A DSP (demand-side platform) is what buyers use. It lets advertisers and agencies bid on CTV ad impressions across multiple publishers from a single interface — setting targeting criteria, bid prices, frequency caps, and creative. DV360 (Google), The Trade Desk, and Amazon DSP are the main platforms used in India.
An SSP (supply-side platform) is what publishers use. It connects the publisher's ad inventory to multiple DSPs simultaneously, runs the auction between competing bids, and returns the winning ad to the publisher's ad server for delivery. Google Ad Manager, Magnite, and PubMatic are active in India CTV.
The connection happens in real time. When a viewer is about to see an ad break, the publisher's SSP broadcasts a bid request to connected DSPs. Each DSP decides whether to bid and at what price. The SSP picks the highest bid above the floor price. The whole sequence takes under 200 milliseconds.
The India-specific point: most premium CTV inventory is not fully open to any DSP in an open auction. JioCinema and Hotstar sell the bulk of their premium inventory (IPL, prime-time VOD) through direct deals or private marketplace (PMP) arrangements with pre-approved buyers. A DV360 or Trade Desk seat does not automatically give you access to the best India CTV inventory — you need a PMP deal with the platform first.
Full guide
For a complete explanation, read: DSPs and SSPs in CTV advertising: how programmatic trading works