SFP+ Direct-Attach Cable Overview and Helpful Insights for You

Source: Dev.to

Cable Overview

High‑speed cables are cable assemblies with fixed connectors at both ends. The connectors used are the same as the interfaces of optical modules, but compared to optical modules, high‑speed cables do not need to be matched with jumpers, and DAC connectors do not have expensive optical lasers. This greatly saves costs and power consumption, making them a low‑cost, high‑efficiency solution for high‑speed data communication.

Cable Classification

Passive Copper Cable

The connector of a passive direct‑attach copper (DAC) cable does not contain active components. It provides a direct electrical connection between the cable ends and can reach a transmission distance of 7 m at 10 Gbps with low power consumption.

Active Copper Cable

The connector of an active DAC cable contains active components and driver chips (linear amplifiers) for transmitting and receiving electrical signals. These components improve signal quality and allow longer distances, reaching 15 m at 10 Gbps with low power consumption.

Active Optical Cable (AOC)

AOC is made of optical fiber, and its connector contains active components such as a post‑amplifier and laser driver. Consequently, the transmission distance is much longer than that of passive or active copper cables—typically up to 300 m.

Internal Structure of DAC and AOC

DAC Internal Structure

1. First layer – wrapped core wire: Two insulated core wires and a ground wire are combined, wrapped with aluminum foil and a self‑adhesive polyester tape.
2. Second layer – cabled core wire: Consists of two or more wrapped core wires, also wrapped with aluminum foil and polyester tape.
3. Third layer – metal shielding mesh: Enhances shielding and overall performance.
4. Fourth layer – outer sheath: Made of polyethylene material.

AOC Internal Structure

An AOC is a fiber‑optic patch cord with optical transceivers at both ends. It requires external power to convert between optical and electrical signals. As a main transmission medium for high‑performance computers and data centers, active optical cables provide stable transport and flexible application, especially in high‑density environments.

Straight Cable and Branch Cable

Straight Cable

A straight (direct‑attach) cable has identical packaging specifications at both ends. It is primarily used for:

• Business data transmission – connecting two devices directly (1–15 m).
• Device stacking – virtualizing multiple devices into a single switch; typically ≤ 5 m.

Note: Straight cables can be used for stacking on regular business ports, but dedicated stacking ports require specialized stacking cables.

Branch Cable

Branch cables have different packaging specifications at each end, forming a one‑to‑many configuration. They are mainly used to connect ports of different speeds within the same cabinet or between adjacent cabinets, such as linking switches to server network cards.

AWG Wire Gauge

AWG (American Wire Gauge) standardizes wire diameter, cross‑sectional area, and current‑carrying capacity.

• Definition: A system for distinguishing wire diameters.
• Characteristics: The larger the AWG number, the smaller the wire diameter and the greater the signal loss. The number indicates how many holes the wire passes through before reaching its final diameter—more holes mean a finer wire.