Cisco Network Protocols


Cisco Unified IP Phones support several industry-standard and Cisco network protocols required for voice communication. The following table provides an overview of the network protocols that the Cisco Unified IP Phones support.

Network Protocol


Usage Notes

Bootstrap Protocol



BootP enables a network device such

as the Cisco Unified IP Phones to discover certain startup information, such as its IP address.


If you use BootP to assign IP addresses to the Cisco Unified IP Phones, the BOOTP Server option shows Yesin the network configuration settings on the phone.



Cisco Discovery

Protocol (CDP)


CDP is a device-discovery protocol that runs on all Cisco-manufactured



Using CDP, a device advertises its

existence to other devices and receives information about other devices in the network.


The Cisco Unified IP Phones use CDP to communicate information such as auxiliary VLAN ID, per port power management details, and Quality of Service (QoS) configuration information with the Cisco Catalyst switch.


Cisco Peer-to-Peer

Distribution Protocol



CPPDP is a Cisco proprietary protocol

used to form a peer-to-peer hierarchy

of devices. CPPDP is also used to copy firmware or other files from peer

devices to neighboring devices.


CPPDP is used by the Peer Firmware Sharing feature.

Dynamic Host

Configuration Protocol


DHCP dynamically allocates and assigns an IP address to network devices.


DHCP enables you to connect an IP Phone into the network and have the phone become operational without you needing to manually assign an IP address or to configure additional network parameters.


DHCP is enabled by default. If disabled, you must manually configure the IP address, subnet mask, gateway, and a TFTP server on each phone locally.


Cisco recommends that you use DHCP custom option 150. With this method, you configure the TFTP server IP address as the option value. For additional supported DHCP configurations, see Dynamic Host Configuration Protocoland Cisco TFTPchapters in the Cisco Unified Communications Manager System Guide.


Hypertext Transfer

Protocol (HTTP)


HTTP is the standard way of transferring information and moving documents across the Internet and the web.



Cisco Unified IP Phones use HTTP for the XML services and for troubleshooting purposes.


Cisco Unified IP Phones do not support the use of IPv6 addresses in the URL. You cannot use a literal IPv6 address in the URL or a hostname that maps to an IPv6 address.



Hypertext Transfer

Protocol Secure



Hypertext Transfer Protocol Secure (HTTPS) is a combination of the Hypertext Transfer Protocol with the SSL/TLS protocol to provide

encryption and secure identification of servers.

Web applications with both HTTP and HTTPS support have two URLs configured. Cisco Unified IP Phones that support HTTPS choose the HTTPS URL out of the two URLs.


IEEE 802.1X


The IEEE 802.1X standard defines a client-server-based access control and authentication protocol that restricts unauthorized clients from connecting to a LAN through publicly accessible ports.


Until the client is authenticated, 802.1X access control allows only Extensible Authentication Protocol over LAN (EAPOL) traffic through the port to which the client is connected. After authentication is successful, normal traffic can pass through the port.



The Cisco Unified IP Phones implement the IEEE 802.1X standard by providing support for the following authentication methods: EAP-FAST, EAP-TLS, and EAP-MD5.


When 802.1X authentication is enabled on the phone, you should disable the PC port and voice VLAN.


Internet Protocol (IP)


IP is a messaging protocol that addresses and sends packets across the network.


To communicate using IP, network devices must have an assigned IP address,subnet, and gateway.


IP addresses, subnets, and gateway identifications are automatically assigned if you are using the Cisco Unified IP Phones with Dynamic Host Configuration Protocol (DHCP). If you are not using DHCP, you must manually assign these properties to each phone locally.


The Cisco Unified IP Phones support concurrent IPv4 and IPv6 addresses. Configure the IP addressing mode (IPv4 only, IPv6 only, and both IPv4 and IPv6) in Cisco Unified Communications Manager Administration .


For more information, see Internet Protocol Version 6 (IPv6)chapter in the Cisco Unified Communications Manager Features and Services Guide.



Link Layer Discovery

Protocol (LLDP)


LLDP is a standardized network discovery protocol (similar to CDP) that some Cisco and third-party devices support.



The Cisco Unified IP Phones support LLDP on the PC port.


Link Layer Discovery


Endpoint Devices




LLDP-MED is an extension of the LLDP standard developed for voice products.


The Cisco Unified IP Phones support

LLDP-MED on the SW port to

communicate information such as:


· Voice VLAN configuration

· Device discovery

· Power management

· Inventory management


For more information about LLDP-MED

support, see the LLDP-MED and Cisco

Discovery Protocol white paper:





Real-Time Transport

Protocol (RTP)


RTP is a standard protocol for transporting real-time data, such as interactive voice and video, over data networks.


Cisco Unified IP Phones use the RTP protocol to send and receive real-time voice traffic from other phones and gateways.



Real-Time Control

Protocol (RTCP)



RTCP works in conjunction with RTP to provide Quality of Service (QoS) data (such as jitter, latency, and round trip delay) on RTP streams.



RTCP is disabled by default, but you can enable it on a per phone basis by using Cisco Unified Communications Manager.


Session Description

Protocol (SDP)



SDP is the portion of the SIP protocol that determines which parameters are available during a connection between two endpoints. Conferences are established by using only the SDP capabilities that are supported by all endpoints in the conference.


SDP capabilities, such as codec types,

DTMF detection, and comfort noise, are

normally configured on a global basis by Cisco Unified Communications Manager or Media Gateway in operation. Some SIP endpoints may allow these parameters to be configured on the endpoint itself.



Session Initiation

Protocol (SIP)


SIP is the Internet Engineering Task Force (IETF) standard for multimedia conferencing over IP. SIP is an ASCII-based application-layer control protocol (defined in RFC 3261) that can be used to establish, maintain, and terminate calls between two or more endpoints.


Like other VoIP protocols, SIP is

designed to address the functions of

signal and session management within a packet telephony network. Signaling allows call information to be carried across network boundaries. Session management provides the ability to control the attributes of an end-to-end call.


You can configure the Cisco Unified IP Phones to use either SIP or Skinny Client Control Protocol (SCCP). Cisco Unified IP Phones do not support the SIP protocol when the phones are operating in IPv6 address mode.



Skinny Client Control Protocol (SCCP)



SCCP includes a message set that allows communications between call control servers and endpoint clients such as IP Phones. SCCP is proprietary to Cisco.



Cisco Unified IP Phones use SCCP for

call control. You can configure the Cisco Unified IP Phone to use either SCCP or Session Initiation Protocol (SIP).


Transmission Control

Protocol (TCP)


TCP is a connection-oriented transport protocol.


Cisco Unified IP Phones use TCP to connect to Cisco Unified

Communications Manager and to access XML services.



Transport Layer Security (TLS)



TLS is a standard protocol for securing and authenticating communications.


When security is implemented, Cisco Unified IP Phones use the TLS protocol when securely registering with Cisco Unified Communications Manager.


For more information, see Cisco Unified Communications Manager Security Guide.



Trivial File Transfer

Protocol (TFTP)


TFTP allows you to transfer files over the network.


On the Cisco Unified IP Phones, TFTP enables you to obtain a configuration file specific to the phone type.


TFTP requires a TFTP server in your

network, which can be automatically

identified from the DHCP server. If you

want a phone to use a TFTP server other than the one specified by the DHCP server, you must manually assign the IP address of the TFTP server by using the Network Configuration menu on the phone.


For more information, see Cisco TFTP

chapter in the Cisco Unified

Communications Manager System Guide



User Datagram Protocol (UDP)


UDP is a connectionless messaging protocol for delivery of data packets.


Cisco Unified IP Phones transmit and

receive RTP streams, which utilize UDP.


Related Topics

802.1X Authentication

Network Configuration Menu

IPv6 Support on Cisco Unified IP Phones

The Cisco Unified IP Phones use the Internet Protocol to provide voice communication over the network. Because Internet Protocol version 4 (IPv4) uses a 32-bit address, it cannot meet the increased demands for unique IP addresses for all devices that connect to the internet. Therefore, Internet Protocol version 6 (IPv6) is an updated version of the current Internet Protocol. IPv6 uses a 128-bit address and provides end-to-end security capabilities, enhanced Quality of Service (QoS), and increased number of available IP addresses.

The Cisco Unified IP Phone supports IPv4-only addressing mode, IPv6-only addressing mode, as well as an IPv4/IPv6 dual stack addressing mode. In IPv4, you can enter each octet of the IP address on the phone in dotted decimal notation; for example, In IPv6, you can enter each octet of the IP address in hexadecimal notation with each octet separated by a colon; for example, 2005:db8:0:1:ef8:9876:ba72:dc9a. The phone truncates and removes leading zeros when it displays the IPv6 address.

Cisco Unified IP Phones support both IPv4 and IPv6 addresses transparently, so users can handle all calls on the phone to which they are accustomed. Cisco Unified IP Phones with the Skinny Call Control Protocol (SCCP) support IPv6. Cisco Unified IP Phones with SIP do not support IPv6.

Cisco Unified IP Phones do not support URLs with IPv6 addresses in the URL. This affects all IP Phone Service URLs, such as services, directories, messages, help, and any restricted web services that require the phone to use the HTTP protocol to validate credentials with the Authentication URL. If you configure Cisco Unified IP Phone services for Cisco Unified IP Phones, you must configure the phone and the servers that support the phone service with IPv4 addresses.

If you configure IPv6 Only as the IP Addressing Mode for phones that are running SIP, the Cisco TFTP service overrides the IP Addressing Mode configuration and uses IPv4 Only in the configuration file.

For more information on IPv6 deployment in your Cisco Unified Communications network, see theInternet Protocol Version 6 (IPv6)chapter in the Cisco Unified Communications Manager Features and Services Guide and Deploying IPv6 in Unified Communications Networks with Cisco Unified Communications Manager, located at