Network Fiber Transceivers: A Comprehensive Guide

TransceiverStill asking for GBICs? Nothing says “I’ve been around” like referring to a transceiver as a GBIC, but I absolutely love hearing it! This guide will walk you through the different fiber transceiver technologies that are most popular today.

Since 1995, we’ve seen fiber transceivers come in more than 15 different form factors, but the SFP and the QSFP modules have paved this road of evolution.

Exploring the Spectrum of Optical Transceivers: From SFP to QSFP-DD

Wait, what?? What is an optical transceiver?  Optical transceivers are hardware components that send and receive data over fiber optic cabling by converting electrical signals into light pulses, and then back again to electrical signals on the other side. 

Compared to copper media, Fiber optic cabling can transport data over much longer distances, at much higher speeds, is about half the diameter, and is immune to electrical interference.

So, what options do we have?  Following the Gigabit Interface Converter (GBIC), Small Form-Factor Pluggable (SFP) were almost 1/3 of the size and by design the same size as an RJ-45 port.  Prior to the SFP, the max number of fiber interfaces a single line card or 1RU switch allowed was (16) X2 ports in a WS-X6516. So, the SFP became the gold standard and remains in the nomenclature today. The ‘Q’ in QSFP represents quad lanes available for transmitting. And the latest OSFP represents an Octal Small Form-Factor Pluggable with 8 lanes.

Types of Optical Transceivers

There are 10 primary versions of the SFP and QSFP form-factors that allow different transmission speeds, and there are various models within each of those categories as well that offer varying connectors, distances, media, etc.

1. SFP
2. SFP+
3. SFP28
4. SFP56
5. QSFP+
6. QSFP28
7. QSFP56
8. QSFP112
9. QSFP-DD
10. OSFP 

SFP  100mb and 1Gbps transmissions over ethernet, as well as 2G and 4G over Fibre Channel. These modules offer RJ-45 or LC connectors and transmits/receives over a single channel. There are 9 different options differing by distance, media, and 2 that use the fiber strands differently (channel, lane, and path are used interchangeably).

A quick note on the BiDi and CWDM parts. Both of these use a technology known as Wavelength Division Multiplexing (WDM). WDM allows the transceiver to transmit and receive 2 different wavelengths in opposing directions over 1 fiber effectively doubling the throughput capacity of the transceiver. A 10Gbps WDM transceiver allows 20Gbps of transmission.

SFP+ This is an “enhanced” version of the SFP that supports data rates of 10Gbps, as well as 4G, 8G, and 16G over Fibre Channel.  The SFP+ also communicates over a single lane and utilizes LC or RJ-45 connectors.

SFP28  Also the same physical characteristics as the SFP and SFP+, but with an upgraded electrical interface that can handle 25Gbps per lane over ethernet and 32Gbps over Fibre Channel.  All SFP28 transceivers utilize LC connectors.

SFP56 Again, same physical chassis of SFP, but uses PAM4 modulation, and is designed for 50Gbps and 100Gbps connections.  While SFP56 are currently only available with LC connectors, look for SFP56 to push copper to 50Gbps! 

Modulation is the process of converting data into radio waves. After the light signal is generated, it needs to be modulated, or packaged, with the electrical data signal.

QSFP+  The “Quad” Small Form-Factor Pluggable (QSFP) introduces 4 channels over a single fiber in a slightly larger form-factor.to allow 4x 10Gbps transmission totaling a 40Gbps throughput.  The QSFP+ also introduces MPO and MPT connection options.  MPO/MPT are capable of bundling multiple fibers in a single connector to support greater throughput.

QSFP28 The QSFP28 simply added 4 channels using the SFP28 technology allowing 4x 25Gbps per channel to total 100Gbps throughput capability.

QSFP56 - The QSFP56 is a slightly more complex improvement of the QSFP28 and was designed to support 200Gbps of throughput. The primary change is the modulation technology which uses PAM-4 rather than NRZ. Without going too much into the details, just think of NRZ as having a maximum transmission value of 25Gbps where PAM-4 allows 50Gbps. Rather than 4x25Gbps in the QSFP28, the QSFP56 transmits over 4 independent channels at 50Gbps totaling 200Gbps throughput. 

Modulation is the process of converting data into radio waves. After the light signal is generated, it needs to be modulated, or packaged, with the electrical data signal.

QSFP112 The QSFP112 pushes throughput capability to 400G. Uses 4 optical pairs, each channel operates at 50Gbps PAM4, resulting in a total of 8 fibers (4x TX and 4x RX). These transceivers can be used to connect a single 400G connection, or break out to 4x100G with a compatible cable.

QSFP-DD The QSFP-DD brings “double density” to the party. The QSFP-DD is built with an additional row of contacts allowing 4 channels of high-speed transmission up to 100Gbps totaling 400G throughput capability.

OSFP The OSFP or Optical Small Form-factor Pluggable doubles the capacity of the QSFP-DD. This transceiver has 8 channels for transmission each capable of 100Gbps totaling 800Gbps throughput capability with development of 200Gbps channels in the works totaling 1.6TB.  Some OSFP modules allow a "breakout mode" which enables the transceiver to connect with multiple lower bandwidth applications including QSFP-DD, QSFP56, QSFP28, and even some SFP28 and SFP+ form factors.

Edgeium Network Solutions

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In this blog post, we’ve explored optical transceivers from SFP to QSFP-DD, highlighting their evolution in response to the growing demands for speed and efficiency in network infrastructure. Whether you're upgrading an existing system or designing a new one, understanding the capabilities and specific applications of each transceiver type is essential.

As technology continues to advance, staying informed about these developments will ensure your network is ready to meet the challenges of tomorrow's data transmission demands.

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