Security presence is hightened as the countdown for the Sochi Winter Olympics started, amid concerns of blasts akin to the Volgograd twin blasts which killed 34 people in December. There is a huge, multilayered security operation where the games are to start on Friday, involving some 100,000 personel, drones, robots, and sonar systems. Rory Challands has been watching the build-up in Sochi.
