A VoIP system uses SIP protocols, enabling call connections between you and your communication target. SIP telephone systems enable simple computers and SIP endpoints to handle incoming and outgoing telephone calls through an internet connection.
Implementing SIP calling allows users to reach their international business contacts and clients more cost-efficiently than with other conventional systems. Companies that transform to VoIP System reduce their expenses by $5,000 per year.
Call audio quality requires disabling SIP ALG on your router, among the initial measures needed to achieve this outcome. In this detailed blog, we will discuss about SIP ALG and why we need to disable it.
What is SIP ALG?
The abbreviation SIP ALG represents the gateway functionality that operates at the Session Initiation Protocol Application Layer. Most commercial routers offer this technology through the application-level gateway name, enabling users to start SIP calls more reliably even behind secure firewall-configured LANs. ALG is a NAT tool that converts private network addresses and ports to public IP addresses and ports.
The SIP ALG operates independently from router firmware to prevent network firewall issues. The ALG assesses the SDP section of data packets before applying the necessary changes to ensure correct transmission. All VoIP systems convert voice signals into data packets for network transmission, and hence, they should enable quality communication.
The multiple processes within SIP combined with fragile data packets result in technology that typically diminishes SIP call quality. Phone system providers usually recommend disabling routing alteration for the security feature because such modifications negatively impact SIP communication quality.
How SIP ALG Works?
SIP ALG (Session Initiation Protocol Application Layer Gateway) is a feature found in many routers designed to assist VoIP traffic by modifying SIP packets as they pass through the network. It aims to resolve NAT-related issues by adjusting the packet headers to ensure proper routing.
However, instead of improving VoIP performance, SIP ALG often causes disruptions such as call drops, one-way audio, and registration failures. Understanding how SIP ALG works helps in diagnosing and resolving VoIP connectivity problems, ensuring a smoother communication experience.
i. NAT Traversal
Standard network operation with NAT changes internal IP addresses into one or several external IP addresses. SIP encounters complications during traffic routing because NAT modifies SIP messages that contain original IP addresses within the payload.
The header modification process in NAT directly affects traffic control through packet headers without altering the payload section, thus causing inconsistencies in the header-payload address.
The working principle of SIP ALG involves analyzing SIP packets to modify both SIP headers and SDP (Session Description Protocol) body communications so that internal network private addresses transform correctly to public addresses or maintain their original state. The correct data transmission between internal and external networks remains consistent because of this process.
ii. Modification of Traffic
The NAT device operates detection functions on traffic, resulting in content modifications. The SIP headers, IP addresses, and ports need modification to match the same properties that NAT utilizes. The firewall requires adjusting its dynamic pinholes to enable SIP traffic transmission.
iii. Handling of SIP Sessions
Active session tracking by SIP ALG enables it to modify the network routing patterns that direct return packets to the correct destination. This approach modifies SIP keep-alive to keep sessions active and manage expiration times.
iv. Resolution of SIP Signaling and Media Paths
SIP ALG maintains correct IP address and port referencing in multiple signaling messages between request and response pairs because it handles the translation process for these connections. It also modifies the essential packets needed to establish RTP/RTCP media paths between client and server for proper functionality.
How SIP and ALG Interact?
SIP (Session Initiation Protocol) and ALG (Application Layer Gateway) interact when SIP ALG is enabled on a router or firewall. SIP is responsible for establishing and managing VoIP Calls, while ALG is designed to assist SIP traffic by modifying packet headers to accommodate Network Address Translation (NAT). However, this interaction can often cause issues such as call drops, one-way audio, and registration failures due to incorrect packet modifications. Disabling SIP ALG is usually recommended for smoother VoIP communication, ensuring that SIP packets remain intact as they traverse the network.
i. The Invite Stage
During an invite call setup, a user activates the initial contact with another party. Communication initiation starts on your side of the connection.
ii. The Invite Response Stage
Upon this connection, simple data packets notify the phone call’s origin.
iv. The Answering Stage
During the answering stage, users confirm the arrival of an incoming call, keeping the actual call separate from the response. At the receiving stage, a new section of the process begins.
v. The Confirmation Stage
During the last stage, the call connection receives its final confirmation. Organizations using this protocol complete the transmission process from their initial (originator) side.
vi. The Call Stage
After completing all four pre-step procedures, the actual call occurs. This is a two-way connection.The sequence takes a few seconds to carry out data communications that appear complicated due to its four-step traveling procedure. From a connectivity standpoint, using a five-step connection process increases the chances of data packet loss during modification sent through the ALG system.
Why Should ALG Be Disabled?
The problem with ALG modifying SIP data packets becomes worse because the implementation of this service remains poor across most of the commercial router market. Although the ALG service aims to establish better connections by modifying data packets, actual results show that the connections become more confusing.
When the system verifies an attempt to connect the ALG changes the packets of information in SIP. A scripting process accomplishes this IP address and port conversion from private to public domains. The risk of scripting causes substantial message content to disappear at some point throughout the translation process. A change in connection status through SIP ALG will influence VoIP telephone operations in various ways.
i. Failed Registrations
The system fails to establish a connection for calls whenever any required acknowledgment during a phone call does not succeed. SIP ALG frequently causes failed registrations that appear due to its background operations.
ii. One-Way Audio
Your communication remains clear, even though the other caller experiences complete audio silence. Poor firewall adjustments or SIP ALG-packet modifications generally cause missing audio during one-way SIP calls.
iii. Dips in Call Quality
Any internet-based call experiences three common indicators of packet loss: static noise, silence periods, and echo effects. Modifying the call quality degrades data for both transmission and receipt.
iv. Lost Connections
This router service allows users to disconnect from the call quickly. A total system data loss immediately disconnects the user from the computer interface.The possibility of incorrect data packet modification increases during SIP calls because it negatively impacts call quality. Users can typically find router service interfaces on the web page to easily disable this feature. However, a new router is necessary if the feature does not appear on their device.
How Do I Turn Off SIP ALG?
Accessing your router controls will enable you to turn off SIP ALG service. The gateway combination of your router and modem occurs when the device functions as a router and modem for particular broadband technologies. These are the popular router brands in the market: Cisco, Linksys, Netgear, D-Link, Asus and TP-Link.
We have gathered information about the leading routers with direct instructions for disabling Application Layer Gateway because this feature disrupts VoIP service.
In most cases, you must log in to your router using the administrator password. To prevent SIP ALG interference, access the security settings, uncheck SIP ALG, save, and reboot your router. Port forwarding is one adjustment skilled users need to make to advanced corporate firewalls.
i. Actiontec
- Select Advanced, perform Yes to validate warnings, and finally, select ALG’s.
- The checkbox for SIP ALG should be removed to disable its functionality.
- Click Apply.
- The gateway issue will trigger an advanced warning. You must click Yes and then select Remote Administration.
- Move to the setting that allows Incoming WAN ICMP Echo Requests (for traceroute and ping) then tap Apply.
ii. Adtran
- The user can find Firewall options by navigating to Firewall / ACLs under the main Firewall menu.
- Click on ALG Settings.
- The SIP ALG setting needs to have its checkbox left blank.
- Click Apply.
iii. Arris
- Most Arris broadband gateways:
- Navigate to the gateway’s IP (192.168.0.1).
- Username: admin Password: motorola
- Navigate to Advanced, then Options.
- Uncheck the SIP box.
- Click Apply.
iv. Asus
- To access the Advanced Settings click on WAN under the specified section.
- Click the NAT Passthrough tab.
- Users should disable SIP Passthrough by changing its settings under this option.
- Click Apply.
v. D-Link
- Click on Advanced Settings.
- Explore the menu for Application Level Gateway (ALG) Configuration.
- Uncheck the SIP option.
- Click Save.
Final Words - SIP ALG
SIP ALG might have been designed to help, but in most cases, it does the opposite—it disrupts VoIP calls by modifying SIP packets in ways that interfere with call quality. If you’re facing call drops, one-way audio, or connection failures, SIP ALG could be the hidden culprit. The good news is that you can easily disable it on most routers, which often resolves these frustrating issues.
VoIP is an essential tool for businesses and individuals alike, and it is crucial to ensure transparent, uninterrupted communication. To significantly improve your VoIP experience, you can disable SIP ALG and optimize your network settings, such as port forwarding and QoS (Quality of Service) settings.
If problems persist after disabling SIP ALG, consider investing in a VoIP-optimized router or consulting your VoIP service provider for further guidance. A properly configured network eliminates unnecessary disruptions, ensuring smooth and reliable VoIP calls whether you’re working remotely, conducting business, or staying in touch with loved ones.
FAQs - SIP ALG
Q1. What is the purpose of SIP ALG in routers?
SIP ALG is designed to help SIP traffic pass through NAT, but it often causes VoIP issues instead.
Q2. Can SIP ALG affect all types of VoIP services?
SIP ALG can interfere with most VoIP services, including business phone systems and residential VoIP providers.
Q3. How do I know if SIP ALG is causing my VoIP issues?
If you’re experiencing call drops, one-way audio, or connection failures, SIP ALG might be the cause. You can check your router settings or test VoIP diagnostics.
Q4. Are there routers that don’t have SIP ALG?
Yes, some VoIP-optimized routers do not include SIP ALG or allow easy disabling of the feature.
Q5. Can a VPN help avoid SIP ALG interference?
A VPN can bypass SIP ALG by encrypting VoIP traffic, but it may introduce additional latency.
