I got a call from a customer of mine asking me to offer a solution for his LAN infrastructure that would save him a whole lot of money.

When I asked him what he really wanted, he replied "Cost saving and getting voice across on a single cable infrastructure, and integration of more applications.’’

The result: A solution called ‘LAN telephony’, which provides the common infrastructure for voice and data, and enables integration of new IP applications.

LAN Telephony
Simply put, LAN telephony is a communication mechanism that uses the enterprise’s data network to transmit packetized voice. This arrangement eliminates the traditional time division multiplexing (TDM) techniques that require the discrete two-wire approach, one for data and another for voice. Even though it sounds and looks deceptively simple, it is an arduous task for the market to accept and implement this emerging communication infrastructure.

Traditionally, enterprises have a telephony infrastructure using proprietary system called PBX. Typically, an ISDN PRI or E1 line is leased from the carrier and connected to the public switched telephone network (PSTN) cloud, enabling voice connectivity across the enterprise. Incidentally, this system has worked extremely well for a number of years.

Even though PBXs are proprietary systems, they were built taking into consideration both reliability and uptime. It was and is always assumed that voice network will be always available and it just works. But for most of its benefits, PBX is a very closed system.

The entire voice system works over the standard telephone cable using TDM, but the data network typically runs on a totally independent cable infrastructure and never communicates with the traditional voice system.

Now the burning question is: how to bring down the cost of infrastructure without compromising upon the functionality of both voice and data?

A Different Ring Is Needed
LAN is one of the oldest infrastructures of an enterprise. It was created to address the concerns of information managers (IS) way back in 1998, when NBX (now part of 3Com) shipped the first packet-based handset on Halloween.

But the time has arrived for enterprises to take the existing infrastructure details and integrate new applications, which aid in bringing down the total cost of ownership.

At the same time, newer IP applications are bringing a whole new set of changes in the LAN infrastructure and hence, it is essential to understand and accommodate these changes and get going.

According to the analysts, LAN telephony market will be about $14 billion by 2005. In 2001, the US alone contributed $1 billion to the LAN telephony market.

Market Trends
Even during the economic downturn, most of the vendors have seen the LAN telephony market grow. IP is no longer scary. Concerns about network reliability, uptime, administration and maintenance work are no more the concerns of IS managers.

Most of the PBX vendors clearly accepted the market reality and announced their LAN telephony support strategy. However, many of those shipments are add-ons to the existing PBXs.

Mostly the circuit-switched voice infrastructure is connected to IP, by using gateways in the LAN environment and is then transmitted across the LAN and finally, to the IP handset. However, all telephony installations may not use IP, many utilize other packet formats. And also not every LAN telephony installations involve a packet handset. Often the call is converted back to circuit; either at the desktop or workgroup (also referred as nodes or zones) level, and a standard analog and digital set can be used.

Why LAN Telephony Now?
A tremendous price advantage in the long run is what LAN telephony is all about, apart from, of course, offering easy manageability and tighter IP application integration in the LAN environment.

It wins hands down on four counts:
n Price: LAN telephony systems are 30–40 percent cheaper than the traditional TDM, PBX solutions. Packet handsets are the only expensive part in the entire solution (some vendors offer almost all features of packet phone over the digital phones).

n Administration: LAN telephony systems neatly fit in the LAN environment like any other IP devices in the enterprise. Benefits include hassle-free maintenance, no need to depend on the traditional voice engineer or a technician to solve any voice-related problems. Data administrators themselves can handle all the problem call escalations.

n New IP applications: Most of the software

vendors have already accepted IP as the default protocol for all applications. Both the availability of IP-related products and the skillset of programmers have become very common. New IP applications can be easily integrated into the existing data network application infrastructure.

n Geographic Reach: It offers multi-site connectivity across different offices spread out geographically, offering low communication infrastructure cost. Collaboration and conferences can be held in real time across multiple offices

Technical Challenges
Even though LAN telephony appears to be a simple and clean technology, the first and the last commandment is the voice quality along with complete reliability.

Technically, the parameters, which influence the data networks, may not be acceptable by the voice network. By their very nature, voice and data are different and the devices, protocols, and the technology, which handle them are also different in nature

Following are some of the IP-based QoS techniques generally used by the equipment manufacturers to address technical problems:

n Compression Technique: Used to address bandwidth-related issues at the cost of latency

n Buffering: Also referred to as jitter. In voice packetization, the packets are sent across the network and some times not all the packets arrive in the preferred order. This phenomenon of time spent waiting for a packet to arrive and re-sequencing packets is called ‘jitter’. Jitter/buffering uses various algorithms for the calculation of packet movement (i.e. when to move forward with or without packet), in order to provide the best speech quality.

n Silence Compression: Silence compression has the intelligence not to send empty voice packets when the user is in silent mode or not speaking for that particular time. This technique is used to improve bandwidth efficiency.

Vendor Selection
Two sets of vendors are fighting it out. One set of people are from pure PBX background (or traditionally voice people) and the second set of people are from pure data communication background. Even though the final solution from both the vendors offer the same result, their approach is totally different.

Data communication vendors claim that they have a ‘pure IP’ solution and they call it IP PBX solution, whereas telecom giants claim that they have a ‘converged solution’ (also referred to as converged PBX).

Whatever be the names and terminologies, both of them are trying to increase their market share and leadership, and at the same time retain the existing customer base.

Which one is better?
It all depends on your business. It is very essential to understand the business needs before leaping into any technology and approach.

In case of IP PBX vendors approach, the entire architecture is based on IP infrastructure, which is currently dominating the market. IP PBX architecture uses packetized voice for all operations until the call actually leaves LAN and enters the PSTN cloud, which is traditionally circuit switched.

But in case of a ‘converged PBX’ solution, both TDM and IP routes are adopted while providing the final solution. Converged PBX offers TCO benefits and these benefits are directly passed on to the end users.

All major communication vendors are supporting LAN telephony and they have announced their strategy and approach towards the IP telephony solutions.

Most of the products are already working and yielding the expected results in the enterprise. However, some of the technical challenges need to be addressed during the actual implementation. The real implementation of LAN telephony and system integration activity is the key for true success of LAN telephony.

Lower per-user equipment cost, reduced administration cost, movement towards standards like H.323, and SIP, are also going to be the key drivers for the LAN telephony market.

Prashanth S Rao
Solutions architect, Nortel Networks India