The following paragraphs, briefly introduce the outline of the thesis.
Chapter 2 is the foundation chapter for multihoming and related terminology. A in-depth state of the art is provided in this chapter, where multihoming support in diverse protocols of different network layers is analysed regarding multihoming goals fulfilment.
Chapter 3, inspired on the previous chapter, introduces two evaluation frame- works, to assess the multihoming support of a protocol. Specifically, REF establishes the required formulation to assess the resilience support of a protocol. Moreover, UEF evaluates to what extent a protocol supports ubiquity and thus, can be tailored for Ubiquitous Computing (UbiComp) systems.
Chapter 4 addresses the optimization problem in multihoming contexts. A Multi- homing aware optimization technique is specified in two distinct algorithms. First, a criteria weighting algorithm is provided to allow user preferences mapping through objective and consistent weights. Second, a path optimization algorithm is speci- fied to enable optimal path selection. Indeed, path optimization, following a MADM approach, is a flexible scheme that can be adapted easily to multihoming scenarios, accommodate more multihoming and traffic performance criteria, without requiring modifications in the optimization process.
Chapter 5 introduces a case of improving the multihoming support of the MIPv6 protocol. Such improvement, relies on a software implementation of the MCoA proto- col, in the OMNeT++ simulator. Experimental results are also discussed, namely the gain in VoIP quality regarding the multihoming support that MCoA includes.
The conclusions that emerged from the research work described in this thesis, are outlined in Chapter 6.
—In 1972, Tinker Air Force Base joined the Net and [..] wanted redundant network
connections. Upon hearing this news, I
distinctly remember thinking “Ah, great idea!” and a second later, thinking, “O *#@* that isn’t going to work!”
John Day, Patterns in Network Architecture
2
Multihoming in IP Networks
T
HIS chapter presents the state of the art on Multihoming and Multiaccess in Internet Protocol (IP) networks. A comprehensive survey of protocols act- ing at different layers of the Transport Connection Protocol (TCP)/IP model is presented. Furthermore, protocols with some kind of support for multihoming, namely, end-host, end-site and hybrid multihoming are also analysed. An overview of multihoming support in operating systems is also included, as well as implementa- tion details in Operating Systems (OSes).Multihoming support in the diverse protocols is analysed through a candidate’s proposed taxonomy. This taxonomy considers multihoming goals fulfillment (i.e. re- silience, ubiquity, load sharing, and flow distribution). This approach of analysing multihoming support is more objective than other approaches that use only one met- ric, such as cost [Richard, 2010], or which focus only on a subset of multihoming proto- cols, such as [Shinta et al., 2006; de Launois and Bagnulo, 2006; Fekete and H¨am¨al¨anen, 2009]. The following paragraphs, present the outline of each section, in the chapter.
Section 2.1 introduces terms used in the multihoming taxonomy. Concepts related to multihoming are defined and end-host, end-site and hybrid multihoming types are
characterized.
Section 2.2 presents design considerations for multihoming solutions and identi- fies the goals that characterize multihoming. In addition, multihoming open issues are also presented.
Section 2.3 highlights protocols supporting multihoming at the application layer and discusses multihoming support in operating systems.
Section 2.4 overviews multihoming support of protocols acting at the transport layer of the Internet protocol suite.
Section 2.5 depicts IPv6 mobility management protocols and their extensions to enhance multihoming support. IPv4 mobility management procotols are excluded, as they have limitations for future mobile networks.
Section 2.6 introduces protocols supporting end-host multihoming. Such kind of protocols operate on end-nodes (i.e. user devices) and implement mechanisms to sup- port multihoming on their own.
Section 2.7 introduces protocols supporting end-site multihoming. With this type of protocols, multihoming is enabled with network assistance.
Section 2.8 provides an overview of hybrid multihoming protocols. These pro- tocols merge functionalities from end-host and end-site multihoming approaches, to enable multihoming by allowing end-nodes to take decisions with the assistance of network. The chapter concludes with Section 2.9.
2.1
Multihoming Types and Concepts
This section introduces concepts related with multihoming, such as multiaddressing, multiaccess and overlapping networks. In addition, three different types of multihom- ing are characterized, namely end-host, end-site and hybrid multihoming.
2.1.1 Concepts
Multihoming is associated with other concepts, including multiaddressing, overlap- ping networks, multiple interfaces and overlay routing. Multiaddressing, for example, corresponds to a configuration in which multiple addresses are assigned to a given host based on prefixes advertised in different connections [Bagnulo et al., 2006]. Over- lapping networks correspond to networks that are configured in a way that there is a common area of coverage. Typically, mobile end-nodes connecting to these (over- lapping) networks must have multiple interfaces, each one specific to the technology
2.1 Multihoming Types and Concepts Multihomed Host IF 1 IF 2 prefix 3 prefix 1 prefix 2 legend: IF - interface IF n prefix n ...
Figure 2.1: Multihomed host
sustaining the respective network [Blanchet and Seite, 2011]. Overlay routing is asso- ciated with inter-domain routing techniques that improve fault-tolerance, and is only applied in an end-site context. Throught this thesis Multihoming is used as per Defi- nition 2.1.
Definition 2.1 (Multihoming)
Multihoming is an entity (host or network) configuration that has several first- hop connections to a given destination. Such connections can be accommodated through single or multiple (physical or logical) network interfaces.
Alternative definitions consider multihoming as the availability of two or more connectivity providers to offer fault tolerance and traffic engineering capabilities [Bag- nulo et al., 2006]. Or simply, a host is considered multihomed if it has multiple IP addresses [Braden, 1989].
2.1.2 End-host Multihoming
End-host multihoming is defined according to Definition 2.2.
Definition 2.2 (End-host multihoming)
End-host Multihoming is an host entity configuration that has several first-hop connections to a given destination and employs its own mechanisms to select con- nection(s).
A multihomed host with different interfaces (logical or physical) is depicted in Figure 2.1. In addition, each interface can have different network prefixes configured.
For instance, interface IF 1 has been assigned two prefixes, namely prefix 1 and prefix 2. Moreover, the host can have multiple physical interfaces which have been associated with a single prefix, as is the case of IF 2 and IF n with prefix 3 and prefix n, respectively. This configuration is possible when virtual interfaces are assigned to a physical inter- face, as depicted in Listing 2.1. Prefix and address terms are used here interchangeably. From an end-host perspective, a multihomed host has multiple prefixes configured on the links it connects to, thus having the possibility to explore several paths to reach a peer, as each prefix is normally advertised by different access routers.
List 2.1: Example of IPv6 aliases configuration for FreeBSD i f c o n f i g i f 1 i n e t 6 2 0 0 1 : db8 : 1 : : 1 / 4 8 a l i a s i f c o n f i g i f 1 i n e t 6 2 0 0 1 : db8 : 1 : : 2 / 4 8 a l i a s
2.1.3 End-site Multihoming
End-site multihoming is defined according to Definition 2.3.
Definition 2.3 (End-site multihoming)
End-site Multihoming is an network entity configuration that has several first-hop connections to a given destination.
Service Provider 1 Service Provider 2 Multihomed network MR 1 MR 2 prefix 2 prefix 1 prefix n prefix 3 legend: MR - Mobile Router
Figure 2.2: Multihomed network
End-site multihoming is defined in Definition 2.3, and corresponds to a site using multiple connections to the Internet to increase network reliability or improve perfor- mance [Abley et al., 2003; Dhraief and Montavont, 2008]. End-site multihoming first
2.1 Multihoming Types and Concepts
came up in the context of ARPANet back in 1972 due to the desire to have redundant network connections, thus allowing for more robust network operation [Day, 2008].
Figure 2.2 illustrates a multihomed site, which has connections to two service providers. A multihomed network can have multiple routers, such as, for example, MR 1 connecting to Service Provider 1 and MR 2 connecting to Service Provider 2. Moreover, a single router can have several external interfaces that connect to the same or different service providers, as the example of MR 1.
Different perspectives can be followed to consider a mobile network as multi- homed [Ng et al., 2007a; Ernst and Charbon, 2004; Choi et al., 2006]. The First ap- proach, the ownership-oriented approach that takes into account the ownership of the Home Agent (HA) and Mobile Routers. A mobile router is defined as an entity providing Internet access to the multihomed network, as mentioned above. If these network elements are controlled by a single entity, this is called the Internet Service Provider (ISP) model, otherwise it is referred to as the Subscriber/Provider model. Second, the problem-oriented approach considers the number of home agents and network prefixes advertised. Finally, the configuration-oriented approach considers different parameters such as the number of home agents, the number of prefixes avail- able and the number of Collocated Care of Addresses (CCoAs).
2.1.4 Hybrid Multihoming
Hybrid multihoming is considered throughout the thesis according to Definition 2.4.
Definition 2.4 (Hybrid multihoming)
Hybrid Multihoming is an entity configuration that has several first-hop connec- tions to a given destination, which require cooperation between nodes and net- work for an efficient operation.
Hybrid Multihoming mixes both end-host and end-site characteristics, but requires the participation of end-host and network entities (e.g. servers) for full multihoming support. Most current proposals are hybrid multihoming solutions that target issues on networks, such as routing scalability, but at the same time also address drawbacks of the current TCP/IP architecture, such as the dual role of IP address (identifier and locator). According to Figure 2.3, MH1 is a multihomed host, but multihoming man- agement requires support from the network (server) to maintain the location informa- tion, so that other end-hosts in the Internet can communicate with MH1.
Service Provider 1 Service Provider 2 MR 1 MR 2 prefix 2 prefix 1 prefix 3 legend:
MR - Mobile Router IF - Interface MH - Multihoming Host 3G IF 1 IF 2 prefix B.1 prefix A.1 Server MH 1 prefix A Network #A Multihomed Network #B
Figure 2.3: Hybrid multihoming scenario