Voice over Internet Protocol computer network

VoIP (Voice over Internet Protocol), VoIP allows you to make telephone calls using your computer network over a data network link like Internet. VoIP can be used to call others using the same service or to their personal telephones. Because of its low calling charges VoIP has a high demand in small to large organizations, and even it has a great impact on the home users also. VoIP needs a broadband connection to provide communication between the users.

Now-a-days many homes today have broadband connections, such as digital subscriber line (DSL) or cable modem connections, and many service providers are beginning to offer telephone service over these broadband connections. You can,in some cases, keep your current phone number if you convert your existing telephone service to a VoIP-based telephone service.

Before going into detail Security requirements of a VoIP network, you need to understand the problem and set of requirements that must be met. Specific VoIP services might have additional requirements

• Integrity
• Privacy
• Authenticity
• Availability/protection from Denial-of-Service(DOS).
  

Discussion

What is VoIP:-

VoIP allows you to make telephone calls using a computer network, over a data network like the internet. VoIP converts voice signal from your telephone into a digital signal that travels over the internet then converts it back at the other end so you can speak to anyone with a regular phone number.

VoIP can be implemented in several ways, from a software program on your computer used with a headset and microphone to adaptors used with regular analogue home phones or you can use dedicated VoIP phones which look and act like regular phones but have specially designed chips to improve call quality.

VoIP is a Layer 3 network protocol that uses various Layer 2 point-to-point or link-layer protocols such as PPP, Frame Relay, or ATM for its transport. VoIP enables Cisco routers, access servers, and multiservice access concentrators to carry and send voice and fax traffic over an IP network. In VoIP, digital signal processors (DSPs) segment the voice signal into frames and store them in voice packets. These voice packets are transported via IP in compliance with a voice communications protocol or standard such as h.323, Media Gateway Control protocol (MGCP), or Session Initiation Protocol (SIP).  Voice signalling traffic often uses Transmission Control Protocol (TCP) as its transport medium.

VoIP is a set of technologies that seeks to replace traditional analog voice services. There are three main compelling benefits to VoIP.

• VoIP makes better use of network capacity. Traditional voice uses a 64-kbps circuit, even when it is not active, but VoIP can use much less and no capacity when the line is not in use.
• VoIP allows new and revolutionary features, such as the flowing

§ Integration of voice and data systems.

§ Voice CODECs can improve sound quality.

§ Integration with new clients. Instead of an analog phone, VoIP clients can include television boxes, Personal Digital Assistants (PDAs), cell phones, laptops, and so on.

• VoIP can save money by avoiding toll calls.

Understanding Security Implications

Security is a top priority in most networks. The many types of security solutions include router access lists, stateful firewalls, and VPNs. These solutions may be standalone or layered. Implementing voice in a secure network environment requires understanding of existing security measures and how they affect the transit of voice though the network. Numerous problems, from device failures to malicious attacks, affect the uptime of networks. Varying levels of security are available to suit individual corporate requirements. The requirements for secured IP telephony include the following:

• It must provide ubiquitous IP telephony services to the locations and  to the users that require them.
• It must maintain as many of the characteristics of traditional telephony as possible, while doing so in a secure manner.
• It must integrate with existing security architecture and not interfere with existing functions.

The starting point for any security implementation is the development of a security policy. The security policy should address the following points that affect voice:

• Transport Security: Traffic traversing public access and backbone networks must be properly secured. IPSec and VPNs provide transport security by ensuring data confidentiality using encryption, data integrity, and data authentication between participating peers. Encryption adds to the overhead and delays the voice packet. You must factor in encryption when testing the delay budget and bandwidth calculations.
• Network security: Cisco Systems firewalls provide stateful perimeter security that is critical to any public-facing network, such as a VPN. When deploying voice and video across VPNs, it is critical to statefully inspect all multiservice traffic traversing the firewall. Firewalls must be configured to allow known signal and payload ports to pass into the network. It is important to understand where the VPN terminates. If the VN terminates inside the firewall, then the traffic passing through the firewall is encrypted and is subject to stateful inspection. If the VPN terminates outside the firewall, then the firewall has access to RTP/UDP/TCP/IP headers and is able to inspect the packet for call setup.
• Intrusion detection: The Cisco Security Agent provides threat protection for server and desktop computing systems, also known as endpoints. It identifies and prevents malicious behaviour, thereby eliminating known and unknown security risks and helping to reduce operational costs. The Cisco Security Agent aggregates and extends multiple endpoint security functions by providing host intrusion prevention, distributed firewall capabilities, malicious mobile code protection, operating system integrity assurance, and audit log consolidation, all within a single product. In addition, because Cisco Security Agent analyzes behaviour rather than relying on signature matching, it provides robust protection with reduced operational costs.

Cisco SAFE Blueprint for VoIP

The Cisco SAFE Blueprint is a flexible, dynamic blueprint for security and VPN networks, based on the Cisco AVVID architecture that enables businesses to securely and successfully take advantage of e-business economies and compete in the Internet economy

Cisco has significantly enhanced the SAFE Blueprint, and extended network security and VPN options to small branch offices, teleworkers, and small-to-medium networks.

SAFE IP telephony emulates as closely as possible the functional requirements of modern networks. Implementation decisions vary, depending on the network functionality required. However, the following design objectives, listed in order of priority, guide the decision-making process.

• Security and attack mitigation based on policy
• Quality of service
• Reliability, performance, and scalability
• Authentication of users and devices ( identity)

• Options for high availability ( some designs )
• Secure management

SAFE IP telephony must provide ubiquitous IP telephony services to the locations and users that require it. It must maintain as many of the characteristics of traditional telephony as possible while doing so in a secure manner. Finally, it must integrate with existing network designs based on the SAFE security architecture and not interfere with existing functions.

Advantages of VoIP

• More efficient use of bandwidth and equipment: Normal telephone networks use a 64-Kbps channel for every voice call. VoIP telephone shares bandwidth among multiple logical connections.
• Lower transmission costs: A substantial amount of equipment is needed to combine 64-kbps channels into high-speed links for transport across the network. Packet telephony statistically multiplexes voice traffic alongside data traffic. This provides substantial savings on capital equipment and operations costs.
• Consolidated network expenses: Instead of operating separate networks for voice and data, voice networks are converted to data packets so that they can be transmitted over the IP. The benefit is cost saving on voice network equipment and operations.
• Improved employee productivity through features provided by IP telephony: IP phones are not only phones; they are complete business communication devices. Software-based phones or wireless phones offer mobility to the phone user.
• Access to new communications devices: Packet technology can reach devices that are largely inaccessible to the modern time-division multiplexing (TDM) infrastructures. Intelligent access to such devices enables companies and service providers to increase the volume of communications that they deliver, the breadth of services that they offer, and the number of subscribers that they serve. Packet technology, therefore, enables companies to market new devices, including videophones, multimedia terminals, and advanced IP phones.

Limitations of VoIP

VoIP has many advantages than the traditional telephone system. VoIP technology has also some limitations as that of the normal telephones and a whole batch of additional ones. The following are some of the issues:

• Delay/latency: VoIP delay or latency is characterized as the amount of time it takes for speech to exit the speaker's mouth and reach the listener's ear.
• Jitter: Jitter is the variation of packet interarrival time. Jitter is one issue that exists only in packet-based networks.
• Pulse Code Modulation: Analog transmission is neither robust nor efficient at recovering from line noise. In the early telephone network line noise resulted in an often-unusable connection. While using the digital representation of signals this line noise has been reduced, then the telephony network migrated to pulse code modulation (PCM).
• Voice Compression: Two basic variations of 64 kbps PCM are commonly used: µ-law and a-law. The compression method used often is adaptive differential pulse code modulation (ADPDM).PCM and ADPCM are examples of waveform codecscompression techniques that exploit redundant characteristics of the waveform itself.
• Echo: Echo is an amusing phenomenon to experience while visiting the Grand Canyon, but echo on a phone conversation can range from slightly annoying to unbearable, making conversation unintelligible.
• Packet Loss: Packet loss in data networks is both common and expected. Many data protocols, in fact, use packet loss so that they know the condition of the network and can reduce the number of packets they are sending.
• Digital-to-Analog Conversion: Digital to analog (D/A) conversion issues also currently plague toll networks. Although almost all the telephony backbone networks in first-world countries today are digital, sometimes multiple D/A conversions occur.
• Dial-Plan Design: One of the areas that cause the largest amount of headaches when designing an Enterprise Telephony (ET) network is the dial plan. The causes of these head pains might be due to the complex issues of integrating disparate networks. Many of these disparate networks were not designed for integration.

Conclusion

In order for VoIP telephony systems to compete with well-entrenched legacy telephony systems, VoIP must offer much more than just the ability to place a phone call.

Today's PBX users expect features users expect features such as voice mail and conference calling. Some businesses use large call centres for their customer support departments. Therefore, VoIP technologies must step up to the challenge and not only match existing supplementary features, but exceed those features.

VoIP technology has much more efficiency than the traditional telephone systems as it has low transmission costs, more efficient use of bandwidth and equipment, improved employee productivity through features provided by the IP telephony. VoIP allows us for access to the new communication devices.