1) The lawyers who have minimum 5 years of experience ( 4 + One Year of Training) and who have passed a special examination of Supreme Court. They are registered on special roll of Supreme Court. Each of them is assigned a code number. They have exclusive privilege of filing cases and Vakalatnama (Power to represent client in Supreme Court). No other advocate can file cases in Supreme Court. They are called Advocate on Record in Supreme Court. Their list is available on website of Supreme Court.
2) Senior Advocates. Each High Court and Supreme Court has power to Designate an Advocate as Senior Advocate. Once an advocate is designate as senior advocate, he cannot file Vakalatnama in any court in India. He cannot argue in any court unless he is also assisted and instructed by other advocate. He cannot draft matters or any kind of documentation for any clients. He cannot receive direct phone calls from clients. He is supposed to maintain aloofness, detachment with cases , objectivity in arguments and certain higher degree of dignity in his day to day behaviour in personal life as well as in Court Life. They are supposed to Lead High Standards of Legal Profession by being an ideal role model for other advocates. The roll of Senior Advocates who are designated by Supreme Court, is found on website of Supreme Court.
Judges of various High Courts, after their retirement in High Court, come to practice in Supreme Court. They are usually, normally designated as Senior Advocate by Supreme Court. The High Court judges who may have some tainted reputation during their tenure, are often denied Designation of Senior Advocate by Supreme Court.
3) Advocates who are practising and arguing mainly in Supreme Court and are based in Delhi, but they are neither advocates on record nor senior advocates nor advocates in next 4th layer advocates. From the first day of their enrollment, they can practice in Supreme Court. No minimum experience is prescribed for them for arguing in Supreme Court.
4) The fourth layer advocates are those who are practising mainly in other courts all over India, but they occasionally come to Supreme Court to argue cases. No minimum experience is prescribed for them for arguing cases in Supreme Court.
All advocates in layer 2, 3 and 4 need an authority from Advocate on Record (1st Layer) before they can argue any case in Supreme Court.