which VoIP protocols to use ?

Posted on 2004-11-23
Last Modified: 2012-06-27
Dear VoIP experts,

I am the IT manager of a medium size company of about
170 users. We are in the market for a new phone system
due to the fact our exsisting PBX has reached its time
(12 years old). Purchasing a system that is VoIP
based/enabled is not a problem, actually a requirement
from our management.

The problem I have is that we have narrowed down the
participants to Cisco, Avaya and Altigen. At the end
of the day most of the main features are an
apples-to-apples comparison, but one thing, which VoIP
protocols to use? H.323, SIP or MGCP? Is there any
information on which one would be better to use/implement?
Question by:anim8n3d
    LVL 3

    Expert Comment

    LVL 5

    Expert Comment

    I know that H.323 is an old protocol, obsoleted by SIP.
    No idea about MGCP.
    LVL 5

    Expert Comment

    mgcp can be simple to setup, but usually you'd use 323 over it.  323 isnt an obsolite protocol, not yet at least.

    if you use Cisco, calls only use 16k of bandwidth (1/2 to 1/3rd of other vendors the last i heard, but that may have changed) and managing callmangers is very very easy once the switches/phones are up.

    I dont expect it to be accepted at the corporate level any time soon, but the Linux based PBX Asteriks is actually on the rise very quickly.  Many of my friends in the business have moved medium (100-300 employee) size company's over to it without any problems at all.

    Of the 3 you've narrowed it down to, I'd recommend Cisco.  More standard, more support, more people have done it and you can find help online about it, and with most of your network likely already Cisco, it's keeping things standard.

    Expert Comment

    I would recommend seriously considering Nortel if you are interested in pursuing VoIP at this time (  They are a telephony company and have been building stable VoIP solutions for many years.  Their current systems are based on H323 but like most of their competitors, they are moving (slowly) to SIP.  I know the temtation is to slide up to the bar and partake of the Cisco cool-aide, but do some serious research and ask for each of the vendors you are considering to provide solid references (of your company's size) who have been using the system for longer than 3-6 months.  Avaya also makes a solid VoIP solution, but the "cover charge" to get the VoIP functionality, may be a little steep.  I work for a fortune 50 company and we have been looking at Cisco and Avaya for well over a year.  The phone on my desk is still an Avaya digital set.  Do the research, there are major pitfalls in any emerging technology.

    As far as codecs are concerned, unless you have a need to squeeze the bandwidth, stick with something like G.711.  It is 64K per channel and no one is going to complain about the quality since the telcos have been using it for years.  Also, do not forget about Quality Of Service (QOS) on you network.  I have seen too many voip solutions reduced to a sputering, choppy mess the moment that "Bob" two cubes down decides to download the latest service pack form microsoft.

    BTW: I do agree with zerofield on Asterisk. It is a serious contender in many applications and is remarkably stable.  I currently use it for my home voice mail and love it.  The down side is it does take a bit of knowledge to get it up and running.

    LVL 12

    Accepted Solution


    To help you choose you need to understand where the protocols came from and are going. To start MGCP is around but is the one of the three that is really not deployed much, Cisco is about the only company that does. For various reasons it never took hold and had a chance to compete.

    The battle between which VoIP protocols to use has been going on for years. Being that my foundation in Convergence started in the voice industry, I was heavily biased towards the use of H.323, being the standard came from the ITU. In the early days, SIP (from the IETF) was very primitive in its call control and implementation. H.323 is very stuctured and reliable but is a compilation of various protocols from various areas. So its a bit like Frankenstein. SIP is text based and very flexable.

    H.323 took a hold a few years ago and seemed to win the VoIP protocol war, the Cisco centric folks think it was mostly part to Cisco, but this is really not the case. The main cause at the time was 911 and CALEA (this enables law enforcement to monitor and record packet based voice networks). CALEA was passed in 1994, but never adheared too for various techinical reasons by the carriers, many extenstions to the time deadline for compliance were passed over the years. But after 911 the goverment could not wait nor extend the deadline for compliance; H.323 was the logical choice at the time for the needs to be able to record and monitor.

    Now years have passed and SIP has leapfrogged past H.323 in features and functionality (with the ability to be recorded and monitored). Also, H.323 is so tightly structured that it is very hard  for it to adapt to the fast moving nature of the IP telephony movement.

    I believe that SIP is the standard to go with for various technical reasons, but more so that the industry has really geared toward the use of it as the de facto standard. This is evident if you look at the services and products being offered by such companies as Microsoft, Vonnage, Polycom, Cisco and countless others.

    Also SIP will allow you to deploy a host of other services for end clients (additional revenues), such as various hard based and soft based phones; deploy additional technologies such as WiFi, Bluetooth and cellular based. By using SIP you can start looking at companies such as Vonnage and other SIP based carriers to terminate or originate calls. Additionally by using SIP you can look at various ASP based applications . SIP is allowing for the VoIP enabling of applications and truly allowing for a Converged Network.

    Kindewst regards,

    Joel Sisko

    LVL 3

    Expert Comment

    Joel has a good summary. All I would add is that you want to pick a protocol that has good vendor support. I worked at Cisco on the first VoIP gateways, and we tried hard to avoid picking favorites and to let the market decide -- so we did them all: H.323, SIP and MGCP. H.323 was further ahead in terms of features than the others due to its long history in video conferencing, but SIP seemed to be "sexier" to many people (I never figured out why that was). H.323's feature richness meant that a lot of it was deployed by carriers and ISPs, so it became even more popular as a result -- the "network effect". Still, different carriers had (still have?) their pet favorites: MCI/Worldcom loved SIP, AT&T and Level 3 loved MGCP, China Telecom, China Mobile, China Unicom loved H.323.

    Today, SIP has matured and there seems to be equally good support for SIP and H.323 from vendors -- not too much to choose between the two. MGCP never seems to have really taken off in terms of deployed units. The only large scale MGCP deployment I know of is AT&T CallVantage, which uses MGCP to control the VoIP terminal adapter. This also seems to be why AT&T has the poorest range of VoIP terminal adapters available!

    And so... I think it does not matter whether you choose SIP or H.323. But I'd stay away from MGCP for enterprise use.


    LVL 12

    Expert Comment


    Think the main reason that SIP has taken off is really the fact that H.323 was after the fact, while SIP was able to capitalize off the sucess and failures of H.323 and be built from the ground up with an open mind to incorporating new technologies. Essentialy it has the right foundation made from one construct, whereas H.323 foundation is a bunch of different buildiou have?ng blocks.

    Also VoIP is almost a rebellion against the "establishment", so by using H.323 (ITU) you are conforming which is not "sexy" for those young and upandcomig programmers.

    So how much traditional PBX experiance due you have? Any structured cabling?

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