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VOIP - PowerPoint PPT Presentation

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VOIP. (Voice Over IP) Yonca Cumurcu Koray Kurt. Today, we will deal with;. What is VoIP? Ways of using VoIP? What is PSTN? Which protocols are used? What are the Challanges? Advantages of the VoIP usage? Which companies produce VoIP software?

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(Voice Over IP)

Yonca Cumurcu

Koray Kurt

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Today, we will deal with;

  • What is VoIP?

  • Ways of using VoIP?

  • What is PSTN?

  • Which protocols are used?

  • What are the Challanges?

  • Advantages of the VoIP usage?

  • Which companies produce VoIP software?

  • VoIP prices?

  • VoIP in Turkey and legal issues?

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What is VoIP?

• VoIP allows you to make telephone calls

using a computer network, over a data network like the Internet

  • VoIP uses the internet as its medium to send voice.

    • For ourpurposes we will restrict it tomean voice communications among 2 or more computers.

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What is VoIP?

  • Voice Calls are transmitted

  • over Packet Switched

  • Network instead of Public

  • Switched Telephone

  • Networks (PSTN)

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What is PSTN?

  • PSTN is abbreveation of Public Switched Telephone Network.

  • A network of fixed-line analog telephone system

  • Is now entirely digital

  • Includes not only fixed telephones but also mobile phones.

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What is PSTN?

  • Two types of PSTN:

  • POTS(Plain Old Telephone Service):analog acoustic signal transformed to (similar) analog electrical signal. (ANALOG Telephony)

  • ISDN(Integrated Services Digital Network): transforming analog acoustic or electric signal to digital values.(DIGITAL Telephony)

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Ways Of Using VoIP

  • PC to PC

  • PC to Phone

  • Phone to PC

  • Phone to Phone

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Scenario 1: PC to PC

  • Need a PC with sound card

  • IP Telephony software(softphone): Skype, Gtalk, VoIP Stunt, ...

  • Video optional

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Scenario 2: PC to Phone

Need a gateway that connects IP network to phone network

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Scenario 3: Phone to Phone

  • Need more gateways that connect IP network to phone

  • networks

  • The IP network could be dedicated intra-net or the

  • Internet.

  • The phone networks could be intra-company PBXs or

  • the carrier switches

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Illustration of Gateway

AT-RG613TX Gateway, 3 x 10/100TX LAN, 2 x FXS, 1 x 100TX WAN port

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Which Protocols are Required for VoIP?

  • UDP (User Datagram Protocol)

  • RTP (Real-Time Transport Protocol)

  • SIP( Session Initiation Protocol)

  • H323

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UDP Protocol

  • Available in transport layer

  • Enable the transmission of information between the correct processes (or applications) on host computers.

  • UDP protocol is commonly used in transport layer as an alternative to TCP protocol.

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UDP Protocol


  • Connectionless protocol

  • Unreliable

  • No sequence numbers

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UDP Protocol

Source port:

Identifies the higher layer process which originated the data.

Destination port :

Identifies with higher layer process to which data is being



The length in octets of the UDP data and payload (minimum 8).

Checksum :

Optional field supporting error detection.

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RTP Protocol

  • provides end-to-end delivery services for data with real-time characteristics (audio and video)

  • includes payload type identification, sequence numbering, and timestamping

  • supports mixers and translators

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RTP Protocol

  • translator: coding transformation

  • mixer: mixing several audio streams into a single audio stream

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SIP Protocol

  • SIP is a application layer control simple signalling protocol for VoIP implementations

  • SIP: not only for VoIP, but in general for multimedia communication

    eg: audio / video conferencing, server-based orp2p

  • provides the market with fast operation, flexibility, scalability and multiservice support.

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SIP Protocol

  • provides its own reliability mechanism

  • creates, modifies and terminates sessions which are internet multimedia conferences, Internet telephone calls and multimedia distribution with one or more participants.

  • well-known port number: 5060

  • support for instant messaging

  • format similar to HTTP

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SIP Protocol

SIP works as follows;

  • Callers and callees are identified by SIP addresses

  • a caller first locates the appropriate server and then sends a SIP request

  • a SIP request may be redirected or may trigger a chain of new SIP requests by proxies

  • Users can register their location(s) with SIP servers

  • SIP messages can be transmitted either over TCP or UDP

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SIP Protocol

  • Request Messages:

    The format of the Request packet

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SIP Protocol

  • Methods Command:

    - Invite: Initiate Call

    - Ack: Confirm Final Response

    -Bye: Terminate and Transfer Call

    - Cancel: Cancel Searches and ‘Ringing’

    -Options: Features Support by Other Side

    - Register:Register with Location Service

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SIP Protocol

  • Response Message:

    The format of the Response message

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H323 Protocol

  • H323 Prtocol is a ITU-T standard (International Telecommunications Union)

  • framework for multimedia communication

  • allow multimedia transmission through an unreliable packet-based network

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H323 Protocol

  • H323 includes

    – Call signaling H.225

    – Media control H.245

    – Audio coding G.711, G.722, G.723, G.728, G.729 (G.711 is most used, G.729 is most quality enhanced)

    – Video coding H.261, H263

    – Data sharing T.120

    – Media transport RTP, RTCP

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H323 Architecture

  • - H323 Terminal

  • Gateway

  • Gatekeeper

  • Multipoint Control Units (MCU)

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VoIP Challenges

  • Packet loss

  • Latency

  • Jitter

  • Echo

  • Reliability

  • Firewalls

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VoIP Challenges

  • VoIP implementations face problems dealing with latency ,echoand jitter

  • Echo: waving of voice

  • Latency: Changing in delivery time between voice packets

  • Jitter: Changing in delivery order of voice packets

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VoIP Challenges

Connection Problems:

  • problems behind NAT between peers.

  • Echo and jitter occurs because of packet loss.

  • Internet stability problems can cause reliability problems and this discourages voip usage.

  • routing VoIP traffic through firewallsblocks voice packets transmission.

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Advantages of VoIP

  • What are the esssential factors that encourages people to use VoIP?

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Advantages of VoIP

  • Cost of equipment and deployement

  • Low price in leased-line(home phone)

  • Portability

  • Flexibility

  • Versatility

  • Interconnectivity

  • Time to market

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VoIP Producers

  • ITSP: Internet Telecommunication Service Provider which provides VoIP softwares

  • Most popular VoIP software and also the producers are MSN, SKYPE…

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Most popular producers in Turkey are

  • Superonline

  • Borusan Telekom

  • Koçnet

  • Sabancı Telekom

  • Turk Telekom

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VoIP Prices

  • Generally,

    Producers get approximately $ 2-3 membership fee monthly .

  • From Soft to Soft is free

  • From Soft to PSDN is cheaper than 80%

  • eg: Calling to USA with Turk Telekom is 0.12 YTL, however; Calling with VoIP Stunt is 0.3 YTL

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VoIP usage area in Turkey and Legal Issues

  • Cellphone usage cost in Turkey is very high

  • Until the half of the last year it was a confused concept and alsoTürk Telekom did not reach the necessary judgement.

  • Today, it is legalized to some degree.

  • However, Türk Telekom brought these producers to justice by esteeming this service as illegal.

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VoIP usage area in Turkey and Legal Issues

  • Judgement come out in favour of the producers.

  • However, Türk Telekom can cut the ISS lines and stop the activities of any voip firms without the judgement decision.

  • Since, the Türk Telekom has voice monopoly, domination on VoIP firms are increased legally or illegaly.

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In Conlusion,

  • We can criticise Türk Telekom because of these immoral attitudes.

  • We can criticise the government because of the latency of these legal arrangements.

  • We can criticise VoIP firms because of the nonconstructed infrastructure

  • However, it is the unchangable fact that VoIP revolution will dominate the all telecommunication world several ten years more…

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  • 1) http://en.wikipedia.org/wiki/Voip

  • 2) http://www.erlang.com/protocols.html

  • 3) http://www.pusulanet.com.tr/voipurun.htm

  • 4) http://www.voip.gen.tr/

  • 5) http://siptutorial.blogspot.com/

  • 6) http://www.linecube.com/rates/compare/

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  • Q1) Is it possible to use voip solutions in wifi enabled cellphones?

  • A1) Yes , it is possible. In many cellphone operating systems there are many softphone applications which enables voip usage. For example, SJPhone is an application deployed for Windows mobile 2005 OS

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  • Q2) Is it possible to call the PC from the phone is used in daily life?

  • A2) YES. It is possible by using DID. By the help of the special numbers which are assigned by the daily phone network to voip network, it is possible to provide the transition. However it can not be used in Turkey because it is illegal. This transmission is also called number of portability. (DID Number)

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  • Q3: What do you think about the differences in price between PSDN and VoIP?

  • A3: Voip networks uses IP networks and over these networks voice packages are transferred. Internet can be used in terms of IP network. So, there is no need to additional investment. However, PSTNs performs communication over the TDM and ATM networks which have high cost. So, cost advantage between them is very high and it explains the difference in cost.