Data services provide the basis for all broadband connections. While loosing some of their earlier significance both in terms of relative transmission volume and revenue, e-mail and web-based service still represent the most widely used services on the Internet. This becomes evident when comparing the nearly 84 billion e-mails sent daily worldwide in 2006 to the 7 billion IM messages (IDC 2005) and a few million VoIP calls.
Most data services are not real-time and thus suffice with available bit rate (ABR) or unspecified bit rate (UBR) as classified in Section 2.5.3. There are exceptions such as virtual private networks (VPN) and terminal services that are more resource demanding. However, all these service types have been studied extensively in literature (Tanenbaum 1996; Sexton and Reid 1997; Maxwell 1999; Chlamtac et al. 2005); having not deviated greatly from the predicted development paths, they will therefore not be analysed further.
An exception to the general rule of foreseeable development is Peer-to-Peer (P2P) technology. P2P utilises the abundance of underutilised end-equipment and broadband transmission capabilities by efficiently building overlay networks with built-in scalability and redundancy. To begin with, they were used for file-sharing but through active research in the past five years they have evolved into “infrastructures” capable of providing
advanced functions such as telephone switching, contributing to the search for extra-terrestrial life54 etc.
2.7.1. Peer-to-Peer Networks (P2P)
Content providers and market supply has traditionally been lagging market demand, mostly due to content owners’ fear of copyright violations. While waiting impatiently, users have built up communities of their own based on the peer-to-peer (P2P) technology. These networks take advantage of the immense number of often underutilised end systems by storing increasing amount of content locally. This shift from expensive centralised hardware, operated and controlled by operators and service providers, to perceivably free decentralised user driven systems has resulted in network communities of unprecedented scales.
After a growth period, dominated by the use of file-sharing applications and motivated to a large degree by access to copyright protected material, peer-to-peer networks are now being adapted into a wide spectrum of mainstream applications. Today, the potentials of peer-to-peer networks are reflected through hugely successful file sharing and VoIP applications, which through active research and development in the past few years can offer stability, redundancy, and scalability at a fraction of the cost of traditional server based services.
Figure 21, Network architecture of peer-to-peer overlay networks
54 See the Home@Seti project (http://setiathome.ssl.berkeley.edu/)
Despite success in some areas, the Achilles heel of peer-to-peer technology has been its inability to represent a complete revenue model accounting for all players involved in the value chain of content distribution. This is largely due to legal uncertainty surrounding the use and conflict of interests, e.g. where users regard traffic and content as free commodities while Internet Service Providers (ISPs) bear increasing cost of transmission and the music industry reports decreasing record sales due to file-sharing.
1st Era 2nd Era 3rd Era 4th Era
Period 1999 – 2001 2000 – 2002 2002 – 2004 Recent trends Architecture Centralised search,
P2P data transfers Decentralised,
partly hierarchical Hybrid Hybrid
Applications Mainly file-sharing Mainly file-sharing File-sharing, Software distribution, Instant
Sharing of data and resources
Distributed search and data transfer
Scalable, resilient structure, parallel multi source up- and download
Integrating P2P functions in special purpose solutions Popular
networks
Napster Gnutella, Freenet FastTrack, eDonkey, BitTorrent, MSN Messanger
Skype, PodCasting, networks for smaller communities
Table 6, Development of peer-to-peer applications
Today, there is an increasing tendency to use peer-to-peer applications for real time communications and for streaming video (Chou et al.
2003; Li 2004). In less than two years after its foundation, the Skype peer-to-peer solution for voice over IP (VoIP) reached global market leadership in VoIP. Peer-to-Peer technology will then not only be used for file sharing but will seamlessly integrate into advanced multimedia services. Among the most likely application types are:
Conversational services
Collaborative tools
Multi user games and e-learning
Manifold types of content distribution
Content distribution networks (CDNs) were introduced to improve the performance of static or transaction-based Web content. In recent time streaming media, radio, Internet TV etc. have become an increasing portion of their content. Starting from a client-server based architecture, popular servers are supported by surrogate or cache servers. In this way an overlay network is established often based on
the infrastructure of a content distribution network to avoid bottlenecks at servers and to reduce the access time to content by shortening transmission paths to clients (Popesccu et al. 2006). Using a rigid infrastructure enables better utilisation of resources and full control over content and its distribution.
One of the main issues of CDNs is where to place the caches or surrogate servers. This is a trade-off between the costs of resources (hardware, provisioning, and transmission resources) and transmission distance to the consumer. Main challenges lie in efficient content management and routing of content to satisfy the user demand, as well as measurement to confirm a sufficient level of the perceived QoS.
Content distribution via peer-to-peer networks goes a step beyond towards a completely distributed structure involving the resources of the peers interested in the content. P2P content distribution allows for more flexibility in the overlay network, which may be structured according to different content e.g. by trackers for each item in the BitTorrent network or according to other criteria. The size of the overlay can automatically adjust to the population of peers and thus user demand with a replication strategy for the data being set up by the P2P protocol.
On the other hand, there are still open issues on control of usage and delivery which are of great concern to content owners and providers. In addition, no guarantee for perceived QoS can be assured in current global P2P overlays, where each peer may enter or leave the network at any time. While ongoing research is addressing QoS in P2P networks (Heckmann 2006), incentives for peer participation are essential to ensure sufficiency of resources. This can be accomplished e.g. through admission control or by inducing peers to contribute resources through some form of incentives.
One of the key issues that can facilitate evolution of future applications is the adoption of Digital Rights Management (or at least avoidance of conflicts with IPR). In contrast to earlier file sharing applications that violate Intellectual Property Rights (IPR) of audio, video, software etc., future applications will take advantage of the technical benefits of peer-to-peer networks, without exploiting intellectual property rights.
Nevertheless, resource and file sharing will prevail, since the volume of interesting unlicensed multimedia content provided by single users and communities on the Internet is increasing.
2.7.2. Multiplayer Games
Home (console) gaming has throughout the past decade become increasingly popular. Today, the tendency is for more and more of these games to connect to the Internet to provide a richer experience. There are three types of multiplayer games, network based games, massive multiplayer on-line games (MMOG), and Gaming-on-Demand.
Network based games are similar in structure to instant messaging where users connect to other users through signalling with a game server, after which users communicate directly in a peer-to-peer fashion. MMOG, on the other hand use client/server architecture where all traffic passes through a common network server (or a cluster of servers) that maintains state of all players. Despite a common source all transmissions from the server are mostly unicast.
The third category, Gaming-on-Demand, decrease the processing power and storage capacity requirements of computer and video games by executing the game at a server and streaming the game experience to the user. The client device only decodes and presents the received streams, and transmits the user commands back to the server. In this way resource limited devices such as IPTV set-top-boxes can be used to play advanced games. Due to its mission critical transmission requirements, this kind of service sets strict requirements on the transmission network in terms of throughput and round trip time (RTT), or around 100 ms according to Laulajainen et al. (2006).
It is a widely-held industry view that network based games and MMOG will not be a major generator of revenues for broadband access providers Chlamtac et al. (2005). With revenues increasing in service provision that passes over the network, network access providers are likely to have a stronger bargaining power when selling advanced transmission functionality to customers.
2.7.3. Future perspectives of data services
Data services are and will be an integral part of future residential broadband services. However, the distinction between data services and other types of services is likely to disappear as applications and services using converged multimedia features increases. Measures by operators to fully capture the value and service delivery of all of these applications are not likely to work and therefore operators have to
embrace Internet services and rather focus on being prepared to offer a variety of transmission services that can meet specific needs.
In the short run the use and consequently the amount of traffic generated by p2p overlay networks is going to cause worries to operators, concerned about the volume and inefficiency of content distribution. Additionally P2P technology poses challenges to content owner since, as the author has shown in Sigurdsson et al. (2006) one of the main drivers for use of current file sharing P2P networks is illegal content. However, when integrated into future services P2P has e.g. the potentials of reducing cost and increasing redundancy and is likely to be incorporated into an increasing number of applications.