Author: Bhumip Khasnabish
Publisher: John Wiley & Sons
ISBN: 0471460885
Category : Technology & Engineering
Languages : en
Pages : 226
Book Description
Im Mittelpunkt der Diskussion stehen hier existierende und neue Technologien für die Vermittlung von Sprachverkehr über das Internet Protocol (IP). - bis vor kurzem stammte der Datenverkehr über Kommunikationsnetzwerke größtenteils aus herkömmlich vermittelten Telefonverbindungen - zukünftig wird dieser Sprachverkehr durch ein riesiges Volumen paketvermittelter Daten (Text- und Audiodateien, Streaming Video usw.) weit in den Schatten gestellt; Telefongespräche werden dann über Internetprotokolle vermittelt - hier erhalten Sie eine detaillierte Einführung in den Aufbau eines effizienten VoIP-Netzwerkes - erläutert Prototyping und Leistungsmessung in solchen Netzwerken - besprochen werden auch Aspekte des Quality-of-Service (QoS)
Implementing Voice over IP
Author: Bhumip Khasnabish
Publisher: John Wiley & Sons
ISBN: 0471460885
Category : Technology & Engineering
Languages : en
Pages : 226
Book Description
Im Mittelpunkt der Diskussion stehen hier existierende und neue Technologien für die Vermittlung von Sprachverkehr über das Internet Protocol (IP). - bis vor kurzem stammte der Datenverkehr über Kommunikationsnetzwerke größtenteils aus herkömmlich vermittelten Telefonverbindungen - zukünftig wird dieser Sprachverkehr durch ein riesiges Volumen paketvermittelter Daten (Text- und Audiodateien, Streaming Video usw.) weit in den Schatten gestellt; Telefongespräche werden dann über Internetprotokolle vermittelt - hier erhalten Sie eine detaillierte Einführung in den Aufbau eines effizienten VoIP-Netzwerkes - erläutert Prototyping und Leistungsmessung in solchen Netzwerken - besprochen werden auch Aspekte des Quality-of-Service (QoS)
Publisher: John Wiley & Sons
ISBN: 0471460885
Category : Technology & Engineering
Languages : en
Pages : 226
Book Description
Im Mittelpunkt der Diskussion stehen hier existierende und neue Technologien für die Vermittlung von Sprachverkehr über das Internet Protocol (IP). - bis vor kurzem stammte der Datenverkehr über Kommunikationsnetzwerke größtenteils aus herkömmlich vermittelten Telefonverbindungen - zukünftig wird dieser Sprachverkehr durch ein riesiges Volumen paketvermittelter Daten (Text- und Audiodateien, Streaming Video usw.) weit in den Schatten gestellt; Telefongespräche werden dann über Internetprotokolle vermittelt - hier erhalten Sie eine detaillierte Einführung in den Aufbau eines effizienten VoIP-Netzwerkes - erläutert Prototyping und Leistungsmessung in solchen Netzwerken - besprochen werden auch Aspekte des Quality-of-Service (QoS)
Packet Guide to Voice Over IP
Author: Bruce Hartpence
Publisher: "O'Reilly Media, Inc."
ISBN: 1449339670
Category : Computers
Languages : en
Pages : 243
Book Description
"A system administrator's guide to VoIP technologies"--Cover.
Publisher: "O'Reilly Media, Inc."
ISBN: 1449339670
Category : Computers
Languages : en
Pages : 243
Book Description
"A system administrator's guide to VoIP technologies"--Cover.
Switching to VoIP
Author: Theodore Wallingford
Publisher: "O'Reilly Media, Inc."
ISBN: 0596517297
Category : Computers
Languages : en
Pages : 504
Book Description
More and more businesses today have their receive phone service through Internet instead of local phone company lines. Many businesses are also using their internal local and wide-area network infrastructure to replace legacy enterprise telephone networks. This migration to a single network carrying voice and data is called convergence, and it's revolutionizing the world of telecommunications by slashing costs and empowering users. The technology of families driving this convergence is called VoIP, or Voice over IP. VoIP has advanced Internet-based telephony to a viable solution, piquing the interest of companies small and large. The primary reason for migrating to VoIP is cost, as it equalizes the costs of long distance calls, local calls, and e-mails to fractions of a penny per use. But the real enterprise turn-on is how VoIP empowersbusinesses to mold and customize telecom and datacom solutions using a single, cohesive networking platform. These business drivers are so compelling that legacy telephony is going the way of the dinosaur, yielding to Voice over IP as the dominant enterprise communications paradigm. Developed from real-world experience by a senior developer, O'Reilly's Switching to VoIP provides solutions for the most common VoIP migration challenges. So if you're a network professional who is migrating from a traditional telephony system to a modern, feature-rich network, this book is a must-have. You'lldiscover the strengths and weaknesses of circuit-switched and packet-switched networks, how VoIP systems impact network infrastructure, as well as solutions for common challenges involved with IP voice migrations. Among the challenges discussed and projects presented: building a softPBX configuring IP phones ensuring quality of service scalability standards-compliance topological considerations coordinating a complete system ?switchover? migrating applications like voicemail and directoryservices retro-interfacing to traditional telephony supporting mobile users security and survivability dealing with the challenges of NAT To help you grasp the core principles at work, Switching to VoIP uses a combination of strategy and hands-on how-to that introduce VoIP routers and media gateways, various makes of IP telephone equipment, legacy analog phones, IPTables and Linux firewalls, and the Asterisk open source PBX software by Digium.You'll learn how to build an IP-based or legacy-compatible phone system and voicemail system complete with e-mail integration while becoming familiar with VoIP protocols and devices. Switching to VoIP remains vendor-neutral and advocates standards, not brands. Some of the standards explored include: SIP H.323, SCCP, and IAX Voice codecs 802.3af Type of Service, IP precedence, DiffServ, and RSVP 802.1a/b/g WLAN If VoIP has your attention, like so many others, then Switching to VoIP will help you build your own system, install it, and begin making calls. It's the only thing left between you and a modern telecom network.
Publisher: "O'Reilly Media, Inc."
ISBN: 0596517297
Category : Computers
Languages : en
Pages : 504
Book Description
More and more businesses today have their receive phone service through Internet instead of local phone company lines. Many businesses are also using their internal local and wide-area network infrastructure to replace legacy enterprise telephone networks. This migration to a single network carrying voice and data is called convergence, and it's revolutionizing the world of telecommunications by slashing costs and empowering users. The technology of families driving this convergence is called VoIP, or Voice over IP. VoIP has advanced Internet-based telephony to a viable solution, piquing the interest of companies small and large. The primary reason for migrating to VoIP is cost, as it equalizes the costs of long distance calls, local calls, and e-mails to fractions of a penny per use. But the real enterprise turn-on is how VoIP empowersbusinesses to mold and customize telecom and datacom solutions using a single, cohesive networking platform. These business drivers are so compelling that legacy telephony is going the way of the dinosaur, yielding to Voice over IP as the dominant enterprise communications paradigm. Developed from real-world experience by a senior developer, O'Reilly's Switching to VoIP provides solutions for the most common VoIP migration challenges. So if you're a network professional who is migrating from a traditional telephony system to a modern, feature-rich network, this book is a must-have. You'lldiscover the strengths and weaknesses of circuit-switched and packet-switched networks, how VoIP systems impact network infrastructure, as well as solutions for common challenges involved with IP voice migrations. Among the challenges discussed and projects presented: building a softPBX configuring IP phones ensuring quality of service scalability standards-compliance topological considerations coordinating a complete system ?switchover? migrating applications like voicemail and directoryservices retro-interfacing to traditional telephony supporting mobile users security and survivability dealing with the challenges of NAT To help you grasp the core principles at work, Switching to VoIP uses a combination of strategy and hands-on how-to that introduce VoIP routers and media gateways, various makes of IP telephone equipment, legacy analog phones, IPTables and Linux firewalls, and the Asterisk open source PBX software by Digium.You'll learn how to build an IP-based or legacy-compatible phone system and voicemail system complete with e-mail integration while becoming familiar with VoIP protocols and devices. Switching to VoIP remains vendor-neutral and advocates standards, not brands. Some of the standards explored include: SIP H.323, SCCP, and IAX Voice codecs 802.3af Type of Service, IP precedence, DiffServ, and RSVP 802.1a/b/g WLAN If VoIP has your attention, like so many others, then Switching to VoIP will help you build your own system, install it, and begin making calls. It's the only thing left between you and a modern telecom network.
Deploying Cisco Voice Over IP Solutions
Author: Jonathan Davidson
Publisher: Cisco Press
ISBN: 9781587050305
Category : Computers
Languages : en
Pages : 616
Book Description
Written by Cisco "RM" CCIEs "TM, " Technical Marketing Engineers, and Systems Engineers who have real-life experience with Cisco "RM" VoIP networks, this guide includes coverage of Virtual Private Networks (VPNs), admission control, security, fax and modem traffic, and unified messaging. Learn from real-world scenarios.
Publisher: Cisco Press
ISBN: 9781587050305
Category : Computers
Languages : en
Pages : 616
Book Description
Written by Cisco "RM" CCIEs "TM, " Technical Marketing Engineers, and Systems Engineers who have real-life experience with Cisco "RM" VoIP networks, this guide includes coverage of Virtual Private Networks (VPNs), admission control, security, fax and modem traffic, and unified messaging. Learn from real-world scenarios.
CVOICE 8.0
Author: Andrew Froehlich
Publisher: John Wiley & Sons
ISBN: 1118181417
Category : Computers
Languages : en
Pages : 626
Book Description
VoIP and convergence are hot topics, and the CVOICE 8.0 exam targets candidates looking to pass Exam 642-437 and pursue their CCNP Voice certification. Companies continue to add VoIP service at a record pace, and network administrators are ramping up their skills. This new member of the Sybex Study Guide series covers everything you’ll need to know to pass the certification exam. VoIP (Voice over IP) is rapidly becoming a preferred solution for companies, and Cisco has responded to the need with a new certification to assure proficiency in VoIP technology Prepares IT professionals for the CVOICE 8.0 exam and includes a CD with the Sybex Test Engine, flashcards, and the Glossary in PDF format. Covers gateway components, dial plans, basic operation and components of VoIP, how to implement a gateway, the function and interoperation of gatekeepers, how to implement an IP-to-IP gateway, and more Administrators of Cisco VoIP networks will find all the essential tools for CVOICE exam success in CVOICE 8.0: Implementing Cisco Unified Communications Voice over IP and QoS v8.0 Study Guide.
Publisher: John Wiley & Sons
ISBN: 1118181417
Category : Computers
Languages : en
Pages : 626
Book Description
VoIP and convergence are hot topics, and the CVOICE 8.0 exam targets candidates looking to pass Exam 642-437 and pursue their CCNP Voice certification. Companies continue to add VoIP service at a record pace, and network administrators are ramping up their skills. This new member of the Sybex Study Guide series covers everything you’ll need to know to pass the certification exam. VoIP (Voice over IP) is rapidly becoming a preferred solution for companies, and Cisco has responded to the need with a new certification to assure proficiency in VoIP technology Prepares IT professionals for the CVOICE 8.0 exam and includes a CD with the Sybex Test Engine, flashcards, and the Glossary in PDF format. Covers gateway components, dial plans, basic operation and components of VoIP, how to implement a gateway, the function and interoperation of gatekeepers, how to implement an IP-to-IP gateway, and more Administrators of Cisco VoIP networks will find all the essential tools for CVOICE exam success in CVOICE 8.0: Implementing Cisco Unified Communications Voice over IP and QoS v8.0 Study Guide.
Practical VoIP Using VOCAL
Author: Luan Dang
Publisher: "O'Reilly Media, Inc."
ISBN: 9780596000783
Category : Computers
Languages : en
Pages : 532
Book Description
This guide shows programmers and administrators how to implement, program and administer VOIP systems using open source tools instead of more expensive options.
Publisher: "O'Reilly Media, Inc."
ISBN: 9780596000783
Category : Computers
Languages : en
Pages : 532
Book Description
This guide shows programmers and administrators how to implement, program and administer VOIP systems using open source tools instead of more expensive options.
Implementing Cisco Unified Communications Voice over IP and QoS (Cvoice) Foundation Learning Guide
Author: Kevin Wallace
Publisher: Cisco Press
ISBN: 0132103400
Category : Computers
Languages : en
Pages : 732
Book Description
Implementing Cisco Unified Communications Voice over IP and QoS (CVOICE) Foundation Learning Guide Foundation Learning for the CCNP® Voice (CVOICE) 642-437 Exam Kevin Wallace, CCIE® No. 7945 Implementing Cisco Unified Communications Voice over IP and QoS (CVOICE) Foundation Learning Guide is a Cisco®-authorized, self-paced learning tool for CCNP Voice foundation learning. Developed in conjunction with the Cisco CCNP Voice certification team, it covers all aspects of planning, designing, and deploying Cisco VoIP networks and integrating gateways, gatekeepers, and QoS into them. Updated throughout for the new CCNP Voice (CVOICE) Version 8.0 exam (642-437), this guide teaches you how to implement and operate gateways, gatekeepers, Cisco Unified Border Element, Cisco Unified Communications Manager Express, and QoS in a voice network architecture. Coverage includes voice gateways, characteristics of VoIP call legs, dial plans and their implementation, basic implementation of IP phones in Cisco Unified Communications Manager Express environment, and essential information about gatekeepers and Cisco Unified Border Element. The book also provides information on voice-related QoS mechanisms that are required in Cisco Unified Communications networks. Fourteen video lab demonstrations on the accompanying CD-ROM walk you step by step through configuring DHCP servers, CUCME autoregistration, ISDN PRI circuits, PSTN dial plans, DID, H.323 and MGCP gateways, VoIP dial peering, gatekeepers, COR, AutoQoS VoIP, and much more. Whether you are preparing for CCNP Voice certification or simply want to gain a better understanding of VoIP and QoS, you will benefit from the foundation information presented in this book. - Voice gateways, including operational modes, functions, related call leg types, and routing techniques - Gateway connections to traditional voice circuits via analog and digital interfaces - Basic VoIP configuration, including A/D conversion, encoding, packetization, gateway protocols, dial peers, and transmission of DTMF, fax, and modem tones - Supporting Cisco IP Phones with Cisco Unified Communications Manager Express - Dial plans, including digit manipulation, path selection, calling privileges, and more - Gatekeepers, Cisco Unified Border Elements, and call admission control (CAC) configuration - QoS issues and mechanisms - Unique DiffServ QoS characteristics and mechanisms - Cisco AutoQoS configuration and operation Companion CD-ROM The CD-ROM that accompanies this book contains 14 video lab demonstrations running approximately 90 minutes. This book is in the Foundation Learning Guide Series. These guides are developed together with Cisco® as the only authorized, self-paced learning tools that help networking professionals build their understanding of networking concepts and prepare for Cisco certification exams.
Publisher: Cisco Press
ISBN: 0132103400
Category : Computers
Languages : en
Pages : 732
Book Description
Implementing Cisco Unified Communications Voice over IP and QoS (CVOICE) Foundation Learning Guide Foundation Learning for the CCNP® Voice (CVOICE) 642-437 Exam Kevin Wallace, CCIE® No. 7945 Implementing Cisco Unified Communications Voice over IP and QoS (CVOICE) Foundation Learning Guide is a Cisco®-authorized, self-paced learning tool for CCNP Voice foundation learning. Developed in conjunction with the Cisco CCNP Voice certification team, it covers all aspects of planning, designing, and deploying Cisco VoIP networks and integrating gateways, gatekeepers, and QoS into them. Updated throughout for the new CCNP Voice (CVOICE) Version 8.0 exam (642-437), this guide teaches you how to implement and operate gateways, gatekeepers, Cisco Unified Border Element, Cisco Unified Communications Manager Express, and QoS in a voice network architecture. Coverage includes voice gateways, characteristics of VoIP call legs, dial plans and their implementation, basic implementation of IP phones in Cisco Unified Communications Manager Express environment, and essential information about gatekeepers and Cisco Unified Border Element. The book also provides information on voice-related QoS mechanisms that are required in Cisco Unified Communications networks. Fourteen video lab demonstrations on the accompanying CD-ROM walk you step by step through configuring DHCP servers, CUCME autoregistration, ISDN PRI circuits, PSTN dial plans, DID, H.323 and MGCP gateways, VoIP dial peering, gatekeepers, COR, AutoQoS VoIP, and much more. Whether you are preparing for CCNP Voice certification or simply want to gain a better understanding of VoIP and QoS, you will benefit from the foundation information presented in this book. - Voice gateways, including operational modes, functions, related call leg types, and routing techniques - Gateway connections to traditional voice circuits via analog and digital interfaces - Basic VoIP configuration, including A/D conversion, encoding, packetization, gateway protocols, dial peers, and transmission of DTMF, fax, and modem tones - Supporting Cisco IP Phones with Cisco Unified Communications Manager Express - Dial plans, including digit manipulation, path selection, calling privileges, and more - Gatekeepers, Cisco Unified Border Elements, and call admission control (CAC) configuration - QoS issues and mechanisms - Unique DiffServ QoS characteristics and mechanisms - Cisco AutoQoS configuration and operation Companion CD-ROM The CD-ROM that accompanies this book contains 14 video lab demonstrations running approximately 90 minutes. This book is in the Foundation Learning Guide Series. These guides are developed together with Cisco® as the only authorized, self-paced learning tools that help networking professionals build their understanding of networking concepts and prepare for Cisco certification exams.
Understanding Voice Over IP Security
Author: Alan B. Johnston
Publisher: Artech House Publishers
ISBN:
Category : Computers
Languages : en
Pages : 296
Book Description
VoIP (voice over IP) networks are currently being deployed by enterprises, governments, and service providers around the globe. Today, the hottest topic with engineers in the field is how to secure these networks. The book teaches practitioners how to design a highly secure VoIP network, explains Internet security basics, such as attack types and methods, and more.
Publisher: Artech House Publishers
ISBN:
Category : Computers
Languages : en
Pages : 296
Book Description
VoIP (voice over IP) networks are currently being deployed by enterprises, governments, and service providers around the globe. Today, the hottest topic with engineers in the field is how to secure these networks. The book teaches practitioners how to design a highly secure VoIP network, explains Internet security basics, such as attack types and methods, and more.
Cisco Voice Over Frame Relay, ATM, and IP
Author: Steve McQuerry
Publisher: Cisco Press
ISBN: 9781578702275
Category : Computers
Languages : en
Pages : 562
Book Description
Authorized self-study guide for voice over data network foundation learning This book will help you to: Configure Voice over Frame Relay, ATM, or IP using Cisco IOS(r) software Analyze existing voice hardware/software, and select the Cisco multiservice access devices that best serve your needs Analyze existing branch and regional office voice networks and services, and choose the optimum transmission method for voice traffic: Frame Relay, ATM, or IP Learn the fundamentals of VoFR, VoATM, and VoIP standards, protocols, and the Cisco hardware that supports these services Learn the basics of the Architecture for Voice, Video, and Integrated Data (AVVID) including CallManager, Cisco IP Phones, and related voice gateway equipment Design, configure, integrate, and optimize an enterprise network in remote branch and regional offices by using integrated access technology that combines voice and data transmission over Frame Relay, ATM, and IP connections, access devices, and CIPT client hardware Learn the fundamentals of PBXs, and apply the principles and concepts to develop a process for integrating Cisco equipment with PBXs and for replacing PBXs Cisco Voice over Frame Relay, ATM, and IPteaches you the Cisco solutions for voice technology (VoIP, VoFR, VoATM). This complete solutions guide helps you analyze existing voice hardware and software and select the Cisco multiservice access devices that best serve the needs of your network environment. In addition to learning how to design, configure, integrate, and optimize networks in remote branch and regional offices, this book also provides you with a fundamental understanding of PBXs, enabling you to develop a process for integrating Cisco equipment with or replacing PBXs. Cisco Voice over Frame Relay, ATM, and IPprepares you for voice and data integration by teaching you how to install and configure Cisco voice and data network routers; how to configure Cisco voice-enabled equipment for Voice over Frame Relay, ATM, and IP; how to configure voice ports, dial peers, and special commands to enable voice transmission over a data network; and how to perform voice traffic analysis to determine how to improve the quality of service (QoS) for delay-sensitive voice traffic. This book features actual router output and configuration examples to aid in the discussion of the configuration of these technologies. At the end of each chapter your comprehension is tested by review questions. Cisco Voice over Frame Relay, ATM, and IP has all of the tools you need to vastly improve your understanding of the Cisco solution to voice networking needs. Cisco Voice over Frame Relay, ATM, and IPis part of a recommended self-study program from Cisco Systems(r) that includes simulation and hands-on training from authorized Cisco Learning Partners, and self-study products from Cisco Press. To find out more about instructor-led, e-learning, and hands-on instruction offered by authorized Cisco Learning Partners, please visit www.cisco.com/go/authorizedtraining. This volume is in the Certification Self-Study Series offered by Cisco Press(r). Books in this series provide officially developed self-study solutions to help networking professionals understand technology implementations and prepare for the Cisco Career Certifications examinations.
Publisher: Cisco Press
ISBN: 9781578702275
Category : Computers
Languages : en
Pages : 562
Book Description
Authorized self-study guide for voice over data network foundation learning This book will help you to: Configure Voice over Frame Relay, ATM, or IP using Cisco IOS(r) software Analyze existing voice hardware/software, and select the Cisco multiservice access devices that best serve your needs Analyze existing branch and regional office voice networks and services, and choose the optimum transmission method for voice traffic: Frame Relay, ATM, or IP Learn the fundamentals of VoFR, VoATM, and VoIP standards, protocols, and the Cisco hardware that supports these services Learn the basics of the Architecture for Voice, Video, and Integrated Data (AVVID) including CallManager, Cisco IP Phones, and related voice gateway equipment Design, configure, integrate, and optimize an enterprise network in remote branch and regional offices by using integrated access technology that combines voice and data transmission over Frame Relay, ATM, and IP connections, access devices, and CIPT client hardware Learn the fundamentals of PBXs, and apply the principles and concepts to develop a process for integrating Cisco equipment with PBXs and for replacing PBXs Cisco Voice over Frame Relay, ATM, and IPteaches you the Cisco solutions for voice technology (VoIP, VoFR, VoATM). This complete solutions guide helps you analyze existing voice hardware and software and select the Cisco multiservice access devices that best serve the needs of your network environment. In addition to learning how to design, configure, integrate, and optimize networks in remote branch and regional offices, this book also provides you with a fundamental understanding of PBXs, enabling you to develop a process for integrating Cisco equipment with or replacing PBXs. Cisco Voice over Frame Relay, ATM, and IPprepares you for voice and data integration by teaching you how to install and configure Cisco voice and data network routers; how to configure Cisco voice-enabled equipment for Voice over Frame Relay, ATM, and IP; how to configure voice ports, dial peers, and special commands to enable voice transmission over a data network; and how to perform voice traffic analysis to determine how to improve the quality of service (QoS) for delay-sensitive voice traffic. This book features actual router output and configuration examples to aid in the discussion of the configuration of these technologies. At the end of each chapter your comprehension is tested by review questions. Cisco Voice over Frame Relay, ATM, and IP has all of the tools you need to vastly improve your understanding of the Cisco solution to voice networking needs. Cisco Voice over Frame Relay, ATM, and IPis part of a recommended self-study program from Cisco Systems(r) that includes simulation and hands-on training from authorized Cisco Learning Partners, and self-study products from Cisco Press. To find out more about instructor-led, e-learning, and hands-on instruction offered by authorized Cisco Learning Partners, please visit www.cisco.com/go/authorizedtraining. This volume is in the Certification Self-Study Series offered by Cisco Press(r). Books in this series provide officially developed self-study solutions to help networking professionals understand technology implementations and prepare for the Cisco Career Certifications examinations.
VoIP: Voice Over Internet Protocol Architecture and Features
Author: Abdul Sattar Mohmand
Publisher: Lulu.com
ISBN: 1435731654
Category : Technology & Engineering
Languages : en
Pages : 255
Book Description
VoIP or Voice Over Internet Protocol is an emerging telecommunication technology that make use of IP network to carry voice just like PSTN (Public Switched Telephone Network) or traditional phones. There are several companies offering low cost and more flexible phones and packages of VoIP systems. Future belongs to VoIP because of its low cost and flexibility and more control.This innovative technology will change the life of people because the dream of video phone is just behind its bars. This book covers the basic architecture, usefulness, challenges and features of the VoIP Phones systems.
Publisher: Lulu.com
ISBN: 1435731654
Category : Technology & Engineering
Languages : en
Pages : 255
Book Description
VoIP or Voice Over Internet Protocol is an emerging telecommunication technology that make use of IP network to carry voice just like PSTN (Public Switched Telephone Network) or traditional phones. There are several companies offering low cost and more flexible phones and packages of VoIP systems. Future belongs to VoIP because of its low cost and flexibility and more control.This innovative technology will change the life of people because the dream of video phone is just behind its bars. This book covers the basic architecture, usefulness, challenges and features of the VoIP Phones systems.