Asynchronous Transfer Mode Project


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This report presents you the comprehensive overview of asynchronous transfer mode along with its working methods, key benefits, history and issues.

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Asynchronous Transfer Mode Project

  1. 1. Yuba Raj Khadka 1801T3090156ABSTRACT The demands for the communication of data and internet in today’s businessenvironment are springing up every day. The applications having high-bandwidth likevideo conferencing and graphics applications calls for efficient and fast transfer ofdata. Today’s networks are running out of bandwidth. The network users areinvariably calling for more bandwidth than their network is capable of. It was 1980’swhen the researchers in the telecommunications company started to look into theother technologies for the following generation of high speed transfer of data, voiceand video and for the development of broadband ISDN (Integrated Services DigitalNetwork).ATM (Asynchronous Transfer Mode) was developed as the result of thisresearch. Unlike Ethernet, Token ring and FDDI, ATM is a different recent technology,capable of transferring data, voice and video simultaneously over the same line. Fortoday’s incorporated network system, it has become one of the most promisingsolutions. This project gives you the comprehensive overview of an ATM including itsarchitecture, reference model, present status on the management of traffic and newdevelopments like MPLS as well as the related technologies using the very ATMprotocol. 1CNW201
  2. 2. Yuba Raj Khadka 1801T30901561 INTRODUCTION ATM (Asynchronous Transfer Mode) is a recent intricate cell multiplexingand switching technology that is capable of transferring data, graphics, voice and datasimultaneously in real time over the same line across LAN (Local Area Network),MAN and WAN. Due to its efficiency of use, it has become one of the most desirabletechnologies in today’s world. So far as the speed of ATM is concerned, it can makeup to 10 Gbps making it one of the fastest network protocol ever been used. The datain an ATM network in transferred in an asynchronous manner which entails that it cantransfer data when it can. The term Asynchronous also cites to the fact that, in thecircumstances of multiplexing transmission, cells which are allocated to the sameconnection may show an irregular form as they are filled on the basis of the actualrequirements as shown in the below figure. Fig: 1-Asynchronous and Synchronous Transfer Mode [14] 2CNW201
  3. 3. Yuba Raj Khadka 1801T3090156 ATM is an ITU-T (International Telecommunication Union-Telecommunication) standard for cell relay where the information’s regarding data;voices, graphics and video are showed in packets with small size called cells viaswitched based network. Based on the rising standards for B-ISDN, ATM converts allthe incoming data into 53 bytes (5 header bytes and 48 bytes of data) cells. ATM technology can transfer various types of data in a real time over thesame line which is because entire bandwidth is employed, as long as it is available. Incase of other network technologies, they do not allow every bandwidth to be utilizedonce a specific function is initiated making it one of the fastest and efficient way fortransferring data, graphics, video, pictures and even the live streaming video andaudio. ATM is a connection oriented network technology in a sense that they shouldinform every switch about the traffic parameters and service requirements beforecommunications between two systems in a network. Every connection in an ATMnetwork is known as virtual channel or virtual circuit (VC). By determining thenumber of VCs, the connections let the network to guarantee QoS (Quality ofService). Here is the figure of private ATM and public ATM network conveying voice,video and data traffic 3CNW201
  4. 4. Yuba Raj Khadka 1801T3090156 Fig: 2- A private and Public ATM conveying voice, video and data traffic [REF 8]1.1 OBJECTIVES The first objective of this project is to let know everyone that there is also anetwork technology with higher speed characteristics besides frame relay andEthernet and other LAN networking technologies and it is called ATM(Asynchronous Transfer Mode). And then you will know about the prominent featuresand the benefits of ATM including its Quality of Service (QoS). Moreover, the basiccell structures and cell header format, ATM network interfaces, ATM applications,network topology and ATM protocol reference model are presented here in detail.Lastly you will be knowing some of the parameters required to control and managebursty traffic in order to guarantee Q0S (Quality of Service). 4CNW201
  5. 5. Yuba Raj Khadka 1801T30901561.2 HISTORY AND DEVELOPMENTS [REF 4] Before ATM, the networking world used to depend upon specialized networkservice. Relying on those specialized network service bring out many problems likeService Dependence, inefficiency and inflexibility. There were many different typesof services that used to depend on the specific type of network. Advancement of thetechnology increased the complexity for networks to handle different types of servicesand also inefficiency of resources raised because of the internal resources was notavailable to other network. ATM firstly known as Asynchronous Time Division Multiplexing wasdesigned to overcome the inefficiencies of classical TDM (Time DivisionMultiplexing). The technique evolved for encrypting transatlantic conversationbetween Churchill and Roosevelt was synchronous. The actual root of this technologylies in the Bell Labs research project which was held in the late sixties. But wasemerged by ex-CCITTs (Committee Consultatif International Telephonique etTelegraphique which is now known as ITU) study group in the mid-eighties. By the year 1991, to pick up the pace for the development ATM Forum wascreated by telecommunication vendors and a group of four computers with the motiveto develop the ATM products and services. Within last few years there is a dramaticincrease in the number of members in Forum and now it has more than 750 members.They include users, computer industries and research organization, communicationsand agencies. 5CNW201
  6. 6. Yuba Raj Khadka 1801T3090156 The task which was finished in November, 1995 was started in 1993 byCCITT under the recommendations on ATM equipment functional operation andnetwork management. Its specifications are transfer up to its standard bodies forapproval due to this the Forum not being a standards body, the ITU-T recognized theATM Forum as a credible working group. The ATM Forum has originated entirelynew specification by extending standards for private network specific requirements. Nowadays, ATM has achieved world-wide acceptance because it influences,many segments of our society like, touching the consumer, public-service andcommercial markets. Due to its high speed and the integration of traffic types itprovides a single network for all traffic types with new application.ATM will operatesnetwork management by using the same technology for all levels of the network.ATM is protocol independent. ATM guarantees quality of service.ATM is designed tobe scalable and flexible in geographic distance. Multimedia will be one of the keyapplications to use ATM. In the near future ATM is intended to be used as a backbonefor other existing services like frame relay. ATM supposed to improve LAN/Client -Server architectures and LAN interconnection. ATM will provide the resources toease the network demands. Many of the details that are necessary to provide ATMbenefits are still in the standards process. ATM is much more emphasized in road thancommunication so wide range of voice service will not be provided further down theroad, further more it is likely be replaced by another technology such as WavelengthDivision Multiplexing 6CNW201
  7. 7. Yuba Raj Khadka 1801T30901561.3 BASIC FEATURES OF ATM [REF 5] [REF 6] Following are some of the basic features of ATM presented by ITU-T in I.150recommendation: ATM technology employs fixed sized packets called cells. Each cell incorporates o a header and an information field, basically applied to find out the virtual channel and also to carry out the sound routing. Due to the way of ATM networks carrying voice traffic, simple fixed sized cells are used. ATM is a connection oriented network technology in a sense that they should inform every switch about the traffic parameters and service requirements before communications between two systems in a network. Separate virtual circuits are used to carry user information and signals. ATM cells, information fields are conveyed transparently via the network inside which no processing like error control are carried out. Different service like data, video and voice can be carried through ATM, Even the connectionless services. An adaptation function is furnished in order to adapt different services so that every services information is fit into ATM cells. The service particular functions like cell loss recovery, clock recovery etc are possible only because of this adaptation function.Some other magnificent principles of ATM are as follows: [REF 2] ATM is a high speed connection oriented network that employs fiber optics wire, switch with switched point to point connection and are connected to each other and to the end stations. 7CNW201
  8. 8. Yuba Raj Khadka 1801T3090156 In order to pass traffic amongst two positions, it makes use of the virtual networking concept. With ATM network, one is able to transfer a broad range of classes of services of multimedia like text, voice, video over a single network effectively. The high data transfer speed (155 Mbps, 622 Mbps and even 2.5 Gbps) supplied by the ATM network allows a high bandwidth distributed applications due to which the applications like video conferencing applications, applications using video on demand mechanisms are possible. Unlike Ethernet, ATM does not share a wire. When a wire is shared, it becomes overloaded since everybody uses it at the same time. However, in ATM, every computer is directly connected to a switch. It endorses both the basic approaches of switching amongst a single incorporated switching mechanism. This makes ATM suitable for every distributed application generating CBR and VBR traffic. 8CNW201
  9. 9. Yuba Raj Khadka 1801T30901561.4 BENEFITS OF ATM High Quality of Service level (QoS) Quality of Service (QoS) In a networking concept, Quality of Service is a broad set of networking techniques, standards and technologies to manage network traffic in a cost-efficient way so that a high quality performance is ensured for the critical applications. The major purpose of QoS is to enable the network administrators use the available resources effectively and assure the ability of network to give predictable results. For instance: QoS can be used in order to prioritize network traffic for latency sensitive software’s like video and voice applications. Delay (latency), error rate, uptime (availability) and throughput (bandwidth) are some of the elements associated with the quality of service. The networking technologies like Frame relay, ATM and even the primitive LAN technologies like token ring and Ethernet endorses the mechanisms of QoS. 9CNW201
  10. 10. Yuba Raj Khadka 1801T3090156 Network characteristics Descriptions Reliability Percentage of packets discarded by a router Bandwidth The rate of carrying traffic by network Latency The delay in data transfer from source to destination Jitter Variation in latency Fig: 3- networking elements associated with QoS QoS is one of the prominent features of ATM. It was projected to ameliorate QoS and usage on high traffic network. Fixed sized small cells and no routing makes network to manage bandwidth more easily than the primitive LAN technologies like Ethernet. Five broad service categories of ATM [CBR (Constant Bit Rate), VBR (Variable Bit Rate), ABR (Available Bit Rate), UBR (Unspecified Bit Rate), WUBR (Weighted Unspecified Bit Rate),] offer a fine control over the parameters of network traffic which are managed and requested. 10CNW201
  11. 11. Yuba Raj Khadka 1801T3090156 The networks in ATM are more cost efficient. With ATM, you can use various applications on the same network making your administration, operation, materials and operation costs lower. Flexibility Various classes of service in order to carry data, voice and video over a single network are endorsed by the ATM networks. Moreover, ATM networks can allocate every connection to cope with the precise demand of every application. ATM networks are flexible in such a way that it can assure bandwidth from the desktop from DS-1 to OC-12 in the United States while E1, E3, OC-3 and DS-3 globally. Scalability Projected to spring up with your endeavor as your demands and necessities, the ATM networks are able to connect to the networks of Frame relay and can also support it to ATM service internationally. Likewise, various speeds are available (DS3, DS1, OC3, NxDS1 and OC12). The good thing about the ATM technology is that the internetworking with Ethernet, broadband and frame relay can go smoothly. 11CNW201
  12. 12. Yuba Raj Khadka 1801T3090156 Manageability The homogeneous network surroundings of ATM plays significant role to improve the network reliability, flexibility and the performance. Also the carrier’s network management platform takes into account the higher manageability in reporting, troubleshooting and in many more. Secure The recovery of failure and the automatic configuration is possible in ATM networks.Some other benefits of ATM are as follows: [REF 6] ATM networks offer high performance through switching of hardware. For high traffic, ATM can render you the dynamic bandwidth. Supports different classes of services needed for the purpose of multimedia (voice and video). The architecture of LAN and WAN are common in the ATM networks. In compliance with international standards. Like primitive telephony services, ATM technology is connection oriented. Simplified network architecture 12CNW201
  13. 13. Yuba Raj Khadka 1801T30901561.5 ATM STANDARDS ITU-T, IETF (Internet Engineering Task Force) and the ATM forum arethe three main groups responsible for determining the implementation standards forATM network.1.5.1 ITU-T The telecommunication standardization area of the ITU in 1988 developedsome standards for the network in ATM technology. In fact, ATM was developedwhen the researchers in the very ITU Company were trying to find some solutions forB-ISDN. The main purpose of ITU-T is to define the standards for telecommunicationservices. The promising technologies like B-ISDN and SONET were developed byITU-T.Fig: some of the ITU-T recommendations associating to ATM 13CNW201
  14. 14. Yuba Raj Khadka 1801T30901561.5.2 IETF IETF define the standards for the internet. The team of the IETF organizationdeveloped a number of standards for IP traffic over the networks in ATM. Below isthe chart showing the lists of RFCs required for the implementation of IP over ATM. Fig: 4 – standards of IETF associating ATM. 14CNW201
  15. 15. Yuba Raj Khadka 1801T30901561.5.3 ATM Forum Non-profit international team of ATM network software developers, hardwaredevelopers and network service providers, ATM Forum comprises of the workingteams who develop and review the specifications of ATM technology. In order to useATM over private and public networks, the standards of ATM defined by ITU-Torganization were extended.Fig: some of the specifications of ATM forum relating to ATM 15CNW201
  16. 16. Yuba Raj Khadka 1801T30901561.6 ATM APPLICATIONSThere are various pragmatic applications using ATM technology. ATM is going to bethe keystone network for various applications even for the information superhighway.Following are some of the notable applications using ATM technology. LANE (LAN emulation) Access to internet, intranet and extranet (e-mail, text imaging, forms processing) Video and desktop conferencing Communications of the multimedia Packetized video and voice VPI/WAN connectivity E-commerce LAN interconnection Web hosting ATM over satellite communications ATM over wireless mobile computing SNA (System Network Architecture) Terminal-host (client-server) data File transfer Remote access 16CNW201
  17. 17. Yuba Raj Khadka 1801T30901561.7 ATM DEVICES AND THE NETWORKING ENVIRONMENT[REF 5] ATM is a multiplexing and cell-switching connection oriented technologycombing the advantages of both circuit switching and packet switching. It offers youthe bandwidth of few Mbps and can even reach up to many Gbps. Due to theasynchronous nature of ATM, it is more effective than the technologies withsynchronous data transfer. TDM (Time Division Multiplexing) is the suitable exampleof synchronous technologies. In case of TDM, every user is allotted to a time slot. Other station cannot sendin that time slot which is shown in the fig: 4. the station can send as much as data onlyif the time slot rises even if every time slots are free. To its contrary, if a station hasnot anything to send at the time when time slot rises, the very time slot has to be sentempty and become wasted. Fig: 5- operation of normal TDM. [REF 5] 17CNW201
  18. 18. Yuba Raj Khadka 1801T3090156 However, in the case of ATM, on demand with the information referring to theorigin of the transmission held in the header of every ATM cell, time slots areavailable. Fig: 6- ATM multiplexing in asynchronous way. [REF 5] Figure 6 depicts the way of multiplexing the cells from 3 inputs. Input 2 doesnot have any data to transfer, so the slot is filled with a cell from third input which isdone by multiplexer. Output slot becomes empty only after all the cells aremultiplexed from input channel. 18CNW201
  19. 19. Yuba Raj Khadka 1801T30901561.8 ATM NETWORK INTERFACES ATM network incorporates a set of central devices called ATM switcheswhich are in point to point connection to each other. Two basic types of interfaces aresupported by the ATM Switches. They are UNI (User Network Interface) and NNI(Network-Network Interface). The end systems of ATM like routers and hosts are connected to an ATMswitch by the UNI while two ATM switches are connected by NNI. Depending on if the ATM switch is publicly owned or located at the clientpremises and functioned by the telephone organization, NNI and UNI can be subgrouped into private and public NNIs and UNIs. A private switch and an endpoint of ATM are connected by a private UNIwhile public UNIs links an endpoint of ATM or private switch to public switch.Within the same public organization, a public NNI links two switches of ATM whiletwo ATM switches are connected amongst the very private organization areconnected by the private NNI.Fig: 7- ATM network interfaces in public and private networks.[REF 8] 19CNW201
  20. 20. Yuba Raj Khadka 1801T30901561.9 NETWORK TOPOLOGY [REF 1] The establishment of ATM Data Link Layer topology was carried out byseeking for the exactly same sets of active VCs in any remote side’s VCs table ofATM port associated to the same type of the local ATM port. This kind of topology isalso employed to the fundamental physical links. Based on the lowest active VCs, itexpects for harmony amongst participating ports VCs table. Using Cisco confidentialscheme, furthermore verifications are done where VC traffic signature of these portsare compared. Significant amount of traffic is required for the Cisco confidentialscheme to work properly. Only same VPs OR same VCs are supported by thismechanism but not the mixture of VPs on one side and VCs mixture on other side. 20CNW201
  21. 21. Yuba Raj Khadka 1801T30901562 HOW ATM WORKS?2.1 ATM CELL BASIC STRUCTURE As we have already mentioned that ATM transfers every data and informationin fixed sized small packets called ATM cells. Fixed sized small cells are usedbecause they are more fitted to transmit video and voice traffic. ATM cell comprisescell header of 5-byte or octets and 48 bytes of user information also known aspayload. In order to support the virtual channel routing and virtual path and to carryout the quick error check for cells which are corrupted, ATM network employs theheader field. Fig: ATM cell basic format 21CNW201
  22. 22. Yuba Raj Khadka 1801T30901562.2 ATM CELL HEADER STRUCTURE An ATM cell header is basically of two formats. They are NNI and UNI. Inorder to communicate between ATM switches, NNI header is used while UNI headeris employed to communicate between ATM switches and ATM end points in ATMprivate network. So we can conclude header is used to communicate amongst ATMswitches.Here is the figure showing you the basic ATM cell, UNI cell and NNI cell. Fig: ATM cell, ATM UNI cell and ATM NNI cell [REF 8] 22CNW201
  23. 23. Yuba Raj Khadka 1801T30901562.2.1 ATM CELL HEADER FIELDS [REF 5] Including VPI (Virtual Path Identifier) and GFC (Generic Flow control) headerfields, various other fields are employed in ATM cell header fields. Following aresome of them which will summarize the ATM cell header fields show in the abovefigure. Virtual Path Identifier (VPI) 8 bits of VPI is in conjunction with the header field VCI. As it passes through ATM switches on the path to its destination, it determines the coming destination of a cell. Generic Flow control (GFC) 4bits of GFC major function is to determine multiple stations sharing the same ATM interface.GFC is generally not in use and its value is put to a default value. Virtual Channel Identifier (VCI) 16 bits of VCI is in conjunction with the header field VPI and does the same function like that of VPI. Congestion Loss Priority (CLP) 1 bit of this header field shows if the ATM cell has to be cast away when there is utmost congestion as it passes via the network. The cells with the CLP bit 1should be discarded in preference to the cell having CLP bit 0. 23CNW201
  24. 24. Yuba Raj Khadka 1801T3090156 Payload Type (PL) 3 bits of his header fields of ATM cell shows in the first bit if it consists of control data or user data. The second bit shows over –crowding when the cell consist user data and the third bit points if the cell in a series is last representing a single frame of AAL5. Header Error Control (HEC) On the header itself, 4 bits of this header field of ATM cell estimates the checksum. 24CNW201
  25. 25. Yuba Raj Khadka 1801T30901562.3 ATM PRPTOCOL REFERENCE MODEL Based on the standards established by the ITU-T, ATM reference model or B-ISDN protocol reference model main purpose is to clear up the functions performedby the ATM networks by teaming them into a function specific, interrelated set ofplanes and layers.The ATM reference model incorporates the following planes. They are control plane,user plane and management plane. Control plane This plane generates and manages requests of signaling. User plane Transfer of data is managed by this plane Management plane This plane is again sub grouped into two components. They are: Layer management is responsible for the layer specific tasks like detecting failures and the problems of protocol. Plane management is responsible for managing and coordinating the functions associated to the whole system. 25CNW201
  26. 26. Yuba Raj Khadka 1801T3090156ATM reference model incorporates the following three layers: Physical layer Correspondent to the OSI (Open Systems Interconnection) reference model, Physical layer, the physical layer of ATM is responsible for managing the medium-dependent transmission. . ATM layer Joined with the adaptation layer of the ATM reference model, ATM layer slightly corresponds with the OSI model, data link layer. The major function of ATM layer is to establish connections and to pass cells via the ATM network. To perform this, it employs information in the header of every cell. ATM Adaptation layer (AAL) Joined with the ATM layer of ATM reference model, ATM adaptation layer is slightly analogous to the data link layer of the OSI reference model. The main function of this layer is to isolate the protocols of the higher layer from the details of the ATM processes. 26CNW201
  27. 27. Yuba Raj Khadka 1801T3090156 Here is the figure illustrating the ATM protocol reference model.Fig: Relating ATM reference model with the lowest two layers of the OSIreference model. [REF 8]Now, let’s study above three layers of the ATM reference model in detail. 27CNW201
  28. 28. Yuba Raj Khadka 1801T30901562.3.1 ATM PHYSICAL LAYERFollowing are the major functions of the ATM physical layer. To convert cells into a stream of bit. To control the transfer and the receipt of bits on the physical media. To track the boundaries of ATM cell. ATM Cells are bundled into the approp riate frame types required for the physical device.The ATM physical layer is further divided into two types: they are PMD (Physical-medium-dependant) and TC (Transmission convergence) sub layer.PMDFollowing are the main functions of PMD sub layer. It is responsible for synchronizing reception and transmission by sending and receiving bits flowing continuously with related information of timing. For the physical medium employed, it fixes the physical medium including cable and connector. SONET/SDH, DS-3/E3, 155 Mbps over STP cable and 155 Mbps over MMF (Multimode Fiber) with 8B/10B encoding schemes are some of the examples of the physical medium standards. 28CNW201
  29. 29. Yuba Raj Khadka 1801T3090156TCFollowing are the main functions of TC sub layer. Responsible for maintaining boundaries of an ATM cell, allowing physical medium to position cells amongst a bit stream. This is also known as cell delineation. Responsible for checking and generating header error control code to check data which are valid. Transmission frame adaptation bundles the acceptable frame into the specific implementation of the physical layer. Cell rate decoupling means the maintaining of synchronization. 29CNW201
  30. 30. Yuba Raj Khadka 1801T30901562.3.2 ATM ADAPTATION LAYER (AAL) The main function of this layer is to support four service classes and to allowavailable applications like CBR video and protocols like IP to run on top of ATM asshown in the below figure.Fig: AAL layer is only located at the edges of ATM network. [REF 9] This very layer is only applied at the end point of an ATM network whicheither could be an IP router or the host system. In this case, you can say it’s beinganalogous to the transport layer situated in the internet protocol stack. The ATM standards like ITU-T and ATM forum has presented some of theAAL standards some of the crucial AALs endorsed by the above standardization ofAAL are as follows: AAL 1: For constant bit rate (CBR) services and circuit emulation. AAL 2: For variable bit rate (VBR) services. AAL 5: For data ( IP datagram) 30CNW201
  31. 31. Yuba Raj Khadka 1801T3090156The AAL is further divided into two sub layers. They are: Segmentation and Reassembly (SAR) SAR is located at the lower section of AAL. The packets are broken down into cells during the transmission by this sub layer and they are again kept together at the destination. Basically concerned with cells, this sub layer is also able to add headers and trailers to the data units which are given to it through CS in order to form user information. Convergence sub layer (CS) Service dependant Convergence sub layer plays crucial role to make systems of ATM give various services and applications. It also accepts bit streams from the application and breaks them unit of 44 or 48 bytes for transmission. The following figure shows you the way of AAL converting payloads or user information into cells. Fig: AAL converting user information into cells [REF 9] 31CNW201
  32. 32. Yuba Raj Khadka 1801T3090156On the basis of types of data, various types of AAL layers are defined which are asfollows. AAL 1 AAL 2 AAL ¾ AAL 5AAL 1This AAL is used to support service class A. Basically, the applications requiringCBR like video and voice conferencing, 64 kbps voice uses this service. This isknown as isochronous. These applications are very sensitive to time and thus end toend timing is predominant and has to be endorsed. Fig: AAL 1 [REF4] 32CNW201
  33. 33. Yuba Raj Khadka 1801T3090156AAL 2 [REF 3] Initially, AAL2 was believed to endorse VBR (Variable Bit Rate) applications.Packetized video and voice is the great example of such VBR applications. AlthoughAAL2 was thought in the early days of the development of ATM, it was not plannedbut later on it came into action when the designers felt the need of AAL for voicetraffic. At the beginning they named that layer as AAL6 but soon they relabeled asAAL 2. In the present context, AAL2 transport voice traffic and also allows varioussmall packetized video to be packed in a sing cell payload of 48 byte. This AAL isused to support service class B. Fig: AAL 2 [REF 4] 33CNW201
  34. 34. Yuba Raj Khadka 1801T3090156AAL ¾ AAL 3 and AAL 4 were designed in order to support connection oriented datatraffic which does not contain delay constraints. These two layers too endorse VBRapplications like transfer of file. Soon,, the designers came to know that there wasonly a few differences between AAL 3 and AAL 4. So both layers were combined toform one AAL ¾. This service is no more in use now since it was replaced by thesimpler AAL 5. This AAL supports both service class C and D. Fig: AAL ¾ [REF 4] 34CNW201
  35. 35. Yuba Raj Khadka 1801T3090156AAL 5This one is the common preferred AAL used in today world. AAL5 came into actionbasically for the applications which do not have any delay constraints. IP traffic, FTP,LAN and Network management are some of the applications in which AAL 5 wasimplemented. Like, AAL ¾, AAL 5 also endorses the service classes C and D. Fig: AAL 5 [REF 4]Here is the table representing the four AALs along with their supported serviceclasses and QoS. Fig: four AALs and their supported service class and QoS. 35CNW201
  36. 36. Yuba Raj Khadka 1801T30901562.3.3 ATM LAYER This layer lies above the physical layer of the ATM Reference model.Multiplexing, network management; routing, switching and traffic management arethe major functions of this layer. It accepts segments of 48 byte from the AAL sublayers and then transforms them into cell of 53 byte by adding header of 5 byte. In thisway, this layer processes outgoing traffic. We have already mentioned above aboutthe format of ATM cell header.Four major functions of ATM layer are as follows: Multiplexing and de-multiplexing of ATM cell This function includes cells multiplexing from individual VPs and VCs into a resulting cell stream in the way it is transmitting. GFC (Generic Flow Control) ATM layer is responsible for controlling the flow of ATM traffic in a network of customer. This function is defined at the UNI of B-ISDN and is no more in use. Generation and extraction This function includes adding the proper ATM cell header to the cell information field which is received from the AAL in the direction it is transmitting. The values of VPI and VCI are received by translating from the SAP identifier and the cell header is removed in the direction it is receiving. 36CNW201
  37. 37. Yuba Raj Khadka 1801T3090156 VPI/VCI translation ATM layer perform this function at the nodes of ATM switching. ATM layer translates the VPI field value of every incoming cell into a novel VPI value which is going out. It translates VCI and VPI values into new values at VC. Fig: virtual path and virtual channels [REF 3] Fig: VPI and VCI switching [REF 3] 37CNW201
  38. 38. Yuba Raj Khadka 1801T30901562.4 ATM ADDRESSING ATM addresses are required to endorse the employment of virtual connections(VCs) through the whole ATM network. Depending on the private or public ATM network, the type of ATM addressesto be used is defined. ATM addresses are generally employs in order to set up VCswithin end points of ATM network. Basically, ATM uses two types of addresses. They are E.164 addresses whichis telephony oriented and is proposed for use in public networks. Other one is AESAs(end system addresses) which is aimed for use in private networks. E.164 addresscannot be more than 15 digits. For instance: 11 numbers are used in the Canada andUnited States: 1-NPA-NXXX-ABCD, for example, 1-416-978-4765 where 1 is thecountry code assigned by ITU , NPA, NXX and the final four digit number representsarea code, office code and the subscriber number respectively. Country code isdifferent for other countries with different format.AESAs are based on the NSAP format having 20 bytes. ATM addresses having 20byte length is composed of three different parts. Here is the figure showing you thethree parts of ATM addresses of 20 bytes. Fig: three distinct parts of the 20 byte ATM addresses 38CNW201
  39. 39. Yuba Raj Khadka 1801T3090156 The AFI (Authority and Format Identifier) determines the type of NSAP, IDI(International Domain Identifier) determines the allocation of address andadministration authority while DSP (Domain Specific Part) consist of information ofrouting.Following are three basic addressing formats used for the private networks: DCC Address format ICD Address format E.164 Address format DCC Address format IDI is a Data Country Code (DCC) which determines various countries as defined by ISO 3166. ISO National Member Authority in each country distributes these addresses. For e.g.: DIN in Germany, ANSI in the USA and BSI in the UK. Its AFI value is 39. Fig: DCC Address format 39CNW201
  40. 40. Yuba Raj Khadka 1801T3090156 ICD Address format In this format, IDI is an ICD (International Code Designer) which is distributed by the ISO 6523 registration authority (British Standards Institute). NSAPs of ICD are aimed for use by international organizations. Since, the number of existing ICDs is limited, now it is so hard to obtain one. Its AFI value is 47. Fig: ICD Address format E.164 Address format E.164 number is the IDI in this address format. This enable to use the E.164 addresses amongst the private ATM networks. Its AFI value is 45 Fig: NSAP E.164 address format 40CNW201
  41. 41. Yuba Raj Khadka 1801T3090156The table given below shows the primary ATM addresses fields along with theirfunctions.Address Fields FunctionsAFI Determines the type of addressDCC Its value is 39 for DCC, 47 for ICDAA Single byte specifies DSP of the addressReserve Reserved for future useRD 2 bytes of routing domain informationArea 2 bytes of area identifierESI 6 bytes of end system identifierSEL I byte of NSAP selectorICD 2 bytes of international code designatorE.164 8 bytes of ISDN telephone number Fig: primary ATM addresses format fields [REF 1] 41CNW201
  42. 42. Yuba Raj Khadka 1801T30901563 ATM TRAFFIC MANAGEMENT [REF 3][REF 4][REF ] An efficient and effective traffic control mechanisms is required in order toguarantee the Quality of Service (QoS) utilizing the existing network resources to itsfullest and to deal with the potential errors that may occur amongst the network. Thefunctions given below make a framework for controlling and managing thecongestion and traffic in ATM networks. From the standpoint of ITU-T Rec. I.371:these functions have to be employed in appropriate combinations.Following traffic control methods should be applied in an ATM network: Network Resource management (NRM) Connection Admission Control (CAC) Usage Parameter Control and Network Parameter Control (UPC/NPC) Priority Control (PC) Congestion Control (CC) Fig: configuration for traffic control and congestion control. (From ITU-TRec. I.371) 42CNW201
  43. 43. Yuba Raj Khadka 1801T3090156Now, let’s study the above traffic control mechanism in detail.3.1 Network Resource management (NRM) Basically used in Broadband Networks, NRM deals with the distribution ofnetwork resources in order to divide traffic in accordance with characteristics ofservices. Virtual path techniques are used as a crucial tool to manage and controltraffic in an ATM network. They are also employed in statistical multiplexing forseparating traffic in order to prevent intervention of statistically multiplexed trafficwith other various traffics. For an instance: guaranteed bit rate traffic.3.2 Connection Admission Control (CAC) CAC is termed as the set of actions performed by the network during callsetup or call renegotiation phase in order to prevent itself from excessive input loadslike to establish if VP or VC connection can be rejected or accepted. Routing is thesuitable example of this CAC action.3.3 User Parameter Control and Network Parameter Control (UPC/NPC) UPC and NPC have the same functionalities on different interfaces. NPCfunctions at NNI while UPC functions at UNI. UPC/NPC are the set of actionsperformed by the network for controlling and managing traffic, on the basis of cellrouting validity and traffic offered at network access and user access respectively.UPC/NPC main purpose is to protect network resources from unintentionalconnection. This would affect the QoS of already established connection. Afteraccepting the connection by CAC, UPC/NPC controls the connection to assure iftraffic conforms to the traffic contract. 43CNW201
  44. 44. Yuba Raj Khadka 1801T30901563.4 Priority Control (PC) In order to increase the performance of higher priority ATM cells, this PCfunction of the network cast away the low priority cell and this is important for aATM network to manage the traffic efficiently.3.5 Congestion Control (CC) Sometimes the network resources become overloaded. This situationtypically refers to congestion. In this case, ATM network cannot guarantee the qualityof service to the connections which are already established and also to the connectionwhich are going to be established. ATM Congestion control means the set of stepsperformed by the network to reduce the spread, intensity and the extent of the networkcongestion. 44CNW201
  45. 45. Yuba Raj Khadka 1801T30901564 CONCLUSION These days, you can find various networks available. However, in thepresent era, ATM is a big concern due to its magnificent features which we havealready discussed above. With ATM, you can find a solution to the problems of thecurrent network. The good thing about ATM is its high speed features and its abilityto supports the traffic of different multimedia applications like data, voice and videoconferencing. All of these features of ATM is making it a compelling solution forboth WAN and LAN. With internationally deployment, ATM has been able to successpartially in the field of network technology but mostly used for IP traffic. However,the latest new technologies like MPLS, DSL and FTTH have inherited the differentcrucial concepts of ATM. ATM development and usage is sure to increase in thefuture because “it meets emerging requirements for scalable transport of myriad enduser services, including data, voice and video”. 45CNW201
  46. 46. Yuba Raj Khadka 1801T30901565 ACKNOWLEDGEMENT It is with great pleasure that I take the opportunity to thank my Lecturer Mr.Gandip Khaling for his enthusiastic supervision, help, and guidance throughout thework in this project. I gratefully acknowledge his assistance in submitting recent references tome. I have constantly benefited from his discussion and encouragement todevelopment of this work. I would like also to thank all those they have helped, advised, and givefruitful discussions during this work. Many thanks also are to the staff of InformaticsCollege. 46CNW201
  47. 47. Yuba Raj Khadka 1801T30901566 REFERENCES 1. [REF 1] Chapter 6, Asynchronous Transfer Mode, Cisco Active Network Abstraction Technology Support and Information Model Reference Manual, Version 3.6 master_tech/6atm.pdf 2. [REF 2] Asynchronous Transfer Mode (ATM) Network, Georgia Electronic Scientific Journal: Computer Science and Telecommunications 2009, No .6 (23), Ojesanmi O. A, 3. [REF 3] Asynchronous Transfer Mode (ATM), Arjan Durresi, Louisiana State University 4. [REF 4] Asynchronous Transfer Mode: An overview, Scot A. Valcourt, ATM consortium Manager, June 24, 1997 5. [REF 5] Module 4 Switched Communication Network, Version 2 CSE IIT, Kharagpur r%20networks/pdf/M4L6.pdf 6. [REF 6] Microsoft TechNet, How ATM works?, March 28, 2003 47CNW201
  48. 48. Yuba Raj Khadka 1801T3090156 7. [REF 7] International Technical Support Organization, Asynchronous Transfer Mode (ATM) Technical Overview, October 1995 8. [REF 8] Asynchronous Transfer Mode Switching, Internetworking technologies handbook 9. [REF 9] Asynchronous Transfer Mode, Link Layer and Local Area Networks 10. [REF 1O] Asynchrnonous Transfer Mode, TelecomSpace Telecom tutorial, forum, latest trends, News 11. [REF 11] Main features of ATM (Asynchronous Transfer Mode),, MuthuKumar, 28 Dec, 2009 Asynchronous-Transfer-Mode.aspx 12. [REF 12] Asynchronous Transfer Mode ATM Network service Features and Benefits, ATM bids, 13. [REF 13] ASYNCHRONOUS TRANSFER MODE, Fundamentals of telecommunications, Roger L. Freeman, 1999 14. [REF 14] MULTIMEDIA APPLICATIONS OVER ASYNCHRONOUS TRANSFER MODE (ATM) NETWORK, Eng. Ayman El-Sayed Ahmed El- Sayed 15. [REF 15] ATM- Asynchronous Transfer Mode, Wireless/Networking, Bradley Mitchell, 1999 48CNW201
  49. 49. Yuba Raj Khadka 1801T30901567 TURNITIN REPORT 49CNW201