Up to now, Internet service providers and large companies have had to create and maintain separate networks for the transmission of voice information, video, traffic required for mission-critical tasks, and all other network traffic. Nevertheless, we cannot fail to note the recent strong tendency to unite all these networks in one network with packet data transmission based on Internet Protocol (IP).
The largest IP network is, of course, the global Internet network. For the last growth of the traffic, transmitted over the Internet Network and the number of existing Internet applications approached the exponential. While the Internet and corporate intranets continue to grow, many analysts predict the emergence of the applications focused on the transfer of non-traditional types of information, for example, the transfer the voice over IP networks (Voice over IP – VoIP) or traffic transmission of video conferences.
Since the number of Internet users and various network applications is increasing every day, the Network needs tools that support both existing and emerging applications and services. However, up to date, the Internet can provide only a non-guaranteed delivery of data (best effort service). Unguaranteed delivery of data does not imply the provision of any guarantees regarding the time and actual arrival of the package to the destination. However, it should be noted that discarding of the packets can occur only at the time of network congestion.
As a rule, packets transmitted over the network differ on the basis of five IP header fields that unambiguously determine the data flow – the source address of the IP packet, the IP packet destination address, the IP protocol field, the source port, and the destination port. Information Flow consists of packets generated by the application running on the source computer, and intended to be passed to the application running on the destination computer. Packages belonging to the same thread have the same values for all five fields in the header of the IP packet. In order to support the transfer of voice, video and data traffic of the application, with the different bandwidth requirements, the core systems of the IP network must possess differentiating feature and different types of network traffic support, depending on its requirements. Unguaranteed data delivery does not involve making any distinction between the thousands of information flows in the core of the IP network. Therefore, the IP network can not provide any guarantee of reliable delivery of the traffic of this application. In other words, non-guaranteed delivery of data prevents the transfer of traffic that requires the allocation of a specified minimum of network resources and guarantees for the provision of certain services. To solve the described problem there have been introduced the notion of quality of service (quality of Service – QoS) in IP networks.
The quality of service functions in IP networks (IP QoS) means providing guaranteed and differentiated servicing of network traffic by transmitting control over the use of resources and network utilization to its operator. QoS is a set of requirements for network resources when transporting a data stream. QoS provides end-to-end data transmission guarantee and a rule-based control over IP performance enhancements, such as the resource allocation mechanism, switching, routing, queuing services mechanisms and packet dropping mechanisms.
Below are some of the main benefits of the quality of service in IP networks.
• Providing the support for existing and emerging multimedia services and Applications. Some new applications, such as voice over networks IP (VoIP), make certain requirements to the quality of service.
• Transfer of control over network resources and their use to the network operator.
• Ensure service guarantee and differentiate network traffic. This condition is necessary to combine audio, video and application traffic within one IP network.
• Allows Internet service providers to offer additional services to customers along with the standard non-guaranteed data delivery service (in other words, to provide services in accordance with the so-called class of service – Class of Service (CoS)). An Internet service provider can define several classes of additional services (for example, “platinum”, “gold” and “Silver” classes) and configure network rules that allow processing traffic of each class in accordance with the specified parameters.
• Provides an opportunity to organize maintenance of network traffic depending on the application traffic, information about which is contained in the Header of the IP packet.
It plays a significant role in the development of new network technologies, such as Virtual Private Networks (VPNs).