■■ MPLS is only applicable in the core of the network where no QoS ser-
vices are required due to the ample bandwidth, but is not applicable on
congestion-prone access links where most QoS problems arise. MPLS is
also of no help for occasional route flapping events in the Internet.
■■ MPLS does not necessarily enhance security. MPLS can provide certain
isolation for networks using MPLS for interconnection, but this isola-
tion does not protect such networks from security threats at the applica-
tion level, where most security threats reside. MPLS can actually be a
vulnerability, since it requires central control that can be targeted for
attack.
■■ The scalability of MPLS is limited by the capability of the network
equipment to process large numbers of MPLS paths across the network.
This is in contrast to the scalability of the Internet that has no known
limits.
■■ MPLS resembles ATM (it can actually be considered a reincarnation of
ATM) and carries the disadvantages of legacy telecom into the IP realm:
■■ Central control
■■ MPLS paths resemble circuit switchingFacility-based domain owners may certainly establish MPLS paths for peer-
ing for VoIP, but this has not happened at present for reasons explained in
Chapter 18, “Quality of Service for Real-Time Internet Communications.”Media and Data Formats
The predominant media types for conferencing are text, audio, and video,
although other real-time media application such as games may also be consid-
ered a conference session. The XML-based documents for presence informa-
tion are also quite large and can be a source of significant traffic, especially for
frugal mobile networks. Various types of data also are exchanged during a
conference (such as Web pages and desktop applications). The protocol for
media transport is the Real-Time Transport Protocol (RTP). In addition, during
a conference, presentations are made. The protocol for synchronizing various
media and data types during a presentation is the Synchronized Multimedia
Integration Language (SMIL—pronounced like “smile”). Finally, recorded
media streams of complete presentations can be uploaded, downloaded, and
replayed using Real-Time Streaming Protocol (RTSP).90 Chapter 5