IEEE 802.21 Transport Solution Using Cross-Layer Optimized Stream Control Transmission Protocol Richard Rouil, Nada Golmie Nicolas Montavont National Institute of Standards and Technology Telecom Bretagne / Institut Telecom USA France richard.rouil@nist.gov, nada.golmie@nist.gov nicolas.montavont@telecom-bretagne.eu Abstract—The Media Independent Handover (MIH) ar- chitecture is designed to facilitate the signaling and enable seamless handovers in heterogeneous networks. In this paper, we propose a solution using the Stream Control Transmission Protocol (SCTP) to efficiently carry MIH messages. The solution uses SCTP’s multihoming and mul- tistreaming capabilities along with cross-layer information available through the MIH. We analyze the performance of the proposed solution for various packet loss conditions. I. I NTRODUCTION Mobile users currently have access to a wide range of wireless technologies. To facilitate handover signaling across heterogeneous networks, the Institute of Electri- cal and Electronics Engineers (IEEE) 802.21 Working Group is developing a Media Independent Handover (MIH) framework [7]. This framework facilitates the exchange of information across different entities of the mobility management protocol stack within a node and between different network entities via the MIH protocol. The MIH Function (MIHF) is the core element of the MIH architecture and provides three services to its users. The Media Independent Event Service (MIES) generates and distributes layer 1 and layer 2 events in a generic format. The Media Independent Command Service (MICS) allows an MIH user to control the behavior of lower layers. Finally, the Media Independent Information Service (MIIS) enables MIH nodes to collect information about surrounding networks via the current connection. MIHFs communicate via the MIH protocol. The actual transport mechanism is not specified but the MIH mes- sages can be carried over layer 2, layer 3, or any layer above. The low packet latency and reliability dictate the selection of the transport protocol. If the necessary signaling is not completed prior to losing connectivity, the mobile node relies solely on local information and may connect to an invalid network. The main reason to trigger a handover is a degredation in signal quality. This also means that the connection is suffering from higher packet loss. Thus the transport protocol carrying the MIH messages must be able to maintain its service under conditions of high packet loss. Traditional transport protocols, namely User Datagram Protocol (UDP) and Transmission Control Protocol (TCP) provide communication between two Internet Pro- tocol (IP) addresses and rely on additional mechanisms such as Mobile IP to handle mobility. This means that the performance of these protocols is dependant on the mobility protocol located at the network layer. In con- trast, SCTP [4] embeds multihoming and multistreaming capabilities. The Dynamic Address Reconfiguration [6] also allows SCTP to perform layer 4 handovers. Due to those capabilities, SCTP is an adequate transport protocol for MIH messages. However, the default re- transmission mechanism and movement detection need to be optimized by using the MIH services. Therefore, in this paper we propose a transport solution for MIH messages using SCTP that combines an interface selec- tion algorithm, cross-layer optimizations, and enhanced control of SCTP by the MIHF. The rest of this paper is organized as follows. In section II we present the solution to transport MIH messages via SCTP while using the MIH services to optimize the behavior of SCTP. Section III provides numerical results demonstrating the performance of the proposed solution for various packet loss conditions. Conclusions are given in section IV. II. PROPOSED TRANSPORT SOLUTION In this section, we present a solution optimizing SCTP to efficiently carry MIH messages. As shown in Figure 1 there are two views to the proposed solution. In the Mobility Control Plane, SCTP uses MIH services such as events and commands to be aware of changes at the lower layers therefore SCTP is located above the MIHF. In the data plane, MIHF sends and receives MIH messages by using SCTP as a transport protocol, thus MIHF is located above SCTP. There are three main components to the proposed so- 978-1-4244-2644-7/08/$25.00 © 2008 IEEE