The Church of South India is a Province (member Church) of the Anglican Communion, in full communion with the Archbishop of Canterbury, and therefore in full communion with The Episcopal Church (USA). Full communion means that each Church recognizes the sacraments (including ordination of the other). Persons ordained in one Church are consider ordained in the other.
The Church of South India was formed in 1947, by a merger of Presbyterian, Methodist, Congregational Churches and the Church of England in India. The Church of South India used the Chicago-Lambeth Quadrilateral (found in the Prayer Book on page 876) as a guideline for the merger. This meant that the Church of England recognized all ordained pastors in the other Churches in the merger, and since 1947, all ministers in the CSI have been ordained by bishops in apostolic succession.
The merger was first imagined at the 1910 Edinburgh Missionary Conference (the predecessor of the World Council of Churches), and it took the next 37 years to negotiate the terms of the merger. The CSI is one of the shining examples of true ecumenism in the twentieth century.