Quality of Service in Wireless Networks

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 CONTENT

  1. Preface………………………………………….………………………………………………….…….……..3

    1. Abstract……………………….………………………………………………………………..….……3
    2. Audiences……………………….……………………………………………………………..….…….3
    3. History..…………………………………………………………………………….………………….3
    4. Research Question…………………….…………………………………………………………..……3
  1. Introduction…………….………………………………………………………………………….…………4
  2. Background Theory.…….……………………………………………………………………….…………..5

    1. What is Quality of service?……………………………….…………………………………..….……5
    2. Architecture of Quality of service………………………………………..……………………………..5
  3. Quality of Service Challenges in Wireless Network..…………..…………………………….…….……….6
  4. Quality of Service Standards…..……………………………………………………………….……………..7

    1. IEEE 802.11e – Quality for Service…………………………………………………………………..7

      1.       Hybrid Coordination Function (HCF)………………………………………………….……8

        1. Contention Mode in HCF………………………………………………………….…..8
        2. HCF Controlled Channel Access (HCCA)……………………………………….……9
      1.    Enhanced Distributed Coordination Function (EDCF)………………………………….…10
  5. Quality of Service Protocol ………………………………………………………………….………………..12

    1. Direct Link Protocol……………..…………………………………………………………………..13
  6. Conclusion…………………………….……………………………………………………….…….………14
  7. References…………………………….………………………………………………………….…….……15

Quality of Service in Wireless Networks

Preface

1.1    Abstract

 The purpose of the paper is to explore protocols and issues relating to Quality of service in wireless network. The IEEE standards 802.11e supports the quality of service. It describes the 802.11e architecture and discussing the MAC techniques such as HCF, EDCA and HCCA as well as explaining their operations related to Quality of service including the contention free period and admission controls in both HCF and EDCA

1.2    Audiences

The intended audience of this document are the School of Life Science and Computing, IT Department and London Metropolitan University.

1.3    History

The report is created on Monday 29th October 2018 and has no existing history.

1.4    Research Question

The question of this paper: 

How is Quality of Service used in wireless networks critically discuss?

2 INTRODUCTION

 Wireless networks is  expandable technology due to its developing, emerging and evolving in the modern times where it is accessible  at any time of place around globe and consists of solutions to universal problems. The information’s about any topic that there is  in world can be sent, shared, shown from computer to another computer is done via wirelessly without the need of wire connection and it is broadcasted from satellites to mobile and computer digital to analogues.

The outstanding of internet speed and interactive programs has support of numerous Quality of service (QoS) protocols for their traffic such as voice, data, video where all of these transported throughout different types of network as well as providing with better network service to real time applications in few parameters such as jitter, packet loss, bandwidth, and delay.

Additionally, wireless networks in recent years have illustrated that any type of data is distributed effectively and efficiently using data services like wireless connectivity and internet. There are many affect that have occurred due the application we use in our daily life and those growing applications are peer to peer of sharing files and documents, multimedia are streaming live and Voice over Internet Protocol (VoIP) of telephone, devices. However, wireless network consists of many tasks due to bandwidth, packet loss, and delay consuming of Quality of service (QoS).

The paper will be commence with background information on Quality of service (QoS) and explaining the architecture. Then it will describe 802.11e and discusses how the standards is related to QoS.  At that point, we will describe and explain the core details of Hybrid Coordination Function (HCF) and follows on to HCF Controlled Channel Access (HCCA) and how contention free period operates in HCF. Finally discussing the Enhanced Distributed Channel Access (EDCA) and two methods Transmit Opportunity (TXOP) and Arbitration Interframe space (AIFS) exploring the Frame Relay and relationship of QoS.  

3 BACKGORUND THEORY

This chapter defines the theory that is been carried throughout the project. It will describe the definition of quality of service in network and briefly explaining the architecture of quality of service.

3.1 What is Quality of Service?

Quality of service (QoS) ensures that the router provides better network services to real time application that are delicate to jitter, packet loss, bandwidth, and delay.

  • Jitter: Jitter refers to packet delay as variation, the siding side the packet are in many time in stream with packets are separated apart. This streaming may become lumpy or delay amongst the packet due network congestion, errors of configuration.
  • Packet loss:  This packet loss outcomes the network errors outstanding congestion or faults
  • Bandwidth: Applications frequently  need of fixed bandwidth in order to deliver the content such as streaming video or audio
  • Packet loss: Congestion occurs delay due to the traffic overload within the network. The routers that stores packets in queues for extra duration earlier forwarding to the network will affect the packets to be delayed.

3.2 Architecture of Quality of Service

The process of Quality of service has three categories that should be in place for starting operation of service in network:

  1. Quality of service nodes within network elements such as traffic shaping tools, queuing and scheduling.
  2. Quality of service will give signals techniques for directing the QoS from end to end between the network elements.
  3. The department of management, accounting and policy has ability of controlling directing the end to end traffic                                                                                            

Figure 1: Architecture of Quality of Service

4  QUALITY OF SERVICE CHALLENGES IN WIRELESS NETWORKS

This chapter will describe the challenges that are occurred with quality of service for wireless

The most common challenge of providing Quality of service is known as congestion. The reason why the network is congested is due to increasing of delay when packet are taking long period of time in queue. Additionally, loss will increase due no room in queue and won’t take more packet despite of those that are coming. Yet, this will reduces the throughputs of all packets that are dropped out. 

Contrast, the next challenge is the routing when the packets are prepared and sent then another pack is going in the same path as pervious pack, the outline of this is packet will not be arriving on time to the destination despite of all this the jitter and delay will not be able to control the routing. (Cse.wustl.edu, 2018)

Moreover, Quality of service challenges in wireless network is propagation delay. Wireless network are calculated and measured in kilometres, all of networks are communicating each other from distance. The propagation delay will cause problems to these networks communication that needs the amount of delay. However, this cause a significant problems to satellite communication and frequently occurs in metropolitan area network (MAN). (Cse.wustl.edu, 2018)

5  QUALITY OF SERVICE STANDARD

This section of chapter describe the mechanism QoS in the IEEE 802.11e and the two techniques of 802.11e that are HCF and EDCF.

The IEEE 802.11 standard for Wireless Local Access Network (WLAN) Medium Access (MAC) and Physical Layer (PHY) doesn’t support the quality of service but the two types of MAC techniques such as DCF and PCF we need to understand beforehand:

  1. Distributed Coordination Function (DCF) allow the individual station to cooperate without using the central control whereas it can be used either IBSS or infrastructure networks. This method functions on list before talk schemes that is recognized in CSMA/CA.
  2.  Point Coordination Function (PCF) is method that creates the contention free access. PCF can be only used in WLAN infrastructure network. If PCF is enables in WLAN systems then the channel of access time will be divided into periodic interval known as beacon intervals.

5.1.          IEEE 802.11e – Quality of Service

This section of chapter describe the mechanism QoS in the IEEE 802.11e and will discuss the admission controls

In 2005, IEEE has developed and produces new standard 802.11e to increase Quality of service support to media access control (MAC) layer. This 802.11e version has developed MAC techniques of 802.11 and known as Hybrid Coordination Function (HCF) with contention operation.

Figure 2: Architecture of IEEE 802.11e

5.1.1.     Hybrid Coordination Function (HCF)

The new version 802.11e has developed techniques from previous version such as PCF and DCF into new technique called as Hybrid Coordination Function (HCF).  HCF is compulsory to be used in order to support the IEEE 802.11e. Moreover, HCF has own two techniques: HCF Controlled Channel Access (HCCA) and Enhanced Distributed Channel Access (EDCA).

Figure 3: HCF operation

HCF has the ability of assigning the transmit using transmit opportunities (TXOP) approved at quality of service station (QSTA). But the station recivies the TXOP using either both of HCF mechanisms: HCCA and EDCA or one mechanisms. The TXOP gives the power to QSTA to utilize the medium at specific point of time during maximum period. However, TXOP are already communicating via beacon procedure at the station that are using EDCA. (eetimes, 2018).

HCF has various rules for data framing and controlling the frame. The first rule is new acknowledgment (ACK) that is broken down into two optional rule command such as block acknowledged and no acknowledgement, but the rules are stated in quality of service data frames. (eetimes, 2018).

5.1.1.1.                Contention Mode in HCF

The 802.11e has eight classes of the data in order to provide for classification of the classes. Both HCF and EDCF has power of polled access of the eight classes whereas this is known as traffic classes (TC). Traffic classes aim is to map the eight classes that are demarcated within the standard 802.1D. Table 1  will show these classes and their usage. The traffic that is enable by QoS to clients has been considered into four categorised and its named as access categories (AC).

Table 1:  Traffic class

Value and TC of 802.1D

Common Usage

AC and Transmit Queue

1

Low priority

0

2

Low priority

0

0

Best effort

0

3

Signalling and control

1

4

Video probe

2

5

Video

2

6

Voice

3

7

Network control

3

 Key components that is needed for any system that supports Quality of service in order for system to work effectively and efficiently.

  1. Need mechanism that has ability to classify the traffic
  2. The mechanism that can manage to mark the traffic accordingly to QoS values
  3. A mechanism that can differentiate and prioritize the traffic that streaming despite of QoS values.

5.1.1.2.                   HCF Controlled Channel Access (HCCA)

This mechanism has been developed and advanced from Point Coordination Function of standard 802.11. This is the mechanism that keeps tracks of HCF client stations and schedules the polling based. Poll access that is developed in HCF will let the stations to request in order of TXOP, as a replacement for one available.  Both HCF operation and HCF admission control will allow the Hybrid Coordination (HC) to figure out what are the resources available with wireless medium and whether to reject or accept the traffic application streams.

HCF has ability of operating using two modes that includes the coexistence with EDCF and using the content free period (CFP) that is similar method of PCF. (Figure 4)

Operation of Contention Free Period HCF  

  1. AP beacon is sent with PCF compensating fiber and parameter set IE in order to specify the start time and length of CFP
  2. The HCF will give TXOP to specific station by sending QoS CF polls.
  3. The  tation will need responds back in the time of SIFS along with data frames or sending QoS null frame. But it should indicated that the station has no frame or traffic.
  4. CFP will end the operation when HC send the HC-frame end, if HC doesn’t send frame then CFP duration will expire.  Figure 5 shows the illustration of this operation

Figure 4: Operation of Contention Free HCF

Figure 5: Operation of Contention Free HCF coexistence with EDCF

5.1.2.     Enhanced Distributed Channel Access (EDCA)

EDCA is introduced by IEEE 802.11e and it has improved the DCF technique in 802.11 in order to provide prioritized Quality of service. The EDCA has about four different type queues first in first out (FIFO) and known as Access Categories (AC). Every data packet at higher layer that has values of priority will plotted rendering to AC. There are several of applications traffic such as video traffic, data traffic, best effort etc. will be given and instructed with Access Categories. However, the AC performs as DCF with having own of parameters contentions. The four types of AC are TXOP limit AC, AIFS, CWmax and CWmin as well as these are declared in beacon operation. (Qiang Ni, 2005)

Figure 6: EDCA Architecture

Collisions will occur when client are communicating at same time on WLAN. This will have an effect on both of packet will return back for anonymous time before packets are sending again. Collisions will not be eradicated but it will kept to observe the WLAN bandwidth. Quality of service uses this method in order to allow priority to higher so that get access to WLAN media first. Quality of service will stay put for some time but only depending on packets priority. Enhanced Distributed Coordination Function has the ability of letting higher priory traffic to pass via Access point (AP) interface faster but for lower priority traffic won’t let them pass.

EDCF two functionality and concept that provides contention free access to the channel:

  1. Transmit Opportunity (TXOP):

 This is used for environment of having large quantity WLAN traffic going via access point. High packet will wait for few second in order to re-transmit. Condition, the traffic is still high, then high priority will resume of re-sending so many frames possible as long as it fit with length of TXOP. TXOP will book a place in the line for high priority packet through first few second of higher priority packet. This will outcome the assurance of higher packet priority handling the frames. However, high priority is not in line then access point will be able to address next packet in queue.

  1. Arbitration interframe space (AIFS):

The EDCA has announced the AIFS instead of DIFS in DCF. Every AIFS has the value of IFS intervals lengths using the equation:

        AIFSAC=SIFS+AIFSNACslot time

.

The AIFSN [AC] is the arbitration IFS number despite detecting the time interval of AIFS [AC] has the AC will calculates the backoff time of CWmin AC that is equal or less than backoff time of CWmax[AC]. The aim of using various parameters contention is to make the low priority class wait longer instead of high priority class. (Qiang Ni, 2005)

The AIFS is the process that provides higher priority to station with shorter AIFS and lower priority to station to longer AIFS. So the shorter is AIFS then higher has opportunity of accessing the medium first.

Figure 7: EDCF Timing Diagram

EDCA Admission Control

The scope of QoS is to protect the higher priority application traffic from the low priority application traffic. The admission control has capability of observing the available resources of the network and logically make a decisions of allowing new application sessions or disallow them. The EDCF mechanism uses the distributed admission control (DAC) scheme. The functionality of DAC is to observe and measure the percentage that are used by each medium AC at the high level function.  However, the percentage that is not used for medium will be known as available budget to AC. Then available budget will be shown at the stations in the way that QoS uses information element (IE) in beacon of AP.

Figure 8: EDCA with Admission Control

6 QUALITY OF SERVICE FOR WIRELESS NETWORKS PROTOCOLS

This chapter will examine other protocols of 802.11e that uses quality of service such as Direct Link Protocols (DLP).

  1.  
  2.  
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  5.  
  6.  

6.1.  Direct Link Protocol (DLP)

The main purpose of direct link protocols is let stations commence a connection to the recipient,  by making the direct link available in order for the sender to prepare and send the frame immediately to the recipient rather than using AP. This protocols makes the recipient to change the information between recipient and the sender.

Moreover, Direct Link Protocol are not required to apply in IBSS despite of frame sent straight STA to another STA. The STA uses both of HCCA and EDCA to communicate directly to develop the efficiency.  DLP and TXOP can work together and called as direct link TXOPs but also connected by TXOP limit. As soon as the direct link is actives and ready the receiver can uses the probes in order to know the quantity of link. However, if the direct link is not available and ready with having no frames that are exchanged during the paths of duration of time out where two of QSTA are return back and communicating using the QAP.  (Qiang Ni, 2005)

The operation of direct link protocols is that station wants new recivver form QSTA that will be send the station in demand of DLP to QAP. Then QAP will get request for different station that will reply back action frame with command that it has been successful, before QAP will send the replay back to DLP, then both of station will be able to communicate effectively.  

Figure 9: DLP operation

7 CONCULSION

To conclude this paper, we have investigated various protocols that are relevant to quality of service 802.11e and described their core details and how their work and what is their role in quality of service.

The paper illustrates the new version 802.11e has developed techniques from previous version 802.11 such as PCF and DCF into new technique Hybrid Coordination Function (HCF). Meanwhile, HCF has own two techniques: HCF Controlled Channel Access (HCCA) and Enhanced Distributed Channel Access (EDCA).

Contrast, the paper examines other techniques such as Transmit Opportunities (TXOP) and Arbitration Interframe space (AIFS) as well as admission control uses QoS in order to protect the higher priority application traffic from the low priority application traffic.

Furthermore, the paper gives an insight of all the categories that are required before using the Quality of service in wireless network. The paper does not shows any implementation of quality of service, instead it shows how quality of service is used in wireless networks.

8 REFERENCES

Books

  1. 802.11 Wireless LAN Fundamentals. (2010). Cisco Press, pp.176 to 180.

CT6052 Chapters Presentation

  1. Benetatos, H. (2018). Chapter 2: IEEE 802.11 and Nework Interface.
  2. Benetatos, H. (2018). Chapter 4: Wireless Topologies.

Websites

  1. Diva-portal.org. (2018). [online] Available at: http://www.diva-portal.org/smash/get/diva2:306415/FULLTEXT01.pdf [Accessed 14 Nov. 2018].
  2. Docwiki.cisco.com. (2018). Quality of Service Networking – DocWiki. [online] Available at: http://docwiki.cisco.com/wiki/Quality_of_Service_Networking#Basic_QoS_Architecture [Accessed 14 Nov. 2018].
  3. Os3.nl. (2018). [online] Available at: https://www.os3.nl/_media/2003-2004/anp/reports/eh_nv-q0s-for-wireless.pdf [Accessed 14 Nov. 2018].
  4. SearchUnifiedCommunications. (2018). What is QoS (quality of service) ? – Definition from WhatIs.com. [online] Available at: https://searchunifiedcommunications.techtarget.com/definition/QoS-Quality-of-Service [Accessed 14 Nov. 2018].
  5. Vijay, B. and Malarkodi, B. (2018). Improved QoS in WLAN Using IEEE 802.11e.
  6. eetimes. (2018). Inside 802.11e: Making QoS a Reality over WLAN Connections. [online] Available at: https://www.eetimes.com/document.asp?doc_id=1271987 [Accessed 20 Nov. 2018].
  7. Cse.wustl.edu. (2018). QoS in Wireless Data Networks. [online] Available at: https://www.cse.wustl.edu/~jain/cse574-06/ftp/wireless_qos/index.html [Accessed 20 Nov. 2018].
  8. Qiang Ni (2005). Performance analysis and enhancements for IEEE 802.11e wireless networks. IEEE Network, 19(4), pp.21-27.

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