Task: Your task is to write a 6-10 page DOUBLE spaced paper (11 point font, 1 inch margins) which discusses an area of distributed or parallel systems.
Grading: The evaluation will be based upon, but not limited to, the following categories:
topic choice coverage of topic accuracy of information presented English (grammar and spelling included) clarity of presentation
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ATM is a switch-based technology. Providing connectivity through a switch (instead of a shared bus) results in several benefits such as: dedicated bandwidth for each connection; higher aggregate bandwidth, well-defined connection procedures and flexible access speeds.
The ATM protocol model consists of the ATM physical layer, ATM layer, and the ATM adaptation layer.
2.1. Physical Medium Sub-layer
The physical medium sub-layer is responsible for sending and receiving a continuous flow of bits with associated timing information to synchronize transmission and reception. Because it includes only physical-medium-dependent functions, its specification depends on the physical medium used. ATM can use any physical medium capable of carrying ATM cells.
2.2. Transmission Convergence Sub-layer
The Transmission Convergence Sub-layer is responsible for the following tasks:
a. Transmission Frame Generation and Extraction: The generation and maintenance of the appropriate physical-layer frame structure.
b. Transmission Frame Adaptation: The packaging of ATM cells into frames acceptable to the particular physical-layer implementation by either mapping the ATM cell flow into the payload of the transmission frame, or the extracting the ATM cell flow from the transmission frame.
c. Cell Delineation: The maintenance of ATM cell boundaries from a continuous stream of bits.
d. Header Error Control Sequence Generation and Verification: The generation and check of the header error control code to ensure the data is valid.
e. Cell Rate Decoupling: The adaptation of the rate of valid ATM cells to the payload capacity of the transmission system through insertion or suppression of idle (unassigned) ATM cells.
3.1. Virtual Connections
ATM is a connection-oriented technology and before data transmission takes place in an ATM network, a connection needs to be established between the two ends using a signaling protocol. There are two layers of ATM virtual connections: Virtual Channel Connections (VCC) and Virtual Path Connections (VPC). A VCC is a logical end-to-end connection that concatenates virtual channel links that exists between two switching points. A VPC is contains bundles of VCCs that are switched together as one unit.
Although users are sharing the same physical medium, the VCC/VPC concepts limits the amount of traffic each user can generate according to the negotiated traffic contract between the user and the ATM network. The ATM cells from the users who exceed their traffic contract are either immediately discarded at the control point or marked as a candidate for discard by downstream control points in case of network congestion.
Each channel and path has an identifier associated with it. All channels within a single path must have distinct channel identifiers but may have the same channel identifier as channels in different virtual paths. Its virtual channel and virtual path number can therefore uniquely identify an individual channel.
The virtual channel and path numbers of a connection may differ from source to destination if the connection is switched at some point within the network. Virtual channels that remain within a single virtual path throughout the connection will have identical virtual channel identifiers at both ends. Cell sequence integrity is maintained through a VCC that can either be switched or semi-permanent. Each virtual channel and virtual path has negotiated Quality of Service (QoS) associated with it. This parameter includes values for cell loss and cell delay. Once a connection is established, QoS can be guaranteed.
By using simplified network architecture with enhanced network services the processing required is reduced and the connection setup time is shortened. This results in increased network performance and reliability.
3.1.1. Setting Up A Virtual Connection
There are four ways in which a virtual channel or virtual path may be set up.
1) The virtual channel/path maybe reserved with the network before transmission begins as in the case of a permanent or semi-permanent connection.
2) New connections maybe setup via a meta-signaling procedure across a meta-signaling virtual channel. (Meta-signaling is used to negotiate signaling resources. It can be used to setup and release point to point or selective broadcast signaling virtual channel connections. The meta-signaling cells are carried on a permanent VCC that has a pre-assigned VPI and VCI.)
3) A connection maybe set up as a result of a user to network signaling procedure.
4) A new virtual channel connection may be setup within an existing virtual path connection between two user network interfaces using a user to user signaling procedure.
3.2. The ATM Cell
ATM is a protocol that transmits data as fixed sized packets called cells. The original designers of ATM purposely called it something other than a packet to reduce confusion as ATM cells could be containing IP packets inside it. Although fixed sized cells are less efficient than variable length ones the trade off in network traffic efficiency would be made up by the increase in speed by creating hardware to do cell passing. Small, fixed cell sizes have certain other benefits the small size means high priority cells get through quicker because they will wait a shorter time for low priority cells already being transmitted to get out of the way -- and this improves throughput.
Unlike IP packet headers, the cell header does not include source or destination addresses, only a virtual circuit identifier (VCI) and a virtual path identifier (VPI), indicating the circuit in which it should be delivered. Processing such a short header is very quick and requires very little intelligence at each point for delivery. ATM switches these days can process 10 to 20 million cells per second, reaching possibly 50 million cells in the near future.
There are two different types of ATM Cells. Cells that travel between two ATM switches are referred to as Network Node Interface (NNI) while cells that travel between an end user to an ATM switch are called User-Network Interface (UNI).
3.2.1. ATM Cell Fields
The ATM cell is composed of a 5-octet header and 48-octet payload. The header field is divided into six different fields. The associated bit sizes differ slightly at the NNI and the UNI.
The Generic Flow Control (GFC) is a 4-bit field in the ATM header used only across UNI to control traffic flow and alleviate short-term congestion. It is often used to reduce cell jitters in CBR services, assign fair capacity for VBR services, and to control traffic for VBR flows.
Virtual Path Identifier / Virtual Channel Identifier (VPI/VCI): The role of the VPI/VCI fields is to indicate Virtual Path or Virtual Channel identification numbers, so that the cells belonging to the same connection can still be distinguished. A unique and separate VPI/VCI identifier is assigned in advance to indicate which type of cell is following. In a UNI cell, the VPI is 8 bits and the VCI is 16 bits. In a NNI cell, the VPI is 12 bits and the VCI is 16 bits.
The Payload Type Identifier (PTI) field is 3-bits long and is used for identifying the payload type as well as identifying the control procedures. When the fourth bit is set to 0, it means that it is a user cell. If the third bit is set to 0 in a use cell, it would indicate that the cell did not experience any congestion in the relay between two notes. The second bit is use to indicate the type of user cell. When the fourth bit is set to 1, the cell is used for management functions as error indications across the UNI.
The Cell Loss Priority (CLP) field is used to tell the system whether ATM cell can be discarded if too much network congestion occurs. ATM cells with the CLP bit set to 0 can be discarded while ATM cells with the CLP bit set to 1 cannot. The user or the network can set this bit.
The Header Error Control (HEC) field is an 8-bit CRC used for sensing and correcting cell errors over all filed over the ATM cell header.
A protocol is used to translate higher layer services into the size and format of an ATM cell. The information transported by the ATM adaptation layer is divided according to the following properties:
1) The information being transported is time dependent or independent: It may be necessary to regenerate the time dependency of a signal at the destination.4.1. ATM Adaptation Layer Types
2) Variable or Constant bit rate.
3) Connection or Connectionless mode information transfer.
AAL-2 supports applications that require variable bit rate (VBR) services with a time dependency between the source and destination. Error recovery is also not supported.
AAL-3 is used to support VBR, delay-tolerant data traffic that are connection-oriented and require some sequencing and/or error detection support.
AAL-4 is used to support VBR, delay-tolerant connectionless data traffic that require minimal sequencing or error detection support. AAL-4 is appropriate for networking applications such as TCP/IP. Since the protocol formats of AAL-3 and AAL-4 are similar, they have been merged into AAL-3/4.
AAL-5 was developed to reduce the overhead related to AAL-3/4. Because it supports connection-oriented service more efficiently, it is used to transfer most non-SMDS data, such as classical IP over ATM and local-area network (LAN) emulation.
The ATM adaptation layer is further divided into two sub-layers:
1) Convergence Sub-layer: A service-dependent sub-layer of the AAL where traffic is adapted based on its type. It consists of the general procedures and functions that convert between ATM and non-ATM formats.
2) Segmentation And Re-assembly sub-layer (SAR): A sub-layer of the AAL which is responsible for processing user data that are different in size and format into ATM cells at the sending site and reassembling the cells into the user-defined format at the receiving site.
CBR: Constant Bit Rate.
Cell: A unit of transmission in ATM. A fixed-size frame consisting of a 5-octet header and a 48-octet payload.
CRC: Cyclic Redundancy Check. A mathematical algorithm that computes a numerical value based on the bits in a block of data. This number is transmitted with the data and the receiver uses this information and the same algorithm to insure the accurate delivery of data by comparing the results of algorithm and the number received.
GFC: Generic Flow Control. GFC is a field in the ATM header that can be used to provide local functions (e.g., flow control).
HEC: Header Error Control. Using the fifth octet in the ATM cell header. The check character is calculated using a CRC.
NNI: Network Node Interface. An interface between ATM switches defined as the interface between two network nodes.
QoS: Quality of Service. It is defined on an end-to-end basis in terms of the following attributes of the end-to-end ATM connection: Cell Loss Ratio, Cell Transfer Delay & Cell Delay Variation.
TC: Transmission Convergence. The TC sub-layer transforms the flow of cells into a steady flow of bits and bytes for transmission over the physical medium.
UNI: User-Network Interface. An interface point between ATM end users and a private ATM switch, or between a private ATM switch and the public carrier ATM network.
VBR: Variable Bit Rate.
VCC: Virtual Channel Connection. A concatenation of virtual channel links that extends between the points where the users of the ATM service access the ATM layer.
VCI: Virtual Channel Identifier. A unique numerical tag as defined by a 16-bit field in the ATM cell header that identifies a virtual channel, over which the cell is to travel.
VPI: Virtual Path Identifier. An eight-bit field in the ATM cell header that indicates the virtual path over which the cell should be routed
Coulouris, George; Dollimore, Jean; Kindberg, Tim; 1994. Distributed Systems: Concepts and Design. Second Edition. Addison Wesley, New York.
Parhami, Behrooz. 1999. Introduction to Parallel Processing: Algorithms and Architectures. Plenum Press, New York.
Zomaya, Albert Y. 1996. Parallel and Distributed Computing Handbook. McGraw-Hill, Montreal, Quebec.
(Web Resources)
ATM Networks: A Series of Tutorials
Tutorials that were given by Professor Raj Jain at Lucent Technologies (AT&T) during the first half of 1996.
http://www.cis.ohio-state.edu/~jain/atm/
This website describes current Asynchronous Transfer Mode (ATM) technologies that network designers can use in their networks today. It also makes recommendations for designing non-ATM networks so that those networks can take advantage of ATM in the future without sacrificing current investments in cable.
http://www.ieng.com/univercd/cc/td/doc/cisintwk/idg4/nd2008.htm
The Networks and Telecommunications Research Group is a "working in a wide range of areas involving core networking and telecommunications technology. " The site contains information about the History of ATM, Adaptation Layers and more.
http://ntrg.cs.tcd.ie/4ba2/atm/index.html
The ATM forum is "an international non-profit organization with the objective of accelerating the use of ATM".
http://www.atmforum.com