The VoIP components

VoIP

VoIP is an acronym for Voice over Internet Protocol. It is used to transfer voice over wireless network. Traditional telephone services are replaced by this VoIP technology. Now-a-days the popularity and applications of VoIP is growing continuously. It is also given as a family of technology which allows IP networks to be used for voice applications like voice instant messaging, teleconferencing and telephony (Frank Ohrtman, 2004). VoIP is also referred as IP telephony, Internet Telephony and broadband phone. To have the Voice conversation over internet or by any other IP-based network VoIP network technology is used. VoIP is one of the new emerging technologies for voice communication. Many of them are attracted to use VoIP because of its flexibility and low cost. For carrying voice signals over IP network the protocols used are commonly referred as VoIP protocols (Collins, 2005). VoIP technology is being implementing by many industries that offer cheap telephonic access. It is the core technology used in several platforms for voice chat communication. VoIP is implemented by many IP network environments like Local Area Network (LAN). Applications of VoIP are much sensitive due to its problems in network bandwidth. VoIP has become popular because it is cost advantage to the customer when compared with traditional telephone technologies (VoIP, 2009). An efficient quality of service is provided by the VoIP to have a communication for long distance calls. There are different ways to have a call over VoIP by IP phones and computer-to-computer. There are many advantages in using VoIP like low price, flexibility in using and the low tax. Traditional technology Public switched Network (PSTN) doesn't provide these advantages, due to this PSTN is replaced by VoIP technology (Endler and Mark Collier, 2007). Hence from the above context it can be understood that VoIP is an effective technology for the communication through voice over internet. It provides many things which cannot be done with the traditional telephonic services. It overcomes the problems which occur in PSTN technology. It provides services like a good quality of service, flexibility in its usage, low cost and easy in its implementation. As technology usage is increasing the VoIP technology is growing faster.

Why VoIP

As technology is growing rapidly the requirement for the user also changes which leads to increase in usage of VoIP. There are number of reasons for the usage of VoIP which attract user. With usage of VoIP service the traditional telephone lines can be eliminated, the call charges for long distances can be reduced; portability is possible in it (VoIP, 2009). For doing a business, communication is the integral part so VoIP is implemented by many of the enterprises for its efficient communication. Some of the reasons why VoIP is implemented by most of the companies are (Marion Tracey, 2009)

• It is very cost effective as it eliminated call charges for long distances
• By using VoIP real time video and audio conferencing and face to face meetings can be organized.
• More flexible to use which enhances the productivity of the organization
• A Quality of Services (QoS) without causing disturbances in long calls

VoIP is used in many business organizations as it provides many facilities to satisfy the user requirements. By implementation of VoIP the day-to-day operations can be simplified. By using it provides the benefits to the organizations like quality in telephone lines, most of the failures are avoided and their occurrences are known before, privacy can be maintained within the organization and helps in future upgrades and purchases (Client Smith and Daniel Collins, 2002). Basically the question why VoIP can be given as worrying about the carrying voice and aim to complete in voice promote. VoIP provides a good security in the organization and allows having a telephone lines in an IP network (cisco, 2009). VoIP is used many business organizations as it is less expensive, very convenient to use, increases the productivity of employs and saves the money of the organization. VoIp allows having IP protocol networks. Hence from the above context it can be understood that VoIP is used in many organizations as it provides a good quality of service, clarity in voice and low cost. Managing of organization can be made efficiently with the usage of VoIP. VoIP uses fewer infrastructures for deploying it in an organization. It provides fast communication in an organization by using VoIP rather than telephone services.

VoIP components and its requirements

There are various components of VoIP, which helps in working of VoIP smoothly. The principal components in order to enable VoIP are as follows: -

1. Front End Server VoIP components
2. Connection to Internet and IP VPN
3. Terminals
4. Ethernet LAN

Front End Server VoIP Components

The principle VoIP components located on Front End Servers are as follows:

• Inbound Routing components.
• Translation Service.
• Outbound Routing components (Thomas Porter, 2006).

Inbound Routing components

The Inbound Routing Components handles incoming calls largely according to preference that are specified by users on their enterprise voice clients (Samuel H. Fuller and Alan Gatherer, 2005). The users specify whether unanswered calls are to be forwarded or simply logged for notification.

Outbound Routing components

The outbound Routing Components routes calls to PBX or PSTN destinations (Anthony Piltzecker, Rand Morimoto and Ron Barrett, 2008). It applies call authorization rules to callers and determines the optimal media gateway for routing each call.

Translation Service

According to the normalization rule that is defined by the administrator the Translation Service translates a dialed number into the E.164 format or to another format (Daniel Gouadec, 2007).

Connection to Internet and IP VPN

An IP VPN (Internet Protocol Virtual Private Network is a computer network that is implemented in an additional software layer on top of an existing larger network for the purpose of creating a private scope of computer communication or providing a secure extension of a private network into an insecure network such as the internet (Dennis Fowler, 1999). Data sent across the public Internet is generally not protected from prying eyes, but it can make Internet communications secure and extend private network with a VPN connection. A VPN connection uses encryption and tunneling to transfer data securely on the Internet to a remote access VPN server on the workplace network. Using a VPN saves money by using the public Internet instead of making long distance phone calls to connect securely with your private network. To make a VPN connection, one must be already connected to the Internet (Joseph A. Demkin, 2001). One can make a VPN connection by first dialing an ISP (Internet Service Provider) or by using an existing connection to the Internet.

Terminals - Terminals are specialized pieces of hardware that connects computers over serial lines as they have only enough computational power to display, send, and receive text. It is impossible to run any programs on them (Syed A. Ahson and Mohammad Iiyas, 2008). It is the computer to which you connect them that has all the power to run text editors, compilers, email, games, and so forth.

Ethernet LAN -One benefit of Ethernet extenders is they can eliminate the need for installing expensive Switches and CAT5 cable. Ethernet extenders can use fiber-optic or copper twisted-pair cables to transparently send packets at full-line rate to a peered LAN up to five miles away. While networks typically deploy Ethernet extenders within a limited geographical area, this area need not be limited to one building (Ted Wallingford, 2005). Ethernet extenders can create effective bridged-Ethernet connections across streets or over a college or enterprise campus and between Ethernet LANs up to five miles apart.

Network design skills required for creating and deploying VoIP in an organization

Every organization needs better quality and service for their voice communication. In order to provide better quality and service to the organization for voice communication VoIP is to be deployed. VoIP solves all the issues of the organization by providing better quality service. Deploying VoIP is too cheaper and it also provides service at cheaper costs rather than traditional telephony (Hermann Kaindl and Mobilkom Austria, 2004). The most major problem in VoIP is the security issue. VoIP is not secured at all as any hacker can intrupt in the same network and there would be no privacy in the organization (Bragg, Mark Phodes-Ousley and Keith Strassberg, 2004). Something that is most valuable or something that others want to disrupt should be kept more secured so that it does not go manipulated. In VOIP deployment, it has got something of value, phone service and information as phone service is a business critical application. When concerned about VOIP security, it helps to began with what you are trying to accomplish (Robert Stephen, Barry J. Stiefel, Simon Desmeules and Stephen Watkins, 2005):

1. Avoid disruption to your VOIP Phone service.
2. Prevent unauthorized calls.
3. Protect sensitivity phone conversation and records.

If a hacker can get into the organization VOIP server, there are several areas where toll fraud can occur and they are:

1. Without proper billing calls can be made by account fraud. Relational database system stores all the CDRs (Call Detail Recorder) of a VOIP system. Access to the CDR could allow a hacker to change the billing information to gain the free calls.
2. Unauthorized access to VOIP server configuration lets a hacker enable this feature for your day to day operation.
3. An incorrectly configured call routing plan could allow the IP phone in your lobby to make international calls. Access by a hacker can allow calls from certain location to any other location (Ted Wallingford, 2006).

From the above content it is clear that, in VOIP system, security is the most vital to be considered in an organization, as not to disrupt the most valuable things. In VOIP system we have to find out the way the hackers interrupt in the networking and then find a solution for this interruption of hackers. This can be avoided by avoiding disruption to VOIP Phone service, prevent unauthorized calls and by protecting sensitivity phone conversation and records.

Impacts of VoIP set up and deployment

Many organizations are deploying VoIP in order to benefit from it. Deploying VoIP in organization can increase the work productivity and competitive advantage. VoIP is the most used technology by organizations because it is a cost saving technology for communication. Earlier adopters used for deploying VoIP can be predictable in network performance by any hacker. To overcome this situation VoIP can be deployed with required modifications in the network. Installing VoIP in organization can maintain robust networks and applications effectively (Ashton and Metzeler, 2008). While deploying VoIP, network traffic, quality of service and performance should be maintained carefully. Planning and management should be carried out effectively in order to deploy VoIP successfully. Usually network administrators play a key role in managing and deploying a network. VoIP deployment can show large impact on telecommunication organizations. Organizations use PBXs and phones to deploy VoIP (Aptela, 2008). Deploying VoIP in mobile industry can show impact on productivity and mobility. Cost is the major aspect in deploying VoIP in the organization. Planning and deploying in VoIP can be done in a step by step process. While deploying VoIP organization may face many challenges like quality, delay variations, call setup and network readiness. In order to deploy VoIP successfully without any challenge, network should be upgraded with more bandwidths and router installations. Successful deploying of VoIP in mobile applications can show major impact on call quality. It can also decrease delays, packet loss and jitter. Deploying VoIP can show impact on the reliability of the network (Net Scout, 2006). Hence from the above discussion it can be understood that, deploying VoIP in organizations can show huge impact on the performance of that firm. Deploying VoIP can show impact on cost of call, quality of call, productivity and mobility. It can decrease the delays occur in communication and packet loss that can occur due to hackers.

VOIP proposed Architecture for the clients

Voice over Internet Protocol (VoIP) is a way for voice communication over internet using internet protocols. VoIP uses different components for pursuing voice communication over internet. VoIP makes use of digital signal processor for converting analog signals into digital signals with the help of compression and decompression algorithms. As long as components are compatible for conversations VoIP can work effectively. If the components are not compatible then architecture should be modified in order to meet the changing technology (Harold F. Tipton and Micki Krause, 2005). As technology increasing day by day methods for distracting those technologies are also increasing. Architecture should be proposed in such a way that it must be secured from hackers or unauthorized networks. In order to provide secured networks VoIP is adopting new architectures for voice communication. Using SIP and H.323 are the emerging architectures for VoIP. SIP and H.323 are protocols which can help network in better signaling (Jaime Delgado, 2000). This proposed architecture comprises of media gateway controllers, H.323 signaling gateway, media gateway and Ethernet switch (Signalogic, 2008). Brief description of components in the proposed network:

H.323 signaling gateway - H.323 signaling gateways takes the incoming messages from SIP and extracts that messages to find communication parameters (Stefan Karapetkov, 2008). This gateway can be useful for communicating with SIP networks.

Media gateway controller - It is a system which can be capable of controlling the signals coming from media gateways. A Media gateway controller accepts the signals from media gateway and forwards it to network in order to receive voice data. In VoIP architecture media gateway controllers can be called as a soft switch.

Media gateway - Media gateway is a device which acts as a circuit switch that can convert digital signals into required format when communication is in the process (Travis Russell, 2002). It also helps in connecting different networks.

Ethernet switch - Ethernet switch is a device which arranges temporary crossover cable connections with the systems which want to communicate with the destination (Bradley Mitchell, 2009). Ethernet switch divides the network into different segments and supports for communication with other computer.

From the above figure one can understand that, In VoIP audio I/O module receives the voice signals from external environment. These signals will be sent to media gateway. Signals will be digitalized at media gateway. Digitalized signals will be controlled by media gateway controllers. Ether switch will communicate these signals or messages to the SIP and H.323 terminals. These SIP and H.323 terminals may be GSM, MELP or remote terminal. VoIP uses this architecture for communicating voice through secured networks.

Hence from the above discussion it can be understood that, SIP and H.323 are the emerging architectures in VoIP for handling the voice communication. New architectures should be proposed for VoIP in order to meet the changing technologies. VoIP architectures can be updated by using SIP and H.323 protocols so that it can provide better signaling in communication.

Quality of Service

Quality of Service refers to the clarity of your phone call over a network. Something that most people take for granted is the quality of telephone service. We all have gotten used to the quality offered by the telephone industry. However, that quality hasn't quite transferred over to VoIP in most service. Service providers and enterprises all over the world are rapidly deploying Voice over IP (VoIP) networks because of reduced capital and operational expenditure, and easy creation of new services (Josep Sole Pareta, 2004). Voice traffic has estrangement requirements on the quality of service, like strict delay and loss requirements. One way to determine the quality of VoIP service is to measure it from a user perceptive view. Models have been developed to evaluate the perceptive quality of voice (Robert Stephens, Barry J. Stiefel, Simon Desmeules and Stephen Watkins, 2005). Quality of service also must ensure that granting a QoS level to one traffic type or call does not violate the data flow requirements of another traffic type or call. The circuit-switched public switched telephone network (PSTN) offers all applications the highest level of QoS. Asynchronous transfer mode (ATM) offers multiple QoS levels appropriate for different traffic types. Frame relay, Internet Protocol (IP), and Ethernet networks can employ various priority mechanisms to offer differential grade of service levels, but cannot guarantee QoS (Ted Wallingford, 2005). There are many factors that go into the end quality of a phone call, including Latency, Jitter, Packet Loss and an overall combination of network equipment and bandwidth.

The three most common quality issues affecting VoIP are:

Latency: Unlike the data on IP networks that can tolerate delay-sensitivity well VoIP is vastly different. VoIP is latency-sensitivity driven. Latency is the delay between the sending of information from an endpoint and the reception of that information at the far endpoint. A consistent latency will result in a delay in reception and response. Low latency queuing is a simplified subset of strict priority queuing (James F. Ransome and John W. Rittinghouse, 2005). A single traffic follow, usually VoIP is preferred over all other flow, which ends up in a default queue. Whenever a VoIP packet is ready for transmission, it is transmitted before any other queued packet, therefore minimizing delay.

Jitter: Jitter buffers are used to change asynchronous packets arrivals into a synchronous stream by turning variable network delays into constant delays at the destination end system. Delay variation, also called jitter, obstructs the proper reconstruction of voice packets in their original sequential and periodical pattern. It is defined as difference in total end-to-end delay of two consecutive packets in the flow (Philip A. Chou and Mihaela van der Schaar, 2007). Removing the jitter requires collecting packets and storing them long enough to allow the slowest packets to arrive in order to be played in the correct sequence (Anthony T. Velte, 2004). Scheduling a later deadline increases the possibility of playing out more packets and results in lower loss rate, but at the cost of higher buffering delay.

Packer loss: Voice data is send in packets. Packet loss is the measurement of packets successfully transmitted to the total number originally sent (Chin-Wan Chung, 2003). A clean and properly maintained LAN and QoS router on the customer premise paired with a CoS (Class of Service) solution at the providers edge can greatly reduce packet loss.

Impact of different carrier technologies on the effectiveness of a VoIP system

Now-a-days many new technologies are upcoming day by day which helps in the deployment and functioning of VoIP. The success of VoIP leads to many extensive range of networking technologies. Many of the new technologies show its unique feature and shows different challenges for the performance of the VoIP. Wireless, peer-to-peer and the new enterprise Voice over IP are the technologies which show problems raised in deploying VoIP in an emerging network environment (Samrat Ganguly and Sudeep Bhatnagar, 2009). Sometimes delay in packet may occur in their transmission which mainly depend upon codec used in that packet. Several new types of equipments and telecommunication services will help in showing special transmission properties causes voice transmission and speech communication to be deteriorate in a way which is different from traditional networks. In voice communication sometimes echoes may be produced which cause disturbances in the network which can be overcome by using echo canceller and echo suppressor technologies. By using these technologies the echoes in voice communication can be reduced (Sebastian Moller, 2000). With the help of new technologies the efficiency, productivity and cost of VoIP decreases. Skype, vonage and several other voice communications are used for communication through VoIP. Apart from the competition in the technologies the impact of new technologies will show changes in the deployment of VOIP. There are number of other factors that affect the performance of VoIP with its new technology features (Erlinda M. Medella, 2005). Wi-Fi is one of the wireless technologies which are also helpful for the communication of Voice in internet protocol. 3G, WLAN and WiMAX are some of the growing technologies which show its impact on wireless communication. Many organizations are using this VoIP technology for its communication; many other technologies are also being used by them to have efficient communications in case of some failures (Richard Swale, 2001). Hence from the above context it can be understood that VoIP is a technology used by many organization for the communication with the clients and with the branches of the organization. VoIP provides an efficient quality of service, low cost and flexibility in usage. These can be achieved by VoIP in an organization with the help of new emerging technologies. Security in WiMAX is not effective when compared with VoIP. VOIP is comparatively more advantageous than other wireless technologies such as WiFi and WiMAX.

Planned Site Assessment

The following is the assessment plan for the VoIP implementation for the Company.

Initial Phase:

In this phase of VoIP assessment for Leeds Western Company is a research exercise because we need to gather existing documentation and supporting information for your existing data network and voice communications infrastructure, including network inventory, capacity, topology, and architecture (Nortel, 2009).

The Company needs to

• Identify the key people involved in this project from their side like their name, telephone contact number, and email id. This will help us to be in touch with the people and update on latest development regarding VoIP implementation.
• Provide the address where the necessary network assessment kit can be shipped.
• Identify the PCs to be used as endpoints during the assessment. On that PCs we will use Soft IP phone which will be used for VoIP assessment.
• Update with the complete and current set of telephony currently being deployed in the company such as communication system, LAN/WAN equipment, ALN/telephony application.
• Provide other additional network information such as location of users, Links type, speeds, utilization, Routing protocol, Quality of service strategy etc.

Apart from this, we will also be going through the following steps listed (Nortel, 2009):

• We will be obtaining diagrams for the existing LAN/WAN infrastructure of the company.
• We will also be identifying the physical and logical locations of important internetworking equipment; for example routers, switches, and firewalls.
• The following documents will be prepared:
• Document regarding Existing network Names, Addresses, and interconnecting devices.
• Document regarding the types and lengths of physical cables and circuits.
• Also we will be analyzing the infrastructure and identify the problems if there are any.

Once the above are information is provided based on that further assessment will be carried on.

Network Assessment tools:

These tools will be used for the assessment of the current Company network to check how feasible the network for VoIP implementation is.

Network assessment tool will assist to perform the followings (Nortel, 2009):

• Simulate Voice over IP traffic flow
• Assess link utilization
• Observe Routing protocol
• Calculate voice quality
• Identify jitter, one-way-delay, and packet loss
• Generate detailed report

The data and reports generated during the network assessment will assist us in making recommendation on any modification to the company that may be required to insure a successful VoIP implementation.

There are several tools which can be used as Network assessment tool:

• Sniffer Portable
• IxChariot
• IXIA Qcheck
• Net IQ Vivinet Assessor
• Viola Networks Net Ally VoIP

Historical Tools:

Historical tools will be used to with the Company network to know more about current network environment such as traffic patterns, utilizations, and peak bandwidth loads.

Real-time tools:

We will be analyzing the outputs of Company's network environments to determine the types of information the output is providing about the customer network.

Day 1 [Set up Assessment]

• We will be traveling to the main site to verify that the network assessment kit has arrived.
• We will be meeting with the customer and participants to provide an overview of the activities explaining the types of tests to be run on the network, such as quality of service, VoIP, firewall and stress tests (Nortel, 2009).
• We will also be setting up network assessment tools. We will deploy endpoint PCs and collect IP addresses of endpoints.
• We will be running the network assessment tool check to ascertain endpoint operation and those software versions are same.
• We will be running some preliminary tests.

Day 2 [Conduct Assessment]

The following will be carried out on Day 2 (Nortel, 2009):

• Load test will be carried out to verify that all of the network traffic carries out VoIP traffic.
• We will also be determining the number of VoIP channels required and enough bandwidth is available on all links.

We will be performing network assessment whereby we will assesses the ability of the data network to handle voice traffic. The following items will be evaluated:

Quality of Service - This is a feature whereby the packets are marked that they are voice and require priority and therefore will be delivered before other data packets in the case that there is congested traffic on their network.

Delay - Packets can be delayed on a network for a number of reasons - the ear hears 150 milliseconds or more delay.

Packet Loss - Lost voice packets can lead to poor quality calls with gaps in the call sometimes even disconnecting the call. If this is already occurring on their network we will suggest their network to be upgraded to components and/or bandwidth (Nortel, 2009).

Bandwidth - The amount of bandwidth on their network affects how much voice and other data traffic can be carried on the network at the same time. We may recommend Leeds Western Company to upgrade the bandwidth on their local area network and/or wide area network depending upon how much voice will now be carried simultaneously.

Conclusions and Recommendations

Voice over Internet Protocol (VoIP) is a packet switched network introduced for voice communication over internet. VoIP is the most popular technology used by many organizations in order to complete their day to day business operations. VoIP was introduced in order to overcome the problems in the traditional approach. The traditional approach used for voice communication was Public Switched Telephone network (PSTN). In this traditional approach circuit switched networks were used for communicating. In PSTN physical connections will be required for every call in order to provide communication between source and destination. Using physical connection for every call increases the infrastructure in the network, so cost of call will be increased. This problem can be reduced by using VoIP technology. VoIP uses internet protocols instead of circuits to pursue voice communication. VoIP converts analog signals into digital signals and vice versa in order to communicate with destination.

Recommendations

VoIP is a system which has restricted regulations and has security constrains, that can be overcome by following recommendations.

• There should be transparency in regulations. Regulating the foster deployment and also the regulatory decision has to be made in a timely fashion and incorporate flexibility.
• By reusing the existing security infrastructure wisely the security of the system can be improved. Without reinvesting on the infrastructure the existing one can be used for improving the security (David Maynor, 2006). This can be done by using a security policy that will provide the framework, justification and metrics for all security related development.
• H.323 is a standard that is recommended to be used in VoIP, which will make VoIP more stable. This will provide the individual functions which will help in transmitting packet-based multimedia system that can interface with circuit-switched network. By using this standards incorporation of audio/video streaming can be done (Goff Hill, 2007). Conferencing can also be provided by using these standards.

By using these recommendations the VoIP can be improved and can be made to work in more effective manner.

Bibliography

• Anthony Piltzecker, Rand Morimoto and Ron Barrett (2008) How to Cheat at Administering Office Communications Server 2007, Syngress Publishers, pp. 462.
• Anthony T. Velte (2004) Cisco 3rd Edition, McGraw-Hill Professional Publishers, pp. 737.
• Aptela (2008) "Are you VoIP Ready", [Internet] available at URL: <http://www.aptela.com/xres/uploads/resource-center-documents/Aptela_White_Paper_-_Are_You_VoIP_Ready.pdf>, [accessed on 27th October 2009].
• Ashton and Metzeler (2008) "Best practice for planning, deploying and managing enterprise VoIP", [Internet] available at URL: <http://www.ca.com/Files/WhitePapers/ashton-metzler_best-practices_voip_20080327.pdf>, [accessed on 27th October 2009].
• Bradley Mitchell (2009) "Ethernet hub/switch network diagram", [Internet] available at URL: <http://compnetworking.about.com/od/homenetworking/ig/Home-Network-Diagrams/Hub-Switch-Network-Diagram.htm>, [accessed on 27th October 2009].
• Bragg, Mark Phodes-Ousley and Keith Strassberg (2004) Network Security: The complete Reference, Tata McGraw-Hill Publishers, pp. 854.
• Chin-Wan Chung (2003) Web and Communication Technologies and Internet-Related Social Issues, Springer Publishers, pp. 773.
• Cisco (2009) "why VoIP", [Internet] available at URL: <http://www.cisco.com/cisco/web/solutions/small_business/resource_center/articles/connect_employees_and_offices/what_voip_can_do_for_you/index.html>, [accessed on 27th October 2009].
• Client Smith and Daniel Collins (2002) 3G wireless networks, McGraw-Hill Publishers, pp.620.
• Collins (2005) Carrier Grade Voice over IP, Tata McGraw Publishers, pp.523.
• Daniel Gouadec (2007) Translation as a Profession, John Benjamins Publishers, pp. 396.
• David Maynor (2006) Syngress Force Emerging Threat Analysis: From Mischief to Malicious, Syngress Publishers, pp.610.
• Dennis Fowler (1999) Virtual Private Networks, Morgan Kaufmann Publishers, pp. 222.
• Endler and Mark Collier (2007) Hacking exposed VoIP, Tata McGraw-Hill Publishers, pp.539.
• Erlinda M. Medella (2005) Ompetition policy in East Asia, Routledge Publishers, pp. 262.
• Frank Ohrtman (2004) Voice over 802.11, Artech Publishers, pp.258.
• Harold F. Tipton and Micki Krause (2005) Information security management handbook, 5th edition, CRC Press Publishers, pp. 578.
• Goff Hill (2007) The Cable and Telecommunications Professionals' Reference: PSTN, IP and cellular networks, and mathematical techniques, Focal Press Publishers, pp.542.
• Hermann Kaindl and Mobilkom Austria (2004) Network 2004, Margret Schneider Publishers, pp. 464.
• Jaime Delgado (2000) Telecommunications and IT convergence, Springer Publishers, pp. 350.
• James F. Ransome and John W. Rittinghouse (2005) VoIP Security, Digital Press Publishers, pp. 402.
• Joseph A. Demkin (2001) The Architect's Handbook of Professional Practice, John Wiley and Sons Publishers, pp. 987.
• Josep Sole Pareta (2004) Quality of Service in the Emerging Networking Panorama, Springer Publishers, pp. 390.
• Marion Tracey (2009) voIp Voice over IP 100 success secrets, Lulu publications, pp.140.
• Net Scout (2006) "VoIP implementation guide for network performance management", [Internet] available at URL: <http://www.comnews.com/WhitePaper_Library/Voice/pdfs/NetScout_wp_VoIP_Network_Management_Best_Practices.pdf>, [accessed on 27th October 2009].
• Philip A. Chou and Mihaela van der Schaar (2007) Multimedia Over IP and Wireless Networks, Academic Press Publishers, pp. 692.
• Richard Swale (2001) Voice over IP, IET Publishers, pp. 484.
• Robert Stephen, Barry J. Stiefel, Simon Desmeules and Stephen Watkins (2005) Configuring Check Point NGX VPN-1/Firewall-1, Syngress Publishers, pp. 625.
• Samrat Ganguly and Sudeep Bhatnagar (2009) "understand how new network technologies impact VoIP", [Internet] available at URL: <http://as.wiley.com/WileyCDA/WileyTitle/productCd-0470319569.html>, [accessed on 27th October 2009].
• Samuel H. Fuller and Alan Gatherer (2005) RapidIO, John Miley and Sons Publishers, pp. 360.
• Sebastian Moller (2000) Assessment and prediction of speech quality in telecommunications, Springer publishers, pp.244.
• Signalogic (2008) "VoIP", [Internet] available at URL: <ftp://ftp.signalogic.com/data_sheets/Hardware/PC104_VoIP_datasheet.pdf>, [accessed on 29th October 2009].
• Stefan Karapetkov (2008) "Migrating visual communication from H.323 to SIP", [Internet] available at URL: <http://www.polycom.com/global/documents/whitepapers/Migrating%20Visual%20Communications%20from%20H323%20to%20SIP_Polycom.pdf>, [accessed on 27th October 2009].
• Syed A. Ahson and Mohammad Iiyas (2008) VoIP Handbook Applications, Technologies, Reliability and Security, CRC Press Publishers, pp. 454.
• Ted Wallingford (2005) Switching to VoIP, O'Reilly Media Publishers, pp. 477.
• Ted Wallingford (2006) VoIP Hacks, O'Reilly Media Publishers, pp. 306.
• Thomas Porter (2006) Practice VoIP Security, Syngress Publishers, pp. 563.
• Travis Russell (2002) Signaling System #7, 4th edition, McGraw-Hill Publishers, pp. 495.
• VoIP (2009) " The Economies of VoIP", [Internet] available at URL: <http://www.tech-faq.com/voip.shtml>, [accessed on 27th October 2009]
• VoIP (2009) "why VoIP", [Internet] available at URL: <http://www.tech-faq.com/why-voip.shtml>, [accessed on 27th October 2009].

We provide a professional essay writing service that thousands of our customers use as an effective way of improving their grades, improving their research and saving them lots of time.

plumber arlington Ritz Carlton Vail teeth whitening systems Buy Hair Removal Wax