]> Simula Metropolitan Centre for Digital Engineering

Pilestredet 52 0167 Oslo Norway dreibh@simula.no https://www.simula.no/people/dreibh

University of Duisburg-Essen, Institute for Experimental Mathematics

Ellernstraße 29 45326 Essen Germany jp@iem.uni-due.de.de

Internet-Draft This document describes a novel mobility concept based on a combination of SCTP with Dynamic Address Reconfiguration extension and Reliable Server Pooling (RSerPool).

Introduction An increasing amount of Internet devices is getting mobile. Therefore, there is a growing demand for software solutions allowing for a seamless handover of communication sessions between multiple networks, e.g. to allow for a laptop or PDA to use a fast Ethernet connection when available, hand over to a WLAN when moving and hand over again to UMTS when the WLAN becomes unreachable - without interrupting the running communication sessions. Mobility handling is a deficiency of the common IP-based networks. Most of the available solutions are based on the network layer. The disadvantage of such solutions is that fundamental changes in the network infrastructure are needed. Therefore, we propose a new solution based on the upper layers to overcome these disadvantages. In this document, we present our mobility solution based on the SCTP protocol with Dynamic Address Reconfiguration extension and Reliable Server Pooling (RSerPool).

Existing Mobility Solutions

Mobile IP and Mobile IPv6 In the concept of Mobile IP every node must register to a Home-Agent (HA) in its own home network. Then, the nodes are reachable under their home addresses managed by the HA. When a node leaves its home network, it must also register at a Foreign Agent (FA) in the new network. After that, a tunnel is established between the HA and the FA. Any traffic to the mobile node is then tunnelled by its HA to the FA and forwarded by the FA to the node itself. Clearly, the detour of all traffic via HA and FA is inefficient and results in an increased transmission delay. Mobile IPv6 is an extension of Mobile IP. In Mobile IPv6, the FA is not needed. The packets will be tunnelled from the HA to the Gateway Router in the foreign network, which forwards the packets to the endpoint. The inefficiency due to the detour of traffic as described for Mobile IP remains.

SCTP with Dynamic Address Reconfiguration Using the SCTP protocol (see together with its Dynamic Address Reconfiguration extension (Add-IP, see ), it is possible for a mobile endpoint to inform its peer on address changes. That is, when a moving mobile client gets in the vicinity of an additional radio station, it sends an "ASCONF Add Address Request" to tell its peer that it is now reachable under an additional network-layer address. After that, the peer endpoint can use this additional address for a new SCTP path. When the first radio station becomes unreachable, the node can send an "ASCONF Delete Address Request" to the peer endpoint. After that, the peer removes the corresponding SCTP path to the unusable network-layer address. The following two cases for handovers are possible:

• Make-before-Break: An additional SCTP path can be used before the original path becomes unusable. This case is trivial, since there is a continuous connectivity.
• Break-before-Make: The original SCTP path becomes unusable before a new SCTP path can be used. For the case that only one endpoint performs a handover procedure at the same time, the mobile endpoint can always use Add-IP to communicate its new address to its peer endpoint. However, when both endpoints perform a handover simultaneously, no endpoint is able to tell its corresponding peer the new address.

Solutions for Simultaneous Handovers

SCTP with Add-IP and Mobile-IP Using SCTP with Add-IP and Mobile IP/Mobile IPv6, the ASCONF messages will be sent to the home address of the peer node. That is, even when both nodes are mobile, each endpoint is able to reach its peer endpoint using the corresponding home address. However, this solution still requires the full Mobile IP/Mobile IPv6 infrastructure.

SCTP with Add-IP and RSerPool Using RSerPool (see , , , , , , , at least one node registers as a Pool Element (PE) at an ENRP server under a Pool Handle (PH) known to both endpoints. Upon handover, it is simply necessary for the PE endpoint to re-register, i.e. to update its registration with its new address. The other endpoint can - in the role of a Pool User (PU) - ask an ENRP server for its peer node's new addresses. After the new address is known, it is able to create a new SCTP path and continue the communication. The usage of RSerPool to provide support for mobile endpoints provides the following advantages:

• Simplicity: No Mobile IP/Mobile IPv6 infrastructure is needed. In particular, it is not necessary that the providers of used networks (e.g. public WLAN access points, UMTS providers, etc.) provide any support for the mobility solution.
• Efficiency: No tunnelling of traffic is necessary.
• Applicability: All major SCTP implementations already support the Dynamic Address Reconfiguration extension. It is only necessary to provide support for RSerPool, e.g. in the form of a userspace library, which is much easier to deploy than kernel extensions.
• Flexibility: RSerPool provides a complete session layer. That is, providing applications on top of RSerPool makes the support for high availability simple.

A more detailed description of our approach for endpoint mobility, as well as a performance analysis using a prototype implementation, can be found in our paper .

Reference Implementation The RSerPool reference implementation RSPLIB can be found at . It supports the functionalities defined by , , , and as well as the options , and . An introduction to this implementation is provided in .

Testbed Platform A large-scale and realistic Internet testbed platform with support for the multi-homing feature of the underlying SCTP protocol is NorNet. A description of NorNet is provided in , some further information can be found on the project website .

Security Considerations Security considerations for RSerPool systems are described by .

IANA Considerations This document introduces no additional considerations for IANA.

References Normative References This document defines a basic set of requirements for reliable server pooling. This memo provides information for the Internet community. This document obsoletes RFC 2960 and RFC 3309. It describes the Stream Control Transmission Protocol (SCTP). SCTP is designed to transport Public Switched Telephone Network (PSTN) signaling messages over IP networks, but is capable of broader applications. SCTP is a reliable transport protocol operating on top of a connectionless packet network such as IP. It offers the following services to its users: -- acknowledged error-free non-duplicated transfer of user data, -- data fragmentation to conform to discovered path MTU size, -- sequenced delivery of user messages within multiple streams, with an option for order-of-arrival delivery of individual user messages, -- optional bundling of multiple user messages into a single SCTP packet, and -- network-level fault tolerance through supporting of multi-homing at either or both ends of an association. The design of SCTP includes appropriate congestion avoidance behavior and resistance to flooding and masquerade attacks. [STANDARDS-TRACK] A local host may have multiple points of attachment to the Internet, giving it a degree of fault tolerance from hardware failures. Stream Control Transmission Protocol (SCTP) (RFC 4960) was developed to take full advantage of such a multi-homed host to provide a fast failover and association survivability in the face of such hardware failures. This document describes an extension to SCTP that will allow an SCTP stack to dynamically add an IP address to an SCTP association, dynamically delete an IP address from an SCTP association, and to request to set the primary address the peer will use when sending to an endpoint. [STANDARDS-TRACK] This document specifies protocol enhancements that allow transparent routing of IP datagrams to mobile nodes in the Internet. Each mobile node is always identified by its home address, regardless of its current point of attachment to the Internet. While situated away from its home, a mobile node is also associated with a care-of address, which provides information about its current point of attachment to the Internet. The protocol provides for registering the care-of address with a home agent. The home agent sends datagrams destined for the mobile node through a tunnel to the care-of address. After arriving at the end of the tunnel, each datagram is then delivered to the mobile node. [STANDARDS-TRACK] This document specifies Mobile IPv6, a protocol that allows nodes to remain reachable while moving around in the IPv6 Internet. Each mobile node is always identified by its home address, regardless of its current point of attachment to the Internet. While situated away from its home, a mobile node is also associated with a care-of address, which provides information about the mobile node's current location. IPv6 packets addressed to a mobile node's home address are transparently routed to its care-of address. The protocol enables IPv6 nodes to cache the binding of a mobile node's home address with its care-of address, and to then send any packets destined for the mobile node directly to it at this care-of address. To support this operation, Mobile IPv6 defines a new IPv6 protocol and a new destination option. All IPv6 nodes, whether mobile or stationary, can communicate with mobile nodes. This document obsoletes RFC 3775. [STANDARDS-TRACK] The Reliable Server Pooling effort (abbreviated "RSerPool") provides an application-independent set of services and protocols for building fault-tolerant and highly available client/server applications. This document provides an overview of the protocols and mechanisms in the Reliable Server Pooling suite. This memo provides information for the Internet community. Aggregate Server Access Protocol (ASAP; RFC 5352), in conjunction with the Endpoint Handlespace Redundancy Protocol (ENRP; RFC 5353), provides a high-availability data transfer mechanism over IP networks. ASAP uses a handle-based addressing model that isolates a logical communication endpoint from its IP address(es), thus effectively eliminating the binding between the communication endpoint and its physical IP address(es), which normally constitutes a single point of failure. In addition, ASAP defines each logical communication destination as a pool, providing full transparent support for server pooling and load sharing. It also allows dynamic system scalability -- members of a server pool can be added or removed at any time without interrupting the service. ASAP is designed to take full advantage of the network level redundancy provided by the Stream Transmission Control Protocol (SCTP; RFC 4960). Each transport protocol, other than SCTP, MUST have an accompanying transport mapping document. It should be noted that ASAP messages passed between Pool Elements (PEs) and ENRP servers MUST use the SCTP transport protocol. The high-availability server pooling is gained by combining two protocols, namely ASAP and ENRP, in which ASAP provides the user interface for Pool Handle to address translation, load sharing management, and fault management, while ENRP defines the high- availability Pool Handle translation service. This memo defines an Experimental Protocol for the Internet community. The Endpoint Handlespace Redundancy Protocol (ENRP) is designed to work in conjunction with the Aggregate Server Access Protocol (ASAP) to accomplish the functionality of the Reliable Server Pooling (RSerPool) requirements and architecture. Within the operational scope of RSerPool, ENRP defines the procedures and message formats of a distributed, fault-tolerant registry service for storing, bookkeeping, retrieving, and distributing pool operation and membership information. This memo defines an Experimental Protocol for the Internet community. This document details the parameters of the Aggregate Server Access Protocol (ASAP) and Endpoint Handlespace Redundancy Protocol (ENRP) defined within the Reliable Server Pooling (RSerPool) architecture. This memo defines an Experimental Protocol for the Internet community. Reliable Server Pooling (RSerPool) is an architecture and set of protocols for the management and access to server pools supporting highly reliable applications and for client access mechanisms to a server pool. This document describes security threats to the RSerPool architecture and presents requirements for security to thwart these threats. This memo provides information for the Internet community. This document describes server pool policies for Reliable Server Pooling (RSerPool) including considerations for implementing them at Endpoint Handlespace Redundancy Protocol (ENRP) servers and pool users. This memo defines an Experimental Protocol for the Internet community. SimulaMet This document describes the Handle Resolution option for the ASAP protocol. SimulaMet Hainan University This document contains the definition of a delay measurement infrastructure and a delay-sensitive Least-Used policy for Reliable Server Pooling. SimulaMet Hainan University This document describes the Takeover Suggestion Flag for the ENRP_HANDLE_UPDATE message of the ENRP protocol. Informative References