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Abstract -- Multimedia Experiments at the University of Pisa: From Videoconference to Random Fractals
N5: High Speed Networking
Multimedia Experiments at the University of Pisa: From Videoconference to Random Fractals
- Giordano, Stefano
- Russo, Franco
- Pierazzini, Giuseppe
Real time services in support of multimedia applications are emerging over
networks originally designed for asynchronous services. The traffic
generated by these applications represents a very critical component of the
whole amount of traffic to be supported by future broadband
Broadband experiments were carried out in Tuscany over a network
infrastructure represented by a 140 Mbit/s DQDB MAN.
The architecture of the MAN is organized into three switching levels: (level
1) the Customer Access Network (CAN), (level 2) the MAN Switching System MSS
and (level 3) the I-MSS (Inter MAN Switching System). A level zero
distributed switching environment is represented by the LANs connected by
multiprotocol routers to the MAN.
The main application areas, based on the connection less data service
provided by the MAN, are the following:
The paper deals with the experiments carried out in the field of desktop
conferencing in a regional environment using the MBONE's tools . Particular
interest is directed to the multicast multimedia IP traffic offered to the MAN.
To support these time constrained applications, new QoS (Quality of Service)
requirements have to be consider and their provisioning is critical due to
the bursty nature of the sources. High variability of the traffic is at the
same time the pros and the cons of modern traffic control strategies.
Statistical multiplexing plays a central role in trying to obtain a better
utilization of resources but, on the contrary, its control is extremely
critical and could drive to conservative solutions.
These problems are complicated by the need to maintain a complete
integration of new services and trasport technologies with the oldest ones.
To provide those services on a "best effort" access class it is necessary to
make performance provisioning based on the statistical behaviours of traffic
- Remote Sensing and Environment Monitoring
- High performance and parallel computing
- Telematics for arts and museums
The paper presents measurements of Ethernet traffic offered to the MAN
collected during its regular use. The traffic is represented by two main
components: traditional data traffic (i.e. file transfer, remote login,
access to WWW servers, etc.), and multimedia real time traffic generated by
voice, video, shared whiteboard.
The two main traffic components revealed to be highly variable and bursty.
Variability in packet arrivals has direct consequences in queueing delays:
greater variability correspond to longer delay. The interest in modeling
bursty traffic offered to a broadband network is central in problems related
to statistical multiplexing. Our measurements show that aggregated traffic
offered to the broadband network is well-described by self-similar processes
instead of traditional Renewal or Markov Modulated Poisson Process (short
range dependence processes).
These results, obtained over a broadband network, confirmed previous
analysis carried out at Bellcore. Increasing the number of sources
multiplexed over an Ethernet LAN (thus increasing the average offered load),
we obtained a self-similar process with an increasing Hurst parameter, which
characterizes the correlation function of the self-similar arrival process.
The interest of this analysis is directed to the performance evaluation of a
broadband network which provides a best effort, asynchronous interconnection
of several remote LANs. Different effects of this arrival processes on
network performances are presented considering a model of the DQDB network.
Our work is directed to point out the need for more realistic traffic
scenarios in the analysis of broadband telecommunication networks. We
considered the analysis of the MAC protocol standardized by the IEEE 802.6
supporting multimedia voice and video applications. The rational behind this
choice is that real traffic sources correspond to the multiplexing of
several services over the network and not to a single isolated video or
voice source. This will be particularly true for LAN interconnection that
will represent the first service to be provided by broadband networks in a
business and educational environment. The implications of the self similar
or "fractal" behaviour of real traffics must be taken into account in
dimensioning future telecommunication networks.