SDH şebekeler ve SDH şebekelerde yönetim

Başlık çevirisi mevcut değil.

Tez No: 75186
Yazar: ZAFER GEDİK
Danışmanlar: PROF. DR. GÜNSEL DURUSOY
Tez Türü: Yüksek Lisans
Konular: Elektrik ve Elektronik Mühendisliği, Electrical and Electronics Engineering
Anahtar Kelimeler: Belirtilmemiş.
Yıl: 1998
Dil: Türkçe
Üniversite: İstanbul Teknik Üniversitesi
Enstitü: Fen Bilimleri Enstitüsü
Ana Bilim Dalı: Elektrik-Elektronik Mühendisliği Ana Bilim Dalı
Bilim Dalı: Belirtilmemiş.
Sayfa Sayısı: 109

Özet

SDH, şebeke bileşenleri arasında senkron işlemleri kullanan optik tabanlı bir taşıyıcı şebekedir. SONET terimi Kuzey Amerika'da, SDH terimi Avrupa'da kullanılır. SDH bir bütünleştirici şebeke standardını-. SDH üzerinden her çeşit trafik taşınabilir. LAN, FDDI, 802.3, 802.5 gibi yerel şebekeler üzerindeki son kullanıcı aygıttan, SDH servis bağdaştırıcı yoluyla SDH şebekeye bağlanırlar. Bu seviş bağdaştırıcı erişim noktası terminal veya bir terminal çoğullayıcı olarak da adlandırılır. Bu servis bağdaştırıcı LANlar, E1, T1 işaterleri gibi asenkron işaretleri alarak ve göndererek son kullanıcı arabağdaşımı desteklemekten sorumludur. Çok çeşitli asenkron kullanıcı trafiği bir kullanıcı yükü zarfında birleştirilerek SDH şebeke üzerinden taşınır. Alıcı taraftada bu işlemin tersi işlemler yapılır. ATM, E1, T1 gibi kullanıcı işaretleri standart bir biçim olan senkron taşıma modülüne (STM) dönüştürülür. STM-n çerçeve 125 jıs'lik bir boşlukta 9 x 270 x n byte kadarlık bir alanı kaplar. STM üç ana bölüme ayrılır. Bunlar; bölüm başlığı (SOH), yönetim birimi göstericisi alanı ve bilgi alanıdır. SDH şebeke üzerinden taşınacak işaretler önce uygun kaplarla (C) eşlenirler. Daha sonra sırasıyla uygun VC, TU, TUG, AU, AUG adımlarıyla işaret STM çerçevesine ulaşır. Her bir adımda işarete gösterici eklenir. Bu hiyerarşinin amacı farklı tiplerdeki trafikler arasında senkronizasyonu sağlamaktır. SDH iletim şebekesi bir halka veya noktadan noktaya olabilir. Halka iki veya dört fiber optik kablodan oluşur, iki veya dört fiber kullanılmasının amacı kanallarda ve kanal/cihaz arabağdaşımında meydana gelebilecek arıza durumunda bu arızaların en kısa sürede iyileştirilmesini sağlamaktır. Yani bir fiber optik kabloda bir arıza meydana gelirse diğer fiber optik otomatik olarak devreye girer. Bu kendini iyileştirme halkası olarak adlandırılır. Senkron iletim için uygulama ve yönetim kanalları STM'in POH ve SOH içinde var olur. POH içine yerleştirilmiş bu kanallar gösterici kaybını (LOP), uzak uçtaki blok hatasını (FEBE), uzak uçtaki alış hatasını (FERF) ve hata kontrolünü gösterirler. SOH içindeki kanallar çerçeve kaybını (LOF), FERF, FEBE ve hata kontrollünü gösterirler. Ek olarak SOH D1 ' den D12 ye kadar olan veri kanallarını, F1 kullanıcı kanalını, E1 ve E2 kanallarını içeren şebeke operator bakım kanallarını destekler. Şebeke yönetiminine işlemleri en iyi şekilde kullanmak, kontrol etmek ve kullanıcının değişiklik gereksinimleri için ihtiyaç duyulur. Yönetimi, şebeke fonksiyonlarını değiştirmeyi, izlemeyi ve başlatmayı içerir. Bunları gerçekleştirebilmek için özel fonksiyonlara ihtiyaç duyulur. Yönetim fonksiyonları insan operatörler tarafından gerçekleştirilebildiği gibi otomatik olarak donanım ve yazılımlada gerçekleştirilebilir. İnsanın şebeke yönetiminden sorumlu olduğu durumlarda çok sayıda yönetim fonksiyonusınırlı sayıdaki uzak yerlerden gerçekleştirilir. Yönetim fonksiyonların otomatik olması durumunda şebeke içinde farklı sistemler üzerinde bu fonksiyonlar yazılım ve donanımla gerçekleştirilir. Mevcut tüm yönetim yapıları ISO, ITU-T, IETF yapılarıdır ve bunlar şebeke fonksiyonları tamanlandıktan sonra ortaya çıktılar. ITU-Tnin yönetim yapısı telekomünikasyon yönetim şebekesi (TMN) olarak bilinir. Bu yapının öncelikli olarak telekomünikasyon (telefon) şebekelerindekullanılması amaçlanmıştır. ISO ilk olarak OSI programın bir parçası olarak başladı ve“OSI yönetim iskeleti”,“OSI sistem yönetimine bakış”ve“Ortak yönetim bilgi protokolü (CMIP)”leri yayınladı. SDH çerçeve başlığı içindeki yönetim bilgilerinin kullanılması ve bu bilgilerin şebeke elemanları arasında değiş tokuş edilmesiyle SDH şebekelerde yönetim çok daha kolay ve hızlı olmaktadır. Belli bir merkezden uzak olarak tüm şebeke elemanları izlenebilir ve hata olması durumunda uzaktan hata düzeltme en kısa sürede yapılabilir. Ses, görüntü ve veri gibi her çeşit kullanıcı trafiği ATM'ler tarafından fiber optik SDH'ler üzerinden band genişliği problemi olmaksızın taşınır. Internet protokol (İP) 'nin gelişiyor olması ve band genişliği ihtiyacının gittikçe artması SDH'lere olan gereksinimi arttırmaktadır.

Özet (Çeviri)

SUMMARY SDH (Senkron Digital Hierarcy) is utilizing sysncronous operations between the network componenets. SDH provides a number of attractive features when compared with current technology. First, It has an integrated network standard on which all types of traffic can be transported. Second, SDH ia a worlwide standard.it is possible for different venders to interface their equipment without conversion operations. Third, SDH efficiently combines, consolidates, and segregates traffic from different locations through one facility. Forth eliminates back-to-back multiplexing overhead by using new techniques in the grooming process. These techniques are implemented in a new type of equipment, called an add-drop multiplexer (ADM). Fifth, the synchronous aspect of SDH makes for more stable network operations. Network experience fewer errors than older asynchronous networks, and provide much better techniques for multiplexing and grooming payloads. Sixth, SDH has improved OAM&P features relative to current technology. Approximately 5 percent of the bandwidth are devoted to OAM&P. Seventh, SDH employs digital transmission schemes. Thus, The traffic is relatively immune to noise and other impairment on the communications channel, and the system can efficient time division multiplexing (TDM) operations. Most of the digital network that are in operation today, have been designed to work as asynchronous systems With this approach, each device in the network runs with its own clock. These clocks are not synchronized from a central reference point The purpose of the terminal clock is to locate the digital 1s and Os in the incoming date stream. Obviously, if bits are lost in certain payloads, such as data, the traffic may be unintelligible to the receiver. What is more, the loss of bits or the inability to locate them accurately can cause further synchronization problems, so the receive usually does not even deliver the traffic to the user. It is simpler to discard it and initiate resynchronization efforts. Because each clock runs independently of others, large variations can occur between the terminal's clock and the rate at which data comes into the terminal. SDH is based on synchronous transmission, meaning the average frequency of all the clocks in the network is the same (synchronous). As a result of this approach, the clocks are referenced to highly stable reference point; so the need to align the data streams or synchronize clocks is unnecessary. XIIISynchronization hierarchy is divided into three main synchronization levels. Primary Reference Clock (PRC) is the highest level of synchronization; it is normaly realized through Cesium clocks or Global Positioning System (GPS) receivers. The goal for the synchronizing elements in the network is to have them tracked to a clock representing the quality of a PRC. The second level is represented by Synchronization Supply Unit (SSU), which is normally a standalone piece of equipment in the network. In the case of a loss of the PRC references, the SSU provides the network with high quality synchronization signal for at least 24 hours. In normal operations, the SSU filters the jitter out of incoming reference, which results from phase noise on the synchronization links between the PRC and the SSU. At the SSU level, a further separation is made to distinguish between Transit and Local SSU Node level. SSTs with a Transit Node quality are of sufficient quality to be placed at each point of the synchronization chain; thus each can be used as a reference for further SSUs. Local Node clocks, in contrast to Transmit Nodes, can only be placed as the least SSU in the synchronization chain. The third and last level is represented by Synchronous Equipment Clock (SEC) which is normally built into the SDH network elements. The SEC filters out jitter reference and provides the SDH network element with a holdover capability of approximately 15 seconds. SDH's frame structure consists of 125 |xs time intervals. This is a special feature that cannot be found in the existing plesiochronous digital hierarchies. Its advantageous that lows level signals can be accessed directly from high- level signals, and that all data manipulations can be carried on at the byte unit level. An STM-n signal can be constructed through the synchronous multiplexing procedure. Moreover American signals can be combined with European signals during this procedure and vise versa. This type of cross- continental unification has never been attempted previously. The basic transmission unit for SDH is STM-1 envelope (frame). The octets are transmitted in sequential order. The envelopes are sent contiguously and without interruption, and the payload is inserted into envelope under stringent timing rules. Notwithstanding, a user payload may be inserted into more than one envelope, which means the payload need not be inserted at the exact beginning of the part of the envelope that is reserved for this traffic. It can be placed in any part of this area, and a pointer is created to indicate where it begins. This approach allows the network to operate synchronously, yet accept asynchronous traffic. SDH STM-n frame structure occupies 9B x 270 x n space over 125 \xs. This means that 9 x 270 x n chunks of bytes are repeated 800 times per second, which translates into the bit rate of 155.52 x n Mbit/s (9 x 270 x n x 8 x 8 kbps). The 9B x 261 x n partition of the frame is used for carrying the payload, the 3B x 9 x n and 5B x 9 x n partitions are devoted to the overhead, and the remaining 1 B x 9 x n is used for the AU PTR (pointer). Typically, n of VC-4 or 3n of VC-3can be mapped into the payload. Since an AU-4 (or AU-3) signal is produced by adding an AU-4 (or AU-3) PTR to the VC-4 (VC-3)signal, the STM-n payload together with the AU PTR make up the composition of n AUGs. The AUG is equivalent to AU-4. On the other hand, BIM of three AU-3s results in AUG. Additional BIM of n AUGs, together with an SOH, produces the STM-n signal. The STM-1 frame is equivalent to STM-n frame reduced by factor of n, and has the 9B x 270 structure and 155.52 Mbps bit rate. The payload of STM-1 consists of 261 9B-sized columns. This corresponds to the space of one VC- 4, or three VC-3s plus an FOH. On the other hand, the VC-4 signal consists of a single column of POH and 260 columns of VC-4 payload. Hence, it can be observed that the maximum payload that can be transmitted via STM-1 is 1 49.760 Mbps (= 9 x 260 x 8 x 8 kbps, or 1 55.52 Mbps x 260/270). Similar to the STM-n frame structure, the overhead portion of the STM-1 frame consists of a pair of SDHs and the AU PTR. The upper three rows are used for regenerator section layer, the lower five rows are for the multiplexer section layer, and the forth row is assigned to the AU PTR. The payload of STM-1 is used to carry the VC-4 or VC-3 signal. The loading of the VC-4 (or the VC-3) onto the STM-1 payload is done in a floating mode, with the pointer indicating the address of its first byte. Since the STM-1 payload consist of 2349B(= 9B x 261), if an address is assigned to each of 3B units of the payload, 783 total number of address are required. The address assignment in the row direction from 0 to 782 immediately after the AU PTR In the case of AU-3.three sets of 3 x 783 addresses are required to assign a unique address to three sets of the AU-3. Therefore, at least 10 bits are required for addressing the STM-1 payload. The address thus assigned also indicates the degree of offset of each address location from the pointer location. The nine bytes of AU-PTR from the fourth row of the STM-1 overhead consist of three triplets of H1, H2, and H3. They are employed to keep track of shifting address of first bytes of the VC-4 or VC-3. If the STM-1 's payload is carrying a VC-4, only the first triplet of H1, H2, and H3 is used. On the other hand, in the case of AU-3, each of the H1, H2, H3 triplets independently keep track of address of each AU-3. From the 24 bits that correspond to the three of H1, H2, and H3, only 10 bits are needed to indicate the address from 0 to 783. The section overhead (SOH) is split into the upper and lower parts by the AU-PTR, which is located in between. The upper part is regenerator section overhead (RSOH) and is used to raise the transmission reliability between regenerators. Each regenerator looks at only this part of the overhead and ignores the information carried in the rest of frame. The lower part corresponds to multiplexer section overhead (MSOH) and is used to carry the information necessary to perform multiplexing and demultiplexing. When an STM-1 signal flows into the multiplexer through the local exchange regenerator, the multiplexer checks and examines only this part of the overhead. The signal elements that form the SM structure include the container, the VC, the TU, the TUG, the AU, the AUG and the STM. The container is the most elemental unit of the SM structure in the sense that all of the American and European PDH tributaries have to mapped into xvthe respective cantainers before they can proceed with the SM process and emerge as a part of STM-n. The virtual container's (VC) function is to support the connections between the path section layers in synchronous transmission. The VC consists of the payload, which carriers the information data, and the POH. The payload portion corresponds to a container, and the whole VC frame is repeated every 125 or 500 us. The four classes of VC, namely, VC-1, VC-2, VC-3, and VC-4, correspond to C1, C2, C3, and C-4, respectively. Similar to C-1, VC-1 can be further categorized into VC-1 1 and VC-1 2. VC-1 and VC-2 are called the lower-order VCs and VC-3 and VC-4 are called high-order VCs. The POH for the lower-order VCs is called V5 and the POH for the higher-order VCs is called VC-3 POH or VC-4 POH. Tributary unit was designed to provide adaptability between higher-order and lower-order path layers. For instance, lower-order VCs can be mapped into higher-order VCs through a TU or a TUG. A TU is created by attaching a TU PTR to a lower-order VC, and here the pointer is used to indicate the degree of offset of lower-order VC relative to starting position of higher-order VCs frame. The TU is categorized into TU-1, TU-2 and TU-3. TU-1 is further categorized into TU-1 1 and TU-1 2, depending on the type of VC it contains. Administrative unit functions as an adapter between the higher-order path layer and the multiplexer section layer. As before, AU consists of the payload and the AU PTR. The payload carriers a higher-order VC, and the AU PTR indicates the relative offset between the starting positions of AU payload and the frame of the multiplexer section layer. In other words, the two types of AU, namely, AU-3, and AU-4, carry VC-3 and VC-4, respectively, and the AU PTR indicates the degree of offset of VC-3 or VC-4 with respect to STM-n frame. One or more administrative units occupying fixed locations on an STM payload is called AUG. An AUG can consist of three AU-3s or a single AU-4. The STM is the final product of SM structure and is the signal that is actually transmitted over the synchronous transmission networks. STM-n is formed by byte interleaving n AUGs and the addition of SOH to the beginning of its frame. Here, n of the numbers 1, 4, and 16 are of primary interest Mapping is the appropriate transformation of tributaries into the corresponding containers or VCs across the SDH network border. Since the tributaries are sent from an asynchronous environment, P/Z/N justification is required before they can be mapped into the synchronous containers or VCs. Aligning refers to the process of loading a VC onto A TU or an AU, along with the“frame offset”information. Here, the frame offset is due to the clock discrepancy between the VC and corresponding TU or AU. The VC is aligned on 1B or 3B-unit basis, and the alignment status is indicated by the TUorAUPTR. Pointer processing is employed when the frame offset occurs due to the differences in the clock frequencies between a VC and the corresponding TU or AU. Pointer processing value involves the indication of the starting position of the VC on the payload space off the TU or AU, and the associated P/Z/N justification information. xviMultiplexing by which multiple lower-order path layer signals are adapted into a higher-order path layer signal, or the appropriate transformation of multiple higher-order path layer signals into a signal element of SM or AM. SDH is a physical layer protocol. IP is a network layer protocol. According to the OSI 7-layer model, a mediating data link layer protocol is required between the two. The physical layer is responsible for transmitting raw bits over a communication channel. The data link responsible for converting the raw bit stream offered by the physical layer into a stream of frames for use by the network layer. The network layer is concerned with getting packets from the source to the destination and deals with such issues as packet routing and congestion control in a subnet Although logically a SDH stream is described as s series of frames, from a data link layer perspective it is noting more than a series of octets. In order to be able to map IP packets into an SPE the beginning and end of a packet (or multiple packets) within the SPE is needed to be able to be clearly determined. Since a SDH network consists of point-to-point links, the use of PPP (point to point protocol) as a data link protocol is a logical choice. The PPP frame format is shown in figure-1. Figure 1 PPP Frame Format Synchronous Digital Hierarchy networks have now been deployed worldwide, complementing or replacing existing Plesiochronous Digital Hierarchy (PDH) transmission system. The major benefits of SDH in transport network are their efficient add/drop capabilities, fast self-healing capabilities, standard signal interfaces and simple network operation, maintenance, administration and provisioning. Particular emphasis has been given to resilience and common transport irrespective of the payload structure. Thus SDH system can transport isochronous, plesynchronous and synchronous traffic. The payload is placed (mapped) into fixed capacity virtual containers (VCs). The traditional and, until recently, the only existing payload has been the Plain Old Telephone service (POTS) and leased lines which neatly map into the predefined VCs. Recently, however, a new type of traffic- Asynchronous Transfer Mode (ATM)- has emerged for transport over telecom networks. ATM is designed as a common service transfer mechanism. Information (data, video and voice) is transmitted using small 53-byte packets called“ cells”. All these type of traffic require different Quality of Service (QoS) from the network with respect to transfer delay, variation in delay, cell loss. Economic transport of a diversity of traffic types with a guaranteed QoS for each user stream is challenging objective to be met by ATM. XVDSDH provides reliable, ubiquitous bulk transport for all traffic types. Reliability is provided through well established fast protection and restoration mechanisms, optimized for direct mapping of present STM services (POTS, leased lines) traffic and existing and growing network infrastructure in the field. SDH network can be a mixture of linear, ring and mesh topologies. The topology of a subscriber access SDH network is usually rings. POTS traffic is“hubbed”towards the Central Office (CO) in which there is a Local Exchange. Sub-Network Connection Protection (SNCP) type rings are well suited to hubbed traffic applications and are the most deployed rings in today's networks. DXCs (Digital crossconnects) are used in the Cos to groom the traffic coming from multiple local/access rings and inter-office (regional) networks and delivering it to the exchanges. In the inter-office networks, traffic demand is predominantly point-to-point; mesh structures with DXCs or Multiplexer Section Shared Protection Rings (MS-SPRING) are suitable in this case. The usual architecture of the backbone network is a mesh and it uses DXCs. The equivalent ring types to SNCP and MS-SPRING are Unidirectional Path Protection Switched Rings (UPPSR) in SDH. In contrast to POTS traffic, which is switched, leased-line traffic is point-to-point it is accommodated by allocating the fixed bandwidth of the available SDH VCs for each end-to-end path. SDH and ATM are two complementary technologies, which together have a distinct role in the future transport network. SDH provides transmission reliability and there is already a growing infrastructure in place. The added ATM VP functionality allows network resources to be efficiently shared, improves bandwidth utilization, and prevents or delays early exhaustion of transmission capacities and network upgrades. Implementing a network management approach based on protocol standards provides several advantages. The major standard-based network management protocols include simple network management protocol (SNMP), common management information protocol (CMIP), and telecommunications management network (TMN). SNMP is a set of management protocol standards that describe the asynchronous requests and responses that govern the exchange of network information between SNMP network management entities. SNMP was originally developed to manage transmission control protocol/internet protocol (TCP/IP) communications over the Internet The SNMP entities are a manager, an agent, and a management information base (MIB). A manager entity is a software program that resides on a network management station. The SNMP manager queries agents using SNMP commands. The manager provides the human interface for the network management system. An agent is a software program that resides in a managed network device. The agent stores management information and responds to the manager's request for data using SNMP responses. The MIB is the logical database for network management information. SNMP is a polling-based protocol. The manager sends a request for information to the agent periodically. This period is called the polling interval. xvniEach poll from the manager and response from the agent consumes network bandwidth. An agent can send a trap message to notify a manager of an important event, such as a link outage. CMIP is an event-driven network management protocol that generates reports to identify important spontaneous events. These event reports provide information that supports the five major functional areas of open systems interconnection (OSI) management fault, accounting, performance, security and configuration management CNIP incurs considerably fewer overheads than SNMP, thereby permitting CMIP to be scaleable to large networks. CMIP supplements event reporting with limited polling for establishing initial network status at start-up and for dead-node identification. TMN is a generic model that describes the functions, interfaces and reference points of management system. TMN is compatible with CMIP and support the same five OSI functional areas. TMN provides five logical layers that differentiate activities: network element, element management, network managnet, service management, and business management TMN uses the conventional manager/agent concept to exchange messages between functions. Operation and management channels for synchronous transmission exist inside the STM's POH and SOH: Inside the POH reside the channels for indicating path AIS (alarm indicating signal), loss of pointer (LOP), FERF, FEBE, and error checking. Inside the SOH there are also channels for indicating the section AIS, LOS, loss of frame (LOF), FERF, FEBE, and error checking. In addition, SOH support the network operator maintenance channel (NOMC), which includes order wire (E1, E2), user channel (F1), and data channels D1 to D12. Also, for OAM proposes, an additional TMN can be employed. SEMF represent the function for accepting the OAM-related signals through the regenerator or multiplexers to be sent to the MCF, or its reverse. MCF receives the message and transmits it through the SOH's DCC, or deliver it to the TMN, and it can also function in the reverse direction. XDC

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