Information Technology Reference
In-Depth Information
Some of the most significant protocols are
Dynamic Host Configuration Protocol (DHCP):
Used to provide device configu-
ration parameters such as IP configuration (address, subnet mask, default gateway)
and TFTP servers (via DHCP option 150).
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TFTP:
To o b t a i n r i n g t o n e s , b a c k g r o u n d s , c o n f i g u r a t i o n f i l e s , a n d f i r m w a r e f i l e s .
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Skinny Client Control Protocol (SCCP):
Used for call control for Cisco IP phones
(Cisco proprietary).
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Real-time Transport Protocol (RTP):
For voice stream (VoIP) station-to-station
traffic in an active call.
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Real-time Transport Control Protocol (RTCP):
For RTP control and repor ting
(accompanying stream to RTP between endpoints).
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Media Gateway Control Protocol (MGCP):
A client/server protocol for control of
endpoints and gateways. In the MGCP model, intelligence resides on the call agent
(server), and the device is controlled by the agent.
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H.323:
An ITU standard for VoIP networks that is a peer-to-peer system (call pro-
cessing logic is local to each device) used for gateways and endpoints.
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Session Initiation Protocol (SIP):
A standard for VoIP networks defined by the
IETF and used for gateways and endpoints. SIP is feature rich (native IM, presence,
and video support), lightweight, and designed for easy troubleshooting (ASCII-based
messages).
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DHCP, DNS, and TFTP
IP phones use DHCP to obtain their IP addressing information: IP address, subnet mask,
and default gateway. DHCP also provides the IP address of the DNS servers and the name
or IP address of the TFTP server. You use TFTP to download the IP phone operating sys-
tem and configuration. Both DHCP and TFTP run over UDP. These protocols are covered
in detail in Chapter 8, “Internet Protocol Version 4.”
SCCP
SCCP is a Cisco proprietary client/server signaling protocol for call setup and control.
SCCP runs over TCP. SCCP is called a “skinny” protocol because it uses less overhead
than the call-setup protocols used by H.323. IP phones typically use SCCP to register
with CUCM and to establish calls. SCCP can also be used by the call agent to communi-
cate with gateways and control analog endpoints such as FXS ports. It is also used to man-
age resources such as DSPs on voice gateways. SCCP is used for VoIP call signaling and
for feat ure s s uch as me s s age-wait ing indic ator s. As show n in Fig ure14 -16, IP phone s com -
municate with the CUCM server using SCCP, but RTP is the protocol used for voice me-
dia streams between IP phones.
