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Compare TCP vs UDP

6 cited papers · March 16, 2026 · Powered by Researchly AI

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TL;DR

TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) are two foundational transport layer protocols that provide end-to-end communication betwee…

TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) are two foundational transport layer protocols that provide end-to-end communication between hosts.¹Iren et al. (1999)¹TCP defines four intertwined congestion control algorithms — slow start, congestion avoidance, fast retransmit, and fast recovery — making it a reliable but complex protocol.²Allman et al. (1999)²

1

The transport layerSami Iren, Paul D. Amer et al.1999ACM Computing Surveys

2

TCP Congestion ControlMark Allman, Vern Paxson et al.1999OpenAlex

TCP (Transmission Control Protocol) — A reliable, connection-oriented transport protocol that implements congestion control, flow control, and guaranteed delivery.

¹It responds to all packet losses by invoking congestion control and avoidance algorithms.²Allman et al. (1999)²

1

The transport layerSami Iren, Paul D. Amer et al.1999ACM Computing Surveys

2

TCP Congestion ControlMark Allman, Vern Paxson et al.1999OpenAlex

UDP (User Datagram Protocol) — A lightweight, connectionless transport protocol. QUIC, a modern protocol built on top of UDP, demonstrates UDP's utility as a basis for multiplexed, secure transport without the overhead of TCP's connection management. (2021)

³

3

QUIC: A UDP-Based Multiplexed and Secure Transport2021OpenAlex

Transport Layer — The layer responsible for end-to-end communication between two or more hosts, encompassing services such as reliability, flow control, and multiplexing.

¹Iren et al. (1999)¹

TCP Congestion Control — TCP's mechanism for managing network congestion through slow start, congestion avoidance, fast retransmit, and fast recovery algorithms.

²Allman et al. (1999)²

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Diagram

TCP Architecture:
 [Sender] --SYN/SYN-ACK/ACK Handshake--> [Receiver]
 | |
 Congestion Control (Slow Start, AIMD) |
 Flow Control (Sliding Window) |
 Reliable Delivery (ACKs, Retransmit) |
 +------ Ordered Byte Stream --------------+

UDP Architecture:
 [Sender] ----Datagram (no handshake)----> [Receiver]
 | |
 No connection state |
 No ordering guarantee |
 No retransmission |
 +------ Best-Effort Delivery -------------+

QUIC (UDP-based modern transport):
 [Sender] --UDP + TLS 1.3 + Multiplexed Streams--> [Receiver]
 | |
 Encrypted headers |
 Stream-level flow control |
 Loss recovery built-in |
 +------- Secure Multiplexed Transport ----------+

Table

Feature	TCP	UDP
Connection	Connection-oriented (3-way handshake)	Connectionless
Reliability	Guaranteed delivery via ACKs and retransmission	Best-effort, no guarantee
Ordering	Ordered byte stream	No ordering
Congestion Control	Slow start, congestion avoidance, fast retransmit, fast recovery	None
Header Overhead	High (sequence numbers, ACKs, window size)	Low (minimal header)
Key Innovation	End-to-end reliable transport with congestion control	Simplicity and low latency
Strengths	Reliable, fair bandwidth sharing, widely supported	Low overhead, suitable for real-time apps
Weaknesses	High latency, poor performance over lossy/wireless links	No reliability, no congestion control
Modern Evolution	DCTCP for data centers	QUIC (UDP-based) for secure multiplexed transport

TCP's throughput can be analytically modeled as a function of loss rate and round-trip time, capturing both fast retransmit and timeout behavior.¹Padhye et al. (1998)¹In data center environments, TCP's demands on limited switch buffer space lead to high application latencies, motivating variants like DCTCP.²Alizadeh et al. (2010)²QUIC, built on UDP, authenticates all headers and encrypts most of them, enabling protocol evolution without requiring middlebox updates. (2021)³

1

Modeling TCP throughputJitendra Padhye, Victor Firoiu et al.1998OpenAlex

2

Data center TCP (DCTCP)Mohammad Alizadeh, Albert Greenberg et al.2010OpenAlex

3

QUIC: A UDP-Based Multiplexed and Secure Transport2021OpenAlex

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TCP performs poorly over wireless and lossy links because it treats all packet losses as congestion, invoking congestion control even for non-congestion-related losses such as bit errors and handoffs.

¹²Balakrishnan et al. (1996)¹

In data center environments, TCP's congestion control mechanisms cause bandwidth-hungry flows to build up queues at switches, negatively impacting latency-sensitive traffic. Alizadeh et al. (2010)

1

A comparison of mechanisms for improving TCP performance over wireless linksHari Balakrishnan, Venkata N. Padmanabhan et al.1996OpenAlex

2

TCP Congestion ControlMark Allman, Vern Paxson et al.1999OpenAlex

TCP provides reliable, ordered delivery through four congestion control algorithms: slow start, congestion avoidance, fast retransmit, and fast recovery.

¹Allman et al. (1999)¹

UDP's simplicity makes it the foundation for modern protocols like QUIC, which adds security and multiplexing on top of UDP without TCP's overhead. (2021)

²

TCP throughput is analytically predictable as a function of loss rate and round-trip time, with timeout events being more frequent than fast retransmit events in practice.

³Padhye et al. (1998)³

TCP suffers significant performance degradation over wireless links due to misidentifying non-congestion losses as congestion.

⁴¹Balakrishnan et al. (1996)⁴

The transport layer broadly encompasses end-to-end communication services including reliability, flow control, and multiplexing across many protocols beyond just TCP and UDP.

⁵Iren et al. (1999)⁵

1

TCP Congestion ControlMark Allman, Vern Paxson et al.1999OpenAlex

2

QUIC: A UDP-Based Multiplexed and Secure Transport2021OpenAlex

3

Modeling TCP throughputJitendra Padhye, Victor Firoiu et al.1998OpenAlex

4

A comparison of mechanisms for improving TCP performance over wireless linksHari Balakrishnan, Venkata N. Padmanabhan et al.1996OpenAlex

5

The transport layerSami Iren, Paul D. Amer et al.1999ACM Computing Surveys

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"QUIC vs TCP performance comparison in web applications"
"TCP congestion control variants: CUBIC, BBR, and DCTCP"
"Wireless TCP optimization techniques: link-layer vs end-to-end approaches"

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