{"id":12825,"date":"2026-07-14T10:58:05","date_gmt":"2026-07-14T02:58:05","guid":{"rendered":"https:\/\/ascentoptics.com\/blog\/?p=12825"},"modified":"2026-07-14T10:58:05","modified_gmt":"2026-07-14T02:58:05","slug":"qsfp56-cable","status":"publish","type":"post","link":"https:\/\/ascentoptics.com\/blog\/qsfp56-cable\/","title":{"rendered":"QSFP56 Cable Guide: DAC vs AOC for 200G Networks"},"content":{"rendered":"

QSFP56 uses four 50 Gbps PAM4 electrical lanes to deliver an aggregate bandwidth of 200 Gbps.\u00a0For applications that demand low power and low latency, the DAC cables can be used, while for others that need extended ranges of transmission and resistance against interference, AOC cables would suffice. Moreover, there is an option for the breakout of the 200G port to satisfy varying networking needs.<\/p>\n

This guide explains the main QSFP56 cable types, their specifications, compatibility requirements, and how to choose the right option for data center, AI, HPC, and storage networks.<\/p>\n

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What Is a QSFP56 Cable?<\/strong><\/h2>\n

A QSFP56 cable is a high-speed fixed interconnect that supports 200 Gigabit Ethernet using four 50 Gbps PAM4 electrical lanes. It uses the same QSFP mechanical form factor as QSFP28<\/u><\/a>\u00a0but requires host hardware with 50G PAM4 SerDes, and it is available as a passive DAC, active DAC, AOC, or breakout cable.<\/p>\n

QSFP56 stands for Quad Small Form-Factor Pluggable 56. The “56” refers to the signaling generation originally designed for approximately 56 GBaud operation, which enables 50 Gbps PAM4 data transmission per electrical lane. Unlike QSFP28, which uses NRZ modulation at 25 Gbps per lane, QSFP56 uses PAM4 modulation to transmit two bits per symbol. This doubles the lane rate without adding physical lanes.<\/p>\n

The key distinction between a\u00a0QSFP56 cable\u00a0and a QSFP56 transceiver is that cables have fixed connector ends and a predetermined length. Transceivers accept separate fiber patch cords, while cables are plug-and-play assemblies. Cables are also typically lower cost and lower latency for short-reach links.<\/p>\n

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QSFP56 Cable Types and Specifications<\/strong><\/h2>\n

QSFP56 cables fall into four main categories. Each type balances reach, power, latency, flexibility, and cost differently.<\/p>\n

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QSFP56 Passive DAC (Direct Attach Copper)<\/strong><\/h3>\n

A passive DAC<\/a> uses twinax copper cable with fixed QSFP56 connectors on both ends. There are no active signal-conditioning components, so the cable relies entirely on the host\u2019s transmitter and receiver quality.<\/p>\n