If you use Voice-over-IP (VoIP) in your organization, you can add an H. 323 or SIP (Session Initiation Protocol) ALG (Application Layer Gateway) to open the ports necessary to enable VoIP through your Firebox. H. 323 is commonly used on videoconferencing equipment. SIP is commonly used with IP phones. Likewise, should I disable ALG?
You should disable SIP ALG because it: Interrupts SIP traffic like calls and conferencing apps. Affects the perceived reliability of desk phones and VoIP apps. Isn't needed when using cloud-based VoIP providers.
Secondly, should I enable H 323? It is recommended though to keep it on unless you experience issues such as in the KB article below. OR the alternative is to open up the actual ports used by your H323 traffic (not using the built in H323 service but by creating a custom service with high ports open as well as necessary).
Herein, what is H323 used for?
H. 323 provides standards for equipment, computers and services for multimedia communication across packet based networks and specifies transmission protocols for real-time video, audio and data details. H. 323 is widely used in IP based videoconferencing, Voice over Internet Protocol (VoIP) and Internet telephony.
What is H323 protocol?
H. 323 is, much like SIP (Session Initiation Protocol), a protocol designed for the setup, management, and termination of a media session. It is one of a set of standards from the ITU-T, which defines a large set of protocols to provide audio and visual communication over a computer network.
Related Question Answers
What happens if I disable ALG?
There will be times when the expected behavior of protocols will not be what is expected by the Security device. In this case, you may not get the same behavior when an ALG is disabled, such as: Sessions not clearing up on time. FTP data channels not working. Should I disable NAT passthrough?
The benefit of disabling VPN passthrough is enhanced security by blocking open communication ports through the firewall that otherwise would be open and accessible. The drawback is that a user behind the gateway would not be able to establish a VPN connection, since the required VPN ports are blocked at the firewall. Why is SIP ALG bad?
A SIP ALG can re-write SIP packet headings, which can mangle the delivery process. This can make the device you're calling believe that your phone is not behind a NAT, when in fact it is. If an ALG disrupts a call, it can lead to incoming call failure, and phones that unregister themselves. What does SIP ALG stand for?
Session Initiation Protocol Application-Level Gateway
How do I know if my SIP ALG is disabled?
Ask your SIP provider - these days many of them have a way of testing for the ALG, some even put it on their "dashboard". Or call their tech support and ask them to confirm. Or just connect the phone and make some calls - you'll soon find out if the SIP ALG is still active, you'll get one-way audio or other issues. Is SIP same as VoIP?
SIP and VoIP are not the same thing, though the terms are often used interchangeably. VoIP stands for Voice over Internet Protocol, which broadly covers any phone calls made over the Internet as opposed to traditional telephone lines. The SIP protocol can be used to enable VoIP. Is H 323 secure?
Security: H. 323 provides authentication, integrity, privacy, and non-repudiation support. Supplementary services: Recommendation H. 323 recognizes the huge potential for applications based on IP telephony and multimedia. Can H 323 also be used for video?
H. 323 is one of the oldest standards which are generally used for VoIP telephony and video conferencing. It is a system of various protocols and elements that allows transferring media data over packet networks. What is the difference between SIP and IP phones?
IP phones are capable of handling voice calls from person to person while SIP phones allow you to do much more, such as making a video conference call. These days, most service providers offer a combined technology of both VoIP and SIP so that you can get everything you need in one convenient monthly service. What is the difference between gateway and Gatekeeper?
A gateway does not handle registration and authentication of devices. A Gatekeeper handles the registration and authentication of devices. The Cisco SIP Proxy would perform this function in a SIP network. The SIP Proxy directs calls between endpoints and gateways. What port is SIP?
port 5060
What is SIP call flow?
Basic SIP session setup involves a SIP UA client sending a request to the SIP URL of the called endpoint (UAS), inviting it to a session. If the user takes the call, capabilities are negotiated and the call commences. If the user does not take the call, it can be forwarded to voice mail or another number. What is video conferencing gateway?
Gateway is a device or software that serves as an interface for incompatible devices and networks that work under different protocols. How does SIP protocol work?
What is SIP? The Session Initiation Protocol is a signaling protocol that enables the Voice Over Internet Protocol (VoIP) by defining the messages sent between endpoints and managing the actual elements of a call. SIP supports voice calls, video conferencing, instant messaging, and media distribution. Is H 323 TCP or UDP?
H. 323 uses TCP port number 1720. What are ALG settings?
Application Layer Gateways (ALGs) manage specific protocols by intercepting traffic as it passes through the security device. After analyzing the traffic, the ALG allocates resources to permit the traffic to pass securely. By default, all ALGs are enabled on a security device. What is ALG passthrough?
Application Layer Gateways (ALGs) manage specific protocols by intercepting traffic as it passes through the security device. After analyzing the traffic, the ALG allocates resources to permit the traffic to pass securely. By default, all ALGs are enabled on a security device. What is IRC8000?
IRC8000 Enables or disables the Internet relay chat protocol on UDP. port 8000 used for text messaging and group forums. Why is SIP better than H 323?
H. 323 fully supports video and data conferencing. Procedures are in place to provide control for the conference as well as lip synchronization of audio and video streams. SIP has limited support for video and no support for data conferencing protocols like T. What communication protocol is needed for video conferencing?
H.323 protocol
Which protocol is used for video conferencing?
323 is a data transfer protocol with non-guaranteed bandwidth applied in both personal and group video conferences. SIP is a network protocol for connecting client applications from different vendors. SIP has replaced H. 323 and is used in video conferencing and IP telephony. What is SCCP and SIP?
SIP is used for establishing, modifying, and terminating IP based communication sessions with one or more participants whereas SCCP is a Cisco proprietary protocol which is used for communication between Cisco Call Manager and Cisco VOIP phones. Cisco devices mainly support both these protocols but run SCCP natively. How does RTP protocol work?
The role of RTP is to ensure a uniform way to transmit data subject to real-time constraints. For this purpose, RTP injects time markers and sequence numbers to the various multimedia streams (audio, video, etc.), controls the destination arrival of the packets, and identifies the type of information transported. 
