What is Tail Drop?
Tail drop is a network management mechanism that helps prevent congestion and manage traffic flow in a network. When the network is congested and the output buffers of a router or switch become full, new incoming packets are dropped instead of being stored in the buffers. This dropping of packets at the tail end of the queue is known as tail drop.
Tail drop is a simple and widely used mechanism that aims to achieve a fair sharing of network resources among different flows. However, it can also lead to some issues, such as the occurrence of global synchronization and the degradation of certain flow performance. To address these issues, there are various countermeasures that can be employed.
Basic Concepts of Tail Drop
When a router or switch receives packets from different flows, it stores them in its output buffers before forwarding them. However, if the buffers become full due to congestion, the router or switch has to make a decision on which packets to drop. Tail drop employs the simple strategy of dropping the most recently arrived packets, or packets at the tail of the queue when the buffers are full.
The basic idea behind tail drop is that when the sender of the dropped packets notices the loss, it will reduce its transmission rate, thereby relieving the congestion. This mechanism encourages the fair sharing of network resources as it creates a form of feedback control.
Countermeasures for Tail Drop
While tail drop is a simple and widely used mechanism, it can suffer from some drawbacks. One notable issue is global synchronization, where all flows in the network may experience drops simultaneously, leading to an unfair sharing of resources. To mitigate this issue, some alternative queue management techniques can be used, such as Random Early Detection (RED) and Weighted Random Early Detection (WRED).
RED and WRED are proactive drop mechanisms that drop packets early based on certain probabilities, rather than waiting for buffers to become full. These mechanisms allow for more control over congestion, prevent global synchronization, and encourage fairness.
Another countermeasure for tail drop is the use of traffic shaping and traffic prioritization techniques. These techniques prioritize certain traffic flows over others, ensuring that critical traffic receives preferential treatment and reducing the impact of congestion.
In conclusion, tail drop is a network management mechanism that drops packets at the tail end of the queue when network congestion occurs. While it is a simple and widely used mechanism, it can suffer from issues such as global synchronization. To overcome these issues, alternative queue management techniques, like RED and WRED, as well as traffic shaping and prioritization, can be employed.