How Voip Phones Register To A Gateway

IP desk phone with loading icon

If yous are a voice network engineer, then information technology has probably happened to you. Your SIP server is all gear up and yous accept plugged in your IP phone. Its lights come on, its screen is activated, you see the loading icon rotating, and then… nothing. For some reason, the phone will not register.

IP phone registration issues are, unfortunately, not uncommon. In this article, nosotros examine the most common causes of registration failures, and best practices for troubleshooting and resolving them.

How does a SIP device register?

To place the registration problems that can ascend, we must commencement understand how the registration of an IP telephone takes place using the SIP protocol. Although we are focusing on IP phones, the same can be applied to whatsoever SIP endpoint, including SIP clients (softphones), vocalism gateways, or teleconferencing systems.

In order for a SIP IP phone to part, it must register to a SIP server, as well known every bit an IP PBX. A SIP account with a SIP URI (compatible resource identifier) and password must exist created inside the SIP server. Depending on the manufacturer of the SIP server, additional characteristics can be configured on each individual business relationship. The IP phone is provided with that SIP URI and countersign, equally well as the IP address of the SIP server. The phone then begins the registration process by sending a registration request to the SIP server. The commutation looks something like this:

illustration of a SIP registration request between a SIP endpoint and a server

The phone sends the registration request to the IP address of the SIP server.
The SIP server responds with SIP lawmaking 401 which ways that the phone is unauthorized to register. In other words, information technology requires a SIP URI and password. In the SIP 401 message, the server requests credentials in what is known every bit a "challenge."
The IP phone responds with a registration request including credentials.
The SIP server checks the credentials, and if correct, will ship back SIP message response code 200 which means OK. In other words, registration is successful.

Once this sequence completes, the SIP server informs the IP phone of boosted settings, such equally the directory number, speed dials, and whatsoever other personalized configurations that accept been set upwardly.

Keep in listen that registration enables a telephone to process phone call control data, i.eastward., the signaling necessary to allow for normal telephony operations. No commutation of voice packets has withal been initiated.

Causes of IP telephone registration failure

There are two primary categories of failures that tin touch IP phone registration. The first has to do with incorrect configuration of parameters on the SIP server and the IP phone. The second deals with problems on the network that may exist blocking SIP messages from reaching their intended destinations. Both of these aspects are farther described below.

Incorrect configuration parameters

Like any other service on a network, the registration of IP phones relies on the right configuration of both the server and the client. In a VoIP environment, this would be the SIP server and the IP phone, respectively. Both the SIP URI and the countersign must be entered correctly for the service to function.

The SIP URI resembles an e-mail address and may look something like this: 2500@yoursipserver.net where 2500 may exist the phone number, and yoursipserver.internet is the address of the SIP server. Yous may too apply an IP address instead of a DNS name, or a label such equally the user's proper noun instead of the number. Each SIP server may take a unlike way of inbound the SIP URI when you configure it. Some permit the whole address to be input in a single field, while others require the number and the SIP server address to exist input separately in ii unlike fields. Verify with the manufacturer that you have entered the URI correctly in both the IP phone and the SIP server.

Some additional configuration issues that are more often manufacturer-dependent are a misconfiguration of the particular phone model on the SIP server, the choice of the apply of TCP or UDP, and the choice of port number to exist used, which by default is 5060, or 5061 for secure SIP.

Network bug affecting registration

IP phone registration is a procedure requiring that the IP phone and the SIP server can communicate with each other over the network. If at that place is no network connectivity, registration will fail.

If the SIP server and the IP telephone are on the same LAN, achieving connectivity is trivial. If both are connected to the same switch, for example, and their IP addresses are configured correctly, at that place is very little that can obstruct connectivity. However, nearly VoIP deployments involve either deject-based SIP servers, remote IP phones in multisite deployments, or VoIP endpoints used by teleworkers. This means that IP phones must communicate over a WAN or over the net to reach the SIP server.

If your IP phones are located on a unlike site than your SIP server, then this introduces a multitude of network factors that can impact the SIP registration process. These include:

Network Address Translation (NAT) – NAT is an ingenious feature that has kept the internet alive using the depleted IPv4 address space during the slow transition to IPv6. Just it causes problems with voice communications. Not only does information technology wreak havoc on voice packets, but it also "breaks" the SIP signaling that takes identify between an IP phone and its SIP server. NAT typically operates on the router at the edge of the enterprise network. If this router is not "SIP-aware," it volition cause bug with your SIP registrations.
Firewall – Some other device that can affect SIP registrations is the firewall. This is a device used to keep your network safe, but information technology tin can besides cause problems with SIP registrations. You should troubleshoot the firewall to ensure that advice betwixt the IP Phones and the SIP server is not blocked in any way, including ports 5060 and 5061, which are used by SIP by default.
DHCP – This is a feature that allows network devices, such as IP phones, to obtain their IP accost, and various other network parameters, from a centralized DHCP server. This greatly simplifies network addressing, especially on large enterprise networks. However, some manufacturers utilize various DHCP options (additional information within the DHCP messages) to allow IP phones to fetch supplementary configuration parameters from the IP PBX. If the DHCP server providing those IP addresses is non correctly configured with those boosted options, IP phones will be unable to discover the server from which to receive these parameters, resulting in a failed registration.
DNS – IP phones may be configured to find their SIP servers using a DNS address rather than an IP address. If this is the instance, and the local DNS service fails, and so phones will be unable to find the SIP server and volition fail to register. Whenever possible, apply IP addresses instead of DNS names, so that any failure in the DNS service will not affect SIP registrations.
Other network malfunctions – If at that place is any malfunction that causes network failure, phones will fail to annals. This includes failures in routing, network infrastructure, ability, internet or WAN connectivity, or deject connectivity. Such problems fall into the category of general network failures that influence other network services beyond just VoIP.

Troubleshooting tips

Keeping the higher up concepts in heed, when a phone fails to register, the following troubleshooting procedures should exist followed:

Configuration parameters troubleshooting

If all IP phones are failing, bank check the configuration and the status of the SIP server
If only a single IP phone is failing, check the configuration on the telephone itself and the credentials configured for this telephone on the SIP server
In both cases, check the transport protocol (TCP/UDP) and ports configured on both the SIP server and the IP phone

Network issues troubleshooting

Before checking any other services, ensure that network connectivity from the subnet in which the failed phone sits is bachelor to the SIP server. This can be achieved by placing a laptop in the aforementioned subnet as the failed IP phone and pinging the SIP server:
- If this is unsuccessful, go on with normal network connectivity troubleshooting
- If this is successful, go along with VoIP-specific troubleshooting described below
If phones in specific network segments are declining:
- Check that DHCP server options are existence provided for that scope of IP addresses, every bit needed
- Check that the DNS service is functioning for that network segment
If phones in specific remote sites are failing:
- Check edge router configuration to ensure that NAT issues are not the problem
- Check firewall rules and verify that they are not blocking SIP letters
- Check local DHCP server options are being provided for that scope of IP addresses, every bit needed
- Check that the DNS service is performance at the remote site

Conclusion

IP telephone registration problems can be frustrating at times, but if you lot have a plan for how to deal with them, you tin can speedily place the problem and resolve it in no time. Nosotros hope this article will become another useful tool in your VOIP troubleshooting toolkit.

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Topics: SIP Phones, IP PBX, Business organisation Telephone System, SIP, Troubleshooting, Vocalism Protocols, firewall