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What is a BiDi transceiver?

Introduction:

BiDi transceivers communicate using only one fiber, where traditional communication is with two lines of fiber. To achieve this they use two different wavelengths (colors). For the 10G, these are the 1270nm/1330nm combination. On one side you will have the transceiver which is sending out the 1330nm light and receives the 1270nm light - the other side has the mirror image so the optic will send 1270nm light and receives 1310nm light. The main advantage with these optics is that you can double your speed over a traditional optical fiber pair. You can also build a redundancy over a fiber pair if you use both the fibers with 10G. These 10G Bidi’s can also be used in a CWDM project when you use a MUX with a 1310nm wideband port.

BiDi transceivers are not in the portfolio of the bigger router and switch manufacturers like Cisco/Juniper and Huawei. Because they are so specialized, only companies whose sole focus is Optical Transceivers supply them. These optics are available in SFP+/SFP10G and in XFP form factors. The basic version can do 20km and there are 40km and 60km models as well. Versions above this are not on the market. The 80km version does not exist because it operates at lower band which has more attenuation then the traditional 1550 band.

Definition:

This new optical transceiver technology allows transceivers to both transmit and receive data to/from interconnected equipment through a single optical fiber. This technology has led to the development of Bi-Directional transceivers, or BiDi transceivers for short.
Difference between BIDI transceiver and Common transceiver

How BiDi transceivers work:

The primary difference between BiDi transceivers and traditional two-fiber fiber optic transceivers is that BiDi transceivers are fitted with Wavelength Division Multiplexing (WDM) couplers, also known as diplexers, which combine and separate data transmitted over a single fiber based on  the wavelengths of the light. For this reason, BiDi transceivers are also referred to as WDM transceivers.

To work effectively, BiDi transceivers must be deployed in matched pairs, with their diplexers tuned to match the expected wavelength of the transmitter and receiver that they will be transmitting data from or to.
If paired BiDi transceivers are being used to connect Device A (Upstream) and Device B (Downstream), as shown in the figure below, then:
  • Transceiver A’s diplexer must have a receiving wavelength of 1490nm and a transmit wavelength of 1310nm
  • Transceiver B’s diplexer must have a receiving wavelength of 1310nm and a transmit wavelength of 1490nm
Diplexers at Work in BIDI optical Ethernet transceivers

QSFP BiDi Transceiver Solution

There exist three types commonly used BiDi transceivers: BiDi SFP+ transceivers, BiDi XFP Transceivers and QSFP BiDi transceivers. As BiDi SFP+ transceivers and BiDi XFP transceivers are designed for bidirectional 10G serial optical data communications, QSFP BiDi transceivers allow reuse of existing 10G fiber infrastructure for 40G connections. In this part, we will discuss QSFP BiDi transceiver in detail.

40G QSFP BiDi transceiver has two 20G channels, each transmitted and received simultaneously on two wavelength over a single MMF strand (OM3 or OM4). It allows the existing 10G cabling system to be repurposed for 40G connectivity. Which means it lets you bring 40G speeds to the access layer using the same 10G cable plant you are using today. In contrast, the general QSFP SR4 transceiver like Cisco QSFP-40G-SR4 requires new patch cables and patch panels since the connector types differ and the size of the fiber trunk needs to be quadrupled.
40G QSFP BiDi transceiver
The QSFP-40G-SR-BD transceiver transmits full-duplex 40G traffic over one dual-fiber LC-connector OM3 or OM4 MMF cable. It is capable of reusing 10G fiber infrastructure. That’s to say it enables data center operators to upgrade to 40G connectivity without making any changes to the previous 10G fiber cable plant. It is a huge cost savings, whether you are upgrading your current data center or building a new one. And it means you can start taking advantage of 40G performance for your organization right now.

Advantages of BiDi transceivers:

The obvious advantage of utilizing BiDi transceivers, such as SFP+- BiDi and SFP-BiDi transceivers, is the reduction in fiber cabling infrastructure costs by reducing the number of fiber patch panel ports, reducing the amount of tray space dedicated to fiber management, and requiring less fiber cable.While BiDi transceivers (a.k.a. WDM transceivers) cost more to initially purchase than traditional two-fiber transceivers, they utilize half the amount of fiber per unit of distance. For many networks, the cost savings of utilizing less fiber is enough to more than offset the higher purchase price of BiDi transceivers.

Cisco BiDi:

Cisco 40-Gbps QSFP BiDi transceiver reduces overall costs and installation time for customers migrating data center aggregation links to 40-Gbps connections.As a result of data center consolidation, server virtualization, and new applications that require higher data transport rates, the data center network is shifting to 10 Gbps at the access layer and 40 Gbps at the aggregation layer. A broad portfolio of high-performance and high-density 10- and 40-Gbps Cisco Nexus Family switches is available at attractive prices for this transition. However, to support 40-Gbps connectivity, data center architects are challenged by the need for a major upgrade of the cabling infrastructure, which can be too expensive or disruptive to allow data centers to quickly adopt and migrate to the 40-Gbps technology.Cisco solves this problem with innovative 40-Gbps Quad Small Form-Factor Pluggable (QSFP) bidirectional (BiDi) technology that allows reuse of existing 10-Gbps fiber infrastructure for 40-Gbps connections.

Conclusion:

BiDi transceivers can be produced either with SC or LC simplex port, that is used both transmission and receiving. By offering a standard, hot swappable electrical interface, it can support a wide range of physical media, from copper to long-wave single-mode optical fiber, at lengths of hundreds of kilometers. The most typical wavelength combination is 1310/1490, 1310/1550 and 1490/1550.

Please click to check more related concepts:

Transceivers Package
Transceivers Wavelength
Fiber mode
Type of inrerfaceTransceiver Terminology
SFP
Bidi
Single-mode

LC

Ethernet Port
SFP+
DWDM
Multi-mode

LX
XFP
WDM


EX
QSFP+



Cloud
X2



802.3 Standard
GBIC



Sfp Ports
CFP



Laser Diode
CSFP



Dark fiber




GPON




EPON




IEEE 802.3




Linux PAM module




Opto Electronics




PAM




PON

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