VoIP / SIP

VoIP (Voice over Internet Protocol) and SIP (Session Initiation Protocol) – are methods of IP (Internet Protocol) signaling to utilize data circuits to carry voice traffic.  There really are two major forms of voice services used by larger sized businesses.  TDM or Time Division Multiplexing was the most common form of voice transmission until the VoIP concept was refined and became commercially usable in the mid 1990s.  TDM circuits are dedicated digital circuits that run between a telephone company central office (switching center) and a business location.  They are not shared circuits – they are private and normally are terminated in a T1 or DS3 directly into your PBX, IP PBX or Predictive Dialer application.  The jury is out as to whether TDM or VoIP is the most cost effective and most of the time it is determined by the size of the business and the specific application.  TDM circuits come into your building on dedicated copper wires, COAX cable or Fiber but the key in all of these circuit types is they are dedicated circuits.  VoIP and SIP are not dedicated circuits.  They flow over the public Internet or private corporate networks and utilize data circuits.  Most data circuits used for VoIP and SIP transmission can be shared with other computer and data applications (thus they are not dedicated).

Primary Differences Between “VoIP / SIP” and “TDM”

Flexibility, quality and cost.  VoIP / SIP transmission is much more flexible than TDM because it is not dedicated.  The SIP trunks can be pointed at almost any data circuit going to any compatible data device.  This allows voice traffic to be easily transferred to another location and it also allows the voice instruments (normally SIP compliant telephones) to access the services anywhere there is Internet access.  TDM circuits are less flexible because they are dedicated.  They terminate in one place, they can only be accessed in this location or on its network (there are exceptions here) and they are limited by the PBX or switching equipment that controls them.

The overall quality of TDM circuits is almost always better than VoIP/SIP.  The trade off is less flexibility and sometimes cost.  A TDM circuit comes into the PBX or IP PBX on dedicated circuits.  These circuits can be tested and maintained to produce consistent and high quality voice transmission.  Trouble shooting is easier than VoIP / SIP because the TDM circuit can be tested end-to-end with highly accurate testing parameters.  VoIP / SIP transmission quality can be very good also, but it is dependent on many uncontrollable factors.  One of the major factors is the Public Internet.  Traffic congestion on the Internet can cause voice quality issues that are difficult to troubleshoot.  Troubleshooting is difficult because the Internet congestion can come or go in seconds and therefore the technician is looking for a “moving target”.  Quality of the data circuits also influence voice quality.  A critical component of Internet transmission is lag time.  Lag time is the round trip timing of the signal.  Voice clipping or missing words in a conversation can occur if lag time is excessive or it varies too much.

Cost differences between VoIP and TDM circuits vary according to number of circuits, signaling format, and overall size of the application.  The only way to really know a true comparison of price is to place equal configurations side by side.  Our Instant Quote can do that for you and our consultants can help you and your company decide which is the best service for your application.  Cost of a TDM circuit has three main variables:

1. The loop price for the “last mile to your office”
2. The port price of the circuit delivering the service
3. The usage cost of the service itself (local, LD, intrastate).

The cost of the VoIP / SIP configuration has the same three variables as TDM plus the voice service charges of the carrier.  The biggest wild card for VoIP / SIP pricing is the cost of the Internet access due to the variance in quality, bandwidth requirement, transmission format used and the termination cost.

A general rule of thumb for cost comparison is small configurations are more cost effective in VoIP / SIP format, medium configurations are more cost effective in a TDM format, and larger configurations can go either way.  The biggest advantage when comparing cost in a call center application is volume of long distance.  A call center running multiple millions of minutes per month will rapidly overcome the higher cost of circuits.  All of these are factors that our consultants can help your company evaluate.  There is a drop-down menu above entitled “Our Process” that will explain the sequence of events we recommend to reach the best solution for your business.

Quality versus Price

There is no denying the fact that TDM circuits are more consistent and reliable than VoIP / SIP.  There also is a major misconception in the marketplace that VoIP / SIP are less expensive than TDM circuits.  The only way to positively know is to run a comparison of the actual cost of your company configuration.  VoIP / SIP is more flexible and in a very high usage environment are going to be less expensive.

 VoIP / SIP Packet Sizes

Internet transmission of voice requires the voice to be placed in packets for transmission.  The size of the packet varies with the format used, the vendor’s individual packet size requirement (determined by their equipment), and the overall voice quality needed by the customer.  As a rule – smaller packets deliver less quality while larger packets deliver better voice quality.  Smaller packets keep bandwidth use costs lower (you use less bandwidth).  TDM circuits are delivered over dedicated circuits but a TDM voice path is 64 Kbps and the bandwidth use does not vary – no higher and no lower than 64 Kbps for each voice path.  There are two major formats for VoIP / SIP transmission.  The highest quality is G 711 and the packet size varies by provider and the equipment they use.  G 711 uses a minimum packet size of 64 Kbps and a maximum size of 90 to 100 Kbps.  The variance is determined by the provider.  G 729 uses a minimum of 22 Kbps and a maximum of 50 Kbps but the overall voice quality is going to be lower than G 711.  There are variables to these numbers due to the differences in the equipment manufacturer’s and provider’s specifications BUT – these are the average sizes.

We Can Help Configure and Price

All of the elements we just discussed go into the design, configuration and pricing of your network.  Our consultants can help compare the results that come from our Quoting System and then fine tune the configuration and pricing to optimize it for your call center.  Our experience and knowledge in all sectors of the industry combined with the quote results will also help us make solid recommendations that you and your company can compare side-by-side for the optimum solution.