VoIP Network Design
That a VoIP network architecture makes sense for your enterprise. But how do you glue all of these disparate piece parts together into one cohesive, converged network? If you have been following this tutorial series, you now have an understanding of the International Telecommunications Union?s (ITU-T) H.323 protocol, the Internet Engineering Task Force?s (IETF) Session Initiation Protocol
plus issues that effect the Quality of Service (QoS) of the VoIP connection
. Now it?s time to put it all together, and look at the design and implementation of the VoIP network. This, and the next three tutorials will address those issues, beginning with the subject of VoIP network design.
Let?s describe the importance of the network design phase anecdotally. Suppose that you are responsible for your organization?s data network. This network has evolved over the years, and is now a distributed system, with
sub networks in several cities that are connected by wide area network (WAN) links.
Design For Services Providers
Driven by competitive pressure and the desire for new service generating opportunities, major Service Providers (SP) have begun rolling out VoIP
(Voice over IP) services to business and consumer markets. The challenge is to design the network to support VoIP service requirements for strict
connectivity, latency, jitter, packet loss, and reliability objectives that are
normally expected from the (circuit-switched) PSTN services. In all cases, these data networks
need to be carefully designed to support their most important and challenging application ? VoIP.
Some of the key components of network design for supporting VoIP are: * Topological design: Core network topology,
soft switch and router placement, and backhaul. Design for reliability and scalability.
* Capacity design: Soft switches, routers, facilities, servers, and other network elements to support voice traffic and signaling.
* Signaling network design: Interconnecting voice end points independent of their access arrangements and corresponding signaling protocols (e.g.,
SIP, SS7, H.323, H.248/Megaco, MGCP). * QoS design: For end-to-end quality of service objectives for latency, jitter,
and packet loss. Traffic policing, queuing, and shaping.
VoIP Network Design Tips Good quality voice-over-IP (VoIP) conversations depend on maintaining strict constraints for packet loss,
delay, and jitter . We?ve found these design tips successful when deploying VoIP in a data network.
* Use the G.711 codec end-to-end, unless lack of capacity requires compression.
Codecs are the hardware or software used to convert from analog to digital and back. The G.711 codec
gives the best voice quality, since it does no compression, introduces the least delay, and is less sensitive
than other codecs to packet loss. Other codecs, like G.729 and G.723, consume less bandwidth by doing
compression, but this introduces delay and makes the voice quality very sensitive to lost packets.
* Keep packet loss well below 1% and avoid bursts of consecutive lost packets.
Packet loss occurs because of congestion or electromagnetic noise. It can also occur when jitter is high
and the jitter buffer is too small to compensate. Increased bandwidth and good tuning can often reduce
network congestion, which, in turn, reduces jitter and packet loss.
Design of VoIP networks This paper addresses the issue of cost-optimal voice over IP (VoIP) network design. In the applied model, the whole VoIP network is divided into two logical components: the access network and the transport network. The access network consists of VoIP end-points that connect to the transport network through edge routers serving as gateways. Since multiple edge routers may be available for any given VoIP node, one task of the design process is to assign a particular edge router to every VoIP node. The edge routers have to be connected in a way that security and availability can be assured for the VoIP traffic. One obvious approach to fulfilling these requirements, which is assumed throughout the paper, is to define a virtual private network (VPN). Supposing a large volume of VoIP traffic, the cost of the VPN can be significant; thus, the other task of VoIP network design is to specify the transport VPN in the most economical way. These two tasks of VoIP network design can be solved separately using existing methods; nevertheless, the specification of VoIP regions influences the cost of the final solution to a great extent.
VoIP Softswitch Network Design and Testing Preface It has been a little over a year since we looked at the evolution of the new public telephone network, and things have moved quickly enough for us to take another look at our progress and current direction. Indeed, the move towards adoption of IP-based integrated services by the service providers has accelerated over the last several months, from the perspective of creating an IP-based infrastructure for consumer and business applications. At the same time, a lot has been learned, and is continuing to be learned from the technical issues and testing challenges we have had to overcome in the design of VoIP networks and services. Some say there are signs the business drivers for the new technology may not be materializing as quickly as industry analysts had hoped and expected. The so-called "killer application" that will capture the fancy of the consumer and will generate wonderful revenue streams for the service providers is not staring us in the eyes.