| Lesson 6 | Internet multicasting |
| Objective | Describe internet multicasting. |
Internet Multicasting
Internet multicasting is an IP-based networking technique used to broadcast various media types from a single source to multiple end-points. In recent years, Internet multicasting has exploded in popularity. Multicasting has become a key tool for an architect as this technology supports:
IP Multicast will be that protocol that adds security, reliability, quality of service, multicast signal tracing, usage accounting and dynamic tunneling to overcome lack of support. This protocol will act like a Swiss army knife for inter-domain IP Multicast, providing all of the missing elements from the current Multicast model. IP Multicasting: A multicast sends information to many recipients at once, as opposed to a unicast, which is a transmission directed to a single recipient. Multicasting can be used to videocast media such as news bulletins, stock quotes, weather reports, and conferences.
Multicasting does not consume bandwidth like classic internetworking, which really is a peer-to-peer (many-to-many) form of networking. Multicasting supports a one-to-many, unidirectional paradigm over the Internet (or VPNs of Internet technology, such as Extranets and Intranets). Despite advances in bandwidth production due to ADSL[1], cable modems, ATM[2], and Gigabit Ethernet[3], many believe that without multicasting, bandwidth production will not keep up with bandwidth demand (that is, without multicasting, the Internet could be really slow).
- Video streaming
- Radio simulation
- Webcasts
- IP Multicast Initiative:
The IP Multicast Initiative ipmulticast.com was a consortium of multicast vendors, large consumers, network providers, and standards bodies. The Initiative offered a variety of information services, memberships, and sponsorships. The IP Multicast Initiative excels as an on-going educational source on Multicasting.
IP Multicast will be that protocol that adds security, reliability, quality of service, multicast signal tracing, usage accounting and dynamic tunneling to overcome lack of support. This protocol will act like a Swiss army knife for inter-domain IP Multicast, providing all of the missing elements from the current Multicast model. IP Multicasting: A multicast sends information to many recipients at once, as opposed to a unicast, which is a transmission directed to a single recipient. Multicasting can be used to videocast media such as news bulletins, stock quotes, weather reports, and conferences.
Multicasting does not consume bandwidth like classic internetworking, which really is a peer-to-peer (many-to-many) form of networking. Multicasting supports a one-to-many, unidirectional paradigm over the Internet (or VPNs of Internet technology, such as Extranets and Intranets). Despite advances in bandwidth production due to ADSL[1], cable modems, ATM[2], and Gigabit Ethernet[3], many believe that without multicasting, bandwidth production will not keep up with bandwidth demand (that is, without multicasting, the Internet could be really slow).
MBone Multicasting
Routers and Switches
Cisco now supports multicasting capabilities in its routers and switches. Therefore, e-Commerce architects should remain aware of opportunities to use multicasting in their solutions.
- MBone Multicasting: Did you know that an entire segment of the Internet is dedicated to Multicasting? It is known as the MBone.
MBone acts as a common, shared utility for Multicasting. MBone can save customers significant costs, and can connect new sets of E-Commerce users together in an entirely unique fashion. Many ISPs already offer their customers access to this service. Mbone (short for "multicast backbone") was an experimental backbone for IP multicast traffic across the Internet developed in the early 1990s. It required specialized hardware and software. Since most Internet routers have IP multicast disabled due to concerns of bandwidth tracking and billing, the Mbone evolved to connect multicast-capable networks over the existing Internet infrastructure. The commercialization of multicast routers is difficult because there are no efficient access control capabilities to the multicast trees (multicast routers and their protocols), and because Internet service providers have difficulty computing charges for multicast traffic. - Multicast in hosts
- Send is easy. just use a class D address as destination
- Receive is more complicated
- Processes create sockets and bind to port
- Process calls setsockopt(s, IP_PROTO, IP_ADD_MEMBERSHIP) | Joins multicast group
- IP-stack sends IGMP report on network
- More than one process may join same group
Can use different (UDP) ports - But only one IGMP report is sent
- When last process leaves IGMP leave is sent
Link-level/Hardware Multicast- Ethernet - good example of hardware multicast
Most Ethernet NICs support multicast - Ethernet multicast addresses:
The low order bit of the high order byte is 1:
*1:**:**:**:**:**
- Many NICs on the same network may listen to the same Ethernet multicast address.
- Other Link-level layers may not support multicast, being NBMA (Non-Broadcast Multiple Access)
eg ATM, FR, X25
Internet Multicasting Considerations
Consider ways multicasting can be used
Multicasting introduces entirely new concepts into the Internet experience. Multicast challenges the architect to bring richer, unidirectional application delivery to e-Commerce through:
When you need to send data to many receivers simultaneously, you have two options: repeated transmission and broadcast.
Repeated transmission may be acceptable if the cost is low enough and delivery can be spread out over time, as with junk mail or electronic mailing lists. Otherwise, a broadcast solution is required. With real-time multimedia, repeated delivery is feasible, but only at great expense to the sender, who must invest in large amounts of bandwidth. Similarly, traditional broadcast channels have been very expensive if they cover significant numbers of recipients or large geographic areas. However, the Internet offers an alternative solution: IP multicast effectively turns the Internet into a broadcast channel, but one that anyone can send to without having to spend huge amounts of money on transmitters and government licenses. It provides efficient, timely, and global many-to-many distribution of data, and as such may become the broadcast medium of choice in the future.
Multicasting introduces entirely new concepts into the Internet experience. Multicast challenges the architect to bring richer, unidirectional application delivery to e-Commerce through:
- Streaming video/audio
- One-way presentations, such as auditorium simulations
- Web radio
- Webcasts
When you need to send data to many receivers simultaneously, you have two options: repeated transmission and broadcast.
Repeated transmission may be acceptable if the cost is low enough and delivery can be spread out over time, as with junk mail or electronic mailing lists. Otherwise, a broadcast solution is required. With real-time multimedia, repeated delivery is feasible, but only at great expense to the sender, who must invest in large amounts of bandwidth. Similarly, traditional broadcast channels have been very expensive if they cover significant numbers of recipients or large geographic areas. However, the Internet offers an alternative solution: IP multicast effectively turns the Internet into a broadcast channel, but one that anyone can send to without having to spend huge amounts of money on transmitters and government licenses. It provides efficient, timely, and global many-to-many distribution of data, and as such may become the broadcast medium of choice in the future.
Breakthrough Technology
Internet is a datagram network
The Internet is a datagram network, meaning that anyone can send a packet to a destination without having to reestablish a path. Of course, the boxes along the way must have either precomputed a set of paths, or they must be relatively fast at calculating one as needed, and typically, the former approach is used. However, the sending host need not be aware of or participate in the complex route calculation; nor does it need to take part in a complex signaling or call setup protocol. It simply addresses the packet to the right place, and sends it. This procedure may be a more complex procedure if the sending or receiving systems need more than the default performance that a path or network might offer, but it is the default model.
Adding multicast to the Internet does not alter the basic model. A sending host can still simply send, but now there is a new form of address, the multicast or host group address. Unlike unicast addresses, hosts can dynamically subscribe to multicast addresses and by so doing cause multicast traffic to be delivered to them. Thus the IP multicast service model can be summarized:
Sending multicast traffic is no different from sending unicast traffic except that the destination address is slightly special. However, to receive multicast traffic, an interested host must tell its local router that it is interested in a particular multicast group address; the host accomplishes this task by using the Internet Group Management Protocol (IGMP).
Point-to-multipoint communication is nothing new. We are all used to the idea of broadcast TV and radio, where a shared medium (the radio frequency [RF] spectrum) is partitioned among users (transmitter or TV/ radio station owners). It is a matter of regulation that there is typically only one unique sender of particular content on any given frequency, although other parts of the RF spectrum are given over to free use for multiparty communication (police radio, citizen band radio, and so on). The Internet multicast model [3] is very similar. The idea is to convert the mesh wide-area network that is the Internet (whether the public Internet, a private enterprise net, or intranet makes no difference to the model), into a shared resource for senders to send to multiple participants, or groups.
To make this group communication work for large-scale systems in the sense of a large number of recipients for a particular group, or in the sense of a large number of senders to a large number of recipients, or in the sense of a large number of different groups it is necessary, both for senders and for the routing functions to support delivery, to have a system that can be largely independent of the particular recipients at any one time. In other words, just as a TV or radio station does not know who is listening when, an Internet multicast sender does not know who might receive packets it sends. If this scenario sends out alarm bells about security, it shouldn't. A unicast sender has no assurance about who receives its packets either. Assurances about disclosure (privacy) and authenticity of sender/recipient are largely separate matters from simple packet delivery models. Security is a topic of much research and the focus for the recently formed Internet Research Task Force (IRTF) research group, Secure Multicast Group (SMuG).
It has been posited that eventually multicasting will draw together television and the Web. If you think about it, TV is based on multicasting as well. The architect should look for opportunities to take advantage of multicasting in e-Commerce solutions.
Adding multicast to the Internet does not alter the basic model. A sending host can still simply send, but now there is a new form of address, the multicast or host group address. Unlike unicast addresses, hosts can dynamically subscribe to multicast addresses and by so doing cause multicast traffic to be delivered to them. Thus the IP multicast service model can be summarized:
- Senders send to a multicast address
- Receivers express an interest in a multicast address
- Routers conspire to deliver traffic from the senders to the receivers
Sending multicast traffic is no different from sending unicast traffic except that the destination address is slightly special. However, to receive multicast traffic, an interested host must tell its local router that it is interested in a particular multicast group address; the host accomplishes this task by using the Internet Group Management Protocol (IGMP).
Point-to-multipoint communication is nothing new. We are all used to the idea of broadcast TV and radio, where a shared medium (the radio frequency [RF] spectrum) is partitioned among users (transmitter or TV/ radio station owners). It is a matter of regulation that there is typically only one unique sender of particular content on any given frequency, although other parts of the RF spectrum are given over to free use for multiparty communication (police radio, citizen band radio, and so on). The Internet multicast model [3] is very similar. The idea is to convert the mesh wide-area network that is the Internet (whether the public Internet, a private enterprise net, or intranet makes no difference to the model), into a shared resource for senders to send to multiple participants, or groups.
To make this group communication work for large-scale systems in the sense of a large number of recipients for a particular group, or in the sense of a large number of senders to a large number of recipients, or in the sense of a large number of different groups it is necessary, both for senders and for the routing functions to support delivery, to have a system that can be largely independent of the particular recipients at any one time. In other words, just as a TV or radio station does not know who is listening when, an Internet multicast sender does not know who might receive packets it sends. If this scenario sends out alarm bells about security, it shouldn't. A unicast sender has no assurance about who receives its packets either. Assurances about disclosure (privacy) and authenticity of sender/recipient are largely separate matters from simple packet delivery models. Security is a topic of much research and the focus for the recently formed Internet Research Task Force (IRTF) research group, Secure Multicast Group (SMuG).
It has been posited that eventually multicasting will draw together television and the Web. If you think about it, TV is based on multicasting as well. The architect should look for opportunities to take advantage of multicasting in e-Commerce solutions.
[1]
Asymmetric Digital Subscriber Line (ADSL): Allows more data to be sent over existing copper telephone lines
[2]
Asynchronous Transfer Mode (ATM): A network technology that transfers data at very high speeds in cells or packets of a fixed size. This enables ATM equipment to transmit video, audio, and computer data over the same network, assuring that a single type of data does not hog the line.
[3]
Gigabit Ethernet: Provides increased network bandwidth and interoperability among existing Ethernets at operating speeds from 10 Mbps to 1000 Mbps.