Use Cases for Peer-to-Peer Session Initiation Protocol (P2P SIP)

Use cases are grouped according to the characteristics of the network environment in which the end users or devices participating in the P2P overlay are communicating with each other.

The global Internet environment consists of a large number of autonomous networks with diverse characteristics. Thus, there is no central administration or network control of the physical network on a global scale. Communication paths between two remote devices may span multiple administrative domains and should be assumed to be insecure. Note that most well-known P2P file sharing overlay networks have operated in this environment.

Skype is an outstanding example of a public VoIP service provider using P2P technology among end user devices, although using a proprietary protocol. Recent research has shown that Skype uses a central login server, responsible for management of registered user names. End users are authenticated via certificate signed by a central server. End user devices are distributed across the global Internet. The number of participating end user devices is very large. A major motivation of using P2P between end user devices for a commercial VoIP service is a reduction in infrastructure and operational costs.

This is a global P2P VoIP network in which there is no central authority such as a single service provider. Anyone can join and leave the network freely and anyone can implement the software to participate in the overlay network. In such a system, the protocols used must be based on open standards. This P2P VoIP network resembles the global Internet itself in that it has distributed management and growth, enables anyone to reach anyone else in the overlay network, and any device supporting the standard protocols can be used.

Presence is a useful and important feature for instant messaging and VoIP applications. Well-known instant messaging application software provides presence, text and media messaging, and supports file transfer between online users. As more and more multimedia consumer electronics devices such as cameras, camcorders and televisions become network aware, instant sharing of multimedia content such as photos and video clips between family members and friends will be desirable. VoIP may not be needed on some of these consumer electronics devices, however presence that enables instant content sharing will be required for many types of consumer electronics devices. A global P2P network supporting presence is an important infrastructure component for this use case.

There are situations where, despite having connectivity to the Internet or even to client server SIP infrastructure such as SIP proxies, users may not like to use the infrastructure because of security concerns or may not be allowed to use the infrastructure. Such situations are referred to here as involving a security demanding environment. Maintaining privacy of communication and secrecy of identities are important in this environment and the P2P architecture's distributed nature may be more attractive than a client server approach.

Certain groups may have their ability to communicate impeded. These users should be able to communicate without the need to connect to any centralized servers, which may be blocked by providers upstream of the user. A fully decentralized system cannot be completely disconnected without removing connectivity at the basic Internet level. Examples: A user wishes to use an IP telephony service to communicate PC to PC with a friend, but the ports commonly used by these services, or the the servers used for authentication, are blocked by the ISP because the ISP also offers communications systems and have a vested interest in denying access. A user with an Internet enabled PDA devices wishes to connect with colleagues, but traditional services are blocked to ensure that SMS or voice minutes are used (at additional cost) instead.

Users occasionally have need to communicate among themselves in a completely anonymous fashion, whether due to political persecution, need for secrecy for commercial reasons, or threats of violence. In such a case, the need for a self organizing, server-less system is imperative. Users on such a system could communicate with reduced risk of the system being monitored or their identities discovered. As with the impeded access scenario, the only way to disable such networks would be to completely disable Internet connectivity.

Certain security conscious small organizations may have need for communications systems that allow members of the organization to communicate directly with one another regardless of their location, with encryption, and without any connectivity to or use of servers, either internal or external to the organization. For these organizations, traditional client-server SIP implementations and more importantly hosted solutions for communications are unacceptable. These entities need a system to facilitate such communications without central servers. Note that these users may overlap with the anonymized communications case also described in this document. Examples: Organizations who are developing technology that might be of interest to a hosted service provider, but because of small size may have no desire or time to maintain centralized servers. Organizations with security needs that preclude any traffic flowing through a central server such as military, national security, or intelligence organizations.

When there is no physical network available for stable deployment of client server SIP or an instant deployment of real-time communication systems is required, the P2P approach may be the only feasible solution. Examples of such environment are isolated wireless ad-hoc networks with no connection to the Internet or ad-hoc networks with limited connectivity to the Internet in situations like outdoor public events, emergencies, and battlefields. Any type of manual configuration is difficult to achieve because technical support is not readily available in such environment. In some cases, connectivity to the global Internet may be available, but be very expensive, of limited capacity, or unstable, such as satellite connections. In such cases, it is preferable to localize communications as much as possible, reducing dependency on any infrastructure in the global Internet.

Groups of individuals meeting together have need for collaborative communications systems that are ephemeral in nature, have minimum (ideally zero) configuration, and do not depend on connectivity to the Internet. These scenarios require an arbitrary number of users to connect communications devices. Example: A group gets together for a meeting, but there is no Internet connectivity. If the users establish a wireless ad hoc network or have a base station, all users may connect and establish chat sessions using an IM protocol with no need for server configuration.

Following a large scale disaster such as a tsunami, earthquake, hurricane, or terrorist attack, access to traditional communications devices of any kind -- Internet, cellular, or traditional PSTN -- may be compromised. Recent events have shown that current first responder radio systems cannot be relied upon to interoperate effectively. A network of devices that can grow organically as responders arrive, requiring only wireless access, is required. As more personnel show up, they should be able to join the network, locate other personnel, and communicate without any centralized configuration required. Example: Following a disaster, the local fire department arrives. Each fire fighter has a wireless handset, and one or more trucks have wireless base stations. When a nearby locality sends additional rescuers, their wireless handsets should be able to instantly join the communications network and communicate.

A network of mobile devices can relay traffic between themselves to reach a base station, even if the base station is out of reach of that device. Example: A user has a handset for communication that cannot reach a base station. Some other user is within range of both that user and a base station. This intermediate user can serve as a relay for the caller who is out of range. A system might make this feature optional for standard communication and mandatory for E911.

Certain locations in the developing world have limited, intermittent, or non-existent connectivity to the Internet. These locations also typically lack experienced people with the specialized skills needed to administer or maintain centralized SIP proxies. Even DNS servers may not exist. A communications system that is able to function reliably for internal communications, even in the presence of degraded or absent connectivity, is clearly needed. Such a system must also scale easily with little or no configuration and ideally should interface easily to existing communications systems when connectivity is available. Example: A village in the developing world has connectivity that is limited by weather (microwave connection) or is solar powered. It would be desirable for intra-village communication to continue to function in the absence of Internet connectivity.

A corporate network or a school campus network is an example of the managed, private network environment. Most likely client server SIP can be used and managed for real-time communication applications in these environment. However, in certain scenarios, P2P SIP may be used instead or as a complementary means, to achieve various goals such as cost and management overhead reduction, scalability, and system robustness.

Many small enterprises have a need for integrated communications systems. These systems have slightly different requirements than more traditional IP PBXs. For small enterprises, there may be no administrator for these systems, requiring the systems to be essentially self-configuring and/or self-organizing. Additional endpoints should be able to be added with no requirements for configuration on central devices. These systems should offer the feature sets similar to those of client server type PBX systems. Connectivity to the PSTN is an important feature for these systems. In addition, they may support features such as call transfer, voice mail, and possibly even other communications modes such as instant messaging or media features such as video or conference services. There are already commercial products of this type. Example: Small organizations without centralized IT

Service providers may wish to connect a farm of proxies together in a transparent way, passing resources (user registrations or other call information) between themselves with as little configuration or traffic as possible. Ideally, the redundancy and exchange of information should require a minimum of configuration between the devices. A P2P architecture between the proxies allows proxy farms to be organizing and operated in this way. With this approach, it is easy to add more proxies with minimal service disruptions and increases the robustness of the system.

A traditional centralized SIP server, such as used in an IP-PBX, forms a single point of failure of an otherwise fault-independent network. Relying on P2P SIP as a backup to the centralized server allows the communications system to continue functioning normally in the event of planned or unplanned service interruptions of the central IP-PBX. Example: A small company has a central IP-PBX. When that device experiences a failure, the handsets are able to transparently continue operation for the 24 hours it takes to obtain a replacement switch.