aloha_net (1st wireless net.)

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SUBMITTED BY BHAGYESH DUBEY (IT Dept.) Note : This presentation is free to use. You can reproduce it as you like.

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ALOHA net ROOT / The beginning. / Why there is need to know about Aloha net? / Aloha Protocol. / Types of Aloha. / Aloha Goals & Problem. / Recommended websites / Slotted Aloha / Unslotted Aloha / Advance form of Aloha / Any Doubt or Question / Comparison

Why there is need to know about Aloha net ? : 

Why there is need to know about Aloha net ? Question: When was the first Wireless Network deployed? 1995 (WRONG). 1987 (NOPE). 1982? (huh-uh). The answer is : 1970. It was called ALOHANET and it anticipated many of the core network protocols in use today, including Ethernet and Wireless Fidelity (aka WiFi ®).

The beginning… : 

The beginning… Most credit Goes to Guglielmo Marconi, “the father of radio”, with the initiation of wireless technology 1894 Marconi experimented with Hertzian Waves (radio waves) to produce and detect waves over long distances 1896 Marconi established the Wireless Telegraph & Signal Company, the first radio factory 1901 St John’s, New Foundland, Marconi received the first trans-Atlantic wireless signal from Poldhu, England 1905 the first distress signal sent using Morse Code 1919 Radio Corporation of America (RCA) was incorporated, and consumer radio broadcasts for news and entertainment soon became popular

US Military jumps into Wireless : 

US Military jumps into Wireless During World War II the US Military used wireless signals with encryption to send battle plans and instructions. US Military started the shift to radio data transmission technology. ARPANET (Advanced Research Projects Agency Network) developed by ARPA of the United States Department of Defense during the cold war, supports research team of University of Hawaii in project of Wireless Network Development.

Aloha: Birth of the Wireless Network : 

Aloha: Birth of the Wireless Network The ALOHA network was created at the University of Hawaii in 1970 under the leadership of Norman Abramson and others (including N. Gaarder and N. Weldon). The idea was to use low-cost amateur radio-like systems to create a computer network linking the campuses of the University.

ALOHA : 

ALOHA In Hawaiian it means Hello ! Or Bye ! Traditional Dance

ALOHA Project : 

ALOHA Project Goal To build computer network in University of Hawaii. To investigate the use of radio communications as an alternative to the telephone system for computer communication. To determine those situations where radio communications are preferable to conventional wire communications

Physical Setup of Aloha : 

Physical Setup of Aloha ALOHANET used a bidirectional star topology consisting of (7) computers over (4) islands.

Problem : 

Problem Limited Resource: Channel Intermittent operation typical of interactive computer terminal don’t need point-to-point channels. (FDMA or TDMA) Spread Spectrum is not appropriate to share the channel.

Approach : 

Frequency Band: Two 100KHz bandwidth channels at 407.350MHz and 413.475MHz. TCU (Terminal Control Unit): Formatting of the ALOHA packets. Retransmission protocol. A Terminal attached TCU by means of RS232. Half duplex mode. (too expensive memory) Packet Broadcasting Channels for design simplicity. Each user transmits its packets over the common broadcast channel. Key innovation of ALOHA Protocol. Approach

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Figure 1.1 Data link layer divided into two functionality-oriented sublayers ALOHA PROTOCOL

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Figure 1.2 Taxonomy of multiple-access protocols discussed in this chapter

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RANDOM ACCESS PROTOCOL In random access or contention methods, no station is superior to another station and none is assigned the control over another. No station permits, or does not permit, another station to send. At each instance, a station that has data to send uses a procedure defined by the protocol to make a decision on whether or not to send. ALOHA PROTOCOL . Topic discussed in this section:

The ALOHA protocol : 

The ALOHA protocol The ALOHA protocol is an OSI layer 2 protocol for LAN networks with broadcast topology. The first version of the protocol was basic:- If you have data to send, send the data. If the message collides with another transmission, try resending “later” .

Types of Aloha : 

Types of Aloha There are basically two types of ALOHA systems:- Synchronized or Slotted and Unsynchronized or Unslotted or Pure.

Slotted Aloha : 

Slotted Aloha Time is divided into equal size slots (= pkt trans. time) Node (w/ packet) transmits at beginning of next slot If collision: retransmit pkt in future slots with probability p, until successful Success (S), Collision (C), Empty (E) slots

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Figure 12.6 Frames in a slotted ALOHA network

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Figure 1.7 Vulnerable time for slotted ALOHA protocol

Slotted ALOHA Channel Capacity : 

Slotted ALOHA Channel Capacity Each user can start his packet only at certain fixed instants. Statistical Analysis It increase the throughput

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The throughput for slotted ALOHA is S = G × e-G . The maximum throughput Smax = 0.368 when G = 1.

Pure (Unslotted) ALOHA : 

Pure (Unslotted) ALOHA Unslotted Aloha: simpler, no synchronization Pkt needs transmission: Send without awaiting for beginning of slot Collision probability increases: Pkt sent at t0 collide with other pkts sent in [t0-1, t0+1]

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Figure 12.3 Frames in a pure ALOHA network

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Figure 12.4 Procedure for pure ALOHA protocol

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Figure 12.5 Vulnerable time for pure ALOHA protocol

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The throughput for pure ALOHA is S = G × e -2G . The maximum throughput Smax = 0.184 when G= (1/2).

Comparison : 

Comparison Slotted Aloha Protocol Advantages: 1.Doubles the efficiency of Aloha. 2.Adaptable to a changing station population. Disadvantages: 1.Theoretically proven throughput maximum of 36.8%. 2.Requires queueing buffers for retransmission of packets. 3.Synchronization required.

Comparison : 

Pure Aloha Protocol Advantages: 1.Superior to fixed assignment when there is a large number of burst stations. 2.Adapts to varying number of stations. Disadvantages: 1.Theoretically proven throughput maximum of 18.4%. 2.Requires queueing buffers for retransmission of packets. Comparison

Advance form of Aloha : 

Advance form of Aloha WiFi (Wireless Fidelity ). Bluetooth - PAN WiMax. 3g. 4g.

Recommended websites : 

Recommended websites http://www.ieee.org/ http://www.iss.net/wireless/WLAN_FAQ.php http://www.practicallynetworked.com/support/wireless_secure.htm http://www.laynetworks.com/ http:// en.wikipedia.org/wiki/ALOHAnet/

Questions ?OrDoubts : 

Questions ?OrDoubts

F.A.Q : 

F.A.Q

Which was first built Slotted or Unslotted ? : 

Which was first built Slotted or Unslotted ? 1971: start operation in University of Hawaii. 1971-72: build additional TCUs. 1972: connect to ARPANET using satellite channel. (56kbps) 1973: Metcalfe’s doctorial dissertation about packet broadcasting. 1973: PACNET, international satellite networks. (9600 bits/s) 1973 ~ : Many researches about “packet broadcasting”. 1976: slotted ALOHA. 1984: unslotted ALOHA in the UHF band by Motorola.

Why Using Packet Switching and Packet Broadcasting? : 

Why Using Packet Switching and Packet Broadcasting? Packet switching can provide a powerful means of sharing communication resources. But it employ point-to-point channels and large switches for routing. By use of packet broadcasting Elimination of routing and switches. System simplicity Some channels are basically broadcast channel. (satellite, ..) Needs unified presentation of packet broadcasting theory.

Which Method is use for Recovery of Lost Packets ? : 

Which Method is use for Recovery of Lost Packets ? Positive Acknowledgements. Transponder Packet Broadcasting. Carrier Sense Packet Broadcasting. Packet Recovery Codes

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SUBMITTED BY:- BHAGYESH DUBEY (IT Dept.)