Understanding VoIP

As you learned in previous articles in this series, traditional telephony relies upon connections to the PSTN via a telecommunications carrier. While companies can implement a PBX internally to reduce the need for access to the PSTN between corporate users, this is still a costly option, and usually requires a significant capital investment and ongoing maintenance expenses for an organization. Furthermore, the addition of new services or features often results in additional costs.

As companies look towards new ways of not only reducing costs but also adding new features to their voice networks, packet-switches telephony is becoming increasingly attractive. Because most companies have already made a significant investment as part of implementing their data network, they are looking for ways to leverage the network to support additional services, such as voice traffic. In the past, the ability to use a single network to provide both data and voice services to users was not practical; not only was the technology to do so still in its infancy, but the bandwidth and quality of service (QoS) techniques necessary to provide what users would consider to be acceptable service were just not available. However, given that many companies have moved to switched high-speed connection all the way to user desktops, this is rapidly changing. Not only is the bandwidth available, but the protocols and associated technologies necessary to implement a “converged” network that handles both voice and data traffic have quickly matured to make the transmission of voice over a data network not only possible, but also a practical solution for many organizations.

To begin, it is important to understand that the transmission of voice traffic over a data network is not limited to Voice over IP (VoIP). While VoIP may be the most popular method of transferring packet-switched voice traffic, it certainly isn’t the only one. Other methods include Voice over Frame Relay (VoFR) and Voice over ATM (VoATM). VoFR does not use IP, and is not an end-to-end solution. Instead, it is typically to create a virtual or emulated tie trunk link between PBXs in remote locations, using Frame Relay PVCs for transport, rather than expensive leased lines. Similarly, voice traffic can also be encapsulated within standard 53-byte cells for transport over ATM networks. Since voice traffic is bursty, VoATM is typically implemented using ATM Adaptation Layer 2 (AAL2) encapsulation, which provides variable bit rate services.

Introduction to IPv6

Before getting into the technical details of this new version of IP, a simple question must be answered – why does the world need a new version of IP at all? There are many answers to this question, but the most basic reason involves the rapid depletion of the IPv4 address space. If you’ll recall from earlier in this chapter, IPv4 uses 32-bit addressing, and this limits the total number of IP addresses available for issue. When the Internet Protocol was first defined, nobody envisioned the phenomenal growth that defines the Internet we know today. As such, what was originally considered an almost endless supply of address space is now challenged as increasingly greater numbers of devices are connected to the Internet. Consider examples like cellular phones, PDAs, and other embedded systems, and it’s easy to see how the need for more IP address space is upon us.

Note: Talking about IPv6 begs a simple question – whatever happened to IPv5? The answer to that is that IPv5 is actually defined, although for a different purpose. IPv5 defines an experiment protocol that was originally developed to provide quality of service (QoS) features on IPv4 networks. You don’t need to know anything about IPv5 for the CCDA exam, but hopefully this helps to clear up what might have been a nagging thought. To that end, it’s also an interesting little piece of tech trivia!

A number of techniques have been developed and implemented to help slow down the need to deploy a new version of IP, and of these, network address translation (NAT) is clearly the most popular. Earlier in this chapter we also looked at the three ranges of IP addresses set aside for private addressing. While this technique has reduced the need for public IP addresses, it is still not a proper solution, and does little to address the foreseeable growth of the Internet in the longer term. Quite simply, a larger IP address space is required, and IPv6 addresses this issue with a 128-bit address space. At this time, a 128-bit address space would be capable of providing more than a thousand IPv6 addresses for each man, woman, and child on the planet.