VoIP

Voice over IP (VoIP)refers to the set of mechanisms that allow the sending of voice communications over a packet-based IP (Internet Protocol) network. 1xEV-DO Rev A introduces new features including end-to-end application-level Quality of Service (QoS) to the wireless network that allow service providers to deliver high quality voice services across their EV-DO infrastructure.

Drivers for VoIP over EV-DO Rev. A

For service operators, there are three primary drivers for VoIP: network efficiency, more efficient use of spectrum and the ability to enhance voice service portfolios.

Network efficiency

Network efficiencies are achieved by using existing resources more efficiently and by consolidating multiple networks, systems, and support organizations. As voice communications move toward digital techniques, the logic of merging separate networks for voice calls and for data sessions is inescapable. Converging the network onto one common, packet-based infrastructure will dramatically reducing the number of systems, employees and facilities required.

Spectrum efficiency

Operating parallel voice and data networks is an inefficient use of spectrum - especially in a CDMA environment where 1xRTT and EV-DO technologies use 1.25 megahertz of spectrum for each radio channel. Using separate radio channels for voice and data prohibits load balancing between the two services, and reduces overall trunking efficiency. As in the case of wireline networks, a transition to VoIP enables wireless carriers to converge all uses, voice and data and other multimedia, onto the same spectrum, eliminating the need for redundant channels, increasing trunking efficiency, and making better overall use of the spectrum.

Advanced Service Creation

VoIP enables the rapid creation of advanced services. Once carriers have a VoIP network in place they own a rich service creation environment in which new services can be created much more easily than they can be in the MSC-centric architecture of legacy cellular networks. New services beyond the traditional telephone services (call-waiting, multi-party calling, call forwarding, etc.) are possible when voice and data communications travel over the same network. Examples include push-to-talk, video telephony, click-to-dial, whiteboarding, and advanced accessibility features.

1xEV-DO Rev A and VoIP
1xEV-DO Rev A adds several advancements for VoIP and other multimedia traffic.

Increased channel capacity on both the forward and reverse links

Compared to EV-DO Rev. 0, EV-DO Rev. A increases the peak forward link data rate to 3.1 Mbps and the peak reverse link data rate to 1.8 Mbps. The dramatically enhanced uplink data rate will enable Rev. A networks to support significantly more voice connections than is possible under Rev. 0.

QoS support over the air link with multiple flows

The EV-DO forward link uses TDM to send packets to various users, which requires a scheduling function to decide which user should gain access to the air link at any given time. EV-DO Rev. A has added the ability for the forward link scheduler to coordinate the use of the EV-DO air link with the various devices that will be using it. Therefore, data devices, which need high data rates but are insensitive to packet delay and jitter, can be handled in one way, while voice devices that need lower data rates but that are highly sensitive to packet delay and jitter will be handled a different way. On the reverse link EV-DO Rev. A permits the use of higher power for QoS packets in order to reduce the number of transmissions and retries necessary to successfully send these packets.

Support for short and multi-user packets

Unlike many data applications, voice applications transmit relatively short packets on a regular basis. In EV-DO Rev. 0, the rigid structure of the physical layer leads to inefficient transmission of these short packets. EV-DO Rev. A has addressed this problem in two ways. Unlike Rev. 0, which allows packets sent over the traffic channel to be a minimum of 128 bytes long, Rev. A supports a wide variety of shorter packets, with physical layer packet lengths as low as 16 bytes. These packets can be transmitted in less time, and allow more users to access the network with low latency. In addition, EV-DO Rev. A includes support for multi-user packets. This capability allows a long physical layer packet (with its associated overhead) to be addressed to separate users, again reducing air link overhead as well as per-user delay.

Support for header compression

In current networks the overhead (non-voice information) required to direct traffic from source to destination is typically 40 bytes and results in an inefficient overhead to payload ratio of 2:1. For example, 20 msec of speech from an 8 kbps voice coder is 160 bits, or 20 bytes, while the associated IP, UDP, and RTP headers used for VoIP routing and control are 40 bytes. Such inefficiency affects the capacity of the network to handle voice traffic. EV-DO Rev. A supports compression of these headers, from 40 bytes down to approximately 2 bytes, thus enabling high VoIP capacity.

Enhanced Idle State Protocol support for faster, variable, paging

While a delay of several seconds in connecting to a server is not noticeable with most data applications, real-time applications such as voice are quite different. Paging channels in digital cellular networks, and EV-DO networks in particular, are logical control channels that allow the devices to receive control messages. Slow paging channels would manifest themselves as slow setup times, slow reaction to dialed digits, etc. during a voice call. Rev. A has addressed this issue by creating a variable, faster paging cycle.

Voice over IP is the natural progression for mobile networks as operators begin to expand their deployments of packet data systems. Airvana is embracing EV-DO Rev. A technology to deliver an end-to-end application-level QoS to the wireless network, enabling service providers to deliver high-quality voice services alongside data and multimedia applications. Airvana is the first company to demonstrate VoIP over EV-DO with QoS.