Tucked away at one end of a road in central Delhi, you are likely to miss the innocuous building that houses Indian Railway Catering and Tourism Corporation (IRCTC) that runs the overloaded online railway reservation system. It is frequently the butt of many jokes and viral memes about those heart-breaking session time outs during booking and exasperatingly slow speeds.Inside the quiet office, techies are silently tapping away at keyboards but the placid surface hides some remarkably frenzied activity. These men and women keep afloat a system that has about 21 lakh daily hits and 3,000 enquiries a second at peak hours.In 2014-15, the IRCTC website saw over 18.3 crore tickets being booked from its e-ticketing portal. Starting mid-Feb, they will limit bookings to six per month per user account. Today, it is India's largest e-commerce players by revenue as filed with the Registrar of Companies. E-ticketing constitutes 55% of total reserved tickets on Indian Railways. IRCTC's total income for the financial year 2014-15 stood at Rs. 1,141 crore. This is inclusive of service charge for online ticket booking, sales of packaged water, Rail Neer, and license fees from catering vendors. In the same fiscal,the total amount earned from users in ticket fares stood at Rs 20,620 crore. Flipkart India, meanwhile filed a revenue of Rs 9,351.7 crore in March 2015 with the Registrar of Companies — less than half of IRCTC in that period.It was a busy 2015 for IRCTC. It introduced a mobile app that currently sees about 2.5 lakh logins a day. It also introduced the option of digital wallets for payments. Currently available in Hindi and English, IRCTC plans to make the website available in Bengali, Telugu, Marathi, Tamil, Gujarati, and Urdu this year. Also on the anvil is the introduction of payment aggregators.Two years ago, responding to widespread criticism of its chaotic systems and limited capacity, IRCTC revamped its e-ticketing tech, naming it NGeT (next generation e-ticketing) system. Last summer, the website added five more servers to its passenger reservation system layer,taking the number up to 11. "Now the site can handle three lakh concurrent user connections," says Sunil Kumar, group general manager for IT at the IRCTC. Traffic, however, still remains a problem. Particularly during the Tatkal booking window.