The internet is expanding rapidly. This expansion is no doubt aided by the ideas and implementations of the TCP/IP protocol stack. Based on the OSI model of design, each layer of the TCP/IP suite is comprised of a series of almost independent protocols which all rely on the underlying IP protocol.
The IP protocol is a datagram model in which all data is split up into segments of a certain size. For the IP protocol, it does not matter what is inside the segment, only that it is from a particular host, and is destined for a specific sink. (These assumptions are valid, even for one to many communication such as Multicasting). Due to the simplicity of the IP protocol, there is nothing to guarantee anything - except that the contents is valid (checksumed), and that it is only for a specific source-sink pair. As the datagrams are in effect stateless, it is up to higher layer to provide any specialist services such as receipt of the packet and even actual application data to the deliveried. As such, hosts do not use the IP packet directly (The onlyexception is the ICMP protocol) but rely on a protocol directly above this bottom IP layer in the TCP/IP suite that is known as 'transport layer' - the protocols that act within this layer are known as 'transport protocols'.
These transport protocols have one function - to enable applications to do something useful. As such, all OS's have a set of API's to enable packet formation and sending. Although applications will create the data to be sent and package it within a transport protocol packet, the packet still has to be set within an IP segment before it can be sent out into the network.
There are two main transport protocols that are commonly used today: User Datagram Protocol (UDP) and Transmission Control Protocol (TCP). The former offers a unreliable way of transferring information, i.e., one does not know explicitly that a send packet is received; whilst the latter offers a reliable service; for every packet of information that is sent, some kind of ‘acknowledgement’ is received by the sending host. UDP can offer a greater raw performance as it does not require the extra overhead of acknowledging information. However, as UDP offers no kind of signalling from the network to discover its' state, it can be potentially dangerous if used maliciously (denial of service attacks).
Currently, the Internet is based mainly on the connectionless communication model of the IP protocol, in which UDP and TCP is encapsulated and used to get packets across the internet. IP has no inherent mechanisms to delivery guarantees according to traffic contracts and hence mechanisms to reserve network resources have to be done via other means. Because of this, IP routers on a given data path from source to destination may suffer from congestion when the aggregated input rate exceeds the output capacity. Consequently, flows tend to experience varying network conditions that affect the original traffic profile from the source.
Whilst TCP has adapted well to the improvements in network speed since it’s incarnation with link speeds of kilobits/sec, with networks becoming standard at 100mbits/sec, a user is often lucky to get over 40mbits/sec when transferring a file without knowledge of ‘tuning’ or tweaking. Research Groups such as Web100 [Web100] are putting effort to achieve 100% utilisation of network resources by placing more informative logging information about a TCP connection. However, these efforts seem to be more of a patch to the problems of TCP rather than a real fix, and as such some research groups believe that TCP have any place in the future of High Speed Grid Networks.
High Performance Protocols
The optimisation of high performance, high throughput network transport protocols is very important. There is a clear need to maximize the network transport performance and efficiency in order to maximise the network resource utilisation. These considerations apply to both the throughput and latency of network connections. This was demonstrated in the case studies shown.
TCP is one of the most widely used transport protocols with friendly congestion control mechanisms. It has been extensively studied, extended, and refined in the last two decades and has proven to be reliable under a variety of network conditions and applications requirements. Increasingly, however, the standard TCP implementations are becoming inadequate to support high-performance distributed science applications emerging in the science community. These science applications are expected to generate petrabits/sec traffic to be distributed to scientists in different geographical location. With the practical throughput of enhanced TCP implementations still far below Gbit/sec speeds, further research and development efforts are required to enhance the existing TCP stack or to develop a new flexible universal transport protocols that will deliver and sustain multi-Gbits/sec to scientific applications.
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