A Dynamic Offer/Answer Mechanism Encompassing TCP Variants in Heterogeneous Environments

Abstract

The Transmission Control Protocol (TCP) has evolved from its initial form defined in RFC 793 in 1981 to cope with the evolution of IP networks in general and of the Internet in particular. Over the years, several factors have led to the design of successive TCP variants: the increasing disparity of end hosts, the variety of data links characteristics (Optical, wireless cellular or satellite), the increase of the delay-bandwidth product in data networks or the use of multiple paths at the same time. In this context, some TCP variants tune the congestion control and avoidance mechanisms to adapt them to specific situations while others make use of TCP options. In practice, such enhanced versions of TCP can be unusable because of the presence of intermediate elements such as firewalls along the path between the two end hosts. Such elements can indeed filter some TCP options or tamper with the way congestion is managed, introducing then unacceptable jitter in the IP flows. In such cases, most TCP variants are designed to fallback to a generic form of TCP. In many situations, this generic TCP version is not the best fit, while another TCP variant could be used to deal with this transient problem. To address this issue, we introduce an original offer/answer (O/A) mechanism allowing end hosts to identify dynamically a suitable TCP variant able to satisfy the specific constraints of each type of packet flows.