A Simple Guide to SFPs, DAC Cables, RJ45, and Network Speeds (1G to 800G)

When you hear terms like SFP, DAC, CWDM, or 100G, it can feel confusing at first. These are common in data centers, ISPs, and modern enterprise networks. Here’s a simple breakdown that anyone can understand.

SFP, SFP+, SFP28, QSFP — What are these?

These are small modules we plug into switches, routers, servers, and transmission devices to connect using fiber or copper. Think of them as the “SIM cards” of high-speed networking.

Common types:

• SFP (1G): Used for 1 Gigabit connections.

• SFP+ (10G): Used for 10 Gigabit links.

• SFP28 (25G): Used for faster 25G links.

• QSFP+ (40G): QSFP means "Quad SFP" — used for 40G.

• QSFP28 (100G): Used for 100G high-speed data center links.

• QSFP56 (200G) / QSFP-DD (400G): Used where ultra-high throughput is needed.

• QSFP-DD / OSFP (800G): Used where ultra-high throughput and next-generation network capacity are needed.

These modules can run over fiber or copper depending on the design.

RJ45 – The connector we all know

RJ45 is the regular Ethernet connector everyone sees at home, office, or ISP networks. It’s used for copper cables like Cat5e, Cat6, Cat6A, Cat8.

• Supports 1G commonly.

• Can support 10G over Cat6A/Cat8.

• Not suitable for longer distances because copper has higher signal loss.

DAC Cables (Direct Attach Copper)

DAC is a ready-made twinax cable with SFP or QSFP heads on both sides. No need for fiber, no separate modules.

Why use DAC?

• Very cheap compared to fiber.

• Very low latency.

• Perfect for short distances (usually 1 to 7 meters).

• Used heavily in data centers for switch-to-server or switch-to-switch links.

Understanding Speeds: 1G to 800G

Higher speeds mean more bandwidth for modern applications like cloud, virtualization, CDN, and content delivery. Here is where they are commonly used:

Speed                            Technology                                         Commonly Used Where

1G                                       SFP, RJ45                                                      Home ISPs, small offices

10G                                       SFP+                                                            ISPs, data centers, enterprise core

25G                                     SFP28                                                            Modern servers, cloud infrastructure

40G                                     QSFP+                                                           Aggregation layers

100G                                  QSFP28                                                          Data centers, carrier networks

200G                                  QSFP56                                                          High-performance computing

400G                                 QSFP-DD                                                         Large ISP backbone, hyperscale cloud

800G                            QSFP-DD / OSFP                                                 Next-gen ISP backbone, hyperscale cloud, AI-driven data center cores

Here you can also explore the networking products and modules (like SFPs, QSFPs and high-speed transceivers) available on the Networking Goods Category. https://dtechtrading.com.np/category/26?page=1