SYNCHRONOUS DIGITAL HIERARCHY

WHAT IS SYNCHRONOUS TRANSMISSIONSynchronous Transmission has been developed to overcome the problems associated with Plesichronous Transmission, in particular the inability of the PDH to extract individual circuits from high capacity systems without having to demultiplex the whole system.

MAIN FEATURE OF SDHNetwork Management CapabilityChannel ExtractionAny existing PDH Transmission Rate to be packaged into an STM-1 frame.

PRINCIPLES OF SDHSDH DIAGRAM

SDH PRINICIPLESThe SDH defines a number of containers, each corresponding to an existing PDH rate. Information from PDH signal is mapped into the relevant container. The way in which this is done is similar to bit stuffing procedure carried out in PDH MUX.Each container then has some control information known as the path overhead added to it.

CONT---------PATH OVER HEAD bytes allow the network operator to achieve end to end path monitoring of things such as error rates.Together the container and the path overhead form a VIRTUAL CONTAINER

FIG

CONT-----------In a synchronous network, all equipment is synchronized to an over all network clock.It is important to note that the delay associated with a transmission link may vary slightly with time. As a result the location of virtual containers within STM-1 frame is may not be fixed.These variations are accommodated by associating a pointer with each VC.

CONT-----------The pointer indicates the position of the beginning of the VC in relation to the STM-1 frame. It can be incremented as necessary to a accommodate movements of the position of the VC.

CONT--------G.709 defines different combinations of virtual containers which can be used to fill up the payload area of an STM-1 frame. The process of loading containers and attaching overhead is repeated at several levels in SDH, resulting the nesting of smaller VCs within larger ones. This process is repeated until the largest size of VC (VC-4 in Europe) is filled, and this is loaded into the pay load of the STM-1

CONT-----------When the payload area of the STM- 1 frame is full, some more information bytes are added to the frame to form a Section Overhead The section overhead bytes are so-called because they remain with the payload for the fiber section between to SDH MUX.

PURPOSE OF SECTION OVERHEAD BYTESTheir purpose is to provide communication channels for functions such as OA&M facilities.User channel Protection switching Section performance Frame alignment Etc.

BYTE INTERLEAVING MULTIPLEXING SCHEMEWhen a higher transmission rate than the 155 Mbits/s of STM-1 is required in a synchronous network, it is achieved by a relatively straight forward Byte interleaving Multiplexing schemeIn this way rates of 622 Mbits/s (STM-4) - 10 Gbits/s (STM-64) can be achieved.

BENEFITS OF SYNCHRONOUS NETWORKNetwork Simplification: A single SDH MUX can perform the function of an entire PDH MUX mountain. FigLeading to significant reduction in the amount of equipment used. Lower operating costs will also result through reduction in spares inventory required, simplified maintenance, and also reduction in floor space required by the equipment, and lower power consumption.

BENEFITS OF NETWORK SIMPLIFICATION CONT-------The more efficient drop and insert of channels offered by an SDH network, together with its powerful network management capabilities, will lead to greater ease in provisioning of high bandwidth lines of news multimedia services as well as ubiquitous access to those services. Thus the simplification of the network, and flexibility this brings opens up the potential for network operator to generate new revenue.

SURVIVABILITYThe deployment of optical fiber throughout the network and adoption of the SDH network element makes end to end monitoring and maintenance of network integrity a possibility. The network management capability of the synchronous network will enable the failure of links or even nodes to be identified immediately. Using self healing ring architecture, the network will be automatically reconfigured with traffic intensity rerouted until such a time as the faulty equipment has been repaired.

SURVIVABILITY CONT-----Thus, failure in the network transport mechanism will be invisible on an end to end basis. Such failure will not disrupt services, allowing network operators to commit to extremely high availability of service figures and guarantee high levels of network performance

SOFTWARE CONTROLProvision of network management channels within the SDH frame structure means that a synchronous network will be fully software controllable. Network management system will not only perform traditional event management functions- dealing with alarms in the network, but will also provide a host of other functions, such as performance monitoring, configuration management, resource management Network Security, Inventory Management and Network Planning and design.

SOFTWARE CONTROL CONT-------The possibility of remote provisioning and centralized maintenance will mean a great saving in time spent by maintenance personnel in traveling to remote sites, and this of course corresponds to expense saving.

BANDWIDTH ON DEMANDIn a synchronous network it will be possible to dynamically allocate network capability, or bandwidth, on demand. User any where within the network will be able to subscribe at very short notice to any service offered over the network, some of which may require large amount of bandwidth. An example of this is dialup video conferencing. User link just by dialing the appropriate number, as opposed to the current situation where videoconferencing link must be booked days in advance.

BANDWIDTH ON DEMAND CONT---Many other new services become possible in a synchronous network. These will represent new source of revenue for network operators, and increased convenience for users. Some examples are high speed packet services, LAN interconnection and HDTV

FUTURE PROOF NETWORKING The synchronous Digital Hierarchy offers network operators a future proof network solution, plus software upgradeability and extensions to existing equipment.

ELEMENTS OF SYNCHRONOUS TRANSMISSION SYSTEMMultiplexers: Synchronous Multiplexers, as defined by ITU-T SDH recommendations, perform both multiplexing and line terminating functions, as shown in FigThus a synchronous MUX replaces a bank of PDH and associated line terminating equipment, while at the same time bringing new functionality.

SDH MUX CONT---------Synchronous Multiplexers can accept a wide range of tributaries, and offer a number of possible output data rate as shown in FigOn the tributary side, all current PDH bit rates can be accommodated.

SDH MUX CONT----------------The synchronous Optical Interface of the synchronous multiplexer can be duplicated for protection. This can be done in two ways, either traditional 1+1 protection can be provided, or the optical port can operate in an EAST/ WEST NODE to allow the implementation of ring topologies.Synchronous ring can improve resilience and reduce both fiber requirement and network cost.

POINT TO POINT CONFIGURATIONSSynchronous Multiplexers can be used effectively high capacity point to point applications where they are cost competitive with PDH solutions. The equipment facilitates provision of new services and provide an upgrade path as network evolves. fig

ADD DROP CONFIGURATIONThis configuration is similar to the previous one but the fact that a number of MUX are used to provide connectivity between nodes along a route. The MUX are configured to add drop channel at these node

RING CONFIGURATIONFor areas of the network requiring high survivability, synchronous multiplexers may be configured as a high capacity self healing fiber ring. The ring structure is able to reconfigure without the intervention of external network management should equipment or cable occur maintaining continuity of service

HUB CONFIGURATIONSBy using tributary interfaces, a terminal can be configured as a fiber hub for use in multi-site network applications, This eliminates the need for back fiber terminals.In addition to its operation capabilities, a synchronous multiplexer offer a Network Management channel which may provide alarm and monitoring information for individual tributaries within an STM-1 signal

HUB CONFIGURATION CONT---Not only does this provide enhanced management abilities, but since management within the SDH is to be standardized, additional cost benefits can be realized by network Operator through more efficient Management System.

CROSS CONNECT FUNCTIONALITYCross Connections in a synchronous network involves setting up semi-permanent interconnections between different channels, enabling routing to be performed down to a VC level.This description seems to suggest that cross connection is similar to switching, but there are fundamental difference between two .

CROSS CONNECT CONT------The main difference is that a switch operates as a temporary connection which is set up under the control of the end user, while cross connection is a transmission technique use to set up a semi permanent connection under the control of the network operator via a network manager.However, as network services evolves to wideband and broadband, it is certainly possible that the switch and cross connect functions will begin to merge. This is particularly true when ATM services begin volume deployment

CROSS CONNECT CONT------There is also a distinction between the plesiochronous cross connect unit which has established itself to some extent within current networks, and the synchronous cross connection function.The traditional PDH X-connect was developed to replace manual digital distribution frames which were seen as reliable and labor intensive as shown in FigSlow to setup, prone to error and expensive.

X-CONNECT CONT-------In deploying a plesiochronous automatic Digital Distribution Frame, this allows traffic passing through the cross connect to effectively share the physical connection at different instances in time. However this requires that all traffic through a PDH X-Connect is synchronized, thus necessitating the expense of providing a justifications mechanism at the interface between it and the network.

X-CONNET CONT-----The traffic rates through plesiochronous cross connect also need to be limited to a manageable size since these cross connect can only easily operate at a single rate. Most choose to switch at the 64 Kbits/s level and interface at 2 Mbit/s. This means that all traffic must be demultiplexed to 2 Mbits/s before it can be connected, thus increasing equipment requirement, sized and cost.

X-CONNECT CONT---With the introduction of synchronous transmission system the need for any justification of signals at the interface with the cross connecting device is removed. Fig shows the difference between PDH and SDH X-Connect.Probably the most important difference between the plesiochronous network digital cross-connect (referred the plesiochronous network digital cross connect (refered as DXC) and the synchronous cross connect function is the actual deployment planning.

CONT---A DXC is required wherever a large add-drop function is performed or where a lot of manual reconfiguration takes place in the network to provide new service or groom existing service for efficient facility utilization.Any of these application required the use of a distinct piece of plesiochronous equipment called a DXC to perform the function.

DXX CONT---The synchronous X-Connect function, when required does not necessarily mean the need for a separate piece of equipment. The flexibility of SDH allows the cross connect functionality to reside in almost any network element, the most obvious being an add-drop MUX.

SDXC (SYNCHRONOUS DIGITAL X-CONNET)There are two types of dedicated SDXC commonly referred to, the SDXC 4/4.SDXC 4/1These are used in special applications to supplement the distributed cross-connect functionality of a synchronous network. The numbering scheme describe the VC level at which they can accept inputs and cross-connect respectively. It can be seen that the difference between the two is the multiplex level at which they can cross connect traffic.

SDXC 4/4The SDXC 4/4 is usually designed to accept input s at 140, 155 or 622 Mbits/s or higher. It can cross-connect at 155 or 140 Mbits/s. It may be used in the core of the transmission network for network protection as an alternative to STM-16 base protection ring architecture.

SDXC 4/1The SDXC 4/1 can usually accept combinations of 2,155 and 622 Mbits/s input. It can cross connect VC-1 containers, i.e 2Mb/s channels, though in many cases 4/1 cross connects will also be able to cross connect VC-2s, concatenated VC-2s, VC-3, and VC-4. These pieces of equipment may be used where special circumstances lead to the requirement for a point of additional flexibility in the outer core transmission network.

SYNCHRONOUS DEPLOYMENTMulti-vendor ConnectivityTechnological Discontinuity.Reduction in equipment.Improved Network Resilience.Network Management.Single Stage Multiplexing.Single Stage Multiplexing.Distributed Bandwidth Management.Software Down loadRing Deployment.

SDH DEPLOYMENTImplementation of New Services.Improved Earning.Deployment TriggersModernisationThe SDH SolutionNetwork EvolutionManagement Services NetworkInternational Services Network

MULTI VENDOR CONNECTIVITY The standardisation of synchronous interfaces means that a planner can mix and match products from different vendors in the network, without having to concerned about their ability to work together. However there is still the possibility of implementing the standards in different ways. Thus the network planner must understand the impact of choosing between such options as, Floating,or Fixed mode mapping, or choosing between asynchronous, bit synchronous or Byte synchronous mapping.

TECHNOLOGICAL DISCONTINUITYBecause synchronous can carry plesiochronous payload it can be deployed in an evolutionary manner. However, because of the changes associated with synchronous systems it does represent something of a technological discontinuity. Thus, in order to effectively overcome the limitations of the PDH, network operators must plan the introduction of the synchronous into their network with care.

REDUCTION IN EQUIPMENTSDH will lead to simplification of the network. The multiplexing structure allows for greater integration of products, along with greater control of equipment. The network planner faces the exciting challenge of using synchronous equipment in such a way as to unleash the full power inherent in it.

IMPROVED NETWORK RESILIENCEA synchronous network will be more reliable due to both the increased reliability of individual elements, and the more resilient structure of the whole network. Synchronous will allow development of network topologies which will be able to achieve network protection , that is survive failures in the network by reconfiguring and maintaining service by alternate means. Network Protection can be achieved the use of cross connect functionality to achieve restoration or through the use of self-healing ring architectures.

NETWORK MANAGEMENTSDH gives the network operator the opportunity to manage network performance effectively and make change flexibility as required. Synchronous equipment will have a significant proportion of its design embedded in software instead of hardware. Therefore, the network manager will be able to control equipment configuration changes through software management. What is ultimately required is the ability for the network manager to implement what is called IN SERVICE PROVISIONING.

NETWORK MANAGEMENT ----This is where a request for service is entered into the network manager via a terminal or other electronic mean and is then broken down into a series of instructions to each network element involved in that service. Each network element is then configured and provisioned in software to support the service request without having to be taken out of service. It is important that the network operator plans his network in such a way as to take advantage of benefits resulting from in service provisioning.

SINGLE STAGE MULTIPLEXINGThe SDH multiplexing structure allows many different tributaries to be multiplexed together into an STM-n signal in a single stage of multiplexing. Thus the network planner is not bound by a rigidly hierarchical network structure, as he was with the PDH. The planner now has at his disposal the bandwidth flexibility essential for the introduction of new services.

DISTRIBUTED BANDWIDTH MANAGEMENTThe plesiochronous cross connect was originally conceived as a devie to sumplify routing and gromming at srtrategic poinit s in the network, However, the necessity to transport traffic to cross connet site often outwidhed the benefirs gained.

DISTRIBUTED BANDWIDTH MANAGEMENT-- In a sunchronoos network, the abitlity of multiplexers to perform routing and frooning down to the VC level means that cross connect functionality can be distributed througout the network. This distributed bandwidth management capability means that standalone cross connects are only required to be deployed at points in the network where exceptional felxibility is required.

DISTRIBUTED BANDWIDTH MANAGEMENT --The distribution of cross conect funactinality, togerhter with the connectivity procide aby rsilient ring structures means that in a sycronos network it becones possible to mange the distrubution of banwith down to th VC level. This distributed badwidth manamenent capabilty is essntial to techniques such as in service provisioning , and flexible badwidth allocation as well as to berfwork managemet techniques tha bneawork operators will be able to talke full adavantage of the power of SDH

SOFTWARE DOWN LOADIn a sychchronous network it wll become posible to down load software an configuration ifomaton to Netowrk Elemant via the Embedded Commmunication channe. (ECC). Using this facility it will become possible to amange sofware relaeases and updatred remotely, with download as done either aurmaically or amanually. This abitly waill further contribute to the redcution of operating cost is a sychronous network.

RING DEPLOYMENTTelecommunication users, particularly business isers are becoming increasing dependent on the efficient transfer of information. Use of telecommunication for vital transactions, such as elecrtroing funds trasfers, order processing ., customer service and inverntory control makes service makes sercie surviability moer important than ever before.

RING DEPLOYMENT ----In many cases, loss of service can hace disastrous results, Conseqently many users are now looking for a gurantee as to conitinuity of service and willing to pay a premium to get it. By using synchronous equpment to implement a survivable network architecture, network operators can thus repsond to this demand, in the process generating additonal revenus.

RING DEPLOYMENT---The synchronous ring structure, with its inherent resilience, is a powreful building block form which surviable neworks cab be bult. Within ETSI TM3 a recommendation (G.sna1) is currently being drafted which describes sychronous network applicatons, including both point to point and ring toplogies. It will describe the way in which SDH rings can be used to provie end to end path protection and multiplex section (MS ) pretection at the tranmission media level against link and node failures.

RING DEPLOYMENT ---Two main types of sychronous ring architecture are being defined.1- The (unidirectional) dedicated path switched ring sends traffic both ways around the ring, and uses a protection switch mechanism to select the alternate signal at the receiver end upon failure detection. This is a Dedicated protection Ring.

RING DEPLOYMENT --- The (bidirectional) sharen ed MS switched ring is able to share protection capabililty which is reseced all the way around the ring. In the event of a failure to route traffic through the spare capacity. To protect all traffic on the ring it is only necessary to reserve enough protection capacity to protect the largest working span. This is Shared Protection Ring (SPRing)

RING DEPLOYMENT ----The ability to share protecton capacityh in bidirectional SPRings can in many instances offer a significant capacity advage over unidirectional DPRings. This means, in economic terms less equipment, lower cost, and less operations effort for the network opeators.

RING DEPLOYMENT--Two types of ring achitecture are best suited to different applications.1- Unidirectional DPRing are best suited to hub taffic applications, whre the simplicity of the implementation and the high availabiity offered by DPRings for the end to end path is important. This would typically occur in the access network.

RING DEPLOYMENT--Bidirectional SPRings are best suited to site /adjacent site and uniform traffic applications, where the capacity advantage of SPRing is significant. This would occur in metropolitan, junction, and trunk network applications.

RING DEPLOYMENT --Another important characteristics of the survivable ring architecture is the aotomous operation at the transmission level for fast recovery form tlink and node failures. This reduces management complexity associated with TMN. This fast switching time at which rings recover from failure means negligible impact on service interruptions.

RING DEPLOYMENT---The autonomous network surviability offered by rings is further enhanced by the inherent Distributed Bandwidth Management capability, where each ADM node on the ring is capable of routing and grooming at the VC level to provide a efficiency of control and management over the transmission network, as well as reduces the required number of stand alone cross connects such as SDXC 4/1 for hubbing of traffic and SDXC 4/4 for network protection.

IMPLEMENTATION OF NEW SERVICESSynchronous technology allows planners to look at their network in terms of service demands rather than just the provisioning of point to point facilities. In order to succeed in an increasingly competitive telecommunication world, service providers must take an integrated approach in network planning in order to achieve a network the power of which is greater than the power of its constituents parts. Only by doing this will the operator be able to build a network infrastructure strong enough to ensure support of any service to anyone, anywhere.

IMPROVED EARNINGBy taking careful of all the issues discussed above, the network operator will be able to acieve a significant incrase in earinings. Synchronous will help him to reduce network costs (e.g through reduction in equipment), improved network survivability (e.g through reduction in equipment), improve network survivability e.g( through the deployment of rings) reduce operating costs (e.g through the deployment of more reliable equipment and the use of network management ) and increas revenues by offering new services.

DEPLOYMENT TRIGGERSChanges to the network are generally made either to grow its capacity of to mederanise it. This secton sets out to examine why such changes to the network might arise, and how they can be achieved. Fig Show a common method of terminating fiber in an exchange, demultiplexing the traffic and managing the routing and grooming function at the DDF.

GROWTHThe need for network growth occurs in response to either geographic movement of end users, increase in number of end users or increased banwdth rquirements, particularly form business users. Such a requirement can currently lead to a number of problems, such as exhaustion of optical channels on the PDH optical line system, and the need to expand the digital distibution frame.Optical fiber channel exhaustion is currently overcome by deploying a new PDH system in parallel to eh old one, and using it to transport new traffic as necessary.Expansion of DDF is an unpleasent task involving much manual reconnection activity with its possible human error.

MODERNIZATION The network may need to modernized for a number of reasons. Some of the most common reason in response to demand for increased quality of service, in order to cut operating costs or in order to offer new services and hence generate new revenus. The DDF is likely to be limiting factor in any network modernisation programme. Any changes made in the current network are likely to have limited effects as a result of the inefficiency of the DDF.

SDH SOLUTION--SDH equipment can be used to overcome the limitations outlined above, as shown in fig. An SDH multiplexer, with its increased capacity, can be deployed in place of its PDH counterpart. There is no need initially for full scale repalcement of DDF. By utilizing the cross connection functionality embeded in the SDH MUX it is possible to automate the mangement of chage in the private curcuits and leave the fairly stable PSTN circuits on the DDF.

SDH SOLUTION---The cross connect capability of the SDH MUX has the added benefit of manageing the routing of thorough traffic, thus further offloading the DDF. Over time, as the use of SDH in this exchange grows, it amy become appropriate to repalce the DDF with a stand alone SDXC. This economic decision will occur as more and more traffic moves off the copper cables and on the fiber.

SDH SOLUTION--Thus SDH has provided a number of benefits in this example. These are:1- Provision for capacity growth.2- Automation of the DDF function a- Faster Implementation of changes b- Improved reliability c- Reduced whole life cost of ownership3- Integration of product functions4- Ability to support enhanced services.

SDH SOLUTIONIt is important to note, however, that no deployment of SDH equpment should take place in isolation from a total network plan. Such a plan will ensure that any piece of equipment deployed will improve monitoring, survivability, provisioning, and control of the complete network.

NETWORK EVOLUTIONThere are several possible deployment methods for synchronous equipment whithin hteth inter office area of a neawork, one of which is the use of the ring topology. Delployement of synchronous rings will bring immence felexibility and resiliene to the nertwork.The junction ara includes a number parucular applications which can utilize rings of synchronous mulitplexers. One example is in the area of restructing local exchanges, to improve fiber utilisation and reduce operating and equipment costs

NETWORK EVOLUTION---Most European networks are characterised by highly interconnected mocal exchanges, which are in turn connected to main local area exchanges for access to higher levels of the transmission hierarchy as shown in fig. Although maintaining a high availablitiy, this method of traffic collection is high in equipment caost and somewhat watesful of fiber.

NETWORK EVOLUTION ----In an attempt to reduof thece costs, some operators have proposed the use of small remote units to concentrate PSTN traffic. These are connected to higher levels of the transmission hierarchy via main local exchange. The transport of the traffic from these remotes to themain local exchange provides an ideal opportunity for the deployment of sychrnous systems to reduce operating costs. Fig show how the remotes would be connected to the main local exchange using sycnronous systems to reduce opertating cost.

NETWORK EVOLUTION ---Fig shows how the remotes would be connected to the main local exchange via using synchronous transmission equipment. The equipment may be deployed either in a flattened ring or in a true physical ring. Such an STM-1 Ring may have several remote connected onto it, with each terminating a mixture of private circuit (PC) traffic and PSTN traffic, as shown in fig.Protection would be provided by routing the high availability private circuit traffic may either be treated similarly, or could be split in some ratio for diverse routing to maintain traffic in the event of a fiber break.

NETWORK EVOLUTION---Consider the particular example shown in fig with an STM-1 ring connecting five remote to a main local exchange.A typical route may be capable of supporting up to 16x2 Mbits/s of traffic, although in practice it may only terminate around half of this. For the purpose of discussion consider a network in which traffic will comprise both PSTN and private circuit (PC) traffic, with around 80-90% of this being PSTN.

NETWORK EVOLUTION---Assuming that two of the remotes connect eight channels of PSTN with two 2Mbps PCs connected directly onto SDH MUX, and the remaining three remote carry sixteen channels of PSTN and four PCs the traffic on the ring is:

NETWORK EVOLUTION---2 remotes with 8x2Mbits/s PSTN +2X2Mbits/s PCs== 8 channels (half routed clockwise and half routed anti-clockwise) + 2 channels (routed both ways)= 8 + (2x2)= 12 channels (from each of the 2 remotes)= 24 channels on ring---------------------------------A

NETWORK EVOLUTION ----3 remote with 16x2Mbit/s PSTN + 4X2Mbits/s PCs = = 16 channels (half routed clockwise, half anti clockwise + 4 channels (routed both ways)= 16 + (4x2)= 24 channels (from each of the 3 remotes)= 72 channels on ring---------------------------------BA+B = 96 (TOTAL NUMBER OF CHANNELS ON RING)

NETWORK EVOLUTIONSince the taotal ring capacitynis 126 channels this givces a fill factor on the ring of 96/ 126 = 75%. This figure follows aroung 25% of the ring capacity for expansion, before the ring would bneed upgardation in its capacity i.e to STM-4. It must be remembered that provision must be mad4e at the tring head for all channls requireing access to the main local exchange. In many instances this will involves use of multiple muxs at the ring head.

NETWORK EVOLUTIONBt taking advantage of the embedded cross connect functinality in the ring head mux, it is possible to goon the 2 M bits/s channels, separating PSTN traffic from other transmission based sevices ans in figure 5.6 A furhter consequence of this is that the number of main local exchange sites may be reudces and they may be relocated at certral sites to simplify adminitration. This can be achieved with syschronous links form the ring head to the exchange at either the STM -1 or STM-4 level.

NETWORK EVOLUTIONFurther links from the ring head would provide access to the higher level of the transmission network.At this stage, the network comprises a number of isolated areas of synchronous transmission equipment, which may be considered as islands. The next stage of development will take one of the two paths. The network operators may choose to ocntinue this staratefgy u ntill islands grow to the extent a which they begin tjo merge. The alternative is to provide links between the islands using higher rate synchronous systems, hence allowing the befefits of the complete sysnchronous network to be realised at an earlier stage.

MANAGED SERVICES NETWORKAnalysis of the continued growth in communications traffic througout Europe shows that the largest areas of expansion are due to non PSTN traffic. In order to maintain the migration to a Managed Transmission Network, supporting new services efficiently, there is a need for greater control over the transmission network.

MANAGED SERVICES NETWORKTo achive this control requires a level of fexibility within both trunk and junction network. This flexibility can be provided by the use of distributed bandwidth management techniques, to allow for effective conrol of the network capacity. By distributing cross connect functionality througout the network, and using flexible synchronous ring architectures, new services can be made available at a relatively low incremental cost to the network operator.

MANAGED SERVICES NETWORKAn intergrated synchronus network allows the end user a range of interfaces, which can accommodate the types of traffic mentioned above within the SDH signal. Thus a synchronous network could act as transpoer tnetwork for a wide ranfg eof secices as shown in figure 5.7 Thses may include any of the follwing

MANAGED SERVICES NETWORKISDN, PSTN,Private Circuits, PSS Telex, Fax , X-400, Cable Tv, Video Phone, computer links LANs, VPN, Cellular and ATM and BISDNThe requirement of such sercice and in parutcular MANs, LANs, and other computer oriented services, raise an issue which relates to the sychronous signal structure itself.In order to serve the requirements of these services it is necessary that the SDH improves upon the granularity of secices rates availble inder the existing PDH.

MANAGED SERVICES NETWORKA typical example would be customer requriement for a 10Mbps data pipe. The only way inwhainc hisn cluld be supported by existing transmission equimpemnt would be cia the use of a 34 Mbps pont to point systems with terminal equimpmnent providing a bit stuffing operation to pack out the spare 24 Mbps of capacity. This would of course be very efficient.

MANAGED SERVICES NETWORKThe way in which the SDH provides a higher granulariy to transmission rates is cia the use of contatenated TUs. Concatenated involves the association of a numbner of TU s within ones STM-1 singals in order to offer a rate that is a muulple of the TU signal. The way in which this is done will not be descirberd in deatail. However deraisn of the first level of contenation of can be found in G709. This describe the method for conruguous contatenation of TU-2 s, which allow transmission rates given by MXTU-2 capacity = MX6312kbits/s ( M= 1 to 21)Thus the 10 Mbps interconnect requiremetn above could be satisfied by the use of two TU-2 concatenated. This would be reffeered to as a TU-2 mc (with a capacity of 13696 kbps)

INTERNATIONAL SERVICES NETWORKAn evolving Managed Transmission Network (MTN) must be based upoi identifiable cost befifits to the network operator, and/or the possibility of increased revenues. The drive for the introduction of an international service network is generated by the need to provide business users with increasing amounts of capacity over leased digital circuits, across international boundaries.

INTERNATIONAL SERVICES NETWORK In the UK, both the areas of leased narrowbnand (Kilostream) and 2 Mbits/s (Mega stream) services have seen a rapid take up (The forecasts for growth in Megastream traffic are now estimated at 50% per annum. With the introduction of digital PBXs and the networking of compituers throughout Euporpe, a need can be identified for Nx2 Mbits/s services can not be supported at all on existing plesiochronous equipment.

INTERNATIONAL SERVICES NETWORK As demand increases for these services to be provided on a PAN European for these services to be provided on PAN European basis, work in taking place on the concept of a Pan European Wideband Leased Line Network (WBLLN). It is likely that such a network will utilize the integration of managed national networks based upon The SDH. Only the SDH offers within realistic timescales. More importantly it is only via the provision of NX2 Mbps on an international basis that moves can be made towards an International Broadband Communication Network, IBCN.

INTERNATIONAL SERVICES NETWORKIn physical term the network will appear in the form shown in figure 5.8. The Services Access Point (SAP) will be located near or possibly on the customers premises, whilst the services Access Node will provide the 1.5 Mbits/s , 2 Mbps and Nx 2 Mbps cross connect facilities for grooming to the MN layer. An overlay of high capacity synchronous links would effectively be formed, to interconnect the international nodes.

INTERNATIONAL SERVICES NETWORKWith regards to management, the network Level Control function shown in figure 5.8 may be centralised or distributed. It would control the elements of the transmission network to set up paths. The service management function engages the resources of this MTN to provide, reallocate and charge for services to the customer. The setting up of the paths across international boundaries will involve peer to peer negotiation between Services Managers according to agreed interworking standards.

NETWORK MANAGEMENTThe topic of network management is a complex one and frequently means different things to different people. It is not the ain of this presentation to delve into Network Management to any great depth. However with the introduction of the SDH, the management of tranmsision network may be viewed In different context.

NMWith the emergence of the ISO OSI seven layer reference model, as a basis for open standards, the opportunity was seen to bring about interoperability in the management of transmission networks. This opportunity was not missed in the definition of the SDH.The SDH provide a method and format of transmission designed for Network Management.

NMThis section will begin by describing the provions for Transmission Management, made within the SDH Signal Structure. This will be followed by a number of general concept refardng the Mangement Hierarchy and Management functionality. Finally the topic of open Network Management Platform will be briefly be covered.

THE PHYSICAL MANAGEMENT PATH.With reference to OSI 7-Layer reference model, layer 1 of this model requires the difinition of Physical path for commnications.Within existing plesiochronous networks, no provisions was made for a standard management path within ITU-T recommendations. To overcome the lack of a management channle, many manufacturers developed propreitary systems, based on either the use of spare bits within the signal frmae or vial line coding methods similar to those used in submarine systems.

THE PHYSICAL MANAGEMENT PATH.Despite the restrictions on transmission rates, some of the methods employed are capable of superviosion and monitoring of equipment and to a limited extent even remote configuration. The major drawbacks with these systems revovle around the fact that management is restrictred to a channle which can only be accessed at a specifir transmission rate e.g. 2 Mbits/s , 8 Mbits/s , 34 Mbtis/s, hence requireing mutiplexing to access it. This restiction linits management to a section by section facility. More importantly, it is possible for inteworking to exist between diffent systems. It is quire probable that one manufacturers equipment will not even support a management channle between two pieces of equipment for a third party.

THE PHYSICAL MANAGEMENT PATH.With the introduction of a new method of transmission, the SDH, the opportunity was taken to implement tohe ideals embodied in the OSI 7 layer referenc emodel to difine a management channel. This began with the definition of ovehead capacity in the STM-1 frame, thus offering a difined management channle of section by section communication. This was extended further to define overheads at the AU level and the TU level thus providing management capacity over the core of the transmission network and slaos a path management channel associtated with a path extending from end to end across an entire network. This is bes t shown by studying Fig 6.1

THE PHYSICAL MANAGEMENT PATH.It is this ability to provide path amangement to the VC-1 (2 Mbits/s) level which highlights a significant advance in telecommunication management with the infroduction of the SDH. However, the move towards management standards did not stop at this point. ITU-T recommendations G.783 and G.784 go on to propose how the management channels should be used; referred to as the Data Communication Channel (DCC) of sometimes the Embedded Communication Channel (ECC) and further propose the protocols which should be employed for the remaining 6 layers of the OSI model.

THE PHYSICAL MANAGEMENT PATH.In these clear definitions and in the continuing work of the SDH study groups, the first major steps have been taken towards the implementation of Open Network Management System in the Telecommunication Industry.

MANAGEMENT HIERARCHY Fig 6.2 shows a simplified model of the Network Management Hierarchy. The definition of distinct levels may vary due to system size and the management strategy, however the principal structure remains the same. The following section describe the Network Control Layer , the element managemetn level of network management , e.g the Service Management Layer, are not described.

NETWORK CONTROL LAYERAt the network Control level the management system is required to provide monitoring and control of a complete management domain (e.g a subnetwork or possibly a complete network.The management system may also be required to perform more analytical processing, such as performance monitoring and cost analysis described in section 6.3.In the early stages of deployment the NCL will be required to communicate with a number of element manages from a range of manufacturers. These element managers may include systems providing supervision of existing plesiochronus equipment via mediation devices. With regards to the degree of funcitonality within the NCL as with the other level of management, this vary. A comparison is shown in Table 6.1

ELEMENT MANAGER LAYERThe element manger would provide many of the facilities descibed within section 6.3. It would also be expected to support addditonal management packafges to provide the funcitons of financial, resource and maintenance analysis on the information it collect.

ELEMENT MANAGER LAYERAlthough the element management may reside within a network element, it is more likely that it will be a software package implemented on some operating system/hardware platform. The size of the platform and its capabilities may vary due to the need for element manager to monitor and control various sized domains. The management systems must however offer the capability of migration form smaller to larfer systems as a network expands.

NETWORK ELEMENTSThere is a degree of management which resides within the elements themselves, and it is feasible that the element manager for a particular management domin may physically reside within a network element.

NETWORK ELEMENTBasic fucntionality witin the element should include the facilities listed in the subsequent section 6.3) applied to the single element. In some circumstances the decision may be taken to implement a distributed management system whereby individual element s perform a high degree of the functionality described. Such an implementation has a number of advantage with regards to the speed at which the network as a whole can react to various events, in particular the case of path restoration for protection purposes.

NETWORK ELEMENTSThe alternative is an element with a minimum functionality, allowing management fucntins to be performed at the Element Mangement Layer. A comparison of the benefits of each strategy is shown in table. 6.1

FUNCTIONALITY OF NETWORK MANAGEMENT SYSTEMThe classification of network management functions is described in ISO as below. The functionality of the a management system should include these features via the initial systems with a provision for additional feature packages or modules.

FUNCTIONALITY OF NETWORK MANAGEMENT SYSTEMConfiguration Management Fault ManagementPerformance managementAccounting Management.

FUNCTIONALITY OF NETWORK MANAGEMENT SYSTEMThe resource manager is not restricted in its capabilities to the management of SDH equipment only. Managed objects defined in line with Open Network Standards could extend to include the following items within its management domain.1- Network Element2- Test Equipment3- Manpower4- Other Management Systems

FUNCTIONALITY OF NETWORK MANAGEMENT SYSTEMSuch a management system would be expected not only to manage synchronous network elements, but also posses the ability to manage additional equipment in the network via direct communication or another management system. Since many existing management systems are propriety in nature, this infer the use of some type of mediation device between the two systems. In addition to the required functionality described above , a management system would be expexted to offer the ability to operate enhanced packeages offering features for Traffic Analysis, Maintenance costing,, Failure analysis etc.