The VOIP Network

Voice Over Internet Protocal

Enterprise VoIP Building Blocks
On an end-to-end enterprise VoIP network, an IP phone replaces the traditional digital phone handset and shares a similar physical appearance. An ordinary PC can also serve as an IP phone (a "soft phone") when VoIP software is installed. Enterprise IP phones typically connect directly to the LAN via Ethernet or sometimes Wi-Fi, while Universal Serial Bus phones exist as an alternative to soft phones. VoIP phones obtain an IP address, normally via Dynamic Host Configuration Protocol (DHCP), which allows them to make and receive calls.

Analog telephone adapters (ATA) allow ordinary telephones to interface with a VoIP-enabled network as an alternative to using an IP phone. ATAs normally feature RJ-11 ports for connecting the phone and corresponding RJ-45 Ethernet ports for connecting to the LAN.

A VoIP softswitch (or "call processor") maintains the mapping of VoIP phone numbers and IP addresses. As the name implies, softswitches involve special-purpose VoIP software responsible for forwarding voice packets between IP phone endpoints or other softswitches. Call-processing software is typically installed on dedicated servers for enterprisewide deployments but some products like Iwatsu ECS (Enterprise Communications Server) can be embedded in routers for smaller-scale needs.
Media gateways are server appliances that (among other functions) interface voice and fax communications between a VoIP network and the public switched telephone network (PSTN). PBX-IP media gateways are one such appliance that extends an organization's traditional private branch exchange with IP capability to simply the transition to VoIP.

VoIP Networks -- Bringing It All Together
Gluing all of this VoIP equipment together is the job of various network technology standards. The two leading protocols for VoIP call management (signaling for call setup and teardown) are Session Initiation Protocol (SIP) and H.323. Early VoIP systems relied on the H.323 standard, while SIP has emerged as the new front-runner thanks to a firewall-friendly, IP-centric design.

Inside a VoIP call, the individual packets of voice conversations are generated from analog voice signals by coder/decoders embedded within IP phones or terminal adapters. Many different audio codecs exist, each making different tradeoffs in sound quality, bandwidth utilization and transmission delay. The G.711 codec standard became well-established together with H.323, and most VoIP endpoints support it today. G.711, however, requires 64Kbit/sec. bandwidth per call on IP networks. Alternative codecs like G.723.1 and G.729 have been gaining in prominence and generally require only 8Kbit/sec. or less per conversation, at the cost of higher latency and potentially lesser audio quality.

For VoIP equipment to work together across the enterprise, compatible protocols and codecs must both be deployed. H.323 and SIP are incompatible with each other, and most codecs likewise do not interoperate. Fortunately, vendors today tend to support multiple VoIP standards in their gear, lessening the interoperability concern that has existed with VoIP from the outset.

VoIP Quality of Service
Implementing enterprise VoIP requires careful attention to quality-of-service (QoS) issues across the corporate WAN.

Various technical challenges exist to build QoS applications on IP generally, and VoIP is no different. Without QoS in place to guarantee network bandwidth and capacity, enterprise networks can't scale to handle the demands of peak calling periods. Approaches to ensuring QoS for VoIP include bandwidth reservation via the RSVP protocol, so-called differentiated services that support traffic classification with service-level policies and Multiprotocol Label Switching (MPLS) traffic engineering.

What About VoIP Security?
The security of VoIP communications continues to be an area of strong focus. Consumer VoIP systems may choose not to encrypt calls, but enterprises generally will require encryption. With this and other security measures in place, VoIP is inherently no less secure than other forms of IP networking. Protecting IP phones from spam, preventing VoIP numbers from being spoofed for outgoing calls and guarding against call eavesdropping are all necessary on converged networks.

Making the Case for VOIP

Making the Case for VOIP

VOIP with Iwatsu