{"id":3578,"date":"2026-05-12T07:45:25","date_gmt":"2026-05-12T07:45:25","guid":{"rendered":"https:\/\/lp.szlogic.cn\/glossary\/what-is-physical-medium-dependent-pmd\/"},"modified":"2026-05-26T07:44:09","modified_gmt":"2026-05-26T07:44:09","slug":"what-is-physical-medium-dependent-pmd","status":"publish","type":"post","link":"https:\/\/lp.szlogic.cn\/ru\/glossary\/what-is-physical-medium-dependent-pmd","title":{"rendered":"PMD (Physical Medium Dependent) Practical Guide for Optical Links"},"content":{"rendered":"<figure class=\"wp-block-image aligncenter size-large\"><img fetchpriority=\"high\" decoding=\"async\" width=\"1200\" height=\"712\" src=\"https:\/\/lp.szlogic.cn\/wp-content\/uploads\/2026\/05\/0cd5f86bb90c45a09b502f640fbf4abe.webp\" alt=\"PMD (Physical Medium Dependent)\" class=\"wp-image-3574\" srcset=\"https:\/\/lp.szlogic.cn\/wp-content\/uploads\/2026\/05\/0cd5f86bb90c45a09b502f640fbf4abe.webp 1200w, https:\/\/lp.szlogic.cn\/wp-content\/uploads\/2026\/05\/0cd5f86bb90c45a09b502f640fbf4abe-300x178.webp 300w, https:\/\/lp.szlogic.cn\/wp-content\/uploads\/2026\/05\/0cd5f86bb90c45a09b502f640fbf4abe-1024x608.webp 1024w, https:\/\/lp.szlogic.cn\/wp-content\/uploads\/2026\/05\/0cd5f86bb90c45a09b502f640fbf4abe-768x456.webp 768w, https:\/\/lp.szlogic.cn\/wp-content\/uploads\/2026\/05\/0cd5f86bb90c45a09b502f640fbf4abe-18x12.webp 18w\" sizes=\"(max-width: 1200px) 100vw, 1200px\" \/><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">The <strong>Physical Medium Dependent (PMD)<\/strong> sublayer is one of the most important elements of the Ethernet physical layer, yet it is often misunderstood. PMD defines how bits are physically transmitted and received over a specific medium\u2014single-mode fiber, multimode fiber, direct-attach copper, or electrical backplane.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">For network designers, test engineers, and procurement teams, understanding PMD is essential because PMD specifications directly influence <strong>interoperability<\/strong>, <strong>reach<\/strong>, <strong>signal integrity<\/strong>, and <strong>transceiver selection<\/strong>.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">This guide provides a professional, standards-aligned explanation of PMD, including the parameters you must evaluate when selecting <a target=\"_blank\" rel=\"\" href=\"https:\/\/www.l-p.com\/store-25432-optics-transceivers-sfp-modules.htm\">optical transceivers<\/a> such as SFP, SFP+, and QSFP modules.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" >&#x27a1;&#xfe0f; What Is the Physical Medium Dependent (PMD) Sublayer?<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">The <strong>Physical Medium Dependent (PMD)<\/strong> sublayer is the lowest functional block of the <a target=\"_blank\" rel=\"\" href=\"https:\/\/resources.l-p.com\/knowledge-center\/ieee-802-3-ethernet-standard-explained\">IEEE 802.3<\/a> PHY. It defines the <strong>optical or electrical characteristics<\/strong> required for successful transmission across the chosen medium.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">In real products, PMD corresponds to the front-end interface of an optical transceiver\u2014its laser, receiver photodiode, modulation circuitry, and related components.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\" >What PMD controls<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li><p>The optical wavelength and spectral width<\/p><\/li><li><p>Transmit (Tx) average power and launch conditions<\/p><\/li><li><p>Receiver (Rx) sensitivity and overload limits<\/p><\/li><li><p>Optical <a target=\"_blank\" rel=\"\" href=\"https:\/\/resources.l-p.com\/knowledge-center\/optical-transceiver-return-loss-back-reflection-guide\">return loss<\/a> and extinction ratio<\/p><\/li><li><p>Supported fiber type and link distance<\/p><\/li><li><p>Electrical transmit\/receive eye masks (for electrical PHYs)<\/p><\/li><li><p>Test point definitions for compliance measurements<\/p><\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">PMD acts as the <strong>bridge between the standardized PHY logic and the physical world<\/strong>, ensuring that multiple vendors\u2019 transceivers interoperate on the same fiber plant.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" >&#x27a1;&#xfe0f; PMD vs. Other PHY Sublayers<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Ethernet PHY architecture typically includes:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><p><a target=\"_blank\" rel=\"\" href=\"https:\/\/resources.l-p.com\/glossary\/pcs-physical-coding-sublayer-ethernet-explained\"><strong>PCS (Physical Coding Sublayer)<\/strong> <\/a>\u2014 encoding, 64b\/66b, <a target=\"_blank\" rel=\"\" href=\"https:\/\/resources.l-p.com\/glossary\/fec-forward-error-correction-in-optical-communication\">FEC<\/a>, and lane distribution<\/p><\/li><li><p><a target=\"_blank\" rel=\"\" href=\"https:\/\/resources.l-p.com\/glossary\/pma-physical-medium-attachment-ethernet-explained\"><strong>PMA (Physical Medium Attachment)<\/strong><\/a> \u2014 serialization\/deserialization, clock recovery<\/p><\/li><li><p><strong>PMD (Physical Medium Dependent)<\/strong> \u2014 medium-specific optical\/electrical parameters<\/p><\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">PMD is the portion directly tied to the optical budget and medium type.<br\/>A single MAC may support multiple PMDs (e.g., SR, LR, ER), each optimized for a different reach or medium.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" >&#x27a1;&#xfe0f; Why PMD Matters in Real Networks<\/h2>\n\n\n\n<figure class=\"wp-block-image aligncenter size-large\"><img decoding=\"async\" width=\"1200\" height=\"712\" src=\"https:\/\/lp.szlogic.cn\/wp-content\/uploads\/2026\/05\/27e048578ea044bf9f40c798076a3c34.webp\" alt=\"Why PMD Matters in Real Networks\" class=\"wp-image-3575\" srcset=\"https:\/\/lp.szlogic.cn\/wp-content\/uploads\/2026\/05\/27e048578ea044bf9f40c798076a3c34.webp 1200w, https:\/\/lp.szlogic.cn\/wp-content\/uploads\/2026\/05\/27e048578ea044bf9f40c798076a3c34-300x178.webp 300w, https:\/\/lp.szlogic.cn\/wp-content\/uploads\/2026\/05\/27e048578ea044bf9f40c798076a3c34-1024x608.webp 1024w, https:\/\/lp.szlogic.cn\/wp-content\/uploads\/2026\/05\/27e048578ea044bf9f40c798076a3c34-768x456.webp 768w, https:\/\/lp.szlogic.cn\/wp-content\/uploads\/2026\/05\/27e048578ea044bf9f40c798076a3c34-18x12.webp 18w\" sizes=\"(max-width: 1200px) 100vw, 1200px\" \/><\/figure>\n\n\n\n<h3 class=\"wp-block-heading\" >1. Guaranteed Interoperability<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Only modules conforming to the same PMD specifications will reliably link up. Wavelength, power levels, and sensitivity must align with IEEE requirements.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\" >2. Predictable Link Reach<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">PMD parameters define the link-loss budget. If a module specifies a Tx power of \u20133 dBm to +3 dBm and an Rx sensitivity of \u201314 dBm, the usable optical budget is built from these numbers.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\" >3. Accurate Testing and Compliance<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">PMD defines standardized test points (e.g., TP2, TP3), ensuring that optical power, jitter, and eye diagrams are measured consistently.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\" >4. Reliability Over Time<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Modules with stronger PMD margins tolerate aging, temperature variation, fiber contamination, and connector reflections better than modules built to minimum requirements.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" >&#x27a1;&#xfe0f; Key PMD Parameters You Must Evaluate<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Each PMD specification includes several critical optical and electrical metrics. Understanding them ensures proper module selection.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\" >1. Wavelength (\u03bb) and Spectral Width<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Common values include:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><p><a target=\"_blank\" rel=\"\" href=\"https:\/\/resources.l-p.com\/knowledge-center\/850nm-optical-transceivers-for-short-reach-mmf-transmission\"><strong>850nm<\/strong><\/a> \u2014 short-reach multimode (SR)<\/p><\/li><li><p><a target=\"_blank\" rel=\"\" href=\"https:\/\/resources.l-p.com\/knowledge-center\/1310nm-optical-module-applications-performance-comparison\"><strong>1310nm<\/strong><\/a> \u2014 single-mode mid-reach (LR)<\/p><\/li><li><p>Specific ranges for LX, BX, CWDM, and DWDM variants<\/p><\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">Spectral width affects dispersion performance, especially for long-reach links.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\" >2. Transmitter (Tx) Average Power<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Specifies minimum and maximum output power.<br\/>Too low \u2192 link may not reach the receiver.<br\/>Too high \u2192 may overload receivers or cause nonlinear effects.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\" >3. Receiver Sensitivity and Overload<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li><p><strong>Sensitivity:<\/strong> the lowest power level at which the receiver meets BER requirements<\/p><\/li><li><p><strong>Overload:<\/strong> maximum input before signal distortion occurs<\/p><\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">These two values define the usable <strong>optical power budget<\/strong>.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\" >4. Extinction Ratio and Return Loss<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li><p><a target=\"_blank\" rel=\"\" href=\"https:\/\/resources.l-p.com\/glossary\/extinction-ratio-importance-signal-quality-data-reliability\"><strong>Extinction ratio<\/strong><\/a> ensures a clear distinction between logical \u201c1\u201d and \u201c0.\u201d<\/p><\/li><li><p><strong>Optical return loss<\/strong> determines tolerance to reflections\u2014critical on long single-mode spans.<\/p><\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\" >5. Supported Fiber Type and Reach<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">PMD tables specify:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><p>Reach for OM2\/OM3\/OM4 multimode<\/p><\/li><li><p>Reach for G.652\/G.655 single-mode<\/p><\/li><li><p>Maximum supported length under IEEE power budgets<\/p><\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\" >&#x27a1;&#xfe0f; PMD in Optical Transceiver Selection<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">When choosing optical modules for <a target=\"_blank\" rel=\"\" href=\"https:\/\/resources.l-p.com\/knowledge-center\/what-is-a-data-center\">data centers<\/a>, industrial networks, or telecom infrastructure, confirming PMD compliance ensures:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><p>True IEEE interoperability<\/p><\/li><li><p>Correct reach over existing fiber<\/p><\/li><li><p>Predictable loss margins<\/p><\/li><li><p>Robust performance in temperature-stressed or noisy environments<\/p><\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">For example, selecting between <a target=\"_blank\" rel=\"\" href=\"https:\/\/www.l-p.com\/products\/475415.htm\"><strong>10GBASE-SR<\/strong><\/a>, <a target=\"_blank\" rel=\"\" href=\"https:\/\/www.l-p.com\/products\/475586.htm\"><strong>10GBASE-LR<\/strong><\/a>, and <a target=\"_blank\" rel=\"\" href=\"https:\/\/www.l-p.com\/products\/476054.htm\"><strong>10GBASE-ER<\/strong><\/a> is essentially choosing different PMDs optimized for 300m, 10km, or 40km.<\/p>\n\n\n\n<figure class=\"wp-block-image aligncenter size-large\"><img decoding=\"async\" width=\"1200\" height=\"712\" src=\"https:\/\/lp.szlogic.cn\/wp-content\/uploads\/2026\/05\/31aebd7127984c4e95dcb31cf479990b.webp\" alt=\"10GBASE-SR, 10GBASE-LR, and 10GBASE-E\" class=\"wp-image-3576\" srcset=\"https:\/\/lp.szlogic.cn\/wp-content\/uploads\/2026\/05\/31aebd7127984c4e95dcb31cf479990b.webp 1200w, https:\/\/lp.szlogic.cn\/wp-content\/uploads\/2026\/05\/31aebd7127984c4e95dcb31cf479990b-300x178.webp 300w, https:\/\/lp.szlogic.cn\/wp-content\/uploads\/2026\/05\/31aebd7127984c4e95dcb31cf479990b-1024x608.webp 1024w, https:\/\/lp.szlogic.cn\/wp-content\/uploads\/2026\/05\/31aebd7127984c4e95dcb31cf479990b-768x456.webp 768w, https:\/\/lp.szlogic.cn\/wp-content\/uploads\/2026\/05\/31aebd7127984c4e95dcb31cf479990b-18x12.webp 18w\" sizes=\"(max-width: 1200px) 100vw, 1200px\" \/><\/figure>\n\n\n\n<h2 class=\"wp-block-heading\" >&#x27a1;&#xfe0f; Example PMD Summary Table <\/h2>\n\n\n\n<p class=\"wp-block-paragraph\"><em>Replace values with the exact parameters from the chosen <\/em><a target=\"_blank\" rel=\"\" href=\"https:\/\/www.l-p.com\/file\/datasheet\/ls-sm3110-10c.pdf\"><em>SFP+ module datasheet<\/em><\/a><em>.<\/em><\/p>\n\n\n\n<figure class=\"wp-block-table\">\n<table class=\"has-fixed-layout\">\n<colgroup><col style=\"width: 220px;\"\/><col style=\"width: 214px;\"\/><col style=\"min-width: 25px;\"\/><\/colgroup><tbody><tr><th colspan=\"1\" rowspan=\"1\" colwidth=\"220\"><p>PMD Attribute<\/p><\/th><th colspan=\"1\" rowspan=\"1\" colwidth=\"214\"><p>Typical Value<\/p><\/th><th colspan=\"1\" rowspan=\"1\"><p>Description<\/p><\/th><\/tr><tr><td colspan=\"1\" rowspan=\"1\" colwidth=\"220\"><p>Wavelength<\/p><\/td><td colspan=\"1\" rowspan=\"1\" colwidth=\"214\"><p>1310nm<\/p><\/td><td colspan=\"1\" rowspan=\"1\"><p>Single-mode, long-reach laser<\/p><\/td><\/tr><tr><td colspan=\"1\" rowspan=\"1\" colwidth=\"220\"><p>Tx Power (Min\/Max)<\/p><\/td><td colspan=\"1\" rowspan=\"1\" colwidth=\"214\"><p>\u20133dBm \/ +3dBm<\/p><\/td><td colspan=\"1\" rowspan=\"1\"><p>Launch power range<\/p><\/td><\/tr><tr><td colspan=\"1\" rowspan=\"1\" colwidth=\"220\"><p>Rx Sensitivity<\/p><\/td><td colspan=\"1\" rowspan=\"1\" colwidth=\"214\"><p>\u201314dBm<\/p><\/td><td colspan=\"1\" rowspan=\"1\"><p>Minimum power for BER compliance<\/p><\/td><\/tr><tr><td colspan=\"1\" rowspan=\"1\" colwidth=\"220\"><p>Rx Overload<\/p><\/td><td colspan=\"1\" rowspan=\"1\" colwidth=\"214\"><p>+1dBm<\/p><\/td><td colspan=\"1\" rowspan=\"1\"><p>Maximum safe input<\/p><\/td><\/tr><tr><td colspan=\"1\" rowspan=\"1\" colwidth=\"220\"><p>Reach<\/p><\/td><td colspan=\"1\" rowspan=\"1\" colwidth=\"214\"><p>10km<\/p><\/td><td colspan=\"1\" rowspan=\"1\"><p>Depends on fiber loss and splices<\/p><\/td><\/tr><tr><td colspan=\"1\" rowspan=\"1\" colwidth=\"220\"><p>Extinction Ratio<\/p><\/td><td colspan=\"1\" rowspan=\"1\" colwidth=\"214\"><p>\u2265 3.5dB<\/p><\/td><td colspan=\"1\" rowspan=\"1\"><p>Laser modulation quality<\/p><\/td><\/tr><\/tbody>\n<\/table>\n<\/figure>\n\n\n\n<h2 class=\"wp-block-heading\" >&#x27a1;&#xfe0f; PMD Testing and Compliance<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">A well-defined PMD test ensures reliable interoperability.<br\/>Key measurements include:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><p>Optical power at transmitter and receiver<\/p><\/li><li><p>Eye-mask compliance<\/p><\/li><li><p><a target=\"_blank\" rel=\"\" href=\"https:\/\/resources.l-p.com\/knowledge-center\/jitter-in-optics-causes-effects-measurement-reduction\">Jitter<\/a> and noise margin<\/p><\/li><li><p>Testing at defined temperature points<\/p><\/li><li><p>Verification of receiver sensitivity under stressed conditions<\/p><\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">These measurements align with IEEE compliance procedures.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" >&#x27a1;&#xfe0f; Troubleshooting PMD-Related Failures<\/h2>\n\n\n\n<h3 class=\"wp-block-heading\" >Low received power<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Check connector cleanliness, unexpected fiber loss, or excessive patching.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\" >Link flaps on long spans<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Inspect Tx power aging or marginal sensitivity\u2014optical budget may be too tight.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\" >Multimode reaches the shorter than expected<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Verify OM3\/OM4 compatibility; bandwidth limitations are medium-specific.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" >&#x27a1;&#xfe0f; Conclusion<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">The <strong>Physical Medium Dependent (PMD)<\/strong> sublayer is one of the foundational concepts behind Ethernet physical-layer interoperability. By specifying optical wavelength, power ranges, sensitivity, reach, and test points, PMD ensures that transceivers from different vendors operate predictably on the same fiber infrastructure.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">For organizations deploying or upgrading networks, understanding PMD is critical to selecting the right optical modules and designing a link that is reliable, standards-compliant, and future-proof.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><a target=\"_blank\" rel=\"\" href=\"https:\/\/www.l-p.com\/store-25432-optics-transceivers-sfp-modules.htm\"><strong>LINK-PP\u2019s optical transceivers<\/strong><\/a> include clearly defined PMD specifications, making them excellent choices for robust, standards-aligned network designs.<\/p>","protected":false},"excerpt":{"rendered":"<p>Physical Medium Dependent (PMD) defines the optical and electrical rules of a PHY\u2014wavelength, power, reach, and test points. Understand PMD specs and how they guide transceiver selection.<\/p>","protected":false},"author":1,"featured_media":3577,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[27],"tags":[24,26],"class_list":["post-3578","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-glossary","tag-link-pp","tag-optics-transceivers"],"blocksy_meta":[],"acf":[],"_links":{"self":[{"href":"https:\/\/lp.szlogic.cn\/ru\/wp-json\/wp\/v2\/posts\/3578","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/lp.szlogic.cn\/ru\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/lp.szlogic.cn\/ru\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/lp.szlogic.cn\/ru\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/lp.szlogic.cn\/ru\/wp-json\/wp\/v2\/comments?post=3578"}],"version-history":[{"count":2,"href":"https:\/\/lp.szlogic.cn\/ru\/wp-json\/wp\/v2\/posts\/3578\/revisions"}],"predecessor-version":[{"id":8039,"href":"https:\/\/lp.szlogic.cn\/ru\/wp-json\/wp\/v2\/posts\/3578\/revisions\/8039"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/lp.szlogic.cn\/ru\/wp-json\/wp\/v2\/media\/3577"}],"wp:attachment":[{"href":"https:\/\/lp.szlogic.cn\/ru\/wp-json\/wp\/v2\/media?parent=3578"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/lp.szlogic.cn\/ru\/wp-json\/wp\/v2\/categories?post=3578"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/lp.szlogic.cn\/ru\/wp-json\/wp\/v2\/tags?post=3578"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}