APTA TransiTech Conference Communications: Vendor Perspective (TT) Phoenix, Arizona, Tuesday, VoIP Solution (101)

Transcription

1 APTA TransiTech Conference Communications: Vendor Perspective (TT) Phoenix, Arizona, Tuesday, VoIP Solution (101)

2 Agenda Items Introduction What is VoIP? Codecs Mean opinion score (MOS) Bandwidth Considerations VoIP (SIP) Connection Model Latency Jitter Buffer & Packet Loss Recovery Why is this technology important?

3 Clever Devices Leading provider of digital information systems, Intelligent Transportation Systems (ITS) solutions and Smart Bus systems In 2012, acquired two ITS firms: Digital Recorders and GreyHawk Technologies Clients include the largest transit operations in North America: Washington DC New York City Transit Chicago Transit Authority New Jersey Transit Ottawa, Canada Panama City, Panama Largest Real-Time Bus Arrival Information (BusTime) system in North America NY Headquarters plus four regional offices Approximately 400 employees

4 What is VoIP Voice over Internet Protocol (VoIP) commonly refers to the communication protocols, technologies, methodologies, and transmission techniques involved in the delivery of voice communications over Internet Protocol (IP) networks, such as the Internet. wikipedia.org

5 Overview In all VoIP systems, your voice is converted into packets of data and then transmitted to the recipient over the Internet and decoded back into your voice at the other end. To make it quicker, these packets are compressed before transmission with a codec (almost like zipping a file on the fly). There are many codecs using different compression methods and bitrates, thus each codec has its own bandwidth requirements and provides different voice quality.

6 Interoperability Mainstream VoIP solutions utilize the SIP (Session Initiation Protocol) which handles the negotiation of sessions The de-facto standard Most SIP compatible devices can talk to any other SIP enabled device The intermediate proxy server will generally resolve any codec issues

7 Popular Alternatives There are many alternate VoIP based systems. Using voice chat in MSN, Google, Yahoo or Skype could be regarded as VoIP, but these are all proprietary systems. Talking to someone using any of these alternatives requires both ends of the call to have the same software installed. These alternate systems use a restricted solution that s not open and offers limited-to-no connectivity beyond their respective networks without incurring additional fees.

8 A codec is a device or computer program capable of encoding / decoding a digital data stream or signal. Codec

9 Mean opinion score (MOS) Mean opinion score (MOS) is a test that has been used for decades in telephony networks to obtain the human user's view of the quality of the network. VoIP Private Radio

10 Bandwidth Bandwidth - the rate of data transfer, bit rate or throughput, measured in bits per second (bps), sometimes referred to as the width of the pipe.

11 Putting it together Inter operability Call quality Network requirements

12 Putting it together (cont.)

13 Which Codec to choose? It becomes quickly evident from the large number of parameters, that there is no perfect codec it s all about balancing your specific requirements and application Audio bandwidth (higher is better) Data rate or bit rate (how many bits per second, fewer is better) Audio quality loss (how much does it degrade the audio, lower is better) Kind of audio (does it only work with speech, or with anything?) Processing power required (less is better) Processor memory required (less is better) Openly available to vendors? ( yes is essential) Inserted delay (audio latency caused by the algorithm, less is better) Resilience (how insensitive to corrupted or lost packets, more is better) ITU standards-based (standardized by the International Telecommunications Union - yes is better)

14 VoIP (SIP) Connection Model User A Proxy User B Call establishment process - session negotiation with a proxy server

15 Latency (and Bandwidth) Latency is the time delay from when you say a word until the other person hears it Sometimes referred to as the "mouth-to-ear" delay. If you think of the Internet as a series of pipes Latency is the length of the pipe between two points Bandwidth represents the width of the pipe The wider the pipe the more data you can send in parallel The key concept - regardless of how much data you are sending, it still has to move the entire distance from point A to point B Moving data takes time; which is called latency

16 Jitter and Packet Loss Jitter is the measure of variability in arrival times between packets. When a packet does not arrive in time to fit into the active voice stream, it has to be discarded. If this happens too often, the listener will perceive reduced voice quality. VoIP utilizes the UDP transport layer [in most situations], which does not provide guaranteed packet delivery (i.e., packets will be lost).

17 Jitter Buffer A temporarily storage area for arriving packets, used as a means of minimizing delay variations. Impact - If the buffer is too small then an excessive number of packets may be discarded, which can lead to call quality degradation. Resolution - Typical range of milliseconds. Adaptive buffers may be set to several 100 s of milliseconds.

18 Packet Loss Recovery A strategy of hiding packet loss errors from the listener Typical approach (Packet Loss Concealment) Lost packets are handled by the receiving device General methods Silence insertion Noise substitution Packet repetition

19 Summary - Why is this technology important Low cost Flexible No major capital investment needed No special licensing or rebanding required (FCC) Vendor independence Improved call quality and geographical range Bidirectional communication

20 Summary - Why is this technology important (cont.) No transmit timer issues (i.e., over heating) Leverage technological improvements and updates over time If you already have a CAD System Then you probably already have many real-time issues to consider; the additional bandwidth requirements of a VoIP call are minimal Public WiFi, video, vehicle monitoring, credit card payment system, etc. No need to rationalize true channel capacity Theoretical capacity models like Erlang C are unneeded No call queuing issues - the total number of available channels is almost unlimited, in real-time! True dynamic talk group capability

21 Thank You Dean Soucy Senior Vice President of Engineering Clever Devices [Mobile] [Office Direct Dial]