cables as an example, the most commonly used 40G cables are the 40G direct attached cable (DAC) and active optical cable (AOC). Each has its unique specification and usage. Which would be the most suitable one for connecting signals across the rack in data center? This article will provide you an ideal answer from the aspect of cabling performance, transmission distance and cost.
Brief Overview of DAC and AOC Cables
QSFP DAC cable is a form of high-speed cable with “transceivers” on either end used to connect 40Gbqs switches to routers or servers. QSFP+ DAC cable usually comes in either active or passive versions. They are widely available for short-reach 40G interconnect (within 7 meter). 40G DAC cables transmit 40GbE over short distances of parallel coaxial copper cabling. It uses a special cabling assembly with four lanes of coaxial cabling. Each transmit 10 Gbps for a total data rate of 40 Gbps. QSFP to QSFP and QSFP to SFP+ cable are the two common types of 40G DAC cables. The picture below shows a QSFP to SFP+ DAC breakout cable connected in a switch.
AOC cable uses electrical-to-optical conversion on the cable ends to improve speed and distance performance of the cable while mating with electrical interface standard. Compared with DAC cables, its smaller size, longer transmission distance, lower insertion loss and electromagnetic interference immunity make it popular among subscribers. 40G AOC cables (see in the image below) can support longer distance than QSFP+ DAC cables (within 15m).
Comparison Between DAC and AOC Cables
After the brief introduction to the DAC and AOC cables, what to be considered next is the detailed comparison from the expects of cost, distance and cabling performance. The following chart shows a vivid comparison between them.
Cost
Cost is typically the No.1 factor affecting your selection. When it comes to 40G DAC cables, it is the same, although it’s quite clear that copper is much cheaper than optical cable. AOC, with connectors embedded with electronics and/or optics is the most expensive one. But it supports the highest transmission distance, many data centers won’t choose it because of the high cost.
While passive copper cable is much cheaper than AOC. However, the truth is that it cannot support 40G transmission in most cases in data center. Active copper cable is less expensive than AOC and can support longer transmission than passive copper cable seems to be a good choice. In this battle over cost, passive copper cable wins. But it is not suggested for 40G transmission in most cases.
Power Consumption
The main reason why DAC active copper cable and AOC can support longer transmission distance than passive cooper cable is that they are supported with active electronics. Passive copper cable requires no power. For 40G transmission, the power required for active copper cable is about 440mW, which is much less than that of AOC—2W. Thus, passive copper cable wins for its low power consumption.
Cooling System
Cooling is always crucial for data center, as it is closely related to the data center reliability and life of use. During DAC cable selection, two main factors can affect the cooling of data center. One is cable size. the other is the power consumption of direct attached cable. For the former factor, the thinner the cable is, the better dispersion devices in data center would have. AOC cable is the thinner than DAC cables. And DAC active copper cable is also thinner than passive cooper cable. The relation between power consumption and data center cooling is easy to understand. Higher power consumption can generate more heat in data center, which will load more burden on the data center cooling system. As mentioned before. AOC cable needs the highest power and DAC passive copper cable needs the lowest.
Transmission Distance
In the past, when the data rate required is less than 5 Gbps, the passive copper cables are used for interconnection. This type of DAC connects two SFP connectors by a copper cable, providing direct connection between cable ends via copper wire. Thus they are not expensive and robust with reliability. As it is passive, they need no power generally. However, when it comes to 40Gbps, they cannot satisfy such data rate in most cases. The passive copper cable with QSFP connectors attached on both ends can only support transmission 40 Gbps over very short distance. Thus passive copper cable is not suggested for regular 40G interconnection, unless 40G transmission is in very short distance.
Then AOC cable is introduced to overcome this challenge. Optical cables are thinner, flexible and can reach much longer distance up to 100 meters or more, which is much longer than that of the passive copper cable. However, AOCs are usually very expensive with the connectors attached on the active optical cable are embedded with optics and/or electronics. The connectors of the DAC active copper cable are embedded with electronics. Although they cannot support transmission distance as long as AOC, active copper cable can support longer transmission distance than that of the passive copper cable via copper wire. 40G transmission distance of active copper cable is about 15 meters.
To sum up, if you have a special requirement of the transmission distance. Then active optical cable wins with a transmission distance up to 100 meters. The active copper cable got the second place. And passive copper cable is at the last place. It is only suggested for 40G transmission over really short distance.
Conclusion
After comparing the performance of the DAC and AOC cables, we understand that the DAC passive copper cable is only suitable for really short-reach applications. While AOC cable possesses the best transmission performance but with higher cost in both material and daily use, and it needs more power as well. As for the DAC active copper cable, it can can support 40G transmission up to 15 meters with low power consumption, and satisfy the regular interconnection requirement for distance and cooling in most data center. What’s more, it is less expensive. fiber-mart.COM offers a full range of 40G QSFP cables including 40G DAC cable and AOC cables. Besides, the QSFP transceivers are also provided.

How to Choose Fiber Enclosure for Your Data Center

The data center is the heart of a fiber optic network. To ensure its long-term reliable network performance, all the optical equipment within data center should be well organized. However, the current multi-fiber counts and high-density optical cabling put strain in the cable management. Fiber patch enclosure provides solid fiber-optic-link protection and space-saving cable management, which is becoming a must-have component in data center. There are several fiber optic enclosures available on the market that are widely utilized in data center or server room. This article will briefly introduce the commonly used fiber enclosure designs to better meet your data center requirement. LC to LC fiber cable and patch panels are mounted in a fiber enclosure in the following picture.
Fiber Enclosure Designs
Rack mount fiber enclosure is the commonly used type in data center as it provide a convenient and rugged termination point for fiber jumper cables. This rack mount enclosures offer a flexible connectivity system using a variety of adapter plates and MPO cassettes. The enclosures work equally as well with armored cable as they do with multiple trunk cables and are available in 1U-4U versions.
1U enclosures fit standard 19-inch racks and have rear cable management rings. 2U, 3U and 4U enclosures are designed for side or rear trunk cable entry, have removable front and rear covers, edge guards on the front for cable assembly protection and front and rear cable management rings. 2U, 3U and 4U enclosures also fit standard 19 and 23-inch racks and have a clear plastic, removable front door that can be outfitted with a label for easy identification of connections.
Except for different size, there are two types of rack mount enclosures: fiber enclosure with a removable lid and slide-out fiber enclosure (see in the following figure). The slide-out version is typically more expensive than the other version. But slide-out fiber enclosure can allow customers to remove the whole enclosure from the rack, thus, it can provide easier internal fiber connection access.
As for the design of the fiber enclosure front panel, two commonly used types are fixed front panels and removable front panel. The fixed front panel can be loaded with appropriate fiber optic adapters, while the removable front pane can accommodate several fiber optic adapter panels or cassettes just as seen in the following image.
How to Select the Fiber Enclosure
If this is your first time to install a fiber optic network, you should follow the instructions below. Only in this way can you satisfy your installation requirement, and matched your budget as well.
Physical requirement
First, list all the requirement that will be mounted in the enclosure and their complete measurements:height, depth, width, weight. All of these figures will ultimately determine what type of fiber enclosure you will need. Note that always select a bigger fiber enclosure for all your existing equipment as well as for future proof.
Critical accessories
A fiber enclosure should provide plenty of grommeted access points through the rear and top of the cabinet, as well as through the bottom for raised floor installations. Not only are the fiber optic cables mounted in the fiber enclosure, but devices like hubs, routers, patch panels, and monitors are needed to be mounted in the enclosure-network.
All servers should be protected by an uninterruptible power supply(UPS) system, available in a variety of rack-mount configurations. Thus power protection is needed. Remember that any accessories that are not rack-mountable will require additional trays, shelves and mounting accessories.
Budget
Money is always a main considerations. Thus choose the fiber enclosure that can meet your premium features at a very competitive price is the number one task. People are usually in a dilemma about whether to choose a equipment that are suitable for now or the expensive one for future proof. It is hard to say, but a premium enclosure is a durable item that will provide services for years to come.
Summary
High density fiber enclosures can maximize the amount of active equipment in a data center by minimizing the footprint of the networking infrastructure, but there’s a problem—all that fiber in a small amount of space creates problems when changes need to be made. Therefore for easiest access, quick-release side panels should be a top priority when selecting an enclosure.
With several years of experience in fiber optic cabling solutions, fiber-mart.COM offers the world-class optical products and services to maximize the performance and scalability of your data center applications. Our fiber enclosures provide the highest fiber densities and port counts in the industry contributing to maximizing rack space utilization and minimizing floor space. For more detailed information, you can directly contact us.