Voice over IP (Internet Protocol)

	What is Voice over IP?	VOICE OVER INTERNET PROTOCOL  What is Voice over IP (VoIP)? Voice traveling over the corporate intranet, public Internet, or over a corporate VPN, such as frame relay or ATM.   Today's networks: Separate infrastructure for voice, data, and video Application integration is difficult Voice network not designed to handle future convergence of voice, video, and data   VoIP enables gateways and routers carry live, packetized voice traffic such as telephone calls over IP-based data networks (intranetworks or internetworks) rather than Public Switched Telephone Networks (PSTN).   Corporations are: Integrating transport of voice and data communication across the same infrastructure Gaining fiscal & technological advantages Designing entirely new voice-and-data integrated internetworks. Overhauling their traditional data networks, redesigning them to include infrastructure to support packetized voice transmission
	Why was it created?
	How does VoIP work?
	Where can I get it?
	Are there standards?
	What else should I know about VoIP?
	VoIP Links

BENEFITS

  Why was it created?

VoIP offers the following benefits:

• Toll bypass (either one- or two-stage toll bypass, depending on the environment in which VoIP is deployed)
• Cost benefits
  • average corporate calling at $.04 /min or $2.40 / hour
  • voice over frame relay at about $.04 /megabyte and voice packetized into 2MB an hour, that is about $.08 / hour
• PSTN voice-traffic and fax-traffic off load
• Convergence allows for reducing the costs of maintaining two separate networks, voice and data
• Adaptive, open, scalable, unified
• VoIP allows for desktop integration and integrated applications
  • Universally accessible voice-mail and fax-mail services

Applications:

• PC to PC document sharing
• Click to talk buttons on websites or within corporations
• Integrating call centers with e-commerce
  • virtual shopping assistants
  • on-line technical assistance

TECHNOLOGY

  How does Voice over IP work?

• Digital signal processors (DSPs) segment the voice signal into frames and store them in voice packets
• Voice packets are transported via IP in compliance with the ITU specification H.323
• The network used could be the Public Internet or an existing VPN such as frame relay or ATM network

VoIP gateways, routers, and switches are equipped to handle origination, transport, and termination of VoIP traffic. The Voice over IP (VoIP) technology transcends the differences among these transport media and mechanisms because the lower-layer media used is transparent to an IP infrastructure. For VoIP, the underlying technology might be ATM, FR, point-to-point lines, or the Public Internet.

Gateways:

• Powerful computers that enable real-time two-way communication between a circuit switched network (PSTN) or a packet switched network (Internet)
• Provides functions such as compressing and converting voice to data, as well as transmitting and receiving data packets over the IP network
• Sits between a PBX and a router
• When the packets hit the destination gateway, the voice is de-packetized and sent out over the PSTN to complete

 

 

IP is considered a connectionless or best-effort transport when used in conjunction with the User Datagram Protocol (UDP). UDP, which is datagram-based (or connectionless), suits the specific requirements of voice traffic, so it is used as the transport for VoIP rather than TCP. TCP offers reliability in that it guarantees retransmission of lost frames, but this reliable delivery is useless in the internetwork transportation of packetized voice because a frame that arrives late as a result of retransmission is as useful as no frame at all---that is, it has no effect. In other words, retransmission of packets is not meaningful. By the time the resent packet arrives at the end user endpoint, the required delivery time has long been transgressed.

Link to: Voice over the Public Internet diagrams and technology

Most technologies for VoIP enable you to balance service levels for sufficient quality of service---granting priority service to voice, for instance, while still servicing data transmission.

MANUFACTURERS & SERVICE PROVIDERS

 Where can I get it?

All of the major hardware players offer some form of voice over IP product line:

• Cisco (leader)
• Ascend (Lucent)
• Nortel
• Ericsson
• Motorola
• Netrix
• Netspeak
• Hypercom

Internet Telephony Service Providers (ITSPs):

• Own their own gateways and routers (less infrastructure for corporation)
• ITSPs can route only the long distance or international portion over the Internet
• ITSPs are treated like ISPs and do not have to pay sky high settlement rates demanded by the International carrier to complete the call
• Better rates!!

ITSPs:

• Netcom
• PSINet
• Qwest
• others

VoIP STANDARDS

 Are there standards?

There is a need to maximize the efficiency of the technology by establishing standards that tie together different manufacturers' products and promote interoperability!

Recently, the International Telecommunications Union (ITU) recognized a set of standards for Internet Telephony

• H.323 Standard
• Removed the barriers that have previously kept Internet Telephony, the PSTN, and the PC constricted by proprietary software and hardware
• PC desktop software, Internet gateways, modems, video conferencing, and the existing public telephone system all will be able to interoperate, expanding the capabilities of each

ISSUES

 What else should I know about Voice over IP?

Delay or latency (the time it takes for VoIP packets to travel between two endpoints) needs to be kept to a minimum for voice traffic.

What’s considered an acceptable delay?

• A maximum of 150 milliseconds, the level at which users begin to notice problems.

What’s the main source of fixed delay?

• The amount of delay is determined by transmission distance, bit rate, switching equipment, and (to some degree) packet size.

Equipment also adds latency:

• End-systems take time to digitize voice signals, and they must add "dejitter" buffering delay to compensate for any variable delay remaining in the system
• That can add up to as much as 80 ms
• Subtract that from the 150-ms "acceptable" delay level, and net managers really are left with just 70 ms to play with if the call is to be of toll quality

Voice packets are very small (80 to 256 bytes), and data packets can be very large (1500 to 18,000 bytes). On relatively slow links, such as WAN connections, large data packets can take a long time to send onto the wire. When these large packets are mixed with smaller voice packets, the excessive transmission time can lead to delay.

 

When using the Public Internet:

• Caller may have to traverse through multiple backbones and routers to reach a destination
• Quality could be unacceptable
• Run the risk of going over a backbone that has been oversubscribed and cause delay.
• Most systems will allow for when the call quality drops below a certain level, it will be routed over the PSTN.

The hardware and software to start VoIP up can very expensive, when comparing to the low-cost calling voice plans available from the major carriers.

  Related Links

Cisco Systems
Voice over IP Solutions
Migrating to Multiservice Networks
 
Data Communications On-line
Tech Tutorials
 
IT Week - Online Briefing
Voice over IP
 
Nortel Networks
Moving Voice onto Data Networks
 
PSINet
Voice Services
 
Netspeak
http://www.netspeak.com/
 
Ericsson
Webswitch 2000
IP Telephony Portfolio Press Release