Iran, Russia and Turkey brokered the deal during talks in the Kazakh capital, Astana.
The implementation of the agreement had a shaky start with fighting flaring in some areas.
The deal bans weapons in parts of Idlib, Latakia, Aleppo and Hama.
There is also hope for aid deliveries to about a million people living there.
The Syrian government has not signed the agreement but state media says leaders support the accord.
The main opposition groups have rejected the deal, saying it lacks "safeguards and compliance mechanisms".
Turkey's President Recep Tayyip Erdogan says "50 per cent of the conflict" would be solved if the deal succeeds.
Does it represent a shift in diplomacy?
Presenter: Sami Zeidan
Guests:
Hillary Mann Leverett, former White House National Security Official
Pavel Felgenhauer, Russian defence analyst
Molham Aldrobi, member of the General Secretariat of the Syrian National Council
