VoIP and Wireless Networkingby Joseph Harden, Patrick Fenton, Martin Hehir and Eoin Duggan
Voice over Internet Protocol, or commonly known as VOIP, is basically a type of software and hardware which allows people to use the Internet as the transmission medium for telephone calls by sending voice data in packets, or datagrams rather than by traditional circuit transmissions of the PSTN. It enables you to communicate with anyone who has a regular phone number.
Emergence of VoIP and wireless VoIP
VOIP has emerged as a viable way to drastically cut costs of telephone calls, since telephone calls over the Internet do not incur a surcharge on what the user is paying for internet access. One may wonder why there exists a demand for wireless VOIP. Again, money is the simple answer here. Businesses take great interest in decreased communication costs while making use of a reliable and good quality service. Wireless VOIP can be classified as VoWiFi, or Voice over Wireless Fidelity. A WiFi certified system is basically a system standard which allows products to talk to each other, even if they are made by different manufacturers. VoWiFi is mainly designed to work on portable wireless devices such as PDAs (Personal Digital Assistants) or laptops. And it is the growing demand for such devices that has played an important role in the emergence of VoWiFi.
Circuit Switching & Packet Switching
To offer VoIP as a credible alternative to the plain old telephone system, one must understand the technologies that lie within, and the advantages that one may have over another. Circuit Switched Networks are the backbone on which the public switched telephone network is built. It provides reliable voice transmission through a system of digitizing voice and establishing a route between caller and receiver on which all digital voice data will be transmitted. One drawback, however, is that there is high bandwidth wastage if there is actually no voice being transmitted.
Packet Switching networks came to attention with the rise of the internet. In a Packet Switching environment, data was digitized and bundled into packets, which were then sent across the network. Unlike Circuit Switching, these packets would not be sent continuously between sender and receiver, they could each possibly follow different paths to the receiver, thus also arriving unordered. As seen, the big advantage of this is high bandwidth utilization, as Packet Switching never establishes a direct channel between sender and receiver.
So, while packet switching ensured better use of the bandwidth, it was also susceptible to losing packets of data. ATM is another method of transferring data that encompasses the best features of both circuit switching and packet switching. It could use circuit switching for connections where consistency and order is critical, like video and voice. The step currently being taken is implementing VoIP software with wireless systems and mobile technology. However, a couple of issues need to be addressed concerning the reliability and efficiency of packet switching across a wireless network. 
Challenges facing VoWiFi
Various challenges over-shadow the growth of VoWiFi. At present the quality of the voice transmission is poor compared to the quality given from a regular telephone, and connecting is also slower. Other issues are roaming access and security. With regard to roaming access, a typical WiFi Access Point offers a communication range of around 100 metres. This area is also known as a hotspot. The difficulty arises when the caller moves in and out of different hotspots. Most PDAs, laptops and WiFi phones perform full WLAN scans when users enter new hotspot areas. These scans tend to produce a latency of around 400 to 600 milliseconds. The latency has the effect of a reduction in voice quality, and the possibility of the call being dropped becomes more likely. Some solution on the table include selective scanning, but even still a latency exists which is not considered adequate.
A more encouraging approach is to have VoWiFi dual-mode phones that would switch to regular cellular phone transmissions when the user moves in and out of a hot spot's range. Indeed many mobile phone companies such as Motorola and Nokia are in the process of producing dual-mode mobiles that will support smooth roaming between WiFi and non-WiFi areas. Battery power is a basic problem for manufacturers to deal with. VoWiFi devices are drained of huge amounts of power in order to detect incoming calls.
Packet Loss and Signal Degradation
Further to latency, VoIP is very sensitive to packet loss. Wireless introduces its own issues of handoffs, and signal degradation. Coupling these two technologies together requires a certain quality of service to ensure that the VoIP over wireless (VoIPoW, which is the same as VoWiFi) is viable as a technology and a business. Some of the QoS guarantees that are given are based on the percentage of packages lost and the percentage of packets discarded because of late arrival. The latter is due to the nature of packet-switching, where packets do not necessarily arrive in order. So the need to ensure voice consistency requires discarding of late packets rather than sending them on. A small percentage of packages lost or discarded would ensure a pretty high quality VoIP transmission. However VoIPoW requires more QoS guarantees. As mentioned before, handoffs between base stations becomes an issue because it introduces additional latency time when VoIPoW users are roaming. Signal degradation is another problem for the obvious reason that if a user roams away from a base station, the signal will get progressively weaker, thereby degrading the quality of the VoIP connection. A possible solution to the latter problem would be to increase the number of base stations, while the former may be solved by increasing the power of the signal from the base stations. VoIPoW is an emerging market which already has its customers, and it must believe that with the expected advances in technology, it can not only address the problems presented above, but to make them seem almost insignificant.  
VoIP that is transported via a wireless network requires three levels of security: One for the voice transmission, another for its associated control signaling and configuration, and another for the WLAN channel by which voice traffic is transported. Current generations of WLAN products use WEP (Wired Equivalent Privacy) as the security mechanism for the network to authenticate the user, and encryption of the data between an Access Point and a Client Station. The authentication that is provided by WEP does not allow for two way authentication, i.e., the user does not authenticate the network. Additionally, reuse of keys in WEP allows for a hacker to break the key fairly easily, and WEP does not allow for any automated key exchange mechanism. Hence, in most cases WEP is not implemented. The 802.11e standard attempts to address the issue of QoS. Replacing the current proprietary voice QoS offerings, this standard would provide a vendor independent QoS service. The 802.11i standard addresses the security weakness in the original 802.11 standard. Two approaches to solve this problem have been studied: Enhanced encryption that can be utilised on existing hardware. Enhanced encryption that may require hardware upgrades. This standard specifies use of the Advanced Encryption Standard (AES).  
Dedicated VoWiFi Product Development
The feasibility of VoIP products are clear and it is obvious why companies are interested in harnessing this emerging technology in order to reduce costs. The added complexity that the use of a wireless network involves may be a deterrent, but it is a fact that within a building (such as an office block), the signal strength of the wireless network in place could be and often is far superior to that of a conventional mobile phone.
In terms of product development, as previously mentioned, Motorola, Ericsson, Nokia, Zyxel, Vonage and Siemens have all launched products that serve to advance the use of VoWiFi. Indeed, as early as 1997, Nokia, Ericsson, Unwired Planet and Motorola joined forces to create an "open protocol for interactive wireless applications". In the short term, this cooperation served to pave the way for limited internet applications like WAP to make their way onto mobile phones, but this convergence of technologies was also to aid the emergence of mobile phones using wireless networks and the regular mobile networks.
Currently service providers for SIP (session initiation protocol) such as sipgate provide rates that no traditional telecoms company can match. Sipgate is not catering for the wireless market, but it is clear that where the VoIP market is being opened up, the VoWiFi market will be sure to follow. 
So do the VoWiFi phones work? In the aforementioned hotspots they work excellently. However, there are currently only 45,000 hotspots in 65 countries, with 127 in Ireland. The hotspots are currently only in densely populated areas but this is sure to expand. The current phone offerings, such as the ZyXel Prestige 2000 work reasonably well, but about an hour and a reasonable level of technical proficiency are required for the initial setup, but pre-configured phones should be easy to provide, should the service take off. As mentioned above, there is definitely room for dual mode mobile phones, and Motorola Inc.'s CN620 phone is a recent example of such, supporting both voice and data services over wireless LANs and GSM cellular networks. It automatically selects the least expensive option for calls .Within a week of the Motorola launch, Hewlett-Packard Co. and T-Mobile USA unveiled the iPaq 6315, a handheld device that allows voice services over GSM and data communications over GSM, Wi-Fi, and Bluetooth technologies. 
This is only a small sample of the products currently coming on-stream, but it shows that the heavyweights of the communications industry have been taking this area very seriously from the developmental stages in the nineties right through to today, where highly sophisticated devices are facilitating the emergence of increasingly cheaper telephone calls. Even apart from the phones themselves, a glance at the Hotspot Directory shows that the infrastructure is surprisingly advanced in Ireland for a technology that has not been publicised.
2004 is the most recent year for statistics, and they show that 113,000 wi-fi phones, using VoIP over wireless, were sold worldwide last year. This may not seem like much, but it did generate $45million in total sales, an encouraging start from a developing business. Projections for the next five years are as follows:
As indicated, the projections for 2005 are 2 million sets sold. There are currently no projections for years after this, but it is believed that 2009 will be the breakthrough year for wi-fi phones in the public consumer market.  
The Future Of Wireless Voip
Today's WLAN products are mostly 802.11b standard or WiFi. The 11Mbps data rate supported by this standard meets most of the data rate needs of today's applications. However, the demand for increased bandwidth is never-ending as customers see applications for wireless video and the like, but the new "A" and "G" standards support 54Mbps (and higher). However, Access Point proximity dictates the exact effective data transfer rate.
As mentioned previously some vendors that have announced support of 802.11a or 802.11g for a wireless VoIP application; most are still 802.11b compliant. Even when these do become available, there is a potential of greater power management demands in both "A" and "G" devices that may impact the length of battery life.
However, the "standards" are still evolving, and as said before, the
two major functional elements that will have the greatest impact on standards
are improvements on QoS and Security. It can safely be assumed that once
these issues are successfully negotiated, VoWiFi will cement its place
as an essential business and customer tool.