Question

We have said that an application may choose UDP for a transport protocol because UDP offers finer application control (than TCP) of what data is sent in a segment and when. a. Why does an application have more control of what data is sent in a segment? b. Why does an application have more control on when the segment is sent?

Short answer

UDP offers more control over segment content and timing due to its simpler, connectionless design.

Step-by-step solution

Understanding UDP Protocol

UDP (User Datagram Protocol) is a connectionless protocol, meaning it does not establish a connection before sending data packets. It allows applications to send messages, called datagrams, to other hosts on an IP network without requiring prior communications to set up special transmission channels or data paths.

Control of Data Sent in a Segment

UDP segments include a small header and no elaborate data split or flow management is done automatically. Applications have direct control over the data that goes into a segment; they take care of forming datagrams and choose exactly which data is transmitted together. There is no mechanism for segment size negotiation or data reorganization, unlike in TCP.

Control of When the Segment is Sent

Because UDP is a stateless protocol, there is no need to wait for acknowledgments, sequence numbers, or handshakes, which are characteristic of TCP. This allows the application to send data immediately when it is ready, providing lower latency and more straightforward timing control compared to TCP where transmission may be delayed by these additional processes.

Key concepts

Connectionless Protocol

UDP, or User Datagram Protocol, is known as a connectionless protocol. This can be seen as one of its defining features. Unlike TCP, or Transmission Control Protocol, which requires establishing a connection before data transmission, UDP does not. The term "connectionless" means that it sends data without setting up a dedicated channel or pathway. This allows data to be transmitted without the usual back-and-forth communication seen in other protocols, like TCP.

As a result, UDP is simpler. There is no overhead from establishing and managing connections. The simplicity allows it to be efficient in scenarios where a real-time response is needed.

Examples of connectionless scenarios include:

• Streaming real-time audio or video
• Online gaming
• DNS lookups

These applications value the speed of data transmission over the reliability of complete, ordered delivery that TCP offers.

Data Transmission Control

One of the main benefits of using UDP is that the application has greater control over the data it sends. With UDP, applications are responsible for handling the data packets, known as datagrams, directly. Applications decide on their own how data is packaged and sent.

Unlike TCP, where the protocol automatically handles data organization and segmentation, UDP places these tasks at the application's discretion. This means applications can:

• Choose the size of each datagram
• Configure data without preset structures
• Send custom-tailored data segments based on immediate needs

Without the overhead of data reorganization or segment size negotiation, applications are free to structure their data segments precisely as required. This level of control can be particularly advantageous in specialized communication scenarios like custom network protocols or IoT applications.

Latency Management

UDP excels in situations where low latency is crucial. Because it is connectionless and stateless, the protocol allows data to be sent immediately, without unnecessary delays that other protocols, such as TCP, might introduce.

In TCP, several processes like handshakes, sequence numbering, and acknowledgment mechanisms are needed to maintain a connection's state. Each of these steps adds time. UDP skips these extra processes, meaning apps can send data instantly once it’s ready.

Reduced latency is crucial for applications such as:

• Live broadcasts
• Real-time online gaming
• VoIP (Voice over Internet Protocol) services

The primary advantage here is ensuring that data reaches its destination as quickly as possible even though it might not be entirely reliable or ordered like TCP. This can often be a worthy trade-off when the immediacy of data transmission outweighs the need for order and reliability.