12.13.06
Posted in Essays, multicast/anycast at 9:14 pm by Sailesh Kumar
Any communication process can be divided into one of the three main categories, unicast, multicast, and broadcast communication. In unicast, messages are sent from one source to one destination; the message may traverse through several intermediate nodes. In broadcast, messages are sent from one source to all destinations which have physical connectivity to the source. Multicast is the process of sending the message from a single source to a subset (containing two or more hosts) of all physically connected destinations. When messages have to be sent from one source to multiple destinations, multicast is generally a much more efficient mode of communication than simply unicasting the message to all destinations. Multicast is efficient because the message need not be replicated for every destination; replication only occurs when the message gets close to the destination. Thus, the links which are close to the source do not require large bandwidth, which is otherwise needed if the same message is unicasted multiple times. Clearly, multicasting has several applications, some of which are multi party video conferencing, broadcasting information to a large number of users, real-time video distribution, etc.
Read the rest of this entry »
Permalink
12.03.06
Posted in Essays, multicast/anycast at 9:44 pm by Michael Roche
IP multicast is a must for the Internet. It provides many advantages over a plain unicast network. With demand growing toward more streaming media, IPTV, and video conferencing applications, multicast becomes more and more of a necessity. There are many advantages that multicast offers to these type of applications. The infrastructure for IP multicast already exists. It is supported by Ethernet and many multicast protocols are already implemented in routers.
Read the rest of this entry »
Permalink
Posted in Essays, multicast/anycast at 9:44 pm by mbecchi
A multicast communication service sends packets from a source to a set of destinations, also called multicast group. The basic underlying idea is to propagate the packets into the network so to reduce the bandwidth involved. If, for instance, a packet has to be sent from a source on ISP x to N recipients connected to another ISP y, then a unique copy of the packet will be first sent from ISP x to ISP y, and then ISP y will locally dispatch N copies of the packet to the interested recipients. In a more general scenario a multicast dissemination tree, that is, a minimum spanning tree rooted at the sender, will be used in order to determine how a multicast packet will be propagated in the network. This solution will involve a degree of bandwidth consumption which is far less than simply having many unicast transmissions between the sender and every recipient.
Read the rest of this entry »
Permalink
12.01.06
Posted in Paper reviews, congestion control at 8:01 pm by Paul Moceri
Streaming media applications such as real-time video and telephony continue to grow and become a large component of Internet traffic. Since such applications favor low delay over reliable transmission they often opt for the unreliable transport protocol UDP. However, UDP lacks built-in congestion control mechanisms leaving applications on their own to implement congestion control, if at all. The other alternative to UDP is TCP which provides congestion control along with reliable transmission. However, applications tend to avoid TCP because delivery guarantees can delay packets to the point that they are unusable to the application and better off dropped. Without proper congestion control, high-bandwidth streaming applications will create havoc on the Internet.
Read the rest of this entry »
Permalink
Posted in Paper reviews, congestion control at 8:00 pm by BrandonHeller
As a network application developer, you have only two realistic choices for your application’s transport layer. You could pick UDP (User Datagram Protocol), which provides unreliable, connectionless data transport, for applications where timeliness is the primary data-delivery concern. You’d be forced to implement congestion control yourself, and one bug could render the network unusable.
Read the rest of this entry »
Permalink
Posted in Paper reviews, congestion control at 7:59 pm by Michael Roche
This paper summarizes the design of Datagram Congestion Control Protocol (DCCP). DCCP is a congestion control protocol to be used with unreliable transfer protocols such as UDP. There are many applications such as streaming media or video conferencing that prefer timely data instead of reliable data. If these applications had the choice of either retransmitting a lost packet or transmitting a new packet, they would choose to transmit the new packet. By the time the old packet would arrive, it would be outdated and useless. In these cases, TCP is a poor choice because of its extra effort given to reliability.
Read the rest of this entry »
Permalink