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
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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:
Multi user VoIP over IEEE 802.11g
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.
Multi user VoIP over IEEE 802.11g
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 Andrew@yahoo.com, 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 Andrew@dcu.ie. 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 Andrew@dcu.ie, but the user is
actually known as Andrew@eeng.dcu.ie. 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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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.
* will add more information while working with it in practical
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.
* will add more information while working with it in practical
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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]
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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]
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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.
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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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