[IEEE 2010 The 9th IFIP Annual Mediterranean Ad Hoc Networking Workshop (Med-Hoc-Net 2010) - Juan Les Pins, France (2010.06.23-2010.06.25)] 2010 The 9th IFIP Annual Mediterranean Ad Hoc Networking Workshop (Med-Hoc-Net) - OLSR based peer to peer instant messaging for Ad-hoc networks
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OLSR based Peer to Peer
Instant Messaging for Ad-hoc Networks
Nesrine Ayed Sahloul, Lamia Ben Azzouz and Farouk Kamoun
University of Manouba, ENSI CRISTAL Laboratory, Tunisia
firstname.lastname@example.org, email@example.com, firstname.lastname@example.org
AbstractInstant messaging is one of the most popular
applications on the Internet. Furthermore, we assist to the
emerging of Peer to Peer systems based on a decentralized
architecture. These systems share similarities with spontaneous
Ad-hoc networks. The crossing of the Ad hoc networks and the
Peer to Peer systems opens a field of possibilities for new
spontaneous collaborative applications such as the instant
messaging. In this work, we propose a Peer to Peer instant
messaging system for Ad-hoc networks based on the IETF work
in progress. This will guarantee the opening and the viability of
Keywords-Instant messaging; P2PSIP, DHT; Ad hoc Network;
Today, instant messaging is becoming the favourite application for a very large number of users. It facilitates communications and informations exchange between users.
These last years, we have witnessed the emergence of Peer to Peer systems. They are based on a decentralized architecture and don't require servers. All peers are equivalent and can be servers or clients. Thus, Peer to Peer architecture allows deployment and development of various applications such as voice over IP, sharing files and instant messaging.
The most existing instant messaging systems adopt a centralized architecture and use owners not standardized protocols [2,3]. However, the IETF has standardised a protocol that allow to set up applications such as voice over IP and instant messaging called SIP/SIMPLE. SIP is a protocol that can establish, modify and terminate multimedia session . Its architecture is composed of two entities SIP servers (registrar server, location server, redirect server and proxy server) and SIP users' agents. Today, an IETF working group propose a version of Peer to Peer SIP protocol. This work is described in the work in progress "P2PSIP"[1,4].
Wireless Ad-hoc networks are a popular subject of research because its easy to deploy. Nodes connect to each other without any infrastructure. Ad-hoc networks present many similarities with Peer to Peer systems. Indeed, in Ad hoc networks, all nodes are equivalent and act as routers. Thus, a client/server architecture is not adapted for these networks and the notion of server becomes obsolete. Furthermore, as Peer to Peer system, Ad-hoc networks are formed spontaneously and not stable. Nodes leave and join the network at any time. The crossing of Ad hoc networks and Peer to Peer systems opens a field of possibilities for new spontaneous collaborative
applications such as instant messaging.
Various research works were interested to combine Ad-hoc and Peer to Peer modes to implement Peer to Peer applications or systems which facilitate the deployment of these applications as the DHT: Distributed Hash Table. However, proposed solutions define owners protocols and present many inconveniences (example: important overhead, scalability, etc).
In this paper, we propose a Peer to Peer instant messaging system for Ad-hoc networks entitled IMOLSR (Instant Messaging over OLSR). To guarantee an opening of the solution, the proposed work is based on the IETF work in progress "P2PSIP". Moreover, because IMOLSR is deployed in wireless networks where the bandwidth is limited, we opt to transport necessary informations to the IMOLSR application by exploiting Ad-hoc routing protocols. In fact, this can minimize the overhead generated by IMOLSR messages.
This paper is organized as follows: in section 2, we present a state of the art of Peer to Peer instant messaging proposed in wired networks and in Ad-hoc networks. In section 3, we describe the proposed solution IMOLSR. Section 4 presents simulations conducted to evaluate performances of IMOLSR application. Finally, in section 5, we outline future work.
II. STATE OF THE ART
In this section, we present Peer to Peer instant messaging systems proposed in the literature for wired and wireless networks.
2.1. Peer to Peer instant messaging for wired networks
Few Peer to Peer instant messaging systems are implemented such as Skype, Wengo and Waste. These systems use owners protocols and don't allow interoperability [3, 13, 5]. However, in the literature, we find various works proposing open systems that use standard protocols such as SIP/SIMPLE. These works are the SOSIMPLE solution [2, 3, 5] and the architecture proposed by the IETF P2PSIP work in progress [1, 4]. Such solutions are defined for structured Peer to Peer system based on DHT (Distributed Hash Table). In this section, we present, in a first step, the DHT system. Then, in a second step, we describe the SOSIMPLE solution. Finally, we present the IETF proposition.
2.1.1. What is DHT?
The DHT (Distributed Hash Table) is a system which allows resources location and discovery in a structured Peer to
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Peer environment. Many DHT such as CHORD, PASTRY and CAN exist. The DHT represents a virtual space: the KeyIds space . Each node and each resource has a single identifier in a common space:
Hash(IP) for a node,
Hash (key) for a resource.
The identifier allows nodes and resources identification in the Peer to Peer environment. Each node is responsible for a zone of KeyIds space and disposes of a routing table to be able to route requests. This table allows locating a node responsible for the zone containing a resource R. A message arrives to a node responsible for the zone containing a resource R in a hops number about log (N).
SOSIMPLE (Self Organizing SIMPLE) [2,3,5] is a Peer to Peer instant messaging system using SIP/SIMPLE protocol. It permits standard functionalities of instant messaging systems such as, registration, location and presence notification. It is based on a structured Peer to Peer network that uses CHORD DHT. SOSIMPLE is based on SIP where each node has a SIP URI resembling an e-mail address. Thus, the register ID is obtained by hashing the SIP URI.
The registration is done in the node having the nearest identifier of the requested node. Resources location and discovery in SOSIMPLE are based on CHORD where nodes are ordered by the ascending order of their identifiers on the virtual ring. For presence notification, a node can send a message SUBSCRIBE to a receiver already contacted asking it to send a message NOTIFY to get informations about its availability.
2.1.3. The IETF work in progress P2PSIP
The IETF work in progress P2PSIP proposes an architecture for Peer to Peer SIP systems .
In P2PSIP architecture there are two types of nodes: super nodes (SN: Super Node) and ordinary nodes (ON: Ordinary Node) (see Figure.1). Super nodes participate in the DHT construction and maintenance.
Figure 1. P2PSIP architecture
Each ordinary node is associated with one or several super
nodes. To discover a resource, an ordinary node sends a request message to the super node. Then, the super node routes the search request message via the DHT.
A peer in P2PSIP is composed of two layers: the SIP layer and the P2P overlay layer. The SIP layer ensure the SIP functionalities such as the initiation call, SIP inscription, and the closing call. The P2P overlay layer registers and provides the location of various SIP resources.
2.2. Ad-hoc Networks Peer to Peer instant messaging.
In the literature, we can find solutions based on clustering for Ad-hoc networks to set up instant messaging system. Others propose SIP version for Ad-hoc networks. Many works are even interested by adapting systems that allow resources discovery in such environment (DHT for Ad-hoc networks).
2.2.1. Solutions based on clustering
The clustering is used to divide an Ad-hoc network into clusters managed by leaders called Cluster Head (CH).
 exploits the clustered Ad-hoc networks to set up a DHT. The proposed architecture is essentially composed of:
The TT-DHT (Top-Tier Distributed Hash Table): that is a virtual network of CHs nodes. It allows data and control messages routing between nodes belonging to the separated LT-DHT.
LT-DHT (Low-Tier Distributed Hash Table): is a virtual network of nodes responsible of intra cluster communications and CHs election. (See Figure.2)
Figure 2. Clustering based on DHT architecture
In this architecture, CH acts as a gateway for Ordinary Nodes associated to it by relaying informations between clusters. The discovery of a resource is done primarily in the cluster which belongs to the requestor node. Then, the discovery request is forwarded to the TT-DHT if the resource is not found.
In , SIP/SIMPLE protocol is adapted for ad-hoc networks by using the clustering concept. The clustering
CH (Application Layed)
CH (Network Layed)
creates a virtual topology to route SIP messages allowing resources discovery and location. Each node is a SIP User Agent and CHs ensure functionalities of a SIP proxy and a SIP Registrar server. In , CH is distant about two or three hops to another CH. Thus, each CH maintains a connectivity with CHs neighbors through nodes called gateway.
Figure 3. SIP/SIMPLE based on clustering
To contact a node, the sender must send a request (REQUEST) to its CH. If a CH knows the target URI, it sends this request to the receiver node. Otherwise, it transmits the message to CHs neighbors. Each CH records its address in the field RECORD-ROUTE of SIP message. This field will contain the list of CHs crossed to reach the receiver node. By receiving the request, the receiver node sends a SIP OK via the opposite way specified by the field Record-route (see Figure.3). After receiving SIP OK, the node which initiates the request can communicate directly with it. The presence notification messages are sent similarly to SIP OK messages.
The clustering allows hierarchical architecture facilitating discovery and location resources in Ad-hoc networks. This method allows also scalability but remains expensive in bandwidth, and slow for an application such as instant messaging. Indeed, the initiation phase, based essentially on the clustering and the creation of virtual topology, generates an important delay and a significant overhead. Moreover, the clustering is generally adapted to large scale networks.
2.2.2. SIP/ SIMPLE in Ad-hoc networks
In this section, we present a framework which proposes a SIP/SIMPLE adaptation for Ad-hoc networks . This framework allows users to participate in conferences and to exchange instant messages with participants. It is based on the broadcast and the multicast. Thus, to discover participants each UA broadcasts a REGISTER message and each node records SIP URI and IP addresses of all nodes in its cache for a limited time. In the same way, to begin a conference, the initiator node (which initiates a conference) broadcasts a REGISTER message with a Conf-ID field containing identifiers of conferences for which this initiator is the leader. On the other hand, to take part in a conference, it is enough to send a message INVITES to the leader who sends a CONF message to all participants. Finally, to leave a conference the leader sends a BYE message to all participants.
This framework  is simple, but it is based on a
broadcast. It is not therefore scalable. Moreover, it generates an important overhead in an environment where the bandwidth is limited.
2.2.3. DHT in mobile Ad hoc networks
The bandwidth limitation and the mobility constitute a challenge to deploy DHT in mobile Ad-hoc networks. Thus, we find in the literature works that present new systems specific to Ad-hoc networks. These systems achieve DHT functionalities. Others works, adapt existing DHT in this type of networks.
Nom  is a decentralized system of resources location and discovery proposed for the mobile Ad-hoc networks. For ensuring DHT functionalities, Nom uses a broadcast. This system is exploited in a framework called DAWN  that ensures instant messaging functionalities. Nom is a simple location and discovery system because it is based on the broadcast. However, it generates a significant traffic which depends on network density. So it is not scalable.
Other research works proposed an adaptation of existing DHT in mobile Ad-hoc networks by using routing protocol. The proposition described in  combines the advantages of DHT PASTRY and those of the ondemand Ad-hoc routing protocol, DSR. This solution proposes two different approaches. The layered approach implements DHT PASTRY directly on top of DSR. The integrated approach called EKTA that inserts PASTRY at the network layer. Thus, PASTRY and DSR form the same structure and allows exploiting the interactions between these two protocols and optimizes the routing performance. The two approaches have an advantage compared other solutions because they are not based on the broadcast.
The use of the DHT Pastry and routing protocol DSR minimizes the overhead generated by the various messages allowing resources location and discovery. However, the two approaches exploit simultaneously Pastry messages and DSR messages to be able to provide instant messaging functionalities. It would be interesting to transmit data that are necessary to PASTRY in DSR message.
III. THE PROPOSED SOLUTION: IMOLSR
The majority of propositions described previously present limits, because they exchange a great quantity of data and generate a significant overhead. These solutions are not scalable and owners. Thus, to define an open Instant Messaging system for Ad-hoc Networks, we chose the IETF P2PSIP protocol which is described in [1, 4]. The proposed application called, in the rest of paper, IMOLSR (Instant Messaging over OLSR) exploits OLSR Ad-hoc routing protocol and CHORD DHT. To minimize the traffic generated by the application, we propose to use OLSR messages to forward necessary informations to IMOLSR application.
In this section, we present firstly the OLSR Ad-hoc routing protocol and we justify its uses. Then, we describe the proposed IMOLSR architecture.
3.1. OLSR Ad-hoc routing protocol
OLSR is a proactive Ad-hoc routing protocol. In fact, the
Res1 Res2 Req
routing of packages is carried out by using a routing table established before any communication. OLSR is a link state protocol where each node regularly broadcasts informations about its neighbors in the network. This routing protocol optimizes the link state algorithm by flooding its neighbors intelligently , via "multipoint relays" (MPR). Indeed, only the MPR nodes relay messages, which significantly...