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Understand telephone and cable networks used for data transmission. Explains the different services offered by Telephone Networks. Discuss the most popular modems are available for data transmission. Introduction : Data communications and networking are changing the way we live. They are 1.
A translating plug nozzle was used. Sixteen airworthy Tu airplanes were built: the prototype Tu, registration number a pre-production Tu, number nine production TuS, numbers to five TuD models, numbers to The last production aircraft, TuD number , was not completed and was left derelict for many years on Voronezh East airfield. There was at least one ground test airframe for static testing in parallel with the development of prototype Although its last commercial passenger flight was in , production of the Tu did not cease until , when construction of the airframe was stopped and left partially complete.
Operational service[ edit ] Tu with distinctive droop-nose at the MAKS exhibition The TuS went into service on 26 December , flying mail and freight between Moscow and Alma-Ata in preparation for passenger services, which commenced on 1 November An Aeroflot freight-only service recommenced using the new production variant TuD "D" for Dal'nyaya — "long range"  aircraft on 23 June , including longer routes from Moscow to Khabarovsk made possible by the more efficient Kolesov RD turbojet engines, which also increased the maximum cruising speed to Mach 2.
In , TuD were used to train pilots for the Soviet Buran space shuttle. In — TuD No.
Further research was planned but not completed, due to lack of funding. They offered a Tu as a testbed for its High Speed Commercial Research program, intended to design a second-generation supersonic jetliner called the High Speed Civil Transport.
In , TuD No. The aircraft made 27 flights in Russia during and Tejavia Systems, the company handling the transaction, reported in September that the deal was not signed as the replacement Kuznetsov NK engines from a Tupolev Tu bomber were military hardware and the Russian government would not allow them to be exported.
In March , it was reported that both aircraft would be preserved,  [ unreliable source? Reasons for failure and cancellation[ edit ] Early flights[ edit ] Tu at the Paris Air Show, 2 June , day before the crash Early flights in scheduled service indicated the TuS was extremely unreliable.
During flights and hours of freight and passenger flight time, the TuS suffered more than failures, 80 of them in flight. After the inaugural flight, two subsequent flights, during the next two weeks, were cancelled and the third flight rescheduled. Failures included decompression of the cabin in flight on 27 December , and engine-exhaust duct overheating causing the flight to be aborted and returned to the takeoff airport on 14 March The flight with passengers suffered the failure of 22 to 24 onboard systems.
Seven to eight systems failed before takeoff, but given the large number of foreign TV and radio journalists and also other foreign notables aboard the flight, it was decided to proceed with the flight to avoid the embarrassment of cancellation. After takeoff, failures continued to multiply.
Due to expected political fallout, Soviet leader Leonid Brezhnev was personally notified of what was going on in the air. With the accumulated failures, an alarm siren went off immediately after takeoff, with sound and volume similar to that of a civil defence warning.
The crew could not figure a way to switch it off so the siren stayed on throughout the remaining 75 minutes of the flight. Eventually, the captain ordered the navigator to borrow a pillow from the passengers and stuff it inside the siren's horn.
After all the suspense, all landing gear was extended and the aircraft was able to land.
Considering the high rate of technical failures their reasoning was sound. Bookings were limited to 70—80 passengers or fewer a flight, falling well below both the Tu's seating capacity and the demand for seats.
With officials acutely aware of the aircraft's poor reliability and fearful of possible crashes, Soviet decision-makers deliberately limited flight frequency to as few as would allow them to claim to be offering a regular service, and they also limited passenger load to minimize the impact and political fallout of a possible crash. The problem, discovered in , may have been known prior to this testing; a large crack was discovered in the airframe of the prototype Tu aircraft during a stopover in Warsaw following its appearance at the Paris Air Show.
While at the time, this approach was heralded as an advanced feature of the design, it turned out that large whole-moulded and machined parts contained defects in the alloy's structure that caused cracking at stress levels below that which the part was supposed to withstand. Once a crack started to develop, it spread quickly for many metres, with no crack-arresting design feature to stop it.
Contraction and expansion happen because of the cooling during ascent and descent, heating during supersonic acceleration and cruise and because of the pressure change from high altitude low outside pressure causing the airframe to expand to ground-level pressure causing it to contract. The airframe cracked in a similar way to that during TsAGI load testing. Aircraft fly with acceptable cracks until they are repaired. The Tu design was the opposite of standard practice, allowing a higher incidence of defects in the alloy structure, leading to crack formation and propagation to many metres.
Decision to go back to passenger service[ edit ] This section does not cite any sources. Please help improve this section by adding citations to reliable sources. Unsourced material may be challenged and removed. December Learn how and when to remove this template message The Soviet leadership made a political decision to enter the Tu into passenger service in November despite receiving testing reports indicating that the Tu airframe was unsafe and not airworthy for regular service.
Aeroflot appears to have thought so little of the aircraft that it did not mention it in its five-year plan for — However, it was not the airline executives' decision and Aeroflot reluctantly put the Tu into passenger service on 1 November Though the decision to cancel the TuS passenger service came a few days after the TuD crashed during the test flight on 23 May , this crash was regarded as the last straw over mounting concerns about the reliability of the Tu Even the fact that the technical reason for the crash was specific to the TuD fuel pump system and did not apply to the TuS did not help.
The decision to pull the TuS out of passenger service after merely 55 flights is thus more likely to be attributable to high incidence of failures during and before the scheduled flights. Cabin noise[ edit ] A problem for passengers was the very high level of noise inside the cabin, measured on average at least dB. In addition, the unique active heat insulation system, which used a flow of spent cabin air, was described as excessively noisy. Passengers seated next to each other could have a conversation only with difficulty, and those seated two seats apart could not hear each other even when screaming and had to pass hand-written notes instead.
Noise in the back of the aircraft was unbearable. Alexei Tupolev acknowledged the problem to foreign passengers and promised to fix it, but never had the means to do so. The request was made despite obviously not helping to foster Soviet technological prestige, which was one of the key purposes of the Tu programme. The design of air intakes' variable geometry and their control system was one of the most intricate features of Concorde, contributing to its fuel efficiency.
Over half of the wind-tunnel time during Concorde development was spent on the design of air intakes and their control system. In late , the USSR requested a wide range of Concorde technologies, evidently reflecting the broad spectrum of unresolved Tu technical issues. The list included de-icing equipment for the leading edge of the air intakes, fuel-system pipes and devices to improve durability of these pipes, drain valves for fuel tanks, fireproof paints, navigation and piloting equipment, systems and techniques for acoustical loading of airframe and controls to test against acoustic fatigue caused by high jet-noise environment , ways to reinforce the airframe to withstand damage, firefighting equipment, including warning devices and lightning protection, emergency power supply, and landing gear spray guards a.
Compressor disc failure in [ edit ] On 31 August , TuD suffered an uncontained compressor disc failure in supersonic flight which damaged part of the airframe structure and systems. The crew was able to perform an emergency landing at Engels-2 strategic bomber base.
Much later than in the West, but since the late s, commercial efficiency was starting to become a factor in aviation development decision-making even in the USSR. In the late s, Soviet insiders were intensely hopeful in conversations with Western counterparts of reintroducing Tu passenger service for the Moscow Olympic games , even perhaps for flights to Western Europe, given the aircraft's high visibility, but apparently the technical condition of the aircraft weighed against such re-introduction even for token flights.
Cessation of TuD production[ edit ] The decision to cease TuD production was issued on 7 January , followed by a USSR government decree dated 1 July to cease the whole Tu programme and to use produced Tu aircraft as flying laboratories. By the way of comparison, Concorde's first flight was originally scheduled for February , but was pushed back several times until March in order to iron out problems and test components more thoroughly. Each bridge has - built in ID normally, serial number - unique Each bridge broadcasts - this ID same that all bridges know which one has the smallest ID Bridge with the smallest ID - is selected as the root bridge root of the tree Assumption: bridge B1 has the smallest ID - so, selected as the root bridge 2.
Algorithm - tries to find the shortest path path with the shortest cost - from the root bridge - to every other bridge or LAN - shortest path can be found by examining the total cost from the root bridge to the destination Fig.
Combination of the shortest paths - creates the shortest tree - shown in Fig. Spanning tree based - marking the ports - which are part of the spanning tree forwarding tree - which, forward a frame that the bridge receives marking also of those ports that are - not part of the spanning tree blocking ports - which block the frames received by the bridge Fig. Maximum data size: incoming frame size - if, is large - for the destination LAN - data must be fragmented into several frames - data need to be reassembled, at the destination No protocol - at the DLL allows the fragmentation and reassembly of frames - this is allowed in network layer Bridge must - discard any frames too large for its system 3.
Data rate: each LAN: type has its own data rate compare the Mpbs data rate of an Ethernet with the 1-Mpbs data rate of a wireless LAN - bridge must buffer the frame, to compensate for this difference 4. Multimedia support: some LANs support multimedia and quality of services needed for this type of communication, others not Two-layer switches Switch Can mean 2 different things Switch meaning can be clarified - by level at which it operates Types: 2-layer switch and 3-layer switch 1.
Manual configuration Network administrator: uses VLAN software - to manually assign the stations into different VLANs at setup Migration - later, from one VLAN to another is also done - manually Note: this is not a physical configuration - it's a logical configuration 'manually': term means that the administrator types the port numbers, IP addresses, or other characteristics - using the VLAN software 2.
Automatic configuration Stations are automatically - connected or disconnected from a VLAN using criteria - defined by the administrator Ex. Semiautomatic configuration Somewhere between -a manual configuration and an automatic configuration Initializing is done manually - with migrations done automatically Communication between switches In multi-switched backbone: each switch must know not only which station belongs to which VLAN - also, the membership of stations connected to other switches Ex.
Table maintenance When a station sends: a broadcast frame to its group members - switch creates an entry in a table and records station membership Switches send - their tables to one another periodically for updating 2. Frame tagging Frame when - is traveling - between switches - an extra header is added to the MAC frame to define the destination VLAN Frame tag is used by the receiving switches to determine the VLANs to be receiving the broadcast message 3.
Time-division multiplexing TDM Connection trunk between switches - is divided into timeshared channels Ex. Cost and time reduction VLANs - reduce the migration cost of stations going from one group to another - physical reconfiguration: takes time and is costly Physically - instead of moving - one station to another segment or even to another switch - much easier and quicker it to - move it by using software 2.