Formal specification and verification of TCP extended with the Window Scale Option

Abstract

The Transmission Control Protocol (TCP) aims to provide a reliable transport service between two parties that communicate over a possibly faulty network. The responsibilities of TCP can roughly be divided into two categories: connection management and data transmission. Connection management sets up the connections, manages the byte streams and their corresponding states and ensures that connections are closed in a safe manner. Data transmission involves the transfer of segments from the sender to the receiver.The specification of TCP is far from formal and very complex. The original protocol was only specified in natural language in RFC 793. As TCP was implemented on a large scale, several ambiguities and other issues surfaced. RFC 1122 clarified some of these ambiguities and proposed solutions for many issues. Moreover, the networks that TCP operates over have changed remarkably over the years, and have now reached a bandwidth and speed that had never been envisioned at the time that the protocol was originally defined. To ensure reliable and efficient operation of TCP over these modern networks, RFC 1323 proposes the Window Scale Option that enables the use of windows larger than 2 16 .For complex systems, formal specification and verification can be used to manage their complexity. The approach is twofold: first, the system is modelled using formal techniques that have mathematical underpinnings, to obtain a specification. To this specification, verification techniques are then applied to verify the correctness of the system.In this work, we give a formal specification of TCP extended with the Window Scale Option using the process algebra µCRL. Due to the complexity of the protocol, our specification focuses on the data transfer phase and connection teardown. From this specification, we obtain a model of unidirectional data transfer and show that its external behaviour is branching bisimilar to a FIFO Queue. In addition, we obtain a model for the connection teardown phase and prove several properties that represent its correctness.1

Automated Attacker Synthesis for Distributed Protocols

“…TCP was previously formally studied using a process language called SPEX [37], Petri nets [16], the HOL proof assistant [7], and various other algebras (see Table 2.2 in [28]). Our model is neither the most detailed nor the most comprehensive, but it captures all possible establishment and tear-down routines, and is tailored to our framework.…”

Assessment of Communication Resource Allocation by the Transmission Control Protocol for the Target Virtual Connection under Competitive Conditions

“…Feedback signals are transmitted in a stream opposite to the stream of information-message transmission. The selective acknowledgement procedure for information exchange is implemented according to RFC 2883 [22].…”

Automatic distributed code generation from formal models of asynchronous processes interacting by multiway rendezvous

“…This library is built upon TCP sockets, and thus satisfies the reliable and ordered communication hypothesis required for the protocol (as was shown in [40]). In addition, the network library provides a integrated deployment service through a "starter" program that is able to automatically distribute and start other programs on a cluster of machines.…”