Information Technology Reference
In-Depth Information
CAC should be used to keep excess voice traffic from the network by ensuring that there
is enough bandwidth for new calls. Call admission control (CAC) is used to control the
number of calls to reduce the WA N bandwidth for a site that has IPT. CAC is configured
for the site on the CUCM servers. A maximum bandwidth or maximum number of calls is
provisioned for the site. CAC enforces a maximum number of calls between two loca-
tions to ensure that call quality will not be degraded by allowing more calls than a net-
work can support. CAC causes excessive calls between two locations to be refused. The
IPT system must then either reroute the call to different available path, such as the PSTN,
or deny the call.
Service Class Recommendations
RFC 4594,
Configuration Guidelines for DiffServ Services Classes
(updated by RFC
5865), provides guidelines for specifying services. Six of these are specific for voice or
video traffic. The 12 service classes are as follows:
Network Control:
For routing and net work control functions
■
Operations, Administration, and Management (OAM):
For net work config ura-
tion and management functions
■
Te l e p h o n y :
Includes VoIP and circuit emulation
■
Signaling:
For peer-to-peer and client/ser ver sig naling, such as SIP, MGCP, H.323,
and H.248
■
Multimedia Conferencing:
For applic ations that c an change their encoding rate,
such as H.323/V2
■
Real-Time Interactive:
For RTP/UDP streams for v ideo conferenc ing applic ations
that cannot change the encoding rate
■
Multimedia Streaming:
For variable-rate elastic streaming media applic ations and
webcasts
■
Broadcast Video:
For inelastic streaming media w ith low jitter and low packet los s,
such as broadcast TV, video surveillance, and security
■
Low-Latency Data:
For data proces sing applic ations, such as web-based ordering
■
High-Throughput Data:
For store- and-for ward applic ations, such as FTP
■
Standard:
For traffic that has not been identified for any preferential treatment
■
Low-Priority Data:
For traffic t y pes that do not required any bandw idth as surance
■
Cisco modified some of the DSCP per-hop behavior (PHB) recommendations (switched
broadcast video and call signaling, for example) from the RFC and added queuing and
dropping recommendations for MediaNetworks. Table 14-15 summarizes these.
