Carrying voice communications in IP (Internet Protocol) packets on the same network as data makes sense because having one network rather than two saves money and makes it easier to implement computer-telephony applications. The question is whether now is the right time for enterprises to begin migrating telephony to IP networks.
The answer depends largely on whether existing private branch exchanges (PBXs) and data networks need replacing or still have some time to run.
"If you have already got a large investment in high-end legacy PBXs and have a pretty smart data network, then although there are still benefits in migrating to voice over IP [VoIP], it is not as justifiable in terms of cost," said Matt Winckless, the RSPCA's IT architecture and standards manager.
Animal charity the RSPCA was an early adopter, going live with full end-to-end VoIP in August 2001. Its network is based on Cisco equipment.
"We were running on 14-year-old PBXs, which were up for replacement anyway," explained Winckless. So, to an extent, the RSPCA was a "greenfield" site. In those circumstances the case for VoIP is overwhelming, according to Paul Strauss, research manager for enterprise networks at analyst firm IDC.
Even sites that are not looking to upgrade in the near future should ensure that they are prepared for VoIP and that all future purchases of equipment are made with that aim in mind, said Strauss. "The strategic benefits of VoIP are so enormous that anybody who is not ready for them is making a terrible mistake," he said.
Nevertheless, Strauss believes it would also be a mistake to rush in and replace legacy systems that are working well, especially as there are still some technical issues with VoIP to be resolved. "There are still compelling reasons to be cautious, and you don't necessarily have to jump in," he said.
Strauss cited feedback from suppliers such as Cisco, which has 40% of the market for enterprise VoIP systems, that suggests companies are heeding this advice to prepare. "Cisco tells me it is selling enormous numbers of Lan [local area network] nodes equipped with electrical power so that telephones can be put in - many times more than the number of actual VoIP systems installed," he said. Strauss believes this is evidence that the market is ready for a dramatic acceleration.
At present, the VoIP field is being led by small and medium-sized businesses and branch offices rather than large enterprise sites, said Strauss. This is largely because suppliers such as 3Com have been successful in promoting smaller-scale "tactical" systems sold for telephony, without emphasising the fact that they are actually sending voice communications as IP packets.
However these systems achieve the benefits of IP transmission, avoiding the need for dedicated bandwidth which is idle when no calls are being made, and stopping the transmission of pauses in a conversation.
"Over a traditional circuit-switched call with 64kbps of reserved bandwidth, utilisation is only about 35%," said Rufus Grig, chief technology officer at VoIP supplier Convergent Systems. With a shared IP network, this wastage is avoided, because spare bandwidth can be soaked up by less-urgent data traffic such as e-mails and file transfers.
There are also savings to be made in administration through having just one network to manage. According to Ben Anrep, network
manager at the Consumers Association, the ongoing maintenance cost of a VoIP network comprising purely suitably configured IP routers will usually work out at less than half the combined cost of the routers, PBXs and multiplexers necessary to run separate voice and data networks.
The extent of these savings naturally depends on how much is being spent on the networks in the first place, and works out greater when there are many sites or there is a substantial amount of international traffic. This suggests that multinationals have the most to gain from VoIP, but at the same time they are hindered from migrating by legacy PBXs that only support circuit-switched voice.
Quality is often cited as an impediment to adopting VoIP, but this no longer applies to private IP networks, because it is possible to allocate and reserve guaranteed bandwidth for voice at the temporary expense of non-real-time data.
Voice over the Internet is another matter, for at present it is impossible to guarantee quality when there is no control over the whole of the end-to-end transmission path. For this there needs to be a protocol for signalling and negotiating quality of service between successive networks along an end-to-end path.
But for enterprises with private networks, the greater technical concerns are over security and availability. With VoIP, voice is just a type of data and so becomes exposed to the same risks and threats as other data. The systems tend to run on ordinary servers and PCs and so are vulnerable to external hackers and viruses to which traditional circuit-switched voice networks are immune.
A related issue is the fact that, generally, lower levels of availability have prevailed - and been tolerated - on data networks than for telephony. But, as Steve Cramoysan, Gartner Group's EMEA team leader for enterprise networking, pointed out, the problem for VoIP is as much perception as reality. "It may well be that VoIP will be just as secure and reliable, but until it has been installed for some time it will be impossible to prove that," he said.
For these reasons the RSPCA was assiduous in piloting VoIP before full roll out. "We needed to ensure that we could obtain from an IP data network the 99.999% level of availability of a traditional voice system," said Winckless. This was achieved through network and system redundancy, and the use of servers dedicated to VoIP. So far there have been no failures.
In some cases, as at the Consumers Association, the use of VoIP is restricted to inter-site traffic to exploit the bandwidth and management cost savings. In others, such as the RSPCA, voice is also carried over the Lan, which confers additional benefits by having just one physical network, reducing costs and also making it easier to integrate voice and telephony for applications such as unified messaging and screen popping in call centres.
Implementing VoIP over the Lan will usually require an upgrade to the existing network to guarantee voice quality, and IP phones will have to be supplied to users. IP phones still cost considerably more than conventional handsets, and in practice most sites will wait until they need an upgrade anyway.
VoIP can also score significantly for teleworking, making it easier to include homeworkers in workgroups. At this level VoIP leads to immediate capital cost savings.
Winckless said, "Our homeworkers can log on and take calls at home as if they were part of their call centre group without having thousands of pounds worth of call distribution equipment in their living room. They can also access their unified messaging mailboxes and do not need answerphones or fax machines. This is quite a saving as we have 500 people working this way."
According to Strauss, in the longer term the real prizes that VoIP will bring are strategic, while the impediments are merely tactical. "Ultimately it will make the telephone a much more productive tool than it is today," he said. It will also act as an enabler for deeper levels of interaction between computing and telephony, and some enterprises, such as the RSPCA, are already reaping the rewards.
The pros and cons of voice over IP
- It is hard to justify the expenditure, particularly in the Lan, if existing networks still have some time to go before they would otherwise need replacing
- There is a perception that quality is not so good, and further progress is needed with the transmission of the silences that naturally occur in telephone conversations
- There are fears that telephony services could be threatened by viruses and denial of service attacks
- If not managed correctly, availability levels could be closer to those of traditional data networks rather than the higher standards expected for voice
- A lack of agreement over standards means interoperability is an issue.
Case study: VoIP on the Consumers Association's Wan
The Consumers Association is implementing VoIP on the wide area network (Wan) that connects its three sites, but it has not yet rolled it out to its local area networks (Lans).
As is the case for many businesses, it is a largely a matter of timing, for there is still some life left in the existing PBX at one of the sites and until this is replaced it would be impossible to transmit data over the Lan there.
Over the Wan, an eight-year-old multiplexer network is being replaced by a router-based IP network. The change is motivated by the prospect of reducing ongoing communications costs by more than half.
The main technical issue being resolved at present is whether to go for G.729 encoding of the voice, which compresses it down to 8kbps per channel, or whether to make do with the more mature but less efficient G.711 encoding which transmits at 64kbps. In either case, the use of packetised voice will avoid the need to transmit the pauses between words. "It is a question of ensuring that G.729 is reliable enough, which it probably is," said the association's network manager Ben Anrep.
The main concern, as for many of the present crop of relatively early adopters, is service availability, given the very high standards that have long prevailed for circuit-switched voice - and which business users have come to expect.
Ironically, the lingering quality issues concern the transmission of the silences rather than the speech. Normally during a conversation there is some background hiss which is heard during the pauses, but VoIP saves bandwidth by not transmitting this. To compensate, some systems attempt to regenerate this at the receiving end. According to Anrep, they fail dismally so the Consumers Association turned this option off. "We found this 'comfort noise' actually made the quality worse," he explained.