Structured Cabling to Support IP Telephony
IP Telephony (Voice over Internet Protocol) in many circles is seen ultimately to be the dominant architecture of enterprise voice systems. IP Telephony involves using the local area network, cabling, router, and data switches,with an application server for all voice communications. IP Telephony has been called the future of enterprise voice communications for a variety of well-substantiated reasons. The basic premise seems simple enough; use a single network of communications devices and cabling for both data and voice traffic. This consolidation will hopefully result in decreased administration and equipment costs, as well as more feature rich voice system with all of the benefits traditionally associated with data. Contact lists, queuing, employee location changes, and new applications are on most typical short list of benefits. However the advent of IP Telephony has created somewhat of a myth in the infrastructure, that a key and prime benefit is the need for less cabling. To assess this, let’s take a look at IP Telephony in more detail. What is IP Telephony? In the simplest terms, IP Telephony is a communications system that uses the office data network to transmit packetized voice. Doing so eliminates the traditional TDM (Time Division Multiplexed) technique. While this may seem incredibly common sensical, it was a long, arduous task for the market to move into this area. Telecommunications technologies are galactically different from that of data, using different standards, transport mediums, and protocols.
Technical Issues At the forefront of all technical issues relevant to IP Telephony is voice quality and reliability. Unlike many data applications, the voice world is totally intolerant of downtime. Even an application up 99% of the time is unacceptable to the voice world as that would mean close to two hours per week of downtime. When many businesses conduct tens of thousands of dollars in sales every hour over the telephone, every second counts. Additionally, voice quality is a serious concern, as the LAN is not specifically designed for real time communications such as voice. People are used to having flawless telephone service. Static, fragmented sentences, and dropped calls are unacceptable. To achieve high quality IP Telephony, the following are some of the techniques employed: Echo Cancellation, Voice Compression, Jitter Buffering, and Silence Suppression.
QoS (Quality of Service) Determining and guaranteeing a high level of service, voice quality, and reliability is critical in any telecommunications system. Unfortunately, prior to the inception of VoIP, real time QoS issues were never a consideration in the modern LAN. Now with voice being transported over the data network, vendors are forced to attempt to put a square peg into a round hole by manipulating current data technologies to accommodate the high demands of voice. Following are a list of some technologies and approaches to IP Telephony QoS.
CBR (Constant Bit Rate): The nature of Ethernet is a “listen then talk” mannerism. A transmitting station on a LAN will send data, listen for any collisions with other data, and if no collisions are detected, continue the transmission. Very often however, a collision is detected. In that case the transmitting station backs off, selects a random delay (of milliseconds), executes the delay and transmits again. Unfortunately this process of detecting packet collisions increases latency across the entire network and can negatively affect voice quality. CBR sends the data regularly in time and at a constant rate; thus eliminating packet collision.
Gigabit Ethernet: A brute force attack on QoS, Gigabit Ethernet simply throws enough bandwidth at the network that voice quality is statistically unlikely to be low.
802.1P: Switches and routers compliant to IEEE standard 802.1P (“P” stands for prioritization) have the ability to prioritize packets based on a 0-7 scale (“0” having the highest priority). This tagging of packets must begin at the desktop with the packet telephone. In addition, this prioritization will not function when transmitted across a hub or repeater, and subsequently highly hubbed networks will have difficulties maintaining QoS. What do these technical points mean to the infrastructure, well it is clear that QoS is going to also need a good QoC (Quality of Connection).
The cabling that supports the infrastructure needs to enable high performance and low delay, to ensure optimum throughput and uptime. Therefore, the first conclusion we can make is that IP Telephony requires higher grade cabling than that historically associated with Voice services, and therefore IP Telephony adds to the trend to higher performance cabling.
Features and Benefits of IP Telephony While the idea of using a single cable for both voice and data is a compelling concept technically, by itself it is not enough to create an entire market. At the end of the day, if all that IP Telephony did was deliver voice on a data network, it simply would not be worth moving from the proven telecom technology. The real drivers for this market are the features and applications, both current and undeveloped, and interestingly enough most if not all require a well-provisioned cabling infrastructure. Following is a list of features and benefits that are worthy of note.
Moves, Adds, and Changes Moves, adds, and changes are three words that bring nightmares to accountants and IT managers alike. This refers to moving an employee’s office location, adding a new employee, or changing an employee’s extension number. In the world of PBX’s it was a time consuming, difficult task, that often required a service technician visit from the PBX manufacturer. With IP Telephony, this is no longer an issue. All moves, adds, and changes, can be administered with the same tools used to control the network, sometimes even within a web browser. This can save immeasurable time in man-hours, and dramatically cut down service costs. However it should be noted that to take advantage of this benefit relies on free cabling ports being available for the employees to move to.
Phone Portability Phone, or handset, portability is probably the coolest feature inherent in IP Telephony. Because the handsets have a unique IP address (or MAC address for Ethernet phones), portability becomes a simple matter. To change offices, or just take calls in a conference room for an afternoon, all a user has to do is unplug the handset, bring it to the new location, and plug it back into the network, provided of course, enough cabling has been provided and is free and available. The system will never miss a beat and the user instantly can make and receive calls as well as utilize every phone feature, as if they had never left the office. This entire process doesn’t require a second of time from the system administrator.
Application Integration For those handsets using IP, integration with scheduling and sales enabling tools such as Microsoft Outlook becomes a relatively simple task. Features such as the sharing of contact lists, directories, and visual integration with the computer will become commonplace in an IP Telephony environment. In addition, the use of IP creates an open development environment for third party applications. It is these products that can truly drive a technology as no vendor can predict what the next killer-app will be; they simply need to make their products open enough to use it.
LAN/WAN Integration As many IP Telephony products operate in native IP format, entrance onto a WAN IP Telephony network becomes a simple task. If an organization is using an IP based LAN Telephony product and wishes to conduct conversations over IP Telephony, then the calls can be placed directly on the WAN without the use of a gateway. In that circumstance, a gateway is only used to convert standard PSTN circuit switched calls to packet for enterprise use, not vice versa. This can save considerable money on call costs.
