SFP bidirectional vs unidirectional ：What's the difference?

The difference between bidirectional (BIDI) and unidirectional SFP modules lies in their design for transmitting and receiving optical signals:

1. Bidirectional (BIDI) SFP:

   • Single Fiber: BIDI SFP modules use a single fiber strand for both transmitting and receiving signals. This is achieved by using two different wavelengths, typically one for sending and another for receiving data. For example, a common configuration is 1310nm for one direction and 1550nm for the other.

   • Cost-Effective: Using a single fiber for both directions can reduce the cost of fiber cabling infrastructure.

   • Applications: BIDI SFPs are often used in scenarios where fiber resources are limited or where reducing cable complexity is a priority.
     
      

2. Unidirectional SFP:

   • Dual Fiber: Unidirectional SFP modules use separate fibers for transmitting and receiving signals. This means each module requires a pair of fibers, typically bundled in the same cable.

   • Same Wavelength: Both transmitting and receiving signals typically use the same wavelength. For instance, both may operate at 1310nm or 1550nm.

   • Applications: Unidirectional SFPs are standard in most fiber optic networks, especially in environments where fiber resources are not constrained.

In summary, the key difference is that BIDI SFPs use one fiber for two-way communication with different wavelengths, making them more cost-effective and ideal for environments with limited fiber availability. In contrast, unidirectional SFPs use separate fibers for each direction, which is a more traditional approach and is used in environments where fiber resources are abundant.

 

What do SFP bidirectional and SFP unidirectional represent respectively?

What is sfp bidirectional?

Bidirectional (BIDI) Small Form-factor Pluggable (SFP) is a type of optical transceiver used in networking equipment for communication over a single fiber optic cable. The key characteristics of a BIDI SFP include:

1. Single Fiber Use: Unlike traditional SFP modules that use separate fibers for transmitting and receiving data, BIDI SFP modules can send and receive signals over a single fiber strand. This is achieved through the use of two different wavelengths in one fiber.

2. Wavelength Division: BIDI SFPs typically operate on two different wavelengths, one for transmitting and another for receiving signals. Common wavelength pairs include 1310 nm/1550 nm or 1490 nm/1550 nm. This allows for full-duplex communication over a single fiber.

3. Cost and Space Efficiency: Because they only require one fiber for operation, BIDI SFPs can significantly reduce cabling costs and complexity. They are especially beneficial in scenarios where fiber resources are limited or expensive to expand.

4. Compatibility and Use: BIDI SFPs are compatible with standard SFP slots in networking hardware like switches, routers, and network interface cards. They are widely used in various applications, including metropolitan area networks, data centers, and in buildings where running multiple fibers may be impractical.

In summary, BIDI SFP modules offer a cost-effective and efficient way to achieve bidirectional communication over a single optical fiber, reducing the amount of cabling required for network infrastructure.

 

What is the advantage of sfp bidirectional?

Bidirectional Small Form-factor Pluggable (SFP) modules, commonly known as BiDi SFPs, offer several advantages in network configurations:

1. Reduced Fiber Usage: BiDi SFPs use a single fiber strand for both transmitting and receiving data. This halves the amount of fiber needed compared to traditional unidirectional SFPs, which require two separate fiber strands. This reduction in fiber usage can significantly lower infrastructure costs and complexity.

2. Cost Savings: The reduced need for fiber cabling not only simplifies the physical network layout but also reduces the overall cost of deploying and maintaining the network infrastructure.

3. Ease of Installation and Maintenance: With only one fiber to manage per connection, BiDi SFPs simplify the installation process. This can lead to quicker deployments and easier maintenance, as there's less cabling to manage and troubleshoot.

4. Efficient Utilization of Existing Infrastructure: In scenarios where existing fiber infrastructure is limited, BiDi SFPs can effectively double the capacity of the network without the need for additional cabling.

5. Wavelength Division: BiDi SFPs typically operate by using different wavelengths for sending and receiving data on a single fiber. Common configurations include 1310nm/1490nm or 1310nm/1550nm pairings. This allows for efficient data transmission and reception in a compact form factor.

6. Space-Saving: By requiring only one port for a single fiber, BiDi SFPs can help save valuable rack space in data centers or networking closets, which is particularly beneficial in dense deployment scenarios.

7. Compatibility and Flexibility: BiDi SFPs are designed to be compatible with standard SFP ports, making them a flexible option for upgrading existing networks or integrating into new deployments.

Overall, BiDi SFPs provide an efficient, cost-effective solution for data transmission in fiber optic networks, particularly in situations where fiber resources are scarce or expensive to expand.

 

How Does BiDi Module Work?

BiDi modules are equipped with WDM couplers/diplexers to combine or separate data transmitted over a single fiber using the different wavelengths of the light. Like traditional transceivers, BiDi transceivers should be deployed in pairs. However, for BiDis, we should use two modules: one for the upstream ("U") direction and another for the downstream ("D")—each part transmits at an opposite wavelength. For example, from point A we have installed a transceiver that transmits TX on 1310nm towards point B on a single fiber. In point B there is a transceiver that receives RX on 1310 nm and transmits back to point A on 1490nm on the same fiber. In point A the RX frequency is listening on 1490nm.

 

How Many BiDi Module Types?

The common types of BiDi transceivers used in today's networks are 1G/10G BiDi SFPs. The most common optical wavelengths for this transceiver are 1310/1490 nm, 1490/1550 nm, and 1310/1550 nm. They are designed for 1/10 GB deployment and can reach up to 80km distance. BiDi variants are also available for the form factor XFP X2 for 10G, GBIC for 1G.

The 25G SFP28 BiDi transceiver supports connections up to 10km over single-mode fiber and uses LC connectors. The wavelengths are 1330TX/1270RX and 1270TX/1330RX.

The 100G QSFP28 BiDi CWDM4 transceiver supports connections up to 2km over single-mode fiber and uses LC connectors. The wavelengths are 1271 nm, 1291 nm, 1311 nm, and 1331 nm.

The 40GBase QSFP+ BiDi has two 20G channels that support connections up to 100 meters on OM3 MMF and up to 150 meters on OM4 MMF. It uses an LC Duplex connector and the wavelength is 850nm. QSFP+ BiDi is a cost-effective solution for a 10G to 40G upgrade.

 

Why BiDi Module?

This single fiber BiDi transmission gradually becomes a popular and cost-effective solution for today's data center and IT infrastructure because of its unbeatable advantages:

• Double Your Network Capacity– One benefit of BiDi is that it allows you to make full use of all your fiber strands and can therefore double your network capacity. This is because one strand is used to carry information in both directions, for example, if you have a six-strand cable you would be able to utilize all six stands rather than three for one direction and three for the other.

• Reliability – Another benefit is increased reliability, single strand solutions are less prone to connection errors due to fewer connections and endpoints.

• Cost – With the reduction of fiber strands by half, the number of patch cords and patch panel ports can be reduced accordingly, as well as reducing the amount of tray space dedicated to fiber management.
  
   

Where BiDi Modules Are Used?

BiDi modules are usually deployed in applications like access PON networks deployment P2P (point-to-point) connection, Digital Video, and Closed Circuit Television (CCTV) applications. They can be installed on servers, switches, routers, OADM to provide high speed and stability optical transmission systems, and Metropolitan Area Networks (MAN). In addition, 25/50G BiDi transceivers are welcomed by 5G networks since they can save fiber resources and support high bandwidth, ultra-low latency, and high reliability for data transmissions.

 

BiDi SFP Applications

At present, the BiDi SFP is mostly used in FTTx deployment P2P (point-to-point) connection. A FTTH/FTTB active Ethernet network consists of a central office (CO) connecting to the customer premises equipment (CPE). BiDi SFP allows a bi-directional communication on a single fiber by using wavelength multiplexing (WDM), which makes CO and CPE connection more simple.

• Bidi SFP Cost high Save fiber

• SFP Cost low Not save fiber

ETU-Link Technology Co., Ltd provides a variety of BiDi SFPs. They can support different data rate and support transmission distance up to max 120 km that can meet the demands of today’s fiber services for carriers and enterprises.

 

What is SFP unidirectional ?

Unidirectional Small Form-factor Pluggable (SFP) modules, also known as traditional or standard SFPs, are optical transceivers used for network communication where separate paths are used for transmitting and receiving data. Key characteristics of unidirectional SFP modules include:

1. Separate Transmit and Receive Paths: Unlike bidirectional SFPs, unidirectional SFPs use two separate fiber strands – one strand for transmitting data and another for receiving data. This is a common setup in most fiber optic networks.

2. Same Wavelength for Transmitting and Receiving: In most unidirectional SFP modules, the same wavelength is used for both transmitting and receiving data. Common wavelengths include 850 nm for multimode fiber and 1310 nm or 1550 nm for single-mode fiber.

3. Compatibility and Use: Unidirectional SFP modules are widely used in various network devices such as switches, routers, and media converters. They are compatible with standard SFP slots and are commonly used in Ethernet and Fibre Channel applications.

4. Greater Distance and Bandwidth Capacity: Depending on the type (single-mode or multimode) and specifications, unidirectional SFPs can support longer distances and higher bandwidths compared to BIDI SFPs.

5. Increased Fiber Use: Since unidirectional SFPs require separate fibers for transmission and reception, they consume more fiber resources compared to BIDI SFPs. This can increase the cabling requirements and costs in large-scale deployments.

In summary, unidirectional SFP modules are the traditional choice for fiber optic communications, offering reliable performance over separate transmit and receive channels. They are widely used in network infrastructures where sufficient fiber resources are available.

 

What is the advantage of sfp unidirectional ?

Unidirectional Small Form-factor Pluggable (SFP) modules, also known as standard or traditional SFPs, offer several advantages for network setups:

1. Higher Compatibility and Standardization: Unidirectional SFPs are widely used and compatible with a vast array of networking equipment. They adhere to well-established industry standards, ensuring interoperability across different devices and systems.

2. Diverse Range of Options: There is a wide variety of unidirectional SFP modules available that cater to different needs, such as different data rates (1G, 10G, etc.), distances (short, medium, long reach), and types of fiber (single-mode, multimode). This diversity allows network designers to choose modules that precisely fit their specific requirements.

3. Simplicity in Troubleshooting and Diagnostics: Since transmission and reception occur on separate fibers, diagnosing and troubleshooting issues can be more straightforward. Isolating whether a problem is with the transmitting or receiving end can be easier compared to bidirectional modules.

4. Flexibility in Network Design: Unidirectional SFPs allow for more flexibility in network designs, especially in complex or large-scale deployments. They can accommodate various topologies and are not limited by the need to pair transmit and receive wavelengths on the same fiber.

5. Reliability and Performance: Unidirectional SFPs have a long track record of reliable performance in a wide range of networking environments. They are less susceptible to certain types of interference since the transmit and receive functions are separated onto different fibers.

6. Scalability: In networks that already have abundant fiber infrastructure, unidirectional SFPs can be a more straightforward choice, allowing for scalability and expansion without the need for significant changes to the existing setup.

7. Potentially Lower Costs for Short Distances: In scenarios where fiber availability is not an issue, such as in densely wired data centers, the cost advantage of bidirectional SFPs may be less pronounced, making unidirectional SFPs a cost-effective choice.

In summary, unidirectional SFPs are a versatile and reliable choice for many network environments, especially where there is an existing fiber infrastructure or where the requirements are varied and complex.

 

Unidirectional Link

Unidirectional links are the links for which either one of the transmission path has failed but not both. Cisco implementations have different mechanisms to detect unidirectional links and avoided the impact caused by them. The mechanisms are as below

• • UDLD – Unidirectional link detection, a Cisco preparatory L2 messaging protocol.

  • STP loop Guard –

  • Bridge assurance –

  • RSTP/MST dispute mechanism.
    
     

Why UDLD needed:

• A typical occurrence of this happens on GBIC interfaces or Small Form-Factor Pluggable (SFP) modules malformed where either RX or TX not working , or two ends connected via some dumb devices making port state up up.

• When there is unidirectional link, one end of the link (the one in blocking state) will not receive BPDUs and when BPDUs are not received on the blocked ports, they will transition through the STP states and start forwarding – when they shouldn’t. This can eventually cause instability on the network or bridging loops to occur.

What UDLD Do:

• UDLD uses echoing mechanism to detect the unidirectional links.

• UDLD actively monitors a port to see if the link is truly bidirectional.

• UDLD keeps the acquired information of the neighbors in a cache table.

• UDLD sends "hello" packets (also called "advertisements" or "probes")at regular interval (15 seconds) on every active interface to keep each device informed about its neighbors. When a hello message is received, it is cached and kept in memory at most for a defined time interval, called "holdtime" or "time-to-live" or “timeout value”,after which the cache entry is considered stale and is aged out.

• If a new hello message is received when a correspondent old cache entry has not been aged out yet, then the old entry is dropped and is replaced by the new one with a reset time-to-live timer.

• If UDLD messages suddenly ceased arriving, switch will try to reconnect its neighbor eighttimes and if this attempt fails take actions based on UDLD operation mode.

• Whenever an interface gets disabled and UDLD is running or UDLD is disabled on an interface, or the device is reset, all existing cache entries for the interfaces affected by the configuration change are cleared, and UDLD sends at least one message to inform the neighbors to flush the part of their caches. This mechanism is meant to keep the caches coherent on all the connected devices.

How UDLD detect unidirectional links:

• Both UDLD enabled switch ports discover each other by exchanging hello messages sent to well-known MAC address 01:00:0C:CC:CC:CC. Each switch sends its own device ID (normally device Serial number) along with the originator port ID and timeout value to its peer. Additionally, the receiving switch echoes back the ID/port pair of its neighbor. If the sending switch does not hear back the exact id/pair combination on sending port from neighbor peer within the holdtime expires, the port is suspected to be unidirectional.

• If UDLD message arriving from a neighbor contains the same ID/port originator pair as used by receiving switch this indicates a self-looped port and marked as unidirectional.

• If a switch port has detected a single neighbor bit that neighbor’s UDLD message contains more than one ID/port pair in list of detected neighbors , this can happen in shared media and an issue in UDLD’s capability to provide full visibility between all connected devices ( as UDLD meant to be work on point to point connections).

Note: - Sudden loss of UDLD messages arriving on a port is not the explicit UDLD detection condition; this is just a presumption that link might unidirectional and in this respects the two UDLD protocol operational/functional modes Normal and Aggressive differs on the reactive action taken.

Precautions for purchasing sfp bidirectional and sfp unidirectional :

When purchasing Small Form-factor Pluggable (SFP) modules, whether bidirectional (BiDi) or unidirectional, there are several key considerations to keep in mind to ensure that you select the right modules for your specific needs:

1. Compatibility with Network Equipment: Ensure that the SFP modules are compatible with your existing network switches, routers, and other hardware. Check the manufacturer’s specifications for compatibility.

2. Data Rate and Distance Requirements: Consider the data rate (such as 1G, 10G, etc.) and the distance that needs to be covered. BiDi SFPs are often used for shorter distances, whereas unidirectional SFPs can cover a broader range of distances.

3. Fiber Type: Determine the type of fiber you will be using - single-mode or multimode. This will influence the choice of SFP module, as they are designed specifically for one type of fiber or the other.

4. Wavelength Specifications: For BiDi SFPs, it’s crucial to match the wavelengths correctly, as they use a single fiber for both transmitting and receiving, but at different wavelengths.

5. Connector Type: Check the connector type (such as LC, SC, etc.) to ensure it matches your fiber cabling.

6. Vendor Lock-In: Be aware of vendor lock-in issues. Some network equipment manufacturers require their own branded SFPs, while others can work with third-party modules. Generic or third-party modules can be more cost-effective but ensure they are fully compatible.

7. Quality and Reliability: Consider the quality and reliability of the SFP modules. Research the vendor's reputation, and look for reviews or testimonials. High-quality modules reduce the risk of network downtime.

8. Warranty and Support: Check the warranty and support options available for the SFP modules. A good warranty and accessible technical support can be invaluable.

9. Regulatory Compliance: Ensure that the SFP modules comply with relevant industry standards and regulations.

10. Price: While it’s tempting to opt for the cheapest option, balance cost with the factors mentioned above. Investing in higher-quality modules can save money in the long run through better performance and reliability.

11. Environmental Conditions: Consider the operating temperature range and other environmental conditions where the SFPs will be used, especially if they are to be deployed in harsh or outdoor environments.

12. Future-Proofing: Think about future scalability. Ensure that the SFPs you purchase align with your potential future bandwidth and network expansion needs.

By taking these factors into account, you can make a more informed decision when purchasing SFP modules, ensuring they meet your specific requirements and provide a reliable, efficient solution for your network.