A Delay Tolerant Network (DTN) is a network capable of handling long delays and data loss efficiently in various challenged scenarios and environments. Owing to the mentioned challenges, it becomes crucial to study how the routing protocols are designed to adapt in such networks. Currently, the research in this domain is focused on the improving the data delivery ratio and minimizing delays in the routing protocols. This paper reviews state-of-the-art routing protocols for Delay Tolerant Networks (DTNs) as well as performs their comparative analysis. DTN routing protocols are grouped into four categories viz encounter based, time based, infrastructure based and hybrid & others. This categorization depends on the information they use for relay selection routing. We have also discussed some of the inherent drawbacks such as energy consumption, delivery rates and buffer constraints of the existing routing algorithms. We have also conducted an empirical analysis and observed the performance of the most popular existing algorithms of encounter and time based category. This paper offers a widespread study of the routing protocols with their pros and cons.

延迟容忍网络（DTN）是一种能够在各种挑战性场景和环境中有效处理长时延和数据丢失的网络。由于上述挑战，研究如何设计路由协议以适应此类网络就变得至关重要。当前，该领域的研究集中在提高数据传送率和最小化路由协议中的延迟。本文回顾了延迟延迟网络（DTN）的最新路由协议，并进行了比较分析。DTN路由协议分为四个类别，即基于遇到，基于时间，基于基础结构以及混合等。这种分类取决于它们用于中继选择路由的信息。我们还讨论了一些固有的缺点，例如能耗，现有路由算法的传输速率和缓冲区限制。我们还进行了实证分析，并观察了最流行的遭遇和基于时间类别的现有算法的性能。本文对路由协议及其优缺点进行了广泛的研究。