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Growth of requirements to throughput of local area networks




Lecture 1. Modern problems of RET

 

1 Requirements to the capacity of the channel for different types of service.

2 Encoders of a voice

3 Voice transfer on channels the Internet.

 

Growth of requirements to throughput of local area networks

Today in increasing frequency there are networks raised the requirement to throughput of channels between clients and servers. It occurs for various reasons:

increase in productivity of client computers;

increase in number of users on a network;

appearance of the applications working with the multimedia information which is stored in files of very big sizes;

increase in number of the services working in real time.

Therefore, a need for the economic decision providing the necessary throughput in all listed cases is had. The situation becomes complicated also the fact that different technology solutions - for the organization of trunks of a network and connection of servers one, and for connection of table clients - others are necessary.

10-Megabitny Ethernet suited most of users for about 15 years.

However its insufficient throughput in the early nineties began to be felt. If for computers on Intel 80286 or 80386 processors with the buses ISA (8 MB/s) or EISA (32 MB/s) throughput of an Ethernet segment made 1/8 or 1/32 channels "memory - a disk", then it was well coordinated with a ratio of volumes of local data and external data for the computer. Now at powerful client stations with Pentium or Pentium PRO processors and the bus PCI (133 MB/s) this share fell to 1/133 that it is obviously not enough. Therefore many segments 10-Megabitnogo Ethernet'a became overloaded, response of servers considerably fell in them, and the frequency of origin of collisions significantly increased, even more reducing rated throughput.

Sharp increase in the transferred information volumes on the local and regional area networks led to exhaustion of the available resources, and real forecasts of needs are specified continuation of growth of flows in tens and hundreds of times. The single technology which is capable to satisfy these needs are fiber optic networks (Sonet, SDH, ATM, FDDI, Fiber Channel). Channels of these networks are capable to provide throughput of 155-622 Mbit\s already today, development and tests of channels with throughput times more, for example, of a gigabit Ethernet are carried at 2-20. The technique of multiplexing of frequencies in optical fiber (WDM) is mastered that allows to lift its broadbandness by 32 times and in the long term to bring high-speed performance of channels to 80 Gbit\s and more. In process of growth of throughput problems of control, synchronization and reliability increase. Practically all networks are built with use of serial links today. It is connected first of all to the cost of cables, though there are exceptions (for example, HIPPI). Different network services impose different requirements to broadbandness of the channel. In fig. 1.6 the frequency ranges for main types of telecommunication services are provided. In the Internet practically all listed services are available already today (except TV of high resolution). Promptly distributed systems of computation (for example, the GREED project), control and information service develop. The modern microprocessor technology assumes achievement of high-speed performance in 5 Gbit\s by 2003-4 years (technology with a characteristic size of objects on a crystal of 80-130 nanometers).

The technique of multiplexing of frequencies in optical fiber (WDM) is mastered that allows to lift its broadbandness by 32 times and in the long term to bring high-speed performance of channels to 80 Gbit\s and more. In process of growth of throughput problems of control, synchronization and reliability increase. Practically all networks are built with use of serial links today. It is connected first of all to the cost of cables, though there are exceptions (for example, HIPPI). Different network services impose different requirements to broadbandness of the

 

channel. In fig. 1.6 the frequency ranges for main types of telecommunication services are provided. In the Internet practically all listed services are available already today (except TV of high resolution). Promptly distributed systems of computation (for example, the GREED project), control and information service develop. The modern microprocessor technology assumes achievement of high-speed performance in 5 Gbit\s by 2003-4 years (technology with a characteristic size of objects on a crystal of 80-130 nanometers).

Such system will wake the master at the appointed time, will warm up a breakfast, will remind of the forthcoming affairs per day, will request and will provide to the master a fresh weather forecast and help about road condition, will timely make the order for the air ticket, etc. All this is technologically possible already today, so far is rather expensive, but the prices very quickly fall. The CAN network developed for data collection and driving can be an example. Rapid extension of the Internet has no analogs in the history so any most fantastic forecast in this area can come true.

Protocols the Internet (TCP/IP) exist about 30 years. Requirements to telecommunication channels and services grew, and this set of protocols doesn't meet the modern requirements. There are new protocols of Delta-t (for control of connection), NetBLT (for transmission of large volumes of data), VMTP (for transactions; RFC-1045) and XTP for increase in efficiency of data transfer (TCP changeover), units of protocols for operation with a multimedia (RTP, RSVP, PIM, ST-II and so forth), but, certainly, the most revolutionary changes will cause implementation of IPv6.

Requirements to throughput of communication links

The architecture of SteelTrace is constructed by the principle of Offline of clients with a controlled cycle of autonomy. The system is calculated that terminal communication links (as a rule it is Wi-Fi or GRPS) can not guarantee a continuous communication with the server and have low throughput. The minimum requirements to conducting communication links are provided in the following table.

Connection type Minimum requirements to a communication channel Interaction
  WiFi Capacity of the channel 20 kbit/s Interaction of stationary and mobile terminal with servers. Synchronization of reference books, broadcast of subjects of the account
  GPRS Capacity of the channel 20 kbit/s Operating time isn't limited Interaction of stationary and mobile terminal with pull web servers.
  Ethernet Capacity of the channel 64 kbit/s Interaction Steel Trace Server with pull web servers, servers of bases dates.

 

 

For execution of direct requests (for example broadcast of weight on the server in the Online mode) to each 10 new user

applications need to increase throughput of the channel by 10 Kbit\s.

 

Encoders of a voice

This technology finds application in military communication systems, in the dispatcher services, and also in systems of peydzherny communication. Developers of transformers of a voice considered features of operation of a throat, vocal chords and all organs of articulation. Ringing and deaf sounds are reproduced different methods here (by means of the pulse oscillator and the noise generator, respectively). The flowchart of the transformer of a sound like vocoder is shown in fig. 2.4.2.1. The initial range of a human voice here is divided into a row of the subranges (in fig. 2.4.2.1 their numbers ravno16) on 200 Hz everyone. These subranges are selected with narrowband filters which rectifiers and low pass filters (20 Hz) follow. Output signals of these filters are multiplexed and will be transformed to the digital form. Frequency of time gating of these signals makes about 50 Hz. Digit capacity of ATsP in this case can make 3 bits. On the receiving end the digital-to-analog conversion (DTAC) and multiplexing is carried out. The balanced amplitude modulators, controlled DACs and the switch, give signals on narrowband filters. All these signals mix up in the adder, and the result is reproduced.

It isn't difficult to see what in case of the diagram shown on fig. 2.4.2.1, necessary high-speed performance of the transferring line makes 3 bits * 50 Hz * 16 channels = 2,4 Kbps. The further scoring can be received for the score of digital compression. The number of channels (filters) and width of the passed frequency band can vary, also quality of a sound playback will change respectively. Minimum possible bandpass range of the transferring line in case of which value of the transferred text still is perceived correctly lies lower than 1 Kbps.

The prior phrase, including gaps and punctuation marks, contains about 150 characters. Its pronunciation requires about 10 sec. (15 characters in sec.). But even the vocoder will need this sentence to transfer at least 10000 bits. From where such difference?

Fig. 2.4.2.1. Flowchart of coding/decoding of a human voice (Vocoder)

 

First, the human speech is individual also this phrase said by different people will sound differently, besides, there is an emotional coloring which practically deprived alphabetic record. Secondly, even the most perfect modern system of compression of sound information isn't ideal and there is a wide field for further enhancement. Ways can be different depending on an objective. If it is required to transfer only information, it is necessary to transform a sound to a symbolical (alphabetic) form, to transfer these data in a digital form, and on the host party to perform the return transformation. Alphabetic representation can be also subjected to some compression, but it will inevitably increase a reproduction delay. In effect, this scheme is development of the ideas pledged in a voice coder.

In case of need transmissions of specific features of a voice, at first the analysis of these personal differences shall be carried out. Features of a voice are in coded form transferred to the receiving end where these data are used further in case of reproduction of the coded text. These diagrams will demand enough powerful signal processors and will probably find application only in the next century.

 

 





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