How to choose a new phone system: choosing your lines

Just as there is some complexity in your choice of IP, digital or analog phone system, there are also things to consider regarding your lines from the outside, ie which type of connection you purchase. Some of the terms are the same but it doesn't mean the same thing.

Analog - 1 user

An analog connection from the outside is just a physical consumer grade line with a number. The regular phone line which most people have in their home is an analog line. Your voice is picked up by your telephone mouthpiece and then sent down the phone line as an analogue wave form. In other words, your quality is 50% or 90% depending on other factors, rather than "yes" or "no" as is the form with digital. Analog phone lines are the old style of provisioning and requires a seperate copper line for each number; once upon a time offices used to have many individual analog lines going into them for many individual analog phones. Nowadays other technologies have largely displaced lines such as these for offices.

With only analog phone lines to the outside, there is no point in purchasing a digital or IP phone system as the advantages of these cannot be realised using an analog line.

ISDN2/ISDN2e - 2-8 users

To transmit data, however, it is far more efficient, and simpler to keep it in its original digital state. ISDN2 is a digital line to the outside; ISDN2 is the smaller of the type of ISDN connections and is usually the connection of choice for the smaller office. ISDN2 is installed in pairs of channels. As ISDN2 is a digital multi-line connection each line is referred to as a 'channel' rather than a line. This means that each ISDN2 line refers to a pair of channels. ISDN2 allows users to send voice, video and data; being digital it gives excellent voice-call quality; it permits fast data transmission and all the possibilities of a digital telephone system. ISDN2 allows offices to do 2 things at once - (ie use one line for data the other for calls) and costs less than two conventional phone lines. The digital nature of ISDN2 allows the use of a variety of services:

ISDN2 also permits the addition of DDI extensions: it is possible to add up to 50 DDI numbers onto 2 incoming ISDN2 lines. However, ISDN2 is limited to 8 channels which is why ISDN30 is more appropriate for 8+ users:

ISDN30/ISDN30e - 8+ users

ISDN30 is a higher capacity version of ISDN2, designed for bigger offices with more simultaneous calls. ISDN30 is the connection of choice for larger small offices of 8 users or more. ISDN30 is an efficient line technology and much of the line management (ie adding additional channels) can be organised without the cost of additional engineering visits.

Each ISDN30/30e connection/line provides 8-30 independent 64k channels. Any of these lines can be combined for bandwidth hungry applications such as high quality video conferencing or transferring large data files. ISDN30/30e can be used for creating a wide area network that will link multiple offices together. ISDN30 is supported by most local exchanges so it is available in most areas. A single ISDN30 connection has between 8 and 30 64k channels, in normal operations these can all be used separately, allowing simultaneous calls to be made, each call utilising one of these channels. Unlike ISDN2 which is limited to 50 DDIs, with an ISDN30 connection, an unlimited number of DDI numbers can be added, allowing anyone to dial directly through to the right department or person without being passed around the company.

SIP

SIP, or session initiated protocol, is a phone line option that differs from analog and ISDN as it is carried over a data network, be it ADSL, SDSL or leased lines. SIP uses a data network but can be partitioned from the data over that network in order to assure quality of service. By utilising your data connection, SIP negates the need to spend money on monthly line rental for ISDN2 or ISDN30 circuits. Calls sent over SIP are much cheaper than calls sent over traditional telephone infrastructure, thereby saving on your monthly call costs. And, because SIP is provisioned over your existing data connection, provisioning is done instantly as there is no need for ISDN circuits to be installed. Unlike with ISDNs where you have a maximum of 30 channels per circuit, a SIP trunk is fully scalable so you can have as many or as few as users as you want. SIP is also the only way to port geographical numbers, so if your office is relocating from London to Manchester and you wish to retain your London number, you will want to use SIP.

But, with SIP, the quality of your connectivity is paramount. Although it is possible to run SIP Trunks over the public Internet, we do not advise this. Phone calls are sensitive to delay, variations in delay and data loss (aka latency, jitter and packet loss). For this reason, we do not recommend that purchase of SIP without good connectivity.

SIP or VoIP

A VoIP phone system is also carried over a data network: its name means "Voice Over IP". Voice over IP is a broad term referring to any method of voice transmission using IP networks as a medium. For example Skype is VoIP, ICQ, Google and some other messengers have VoIP plug ins. VoIP can be over ADSL, SDSL or leased lines. SIP, however, is a highly specific form of VoIP which specifically delivers the PSTN (Public Switched Telephony Network) to SIP endpoints (User Agents). More specifically, VoIP is a technology used in modern telecommunication networks whereas SIP is one of various possible signalling protocols (control protocol) used when using VoIP.

Why use SIP?

SIP offers cost savings:

One of the beauties of SIP is the ability to integrate an IP PBX application server alongside data servers on a single network - and to administer them all from that same converged network environment. Don’t use a SIP architecture, however, and your business is left staring at The Great Voice and Data Divide from disjointed phone equipment and data systems and their equally disjointed administration.

Worse for your enterprise if it maintains multiple offices, bypassing SIP inhibits the ability to standardise technology across sites for users, desktops and customer features, which can lead to business process disparity from site to site, business continuity management issues and inconsistent service levels for customers, not to mention the expense of maintaining lines between remote office locations.

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