Laymen explanation
If you're using Wi-Fi in your house, the odds are good that you just went with the free router that the ISP provides. It's convenient since you don't need to set up anything, and it saves both time and money.
And then the problems start - the network is slow, or doesn't reach most parts of your house - and there's not much you can do about it.
Technical explanation
Router is a gadget which helps us in net connectivity in home. This device lasts for years and it is key for network performance and net access use-cases. So, it is important to think a while before purchasing a router for your home.
Router with or without Internet
The most common use of a Wi-Fi router is to share an Internet connection between various devices, but that's not its only use. You can even use the router even without an active Internet connection to connect your devices like smartphones, tablets, TVs, computers to each other for streaming videos, file transfers and more. In such a case, you'll obviously have no ISP and will need to invest in a router of your own.
There is no straightforward method to measure the range of the WiFi router, since it depends on a wide variety of factors.
Walls play a large part in blocking the WiFi signals. Concrete walls and even thin wooden doors create a hindrance for the signals. A study says that the signal strength gets very weak after 3 to 4 walls. So if the router you got from the ISP isn't up to the mark, you must look at this dBi specification, and go with a higher number.
Some models can only communicate over a single radio band, while others can use two. Single-band routers operate on the 2.4GHz frequency band and are typically the least expensive models.
If one or more of your devices will be streaming video from a service such as Netflix, or connecting to an online gaming service such as Xbox Live, consider a dual-band router. These have two radios; one connects to the 2.4GHz band, and the other connects to the 5GHz band. The 5GHz band is typically less crowded than the 2.4GHz band and offers more throughput, with minimal signal interference, making it ideal for video streaming and gaming duty.
Then there are tri-band routers. These have three radios—one that operates at 2.4GHz and two that operate at 5GHz. These models are a good fit for multi-device households that experience heavy network traffic via lots of video streaming, torrent downloading, file transfers, and online gaming.
Wireless Ethernet networks use 802.11 protocols to send and receive data.
802.11n router is a good fit for households that have a handful of these devices sharing Internet access. However, if you're using your network to share large files and have several smart TVs, gaming consoles, mobile devices, and media streaming devices connecting wirelessly, a more powerful router that offers the latest Wi-Fi technology may be in order.
The newest class of Wi-Fi routers use 802.11ac technology, which brings several performance improvements over previous protocols, including wider channel bandwidth (up to 160Hz compared with 40Hz), more MIMO spatial streams (up to eight), and beamforming, a technology that sends Wi-Fi signals directly to a client rather than broadcasting in all directions.
In 802.11ac, up to four clients can have their own data stream instead of waiting in turn to receive data from the router. This protocol offers downstream Multi User-Multiple Input Multiple Output (MU-MIMO) technology, which is designed to provide bandwidth to multiple devices simultaneously rather than sequentially.
With QoS settings, you can decide which applications and clients get network priority. For example, if one device is streaming Netflix video, and another device is downloading files or running a print job, you can give priority to the streaming device to avoid choppy, out-of-sync video.
A guest network lets you offer Wi-Fi connectivity to guests without leaving your entire network vulnerable. In a nutshell, you're creating a separate network for guests with a Service Set Identifier (SSID) and password that is different from your main network credentials.
Parental controls allow you to limit network access for certain users to specific times and days and is ideal for parents who want to keep tabs on their child's online gaming and social networking activities.
Most current routers have built-in support for IPv6 addressing, but it's a good idea to verify this if you want to be ready for the transition when IPv4 finally does hit the wall.
http://in.pcmag.com/wireless-networking/40488/guide/the-best-wireless-routers-of-2016
http://gadgets.ndtv.com/laptops/features/buying-a-wi-fi-router-here-are-the-features-and-specifications-that-matter-675929