Types of data transfer. What is broadcast, multicast and unicast (Unicast, Multicast, Broadcast) Typical IPTV network diagram

People! What is a broadcastcast and what is a podcast? and got the best answer

Answer from Evgeny Usenko[guru]

Term

[edit] Process

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Reply from 2 answers[guru]

Hello! Here is a selection of topics with answers to your question: People! What is a broadcastcast and what is a podcast?

Reply from Asking Questions[newbie]
Podcasting (English podcasting, from iPod and English broadcasting - ubiquitous, wide-format broadcasting) is the process of creating and distributing audio or video broadcasts (that is, podcasts) on the World Wide Web (usually in MP3 or Ogg/Vorbis format for audio and Flash Video and others for video broadcasts). As a rule, podcasts have a specific topic and frequency of publication (however, there are exceptions).
The target audience of podcasting is users of personal or laptop computers, as well as owners of portable players. For convenient listening to podcasts, many software products have been created, such as iTunes or AmaroK, which monitor the updating of podcast feeds and automatically download them.
A podcast terminal is a website that supports hosting of media files and, to some extent, automates the posting of recordings and subscription to updates.
A podcast is either a single file or a regularly updated series of such files published at one address on the Internet.
A podcaster is a person who engages in podcasting on an amateur or professional basis.
Term
The podcasting phenomenon corresponds to the concept of an audio blog, with the only caveat that a blog is usually understood as a sequence of entries in the form of ordinary web pages (in HTML format), and a podcast always provides automatic checking for updates using the RSS format. Other terms have been suggested:
webcasting - not widely used
rsscasting - difficult to pronounce
Competing with iPod maker Apple, mp3 player makers are trying to introduce their own podcasting names. For example, Creative, which produces players under the Zen brand, proposed the term Zencasting.
Process
The process of creating and publishing a podcast occurs in several stages:
Searching for an idea for a podcast, determining its topic. Before recording periodic podcasts, as a rule, a plan (show notes) is drawn up, which facilitates the narration process during recording.
Preparation of equipment. Typically, a digital or analog microphone is used for recording. To increase the recording quality, the audio signal is processed using a digital or analog mixer, various filters are used, etc.
Podcast recording. The audio signal is captured either by software or hardware. When using software (that is, audio editors), each person's signal is recorded on a separate audio track. Communication between remote interlocutors is carried out via Internet telephony.
Installation. When editing a podcast, the sequence and overlay of audio tracks are synchronized, noise and interference are removed, and various musical accompaniments are added. In podcasts, podsafe music is used as background music.
Publishing a podcast. A finished podcast, with a bitrate from 64 to 128 Kbps, is usually published on various podcast terminals, blogs and websites dedicated to this podcast.

Broadcast

Because the broadcast transmission type is used to send packets to all hosts on the network, the packets use a special broadcast IP address. When a host receives a packet with a broadcast address in its header, it treats the packet as if it were a unicast packet.

When a host needs to transmit some information to all hosts on the network, the broadcast data transmission method is used. Even when the address of special services or devices is unknown in advance, broadcast is also used for detection.

Examples when broadcast data transmission is used:

· creating a map of the membership of upper-level addresses to lower ones (for example, what IP address is on a specific device with its MAC address)
· address request (ARP protocol can be taken as an example)
routing protocols exchange information about routes (RIP, EIGRP, OSPF)

When a host needs information, it sends a request to the broadcast address. All other hosts on the network will receive and process this request. One or more hosts will enclose the requested information and respond to the request. Those responding to the request will use unicast as the data transfer type.

Similarly, when a host needs to send information to all hosts on the network, it creates a broadcast packet with its information and transmits it to the network.

Unlike unicast transmission, where packets can be routed across the entire network, broadcast packets are typically limited to the local network. This limit depends on the router configuration, which limits the network and monitors the type of broadcast (broadcast).

There are two types of broadcast data transmission: directed broadcast and limited broadcast.

Directional broadcast.

A directed broadcast is sent to all hosts on a specific network. This type of broadcast is useful for sending broadcast traffic to all hosts outside the local network.

For example, a host wants to send a packet to all hosts on the 172.16.5.0/24 network, but the host itself is on a different network. In this case, the sending host will include the address 172.16.5.255 in the packet header as the broadcast destination address. Although routers must restrict (not transmit) directed broadcast traffic, they can be configured to allow broadcast traffic to be transmitted.

Limited broadcast.

Limited broadcast is used to transmit data to all hosts on the local network. In such packets, the IP address 255.255.255.255 is inserted as the destination. Routers do not transmit such broadcast traffic. Packets transmitted by a limited broadcast will only be distributed on the local network. For this reason, IP LANs are also called broadcast domains. Routers form the boundary for the broadcast domain. Without the border, packets would be distributed throughout the network, to each host, reducing the performance of network devices and clogging the bandwidth of communication channels.

Let me give you an example of a limited broadcast: the host is inside the 172.16.5.0/24 network and wants to broadcast a packet to all hosts on its network. Using the IP address 255.255.255.255 as the destination, it sends a broadcast packet. This packet will be received and processed by all hosts only on this local network (172.16.5.0/24).

There are three main methods of transmitting traffic in IP networks: Unicast, Broadcast and Multicast.

Understanding the difference between these methods is very important for understanding the benefits of IP television and for the practical organization of broadcasting video over an IP network.

Each of these three transmission methods uses different types of IP address assignments according to their purposes, and there is a large difference in the degree of their impact on the amount of traffic consumed.

Unicast traffic (single-purpose packet transmission) is used primarily for “personal” services. Each subscriber can request personal video content at any time convenient for him.

Unicast traffic is routed from one source to one destination IP address. This address belongs to only one single computer or subscriber STB on the network as shown in the figure below.

The number of subscribers who can receive unicast traffic simultaneously is limited by the flow width (flow rate) available in the backbone of the network. For the case of a Gigabit Ethernet network, the theoretical maximum data flow width can approach 1 Gb/s minus the bandwidth required for transmitting service information and technological equipment reserves. Let's assume that in the backbone part of the network, for example, we can allocate no more than half of the bandwidth for services that require unicast traffic. It is easy to calculate for the case of 5Mb/sec per MPEG2 television channel that the number of subscribers simultaneously receiving unicast traffic cannot exceed 100.

Broadcast traffic uses a special IP address to send the same data stream to all subscribers on a given IP network. For example, such an IP address could end in 255, such as 192.0.2.255, or have 255 in all four fields (255.255.255.255).

It is important to know that broadcast traffic is received by all turned on computers (or STBs) on the network, regardless of the user's wishes. For this reason, this type of transmission is used mainly for network layer overhead information or for the transmission of other exclusively narrowband information. Of course, broadcast traffic is not used to transmit video data. An example of broadcast traffic transmission is shown in the figure below.

Multicast traffic (multiple packet transmission) is used to transmit streaming video when it is necessary to deliver video content to an unlimited number of subscribers without overloading the network. This is the most commonly used type of data transmission in IPTV networks, when the same program is watched by a large number of subscribers.

Multicast traffic uses a special class of destination IP addresses, for example addresses in the range 224.0.0.0 ..... 239.255.255.255. These can be Class D IP addresses.

Unlike unicast traffic, multicast addresses cannot be assigned to individual computers (or STBs). When data is sent over one of the multicast IP addresses, the potential receiver of the data can decide to accept it or not, that is, whether the subscriber will watch this channel or not. This transmission method means that the operator's IPTV head-end equipment will transmit one single data stream to many destination addresses. Unlike the case of broadcast transmission, the subscriber has a choice whether to receive data or not.

It is important to know that to implement multicast transmission, an IP network must have routers that support multicast. Routers use the IGMP protocol to track the current state of distribution groups (namely, the group membership of a particular end node on the network).

The basic rules of operation of the IGMP protocol are as follows:

- the end node of the network sends an IGMP report type packet to ensure that the process of connecting to the distribution group is started;
- a node does not send any additional packets when disconnected from a distribution group;
- the m ulticast router sends IGMP requests to the network at certain time intervals. These queries determine the current state of distribution groups;
- the node sends an IGMP response packet for each distribution group as long as there is at least one client of this group.

traffic network server broadcast

The load on the backbone of the multicast network with traffic depends only on the number of channels broadcast in the network. In a situation with a Gigabit Ethernet network, assuming that we can allocate half of the backbone traffic for multicast transmission, we get about 100 MPEG-2 television channels, each with a data flow rate of 5 Mb/sec.

Of course, the IPTV network contains all 3 types of traffic simultaneously: broadcast, multicast and unicast. An operator, when planning the optimal amount of network capacity, must take into account the different mechanisms of influence of different IP addressing technologies on the volume of traffic. For example, the operator must be clear that providing video-on-demand services to a large number of subscribers requires very high backbone network capacity. One solution to this problem is decentralization in the network of video servers. In this case, the central video server is replaced by several local servers, spaced apart and close to the peripheral segments of the multi-level hierarchical architecture of the IP network.

IPTV. IP television.

What is IPTV?. IP television It is customary to call the digital technology of multi-program interactive television broadcasting on an IP network using packet transmission of video data over the IP protocol (Video over IP). In practice, it looks like this: the head-end IPTV equipment transmits, and the subscriber equipment receives streaming video. This term refers to technologies for compressing, trimming, and buffering video data that allow video to be transmitted in real time over the Internet. The main feature of streaming video is that when transmitting it, the user does not have to wait for the file to be completely downloaded in order to view it. Streaming video is sent in a continuous stream as a sequence of IP packets and is played as it is transmitted to the subscriber device.

To view streaming video, a special set-top box is used on the TV, or in modern terminology, a Set top Box (STB), which, on the one hand, is connected to the operator’s network (broadcast environment), and on the other, has a connection to the TV. The STB subscriber device decodes video data and displays the decrypted video on the TV screen.

An IPTV subscriber receives from the operator a package of services, the most important difference from the services provided by classic cable television is interactivity, that is, the subscriber has the opportunity to quickly select and change the composition of the services to which he is subscribed, and at any time order an additional service, for example, an additional paid viewing of a movie. Of course, interactivity can also be implemented on the basis of a DVB-C cable network with a return channel, but such solutions are not widespread. Let's take a closer look at the composition of possible services that IP television can provide.

The basic service, first of all, is multi-program broadcasting of television channels, or IP television itself. Here two options for watching TV programs can be implemented: first, the operator creates several packages of TV channels, from which viewers can choose the desired set, and each package has its own subscription fee; second - viewers form individual packages from channels broadcast by the operator; The subscription fee is determined by the cost of the selected channels included in the individual package. The interactivity of IP television allows us to offer the subscriber a number of additional services.

IPTV services.

Service "Almost a video on demand" or, which sounds much better from a marketing point of view, "virtual cinema"(Near Video on Demand) is a broadcast of films from the operator’s video server with a strictly defined schedule of sessions, when the subscriber buys a session convenient for him in time to watch the film. The inconvenience for the subscriber is that he cannot start watching the movie at any arbitrary point in time. The advantage for the operator is the use of conventional IP-multicast technology, which greatly saves the amount of traffic in the operator’s backbone network. More about the technology IP multicast will be discussed further. To reduce traffic volumes, the operator provides the opportunity to watch a small number of films; usually the number of films in a “virtual cinema” does not exceed two to three dozen; as a rule, these are new films that have recently been released.

Service "Video to order"(Video on Demand) – a film from the operator’s video server is personally broadcast to the subscriber at any point in time arbitrarily chosen by the subscriber. Unlike the service "virtual cinema" the number of films here is much larger and can sometimes reach several thousand. A number of very convenient user functions of the virtual video player appear - rewind, forward, pause. In this case, the volume of traffic here depends not on the number of films, but on the number of users of this service, since “personal” transmission of video data to the subscriber using IP addressing technology is used “ unicast". More about addressing unicast will also be discussed below.

Service "Personal video recorder"(Personal Video Recorder) - on the operator’s video server, the subscriber is allocated a certain amount of memory and is provided with an interface with functions similar to a VCR for digital recording and playback of TV shows. The subscriber can, at will, record, erase, play, and rewind his personal recordings. IP-unicast technology is also used here.

Service "Paid View"(Pay per View) – purchase and viewing by the subscriber of separately selected programs (for example, the World Cup final). The broadcast is carried out in real time and IP-multicast technology is used.

Service "Time-shifted television"(Time Shifted TV) – the subscriber purchases the service of viewing programs pre-recorded on a video server. The service and the service functions implemented in it are close to “video on demand”. IP-unicast technology is also used.

Services "Services upon request"(Services on Demand, SoD) - this is an order of goods and services to your home, various reference information, transport schedules, hotel services, etc. These services are close to similar services on the Internet.

Typical IPTV network diagram.

In the diagram above we see the components of an IP-TV network.

1. Components of the head hardware IP-TV system, including:

Head station;
- conditional access system;
- video servers;
- billing system servers;
- management system servers;
- middleware servers;

2. Components of the backbone (backbone) transport network, including:

The actual backbone optical network based on IP technology or ATM technology;

High-performance switches (routers) with optical interfaces;

3. Transport access level, consisting, for example, in the case of an xDSL network, of a head DSL device DSLAM (DSL access multiplexor) installed in the PBX premises and a copper pair (telephone line) directly connected to the subscriber’s home.

Basic IPTV protocols.

A number of network protocols are used to transmit streaming video, of which the most important are RTSP and protocol IGMP.

RTSP(Real-Time Streaming Protocol) is a protocol with the possibility of controlled transmission of video streams on the Internet. The protocol ensures the transfer of information in the form of packets between the server and client. In this case, the recipient can simultaneously play the first data packet, decode the second and receive the third.

Protocol from the same group RTP(Real-time transport protocol) detects and compensates for lost packets, ensures the security of content transmission and information recognition. The protocol works together with RTP RTCP(Real-Time Control Protocol). It is responsible for verifying the identity of sent and received packets, identifying the sender and monitoring network congestion.

A standard protocol is used to join or leave a distribution group IGMP(Internet Group Membership Protocol).

The stream of television channels generated by the IPTV head station is a stream of IP packets transmitted in the network via a separate group IP address corresponding to a given TV channel. Thus, broadcasting several channels represents the formation of several streams of multicast traffic, when each channel is uniquely identified by a unique multicast address.

When using MPEG-2 as the most common digital video compression format, each television channel occupies from 3.5 to 6 Mbit/s in the IP network. The operator's network is loaded with a television channel only if there is a subscriber to this channel who has selected it for viewing, that is, has requested to watch it at the moment. The transmission of the television channel selected by the IP network subscriber is implemented on the basis of IP - multicast technology or, in the case of viewing video on demand, on the basis of IP - unicast.

To ensure minimal delays and guaranteed video data transfer speeds in the IP network, support is used Quality of Service(QoS), for which, for example, the well-known RSVP protocol(Resource Reservation Protocol), which ensures the reservation of the required bandwidth in the channel. Used to provide network routers with general traffic characteristics (for example, data transfer rate, variability). Routers then bring together requests for resource allocation on common sections of video traffic routes. The protocol is actively used by Cisco routers.

Transmission of Unicast, Broadcast and Multicast traffic.

There are three main methods of transmitting traffic in IP networks, these are - Unicast, Broadcast And Multicast.

Understanding the difference between these methods is very important for understanding the benefits of IP television and for the practical organization of broadcasting video over an IP network.

Unicast traffic (single-purpose packet transmission) is used primarily for “personal” services. Each subscriber can request personal video content at any time convenient for him.

Unicast traffic is routed from one source to one destination IP address. This address belongs to only one single computer or subscriber STB on the network as shown in the figure below.

Number of subscribers who can receive unicast traffic at the same time is limited by the flow width (flow speed) available in the backbone of the network. For the case of a Gigabit Ethernet network, the theoretical maximum data flow width can approach 1 Gb/s minus the bandwidth required for transmitting service information and technological equipment reserves. Let's assume that in the backbone part of the network, for example, we can allocate no more than half the bandwidth for services that require unicast traffic. It is easy to calculate for the case of 5Mb/sec per MPEG2 television channel that the number of simultaneously receiving unicast subscriber traffic cannot exceed 100.

Broadcast traffic (packet broadcast) uses a special IP address to send the same data stream to all subscribers on a given IP network. For example, such an IP address could end in 255, such as 192.0.2.255, or have 255 in all four fields (255.255.255.255).

Multicast traffic (multicast packet transmission) is used to transmit streaming video when it is necessary to deliver video content to an unlimited number of subscribers, without overloading the network. This is the most commonly used type of data transmission in IPTV networks, when the same program is watched by a large number of subscribers.

Multicast the traffic uses a special class of destination IP addresses, such as addresses in the range 224.0.0.0.....239.255.255.255. These can be Class D IP addresses.

The basic rules of operation of the IGMP protocol are as follows:

The end node of the network sends an IGMP report type packet to initiate the connection process to the distribution group;

A node does not send any additional packets when it disconnects from a distribution group;

The m ulticast router sends IGMP requests to the network at certain time intervals. These queries determine the current state of distribution groups;

The host sends an IGMP response packet for each distribution group as long as there is at least one client of that group.

In IP networks there is 3 main methods of data transfer: Unicast, Broadcast, Multicast.

Unicast(unicast) – the process of sending a packet from one host to another host.

Multicast(multicast) – the process of sending a packet from one host to a limited group of hosts.

Broadcast(broadcast) – the process of sending a packet from one host to all hosts on the network.

These 3 types of data transfer are used for different purposes, let's take a closer look.

Unicast

The Unicast data transfer type is used for normal host-to-host data transfer. The Unicast method works in client-server and peer-to-peer networks.

In unicast packets, the specific IP address of the device for which this packet is intended is used as the destination IP address. The IP address of a specific device consists of a portion of the network address (in which this device is located) and a portion of the host address (the portion that determines this specific location in its network). This all leads to the ability to route unicast packets throughout the network.

Multicast and broadcast packets, unlike unicast packets, have their own special (reserved) IP addresses for use in the packet header as a destination. Because of this, broadcast packets are mostly limited to the local network. Multicast traffic can also be limited to the boundaries of the local network, but on the other hand it can also be routed between networks.

In IP networks, a unicast address is an address, that is, the address of the end device (for example, a computer). For the unicast data transfer type, host addresses are assigned to two end devices and are used as the source IP address and destination IP address.

During the encapsulation process, the sending host places its IP address in the unicast packet header as the source address, and the receiving host's IP address is placed in the header as the destination address. Using these two IP addresses, unicast packets can be transmitted across the entire network (i.e., across all subnets).

Multicast

The multicast transmission type was developed to save bandwidth in IP networks. This type reduces traffic by allowing hosts to send a single packet to a selected group of hosts. To reach multiple destination hosts using unicast data transmission, the source host would need to send the same packet to each destination host. With the multicast data transfer type, the source host can send just one packet, which can reach thousands of destination hosts.

Examples of multicast data transmission:

video and audio mailing
exchange of route information used in routed protocols.
software distribution
news feeds

Multicast clients

Hosts that want to receive specific multicast data are called multicast clients. Multicast clients use services initiated (started) by client programs to distribute multicast data to groups.

Each multicast group represents one multicast destination IP address. When a host broadcasts data for a multicast group, the host puts the multicast IP address in the packet header (in the destination section).

For multicast groups, a special block of IP addresses is allocated, from 224.0.0.0 to 239.255.255.255.

Broadcast

Examples when broadcast data transmission is used:

creating a map of the membership of upper-level addresses to lower ones (for example, what IP address is on a specific device with its MAC address)
address request (ARP protocol can be taken as an example)
routing protocols exchange route information (RIP, EIGRP, OSPF)

Similarly, when a host needs to send information to all hosts on the network, it creates a broadcast packet with its information and transmits it to the network.

There are two types of broadcast data transmission: directed broadcast and limited broadcast.

Directional broadcast

A directed broadcast is sent to all hosts on a specific network. This type of broadcast is useful for sending broadcast traffic to all hosts outside the local network.