Ahfrucf-In this paper we present a comparative study of two schemes to provide sunhability for guaranteed QoS connections in a possible Next Generation Internet network architecture. In the first scheme a QoS connection is provided standby backup resources on a disjoint path by reserving resources on both the working and backup path. In order to reduce the amount of backup resources required a method for sharing backup resources when the working connections have disjoint routes has been included. In the second scheme a dynamic search for restoration resources is conducted over a preplanned set of alternate paths upon notification of a failure. A simulation based performance study shows that the first scheme results in much higher connection blocking under normal operations, slightly faster restoration times, and longer transient congestion times after fault recovery due to non-optimal backup routing. The Next Generation Internet (NGI) will provide QoSbased services in addition to traditional best effort service. A certain set of users (e.g., military) can be expected to demand a cost effective level of fault tolerance for QoS-based services. Hence there is a need for techniques to ensure the survivability of certain services in NGI architectures. Note that some QoS services will likely follow fixed routes (e.g., Guaranteed Service class in IntServ model [ 171) and thereby be subject to single point failures (e.g., link failure) as in circuit switched networks. , The subject of providing survivability in the face of failures has been extensively studied for circuit switched networks and recently for ATM networks [3], [9], [18]. This includes work on network design and capacity allocation, as well as work on traffic restorationhetwork management algorithms for fault recovery. A variety of survivability techniques have been proposed for circuit switched.and ATM networks at the physical layer, logical layer and the traffic layer. At the physical layer most of the work focuses on SONET rings or automatic protection switching both of which involve provisioning idle spare capacity. At the logical and traffic layer several approaches for provisioning spare network capacity in mesh type topologies have been proposed along with traffic restoration techniques. It is well known that a mesh type topology together with traffic restoration techniques is more capacity efficient than physical layer approaches. The traffic restoration techniques typically differ in specification of the location of rerouting, the rerouting algorithm and the reservation or  Dept. of Computer Networking University of Missouri -Kansas City Kansas City, MO 641 IO USA nonreservation of resources in the event of a failure. From the literature it is clear that no one approach is cost effective or optimal for all networks and a multi-layer survivability approach with a combination of techniques is suggested. Such survivability issues have received little attention in the context of NGI architectures as the focus thus far has been to develop a QoS based architecture. In this paper we investigate two schemes for survivability applicable at both the traffic or logical layers in any packet switched network that supports explicit path establishment. In the first scheme a guaranteed QoS service is provided reserved standby backup resources on a path which is disjoint with the working path. In order to reduce the amount of backup resources required, the method for sharing backup resources proposed in [4] is adopted. In the second approach a dynamic search for restoration resources is conducted over a preplanned set of alternate paths upon notification of a failure. A comparative simulation based study of the performance of the two survivability schemes is presented. The study considered both steady state and transient network behavior and shows that the first scheme results in much higher connection blocking under normal operations, slightly faster restoration times and longer transient congestion times. In the next section, we discuss NGI architectures and the two survivability schemes studied in detail. In Section 111, we present the results of our simulation based performance evaluation. Lastly in Section IV we summarize our findings. Curently two different QoS-based services frameworks are being considered for the NGI namely: ( I ) the Integrated Service (IntServ) model and (2) the Differentiated Service (DiffServ) model. In the IntServ model, per connection QoS-based services are classified into three types. Guaranteed Service, Controlled-Load Service and Best-effort Service [ 171. The Guaranteed Service class is intended to provide a guarantee of bandwidth, a end-to-end delay bound and no packet loss, to applications with a stringent real-time delivery requirement. The Controlled-Load service is aimed to be used for those classes of applications that can tolerate some amount of loss or delay, i.e. adaptive real-time applications. Controlled load service provides a loose guarantee of service on' delay and packet loss. Best-effort Service corresponds to current Internet service in that no guarantees are made.
This idea has been extended by Srikitja, Tipper and Medhi REF , providing a comparative study of two RSVP-based restoration schemes.
On providing survivable QoS services in the next generation Internet
MILCOM 1999. IEEE Military Communications. Conference Proceedings (Cat. No.99CH36341)
MILCOM 1999. IEEE Military Communications. Conference Proceedings (Cat. No.99CH36341)
Computer Science