The Wireless Sensor Network consist lot of tiny sensor nodes in which sensor nodes (WSN) send data to sink node. The Wireless Sensor Networks are used in climate change impact, water cycle management, vehicle traffic monitoring, freight shipping etc. There are two types of traffic in WSN. They are source traffic and transit traffic. The source traffic occurs in sensor nodes where as transit traffic occurs in other nodes. The upstream traffic can be classified as event based, continuous based, query based and hybrid delivery. Because of many-to-one nature there is more congestion in upstream traffic. The packet loss due to collision is one of the reasons for congestion. Due to packet loss the retransmission of packets will take place. So the sensor nodes consume more power. While designing a protocol for WSN we have to consider energy efficiency and reliability. There are two types of reliability hop-by-hop and packet reliability. In this paper we propose packet reliability technique for reliable data transfer.