Course Code (MSc-TNS)         Asynchronous Transfer Mode (ATM)                 Switching Report                   Assignme...
Abstract: Asynchronous Transfer Mode (ATM) switching is a switching technique use forBroadband Integrated Services Digital...
asynchronous nature of ATM makes it more efficient as compare to the synchronoustechnique such as time-division multiplexi...
The simplest type of switch architecture is single bus. It consists on single bus which inparallel connects multiple circu...
Multi- BusesFigure 3: Multiple Buses2.3. Self-Routing Bus:Self routing is a complex switching architecture and use amalgam...
Figure 4: Self Routing3. Switching Operation:ATM switch carry out a number of operations through input and output ports. G...
3.3.   Management Platform: This platform is to control and maintain the operation of    network, and to guarantee that ev...
4.2 .Output Module: The function of the output module is the converse of input module. It    prepares the ATM cells for ph...
making all decisions in relation to admissions control, and switch resource allocation for    different connection.5.2.   ...
virtual path is working as similar as pipes with a specified bandwidth assigned to it. To     implement dynamic routing in...
7. Conclusion   In this brief report our central focus was on ATM switching. ATM switching was   elaborated in a detail wh...
8. Glossary   ATM - Asynchronous Transfer Mode   B-ISDN - broadband integrated services digital network.   CAC - connectio...
Bibliography[1]. McDysan, David E., and Darren L. Spohn. Hands-on ATM. New York: McGraw-Hill,1998. Print[2]. Kasera, Sumit...
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M Sc Tns 2823134 Assignment 1 Atm Switching Abidafsar

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M Sc Tns 2823134 Assignment 1 Atm Switching Abidafsar

  1. 1. Course Code (MSc-TNS) Asynchronous Transfer Mode (ATM) Switching Report Assignment 1Author:Abid Afsar 1Abid Afsar
  2. 2. Abstract: Asynchronous Transfer Mode (ATM) switching is a switching technique use forBroadband Integrated Services Digital Network (B-ISDN). In this paper we will investigatethe ATM switching architecture, operation, functional components and feature such as,switch fabrics, switch buffering, and so on. We will explore the ATM switching designstypes, and the trade-offs it involve. ATM switch sends information in the form of cell relay orcell and use virtual channel for internal routing. The core duties of ATM switching involverouting, cell forwarding, and management. Moreover, the ATM switching techniques werenot a part of ATM standards.Keywords: ATM, Cell Relay, B-ISDN, virtual channel, switch architecture, ATM standards.1. IntroductionAsynchronous Transfer Mode (ATM) is a standard network switching method formed byInternational Telecommunication union telecommunication standardisation Sector (ITU-T). Itwas developed in the early 1980’s for the purpose to unify telecommunication and computernetworks, and to get together the requirements of Broadband Integrated Services DigitalNetwork. The need of ATM is vital for an increase integration of every sort of applicationsuch as data and voice, audio and video, and so on. The internet is evolving at a very highspeed and this shift in network paradigm brings a unique amalgamation of multimedia, highspeed, and real time services.The integration of communication needs powerful switches to process, and to performrouting with a high accuracy. ATM is a connection oriented switching technique, it usevirtual channel to connect network nodes. The virtual channel (VC) has a uniqueidentification and is refereed as virtual channel identification (VCI). ATM switching takesdifferent approach in regards to packets propagation, and size constraints as compare topacket switching, frame really and Ethernet. It use cells of equal size, and propagates it byusing time division multiplexing mechanism. ATM taking services of data link layer andphysical layer of Open System Interconnection (OSI) model. ATM inherits the features ofcircuit switching because it based on cell switching and multiplexing technology. The 2Abid Afsar
  3. 3. asynchronous nature of ATM makes it more efficient as compare to the synchronoustechnique such as time-division multiplexing because it do not waste empty slots.2. Switch Fabric Architecture:ATM switch architecture is available in several flavours. The most know architectures whichare widely used are single bus, multiple bus and self routing. Self routing can be furtherdivide into two forms blocking and non-blocking switch architecture. The core purpose ofthe ATM switch fabric is to transfer cell from one point to another. The switching use thecombination of software and hardware to pass the incoming data from network node toinput ports and from output ports to other network node, the process is referred as switchingfabrics or switching matrices. The switch designs can be hybrids and can accommodate onelarger switch fabrics to connect other switches or combinations of smaller switch fabricsmake one larger switch fabrics. We will discuss the switch architecture in terms components,and attributes such as, input module (IM), output module (OU), admission connection control(CAC), switch management (SM), scalability, blocking level, maximum overall speed, andsupport of multicast. Diagrammatically the switch architecture can be represented as Figure 1: A generic view of ATM switch2.1. Single Bus: 3Abid Afsar
  4. 4. The simplest type of switch architecture is single bus. It consists on single bus which inparallel connects multiple circuit board trace. The speed of single bus is between 1 and 10Giga bit per second (Gbps). The complexity level involved with single bus is low. In terms ofscalability the single bus performance is poor because of the load on single bus. The blockinglevel at each port is low due to bus controller call to arbiter to decide that who will get the busfirst and so on. And multicasting is easy in this sort of bus for the reason that all outputlistening to the same bus. Diagrammatically it is represented as, Bus Figure 2: Single Bus2.1. Multi Bus:Multi bus switching architecture works on the concept of broadcasts and do broadcast oneach input port. It eliminates the requirement of bus arbitrations unlike single bus. As thearchitecture is changed it adds extra requirements to output port. In multiple buses each busshared with multiple circuit board trace. The maximum speed range is between 1 to 20 Gbps.In relation to output port, if it receives numbers of cells simultaneously then the inputbuffering technique is used for arbitration purpose. And bus control entails blocking tomange output ports. This architecture of bus is also called knockout switch architecturebecause every outputs inlet receives only limited number of inputs simultaneously whichmakes it favourable choice for scalability. And multicasting is entailed in the nature of thissort of bus. Diagrammatically it is represented as, 4Abid Afsar
  5. 5. Multi- BusesFigure 3: Multiple Buses2.3. Self-Routing Bus:Self routing is a complex switching architecture and use amalgamated switching attributesand components. It is widely in use in Batcher Banyan networks; it can easily scale largesize of switching components, and is suitable for Very Large Scale Integration (VLSI). It stillneeds in-depth research due to its complex nature of operations. The speed of self routing andinputs are same, therefore it has a high probability of blocking. As compare to thecounterparts of switching architecture it run with high speeds. Diagrammatically it isrepresented as Self Routing (Blocking) Self Routing (Non-Blocking) 5Abid Afsar
  6. 6. Figure 4: Self Routing3. Switching Operation:ATM switch carry out a number of operations through input and output ports. Generallyswitch involved a list of jobs such as routing, cell forwarding, and connection controlsmanagements with other switches and so on.3.1. User platform: The job of switch is to route input cells to designated output ports. The cells are encapsulated in a header with payload bytes. When these cells reach to input ports a virtual connection is established which are uniquely identified by virtual path identifier and virtual circuit identifier (VPI/VCI) and drive these cells to expected end user node. In user plan the core functions are mainly performed by input module, switch matrix, and output modules.3.2. Control Platform: The control platform is responsible for connection establishing, and controls of virtual path and virtual circuit (VP/VC). The information in the payload in this case in not visible to the network. In this platform the switch tagging signal and even produce some signal by itself. The Connection Admission Control (CAC) doing the job of signalling and which is indispensable. The switch fabric may or may not receives the signalling or may be pass by Signalling System No. 7 (SS7) network signalling protocol standard. 6Abid Afsar
  7. 7. 3.3. Management Platform: This platform is to control and maintain the operation of network, and to guarantee that everything is working at optimum rate. The management operations are further categorised as, traffic management operation, accounting management operation, performance management operation, fault management operation, security management operation and so on. These operations are accomplished by switch management module; it is also responsible for ATM Operation and Management layer (OAM) functions. Furthermore, it has to determine OAM signalling and may produce OAM signal. The switch management module also reinforce UNI interface that is called Interim Local Management Interface (ILMI).3.4. Traffic Control Operations: The operations such as connection admission control (CAC), congestion control, and network parameter UPC/NPC are also reinforcing by switching technique. The operation to control congestion is the responsibility of switch management module, and the operations to maintain network parameter UPC/NPC is the responsibility of input module.4. Switch Interfaces4.1 Input Module: The function of input module (IM) is to manage table lookup and VCI/VPI translation. When a cell arrives at input module in first attempt it is VPI value is extracted in cell header because VPI value is used in the address table for link identification. The VPI/VCI are not unique on every link and chances of duplication can occur, to resolve this issue ATM switch use separate address table for each link and also add link identifier with VPI/VCI. A number of methods can be used for table lookups such as hashing, search trees or content addressable memories and so on. It can be determine from the table lookups that the particular VPI value may matches VPC or VCC. If the VPI value corresponds to VCC then the concerned information can be fetched from translation lookup table, such as new VPI value, outgoing interface identifier, cell priority, jitter, and delay. In addition the input module convert SONET optical signal to electrical signal, doing HEC error check for every incoming cell and discard faulty of damage cells, it differentiate between OAM cells and signalling cells. 7Abid Afsar
  8. 8. 4.2 .Output Module: The function of the output module is the converse of input module. It prepares the ATM cells for physical transmission medium. It converts the electrical signals into optical signals, create new HEC field and encapsulate it in header, multiplex user cells, OAM cells, and signalling cells; doing cell rate decoupling.5. Cell Switch fabric: The main purpose of the cell switch fabric module is to transfer packets from input ports to out ports. A typical switch fabric is a combination of switch elements and transmission links. Switch fabric is also called interconnection structure. The transmission link only carries packets and has no power to make intelligent decisions. On the other hand switch elements are performing intelligent decisions such as internal routing, management and so on. In addition, it also accomplishing activities such as cell buffering, multitasking and broadcasting, cell priority and delay scheduling, provide redundancy in relation to fault tolerance, monitor congestion, traffic concentration and multiplexing.5.1. Connection Admission Control (CAC): The function of CAC is to establish, terminate, modifies VP/VC connections. The CAC core duties cover the followings issues such as to work with higher layer signalling protocol, VPCs/VCCs switch resource distribution and section of route, parameters generation of UPC/NPC, negotiations in regards to user traffic contracts, and modification of VPCs/VCCs, provide signalling reinforcement to ATM Adaptation layer (AAL) in terms of interception or generation of signalling cells, and making decisions on VPCs/VCCs request acceptance or refusal. In case of centralised CAC the single processing unit receives the signalling cells from input module. And further CAC performed interpretation of incoming signalling cells and 8Abid Afsar
  9. 9. making all decisions in relation to admissions control, and switch resource allocation for different connection.5.2. Switched Management: The function of the switched management is to manage the internal operations and components, elements of the switch which are listed as support of network management, configuration management, customer network management, switch and their security control, traffic management and performance management. In relation to switch management area and research. The area is under development and have no particular standards are established until today. The switch management is a wide and complex area, entails a number of management operations and the level of management can vary from nominal to complex. The initial jobs of switch management is to gather information and their management, close contacts with network manger and user, and supervisions and coordination of all operations performing in relation to switch. A bottleneck situation arises when switch is overloaded in centralized switch management. This can negatively affects the overall performance of the switch management. Therefore, it is vital that a switched management administer and supervise all incoming inputs to input module, and similarly for output module.5.3. Concentration: In ATM switch the concentration work is to resolve all the traffic flow at the input module before recuing the switch fibre module. Concentrator workout to combine lower variable bit rate to higher variable bit rate for the sake to standardize the flow or speed of traffic at input interface.5.4. Routing and Buffering: Routing and buffering is a core function of switch fabric. Although ATM switch is not oblige to use routing protocol. Two types of routing are normally which are dynamic and static, if static routing protocol is in implementation then dynamic routing is not required. In ATM switch the concept of virtual path was purposely added to make things easier for routing. The incoming cell arrives at input ports at switch fabric are simply route to the anticipated output ports. The role of the 9Abid Afsar
  10. 10. virtual path is working as similar as pipes with a specified bandwidth assigned to it. To implement dynamic routing in ATM switch it use a link-state routing protocol is referred as Public Network Network Interface (PNNI). Buffers are required when an input or output module receives a number of cells simultaneous for same input or output.5.5. Shared Memory Approach: in this approach the incoming cells are in first attempt converted from parallel to serial structure and stored in a random access memory sequentially. The controller job is to make decisions in regards memory reading, writing, and sequence. It can also inspect cell header, and switch fabric internal routing tags.6. Switched Designs Principal6.1. Buffering Approaches: The use of buffer has a positive effect on switch performance and efficiency. Three approaches of buffering are applied in switch which are input buffering, internal buffering and out buffering. The input buffer is placed before the input module to control the simultaneous traffic for the input ports but this is suffer from head of line problem and it is still subject for further study. Out buffer is implementing at the exit point of out module to manage the flow of cells to the next network node and improve the level of traffic which are passing through. It improves the overall delay time and throughput but it entails speed factor which negatively impact the level of scalability for large networks. Internal Buffering6.2. Internal Blocking: The internal blocking is a one of the operating mode of ATM switches. It arises when N numbers of cells are addressed to N number of multiple outputs which result conflict or collide with each other at output ports level. In general unblocking switches are preferable to blocking switches but un-blocking fabric switch do not use buffer which is known cause of congestion and collision. It negatively affects the throughput, performance of the fabric module. It also affects the scalability of the fabric switch. 10Abid Afsar
  11. 11. 7. Conclusion In this brief report our central focus was on ATM switching. ATM switching was elaborated in a detail which involves switching architecture approaches that entails single bus, multi bus, and self-routing. In this paper ATM switching system is consist on interfaces which is composed of input and output module, the switched management performing duties such as connection, OAM layer functions, and cell fabric switch module were briefly studied. Furthermore, the cell switch fabric is also refereed as switch matrix that constitutes concentration, buffer management, and shared memory were discussed. 11Abid Afsar
  12. 12. 8. Glossary ATM - Asynchronous Transfer Mode B-ISDN - broadband integrated services digital network. CAC - connection admission control NNI - network to node interface PNNI - private network to network interface PVC – permanent virtual circuit VC - virtual circuit VCI - virtual circuit Identifier VCC - virtual channel connection HEC- header error check 12Abid Afsar
  13. 13. Bibliography[1]. McDysan, David E., and Darren L. Spohn. Hands-on ATM. New York: McGraw-Hill,1998. Print[2]. Kasera, Sumit. . Atm Networks Concepts And Protocols. Second ed. New Delhi: TataMcGraw-Hill Professional, 2008. Networking Ser. Google. Tata McGraw-Hill PublishingCompany Limited, 01 Jan. 2008. Web. 12 Nov. 2011. <http://books.google.ie>.[3]. Perros, Harry G. "An Introduction to ATM Networks - Harry G. Perros." Google Books.N.p., n.d. Web. 14 Nov. 2011. <http://books.google.ie/books?id=ghy9BOw6svMC>.[4]. "Asynchronous Transfer Mode (ATM) Switching." CCS Voice, Data, Video, Fiber OpticCabling Los Angeles, California. N.p., n.d. Web. 14 Nov. 2011. <http://www.ccs-cabling.com/>.Reading List[1]. "ATLAS I Overview Transparencies (ICS-FORTH, ATM Switch)." CARV-ICS-FORTH, Heraklion, Crete, Greece. N.p., n.d. Web. 14 Nov. 2011.<http://archvlsi.ics.forth.gr/atlasI/gen_talk1.html>. 13Abid Afsar
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