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Statistical Aggregation of Data with Different QoS

IP.com Disclosure Number: IPCOM000131179D
Original Publication Date: 2005-Nov-09
Included in the Prior Art Database: 2005-Nov-09
Document File: 3 page(s) / 56K

Publishing Venue

Motorola

Related People

Baruh HASON: AUTHOR [+3]

Abstract

A bridge is expected to provide QoS according to QoS tag carried by the PDU. The PDUs, which entered the bridge from different ports, and forwarded to the same output port are reordered according to the QoS tag they carry. The reordering gives higher transmission chance to high priority PDUs. On the other hand the aggregation is done statistically for reducing the starvation problem of low priority PDUs.

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Statistical Aggregation of Data with Different QoS

Baruh HASON, Yael DUX, Doron NADJAR

Abstract

A bridge is expected to provide QoS according to QoS tag carried by the PDU. The PDUs, which entered the bridge from different ports, and forwarded to the same output port are reordered according to the QoS tag they carry. The reordering gives higher transmission chance to high priority PDUs. On the other hand the aggregation is done statistically for reducing the starvation problem of low priority PDUs. 

Introduction

A bridge or a switch is a multiple port device connecting different access networks. Within the context of this article, all ports of a switch are considered to be connected to access networks using the same protocol, whereas a bridge connects access networks using different protocols. The term bridge will be used to cover both kinds of devices. When a bridge receives a protocol data units (PDU) at one of its ports, according to the rules dictated by the bridging table, it forwards this PDU to one of its ports. If necessary this port does the protocol translation between the input port and output port. The formation of the bridging table and the protocol translation are out of the scope of this article. The forwarding task involves many to one mapping. In other words, each one of the ports is required to provide channel access services for PDUs forwarded from different other ports. Since, the outputting of a PDU at a given port is considered to be a sequential operation, the PDUs coming from other ports of this bridge and forwarded to the current port need to pass a process of queuing/ordering. This article suggests a re-ordering mechanism when the channel access function of a given port of the bridge is expected to take into consideration the Quality of Service QoS requirement reflected by the QoS tag of the PDU.

The Problem

            The necessity of such a mechanism can be illustrated by the following example.

Assume a bridge with 3 ports. For simplicity it will be assumed that all ports are operated at the same transmission rate and the PDU size in each one of the access networks to which the ports are connected are the same. In the current example the PDUs entering the port 1 are streaming video packets (high priority) and the PDUs entering the port 2 are file transfer packet (low priority). All PDUs should be forwarded to port 3. (See Figure 1) The forwarding is done according FIFO principles.

Figure 1 PDU forwarding according to FIFO

As can be understood from the figure, even if the instantaneous throughput towards network 3 is not disturbed, a delay gap is caused between streaming video packets. Further more, if the aggregate throughput required from the PDU streams entering the port 1 and the port 2 is higher than the throughput provided by the port 3, the streaming video PDUs will suffer transmission rate reduction, during the time the file transfer PDUs enter port 2. (This will cause additional delay.)

The Sug...