Networking Solutions for VoIP Table of Contents QOS: THE PRIME MOVER .............................................................................................................................................. 3 BENEFITS OF VOIP ........................................................................................................................................................... 3 VOIP NETWORK COMPONENTS AND PROTOCOLS ............................................................................................... 4 CODECS .............................................................................................................................................................................. 5 SIGNALING PROTOCOLS ............................................................................................................................... 5 THE LLDP-MED PROTOCOL ......................................................................................................................... 5 SECURITY ........................................................................................................................................................... 5 NETWORK PLanning – GENERAL CONSIDERATIONS ......................................................................................... 6 CHOOSING A SWItcH: BANDWIDTH & PORTS ....................................................................................................... 6 CHOOSING A SWItcH: POWER OVER ETHERNET .................................................................................................. 7 REFERENCE DESIGNS ...................................................................................................................................................... 8 20 PHONES ........................................................................................................................................................ 8 200 IP PHONES ................................................................................................................................................. 10 1000+ IP PHONES ........................................................................................................................................... 12 MANAGED INFRAstRUctURE ...................................................................................................................................... 16 Page 2 VoIP has become a mainstream technology. Today, the question for business telephony at any scale is no longer whether to switch to VoIP, but when. This paper focuses on the internal networking aspects of making a successful transition to VoIP, with emphasis on network design and switching technology. QoS: THE PRIME MOVER The most important factor that has moved VoIP into the mainstream is improved quality of service (QoS)1. Businesses that have held back because of VoIP’s early reputation for poor voice quality need no longer be concerned that important transactions (such as sales) will be impeded by poor QoS, or that their company will make a less than fully professional impression on callers with VoIP. Today, excellent quality of service can always be achieved with VoIP, but it’s not guaranteed. QoS ultimately depends on the switches that control the VoIP traffic, and of course, the network over which that traffic travels. It’s understandable that the focus of attention in a transition to VoIP is typically on the service provider, the delivery model (onsite vs. hosted) and the IP phones, but the switches have the most important impact on the user experience. With NETGEAR switches, VoIP traffic can be automatically prioritized to maintain the desired QoS, even when the network is saturated. The key factors required to ensure a successful VoIP network with reliable QoS are as follows: • Voice packet prioritization. The switch(es) that manage the traffic must be able to prioritize voice traffic when necessary to maintain QoS. • Adequate bandwidth. The network and the switch(es) that control it must be able to handle the additional load imposed by a VoIP deployment. • Resilience. The network switch(es) must have access to an alternate power supply should the main source of power fail. • Security. The network must be protected from hacking, including physical hacking. The first factor – packet prioritization – deserves more explanation. VoIP streams are not forgiving when it comes to dropped packets, signal delay and other factors that don’t affect data traffic. Therefore, to ensure a consistently high level of QoS, the switches must be able to prioritize network traffic, giving voice packets top priority. NETGEAR switches accomplish this automatically. BENEFITS OF VoIP This guide will help you understand the basics of VoIP so you can successfully plan and specify a VoIP network. It includes reference designs for VoIP networks with 20, 200 and 1,000 IP phones. Before covering design issues, however, it’s worth reviewing just why VoIP has become the solution of choice for organizations of all sizes. 1 The term “Quality of Service” and its abbreviation, QoS, has long been used in the literal sense of voice quality, i.e. how closely what the user hears matches the original. Recently, however, the term has begun to be used to describe the voice packet prioritization technology that is used to ensure high QoS even during periods of network congestion. In this document, QoS refers only to the original meaning of the term. Page 3 VoIP’s packet-switched solutions are winning the marketing battle over conventional circuit-switched telephony because they offer advantages that conventional POTS (“Plain Old Telephone Service”) just can’t match. These include: • Price. VoIP is substantially less expensive than circuit-switched telephony. In fact, online services like Skype enable individual users to international calls of unlimited duration for free. VoIP for business purposes isn’t free, but it is dramatically cheaper than today’s circuit-switched options. • Quality of service (QoS). In the past, the reduced cost of VoIP came with a penalty: reduced QoS. Today’s VoIP technology can provide voice quality that equals or even exceeds what conventional circuit-switched systems offer. • Complexity. Switching to VoIP typically reduces the complexity of dealing with “the phone company” and its arcane pricing structures, which even highly-paid consultants can’t always understand. • Features. VoIP can now match conventional telephony feature-for-feature, ranging from basics like voice mail to emerging capabilities like presence sensing. • Integration. More and more of today’s business applications, including CRM and call center applications, are grounded in internet-related technical standards. VoIP technology can be integrated with these applications much more easily than the analog technology of conventional telephony. • Ease of administration. Adding, removing or changing internal numbers is a simple process with VoIP’s web-based interfaces, and with auto discovery features, activating a new phone is virtually automatic. • Deployment advantages. VoIP can be piggy-backed on an existing network infrastructure, including the physical cabling. This means lower initial cost (with no new wiring) and lower maintenance cost as well. • No risk of obsolescence. VoIP is the wave of the future. Companies who adopt VoIP have no risk of ending up with a “dinosaur” phone system that can’t operate efficiently in an all-digital world. VoIP NETWORK COMPONENTS AND PROTOCOLS No matter what the size of a VoIP network, it will always include one or more of the following components: • User agents. These may be commercial IP phones, or “soft phones” residing in a desktop or laptop PC. • Voice gateway. The gateway acts as the bridge between a VoIP network and the PSTN network of the “outside world.” • IPBX. The IPBX (sometimes referred to as an IP PBX) replaces the conventional PBX of the past, and performs all its functions (voice mail, call forwarding, conference calling and many, many more). It connects to the PSTN network via the voice gateway. The IPBX is available in three deployment options: – a dedicated, on-site hardware device – software that runs on a standard on-site server – a managed service via the cloud • Switches to manage network traffic. The switches are crucial, because if they lack the appropriate capabilities or bandwidth capacity, QoS will suffer, leading to user complaints, poor customer service and problems with external telephone communication in general. • Cabling. For adequate performance, Cat5E or better cabling is recommended. Decisions involving these components can directly affect QoS, based on which protocols they support. For example, some IP phones use protocols that deliver higher voice quality, but also require more bandwidth. Before reviewing those protocols, it’s worth taking a moment to examine QoS in a little more detail. QoS is ultimately a subjective measurement, because different individuals will invariably disagree as to how well a system can reproduce a voice that’s known to them. However, one decades-old attempt objectify QoS does exist. Developed initially for evaluating circuit-switched equipment, it provides a measure of quality known as Mean Opinion Score (MOS) based on individuals sitting in quiet rooms and rating voice quality. MOS can range from 1.0 (unintelligible) to 5.0 (ideal). Normally a score above 4.0 is considered to be acceptable, but what’s most important is that QoS can be quantified, and components/protocols can be evaluated based