Internet speed is not determined by a single device.
It is the result of the entire network chain working together—from your Internet Service Provider (ISP) all the way to your computer.
This article explains, in practical terms, every key factor that affects home network speed and stability, with a specific focus on ruling out software-side interference factors (such as firewalls, running background programs, and virus or malware infections) to help everyday users troubleshoot slow internet issues.
Quick Answer -- Most Probable Causes
*Insufficient configuration of the network patch cord connecting the computer
*Poor contact of the network cable or the wall-mounted faceplate
*Insufficient router configuration
*An excessive number of concurrent internet users in the same building
Specific Causes
1. Broadband Plan and ISP: The Source Limit
Your internet speed starts with your ISP service plan.
The bandwidth of a broadband plan is the hard upper limit of internet speed. No matter how much the downstream equipment or cabling is optimized, the actual speed cannot exceed the plan’s bandwidth limit.
A 100 Mbps plan has a theoretical download speed of 12.5 MB/s
500 Mbps corresponds to 62.5 MB/s
1000 Mbps (Gigabit) corresponds to 125 MB/s
Broadband plans can be divided into two types:
Shared Bandwidth (typical home plans)
The entire building or residential community shares the ISP’s backbone fiber bandwidth. During peak hours (19:00–23:00), when many users are online simultaneously, bandwidth is divided among users and actual speed may drop to half of off-peak performance.
Dedicated Bandwidth (enterprise lines / premium home plans)
Independent bandwidth resources are allocated to the user and are not affected by other users’ internet activity. Speed stability is extremely high and suitable for scenarios with strict performance requirements.
How to identify if broadband is the cause of network disconnection？
If the network status shows “Ethernet connected” but there is no internet access, it is usually due to an expired broadband plan or an ISP-side issue.
If the internet was working normally before but suddenly shows “Ethernet disconnected”, the cause is usually a local connection interruption, such as a problem with the network adapter, network cable, or router port.
2. Network Adapter (NIC): The First Speed Limitation
The network adapter (also called a Network Interface Card) is the core component that connects a device to the network. Its specifications and quality directly affect data transmission efficiency.
Network adapters are divided into wired and wireless, and are usually integrated into the motherboard of modern computers.
Low-quality or aging network adapters are prone to packet loss, increased re-transmission rates, and unstable speed negotiation, resulting in real-world speeds far below theoretical values.
Today, Gigabit Ethernet adapters are the mainstream and are compatible with Gigabit home broadband.
Only very old computers (around 10 years old) or extremely low-end motherboards may still use 100 Mbps Ethernet adapters, which cap speed at only 12.5 MB/s.
3. Ethernet Patch Cables: A Common Reason for Lower Speed
Many users unknowingly use incompatible or outdated Ethernet cables, preventing their network from reaching expected speeds.
Cable Categories and Quality
Category 5: Not Recommended
This is an early, outdated specification that supports only up to 100 Mbps, meaning a maximum download speed of 12.5 MB/s, which is far below the requirements of modern broadband connections.
Many users upgrade to high-speed internet plans but see no improvement simply because they are still using old Ethernet patch cables.
Category 5e: Best Cost-Performance Choice
Supports Gigabit Ethernet (1 Gbps) and is more than sufficient for daily home use, including video streaming, office work, and gaming. It balances practicality and affordability.
In most countries and regions, 100 Mbps is still the most common entry-level home broadband speed, followed by the 200–500 Mbps range.
If your broadband plan is below 1 Gbps (expected download speed under 125 MB/s), Cat5e is the optimal choice.
Category 6: An Advanced Option
Supports 1 Gbps and can even support 10 Gbps over short distances.
If your home has Gigabit broadband or higher, or if you want better stability over longer cable runs (such as connecting routers across rooms or powering surveillance cameras), Cat6 is more suitable.
Its interference resistance is far superior to Cat5e, making it the preferred choice for Gigabit and higher networks and suitable for future upgrades.
Category 6A: For High-End Requirements Only
Supports 10 Gbps transmission, with a theoretical download limit of approximately 1250 MB/s.
However, it is significantly more expensive than Cat6, and the broadband plan itself is also costly. For ordinary households, this extra expense is unnecessary.
Cable Material Selection
It is recommended to prioritize pure copper patch cables for better signal transmission efficiency and stability.
CCA (copper-clad aluminum) cables are cheaper but have weaker signal transmission and attenuation resistance. They are more suitable for short-distance, low-speed, or temporary use. For long-term fixed installations or high-speed broadband, their performance is inferior to pure copper cables.
About Shielded (STP) Ethernet Cables
STP cables are not necessary for everyday residential use.
They contain a metal shielding layer designed to resist strong electromagnetic interference and are more expensive. They are suitable for data centers or industrial environments with dense electronic equipment.
In typical home environments, electromagnetic interference is minimal. Unshielded Cat5e, Cat6, or Cat6A cables are sufficiently stable, and using STP cables usually provides no practical benefit.
4. Wall Network Outlets and RJ45 Connectors: Poor Contact
They are the “junction points” of signal transmission.
RJ45 Connectors
Finished patch cables come with pre-installed RJ45 connectors.
Users can visually inspect connectors for damage. Bent pins, oxidation, or darkened metal contacts may cause speed fluctuations.
During troubleshooting, unplug and replug both ends several times to clear dust. If damage is suspected, replacing the patch cable is the fastest way to verify the issue.
Wall Network Outlets
If speed is abnormal, unplug and replug the patch cable connected to the outlet 2–3 times to ensure a firm connection.
You can also test the same cable on a different wall outlet. If speed returns to normal, the original outlet or connection likely has poor contact.
Avoid frequent plugging/unplugging or physical impact on wall outlets to prevent loosening.
5. In-Wall Cabling: Check Last
In-wall cables are installed by contractors and cannot be easily replaced by residents. In addition to confirming cable specifications with property management or installers, the following methods can help identify issues:
Comparative Testing
Use a high-quality patch cable to connect your computer directly to the router’s LAN port and test speed.
Then use the same setup to test different wall outlets. If one room consistently shows significantly lower speed and replacing patch cables does not help, the in-wall cable or outlet for that room is likely faulty.
Observing Usage Patterns
If rooms farther from the router are more than 50% slower, or outlets near electrical panels or air conditioners show abnormal speeds, the in-wall cable may be running parallel to power lines, suffering from electromagnetic interference, or may have been excessively bent during installation.
Aging cables, rodent damage, or water ingress can also cause sudden speed drops. These issues usually affect the entire home’s wired network and require professional inspection.
If serious problems are suspected, network technicians can use cable testers and tone tracers to quickly identify continuity and crosstalk issues.
6. Router: Insufficient Configuration
The router is the core device of the home network, acting as a signal distributor. It receives the internet connection from the Optical Modem and enables multiple devices to access the network simultaneously while providing wireless coverage.
Router Types:
100 Mbps routers
Support only 10/100 Mbps and are suitable for broadband below 100 Mbps.
Even with a Gigabit plan, speed will be capped at 100 Mbps (12.5 MB/s).
Gigabit routers
Support 10/100/1000 Mbps and are suitable for 200M, 500M, and 1000M broadband plans. This is the mainstream home choice today.
However, if CPU performance is insufficient or NAT forwarding capacity is limited, the router may still fail to sustain full Gigabit speed under multi-device load.
2.5 Gbps routers
At least one port supports 2.5 Gbps, with the rest being Gigabit ports. Suitable for 2 Gbps broadband.
10 Gbps routers
Support 10 Gbps transmission and are suitable for 10 Gbps broadband.
Intended for enterprise or very high-concurrency scenarios; unnecessary for typical home use.
Some ISPs provide routers as free gifts or low-cost rentals. These devices are often entry-level models with limited wireless coverage and multi-device performance. In large homes or device-heavy environments, congestion may occur.
After ruling out other causes, users could verify whether their router matches their broadband plan.
How to find the Router
Many home “routers” are actually router + AP all-in-one devices, which causes confusion with standalone wireless access points (APs).
Multiple APs can be installed in a home, but typically there is only one router per household.
Starting from the LAN port of the optical modem, the router is the box with antennas and multiple Ethernet ports connected to it. The modem is usually located in the low-voltage cabinet, entryway, or living room.
7. Optical Modem (ONU): Cache Accumulation
The Optical Network Unit (ONU) converts optical signals from the building into electrical signals usable by home devices. Its performance directly affects signal conversion efficiency.
ISPs usually provide the ONU as part of the broadband service, either free or with a small deposit. Installation and configuration are handled by technicians. When upgrading plans, the ISP typically checks compatibility and replaces the ONU if needed.
If the ONU is placed in a sealed low-voltage cabinet, heat buildup may cause slow speeds or intermittent disconnections.
Long uptime without rebooting can also lead to cache accumulation and reduced performance.
When checking the router, reboot the ONU as well by unplugging it for one minute before reconnecting.
Dont’t fully enclose the low-voltage wiring box; leave some gaps for heat dissipation.
8. Building and ISP Infrastructure
This part lies outside the home network. From building-level signal distribution equipment to the ISP’s core facilities, these components collectively determine baseline stability and performance.
Failures at this level cannot be fixed by residents and require ISP intervention.
Key Components and Influences
Optical splitters:
Installed at the base of the building to divide the ISP’s backbone fiber among residents. Common configurations include 1:16 and 1:32.
Since total backbone capacity is limited, the more users share it, the more likely bandwidth contention occurs during peak hours. As a result, speeds may drop to half of off-peak levels between 19:00–23:00.
Indoor fiber drop cables:
Thin fibers connecting the splitter to each home’s ONU. These are fragile and prone to degradation from compression, excessive bending, or aging. Distant users may experience speeds 20–30% slower than those closer to the splitter.
Building low-voltage cabinets:
These house splitters and other equipment. High humidity, excessive heat, or proximity to power equipment can interfere with signals and cause speed fluctuations.
In newer residential buildings, signals from the main cabinet are further distributed through Floor-Level Cabinets into individual homes.
Office buildings and commercial properties usually have more complex low-voltage room layouts to support high-density networking.
Troubleshooting Summary (From Easiest to Most Complex)
1.Check whether the Ethernet patch cable is loose; replug it several times
2.Check whether the broadband plan has expired
3.Update network adapter drivers and confirm adapter specifications in Device Manager
4.Check the patch cable category and ensure it is not a low-grade cable
5.Inspect RJ45 connectors for damage or deformation
6.Test the same cable on a different wall outlet
7.Locate and reboot the optical modem in the low-voltage cabinet
8.Check whether the router configuration is insufficient
9.Ask property management about the specifications of in-wall cabling
If your internet speed is slow at night but fast during the day, it simply means you’re out of luck—too many people are online at the same time.