{"id":19818,"date":"2026-07-16T06:41:24","date_gmt":"2026-07-16T06:41:24","guid":{"rendered":"https:\/\/www.fibermall.com\/blog\/?p=19818"},"modified":"2026-07-29T01:36:39","modified_gmt":"2026-07-29T01:36:39","slug":"qsfp-transceiver-40g-the-complete-sr4-lr4-er4-guide","status":"publish","type":"post","link":"https:\/\/www.fibermall.com\/blog\/qsfp-plus-40g-transceiver-guide.htm","title":{"rendered":"QSFP+ Transceiver 40G: The Complete SR4, LR4 & ER4 Guide"},"content":{"rendered":"\n

A data center architect told me last month that his team still runs 40G aggregation in every leaf-spine row. I asked why they hadn’t moved to 100G. His answer was simple: the upstream spine was 40G, the servers only needed 10G, and OM4 fiber was already in place. Buying QSFP28 optics would have left them throttled at 40G anyway.<\/p>\n\n\n\n

That conversation is exactly why this guide exists. A qsfp+ transceiver isn’t legacy dead weight in 2026. It’s a precision tool for brownfield 40G aggregation, 4\u00d710G breakout, and any network layer where 40G is the real bottleneck. You don’t always need the newest generation. You need the generation that matches the fiber, the port speed, and the budget.<\/p>\n\n\n\n

Below, you’ll get a complete variant matrix, a worked port\/cable\/power example, and a migration checklist that shows when to stay on 40G and when to move to 100G QSFP28. If you already know your fiber type, explore FiberMall’s optical transceiver solutions to compare compatible modules.<\/p>\n\n\n\n

\"What<\/figure>\n\n\n\n
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Table of Contents<\/p>\nToggle<\/span><\/path><\/svg><\/svg><\/span><\/span><\/span><\/a><\/span><\/div>\n

  • What Is a QSFP+ Transceiver?<\/a><\/li>
  • QSFP+ Transceiver Variants at a Glance<\/a><\/li>
  • The 4\u00d710G Lane Architecture<\/a><\/li>
  • SR4 vs LR4 vs ER4: Which Reach Do You Need?<\/a><\/li>
  • Connectors: MPO vs LC<\/a><\/li>
  • Power, Heat, and Cost per Gigabit<\/a><\/li>
  • 4\u00d710G Breakout: One QSFP+ Port, Four SFP+ Links<\/a><\/li>
  • A Worked Example: 40G Aggregation in a Leaf-Spine Row<\/a>
    • Option A: Four Individual SFP+ SR Links<\/a><\/li>
    • Option B: One QSFP+ SR4 Breakout Connection<\/a><\/li><\/ul><\/li>
    • QSFP+ Transceiver vs QSFP28: Stay, Migrate, or Hybrid?<\/a><\/li>
    • Vendor Compatibility and Coding Reality<\/a><\/li>
    • How to Choose a QSFP+ Transceiver<\/a><\/li>
    • FAQ<\/a>
      • What does QSFP+ stand for?<\/a><\/li>
      • What is the difference between QSFP+ and QSFP28?<\/a><\/li>
      • Can I use a QSFP+ module in a QSFP28 port?<\/a><\/li>
      • What is the difference between QSFP+ SR4 and LR4?<\/a><\/li>
      • How far can QSFP+ LR4 reach?<\/a><\/li>
      • Can QSFP+ be broken out to 10G?<\/a><\/li>
      • Does a switch still see one 40G interface after breakout?<\/a><\/li>
      • Is QSFP+ backward compatible with QSFP28?<\/a><\/li>
      • Can all QSFP+ SR4 modules support 4\u00d710G breakout?<\/a><\/li><\/ul><\/li>
      • Conclusion<\/a><\/li><\/ul><\/nav><\/div>\n

        <\/span>What Is a QSFP+ Transceiver?<\/strong><\/strong><\/span><\/h2>\n\n\n\n

        A qsfp+ transceiver is a hot-pluggable optical module that carries four 10 Gbps electrical lanes over a single physical port. QSFP+ stands for Quad Small Form-factor Pluggable Plus. The plus (+) marks the 40G Ethernet generation, not the older 4G QSFP used in Fibre Channel and InfiniBand.<\/p>\n\n\n\n

        The four lanes are aggregated into a 40 Gbps data transmission rate. The module follows the SFF-8436 mechanical specification and the IEEE 802.3ba 40GBASE family of standards. You can think of it as four SFP+ transceivers sharing one housing, one connector, and one switch port.<\/p>\n\n\n\n

        QSFP+ ports are common on data center switches, storage controllers, and telecom line cards that need density without jumping to 100G. If you want the full family overview, see our guide to the complete QSFP transceiver family.<\/u><\/a><\/p>\n\n\n\n

        <\/span>QSFP+ Transceiver Variants at a Glance<\/strong><\/strong><\/span><\/h2>\n\n\n\n

        Not every 40G QSFP+ module<\/a> is interchangeable. QSFP+ SR4, QSFP+ LR4, QSFP+ ER4, and related variants differ in wavelength, fiber type, connector, transmission distance, optical architecture, and power consumption.<\/p>\n\n\n\n

        The following table summarizes commonly deployed QSFP+ optical variants. Some products, including CSR4, eSR4, LR4-Lite, PLR4, and PSM4, are vendor-specific or industry-defined implementations rather than universally standardized IEEE interfaces. Their exact specifications should therefore be verified against the manufacturer\u2019s datasheet.<\/p>\n\n\n\n

        Variant<\/strong><\/td>Wavelength<\/strong><\/td>Fiber<\/strong><\/td>Connector<\/strong><\/td>Reach<\/strong><\/td>Typical Power<\/strong><\/td>Common Use<\/strong><\/td><\/tr>
        40GBASE-SR4<\/a><\/td>850 nm<\/td>OM3\/OM4 MMF<\/td>MPO-12<\/td>OM3 100 m \/ OM4 150 m<\/td>~1.5 W<\/td>Data center top-of-rack<\/td><\/tr>
        40GBASE-CSR4<\/a><\/td>850 nm<\/td>OM4 MMF<\/td>MPO-12<\/td>300\u2013400 m<\/td>~1.5 W<\/td>Extended-reach multimode<\/td><\/tr>
        40GBASE-eSR4<\/td>850 nm<\/td>OM4 MMF<\/td>MPO-12<\/td>300 m (up to 400 m)<\/td>~1.5 W<\/td>Longer MMF links<\/td><\/tr>
        40GBASE-LR4<\/td>1310 nm CWDM<\/td>SMF<\/td>LC duplex<\/td>10 km<\/td>~3.5 W<\/td>Campus \/ DCI<\/td><\/tr>
        40GBASE-LR4-Lite<\/td>1310 nm CWDM<\/td>SMF<\/td>LC duplex<\/td>2 km<\/td>~3.5 W<\/td>Short single-mode spans<\/td><\/tr>
        40GBASE-ER4<\/td>1310 nm CWDM<\/td>SMF<\/td>LC duplex<\/td>40 km<\/td>~3.5 W<\/td>Metro \/ long-haul<\/td><\/tr>
        40GBASE-PLR4<\/td>1310 nm parallel<\/td>SMF<\/td>MPO-12<\/td>10 km<\/td>~3.5 W<\/td>4\u00d710G breakout over SMF<\/td><\/tr>
        40GBASE-PSM4<\/td>1310 nm parallel<\/td>SMF<\/td>MPO-12<\/td>2 km<\/td>~3.5 W<\/td>4\u00d710G breakout over SMF<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

        SR4 and its extended cousins use parallel optics over one MPO ribbon. LR4, ER4, and LR4-Lite use four CWDM wavelengths over a single LC duplex pair. PLR4 and PSM4 bridge the two worlds by splitting one 40G MPO port into four 10G single-mode links. For cable and harness details, see our QSFP cables and MPO breakout guide.<\/p>\n\n\n\n

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