Difference between TCP vs MPTCP

Introduction :

In modern networks, the traditional Transmission Control Protocol (TCP) has used for its reliable, ordered end to end communication over a single path. But as devices increasingly have multiple network interfaces (e.g. Wi-Fi, cellular, Ethernet), Multipath TCP (MPTCP) emerges as a powerful extension. It allows a single logical connection to span multiple simultaneous paths. By doing so, it seeks to combine the reliability and robustness of TCP with improved throughput, fault tolerance and seamless handovers across heterogeneous networks.

TCP vs MPTCP

The figure depicts both the scenarios i.e. traditional TCP and MPTCP between Mobile phone as client device and remote cloud server. As shown, legacy TCP allows only one connectivity either Wi-Fi or 5G at a time. MPTCP allows both the technologies (Wi-Fi & 5G Cellular ) to be used simultaneously as per some conditions e.g. bandwidth, latency, loss, cost etc.

TCP

Transmission Control Protocol (TCP) is one of the core protocols of the Internet that ensures reliable communication between devices. It establishes a single connection between two endpoints and guarantees that data is delivered accurately and in order.

TCP manages packet transmission, error checking and retransmission if needed, making it ideal for applications like web browsing, email and file transfers. Its simplicity and reliability have made it the foundation of most Internet communications. The TCP specifications have been defined in RFC9293 by Internet Engineering Task Force (IETF).

Image Courtesy (IETF) : RFC 9293

The figure depicts tcp header format. Here “data offset” field indicates number of 32-bit words in the TCP header. It provides information about where the data begins. This will tell us about number of bytes in “options” field also.

MPTCP

Multipath TCP (MPTCP) is advanced extension of traditional TCP that allows single connection to use multiple network paths simultaneously. This means device can send and receive data over Wi-Fi, Ethernet and mobile networks at the same time.

MPTCP offers improvement in speed and reliability and offers seamless connectivity. If one network path fails, MPTCP automatically switches to another without interrupting the session. It enhances performance and resilience, especially in mobile and high availability environments, while remaining compatible with existing TCP infrastructure.

MPTCP protocol is located at transport layer. It is designed to be transparent to both higher (i.e. application) and lower layers (i.e. IP/MAC/PHY). It is a set of additional features on top of standard TCP Fig-2 : Image Courtesy : RFC 8684

Image Courtesy (IETF) : RFC 8684

MPTCP does not replace the TCP header but extends it using TCP options. This ensures backward compatibility with traditional TCP stacks and middleboxes. All MPTCP operations are signaled using optional TCP header fields.

Before use, MPTCP checks whether remote host or middlebox used in between support it or not. For this, it sends “MP_CAPABLE” option to tell other host to use MPTCP if supported. If MPTCP is not supported, returned “SYN+ACK” packet will not contain MPTCP options in the “TCP option field”.

Key differences

Conclusion: While standard TCP remains ubiquitous and well understood, its single path model limits flexibility in multi interface environments. MPTCP, by contrast, enhances connection resilience and performance by distributing traffic across multiple subflows, masking path failures and dynamically adapting to network conditions. However, this added flexibility comes with complexity, overhead and compatibility challenges. In many contexts, the choice between TCP and MPTCP depends on whether the environment can support its extensions and whether the benefits such as improved bandwidth utilization and seamless failover outweigh the trade-offs.