Theodore E. Tedijanto

NBBS traffic management overview

In this paper, we describe an integrated set of procedures used for bandwidth management and congestion control in high-speed packet-switched networks such as asynchronous transfer mode (ATM), which are part of IBMs Networking BroadBand Services (NBBS) architecture. These controls are designed to support a wide variety of services with different characteristics in the network and operate at different time scales: connection-level controls such as path selection, admission control and bandwidth allocation, and packet-level controls that discriminate between packets from different connections to support multiple levels of service guarantees. Connection-level controls are applied at connection setup time and are based on the connection characterization and the network state at that time. They perform efficient allocation of resources to ensure performance guarantees for connections while achieving high utilization of network resources. Various packet-level controls developed include access or rate control and intermediate node buffer management and scheduling. For connections that do not require explicit service guarantees, NBBS offers an available bit rate service. This service mostly relies on packet-level control in the form of an end-to-end rate-based flow control algorithm that regulates the flow of traffic into the network. This paper, in addition to providing an overview of the different mechanisms used for traffic management in NBBS, highlights how they interact to ensure efficient network operation.

Effectiveness of dynamic bandwidth management mechanisms in ATM networks

The leaky bucket, a credit management system that allows cells to enter the network only if sufficient credit is available, is considered. Motivation for an in-depth study of dynamic control algorithms, to avoid congestion in high-speed networks under time varying traffic statistics, is provided. The need for real-time traffic measurements and dynamic control actions for long-lived connections is demonstrated. In particular, it is shown through simulations that implementing access control algorithms based on the bandwidth allocation procedures only at connection setup is not sufficient for congestion-free operation of the network. It is further shown that if the bandwidth allocation and the leaky bucket parameters are not dynamically adjusted, the performances of the connections depend on their initial parameters and can be very undesirable as the traffic parameters change over time. Moreover, if corrective actions are not taken, congestion may build up in the network even in the presence of leaky buckets. The simple dynamic approach proposed limits the congestion periods in the network to the time scales of the connection-level controls. Therefore, the probability of many connections sending excess traffic into the network at the same time is greatly reduced, alleviating the congestion problem.<<ETX>>

NBBS path selection framework

This paper describes the path selection function in Networking BroadBand Services (NBBS), which is IBMs architecture for high-speed, multimedia networks. The distinguishing feature of a multimedia network is its ability to integrate different applications with different traffic characteristics and service requirements in the network, such as voice, video, and data. In order to meet their service requirements, it is necessary for the network to provide unique quality-of-service (QOS) guarantees to each application. QOS guarantees, specified as multiple end-to-end performance objectives, translate into path and link constraints in the shortest path routing problem. For a general cost function, shortest path routing subject to path constraints is known to be a nonpolynomial- (NP-) complete problem. The NBBS path selection algorithm, a heuristic solution based on the Bellman-Ford algorithm, has a polynomial order of complexity. The algorithm finds a minimum hop path satisfying an end-to-end delay (or delay variation) constraint, that in most cases also optimizes a load balancing function. To reduce the number of path constraints, other QOS requirements such as packet loss ratio are implemented as a link constraint. The notion of primary and secondary links is used to minimize the long-term overall call blocking probability by dynamically limiting the hop count of a given path. The path selection algorithm developed for point-to-point connections is described first, followed by its extension to the case of point-to-multipoint connections.

Distributed call rerouting in multiclass broadband networks

Broadband integrated services digital networks (B-ISDN) must handle multiclass traffic with diverse quality of service requirements. We consider a multiclass routing model in which routes are calculated in a distributed fashion by the call originating nodes. Within this general context, we address the problem of rerouting a set of previously routed calls to avoid a failed link. Under the approach we propose, a single node executes an aggregate, global rerouting of all affected calls and then converts the set of aggregate routes into an allocation of bandwidth on each link to call origination nodes for the purpose of rerouting. The bandwidth allocation is distributed to each origination node, which in turn then calculates routes for the individual calls. The problem faced by each call origination node is a variant of the socalled bandwidth packing problem. We develop and analyze an approximate algorithm for solving this problem in the specific context that arises in our setting.

A note on the comparison between Bernoulli and limited policies in vacation models

Abstract A vacation model is a single-server queueing system where the server occasionally takes a vacation, i.e., becomes unavailable to the customers for a period of time. Under a limited service policy with parameter m , m = 1,2,…, the server can serve a maximum of m consecutive customers before it has to take a vacation. Under a Bernoulli service policy with parameter p , 0 ⩽ p ⩽ 1, at every service completion, the server serves the next customer (if available) with probability p or starts a vacation with probability 1 - p . Under both policies, the server takes a vacation if no customer is present. In this note, the waiting time under a Bernoulli policy with parameter p is shown to dominate that under a limited policy with parameter m when the parameters are related by p = ( m −1)/ m and the vacation lengths are identical and deterministic. The comparison is in the convex increasing ordering and holds both in the transient and steady-state regimes.

Dynamic connection admission mechanisms for the Networking BroadBand Services architecture

Networking BroadBand Services (NBBS) is IBMs control point architecture for next generation high‐speed packet‐ or cell‐switched networks and is implemented in a family of network switching nodes. In this paper, we describe the traffic estimation and dynamic bandwidth adaptation function of the NBBS architecture. The dynamic Connection Admission Control (CAC) procedures we describe in this paper enable more efficient bandwidth management in high‐speed networks. The dynamic CAC procedures we propose rely on traffic identification at the access points to the network and adjustments in bandwidth allocated through the network. This framework allows the NBBS network to provide enhanced variable‐bit‐rate services for non‐stationary traffic sources in addition to providing standards compliant variable‐bit‐rate services based on deterministic rule‐based traffic descriptors. The traffic estimation methodology discussed here can also be used to devise easy‐to‐implement statistical conformance tests for Usage Parameter Control (UPC) mechanisms.