Asynchronous Transfer Mode (ATM)
#1

Definition
These computers include the entire spectrum of PCs, through professional workstations up to super-computers. As the performance of computers has increased, so too has the demand for communication between all systems for exchanging data, or between central servers and the associated host computer system.The replacement of copper with fiber and the advancement sin digital communication and encoding are at the heart of several developments that will change the communication infrastructure. The former development has provided us with huge amount of transmission bandwidth. While the latter has made the transmission of all information including voice and video through a packet switched network possible.

With continuously work sharing over large distances, including international communication, the systems must be interconnected via wide area networks with increasing demands for higher bit rates.
For the first time, a single communications technology meets LAN and WAN requirements and handles a wide variety of current and emerging applications. ATM is the first technology to provide a common format for bursts of high speed data and the ebb and flow of the typical voice phone call. Seamless ATM networks provide desktop-to-desktop multimedia networking over single technology, high bandwidth, low latency network, removing the boundary between LAN WAN.

ATM is simply a Data Link Layer protocol. It is asynchronous in the sense that the recurrence of the cells containing information from an individual user is not necessarily periodic. It is the technology of choice for evolving B-ISDN (Board Integrated Services Digital Network), for next generation LANs and WANs. ATM supports transmission speeds of 155Mbits / sec. In the future, Photonic approaches have made the advent of ATM switches feasible, and an evolution towards an all packetized, unified, broadband telecommunications and data communication world based on ATM is taking place.

These computers include the entire spectrum of PCs, through professional workstations upto super-computers. As the performance of computers has increased, so too has the demand for communication between all systems for exchanging data, or between central servers and the associated host computer system.
The replacement of copper with fiber and the advancement sin digital communication and encoding are at the heart of several developments that will change the communication infrastructure. The former development has provided us with huge amount of transmission bandwidth. While the latter has made the transmission of all information including voice and video through a packet switched network possible.

With continuously work sharing over large distances, including international communication, the systems must be interconnected via wide area networks with increasing demands for higher bit rates.For the first time, a single communications technology meets LAN and WAN requirements and handles a wide variety of current and emerging applications. ATM is the first technology to provide a common format for bursts of high speed data and the ebb and flow of the typical voice phone call. Seamless ATM networks provide desktop-to-desktop multimedia networking over single technology, high bandwidth, low latency network, removing the boundary between LAN WAN.
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#2
[attachment=3039]


A SEMINAR REPORT ON
ASYNCHRONOUS TRANSFER MODE(ATM)

INTRODUCTION
High performance, cell-oriented switching and multiplexing technology

Utilizes fixed-length packets to carry different types of traffic

Helps in efficient multimedia applications, high-speed LAN connections and used in broad range of networking

devices
OVERVIEW
BENEFITS OF ATM

high performance via hardware switching
dynamic bandwidth for bursty traffic
class-of-service support for multimedia
scalability in speed and network size
common LAN/WAN architecture
opportunities for simplification via VC architecture
international standards compliance

ATM CELL HEADER FORMAT
ATM REFERENCE MODEL
ATM ADDRESS FORMAT
ATM SERVICE CLASSES
constant bit rate (CBR)


variable bit rate“non-real time (VBR“NRT)

variable bit rate“real time (VBR“RT)

available bit rate (ABR)

unspecified bit rate (UBR)
ATM TECHNICAL PARAMETERS

cell loss ratio (CLR)
cell transfer delay (CTD)
cell delay variation (CDV)
peak cell rate (PCR)
burst tolerance (BT)
sustained cell rate (SCR)
ATM STANDARDS

A cohesive set of specifications that provide a stable ATM framework.
Provide the end-to-end service definitions
An important ATM standard is interworking between ATM and frame relay
Two ATM networking standards
1)broadband intercarrier interface (B“ICI) 2)public network-to-network interface (P“NNI)

DATA INSERTION SCHEMES

RFC1483-specifies how interrouter traffic is encapsulated into ATM
LANEMPOA- support dynamic use of ATM SVCs
voice and video adaptation schemes-for efficient traffic that no natural breaks, such as a circuit carrying bits

at a fixed rate
ATM LAN EMULATION(LANE)
VIDEO OVER ATM

Handled by VBR“RT VCs using AAL“5 for MPEG2 on ATM for video-on-demand applications
MPEG2 coding can result in two modes:
program streams”variable-length packets carrying single or multiple programs
transport streams”188-byte packets that contain multiple programs
Time stamps are inserted into MPEG2 packets during the encoding and multiplexing process to make better use of

networking resources.

VOICE OVER ATM

VBR“RT connections is used over ATM which uses silence period.
Various dynamic compression techniques are used to free bandwidth and alleviate congestion
A further enhancement is to support voice switching over SVCs which interprets PBX (private branch exchange)

signaling and routing voice calls to the appropriate destination PBX

NETWORK TRAFFIC MANAGEMENT

objectives :To deliver quality-of-service (QoS) for multimedia applications and provide overall optimization of

network resources.

categorized into three distinct elements
nodal-level controls that operate in real time
network-level controls operate in near real time
network engineering capabilities operating in non real time
ATM APPLICATIONS
ATM AND IP INTERWORKING

ATM and IP offer: Scalability, traffic engineering, service differentiation, high availability, value-added

applications such as Virtual Private Networks (VPNs)
Some specifications of ATM and IP
Multi-Protocol over ATM (MPOA) as addition to LAN Emulation (LANE)
Additions to ATM's superior routing protocol PNNI
adoption of Frame-based ATM over Sonet/SDH (FAST)

CONCLUSION

ATM technology is the only technology that can guarantee a certain and predefined quality of service.
The growth of the Internet, need for broadband access and e-commerce are spurring the need for a reliable,

flexible, scalable, predictable, versatile transport system and that is given by ATM Technology.
For voice, video, data and images together, the next generation network depends on ATM.
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#3


Asynchronous Transfer Mode (ATM)

ATM

Definition

Acronym for automated teller machine, a machine at a bank branch or other location which enables a customer to perform basic banking activities (checking one's balance, withdrawing or transferring funds) even when the bank is closed.


Read more: http://investorwords308/ATM.html#ixzz1Zz5X2CDE
ATM Introduction
Asynchronous Transfer Mode (ATM) is the CCITT standard for broadband ISDN. It supports integrated voice, data, and video communications both for services available and for future services not yet defined [12] [6]. In ATM the information to be transmitted in divided into short 53 byte packets or cells, which have a 5 byte header. The reason for such a short cell length is that ATM must deliver real time service at low bit rates and thus it minimizes packetization delay. ATM networks are connection oriented with virtual channels and virtual paths. The virtual channel carries one connection while a virtual path may carry a group of virtual channels. This ensures that cell sequence is maintained throughout the network. The virtual channel is identified by the Virtual Channel Identifier, (VCI), and the virtual path is identified by the Virtual Path Identifier, (VPI). Both the VCI and VPI may change within the network and they are stored in the header of the cell. There is a Payload Type, (PT), field in the header which indicated whether the cell is user data or connection management information and also to indicate congestion in the network. There is also a Cell Loss Priority, (CLP), bit which is set high to indicate that the cell is low priority and set low to indicate high priority. There is a Generic Flow Control, (GFC), field which is for further study, but is essentially used for controlling the source to network connection. The whole header is protected an eight bit CRC contained in the Header Error Control, (HEC), field. The typical header therefore looks like that shown in Figure 2 for the user to network interface as specified by the ATM Forum [1].

As ATM will be a broadband service the network will be a high speed one. To lessen the effect of the relatively slow processors within the network only a subset of functions will be carried out in the network. Error detection, correction, and flow control are done at the network edge rather than within the network. At the start of a call to set up a connection in terms of a virtual channel, there is negotiation between the user and the network on the parameters. Once admission is achieved the call is then monitored to ensure that it is compliant with the call setup paprameters. The network may drop low priority cells if congestion is about to or has occured. High priority cells may only be dropped when there are no lower priority cells left to drop. Services not sensitive to cell loss may have some low priority cells and these cells may be dropped. Because of this it is possible to get much higher utilisation than with previous networks
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#4
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#5
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#6
[attachment=9822]
Asynchronous Transfer Mode (ATM)
Issues Driving LAN Changes

• Traffic Integration
– Voice, video and data traffic
– Multimedia became the ‘buzz word’
• One-way batch Web traffic
• Two-way batch voice messages
• One-way interactive Mbone broadcasts
• Two-way interactive video conferencing
• Quality of Service guarantees (e.g. limited jitter, non-blocking streams)
• LAN Interoperability
• Mobile and Wireless nodes
ATM
• ATM standard (defined by CCITT) is widely accepted by common carriers as mode of operation for communication – particularly BISDN.
 ATM is a form of cell switching using small fixed-sized packets
ATM Conceptual Model Four Assumptions
1. ATM network will be organized as a hierarchy.
User’s equipment connects to networks via a UNI (User-Network Interface).
Connections between provided networks are made through NNI (Network-Network Interface).
2. ATM will be connection-oriented.
A connection (an ATM channel) must be established before any cells are sent.
ATM Connections
• two levels of ATM connections:
virtual path connections
virtual channel connections
• indicated by two fields in the cell header:
virtual path identifier VPI
virtual channel identifier VCI
3. Vast majority of ATM networks will run on optical fiber networks with extremely low error rates.
4. ATM must support low cost attachments.
• This decision lead to a significant decision – to prohibit cell reordering in ATM networks.
è ATM switch design is more difficult.
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#7
[attachment=10984]
Asynchronous Transfer Mode (ATM)
An Overview of ATM

• ATM is Asynchronous Transfer Mode.
• ATM is originally the transfer mode for implementing Broadband ISDN (B-ISDN).
• In 1988, CCITT (from ITU) issued the first two recommendations relating to B-ISDN:
– I.113 Vocabulary of Terms for Broadband Aspects of ISDN
– I.121 Broadband Aspects of ISDN
• In 1911, the ATM Forum was created with the goal of accelerating the development of ATM standards.
• Connection-oriented packet-switched network
• Used in both WAN and LAN settings
• Signaling (connection setup) Protocol:
– Q.2931
• Packets are called cells (53 bytes)
– 5-byte header + 48-byte payload
• Commonly transmitted over SONET
– other physical layers possible
• Connections can be switched (SVC), or permanent (PVC).
Variable vs. Fixed-Length Packets
• No Optimal Length
– if small: high header-to-data overhead
– if large: low utilization for small messages
• Fixed-Length Easier to Switch in Hardware
– simpler
– enables parallelism
Big vs. Small Packets
• Small Improves Queue behavior
– finer-grained pre-emption point for scheduling link
• maximum packet = 4KB
• link speed = 100Mbps
• transmission time = 4096 x 8/100 = 327.68us
• high priority packet may sit in the queue 327.68us
• in contrast, 53 x 8/100 = 4.24us for ATM
– near cut-through behavior
• two 4KB packets arrive at same time
• link idle for 327.68us while both arrive
• at end of 327.68us, still have 8KB to transmit
• in contrast, can transmit first cell after 4.24us
• at end of 327.68us, just over 4KB left in queue
• Small Improves Latency (for voice)
– voice digitally encoded at 64KBps (8-bit samples at 8KHz)
– need full cell’s worth of samples before sending cell
– example: 1000-byte cells implies 125ms per cell (too long)
– smaller latency implies no need for echo cancellors
• ATM Compromise: 48 bytes = (32+64)/2
• ATM operates on a best effort basis.
• ATM guarantees that cells will not be disordered.
• Two types of connections:
– Point-to-point
– Multipoint (Multicast)
• Four Types of Services:
– CBR (Constant Bit Rate)
– VBR (Variable Bit Rate)
– ABR (Available Bit Rate) Flow Control, Rate-based, Credit- based
– UBR (Unspecific Bit Rate) No Flow control.
• Aggregate Bandwidth vs. Shared Medium (FDDI, Fast Ethernet).
ATM Characteristics
• No error protection or flow control on a link-by-link basis.
• ATM operates in a connection-oriented mode.
• The header functionality is reduced.
The information field length is relatively small and fixed
ATM Layer Service
• Transparent transfer of 48-octet data unit
• Deliver data in sequence on a connection
• Two levels of multiplexing
• Three types of connections
– Point-to-point
– Point-to-Multipoint
– Multipoint-to-Multipoint
• Transport is best-effort
• Network QoS negotiation
• Traffic control and congestion control
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#8

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