Reliance Jio's 4G download speed declined by about 8 percent in December to 18.7 megabits per second (Mbps) but still continued to lead the chart for the past 12 months in a row, according data published by telecom regulator Trai.

Jio network recorded an average download speed of 20.3 Mbps in November.

Performance of Bharti Airtel's 4G network marginally improved in December to 9.8 Mbps from 9.7 Mbps in November, according to the data published by the Telecom Regulatory Authority of India (Trai) on MySpeed Portal.

Though Vodafone and Idea Cellular have merged their businesses and now operate as Vodafone Idea, Trai published their network performance separately.

4G download speed on Vodafone network declined slightly to 6.3 Mbps from 6.8 Mbps in November, while that of Idea dipped to 6 Mbps from 6.2 Mbps.

Idea, however, continued to top the chart in terms of 4G upload speed despite dip in network performance. The upload speed on Idea network declined to 5.3 Mbps in December from 5.6 Mbps in November.

The download speed plays an important role when a user watches any video, browse the internet, access e-mails; and a good upload speed is required when a user wants to share data such as images, videos and any other files through e-mail or social media applications.

Vodafone continued to show improvement and recorded increase in upload speed at 5.1 Mbps in December from 4.9 Mbps in November.

Jio upload speed declined to 4.3 Mbps in December from 4.5 Mbps in November.

Airtel, too, recorded marginal dip in upload speed at 3.9 Mbps from 4 Mbps during the months under review.

Both Jio and Idea have continued to maintain their leadership in their respective segments for the past several months.

The average speed is computed by Trai based on data it collects with help of its MySpeed application on a real-time basis.