1.multi user voip extra copy 210911

8/4/2019 1.Multi User Voip Extra Copy 210911

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Table of Contents

Introduction................................................................................................................3

1.1 History of Voice over Internet Protocol.............................................................. 3

VoIP over IEEE 802.11g WLAN....................................................................................7

1.2 Introduction ....................................................................................................... 7

1.3 IEEE802.11 Architecture: ................................................................................... 9

1.3.1 OSI Reference Model and IEEE 802.11: ....................................................... 9

1.3.2 The Physical Layer: ................................................................................... 10

1.3.3 Medium Access Control (MAC): .................................................................. 11

1.3.4 Management: ............................................................................................ 12

1.3.5 IEEE 802.11 standard protocols: ............................................................... 131.4 VoIP Components: .......................................................................................... 14

1.5 Difference between PSTN and VoIP: ................................................................ 17

1.6 The Session Initiation Protocol (SIP) ................................................................ 19

1.6.1 SIP Components: ....................................................................................... 20

1.7 REAL TIME TRANSPORT PROTOCOL (RTP): ....................................................... 23

1.8 RTCP ................................................................................................................ 24

1.9 Voice compression technology ........................................................................ 25

1.9.1 Speex codec: ............................................................................................ 25

1.10 Power consumption ....................................................................................... 26

Introduction..............................................................................................................27

1.11 Wi-Fi Direct and existing Wi-Fi standards ..................................................... 28

1.12 Architectural overview ................................................................................... 28

1.12.1 Components: ........................................................................................... 28

1.12.2 Functions and services: ........................................................................... 29

1.13 Functional description and procedures .......................................................... 30

1.13.1 Introduction to p2p discovery .................................................................. 30

1.13.2 Device Discovery procedures: ................................................................. 30

1.13.3 Service Discovery procedures ................................................................. 34

1.13.4 Group Formation Procedure: ................................................................... 36

1.13.5 P2p invitation procedure: ........................................................................ 38


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1.14 Group operation: ........................................................................................... 38

1.14.1 P2P Group id: ........................................................................................... 39

1.14.2 Starting and maintaining a P2P group session ........................................ 39

1.14.3 Connecting to P2P group ......................................................................... 39

1.14.4 P2P group owner services for P2P client discovery ................................. 401.14.5 Persistent Group operation ...................................................................... 40

1.14.6 Communicating in a P2P group ............................................................... 41

Bibliography.............................................................................................................42

Table of figuresFigure 1: History of VoIP 5

Figure 2: VoIP network 7

Figure 3: VoIP protocols and gateway 9

Figure : Session Initiation Protocol 12

Figure : Proxy server 13

Figure: Redirect server 13

Figure: Registration server 14

Figure : VoIP functionality 14

Figure : Invite request 15

Figure 11: Real Time Transport Protocol 16

Figure : RTP header 17

Figure : VoIP codecs 19

Fig.1: OSI Reference Model 22

Figure : Wi-Fi direct

List of tablesTable 1: Differences between PSTN and VoIP 10

Table: IEEE 802.11 standard protocols 26

Multi user VoIP over IEEE 802.11g


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Introduction

In the recent years internet has further developed itself into providing Internet Telephony or

Voice over Internet Protocol (VoIP). This allows users to make voice or video calls over the

internet. All the user needs is a computer with a network connection, a soundcard, and a

microphone. Enterprises, ISPs, ITSPs (Internet Telephony Service Providers), and carriers viewVoIP as a viable way to implement packet voice. VoIP is a cheaper way of communicating over

the internet. Various infrastructures have been developed to increase both the efficiency and

effectiveness of both the VOIP systems and the VOIP architecture.

Voice over Internet Protocol (VoIP) is the technology used to transmit conversations

digitally over the Internet. Voice-over-IP (VoIP) is getting widespread adoption both from

business and residential customers as it enables to combine communication and network

infrastructure. Main reasons for implementing the VoIP are it allows long distance

communication such as voice, video and data which can be carried over a single network

infrastructure leads into reducing cost by simplifying the network management through the

common use of equipment. VOIP makes good use of internet technology so that it is able to offermore services with lower or even no cost .VoIP combining with embedded technology can offer

wide range of handheld devices for communicating over internet.

1.1 History of Voice over Internet Protocol

Voice over Internet Protocol owes its existence to the difference in price between long-

distance connections and the use of data networks. This technology uses data networks such as

the Internet to transmit voice information from a simple PC. A telephone conversation is

conducted via microphone and loudspeaker connected to the sound card. Microsoft NetMeeting

is the most common Internet telephony program. Its features also include Internet videocommunication (image telephony). Or, especially adapter can be used to hook standard

telephones up to the data network. All devices that support the same standard can be connected

over one data network. Gateways are also available for connecting these devices to telephones in

the normal telephone network. These possibilities have led to the creation of IP-based telephone

systems using voice over internet protocol. The development of voice over internet protocol

technology is summarized and predicted in the following:

Will add more if needs



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Figure 1: History of VoIP

VoIP is a method for taking analog audio signals and turning them into digital data that can be

transmitted over the internet or A technology used to transmit voice conversations over a data

network using IP. This technology is done by digitizing voice into discrete packets that are

transferred independently over the network, instead of traditional circuit-committed protocols of

the PSTN.Voice can be transmitted over data network in 2 ways:

1) Voice is transmitted over TDM, FR or ATM data networks without using IP. These

are called VoDSL, VoTDM, VoFR or VoATM. These applications have network

dependency. This means that endpoints that voice data transfer occurs must be

connected to same network. Therefore, these applications cant be reached from

everywhere.

2) Voice is transmitted by converting them into IP packets. IP is a protocol that can be

transmitted on every type of data networks. Therefore, it has no network

dependency. These applications are called VoIP.

Types of VoIP

Voice transmission can be carried out over IP networks in 3 ways:

1) IP to IP (Computer to computer)Typically, server-client based programs are used. Users are connected to same server by

using their client programs on their PC. Therefore, people who connects to same server

talks to each other. Typical examples are MSN and ICQ.

2) IP to PSTN (Computer to Phone)



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It is carried out by the help of client programs that uses such SIP and H.323 standart VoIP

protocols. This client programs connects to commercial servers. Therefore, a call is

started between computer and fixed or mobile phones. In this type of VoIP, a call that

starts from Internet needs to finish in PSTN network. For this , it is necessary to use a

media gateway. This media gateway makes circuit-switched and packet-switched

environments compatible.

3) PSTN to PSTN (Phone to Phone)

A call starts from PSTN is transmitted over internet and again it ends on PSTN. For end

users, it is not different from traditional call. This type application may be used for long

distance voice transmission to decrease bandwidth cost.

In order to understand VoIP better, it may be useful to remind circuit-switching and packet-

switching briefly. Because VoIP uses packet-swtiching.

Packet Switching

Internet Protocol breaks data into packets. Each packet contains information about the

IP address of the source and destination along with the data load. Once packets reach

their destination, the packets are reassembled to make up the original data again. To

transmit data in packets, it has to be digital data.

In packet switching, the packets are sent towards the destination irrespective of each

other. Each packet has to find its own route to the destination. There is no predetermined

path. Each packet finds its way using the information it carries, such as the source and

destination IP addresses.

Comparision of PSTN and VoIP

Traditional PSTN phone system uses circuit switching while VoIP uses packet switching.

PSTN is old and expensive. VoIP is more modern.

There is circuit dedication for PSTN and cost is not shared between speakers. There is no

circuit dedication for VoIP and cost is shared.

PSTN is more reliable than VoIP. Because in VoIP, no circuit dedication. Therefore,

circuit is also open for other services. There is a big possibility of congestion and this

may result in delays and even packet loss.



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Advantages of VoIP

VoIP uses less bandwidth when it is compared to PSTN. Therefore, it decreases the cost

of operators. Moreover, the internet users can also open other applications while using

VoIP because of the less bandwidth.

VoIP applications also offer low or no cost for customers. Only a headphone and

microphone is enough for a basic VoIP application.

VoIP is more efficient than PSTN. Because average %30 of phone talks does not include

audio signals. We know that if there is no audio signal then there is no data packet in

VoIP. When there is no packet, there is no data transfer and network is closed. This

means that %30 less bandwidth is used in VoIP compared to PSTN.

In VoIP, the cost is shared between endpoints.

9. Disadvantages of VoIP

VoIP is less reliable than PSTN. Because latency, jitter and loss packet factors that are

seen in VoIP applictions make VoIP less reliable.

VoIP is dependent on wall power. This means that when electricity goes off, we cant use

VoIP. However, there is no such a problem on PSTN.

VoIP has no integration to other systems like digital video recorders, digital tv home

security systems.

VoIP applications can be attacked by worms and viruses, nd can be exposed to hacking.

There is no universal and specific VoIP standards. This may result in conflict between

systems using different standards.



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Since the mid 1990s, IP telephony service has

advanced rapidly, and it is anticipated as a viable alternative to the traditional voice

service over public switched telephone networks (PSTN) due to its cost effectiveness

On the other hand, the Wireless Local Area Network (WLAN) becomes popular to support high-data-rate Internet access for users in proximity of an access point (AP). The main advantages of

WLAN are its simplicity, flexibility and cost effectiveness. In the past several years, the IEEE

802.11 WLAN has become a ubiquitous networking technology and has been widely deployed

around the world. Although most existing WLAN applications are data centric, such as webbrowsing, file transfer and electronic mail, there is a growing demand for multimedia services

over WLANs.

Recently, VoIP over WLAN (Voice over WLAN, VoWLAN) has been emerging as an

infrastructure to provide wireless voice service with cost efficiency. Driven by the demand from

education, health care, retail, logistics, etc., VoWLAN will experience a dramatic increase in the

near future. However, supporting voice traffic over WLANs poses significant challenges since

the performance characteristics of the physical and MAC layers are much worse than that of

their wireline counterparts. Therefore, the applications of VoWLAN raise several deployment

issues concerning the system architecture, network capacity and admission control,

QoS provisioning, etc.

VoIP over IEEE 802.11g WLAN

1.2 IntroductionWireless technology is already available long time ago but its getting more popular now

a days. Due to high cost, low transmission rate, occupational safety concerns and licensing

requirements this technology was not popular in the past. Now WLAN is using everywhere due

to convenience, availability, mobility, reduced cost of ownership and installation flexibility that

making sudden growth in deployment as well as manufacturing of WLAN hardware. At present

there are some organizations like FCC, IEEE, the Wi-Fi Alliance and WLANA are trying to

increase growth of the WLAN technology. WLAN provides mobility to the users so that we can

roam around within the coverage range of WLAN and also it gives fast and less expensive



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connectivity without cabling for reliable data exchange between users. WLAN used to extend the

network by reducing the cost of additional cabling. To connect building to building or more than

two buildings we can use WLAN technology to make access common network among those

users. There are two techniques that used to connect building to building technology. One is

point to point connection which uses directional antenna and another type is point to multipoint

connection in which Omni-directional antenna is used and these types benefit organizations fromrenting expensive leased lines and digging the ground between buildings. Previously WLAN is

used in defense force after that, enterprises started using this technology and now it is available

to home users also. Now a days, homes and small offices are using Wireless LAN which gives

ease and speed of deployment that makes simple and effective solution to interconnect easily.

Using WLAN, we can create ad-hoc network (IBSS or Peer to Peer network) for temporary

needs like file sharing and network for duration of meeting between group of people each with

laptop or handheld devices.

VoIP is placed on IP-based WLAN IEEE 802.11 standards. Combination of these two

technologies and collaboration with Next Generation Networks (NGNs) might be a leading

application in the world of communication [44]. VoIP over WLANs main designing issue is to

verify the network voice capacity.

Limitations and challenges:

A wireless LAN cannot be replaced by Wired LAN if we consider data rates and error

rates.

Due to susceptibility of radio transmission to noise and interference the reliability of data

transmission will comparatively less than Wired LAN.

Strength of the transmitted signal will fluctuate in various paths that causes fading

Security problem arises due to vulnerable to eavesdropping

Spread spectrum techniques also effects the data rate which enforce to ISM band users



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1.3 IEEE802.11 Architecture:Most wireless networks are based on IEEE 802.11 standards. A basic wireless network forms

with multiple stations communicate using radios that broadcast in either the 2.4GHz or 5GHz

band. IEEE 802.11 standards services include managing associations, delivering data and

security. There are main three parameters that characterize Wired and Wireless LANs. Those

are transmission media, topology and medium access control techniques.

1.3.1 OSI Reference Model and IEEE 802.11:

Fig.1

If we consider topology of 802.11 standard networks, it supports two types of modes of basic

service set (BSS).

Infrastructure modeo In this mode, one station (STA) acts as master which is called AP (access point)

and all other stations associate to the AP. In this BSS, any station wants to

communicate with another station, communication should be done through AP

and messages should pass via AP.

Ad-hoc mode

o In this mode, stations will communicate directly without an AP. It is also called as

Independent BSS (IBSS).

Infrastructure Mode: Ad-hoc Mode:


Application layer

Presentation layer

Session layer

Transport layer

Network layer

Data Link layer

Physical layer

(PHY)

Logical link layer (LLC)

802.2Medium Access Control

(MAC)

Network

Operating

System

(NOS)

802.11


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Fig.2

There are nine services defined by the IEEE 802.11 architecture. These services are divided

according to station services and distribution services. Station services include authentication, de

authentication, privacy and delivery of the data. The distribution services compromise

association, disassociation, re association, distribution and integration.Authentication and de authentication services in Wireless LAN are equivalent to the function of

physically connecting to the network cable of Wired LAN. Authentication service provides

identity of one station to the other to use network for data delivery. Once a station got de

authenticated means it cant access the service of IEEE 802.11 WLAN.

1.3.2 The Physical Layer:

Physical layer (PHY) provides a frame exchange between MAC and PHY under the control of

the physical layer convergence procedure (PLCP) sub layer and using signal carrier and spread

spectrum modulation to transmit data frames over the media under the control of the physical

medium dependent (PMD) sub player. Finally PHY provides a carrier sense indication back tothe MAC to verify the activity on the media.

There are three different physical layer specifications are described in Wireless LAN.

Spread Spectrum

o FHSS(frequency hopping spread spectrum)

2.4GHz ISM band at 1Mbps and 2Mbps

PHY uses 79 non-overlapping 1 MHz channels to transmit 1 Mbps data

signal

o DSSS(direct sequence spread spectrum)

2.4GHz ISM band at 1Mbps and 2Mbps

IEEE 802.11 uses a simple 11 chip barker code with QPSK or BPSK

modulation

Infrared signal



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1.3.3 Medium Access Control (MAC):

IEEE 802.11 medium access control (MAC) provides a functionality to make a reliable data

transmission over wireless media which is noisy and unreliable. MAC also gives functionality to

access control and security. Due to noise, interference and other propagation effects result in loss

of frames and also error correction codes, frames may not receive properly. To reduce frame

losing, we can implement at higher layers like TCP but retransmission timers will be order ofseconds so that its more efficient to deal with errors at MAC level.

In IEEE802.11 standards, there are three types of frames are defined. Those are control frames,

data frames and management frames. In control frames, we have subtypes. Those are RTS, CTS,

ACK, Power Save Poll, CF-End and CF-End + ACK. There are eight data frame subtypes in two

groups. In first group, simple data, data with contention-free acknowledgement (CF-ACK), data

with CF-Poll, data with CF-ACK and CF-Poll. In second group, there are CF-ACK, CF-Poll, and

CF-ACK+CF-Poll. In management frames, we have several subtypes. Those are Beacon frames,

Probe request & response frames, Authentication & DE authentication frames, Association

request & response frames, Re-association request & response frames, Disassociation frames and

Announcement traffic indication map frame.

The first function of the MAC is to provide reliable data delivery service to the users of the MAC

through frame exchange protocol at the MAC level. The minimal MAC frame exchange protocol

consists of two frames, a frame sent from the source to the destination and an acknowledgement

from destination to the source. WLAN has hidden node problem which doesnt exist in Wired

LAN. In order to overcome from this, two more frames added, one is Request to send frame

(RTS) and another is clear to send frame (CTS).The second function of MAC is to fairly control

access to the shared wireless medium. MAC has basic access mechanism called distributed

coordination function (DCF) and centrally controlled access mechanism called point

coordination function (PCF).In basic access mechanism, carrier sense multiple access with collision avoidance (CSMA/CA)

is used which is based on listen before talk mechanism. Station starts using medium for own

transmission when its idle depends on timing intervals. There are two basic intervals defined by

PHY, short inter frame space (SIFS) and slot time. Three additional intervals are defined on

basic intervals priority inter frame space (PIFS), distributed inter frame space (DIFS) and

extended inter frame space (EIPS). Based on these five intervals, DCF and PCF are

implemented. In DCF, whenever MAC receives request to send a frame, it will check the

medium by physical and virtual carrier sense mechanism. If medium is free for an interval of

DIFS, MAC will start transmission otherwise it uses back-off interval using binary exponential

back-off mechanism until back-off interval expires. PCF (centrally controlled access mechanism)uses polls and response protocol to eliminate the medium contention. Its always located in AP.

IEEE 802.11 MAC takes MSDUs and adds headers and trailers (MAC service data unit) which

takes from the higher layers of the protocol stack to send equivalent layers of the protocol stack

in another station. These MSDUs are called as MAC protocol data unit (MPDU). Generally

IEEE 802.11 frame format is shown below. MAC contains three different frame types: control

frames, data frames and management frames in which several subtypes are also defined.



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Management frames are used for station association/disassociation with AP, timing and

synchronization among stations with AP and authentication and de authentication. Control

frames are used for handshaking and positive acknowledgement during data exchange. Data

frames are used for the transmission of data. MAC header provides information on frame control,

duration, sequence control and addressing.

Fig.3 IEEE802.11 MAC frame format

1.3.4 Management:

IEEE 802.11 WLAN must deal with some challenges like intermittent connection,

eavesdropping, mobility and power management. To overcome all these challenges, IEEE

802.11 standard defines tools: authentication, association, address filtering, power management,

privacy, and synchronization. Authentication mechanism comprises of one station to prove its

identity to another station in the WLAN. The steps involve in authentication process are

exchange of questions, assertions and results. There are two algorithms defined in IEEE 802.11

standard. One is open system authentication and second one is shared key authentication.

Association is the process of a mobile station connecting to an AP and requesting service from

the WLAN. Because IEEE802.11 is the alternative solution to the wired connection so stations

will move within the range and all stations should maintain connection with AP.

Power management is the most complex part in IEEE802.11. In this mechanism, mobile stations

will be in power saving mode in which stations will turn off their transmitter and receiver. There

are different mechanisms for Infrastructure Mode and Ad-hoc Mode. In Ad-hoc Mode or

independent BSS (IBSS) power management will be distributed among mobile stations. A

station must successfully complete a data frame handshake with another station with the power

management bit set in the frame header before it goes to low power operating mode. So until

completion of handshake, the station must remain in the wake state. The station must wake up to

receive beacon transmission and it should awake for a period of time after each beacon which is



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called as announcement or ad-hoc traffic indication message window (ATIM). Sending station

should get an acknowledgement of an ATIM window from destination before it transmits the

data frame to the destination. Burden will be more on sending station than on receiving station

with power management mechanism. However, there is a minimum duty cycle required of both

senders and destinations, in the ratio of the time of the ATIM window to the time of the beacon

period.Timing synchronization is distributed among mobile stations in IBSS due to absence of AP.

whichever station starts basic beaconing process i.e. a station starts BSS will begin by resetting

TSF (timer synchronization function) to zero and transmits a beacon with beacon period. After

receiving TBTT (target beacon transmission time) each station in IBSS starts sending beacon

frames. At least one beacon frame should send in one beacon period and to avoid collision of

beacon frames, each station will choose random delay values. If a station receives beacon from

another station before the delay expires, the received station will stop beacon transmission.

Beaconing also plays a major role in power management in IBSS. There should be at least one

station in the IBSS awake and able to respond to probe request frames. In IBSS, a station will

update TSF timer with the value of a received beacon frame. IEEE 802.11 developed MAC level

privacy mechanisms to protect the content of data frames from unwanted monitoring and

eavesdropping due to medium difference between Wired and Wireless LANs. To overcome

security and privacy issues in Wireless LAN, IEEE 802.11 defines an optimal MAC layer

security system known as wired equivalent privacy (WEP). This can be done with fixed shared

key authentication service. Another privacy protocol specification used in wireless LAN is

Wireless protected access (WPA).

1.3.5 IEEE 802.11 standard protocols:

Protocol Frequency speedAccessmethod

Spread spectrum

802.11 2.4 GHz 1-2 Mbps CSMA/CA FHSS/DSSS

802.11a 5 GHz Up to 54 Mbps CSMA/CA OFDM

802.11b* 2.4 GHz Up to 11 Mbps CSMA/CA DSSS

802.11g

2.4 GHz Up to 54 Mbps CSMA/CA

DSSS/OFDM

802.11n 5/2.4 GHz Up to 150 Mbps CSMA/CA OFDM



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Table 4:IEEE 802.11 standard protocols

*due to the backward compatibility 802.11b became very popular

1.4 VoIP Components:The basic steps involved in originating an Internet telephone call are conversion of the analog

voice signal to digital format and compression/translation of the signal into internet protocol

packets for transmission over the internet; the process is reversed at the receiving end. Compare

to current PSTNs, in order to enable organizations to adopt VoIP as a viable solution the VoIP

components must perform functions such as

Signaling: Signaling is the way that devices communicate within the network, activating and

coordinating the various components needed to complete a call (accomplished by exchange ofdatagrams between end terminals).

Database services: A VoIP network uses an IP address and port number to locate an end point,

address abstraction could be accomplished with DNS

Call bearer control: The connection of a call is made by two endpoints opening a

communication session between one another. In a VoIP implementation connection is a

multimedia stream transported in real time. Once communication is complete, the IP sessions are

released and optionally network resources are freed.

Codec Operations: The process of converting analog waveforms to digital information is done

with a coder-decoder (VOCODER), the data stream from the vocoders are put into IP packets

and transported across the network to an end terminals. Two end points will use same ITU

encoding standards (ex: G.7 family) and common set of CODEC parameters

The major components of a VoIP network, while different in approach, deliver very similar

functionality to that of a PSTN and enable VoIP networks to perform all of the same tasks that

the PSTN does. The one additional requirement is that VoIP networks must contain a gateway

component that enables VoIP calls to be sent to a PSTN, and vice - versa. There are four major

components to a VoIP network.

- Call Processing Server/IP PBX

- User End-Devices

- Media/VOIP Gateways

- IP network



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Figure 2: VoIP network

-

Call Processing Server / IP PBX:

Once a call has been set up, speech will be digitized and then transmitted across the network asIP frames. Voice samples are first encapsulated in RTP (Real-time Transport Protocol) and UDP

(User Datagram Protocol) before being transmitted in an IP frame.The call processing servers /IP PBX are usually software based and can be deployed as a single

server, cluster of server or a server farm with distributed functionality. VoIP communications

require a signaling mechanism for call establishment known as control traffic and VoIP payload.

VoIP control traffic follows the client -server model with VoIP terminals including messaging

servers that hold voice mail messages representing the clients that communicate to the call

processing servers.

Call processing servers do not handle VoIP payload traffic exception to routed voice traffic to

another call processing server, conferencing functionality and music on hold. Voice traffic flowsin a peer-peer fashion from every VoIP terminal to every other VoIP terminal determining the

traffic flows. Call processing servers negotiate those flows with in the control messages

User End-Devices:

The user end-devices consist of VoIP phones and desktop-based devices. VoIP phones may be

software based (applications running on notebooks) or traditional handsets.

VoIP phones use the TCP/IP stack to communicate with the IP network, as such, they areallocated an IP address for the subnet on which they are installed. VoIP phones use DHCP to

auto-configure themselves and also use additional protocols to support VoIP-enabled features,

such as built-in IM applications or directory search functions.

VoIP Gateways:

Gateways are mainly used for call admission and control and bandwidth management. The major

function of media gateways is analog-to-digital conversion of voice and creation of voice IP

packets (CODEC functions), in addition to it media gateways have optional features such as

voice compression, echo cancellation, silence suppression and statistics gathering. The media



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gateway forms the interface that the voice content uses so it can be transported over the IP

network. Media gateways are the sources of bearer traffic. Typically, each conversation (call) is

a single IP session transported by a Real-time Transport Protocol (RTP) that runs over UDP or

TCP.

Media gateways exist in several forms. Their features and services can include some or all of the

following:- Trunking gateways that interface between the telephone network and a VoIP

network. Such gateways typically manage a large number of digital circuits.

- Residential gateways that provide a traditional analog interface to a VoIP

network. Examples of residential gateways include cable modem/cable set-top boxes, xDSL

devices and broadband wireless devices.

- Access media gateways that provide a traditional analog or digital PBX interfaceto a VoIP network. Examples include small-scale (enterprise) VoIP gateways.

- Business media gateways that provide a traditional digital PBX interface or an

integrated soft PBX interface to a VoIP network.

- Network access servers that can attach a modem to a telephone circuit and

provide data access to the Internet.

Figure 3: VoIP protocols and gateway

Gateway communication should be secured with internet protocol Sec to prevent

interference with calls and to prevent unauthorized calls from being setup. The gateway itself is

vulnerable to internet protocol based attacks and can be mitigated by using internet protocol Sec

and by removing any unnecessary services and open ports, as should be done with any server.


Digital voice gateway

V.90

modem

ISDNG3

Fa

x

G4

Fax

POT

SMTP trapsSMTP

Syslog, propRTP

NTP Telnet,SSH,W

TFTP

h.323 control ALG,SIP

sccp


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1.5 Difference between PSTN and VoIP:

In the Public Switched Telephone Network (PSTN), the system works by setting up a

dedicated channel established between two points for duration of the call. These telephony

systems are based on copper wires carrying analog voice data over the dedicated circuits known

as circuit switching networksCompared to newer Internet telephony networks based on digital technologies, VoIP uses

packet-switched telephony. Using this system, the voice information travels to its destination in

countless individual network packets across the Internet. Individual packets may and almost

always do take different paths to the same place. It's not enough to simply get VoIP packets to

their destination. They must arrive through a fairly narrow time window and be assembled in the

correct order to be intelligible to the recipient. VoIP employs encoding schemes and compression

technology to reduce the size of the voice packets so they can be transmitted more efficiently.

PSTN VoIP

Dedicated Lines All channels carried over one Internet

connection

Each line is 64kbps (in each direction) Compression can result in 10kbps (in each

direction)

Features such as call waiting, Caller ID and

so on are usually available at an extra cost

Features such as call waiting, Caller ID and

so on are usually included free with service

Can be upgraded or expanded with new

equipment and line provisioning

Upgrades usually requires only bandwidth

and software upgrades

Long distance is usually per minute orbundled minute subscription

Long distance is often included in regularmonthly price

Hardwired landline phones (those without anadapter) usually remain active during power

outage

Lose power, lose phone service withoutpower backup in place

When placing a 911 call it can be traced to

your location

911 emergency calls cannot always be traced

to a specific geographic location

Table 1: Differences between PSTN and VoIP

Protocols:

There are a number of different protocols associated with VoIP, that provide for signaling,quality of service, and media transport. Shown below is a list of the types of protocols and the

protocols themselves.

Signaling Protocols

H.323

SIP

SDP



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Quality of service Protocols

RSVP

RTCP

RTSP

Media Transport Protocol

RTP

These protocols are at the heart of any IP session and integral in keeping VoIP to a good standard

of service

i) H.323

H.323 provides for call connection, call management, and call termination, in a VoIP session. It

is a signaling protocol recommended by the International Telecommunications Union (ITU). The

ITU describes and defines its own set of protocols that differ from those of the InternetEngineering Task Force (IETF). H.323 includes H.245 for control, H.225.0 for connection

establishment, H.332 for large conferences, H.450.1 H.450.2 and H.450.3 for supplementary

services, H.235 for security, and H.246 for interoperability with circuit-switched services

ii) SDP

The Session Description Protocol is a signaling protocol that is used to describe multimedia

sessions for VoIP. It provides information about the media streams being transmitted including

the number and type of each media. Other information it provides is the payload type that can be

transmitted, port numbers, and initiator information including name and contact number.

iii) RSVP

The Resource Reservation Protocol is not strictly a quality of service protocol. RSVP handles

routing and, as the name suggests, reservation of resources. The resources include bandwidth,

grade of service, carrier selection, and payment selection. The grade of service and bandwidth

relate it to being a quality of service protocol. These reservations can take place either before or

after the data begins to be transmitted. Due to the complexity of RSVP, because of extensive

features, it is becoming redundant. It has been proposed that the services be completed using

Real Time Control Protocol (RTCP) messages. An RTCP message can be modified to contain an

additional field that would specify the desired grade of service

iv) RTSPThe Real Time Streaming Protocol is used to control video and audio media across a network. It

gives the user VCR like controls over this media, by controlling a stored media server. It

instructs the server using these controls what to do with the media. This is useful for voicemail in

IP telephony, or recording a video or audio conference so that it can be listened to again in the

future.



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1.6 The Session Initiation Protocol (SIP)

Session Initiation Protocol is a signaling protocol specified by the Internet Engineering

Task Force used to set up and tear down two-way communications sessions. It provides the

necessary tools for location services, call establishment, call management, and call termination.

Session internet protocol operates on the application level so can be used with several differentprotocols. Using transmission control protocol allows use of providing more security whereas,

user datagram protocol allows for faster, lower latency, connections.. The usual components

software contains client and server components. The client piece makes outgoing calls and the

server is responsible for receiving incoming calls. The proxy server forwards traffic, the registrar

server authenticates requests, and the redirect server resolves information for the usual

components client. The endpoints begin by connecting with a proxy and/or redirect server which

resolves the destination number into an internet protocol address. It then returns that information

to the originating end point which is responsible for transmitting the message directly to the

destination. SIP does not classify the type of session that is set up, so it could just as easily set up

an audio call with or without other data. SIP is similar in syntax to Hypertext Transfer Protocol

(HTTP), requests are generated by one host and sent to another. A SIP request contains a header

field that gives details about the call, and a main body which describes the media being used. A

security advantage of session internet protocol is that it uses one port. The main concerns for

security of are confidentiality, message integrity, nonrepudiation, authentication and privacy.

New security mechanisms were not created for session internet protocol instead, session internet

protocol uses those provided by Hyper Text Transfer Protocol and Simple Mail Transfer protocol

as well as Internet Protocol Security

Figure: Session Initiation Protocol



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1.6.1 SIP Components:

Usual components of a Session initiation Protocol system is the user agent, proxy server,

registrar server, and the redirect server

Proxy Server

This server receives particular request, processes it and then forwards it onto the relevant server.

In some cases the proxy server will make small alterations to the header field of a SIP request. A

proxy server has no way of knowing whether the next server to receive the request is a proxy

server or a redirect server therefore request can traverse many servers, on the way to its intended

receiver.

Figure : Proxy server

Redirect Server:

A redirect server also receives requests, and processes them. However instead of the server

forwarding the request onto the next relevant server, it sends back the relevant information

needed to find the appropriate server, to the original proxy server. Therefore redirecting the

proxy server to the address of the next server needed to process the request.

Figure: Registration server



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Figure: Redirect server

Consider the VoIP situation portrayed in the shown figure is a diagram of what SIP is doing in

the background. User one decides to make an IP call to user two. User one enters an IP address

or email address, lets say [email protected], into its application and presses send. A request

is then sent to the proxy server (1), and this server looks up the name yahoo.com. It then

forwards this request to the server that handles requests for yahoo.com (2). The server then looks

up and recognizes that Andrew is a user, but he is currently not at this location, but sees a note

that data should be forwarded to [email protected]. This server then redirects the original proxy

server to try this address (3). The proxy server then sends this request to the dcu.ie server (4).

This server looks up its database (5,6), and sees that it has a user [email protected], but the user is

actually known as [email protected]. Therefore the main DCU server sends the request to theengineering server (7). The engineering server then finds where the user is logged in, and sends

the request to the user at the desktop (8). The user then accepts the request and a VoIP session is

opened (9,10,11,12).

7

10

4

PC-1

PC-2

SIPPROXYSERVER

SIPREDIRECTSERVER DATABASE

SIP PROXYSERVERSIPPROXYSERVER

1

2

3

5

6

8

9

11

12

Figure : VoIP functionality



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6

In a SIP request, like the ones that would be used in the situation above, the header field contains

information on the sender, including numbers and addresses. It also gives information on call

services, in general the header field describes the call being set up. The body of a SIP message

describes the media content that is being sent. The body is usually an object described by a

particular protocol. SIP defines several different request methods these are explained.

Invite

The INVITE request is used to invite a user to participate in a VoIP call. The header field usually

consists of the addresses of the person calling, and the intended receiver. It gives the subject of

the call, the features to be used, and preferences for how the call should be routed. The body of

the INVITE request contains an object that describes the media content of the session. It gives

information on what ports to be used and what protocols are used when sending media.

Figure : Invite request

Options

OPTION is a signaling message that gives information about the capabilities of the caller, i.e. if

the user can receive both data and voice. It has nothing to with setting up the call.

Ack

ACK is used to maintain reliable message exchanges. This is used in response to invitations.

Cancel

Cancel terminates a particular request but doesnt terminate the call. Lets consider the case

where two users were having a conference and they decided to invite another user three in, but asthey were inviting the user three they realized there was actually no need for him to be included.

In this case they would send a CANCEL request. This request appears at user threes end advising

him to reject the call, but it doesnt actually stop him from answering it. If though the user three

had already accepted the request, before the CANCEL command could be sent, it would have noeffect.



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Bye

The BYE request terminates the connection between two users in a VoIP call. Although the

functions described above make SIP a very useful protocol for setting up and managing VoIP

calls, it still needs to implement other protocols to allow it to transport the media, and to give

information about how this data is being controlled.

* will add more information while working with it in practical

1.7 REAL TIME TRANSPORT PROTOCOL (RTP):Voice packets sent over the internet by using UDP as main transport mechanism. Packet

loss and delay jitter are main problems when we send directly by using UDP. For overcoming

packet loss retransmission mechanism is not possible in VOIP for real-time services.

To overcome this problem the receiver must know when the packet is sent. By using time

stamping on the data packets while sending we can know when the data is sent at the receiver

side. For this we are using separate protocol called RTP.Main features of RTP are time stamping and sequence numbering. RTP uses UDP port for

communicating with other protocols. Services include payload type identification, sequence

numbering, time stamping and delivery monitoring.

Figure 11: Real Time Transport Protocol

In programmer point of view RTP is a part of application layer for voice over IP. For

Network theory view it is more like a transport protocol.

RTP header

Figure: RTP header



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Synchronization source identifier:

This will be different from IP address, sender chooses a random number while using .main use of

SSRI is to identify particular RTP stream between 2 hosts, which is for identifying source of

RTP stream.

Payload:

In the RTP header pay load indicates type of encoding used for multimedia stream(audio/video).we can send the payload size as 7 bits (27= 128).in matter of fact if sender changes

the payload type on fly, it has to update the pay load in the header so that the receiver will adjust

the vocoders as per the encoding technique updated. In the RTP payload header we can send 128

types of payload types, some of them are standardized and remaining are free.

Ex:

Payload: 0 PCM - law

7 LPC (8 kHz)

14-mpeg(90 khz)-audio

31-mpeg-1 video

32-mpeg-2 video

Sequence number:

Incremented by 1 for each RTP packet and used for detecting packet loss

Time stamping:

It denotes sampling instant of first byte in the RTP data and to remove packet jitter .it is

derived from sampling clock at the sender.


1.8 RTCP

used during multicast audio video transmission

RTCP packets are distributed to all the participants using IP multicast

Distinguished from RTP through the use of distinct port numbers.

RTCP packets contains sender receiver reports

Number of packets sent

Number of packets lost

Inter arrival time jitter

Different application use different algorithms to use RTCP methods

Internally RTP used in cooperation with RTCP. RTP transports audio packets over the internet.

RTCP responsible for monitoring the transmitting statistics and maintaining QOS

RTCP packets types:

Receiver reception packets,

Sender report packets

We can use this information to synch different media streams with in a RTP session.




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1.9 Voice compression technologyVoice compression is the process where voice data is compacted into less bulk for better

transportation. This technology will reduce the volume of audio data. Less bulk data is surely

helpful to relieve the network load and ensure real time response in VOIP calls.

CELP (code exited linear prediction) is generally considered to be the most successful

compression algorithm. CELP speech coding is based on source filter model. CELP can recordand store speakers voice with an unconceivable low bit rate, normally it is able to control

transmission rate between 2 kbps to 16 kbps.

Figure : VoIP codecs

1.9.1 Speex codec:

Speex is an open source codec with wide range of bitrate and Speex (www.speex.org) is flexible.

Speex is designed for packet networks and VoIP applications. It can support good quality speech

Speex can encode wideband speech in addition to narrow band speech. Speex designed for VoIP

instead of mobile phones means that Speex is robust to lost packets but not to corrupted packets.

This is based on assumption that in VoIP packets arrive unaltered or dont arrive at all. Speex has

modest complexity and it is targeted at wide range of devices. All the design goals led Speex to

the selection of CELP as encoding technique. Main reason behind this is CELP could work

reliably and scale well for both low bit rates and High bit rates.

Speex is primarily designed for three different sampling rates. Those are Narrow band,

wide band, ultra wide band respectively 8 kHz, 16 kHz, 32 kHz. Sampling rate is number of

samples taken from signal per second and is expressed in Hertz (Hz). Bit rate is the number of

bits required per unit time of time required to encode the speech. It is measured in bits per

second (bps). Speex uses Variable bit rate, average bit rate, voice activity detection, and Dis-

continuous transmission



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The main features of Speex can be summarized as follows:

Free software/open-source, patent and royalty-free

Integration of narrowband and wideband using an embedded bit-stream

Wide range of bit-rates available (from 2.15 kbps to 44 kbps)

Dynamic bit-rate switching (AMR) and Variable Bit-Rate (VBR) operation

Voice Activity Detection (VAD, integrated with VBR) and discontinuous transmission (DTX) Variable complexity , Ultra-wideband sampling rate at 32 kHz

Embedded wideband structure (scalable sampling rate)

Intensity stereo encoding option, Fixed-point implementation

1.10Power consumptionPower conservation is achieved by minimizing the time for the STA to be awake and by

maximizing the time when the STA is in doze mode. Power management for infrastructure BSSs

and IBSSs work in different ways. In an infrastructure BSS, each STA is associated with an AP.

A STA with power management engaged will enter doze mode after it has been idle for a periodindicated by the expiration of the idle timer.The 802.11 standard defines procedures that can be

used to implement power management during inactive periods. In particular, three distinct

building blocks are provided to support power savings: a Wakeup Procedure, a Sleep Procedure,

and a Power-save Poll (PS-Poll) Procedure. A station (STA) can combine these power

management building blocks in various manners for different applications.

Wakeup Procedure: There are two reasons for the STA to wake up: to transmit pending data or

to retrieve buffered data from an access point (AP).

Sleep Procedure: Similar to the wakeup procedure, a STA in the active mode needs to complete

a successful STA initiated frame exchange sequence with PS bit set to sleep to transition into the

sleep mode.

PS-Poll Procedure: Instead of waiting for the AP to transmit the buffered downlink frames, a

STA in sleep mode can solicit an immediate delivery from its AP by using a PS-Poll frame.

Upon receiving this PS-Poll, the AP can immediately send one buffered downlink frame

(immediate data response) or simply send an acknowledgement message and response with a

buffered data frame later (delayed data response).

It is possible for a STA to use information such as the inter-arrival time of downlink

voice frames, along with a Power-save mechanism, to put itself to sleep between two consecutive

voice frames. The following two subsections explain two legacy power management techniques

for putting a STA to sleep between voice frames using the CSMA/CA channel access mechanismduring a VoIP call.



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Chapter 3

Wi-Fi Direct

Introduction

In General Wi-Fi allows the deployment of local area networks for client devices, where cables

cannot be run, such as outdoor areas and historical buildings can host wireless LAN, typically

reduces the costs of network management and expansion. Normally Wi-Fi networks are set up in

infrastructure mode, where the access point acts as a central hub. Wi-Fi has always claimed to

support a second mode, "ad-hoc mode", where networking is automatically provided between

Wi-Fi enabled devices, using ad-hoc mode, two Wi-Fi devices can theoretically set up a

connection between them entirely automatically.

Wi-Fi Direct is an upcoming program from the Wi-Fi Alliance that defines a new wayfor Wi-Fi devices to work together, to meet the increasing demand for easy, portable wireless

network connectivity. Wi-Fi direct is a P2P wireless networking, allowing devices like

notebooks, tablets, cameras, and printers can "find" each other and establish wireless

connectivity in the absence of an access point, or a hotspot.

Wi-Fi Direct: A set of software protocols that allow Wi-Fi devices to talk and connect

to each other without prior setup or the need for joining a traditional wireless access points.

A Wi-Fi Direct network can be one-to-one, or one-to-many. The number of devices in a

Wi-Fi Direct network is expected to be smaller than the number supported by traditional

infrastructure mode. All Wi-Fi Direct devices will allow the user to connect to an infrastructure

or a Wi-Fi Direct network. Some Wi-Fi Direct devices will support connections to both aninfrastructure network and Wi-Fi Direct network at the same time. Wi-Fi Direct is developed

within the Wi-Fi Alliance by member companies and Legacy Wi-Fi devices are supported as it

operates on 802.11 devices (b/g/n) but is not linked to any specific IEEE 802.11 alternation

Figure 3.1 . Wi-Fi direct[10]



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1.11 Wi-Fi Direct and existing Wi-Fi standards

Wi-Fi Direct device will be able to make device-to-device connections with existing IEEE

802.11 a/b/g/n standards The peer to peer networks always allows devices to exchange data with

each other without an access point, but implementations effects poor security and degraded

throughput. Wi-Fi Direct is a substitution of the effected ad-hoc networking mode as a part of802.11.The best advantage of the new method that it can preserve the full bandwidth of 802.11,

and overtakes incompatibility issues that ad-hoc would suffer. The most significant difference

between traditional Peer-to-Peer networking and Wi-Fi Direct is security. Wi-Fi Direct

connections will work, at typical Wi-Fi ranges, protected by WPA security protocols and

including WMM QoS mechanisms. It supports WPS and WPA2 by default. The new

specification places a premium on security; it was developed to have separate security domains,

so your WLAN connection is a separate security domain from your Wi-Fi Direct network.

Another difference, Wi-Fi Direct devices can also simultaneously connect to existing wireless

networks. More granular control and better discovery of devices also differentiate Wi-Fi Direct

from ad-hoc networking. Wi-Fi Direct adds up technology known as Soft Access Point, in few

words, is software-based access point functionality built into Wi-Fi Direct certified devices.

These devices are capable of routing and directing network traffic just like access points and

routers. Wi-Fi Direct devices may not provide the overall range of a wireless router or AP.

There's more flexibility with APs and routers, as they can be placed strategically to provide

optimized signal strength. Also, there are security considerations with Wi-Fi Direct; there is a

good chance that IT departments with corporate wireless networks may have issues with

controlling Wi-Fi Direct devices.

1.12Architectural overview1.12.1Components:

In the Wi-Fi direct network architecture, device to device interaction can be done by using Wi-Fi

direct enabled devices (P2P device). These P2P components support Wi-Fi simple configuration[8] and P2P discovery mechanism and also may support concurrent operation by working with

WLAN and P2P at the same time by using dual mac layer support [10].

P2P device is a WFA P2P certified device that is capable of acting as both a P2P Group Owner

and a P2P Client.

P2P group owner: It acts as an AP (access point) that offers Basic Service Set functionality with

WSC internal registry functionality .It provides communication between associated clientsincluding legacy clients and sometimes it may provide simultaneous W LAN connection

between associated clients and P2P Group Owner transmits Beacon frames using

OFDM(orthogonal frequency division multiplexing)

P2P Client role: It functions as non-access point device role. It offers WSC enroller

functionality.



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In P2P topology, all clients are connected to P2P group owner in 1: n manner, the clients

in P2P group may be P2P client or Legacy client .This P2P group consists of one service set

identifier SSID and security domain is provided with that SSID. The P2P group may consist of

concurrent connection between WLAN and associated clients. This is possible by dual MAC

layer support. One MAC entity works at WLAN-STA and other MAC entity works at P2P

device communication. Achievement of Dual MAC layer functionality is possible by twoseparate MAC entities each associated with its own PHY entity, two virtual MAC entities over

one PHY entity or any other approach.

P2p GROUP

WLAN BSS

P2P device WLAN-STA

AP

P2P

devic

e

Figure 3.2 P2P device concurrent connections[10]

P2P devices have a unique P2P device address, it may be globally administered MAC address, or

its globally administered MAC address with the locally administered bit set. This The P2P

Device Address shall be used as the receiver address (RA) for all frames sent to a P2P Device

during P2P Discovery and it shall be used as the transmitter address (TA) for all frames sent by a

P2P Device during P2P Discovery. P2P device will acts as group owner or client role when it is

in a P2P group. The P2P device will assign an interface addressing mechanism, which is used tocommunicate with P2P group owner or clients with in P2P group. Interface address may be as

same as device address provided the requirements for P2P interface address in this clause are

satisfied.

1.12.2Functions and services:

In a Wi-Fi direct (peer to peer) network, it is assumed that all the STA functions and services by

P2P group owner should pass WFA certifications which are implemented in P2P devices.

WFA certification for at least 802.11g, which includes WPA2

Wi-Fi protected Setup

Wi-Fi multimedia

P2P specifications and services can be described as

P2P Discovery provides a set of functions to allow a device to easily and quickly identify and

connect to another P2P Device and its services in its vicinity.



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P2P Group Operation resembles infrastructure BSS operation as defined in IEEE Std.802.11-

2007 [7], and provides additions for a P2P Group operation.

P2P Power Management provides a set of functions to reduce power consumption of P2P

Devices.

Managed P2P Device Operation (optional) describes the ability for P2P Devices to operate in

an enterprise environment where P2P Devices may be managed by the Information Technology(IT) department of the enterprise.

1.13Functional description and procedures

1.13.1Introduction to p2p discovery

The major components in P2P discovery are following

Device Discovery enables two P2P Devices coming on a common channel and

exchanging device information. For example, Device name and device type is exchanged.

Service Discovery is an optional feature that allows a P2P Device to discover available

higher-layer services prior to forming a connection.

Group Formation is used to determine which device will be the P2P Group Owner and

form a new P2P Group.

P2P Invitation is used to invoke a Persistent P2P Group or invite a P2P Device to join an

existing P2P Group.

1.13.2Device Discovery procedures:

The main objective of this device discovery is to find P2P devices and finding with which we

can establish connection. Probe request frames and probe response frames are used For

exchanging information between devices containing device type attributes as P2P informationelement (IE), P2P Wildcard SSID element, a Wildcard BSSID, and a destination address that is

either a broadcast address or P2P device address.P2P device will not respond to probe request

unless it is a P2P group owner or it is in listen state or it is associated with AP on the channel on

which probe request sent.

1.13.2.1 Basic mechanisms of device discovery

A P2P Device Discovery consists of two major phases: Scan phase and Find phaseA P2P Device

in the Scan Phase may discover a P2P Device in the Listen State. The Find Phase is used to

ensure that two P2P Devices that are both in Device Discovery arrive on a common channel to

exchange device information. [10] If a P2P Device, wishes to connect it may do one of thefollowing. A P2P Device that is already operating as a P2P Group Owner stays on the Operating

Channel and waits for other devices to discover it.



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1.13.2.1.1 Listen state:

In the Listen state A P2p device which is not in a group will use the listen state dwelling in

orthogonal channels in the 2.4 GHz band to become discoverable. It shall respond only to Probe

request frames. If one or more device attributes are present in Wi-Fi simple configuration IE in

the probe request frame, the P2P device in the listen state shall only respond with a proberesponse frame if it has a primary or secondary device type value matches to any of attributes.

An example of credentials being available and for immediate usage includes PBC method,

display method and keypad method.

P2p device in the listen state shall set the source address (SA) and BSSID to its P2P

device address, and shall set the SSID to the P2P Wildcard SSID in all Probe Response frames

that it sends. The P2P Device shall set the ESS bit of the Capabilities field in the Probe Response

frame to 0 and IBSS bit to 0.

1.13.2.1.2 Scan phase:

It may be used by a P2P Device to find P2P Devices or P2P Groups and to locate the best

potential Operating Channel to establish a P2P Group. In the Scan Phase, devices collectinformation about surrounding devices or networks by scanning all supported channels. The P2P

Device in the Scan Phase shall not reply to Probe Request frames. A P2P Device may send a

Probe Request frame containing the P2P IE and the Wildcard SSID to elicit Probe Response

frames from both legacy networks and P2P Group Owners. Inclusion of the P2P IE in the Probe

Request frame is required to enable the P2P Group Owner to include the P2P Group Info

attribute in the Probe Response frame. P2P Clients shall not reply to Probe Request frames so

they can only be discovered by the Probe Response frame from the P2P Group Owner containing

the P2P Group Info attribute, A P2P Device may narrow its scan to either: A specific device

type or device types by including the WSC IE with one or more Requested Device Type attribute

in the Probe Request frame.

Filed Size Value

(hexadecimal)

Description

Element 1 0xDD IEEE 802.11 vendor specific usage

Length 1 Variable Length of the following fields in the IE in octets. The

length filed is a variable, and set to 4 plus the total length

of P2@ attributes

OUI 3 50 6F 9A WFA specific OUI

OUI type 1 0X09 Identifying the type or version of p2P IE. Setting to 0x09

Indicates WFA P2P v1.0P2P

attribute

Variable One of more P2P attributes appears in the P2P element

Table 3.1 P2P IE [10]



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The Requested Device Type attribute has the same format as the Primary Device Type attribute

in the WSC specification [8]. A specific P2P Device by including the P2P Device ID attribute in

the P2P IE in the Probe Request frame. This provides a mechanism to scan for a specific P2P

Device.

1.13.2.1.3 Find phase:

Find phase is used to make suretwo simultaneously searching P2P Devices arrive on a common

channel to enable communication. Find phase is achieved by cycling between states where the

P2P Device waits on a fixed channel for Probe Request frames (the Listen State) or sends Probe

Request frames on a fixed list of channels (the Search State). Convergence of two devices on the

same channel is assisted by randomizing the time spent in each cycle of the Listen State

1.13.2.2 P2P Device discovering of a device with in P2P group

A searching P2P Device discovers a P2P Group Owner in the Scan Phase through received

Beacon frames, or Probe Response frames. The searching P2P Device will also discover other

P2P Devices that are associated to that P2P Group Owner from Group Information

AdvertisementA searching P2P Device should be aware that the target P2P Device may use P2P power saving

and this may impact communication with the P2P Device. If the target P2P Device is a P2P

Client in a P2P Group, a searching P2P Device may send a Device Discoverability Request

frame to the P2P Group Owner with the P2P Device ID of the target P2P Device. The P2P Group

Owner indicates to the target P2P Device the request to be available for discovery and sends a

Device Discoverability Response,

If a P2P Device desires to join a P2P Group it may do either Use Wi-Fi Simple Configuration [8]to obtain Credentials. Wi-Fi Simple Configuration will take place on the Operating Channel of

the P2P Group Owner. Or if the P2P device is provisioned, then it will connect to the peer to

peer group If a searching P2P Device does not want to join the P2P Group that the discoveredP2P Device is a member of, the searching P2P Device may do either Send a P2P Invitation

Request frame to request that the target P2P Device joins a P2P Group of which the searching

P2P Device is the P2P Group Owner or a P2P Client Or Initiate Group Owner Negotiation toattempt to form a new P2P Group. The P2P Device Limit field bit in the Device Capability

Bitmap field of the P2P Capability attribute indicates if the target P2P Device is able to establish

an additional P2P connection



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Figure 3.3 .device discovery in a p2p group

1.13.2.3 Connecting to a legacy client:

A Legacy Client can only discover a P2P Group Owner. When a P2P Group Owner receives a

Probe Request frame from a Legacy Client in its Operating Channel, the P2P Device shall

transmit a Probe Response frame as defined in IEEE Std. 802.11-2007 [7].A Legacy Client that

does not support Wi-Fi Simple Configuration [8] has to be provisioned using methods outside

the scope of this specification. The P2P Group Owner shall generate the Credentials used for

provisioning.

1.13.2.4 Associated with an infrastructure AP

A searching P2P Device may discover a P2P Device associated with an infrastructure AP in the

Scan Phase through Probe Response frames. A P2P Device associated with an infrastructure AP



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receiving a Probe Request frame with a P2P IE and either a wildcard SSID or a P2P wildcard

SSID may respond with a Probe Response frame with a P2P IE. A searching P2P Device should

be aware that the P2P Device may use power saving

1.13.3Service Discovery procedures

The service discovery procedure is an optional frame exchange that may be performed at anytime to any discovered P2P device, it is used to find compatible list of all services and

information about single/multiple services offered by a P2P device. This service discovery

procedure enhances the generic advertisement service (GAS) protocol/frame exchange as defined

in IEEEP802.11u [9] with unicast public action frames, in single or multiple GAS initial

request/response frames.

1.13.3.1 Service discovery query frame:

Service discovery query frame supports different query types, which changes the content of filed

in the vendor specific content filed.

Field Name Size

(octates)

Value Descriptions

OUI

subtype

1 0x09 WFA OUI Subtype

Service

Update

Indicator

2 Variable The Service Update Indicator is a counter that is

incremented when a change has occurred in the

service information of the P2P Device sending thisService Discovery Query or Response frame.

Service

TLV

variable Variable service TLV

Table3.2 Service discovery vendor specific content[10]

To request compatible list of all services, service discovery frame uses GAS initial request

frame including a single service request type length value (TLV) with the service protocol type

field equal to 0 and a query data length of 0.

Table 3.3 Single service request type length value (TLV)[10]


Field name Size

(octets)

Value Description

Length 2 Variable Length of the service request TLV

Serviceprotocol type

1 Table(SPA)

Service protocol types

Service

transaction ID

1 Variable Service transaction ID is a nonzero value used to

match the service request /response TLVs

Query Data Variable NA Query data for the requested service information.


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A service transaction ID is maintained in all the request and response frames in order to match

the response to query. For a specific layer, service protocol type field value will be set to non-

zero value defined in table 3.4

To request information about multiple services of a single or multiple higher layer service

protocol types, query frame includes multiple TLV, each containing service protocol type filedset to one of the non-zero values as in table 3.4. For Requesting specific service of a specific

higher layer service prototype, the query frame will set the TLV as per table 3.4 and query data

filed will include the service information as per the requested protocol type.

Valu

e

Meaning

0 All service protocol types

1 Bonjour

2 Upnp

3 Ws discovery

4-254 Reserved

255 Vendor specific

Table3.4 Service Protocol Types[10]

1.13.3.2 Service discovery Response frame:

Response frame uses the gas initial response frame as defined in IEEE p 802.11u [] with service

transaction id to match request and response frames If the service discovery frame is for all

services and higher layer service protocol types, the service discovery response frame may

contain multiple service response TLVs containing service protocol type filed set to one of the

non-zero values defined in table 3.6. The status code filed of each returned service TLV is set to

as per table 3.6.

Table3.5:Service Response TLV Fields [10]


Field name Size

(octets)

Value Description

Length 2 Variable Length of the service response TLV

Service

protocol type

1 Table 63 Service protocol types

Service

transaction ID

1 Variable Service transaction ID is a nonzero value used to match

the service request /response TLVsService

response Data

Variable NA Response Data is dependent on the requested service

information type in the Query Data field of the Service

Request.

Status code 1 Table 65 Status code for the requested service information.


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Available service information is contained in the response data field. The response data field

shall contain the service information type and service data belongs to service protocol type, if no

services are available a single service response TLV is returned with the service protocol type

field equal to 0 , the status code filed set to an appropriate error code , and a null value in the

response data field. If the service query frame is for all services of a specific higher layer

protocol type, then each response TLV will contain the service protocol type filed set to therequested service protocol type.

Table 3.6: Service Discovery Status Codes[10]

1.13.4Group Formation Procedure:

1.13.4.1 General procedures

Group formation procedure uses authentication provided by Wi-Fi simple configuration

determining correct devices. Consisting of group owner negotiation and provisioning state, it is

used to determine which device shall be the P2P group owner, exchange credentials for the P2P

group and determine whether it shall be persistent P2P group or a temporary P2P group.

In the group formation procedure provision phase, due to waiting for user input, Wi-Fi

simple configuration may take up to 2 min to complete. The delay caused by provisioning state by executing group formation procedure multiple times is unacceptable, a P2P device shall

obtain any information required to execute provisioning prior to the group formation, including

information such as a PIN that is obtained from a user, so that group formation procedure will

take no more than 15 sec. The P2P groupowner will act as a WSC Registrar and the selected

PIN from the display of either P2P client or P2P group owner is indicated using Device password

ID attribute in the WSC M1/M2 messages.

1.13.4.2 Group owner negotiation:

Using the find phase, prior to beginning of group formation procedure the P2p device shall arriveon a common channel with the target P2p device, group formation begins with the group owner

negotiation and complete with the provisioning.


Valu

e

Meaning

0 Success

1 Service protocol type not available

2 Request information not available

3 Bad request

4-255 Reserved


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Figure 3.4 .Group Owner Negotiation [10]

GO negotiation is three ways frame exchange as shown in fig 3.4used to agree which P2P

device shall become P2P group owner and to agree on characteristics of P2P group. Mainintention of group owner negotiation is to exchange the group owner intent attribute to

communicate a measure of desire to be P2p group owner which is illustrated infigure 3.5

Figure 3.5Group Owner determination flowcharts [10]

The Tie breaker bit in a first GO Negotiation Request frame (for instance after power up) shall

be set to 0 or 1 randomly, such that both values occur equally on average. On subsequent GO

Negotiation Request frames except retransmissions; the Tie breaker bit shall be toggled. The Tiebreaker bit in a GO Negotiation Response frame shall be toggled from the corresponding GO

Negotiation Request frame. If the Intent values in the GO Negotiation Request and Response

frames are equal and less than 15, then the device sending the Tie breaker bit equal to 1 becomesthe GO.



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1.13.4.3 Provisioning:

In the group formation procedure , to allow for P2P device configuration , P2P device may delay

starting the provisioning phase until the expiration of the maximum of the group owners GO

configuration Time and the P2P clients configuration Time from the respective configuration

time out attributes exchanged during group owner negotiations, Provisioning shall be executed as

defined in Wi-Fi simple configuration[8] modifying to act P2P group owner as access point withinternal registrar, and P2P client to serve as the STA enrolee

1.13.5P2p invitation procedure:

P2p invitation procedure is an optional procedure used to invite a P2P device to join in P2P

group by group owner or inviting a P2P device by a P2P group client wishing to make use of

some services of the P2P device or requesting to invoke persistent P2P group for which both

devices have already provisioned and one of the device is persistent group owner.

1.13.5.1 Invitation request frame:

In the P2p invitation request frame, the invitation type in the invitation flags attribute shall be set to

0- If a P2P group device invites another P2P device to join the group.

1- If a persistent group member invites another P2P device in that group requesting that

P2P group be invoked.

P2P invitation request frame transmitted by the group owner will include the P2P group id, P2P

group BSSID, channel list, operating channel and configuration timeout attributes in the P2P IE.

The channel list attribute will indicate the channels that the P2P device can support as operating

channel of the P2P group.P2P invitation request frame transmitted by a P2P client shall include

the P2P group ID, channel list and configuration timeout attributes. The channel list attribute

shall indicate the channels that the inviting P2P device can support as operating channel of the

P2P group.

1.13.5.2 Invitation response frame:

The P2P device accepting the invitation request frame will set the status attribute in the response

to success. A P2P INVITATION response frame transmitted by the persistent P2p Group owner

in response to request to invoke that P2P group will Includes the P2P group BSSID ,channel list,

operating channel and configuration timeout attributes and similarly if the invitation response

frame transmitted by the invited persistent group P2P client ,the frame will include channel list

and configuration timeout attributes. The channel list indicates the operating channels the P2P

client can support .the channel in the channel list only includes from the channel list attributes in

the request frame.

1.14Group operation:

P2p group operation will be similar to infrastructure basic service set operation by assuming

group owner as Access point and P2P client as functional role of sta.



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1.14.1P2P Group id:

The P2P group owner shall assign a globally unique P2P group id for each P2P group when the

P2P group is formed and this shall remain the same for the life time of the P2P group.

The P2p group ID assures that different P2P devices create P2P groups differentiated from each

other. The P2P group owner determines the fresh credentials for each group formed .the

credentials for a P2P group issued to a P2P device shall-use wpa2-psk as authentication type

-use AES as encryption type

-use a network key type of 64 HEX characters

-use a different SSID for each group to assure that all P2P groups are unique.

Each SSID shall begin with the ASCII characters DIRECT-enables users of legacy clients to

differentiate between a P2P group and an infrastructure network.

1.14.2Starting and maintaining a P2P group session

In the group formation procedure, GO set by the configuration for connecting legacy clients or

cross connection etc., and will assign a P2P interface address that it shall use as its Mac address

and BSSID for the duration of the P2P group session. On the operating channel selected by

group owner in a certain frequency band in a particular regulatory domain, the group owner will

transmit beacon frames advertising the timing synchronization, required optional parameters,

supported capabilities, membership, and services available within the P2P group. The group

owner will respond to the probe request frames obeying the rules in IEEE std. 802.11-2007[7],

with the following modifications. The P2P wild card SSID shall be treated the same as the

wildcard SSID for the purposes of deciding to transmit a response. When GO transmits probe

response frame it should include the P2P group info attribute in the P2P IE in the probe response

frame in respect to probe request frame. The group owner may filter P2P group information

returned in the probe response frame to include only devices with matching primary or secondary

device type values.

If a Device ID attribute is present in the P2P IE in a probe request frame, A P2P group owner

shall only respond with probe request frame if its device address of a connected P2P client

matches that in the device address field in the device attribute. In all the probe response frames

GO will set the SSID to the SSID of the group and shall set the SA, BSSID to its P2P interface

address and ESS subfield to 1, IBSS subfield to 0 in the capacity info field of beacon and probe

response frames that it sends.P2P device shall include the WSC IE including device name and

primary device type attributes in all the transmitted beacon, probe request and response frames

.both the device name and primary device type.

A client acquires the group credentials through static configurations or through the WSC

configuration .when using Wi-Fi simple configurations [8], the P2P group owner shall serve asthe WSC registrar and the client shall act as WSC enrol

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