1 INTRODUCTION MAIN PART... 2

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1 CONTENTS 1 INTRODUCTION MAIN PART A BRIEF OVERVIEW OF THE ATM TECHNOLOGY: ATM Technology in two-way video applications Basic ATM technical characteristics B-ISDN protocol reference model ATM Cells and the Adaptation Layer Concept Virtual Paths / Virtual Channels and Virtual Circuits ATM Service Categories and QoS in ATM THE DETAILED DESCRIPTION OF THE PROJECT: DEVICES USED AT THE PROJECT: About the FORE SYSTEMS Inc Details About The Switches In The Subnetwork Forerunner ASX-1000 Backbone switch ForeRunner LE-155 ATM Workgroup Switch StreamRunner AVA/ATV-300 ATM Video Product Family THE BUILDING BLOCKS OF THE PROJECT AVA/ATV 300 AND THE SVA 5.0 SOFTWARE StreamRunner AVA StreamRunner ATV Cell Chaining AVA-300 and ATV What is a CellChain? CellChain used in the project SVA 5.0 Software Devices Managers Traders Managers and the ATM Network A few words on SVCs and PVCs CONCLUSION REFERENCES APPENDICES... 32

2 1 INTRODUCTION ATM (Asynchronous Transfer Mode) is one of the most popular and very rapidly improving areas in the field of computer networking. There are many reasons that made this newly developing technology so popular. One of these reasons, is ATM s ability to carry different service types on the same media. This ability of ATM comes from its ability of controlling latency and jitter for timing sensitive applications like videoconference. Also, ATM s ability to scale to high bandwidths makes this technology very suitable for real time applications. Actually, ATM is an implementation of B-ISDN (Broadband-Integrated Services Digital Networks). Since the main idea of ISDN is integrating digital services, ATM s main source of ability of carrying different traffic types comes from its basic building block, B-ISDN. In this project, the main aim was to show the ATM s power in real time applications. For this purpose E.M.U s(eastern Mediterranean University s) pure ATM Sub network between the Department of Computer Engineering and the Department of Electrical & Electronics Engineering is used. University s ATM Network is completely build with FORE SYSTEMS, Inc. s devices. Some of the devices in this ATM network can be listed as an ATM backbone switch, ATM workgroup switches and special devices for video & voice over ATM. The details about the features of these devices will be explained later in this report. The main task to be accomplished in the project is building a two-way communication path between the two departments, which will be carrying video and voice as the means of communication. Simply this project can be summarised as using an ATM sub network as a video conference environment on a campus network. The unofficial aim of the project can be stated as a preliminary prototype of the videoconference and distant learning environments, which will be very crucial tools of the university education in the near future. 1

3 2 MAIN PART 2.1 A Brief Overview of the ATM Technology: ATM Technology in two-way video applications Asynchronous Transfer Mode (ATM) has been defined as a networking technology to support data, voice, and video transmission. In particular, ATM is being developed to support numerous high-end applications, such as high-end video, which includes the emerging MPEG and MPEG2 video standards. While the predominant standard for videoconferencing today is the circuit-switched H.320 protocol suite, one key reason for the adoption of ATM is its ability to scale to higher bandwidth and to provide control for latency and jitter in the network and enable numerous emerging video applications. [1] A significant level of research has been conducted to determine the recommended tolerable levels of latency and jitter. Based upon the extensive research in this field, carriers are defining the requirements for latency and jitter on a per-switch level to support two-way high-end video. These per-switch requirements are as follows: [1] A cell loss ratio across the network of less than 1.7 x 10 9.A cell transfer delay (99th percentile) of 4 milliseconds across the network and 150 microseconds per switch [1] A cell delay variation (99th percentile) across the network (not per switch) of 500 microseconds. [1] For the next several years of MPEG and MPEG2 equipment evolution, the preponderance of delay, which is on the order of hundreds of milliseconds, will be introduced in the video compression equipment. Therefore, it is not likely that MPEG or MPEG2 formats will be used for two-way communications in the near-term; rather, they will be used for store-andforward applications such as video broadcasting in the wide area or LAN video such as corporate training. In such applications, the delay can be much greater than the specifications noted above. Hence, ATM switches that meet or exceed these latency and jitter requirements are capable of supporting high-end video applications in the wide area. Given that local-area (campus) transmission introduces lower transmission delay and allows for greater control over both video encoding and decoding equipment as well as over the network itself, it is 2

4 clear that local-area ATM switches can even exceed the above requirements and allow for high-end video applications. Since end-to-end delay of a few hundred milliseconds is acceptable in traditional two-way real-time video, ATM networks can easily meet the requirements. For high-end, two-way video, the high transmission speeds of ATM networks also ensure that absolute increases in delay time are not critical. In fact, the encoding operation delay (compression delay) will itself be more significant than the delay of the ATM network and its component switches. [1] From the above statement we can deduce the following result: In an well-organised ATM Network, the network itself will not produce any, or at most will produce human tolerable delays in a two-way video application Basic ATM technical characteristics B-ISDN protocol reference model The B-ISDN protocol reference model(refer to fig 1) is composed of; A User Plane A Control Plane A Management Plane Figure 1 In particular; The user plane, with its layered structure, provides for user information flow transfer, along with associated controls ranging from flow control to error recovery, etc.; [2] 3

5 The control plane has a layered structure and performs the call control and connection control functions; it deals with the signalling necessary to set up, supervise and release calls and connections; [2] The management plane provides two different types of functions: [2] plane management functions, not layered, that are related to a system as a whole and provide coordination between all the planes and; layer management functions, that are related to resources and parameters residing in its protocol entities; layer management handles the operation and maintenance (OAM) information flows specific to the layer concerned. ATM Layers The ATM Layers do not map directly with the OSI layers but we can say that The ATM layer performs the operations similar to the ones found in layers 2 and 3 (Data-Link and Network Layers) of the OSI Model. The AAL combines features of layers 4,5 and 7 (Transport, Session and Application Layers) of the OSI Model. The physical layer can be a SONET or SDH carrier. In terms of ATM protocol stack, above the Physical Layer there is the ATM Layer that provides call transfer for all services and the ATM Adaptation Layer (AAL) providing service-dependent functions to the layers above (indicated as higher layers). The layer above AAL in the control plane provides call control and connection control; the management plane provides network supervision functions. The functions of each layer are detailed in Figure 2, which also shows sublayers: Convergence Sublayer (CS) and Segmentation and Reassembly Sublayer (SAR) for the AAL, Transmission Convergence (TC) and Physical Medium (PM) for the PHY. [2] ATM provides convergence functions at the ATM Adaptation Layer(AAL) for connectionoriented or connectionless Variable Bit Rate(VBR) applications. It supports isochronous applications (voice, video) with Constant Bit Rate (CBR) services. [3] A convenient way of thinking of the AAL is that it is actually divided into two sublayers, SAR(segmentation and reassembly) and CS(Convergence Sublayer). [3] 4

6 The SAR sublayer is responsible for processing user PDUs(Protocol Data Unit),which are different in size and format, into ATM cells at the sending side and reassembling the cells into the user-formatted PDUs at the receiving side. [3] The CS s functions depend upon the type of traffic being processed by the AAL, such as voice, video, or data. We can illustrate the ATM Layers as in Figure 3. [3] Layer Management Higher Layer Functions Convergence Segmentation and Reassembly Generic Flow Control Cell Header generation/extraction Cell VPI/VCI translation Cell multiplex/demultiplex Cell rate decoupling HEC header sequence generation/verification Cell delineation Transmission frame adaption Transmission frame generation/recovery Bit timing Physical medium Higher layers CS AAL SAR ATM TC Physical Layer PM Figure 2. Functions of the B-ISDN in relation to the Protocol Reference Model. Source: ITU-T; I.371 AAL AAL Connection Oriented VBR AAL Connectionless VBR AAL SAR AAL SAR AAL SAR ATM SDH/SONET (Physical Layer) Figure 3. The ATM Layers AAL CBR } CS } SAR 5

7 ATM Cells and the Adaptation Layer Concept ATM is a packet technology that directs traffic using a label contained in the packet s header. Unlike other packet technologies, such as X.25 or frame relay, ATM uses short, fixed-length packets called cells. Each cell is 53 bytes long(48 bytes for the information field and 5 bytes for the preceding header). The header field contains information about the virtual channel (VCI: Virtual Channel Identifier) and virtual path (VPI: Virtual Path Identifier) in use, payload type (PT) and cell loss priority (CLP). The ATM Adaptation Layer (AAL) accomplishes inserting payload data into the 48-byte information field of the ATM cell. The AAL is what gives ATM the flexibility to carry entirely different types of services within the same format. It is important to understand that the AAL is not a network process but instead is performed by the network terminating equipment. Thus the network s task is only to route the cell from one point to another, depending on its header information. It should be noted that up to four bytes may be used by the adaptation process itself with some AAL types, leaving 44 bytes for payload information [2] ATM CELL The ATM cell is the basic unit of information transfer in the B-ISDN ATM communication. The cell is comprised of 53 bytes. Five of the bytes make up the header field and the remaining 48 bytes form the user information field. [5] Figure 4 represents the structure of the Network Node Interface (NNI) ATM Cell Header and the Figure 5 represents the structure of the User Node Interface (UNI) ATM Cell Header: [5] Figure 4 Figure 5 6

8 The header field is divided into GFC, VPI, VCI, PT, CLP AND HEC fields. [5] The associated bit sizes differ slightly at the NNI and the UNI. The bit sizes are represented in Figure 6. [5] Figure 6 Generic Flow Control (GFC): Although the primary function of this header is the physical access control, it is often used to reduce cell jitters in CBR services, assign fair capacity for VBR services, and to control traffic for VBR flows. Such functionality requires the power to control any UNI structure, be it a ring, a star, some bus configuration, or any combination of these. [5] 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 be distinguished. A unique and separate VPI/VCI identifier is assigned in advance to indicate which type of cell is following, unassigned cells, physical layer OAM cells, metasignalling channel or a generic broadcast signalling channel. [5] Payload Type (PT) / Cell Loss Priority (CLP) / Header Error Control (HEC): When user information is present or the ATM cell has suffered traffic congestion then the PT field will yield this information. [5] 7

9 The CLP bit is used to tell the system whether the corresponding byte is to be discarded during network congestion. ATM cells with CLP=0 have a priority in regard to cell loss than ATM cells with CLP=1. Therefore, during resource congestions, CLP=1 cells are dropped before any CLP=0 cell is dropped. [5] HEC is a CRC byte for the cell header field and is used for sensing and correcting cell errors and in delineating the cell header. [5] ATM ADAPTATION LAYERS Some important standardised AAL s are; AAL 1 - Constant Bit Rate (CBR) services. AAL1 handles traffic where there is a strong timing relation between the source and the destination. Examples include PCM-encoded voice traffic, constant bit rate video and the emulation of public network circuits (e.g. the transport for E1 links). [2] AAL 2 - Variable Bit Rate (VBR) timing-sensitive services. AAL2 handles traffic where a strong timing relation between the source and the destination is required, but the bit rate may vary. Examples include variable bit rate voice and compressed, for instance MPEG-coded, video. [2] AAL 3 / 4 - Connection-oriented and connection-less VBR data transfer. AAL3/4 is a fairly complex layer that can handle VBR (i.e. bursty) data both with and without preestablishing an ATM link. Examples for the connection-oriented type include large file transfers like CAD files or data back-up. The connectionless type is intended for short, highly bursty transfers as might be generated by LANs. [2] AAL 5 - Simple and Efficient Adaptation Layer (SEAL). AAL5 may be looked upon as a simplified version of AAL3/4 that is designed to meet the requirements of local, high-speed LAN implementations. AAL5 is intended for connectionless or connection-oriented VBR services. [2] 8

10 Virtual Paths / Virtual Channels and Virtual Circuits The concept of virtual circuits, which are known as Virtual Channel Connections (VCCs), can be described in the following way: (Refer to Figure 7) A VCC is set up between any source and any destination in the ATM network, regardless of the way it is being routed across the network. Fundamentally, ATM is a connection-oriented technology. The way the network sets up the connection is therefore by signalling, i.e. by transmitting a set-up request; which passes across the network to the destination. If the destination agrees to form a connection, the VCC is set up between the two end-systems. A mapping is defined between the Virtual Channel Identifiers (VCIs) / Virtual Path Identifiers (VPIs) of both UNIs, and between the appropriate input link and the corresponding output link of all intermediate switches. A VCC is a connection between two communicating ATM end-entities. It may consist of a concatenation of several ATM VC links. All communication proceeds along this same VCC which preserves cell sequence and provides a certain quality of service. Note that the Virtual Channel Identifier (VCI) in the ATM cell header is assigned per network entity-to-entity link, i.e. it may change across the network within the same VCC. Virtual Path (VP) groups VCs carried between two ATM entities and may also involve many ATM VP links. The VCs associated with a VP are globally switched without unbundling or processing the individual VC in any way or changing their VCI numbers. Thus the cell sequence of each VC is still preserved and the quality of service of the VP depends on that of its most demanding VC. As the cell address mechanism uses both the VCI and the VPI, different VPs may also use the same VCI without conflict. A cell may also not be associated with any VP. In this case it would have a null VPI and only a unique VCI. By means of VCs and VPs, virtual circuits can be set up either permanently (by using so-called Permanent Virtual Channels, (PVCs) or on demand ( Switched Virtual Channels, SVCs). It is likely that VPs will be used mostly between switches (i.e. across NNIs) to carry across large numbers of virtual circuits. In any case, all the ATM switch has to do is to identify, on the basis of the cell s VPI, VCI or both, which output a received cell needs to be routed to and what the new VPI/ VCI on this output link is. The operation of an ATM network is therefore very simple and inherently can scale to very high speeds. [2] Virtual Path Media Virtual Channels Virtual Channels Figure 7 9

11 ATM Service Categories and QoS in ATM The introduction of new ATM service categories increased the benefits of ATM, making the technology suitable for a virtually unlimited range of applications. An ATM network can provide Virtual Path (VP) or Virtual Channel (VC) Connections with different levels of service. The concept of negotiating the behaviour expected from the ATM layer in terms of traffic and performance for each connection allows users to optimise network capabilities to suit the applications requirements. [2] The first ATM implementations offered limited options. A typical network behaviour, common to the most of the first generation ATM networks, is to reserve a fixed amount of bandwidth for each connection for the duration of the call on the basis of the maximum emission rate of the source (i.e. the peak cell rate, PCR) and to provide a single level of quality of service. The ATM service categories represent new service building-blocks that make it possible for users to select specific combinations of traffic and performance parameters. [2] ATM is a multiservice technology. Actually, most of the requirements that are specific to a given application may be resolved at the edges of an ATM network by choosing an appropriate ATM Adaptation Layer (AAL). However, in accordance with the standards definitions the ATM-layer behaviour should not rely on the AAL protocols since these are service specific (and are in many cases supported by the user terminal, i.e. outside the core network visibility), nor on higher layer protocols which are application specific. [2] Given the presence of a heterogeneous traffic mix and the need to adequately control the allocation of network resources for each traffic component, a much greater degree of flexibility, fairness and utilisation of the network can be achieved by providing a selectable set of capabilities within the ATM-layer itself. The Service Categories have been defined with this goal in mind. [2] 10

12 Some Service Categories are; Constant Bit Rate (CBR) : The CBR service category is used by connections that require a static amount of bandwidth, characterised by a Peak Cell Rate (PCR) value that is continuously available during the connection lifetime. The source may emit cells at or below the PCR at any time and for any duration (or may be silent). This category is intended for real-time applications, i.e. those requiring tightly constrained Cell Transfer Delay (CTD) and Cell Delay Variation (CDV), but is not restricted to these applications. It would be appropriate for voice and video applications as well as for Circuit Emulation Services (CES). The basic commitment made by the network is that once the connection is established the negotiated QoS is assured to all cells conforming to the relevant conformance tests. Cells, which are delayed beyond the value specified by Cell Transfer Delay (CTD), are assumed to be of significantly less value to the application. [2] Examples are: - Video-conferencing - Audio/Video Distribution (e.g. television, distance learning, pay-per-view) In the multimedia area, a near-term solution for residential services foresees VoD based on MPEG2 (Transport Stream, CBR mode) over AAL5 with transportation being provided by the ATM-layer with CBR service. [2] Real-Time Variable Bit Rate (rt-vbr) The real-time VBR service category is intended for real-time applications, (i.e. those requiring tightly constrained delay and delay variation), as would be appropriate for voice and video applications. Sources are expected to transmit at a rate that varies with time. Alternatively, the source can be described as bursty. Traffic parameters are Peak Cell Rate (PCR), Sustainable Cell Rate (SCR) and Maximum Burst Size (MBS). Cells that are delayed beyond the value specified by CTD(Cell Transfer Delay) are assumed to be of significantly less value to the application. Real-time VBR service may support statistical multiplexing of real-time sources. [2] 11

13 Non-Real-Time VBR(nrt-VBR) The non-real time VBR service category is intended for non-real time applications that have bursty traffic characteristics and can be characterised in terms of a PCR, SCR and MBS. For those cells that are transferred within the traffic contract the application expects a low Cell Loss Ratio(CLR). For all cells it expects a bound on the Cell Transfer Delay (CTD). Non-real time VBR service may support statistical multiplexing of connections. [2] Typical applications for VBR: VBR is suitable for any application for which the end-system can benefit from statistical multiplexing by sending information at a variable rate and can tolerate or recover a potentially small random loss ratio. This is the case for any constant bit rate source for which variable rate transmission allows more efficient use of network resources without performance impairment. Real-time VBR, in particular, can be used by native ATM voice with bandwidth compression and silence suppression. For some classes of multimedia communications real-time VBR may be very appropriate. [2] Non-real time VBR can be used for data transfer, e.g. for response-time critical transaction processing applications (e.g., airline reservations, banking transactions, process monitoring) and frame-relay interworking. [2] Available Bit Rate (ABR) ABR is an ATM layer service category for which the limiting ATM layer transfer characteristics provided by the network may change subsequent to connection establishment. A flow control mechanism is specified which supports several types of feedback to control the source rate in response to changing ATM layer transfer characteristics. Many sources (applications) have the ability to reduce or increase their information rate if the network requires them to do so. It is expected that an end-system that adapts its traffic in accordance with the feedback will experience a low Cell Loss Ratio (CLR) and obtains a fair share of the available bandwidth according to a network specific allocation policy. Cell Delay Variation (CDV) is not controlled in this service, although admitted cells are not delayed unnecessarily. ABR service is not intended to support real-time applications. On the establishment of an ABR connection the end-system shall specify to the network both a maximum required bandwidth and a minimum useable bandwidth. These shall be designated as Peak Cell Rate (PCR) and the Minimum Cell Rate (MCR) respectively. The MCR may be specified as zero. The bandwidth available from the network may vary, but shall not become less than MCR. A 12

14 source, destination and network node behaviour is specified along with details of a ratebased flow control mechanism. [2] Examples include LAN interconnection / internetworking services, which are driving the business service market for ATM. These are typically run over router-based protocol stacks like TCP/IP, which can easily vary their emission rate as required by the ABR rate control policy. The support through ABR is likely to result in an increased end-to-end performance (goodput). Another application environment suitable for ABR is LAN Emulation. Other application examples are critical data transfer (e.g. defence information, banking services), supercomputer applications, and data communications, such as remote procedure call, distributed file services and computer process swapping/paging. [2] Unspecified Bit Rate (UBR) The Unspecified Bit Rate (UBR) service category is intended for non-real-time applications, which do not require tightly constrained delay and delay variation. Examples of such applications are traditional computer communications applications, such as file transfer and . UBR sources are expected by nature to transmit non-continuous bursts of cells, otherwise a traffic-shaping algorithm is required. UBR service supports a high degree of statistical multiplexing among sources. UBR service does not specify traffic related service guarantees. Specifically, UBR does not include the notion of a per connection negotiated bandwidth. There may not be any numerical commitments made as to the cell loss ratio experienced by a UBR connection or as to the cell transfer delay experienced by cells on the connection. [2] Typical applications for UBR UBR can provide a suitable solution for less demanding applications. Most data applications, e.g. file transfer submitted in the background of a workstation with minimal service requirements, are very tolerant to delay and cell loss (store and forward networks are in fact widely used for these applications). [2] Examples may include: - Text/Data/Image Transfer, Messaging, Distribution, Retrieval - Remote Terminal (e.g. telecommuting) - The above services can take advantage of any spare bandwidth and will profit from the resultant reduced tariffs ( cheap services). [2] 13

15 2.2 The Detailed Description Of The Project: At the previous section, some details about the ATM Adaptation Layers, Virtual Circuits and different service types were theoretically explained. One of the most popular topics in today s communication technology is telecommunication using both video and voice. By the invention of ISDN and afterwards by the development of ATM technology this topic gained more popularity and started to be applied on computer networks. Today we are able to communicate using video and voice over computer networks. The main problem that should be mentioned at this point is the delay problem in timing sensitive applications. The critical point about the timing sensitive applications is not the amount of bandwidth, as it is usually thought. A good explanatory example can be given using the Ethernet access method. Assume that, a videoconference application using the wavelet video compression is used on an ethernet network. The average bandwidth needed would be about 5Mbps. If we look from the bandwidth point of view, the well known 10 Mbps Ethernet seems to be more than enough. But this does not reflect the actual case. Ethernet does not have any priority mechanisms and also it cannot distinguish between timing sensitive and regular data. Now let s assume that two users start an FTP session along with their video conference session. The result will probably be a disaster. Ethernet will not be able to distinguish between video, which should not be delayed, and FTP packets and the users will start receiving delayed images. As you can understand from the above example, the main idea in videoconference applications, especially if the communication path goes over a backbone, is separating traffic types and guaranteeing that the video data will not be disturbed by other traffic types. 14

16 As explained at the previous section, ATM has the ability to distinguish between different service types and hence providing quality of service to delay-sensitive applications. This fact perfectly fits ATM networking to videoconference applications. In this project, the main aim was to prove that ATM Networks are very successful in carrying different traffic types with a certain guaranteed Quality of Service. To accomplish this task, videoconference was selected as the example to delay sensitive applications. The network used was the campus wide ATM network of the Eastern Mediterranean University. The sub network used for the project is the one between the Department of Computer Engineering and the Department of Electrical & Electronics Engineering. The sub network can be explained as following: There is an ATM workgroup switch at each department. These workgroup switches are able to provide 155Mbps ATM from their ports. These switches are both connected to the ATM backbone switch, which is situated at the E.M.U. Computer Centre. The distance between the Computer Engineering Department and the Computer Centre is estimated to be about 400 meters. The distance between the Electrical & Electronics Engineering Department and the Computer Centre is also estimated to be about 400 meters. As it can easily be deduced the sub network is pure ATM. (There are no other network access methods in the ATM Cloud) The sub network used at the project is illustrated at Appendix 1. Also another important point about the project is the type of videoconference devices used. As it was mentioned before in the introduction part of this report, all the devices are the products of FORE SYSTEMS, Inc. s devices. This company has two types of devices for videoconference applications. One of these devices is called Streamrunner AVA-300 and is able to convert analog video input to digital, then to 53-byte ATM Cells and send them to the ATM switch. By the help of these Streamrunners, throughout the trials, the video signals were directly send to the ATM network. That is to say, no external effects, like the port speeds of the PC s etc., were affecting the communication. 15

17 Every single device and software used was able to directly communicate with the ATM network. Since some external effects may lead the system to produce delays that can thought to be sourced from the network itself, using devices and software that can directly work with ATM is very important in order to be able to prove ATM s power in quality of service. Another important point about the project is the media used. The physical connections of the sub network are done using 62.5 / 125 Multi-Mode Fiber Optic cables. Since the switches are also used for the departments regular needs, like university s Local Area Network or Internet access, the communication path can sometimes be heavily loaded which will provide the opportunity to show that ATM has the ability to manage different service types. At the next section of this report, the devices mentioned in this section are going to be discussed in detail. To see the illustrations of the subnetwork, which is used during the project, please refer to appendices; Appendix I - The ATM Cloud between the Computer Engineering Department and the Electrical and Electronics Department. Appendix II Detailed Network Configuration of the Computer Engineering Department Appendix IV Detailed Cable Connections and corresponding port numbers 16

18 2.3 Devices Used At The Project: About the FORE SYSTEMS Inc. FORE SYSTEMS Inc. is the worldwide leader in the design, development, manufacture and sale of high-performance networking products based on ATM(Asynchronous Transfer Mode) technology. FORE offers the most comprehensive ATM product line available today including the Forerunner ATM switches and adapter cards, Token Ring switch, PowerHub LAN Switches and CellPath WAN multiplexers for ATM connectivity, Streamrunner ATM multimedia products, ForeThought internetworking software, and ForeView network management software. FORE has delivered ATM and LAN switching solutions to over 6,000 customers, including Fortune 500 companies, telecommunication service providers, government agencies, research institutions, and universities. FORE shipped the first commercial ATM adapter cards and switches in 1991 and Since that time, FORE SYSTEMS led the way with new generations of ATM products that offer improved features and price/performance. FORE SYSTEMS customers include, NASA with ATM video products, Metronet (Telecomunications access provider) with internetworking solutions, Ohio State University with WAN Access Multiplexers, Highway 407(Canada s new electronic Toll collection system, worlds first electronic Toll collection) with edge switches. FORE SYSTEMS is the first company to reach 200,000 ATM-based port milestone. Also FORE is a principal member of ATM Forum. FORE SYSTEMS Inc. can be reached at ; and info@fore.com 17

19 2.3.2 Details About The Switches In The Subnetwork Note : For more details about the devices that will be explained in this section, please refer to the Appendix V FORE SYSTEMS Data Sheets Forerunner ASX-1000 Backbone switch The Forerunner ASX-1000 ATM switches are designed specifically to meet the unique needs of enterprise networks. They offer the most advanced reliability features of any ATM enterprise switch available today. ASX-1000 is a scalable 2.5 Gbps to 10 Gbps backbone switch supporting up to 128 ATM ports. Designed for growth, the ASX-1000 is a world class ATM backbone switch that supports in-service expansion of port and switching capacity. The ASX-1000 switch architecture is based on output-buffered, distributed shared memory switching technology. This design enables these switches to support the performance and throughput demands of the most demanding networking environments. All Forerunner ATM switches allow multiple links to be connected between switches. In the event of a link failure, traffic is automatically reconnected using the ForeThought management software. Redundant load sharing power supplies with dual power cords and redundant fans are standard. The ASX-1000 is intelligently partitioned which means virtually all components -power supplies, network modules, fan trays, switch control processors and switch fabrics can be removed and inserted, hot swapped while the unit is in operation. Each 2.5 Gbps switch fabric houses a separate switch control processor. In the event of a SCP failure, the remainder of the switch is unaffected, and continues to operate. A complete range of LAN and WAN ATM interface types is available with the ASX-1000 including 155 Mbps SONET/SDH(Both UTP Cat 5 copper and fiber), 25 Mbps, T1,E1,J2, DS3,E3, Circuit Emulation services, and 622 Mbps OC-12c/STM-4c. ASX-1000 is the first enterprise ATM switch to cross the treshold of 1,000,000+ cell buffers per ATM switch. 18

20 ASX-1000 is the main backbone switch of E.M.U. s campus network ForeRunner LE-155 ATM Workgroup Switch The ForeRunnerLE 155 s QoS capabilities enable a broad range of workgroup applications not available from other LAN technologies including high resolution video conferencing, high-performance groupware, video-on-demand, and computer telephony integration. And, as a member of the ForeRunner family, the ForeRunnerLE 155 leverages FORE s awardwinning ASX switch architecture, ForeThought Internetworking Software and ForeView network management. The ForeRunnerLE 155 features an improved 2.5 Gbps non-blocking switching fabric and an integrated CPU to reduce cost and increase reliability. The ForeRunnerLE 155 provides a minimum of 12 ports of 155 Mbps SONET/SDH. An additional four 155 Mbps ports (UTP5 or MMF) or one 622 Mbps port (MMF) can be added to the base 12-port configuration. The ForeRunnerLE 155 also provides key networking features including: User Network Interface (UNI 3.0/3.1); multicast and broadcast support; ForeThought Bandwidth Management including four priority levels, large, dynamically allocated output buffers, Per-VC queuing, and Early and Partial Packet Discard. ForeThought software provides standards-based ATM internetwork functions: switched virtual circuits (SVCs), LAN Emulation, Classical IP-over-ATM, and virtual work-groups, as well as value-added features such as LANE services redundancy, dynamic routing information with ForeThought PNNI, and IP multicast. The ForeRunnerLE 155 supports ATM Forum, IETF and ITU (CCITT) standards. It complies with the UNI 3.0/3.1 specification for signaling, addressing (OSI NSAP), traffic management (UPC Policing) and network management (ILMI and SNMP MIBs). The ForeRunnerLE 155 also supports Classical IP (RFC 1577) and Ethernet/Token Ring LAN Emulation specifications including support for large message transfer units (MTU). 19

21 At this project, ForeRunner LE-155 ATM workgroup switches are the workgroup switches which the StreamRunner video devices are connected to. The video devices will be explained in detail at the coming subsection and also at the next section in detail. At the E.M.U s campus network there is at least one Forerunner LE-155 workgroup switch at each department StreamRunner AVA/ATV-300 ATM Video Product Family The StreamRunner AVA/ATV ATM video product family provides unprecedented fullmotion JPEG video imaging. Unlike many of today s application-specific video products, the StreamRunner AVA/ATV can support a wide variety of networked video applications, from video surveillance and video-conferencing to live video broadcasts across an ATM network. By leveraging the ATM network to consolidate data, voice and, video traffic, more flexible implementation strategies and significant cost savings can be realised. There are two hardware CODECS comprising the StreamRunner AVA/ATV product line The StreamRunner AVA-300 for video encoding and transmission, and The StreamRunner ATV-300 for video decoding and reception. The StreamRunner AVA-300 encodes analog video signals for transmission over ATM switched virtual circuits (SVCs) or permanent virtual circuits (PVCs). The StreamRunner AVA-300 video channel supports uncompressed or Motion JPEG compressed video for highquality, low-latency transmission of full-motion, true-color video. Video signals can be multicast to a virtually unlimited number of receiving sites. Video from an AVA-300 can be displayed on ATV-300, UNIX workstations and Windows 95/NT PCs. The StreamRunner ATV-300 module receives and decodes up to four AVA-300 video channels. The decoded channels are converted back into analog signals and displayed on a standard TV monitor or VCR. Since these two devices are the main building blocks of the project, the devices and their software SVA 5.0 will be subjected to a detailed investigation at a separate section. 20

22 2.4 The Building Blocks Of the Project AVA/ATV 300 and The SVA 5.0 Software StreamRunner AVA-300 As new applications drive the requirement for more bandwidth, users are turning to ATM to provide a method for implementing high quality video transfer. The AVA-300 provides an efficient platform for one-way video and audio multicasts. The AVA-300 is a standalone device that is suitable for a wide variety of applications. [4] The output from a camcorder, VCR, or any other standard video/ or audio source may be directly connected to an ATM network through the AVA-300. The AVA-300 converts video and audio inputs from their analog format to an uncompressed or compressed digital format encoded over an ATM cell stream. The ATM network can then be used to switch or multicast the video and audio to any number of desired locations. [4] The only additional hardware that is required to display and playback audio on a UNIX workstation or Windows NT/95 workstation is an ATM network interface card. [4] Some of the technical specifications of the AVA-300 can be summarised as; [4] 155Mbps MMF (SC connectors) or 155Mbps intermediate reach SMF (SC connectors) ATM Interface. Note: In the project the MMF interface is used. 50 Hz. PAL or 60 Hz. NTSC software selectable Video Formats. Video Connectors : 6 RCA/Phono sockets configurable as 6 composite channels or 3 S-Video channels. Video inputs may be multiplexed onto a maximum of 4 video output streams. Audio Connectors : 6 RCA/Phono input sockets equalling 3 stereo input channels; one input channel selectable for ATM network transmission data time. ATM Protocols : ATM Forum s UNI 3.0 and UNI 3.1 supported by accompanying SVA 5.0 software 21

23 2.4.2 StreamRunner ATV-300 ATM provides both greater bandwidth and a method for implementing high-quality video and audio transfer. The ATV-300, when used together with the AVA-300, provides a flexible, high-performance solution fro video and audio signal transmission over an ATM Network. [4] The AVA-300 digitises video and audio signals for direct transmission onto an ATM Network. These digital media streams may be received and processed by UNIX workstations and Windows NT-equipped PCs that are directly connected to the ATM network. They may also be received and processed by the ATV-300. [4] The ATV-300 is a dedicated unit for receiving and decoding the digital streams generated by an AVA-300, either via an ATM network or by direct connection. The ATV-300 is suitable for situations in which high-quality output signals are required or in which it would be unsuitable to place a desktop computer. [4] As it can be understood from the above explanation, ATV-300 is an optional device. In a project like this one, it may or may not be used whereas an AVA-300 is essential. Now let s summarise ATV-300 s technical specifications: [4] 155Mbps MMF (SC connectors) or 155Mbps intermediate reach SMF (SC connectors) ATM Interface. Note: In the project the MMF interface is used. 50 Hz. PAL or 60 Hz. NTSC software selectable Video Formats. Digital Video: Concurrent decompression of up to 4 multiple AVA format Motion JPEG digital video streams. Picture-in-picture and tiled video presentation Video Connectors: 2 RCA/ Phono sockets for S-Video output. Digital Audio : 8 or 16 bit PCM, sampling rate from 5 khz to 44.1 khz(cd) and 48kHz(DAT) ATM Protocols : ATM Forum s UNI 3.0 and UNI 3.1 supported by accompanying SVA 5.0 software 22

24 2.4.3 Cell Chaining AVA-300 and ATV What is a CellChain? The CellChain is a mechanism that allows a number of ATM devices to share the facilities of a single ATM switch port. Each device sharing the switch port is linked to the others by a uni-directional ATM transmission link. The high bandwidth available on a single ATM switch port and the low data rates that many ATM devices require made it attractive for a number of devices to share the same switch port. [4] An ATM switch port consists of a transmit and receive interface. Each ATM device that connects to the switch also has a transmit and receive interface. In a CellChain system, the transmit interface from the ATM switch port is connected to the receive interface of the head device in the CellChain. The transmit interface from the Head device is then connected to the receive interface of the second device in the CellChain. This process continues until the transmit interface from the final device on the CellChain is connected back to the receive interface on the switch port to which the head device is connected. [4] Since the interconnection between the devices uses standard ATM technology, the interdevice distance is constrained only by the limitations of the particular ATM Physical layer employed. The ATM Forum standard for framing ATM cells over SONET OC3c (155 Mbps) includes multimode or singlemode fiber. In a case- for example, where multimode fiber is used to link the devices, each unit could be seperated by up to 2000m with no interventing regenerator plant. [4] Important Notes on CellChain: Only a single ATV-300 should be connected in a device CellChain and, if present, it must be the head device. [4] It is not generally possible for devices on the same CellChin to exchange information. For example, it is not possible for an ATV-300 on a CellChin to receive and display a video stream from an AVA-300 on the same CellChain. This would require the switch port to loop back cells it receives directly back out onto the same port, rather than out to a different port 23

25 on the same switch. This kind of functionality is unusual for ATM switches and therefore cannot be relied upon. [4] CellChain used in the project There is a Cellchain connected to the ForeRunner LE-155 ATM workgroup switch of the Computer Engineering Department and the another one connected to the ForeRunner LE-155 ATM workgroup switch of the Electrical & Electronics Department. Each of the two cellchains contains an AVA-300/ATV-300 pair. Since there are ATV-300s in the chains, the ATV-300s become the head devices. We can illustrate the cell chain as in Figure 8. RxTx ATV-300 UNIT 0 LE 155 ATM Workgroup Switch Tx Rx Tx Rx AVA-300 UNIT 1 Figure 8. Cell Chain configuration used at the Project Actually, physically connecting devices in the correct cellchain configuration is not enough. After the physical connections are correctly done, there is a software configuration that should be accomplished. 24

26 2.4.4 SVA 5.0 Software The SVA 5.0 contains both the configuration and the display components. The main application for displaying the video streams was svc-rtds, which stands for Real-Time Display Software. We can summarise the software architecture as; The SVA software uses client server architecture to separate the management of devices from their use by applications. [4] Devices The AVA-300 and ATV-300 hardware components are sometimes referred to as devices. These components are stand alone devices whose only connection to other computers is through the ATM network. They are managed over the network by device-specific managers, which are described in the next section. [4] Managers Managers are SVA software applications that have two primary functions: 1. maintain ATM signalling on behalf of device 2. make the device accessible to other applications Managers control all aspects of a device s operation, particularly the interaction with the ATM network to establish Switched Virtual Circuits (SVCs) dynamically for the video and audio streams generated or consumed by the device. Maximum performance is ensured since all video and audio data is communicated directly over the ATM network and does not floe through the manager. [4] Together, devices and managers constitute a service, which provides video and audio streams for use by applications. One such application is svc-rtds, which stands for Real-Time Display Software and conveys the fact that svc-rtds provides real-time presentation of video and audio streams on the workstation. [4] 25

27 Traders Traders provide a distributed database which managers register their existence and form which applications locate all running managers. In this way applications do not need to know the location of managers, just the name of the host machine(s) running trader(s). Figure 9 illustrates the interaction between managers, trades, and applications. [4] Manager: AVA-300 Room 1 Manager: AVA-300 Room 2 All register with Manager: ATV-300 Reception Area Trader AVA-300 Room1 AVA-300 Room 2 ATV-300 Reception Area Look up Manager APPLICATION Figure 9. How Managers, Traders and Applications Interact. Managers register with one or more traders. Applications must look up managers in the trader to determine where the managers are located before they can invoke any operations on the manager s RPC interface. [4] Managers and the ATM Network Managers implement ATM signalling using a technique called proxy signalling. Proxy signalling relies on the devices being able to forward all signalling messages they receive form the ATM Network to their manager, and on the manager being able to send signalling messages to the ATM network via devices. This means that the device appears to be the producer and consumer of all signalling messages sent to and received from the ATM 26

28 network. The network is unable to distinguish whether the device itself is implementing ATM signalling, or the manager is doing so on behalf of the device. [4] Permanent Virtual Circuits (PVCs) provide the communication paths required for forwarding signalling messages to and from the device. Once configured, PVCs are remembered by the network and require no further interaction with the signalling protocols. The SVA software supports two types of ATM signalling. ATM Forum s UNI 3.0 ATM Forum s UNI 3.1 Both UNI signalling protocols provide similar functionality, so SVA managers can provide the same service regardless of which version is being used. SVA managers, which are applications from the network s point of view, implement both versions. [4] Deciding which protocol to use is based on the command line arguments given to manager when run. It is not possible to dynamically switch between UNI 3.0 and UNI 3.1 at the run time. [4] A few words on SVCs and PVCs Switched Virtual Circuits (SVCs) PVCs are used for signalling and private communication between a device and its manager. All other communication between devices and applications is typically achieved through dynamically-created Switched Virtual Circuits; all video and audio data is sent over SVCs. An important function provided by managers is the dynamic creation of SVCs between their client applications and the device they can manage. [4] Managers make use of multicast SVCs to optimise the use of network resources. That is, if more than one application requests the same video and audio stream, the manager creates a single multicast SVC to carry the data to all interested applications. The use of multicast SVCs ensures that the same data is not sent multiple times over the same shared network link. [4] 27

29 Consider a video stream being generated by an AVA-300, which is being received by three workstations. The network configuration is such that the workstations are connected to the same ATM switch, but there is a second switch between the AVA-300 and the workstation switch. [4] Multicasting means that only a single video stream is required between the AVA and the switch to which it is directly connected. The switch that the workstations are connected to creates or copies a separate video stream for each workstation receiving the video. This reduces the load on the network (i.e. only a single video stream between switches) and also on the AVA-300 since it can generate a single high-quality video stream, which can be received by multiple workstations. [4] Permanent Virtual Circuits (PVCs) Although SVCs are the preferred means of carrying video and audio data, there are certain circumstances in which their use is not possible. For example, there may be an ATM switch that does not support SVCs or video and audio streams may be wanted to be sent to a SVA incompatible device or software application that doest not fully support SVCs. [4] To address these situations, the SVA software allows the use of permanent Virtual Circuits (PVCs) to carry video and audio streams from an AVA-300 to a client application, ATV-300, or any other device or application. [4] 28