Overview
The Configurable SIP Parameters via DHCP feature allows a Dynamic Host Configuration Protocol (DHCP) server to provide Session Initiation Protocol (SIP) parameters via a DHCP client. These parameters are used for user registration and call routing.
The DHCP server returns the SIP Parameters via DHCP options 120 and 125. These options are used to specify the SIP user registration and call routing information. The SIP parameters returned are the SIP server address via Option 120, and vendor-specific information such as the pilot, contract or primary number, an additional range of secondary numbers, and the SIP domain name via Option 125.
In the event of changes to the SIP parameter values, this feature also allows a DHCP message called DHCPFORCERENEW to reset or apply a new set of values.
The SIP parameters provisioned by DHCP are stored, so that on reboot they can be reused.
To perform basic Configurable SIP Parameters via DHCP configuration tasks, you should understand the following concepts:
Cisco Unified Border Element (CUBE) Support for Configurable SIP Parameters via DHCP
The CUBE provides the support for the DHCP provisioning of the SIP parameters.
The NGN is modeled using SIP as a VoIP protocol. In order to connect to NGN, the User to Network Interface (UNI) specification is used. Cisco TelePresence Systems (CTS), consisting of an IP Phone, a codec, and Cisco Unified Communications Manager, are required to internetwork over the NGN for point-to-point and point-to-multipoint video calls. Because Cisco Unified Communications Manager does not provide a UNI interface, there has to be an entity to provide the UNI interface. The CUBE provides the UNI interface and has several advantages such as demarcation, delayed offer to early offer, and registration.
The figure below shows the CUBE providing the UNI interface for the NGN.
DHCP to Provision SIP Server, Domain Name, and Phone Number
NGN requires CUBE to support DHCP (RFC 2131 and RFC 2132) to provision the following:
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IP address for CUBE’s UNI interface facing NGN
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SIP server address using option 120
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Option 125 vendor specific information to get:
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Pilot number (also called primary or contract number), there is only one pilot number in DHCPACK, and REGISTER is done only for the pilot number
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Additional numbers, or secondary numbers, are in DHCPACK; there is no REGISTER for additional numbers
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SIP domain name
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DHCPFORCERENEW to reset or apply a new set of SIP parameters (RFC 3203)
DHCP-SIP Call Flow
The following scenario shows the DHCP messages involved in provisioning information such as the IP address for UNI interface, and SIP parameters including the SIP server address, phone number, and domain name, along with how SIP messages use the provisioned information.
The figure below shows the DHCP and SIP messages involved in obtaining the SIP parameters and using them for REGISTER and INVITE.
DHCP Message Details
The DHCP call flow involved in obtaining CUBE provision information, including the IP address for UNI interface and SIP information such as phone number, domain, and SIP server, is shown in the figure below.
The DHCP messages involved in provisioning the SIP parameters are described in Steps 1 to 6.
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F1: The CUBE DHCP client sends a DHCPDISCOVER message to find the available NGN DHCP servers on the network and obtain a valid IPv4 address. The Cisco Unified Border Element DHCP client identity (computer name) and MAC address are included in this message.
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F2: The CUBE DHCP client receives a DHCPOFFER message from each available NGN DHCP server. The DHCPOFFER message includes the offered DHCP server’s IPv4 address, the DHCP client’s MAC address, and other configuration parameters.
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F3: The CUBE DHCP client selects an NGN DHCP server and its IPv4 address configuration from the DHCPOFFER messages it receives, and sends a DHCPREQUEST message requesting its usage. Note that this is where CUBE requests SIP server information via DHCP Option 120 and vendor- identifying information via DHCP Option 125.
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F4: The chosen NGN DHCP server assigns its IPv4 address configuration to the CUBEDHCP client by sending a DHCPACK message to it. The Cisco Unified Border Element DHCP client receives the DHCPACK message. This is where the SIP server address, phone number and domain name information are received via DHCP options 120 and 125. The CUBE will use the information for registering the phone number and routing INVITE messages to the given SIP server.
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F5: When NGN has a change of information or additional information (such as changing SIP server address from 1.1.1.1 to 2.2.2.2) for assigning to CUBE, the DHCP server initiates DHCPFORCERENEW to the CUBE. If the authentication is successful, the CUBE DHCP client accepts the DHCPFORCERENEW and moves to the next stage of sending DHCPREQUEST. Otherwise DHCPFORCERENEW is ignored and the current information is retained and used.
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F6 and F7: In response to DHCPFORCERENEW, similar to steps F3 and F4, the CUBE requests DHCP Options 120 and 125. Upon getting the response, SIP will apply these parameters if they are different by sending an UN-REGISTER message for the previous phone number and a REGISTER message for the new number. Similarly, a new domain and SIP server address will be used. If the returned information is the same as the current set, it is ignored and hence registration and call routing remains the same.
Feature Information
The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
Feature Name |
Releases |
Feature Information |
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Configurable SIP Parameters via DHCP |
Baseline Functionality |
The feature introduces the configuring of SIP parameters via DHCP. |