Information Technology Reference
In-Depth Information
SIP proxy server: Routes messages between SIP UAs. It acts as an intermediate that
receives SIP requests from a client and forwards the requests on behalf of the client.
SIP proxy servers perform authentication, authorization, routing, reliable request re-
transmission, and security.
SIP redirect server: Call control device used to provide routing information to
user agents. It provides information about the next hop or hops that a message
should take.
SIP registrar server: Stores the location of all user agents in the domain or subdo-
main. It processes requests from UACs for registration of their current locations. SIP
proxy servers or redirect servers can contain registrar servers.
SIP location services: Provide logical location of UAs; used by the proxy, redirect,
and registrar servers.
Back-to-back user agent: Call control device that divides a voice call into two
call legs.
Ta ble 1 4 -1 1 summarizes protocols used in VoIP networks.
Ta b l e 1 4 -1 1
Significant Protocols in VoIP Networks
Protocol
Description
DHCP
Dynamic Host Control Protocol. Provides IP address, mask, gateway, DNS ad-
dress, and TFTP address.
TFTP
Tr iv ial File Tran sfer P rotocol. P rov ide s the IP phone config urat ion and operat ing
system.
SCCP
Skinny Client Control Protocol. Establishes calls between IP phones and CUCM.
RTP
Real-time Transport Protocol. Used for the transmission of real time traffic such
as voice and video.
RTCP
Real-time Transport Control Protocol. Provides out of band statistics and control
information for RTP streams.
H.323
An ITU standard for VoIP networks. H.323 is older and more stable than SIP, but
is also more process intensive and is limited to traditional voice and video func-
tionality.
SIP
Session Initiation Protocol. An IETF standard for VoIP networks. Newer and less
mature than H.323, but also less process intensive and has support for new fea-
tures such as IM and presence.
IPT Design
This section covers network design issues and solutions that a designer needs to be aware
of when designing a network for IPT. Topics such as bandwidth requirements, delay, and
QoS schemes should be considered.
 
 
 
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