Two pilot studies have been successfully concluded in Italy's Piedmont region. The trials aimed to establish to what extent the technology could offer a solution to organisations with a need to share information and to distribute large files like data, video, audio or graphics. The technology was especially useful in mountainous Piedmont where a broadband connection is often not possible.
During the trials, a number of schools and public offices used the technology.
Schools accessed web materials and courseware; public offices were able to share databases. Content delivery takes place through the client interface Casablanca. The new software version offers to take full advantage of two new channels that have recently been added. Three channels will now serve Europe: One for German users, another Italian and a third for the rest of Europe.
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Multicasting on the Internet and Its Applications. Multicasting on the Internet and its Applications. Upper layer protocols detect also if a received packet is relevant for this host. Normally sender does not keep state information about receivers in IP multicast, i. This kind of transport is appropriate in many streaming applications, for example transferring video and audio from media servers or in video conferences. Video and audio decoders can manage with some missing datagrams without information content to disturb too much.
These are intended for real-time transfer of video and audio over IP unicast or multicast network services. There are many situations, where multicast transport must be reliable. For example in multicasting web-applications and in cache or other database replication reliable transport is required.
Normal TCP is not possible, because it is designed to be one to one protocol.
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TCP can keep state information only about one connection, whereas in multicast connection there is in principle state information for each sender-receiver pair. One multicast transport connection can involve hundreds or even thousands of receivers. Different receivers may lose different packets and packets can arrive in different order. Reliable transport protocol must handle all these situations, so that every receiver receives consistent information.
Therefore, designing reliable, scaleable and efficient multicast transport protocol is a really demanding project. There exists many proposals for this kind of protocol and active research is still going on. IP unicast routing is relatively simple compared to IP multicast routing. In unicast routing, each host has unique IP address, which determines route to that host.
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When doing multicast routing, the problem to solve is much harder. Now destination address does not specify route to some place, but merely a transmission session.
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Multicast routers should forward datagrams to all participants in this session. The basic approach is that multicast capable routers communicate with neighbouring multicast routers and exchange information about group membership and network topology. Because each physical network can have several multicast capable routers, one of them is selected as the designated router for this network.
This router then communicates with other designated routers in neighbouring networks to construct a spanning tree for each multicast source. Now datagrams from source to other group members is transferred along this spanning tree. Spanning tree is loopless and guarantees, that each receiver gets it's datagrams along the shortest possible route. Constructing and maintaining spanning trees for sources is difficult task.
Hosts join and leave groups which means that spanning trees must be updated all the time. Also new sources appear and old ones go away, so spanning trees must be constructed and deleted. There are two basic methods for handling of spanning trees. The first one assumes that group members are located densely throughout the network and there is plenty of network resources available between members.
Multicast routing protocols working in this mode are called "dense-mode" routing protocols. They periodically flood group information between routers to construct and update spanning trees. Flooding is not a problem, if network is limited in size and there is enough bandwidth available. The second assumption is that group members are sparsely distributed throughout the network and there is limited network bandwidth available. Therefore flooding is not possible to distribute routing information between routers but more sophisticated procedures must be used.
Routing protocols working in this mode are called "sparce-mode" protocols. Some of these protocol do not build a different spanning tree for each source - destination group pair, but build one spanning tree per multicast group.
Because not all internet backbone routers support native IP multicast, MBone is constructed with tunnels across networks that do not support multicast routing. MBone therefore is a virtual network layered on top of internet. Encapsulation in tunnels is IP in IP, i. Tunnel endpoints are routers or workstations with mrouted software.
Implementing multicast routing in the whole internet is not yet possible, because none of the current multicast routing protocols scale to such a big network. Address space for multicast addresses in IPv6 addressing scheme is much larger than in IPv4 scheme. Binary prefix of multicast addresses in IPv6 is The rest bits are divided to three fields: 4 bits for flags, 4 bits for scope and remaining bits for group ID.
Low order bit of flags indicates permanently or non-permanently-assigned multicast address. Other flag bits are zero. Scope field is used to limit the scope of the multicast group. Possible scopes are node-local, link-local, site-local, organisation-local and global scope. Non-permanently-assigned multicast addresses are meaningful only within a given scope. In modern networking, security issues must also be considered. Security issues in IP multicast concentrates around applications used.
Because there are no application level proxies for multicast applications, security is only depended on desktop applications. Today's applications are developing rapidly and correctness of programs can not be guaranteed.
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Typical security problem in multicast application and in any application reading unchecked data from network is overwriting buffer area in memory, typically in stack. If application receives data from multicast stream and places that unchecked in buffer allocated from stack, application program may end up running code from attacker.
Therefore allowing IP multicast traffic to secure networks with unmature and experimental multicast applications is a big unknown.
vilsedonto.ml Privacy in multicasting is also sometimes important. For example many video conferences are private in nature, so outsiders should not be able to join conference session or to monitor the session. Privacy is easy to achieve by agreeing on secret key to be used to encrypt session data.
Key exchange can be made before session for example by sending PGP encrypted mail, which contains key to be used. To join the session, participant enters the key to her conference application, which uses that key to encrypt and decrypt data to and from other participants. ATM networks will be the future trend in the backbone networks. Currently the only problem is the unavailability of ATM specific services and protocol stacks capable to offer ATM services to applications. Winsock 2 protocol might help this and it is possible that native ATM services will be much more important that today.
ATM's native transport system is very capable of transmitting real-time video and audio, which are the core systems requiring multicasting. The bandwidth ATM networks are capable of offering is also a very important factor when defining the needs for new infrastructure.
Even though ATM is very connection oriented and ordinary IP multicasting methods are not directly available. The specification has few features that support also other higher level protocols and there has been deliberate attempt to create this method to work with other protocols also.
Currently IPv4 is very clearly the dominant protocol in the large scale networks, but IP is really not optimal choice for true real-time applications and the overhead IP protocol creates in video or audio transmission is quite useless. Large bandwidth and cell structure are very important things when deciding infrastructure for real-time applications. Because of cell structure it is possible to reserve certain capacity for application pushing continuous stream of data into network.
Multicasting is the only reasonable solution if this kind of stream must be directed to several locations. Otherwise there will be resending several times and useless consume of valuable network resources. Despite of current development around video-on demand there will always be certain need for the transmission of the same video to several locations at the same time. Video conferencing is the other bandwidth consuming service important for many companies.
The importance of clear picture and hi-fi quality voice is quite big even in standard every day videoconferences.
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