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SCCP Transactions

SCCP transactions are the processes that need to take place in order for an SCCP call to proceed. SCCP transactions include the following processes:

Client Initialization

To initialize, the SCCP client needs to know the IP address of the CallManager, its own IP address, and other information about the IP gateway and DNS servers. Initialization takes place on the local LAN. The client sends a Dynamic Host Control Protocol (DHCP) request to get an IP address, the DNS server address, and the TFTP server name and address. The client needs the TFTP server name to download the configuration file called sepmacaddr.cnf. If the TFTP name is not given, the client uses the default filename in the IP phone. The client then downloads the .cnf (xml) configuration file from TFTP server. CNF files contain the IP address or addresses of the primary and secondary Cisco CallManager. With this information, the client contacts the CallManager to register.

Client Registration

The SCCP client, after initialization, registers with the CallManager over a TCP connection on well-known default port 2000. The client registers by providing the CallManager with its IP address, the MAC address of the phone, and other information, such as protocol and version. The client cannot initiate or receive calls until it is registered. Keepalive messages keep this TCP connection open between the client and CallManager so that the client can initiate or receive calls at any time, provided that a policy on the J-series device allows this.

Table 77 lists SCCP messages and indicates messages that are of interest to the J-series device.

Table 77: SCCP Registration Messages

RegisterMessage		b
IPortMessage		b
	RegisterAckMessage	b
	CapabilititsRequest
CapabilitiesResMessage
ButtonTemplateReqMessage
	ButtonTemplateResMessage
SoftKeyTemplateReqMessage
	SoftKeyTemplateResMessage
LineStatReqMessage		b
	LineStatMessage	b

Call Setup

IP phone-to-IP phone call setup using SCCP is always handled by the CallManager. Messages for call setup are sent to the CallManager, which returns messages appropriate to the status of the call. If call setup is successful, and a policy on the J-series device allows the call, the CallManager sends the media setup messages to the client.

Media Setup

The CallManager sends the IP address and port number of the called party to the calling party. The CallManager also sends the media IP address and port number of the calling party to the called party. After media setup, media is transmitted directly between clients. When the call ends, the CallManager is informed and terminates the media streams. At no time during this process does the CallManager hand over call-setup function to the client. Media is streamed directly between clients through RTP/UDP/IP.

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