Version : 1
Date : Sept. 4th, 1997
Author : SIEMENS
Confidentiality : Public
Status : final
Table of Contents:
3.4 Local and Networked Access *
3.4.2 Requirements of the Network **
188.8.131.52 Local Area Network (LAN) ** *
3.4.5 Network link services ** *
3.4.8 Further Readings (to be continued): *
3.4.9 Appendix 1: TEN-34 - A Milestone in European Research Networking *
For digital libraries, it is essential that a appropriate network environment is available to guarantee the full state-of-the-art access to the information and leads to significant benefits and effectiveness of usage. Networks used for that purpose have to take advantage of existing public network with a wide range of different bearer services and topologies. For in-house networks, a combination of sometimes already existing network solution and new installation has frequently to be chosen to build up a heterogeneous network that brings the necessary bandwidth on different work places.
For multimedia application there is a need to transfer the data not only in real-time (e.g. preview, prelistening) but faster than real-time (e.g. transfer to a workstation). The data transfer has to be continuos, no interruption as often seen in normal office application can be accepted. Safety concepts as well as recovery mechanism has to be provided by the lower levels of OSI level model.
The digitisation of an analog signal for both audio and video signals is based on the same principal. The analog signal is sampled at equidistant intervals and digitised. The higher the resolution of the AD conversion (8, 16, 24 bit), the smaller the quantisation error but the larger the volume of data that results. The same is true of the sampling frequency that determines the frequency response (the highest frequency contained in the signal). Again, an increase in the sampling frequency increases the volume of data proportionately and, therefore, the required bandwidth. Figure 1 describes this correlation in brief:
Figure 2 shows the schematic structure of a playback unit. It is clear that the linear path between mass memory, in which the digitised recording is located, and the replay hardware has a channel capacity that corresponds to the required bandwidth.
To give an idea of the size of the data volume, calculation examples of the bandwidth requirements for both audio and video transmissions are presented in brief below.
Bandwidth = 2 * 44100 *16 » 1,5
Bandwidth = 1024 * 768 * 24 * 24 »
Section 1 contains the typical LAN environment. Today, transfer rates of up to 1 Gbit/s are available in this section. This section normally spans a single building complex.
Section 2 is a mixed sector in which both LAN and WAN elements occur. This sector is usually reserved for the area of commerce, i.e. company networks, etc. (Intranet). The data transfer rates lie between 64 kbit/s and 34/155 Mbit/s.
Section 3 belongs to the large sector encompassing switched connections in the public telephone network. In the broadest sense of the word, it involves WAN connections. This sector is characterised by its fast and flexible setting up of connections and is, therefore, to be found in the mobile commercial sector and in the private sector (private homes). Here, the data transfer rates lie between approximately 300 bit/s and 128 kbit/s
A brief discussion of WAN and LAN technology can be found below.
At network protocol level, the IP protocol extension "RESOURCE RESERVATION PROTOCOL" (RSVP) should be mentioned in this context. This protocol must, however, be supported by all the active network components (router, switches, etc.) in the active information path in order to achieve this functionality. What takes place is merely that certain IP packets are assigned a priority.
In oder to avoid this situation the Ethernet architecture used in multimedia network solution is built up in a star configuration called "switched". In such an architecture, each partner of the network has its own private access to the network, no shared media is used. This guarantees the whole bandwidth from 10 Mbit/s or 100Mbit/s for every user. The switch manages the routing inside the network.
Using this network topology is very cost-effective and allows the usage for multimedia application where the need for the bandwidth is not too high. However, the number of users are limited by the size of the Ethernet switch. Out of cost reasons From a certain size of the switches, it is appropriate to build up smaller network groups and to connect them with a powerful backbone by means of routers. Such topologies are discussed below.
An FDDI network can also be configured as a star instead of a ring architecture to a concentrator. If more than one network group has to be connected, a backbone like ATM can be used.
The principal structure of a network always remains the same, no matter if it is a LAN-, WAN, or MAN (Metropolitan Area Network)-configuration. ATM-switches are connected via network node interfaces. The user does not have to know if he works in a LAN or WAN environment. The "Virtual Channel Connection" (VCC) is a connection oriented way which will be established between two communication partner. If the communication is realized via VCC, it then secures the cells transfer and offers a certain quality of service.
The ATM switch only has to handle address information. The function of the ATM is very simple and enables the switch to work very fast. Data rates of 155 Mbit/s per channel and more are actually available. Therefore, ATM is an ideal backbone for multimedia network solution.
The topology in WAN networks is always as shown below:
|public telephone network||
The connection to the enduser, the so-called "last mile" is another important aspect for WAN's. For private users, only two technologies to be used for multimedia network access are already established: CATV and ISDN. The connections of these services are already installed in nearly every home. For business networks many buildings are already connected with fiber optic cable. The in-house connection can then be done with a local network.
WAN's are supporting narrowband services like ISDN BA, wideband services like 2 Mbit/s leased lines and broadband services including multimedia services like switched digital vidoe, LAN interconnection and high speed data services.
Using a standard interface, ISDN provides high-speed simultaneous digital transmission of voice, data and video and allows for universal connectivity to the public telephone network.
Each ISDN line is made up of separate 64-Kbps "channels" for sending and receiving calls, plus a channel that is used primarily for signalling. Standard ISDN BRI lines have 2 channels, more powerful ISDN PRI lines have 23 channels. Each channel can be used separately for an arbitrary communications task including voice calls, faxes, and data transmission. The channels can also be combined for information-intensive applications like video conferencing.
More information to ISDN see
ADSL being studied by ANSI (American National Standard for Information), defines three channels: analog telephone channel, a mono-directional data channel with up to 6Mbit/s and a data back channel with up to 16 kbit/s. ADSL is a member of a continuum of last-mile transport systems called DSL, or Digital Subscriber Line.
Now, the only form of DSL really being deployed is HDSL, which is more or less a direct replacement for traditional T1 service. T1 lines have been around forever but require technicians to tune the line to perfection; HDSL modems can handle dreadful lines cheerfully, so should be much cheaper to install and run.
More information to ADSL see
A principle scheme for a heterogeneous LAN and WAN
network solution is shown in the drawing below.
PHOTONET can be used as a powerful backbone for all applications with high data rate as in multimedia libraries. A connection to the national host is available.
For more information see:
In view of the current network technologies, especially in the WAN and Internet environments, there is a need for the use of data compression technologies. The main video compression standards today are MPEG-1, MPEG-2. MPEG stands for Moving Picture Experts Group and is an international standard. The MPEG-1 compression targets a bandwidth sweetspot of 1-1.5 Mbps offering VHS quality video at CIF (352x288) resolution and 30 frames per second. MPEG-1 requires expensive hardware for real-time encoding. While decoding can be done in the software, MPEG-1 does not offer resolution scalability and the video quality is highly susceptible to packet losses.
The MPEG-2 compression is similar to MPEG-1 and targets a bandwidth of 4-15 Mbps, providing broadcast quality full-screen video. MPEG-2 also offers limited bandwidth scalability by allowing resolution, frame rate and frame quality to be scaled. Compared with MPEG-1, it requires even more expensive hardware for encoding and decoding.
The MPEG standard is useful for the broadcast and CD-ROM applications in Campus and Extranet environments in which companies can afford the cost of high bandwidth networks. These can be either leased lines or upcoming ATM technologies.
In low band networks, the compressed video or audio has to be downloaded before it can be viewed or played (download-and-play technologies ). This is only useful if the sequences are not too long.
More technical information can be found under http://www.mpeg.org/index.html
Other technologies have to be used for transferring video and audio data over the Internet.
More and more products which support real-time audio-video streaming over the Internet are available. Vendors are Macromedia, Microsoft, Netscape, progressive Networks, VDO, Vivo, Xing, and others.
The streaming technologies over the Internet use techniques for adapting the frame rate, quality and resolution to the available network bandwidth:
Bandwidth/Resolution 640X480 320X240 160X120
1 Mbps 20 fps 30 fps 30 fps
256-512 Kbps 10 fps 20 fps 30 fps
ISDN (128 Kbps) 2-4 fps 10 fps 30 fps
28.8 Kbps 1 fps 2-3 fps 10-20 fps
fps = frames per second
Mbps = Megabit per second
Kpbs = Kilobit per second
This technology is very interesting for serving a broad range of users: commercial users, who can afford the cost of a higher bandwidth as well as private users, which are connected via telephone lines to an Internet provider. Examples can be found under
For more information about the streaming technology, refer to:
An important part is the interworking with other teleservices and message handling systems. The Multimedia Mailservice is realised on different workstations which have multimedia functionalities, using camera, loudspeaker, ...
For libraries that service could be used for "quick and dirty" information for fast access.
Catalogues can be used for more structured access to an archive. Three different types of solutions are available:
Tools for retrieving information are Gopher, WAIS and World Wide Web (WWW). Especially WWW clients, with their easy to handle graphical user interface and the hypermedia structure of the used Hypertext Markup Language (HTML), have found wide acceptance.
One problem is still unsolved: online payment via the Internet is not secure. Therefore, commercial services by means of the Internet are still not as successful as could be. A main difference between Internet and commercial online information services like CompuServe, is that the latter operates its own networking infrastructure, which is centrally managed. This type of communication provides more security.
Nowadays, two important access subsystems offer different possibilities to create the own access for distributed networked systems such as Internet. The following chapters give a short overview.
CORBA provides the mechanisms by which objects transparently make requests and receive responses, as defined by OMG's ORB. The CORBA ORB is an application framework that provides interoperability between objects, built-in (possibly) different languages, running on (possibly) different machines in heterogeneous distributed environments. The application communicates with the distributed object that is actually performing the operation. This is basic client/server functionality, where a client issues a request to a server and the server responds back to the client. Data can pass from the client to the server and is associated with a particular operation on a particular object. Data is then returned to the client in form of a response.
For more information see:
To enable a Java application to execute anywhere on the network, the compiler generates an architecture neutral object file format. The compiled code is executable on many processors, given the presence of the Java runtime system.
Java generated bytecode instructions are designed to be both easy to interpret on any machine, and easily translated into native machine code on the fly. It is intended to be used in networked/distributed environments. Java has an extensive library of routines for coping easily with TCP/IP protocols like HTTP and FTP. Java applications can open and access objects across the net via URLs with the same ease that programmers are used to when accessing a local file system.
The Java system itself is quite portable. The new compiler is written in Java and the runtime is written in ANSI C.
Orbix improves the flexibility of Java applications and the level of complexity at which objects can interact. Using OrbixWeb, a Java application can easily communicate with CORBA objects located on remote hosts, across heterogeneous platforms, and implemented in a wide range of programming languages. It supplements Java with standards-based support for a client/server application model. Dynamically downloaded Java applets can communicate directly with back-end services, without imposing limitations on the service implementation (such as hardware, OS, or language considerations)..
The standardised approach to client-server interaction is a very important element in an application designed for the Internet or an enterprise Intranet.
For more information see
In the future, technologies using TV cable networks
will be available, radio links and satellite connections. With increasing
bandwidths, the quality of the multimedia data will improve.
IEEE Communications Magazine, Vol. 14, No. 2, February, 1997)
Robert Orfali, Dan Harkey, Edwards Wiley, 1997
CORBA Distributed Objects, using Orbix
ACM Press, Addison-Wesley, 1997
Publication date: May 1, 1997
Java Programming With CORBA
Andres Vogel, Keith Duddy
Client/Server Programming with Java and CORBA
Robert Orfali, Dan Harkey
Core Java, 2nd Edition. by Gary Cornell and Cay S. Horstmann.
The European National Research Networks
High speed initiatives on other continents:
of Interim Results per Experiment
2. Usage of the JAMES Network
3. Joint Experiments with JAMES
5. Detailed Test Descriptions
5.1 TCP-UDP/IP Performance over ATM
5.2 SVC Tunnelling through PVPCs
5.3 Classical IP and ARP over ATM
5.4 IP routing over ATM with NHRP
5.5 European ATM Addressing
5.6 ATM Network Management
5.7 CDV over concatenated ATM networks
5.8 Assessment of ATM/VBR class of service
5.9 Performance of the Native ATM Protocol
5.10 IP resource reservation over ATM
5.11 Security in ATM Networks