Quality Of Service Computer Network

Published Date: 02 Nov 2017

There are different types of network. Network can be wired and wireless. MANET’s is an adhoc network whose topology changes any time. There are a lot of issues regarding QOS. Quality of service can be delay, bandwidth, speed, cost etc. Quality of service sometimes refers to the level of quality of service. In this paper we focus on access of shared medium in wireless networks. We investigate different access medium techniques and proposed new technique to avoid this problem upto certain level. The main problem in shared medium is collision and bandwidth usage. We proposed a registration based concept for access of shared medium to avoid collision and for better bandwidth usage.

1. Introduction

Mobile ad hoc networks (MANETs) are infrastructure-less and intercommunicate using single-hop and multi-hop paths Nodes act both as hosts and routers Topology changes could occur randomly, rapidly, and frequently. Routing paths are created and deleted due to the nodal mobility.The network Quality of Service (QoS) is a relatively new term, which is defined as: "The capability to control traffic-handling mechanisms in the network such that the network meets the service needs of certain applications and users subject to network policies". To provide the capabilities of measure and control required by either definition, QoS networks must have mechanisms to control the allocation of resources among applications and users. QoS: A set of service requirements that are met by the network while transferring a packet stream from a source to a destination. QoS metrics could be defined in terms of one or a set of parameters Examples: delay, bandwidth, packet loss, delay-jitter, etc.

The use of QoS-aware applications are evolving in the wireless environments Resource limitations and variations adds to the need for QoS provisioning Use of MANETs in critical and delay sensitive applications demands service differentiation. The notion of QoS came up as a response to the new demands imposed on the network performance by modern applications, especially multimedia real-time applications. Those applications made it necessary to set limitations on what can be defined as an acceptable time Main problems regarding QOS are:

Bandwidth allocation

Mobility

Hidden terminal problem

Route maintenance and Recovery

Information Security

2. Background Study

I. Soft QoS:

After the connection set-up, there may exist transient periods of time when QoS specification is not honored

The level QoS satisfaction is quantified by the fraction of total disruption QoS Adaptation. As available resources change, the network can readjust allocations within the reservation range (dynamic QoS) Applications can also adapt to the re-allocations

Since wireless channel is time varying, the SNR in channels fluctuates with time

Adaptive modulation which can tune many possible parameters according to current channel state is necessary to derive better performance

Major challenge: channel estimation – accurate channel estimation at the receiver and then the reliable feedback to the transmitter

Wireless channel coding needs to address the problems introduced by channel or multipath fading and mobility

Cross-layer issue: Joint source-channel coding takes both source characteristics and channel conditions into account.

II. Ticket-based probing Algorithm

During the QoS-satisfying path search, each probing message is provided a limited number of tickets to reduce the scope of flooding

When one or more probes arrive at the destination, the path and delay/bandwidth information is used to perform reservation for the QoS-satisfying path

A simple imprecise model is used for the algorithm

The end-to-end bandwidth can be calculated and allocated during the admission control phase

Using TDMA, time is divided into slots, which in turn are grouped into frames. Each frame contains two phases: control and data. During the control phase, each node takes turns to broadcast its information to all the neighbors in a predetermined slot. At the end of control phase, each node knows about the free slots between itself and its neighbors. Thus bandwidth calculation and allocation can be done in a distributed manner. Divide bandwidth into different small frequency channels each channel has the ability to support user. Guard bands are used to separate channel preventing co-channel interference. Guard bands are wastage of bandwidth showing in figure below.

Code

Time

Node

Node 22 2

Node

Node

Frequency

Entire bandwidth is available to the user for finite period of time.

Users are allotted time slots for a channel allowing sharing of a single channel.

Logical channel allocation.

Requires time synchronization.

Each of the users takes turn in transmitting and receiving data in a round robin fashion.

Shown in 2nd diagram below:

Frequency

Code

User 1

User 2

User 3

User 4

Time

Collision Interval

III. RANDOM ACCESS

Retransmit

Time

Each user has one packet to transmitted in the diagram

3. Problem Definition

From above discussed techniques we examined there is low performance under heavy load conditions (large number of nodes) and collision increases as number of users increases.

4. Proposed Technique

Slot is divided into smaller reservation slots. During reservation period, users can reserve future bandwidth slots each user will have to send registration token for reserve a bandwidth. Registration token will contain the user’s ID and time required for bandwidth slot. Reservation tokens will reserve the bandwidth slot mean that we have to reserve one token to the user for use.

5. FUTURE WORK

Wireless medium works on shared access. The usage of share medium properly is a sign of good network service. If multiple users transmit their packets on the shared medium at a same then there are a lot chances of information lose and collision. As the number of users increases the chances of collision will also be increases. In this paper we proposed the concept of registration the shared medium before its usage but still collision may occur during registration. In future we will focus on this issue and resolve this problem.