An Introduction to the Ericsson Transport Network Architecture ...

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Control and Operation of SDH Network Elements Johan Blume, Leif Hansson, Peder Hagg and Leif Sundin own management system with proprietary Increasingly, flexible and powerful network management solutions allowing Network interfaces and functionality. This situation Elements and Operations Systems to work in a multi-vendor environment are often necessitates adaptations when new becoming a key issue to network operators. The Synchronous Digital Hierarchy equipment is introduced on a market, currently being standardised provides the required capabilities. which is costly in terms of time, resources The authors describe the main characteristics of SDH management and discuss and money, both for the supplier and the some implementation aspects of control systems developed for Ericsson's SDH operator. Network Elements. digital communication systems telecommunication networks telecommunication network management Background and Driving Forces Today's transmission network typically consists of inflexible equipment without provision for remote reconfiguration, and fixed hard-wired point-to-point connections. This means that each change of configuration - when supplying a 2 Mbit/s leased line, for example - requires hardwiring, which is time-consuming and therefore costly. The Synchronous Digital Hierarchy (SDH) eliminates these disadvantages by providing flexible Network Elements (NE) capable of being configured remotely. This makes it possible to provide new broadband services - such as 2 Mbit/s leased lines - to customers in a short time and at low cost. One of the major driving forces behind SDH is improved and standardised management interfaces and functions, allowing the SDH Network Elements and Operations Systems (OS) to interwork in a multi-vendor environment. 23 Benefits of SDH and ETNA Functional overview Introducing SDH in the transport network will improve operation and maintenance, and so reduce the operational cost for the Telecom operator. SDH also enables the operator to control the network more efficiently, in comparison with the conditions afforded by existing transmission systems. SDH makes it possible to set up new connections from a remote site within a few seconds. This enables a Telecom operator to respond quickly to customer demands for new or higher capacity. It also reduces the operational cost because less manpower is required. Abbreviations ACSE Association Control Service Element API Application Programmer's Interface AUI Attachment Unit Interface CLNP Conectionless Network Protocol CMISE Common Management Information Service Element CP Central Processor CPU Central Processor Unit CS Control System CSA Control System Application CSP Control System Platform DCC Data Communications Channel DCN Data Communications Network ECC Embedded Control Channel ETNA Ericsson Transport Network Architecture FMAS Facility Management System GNE Gateway Network Element GUI Graphical User Interface ICN Internal Communications Network IM Information Model IPC Inter-Process Communication ISDN Intergrated Sevices Digital Network LAPD Link Access Protocol on D-channel LAN Local Area Network Another characteristic of today's transmission networks is that each vendor has his LLC MAC MAU MCF MIB MO NE OS OSI PDH PI PM ROSE SDH SDXC SEMF SMS SMUX SNI SNPA su TAU TMN UP Logical Link Control Medium Access Control Medium Attachment Unit Message Communications Function Management Information Base Managed Object Network Element Operations System Open Systems Interconnection Plesiochronous Digital Hierarchy Physical Interface Performance Monitoring Remote Operations Service Element Synchronous Digital Hierarchy SDH Digital Cross Connect Synchronous Equipment Management Function SDH Management Subnetwork SDH Multiplexer Switching Network Interface Sub-Network Point of Attachment Support Unit Termination Access Unit Telecommunications Management Network Unit Processor Self-healing networks can be configured in such a way that faults in the network - e.g. cable breaks - will not affect the traffic for more than a few milliseconds, or seconds, depending on the size of the network and the restoration principle applied. At present it can take hours, or even days, to locate the fault and take appropriate actions. Two different principles are applied to protect the network against the effects of a fault: protection switching and protection routing. Protection switching is performed by the SDH NE without assistance from a central network management system, such as Ericsson's FMAS. This means very fast restoration but utilises network resources quite inefficiently. It is anticipated that rings will be a commonly used network topology in SDH networks, especially in local networks. In the event of a cable break, the traffic can be ERICSSON REVIEW No. 3, 1992
JOHAN BLUME LEIF HANSSON PEDER HAGG LEIF SUNDIN Ericsson Telecom AB restored by sending it the opposite way round the ring. Protection routing requires assistance from the FMAS and takes a somewhat longer time (5-10 seconds) but can be used for any type and size of network. In this case alarm information is sent to the FMAS from all affected NEs. The FMAS analyses the fault situation and calculates a new, optimised way through the network. Cross-connect commands are then sent to the NEs to set up the new connection. If desired, the operator can set conditions for rerouting: that the route should not pass through a particular node, for example. The Performance monitoring parameters enable the operator to identify potential problems before they cause degradation of end-user service. They also offer a tool for verifying the quality of the connection. This is important since many customers require a high guaranteed quality level, which makes it necessary to be able to measure that level. The parameters used conform to CCITT Recs. G.821, G.82x and G.784, Box 1. An important issue is protection of the SDH NEs from unauthorised access. This becomes important in cases where available functions may cause serious problems if used incorrectly. Each operator must have a unique Userid and password, issued by the system administrator. He is also assigned one of several 'user categories'. The user category determines what functions the user is allowed to access. User categories - of which some exemples follow - can be configured as desired: - System manager: handling of user categories and database management - Read access: only read access to management information - Configuration manager: access to installation and configuration functions - Data communication manager: handling data communication facilities. BOX1 PERFORMANCE PARAMETERS In the future, the demand for high-quality connections will be even greater than today. It is therefore important to use relevant and accepted parameters when measuring and verifying the quality of connections. The quality parameter currently in use is Bit Error Ratio (BER), with alarm thresholds at (normally) 10 3 or 10*. This is not good enough for data traffic. Another drawback of BER is that it does not give any information as to how faults are distributed in the time domain. Normally, faults are not distributed uniformly, but "burstily". To meet these new requirements, CCITT has defined quality parameters in Rec. G.821: ES Errored Seconds SES Severely Errored Seconds DM Degraded Minutes UAS Unavailable Second No. of errors during 1 s >0 BER, measured during 1 s >10' BER, measured during 1 min. MO* 10 consecutive SES gives 10 UAS These parameters are initially intended for 64 kbit/s connections. Annex D to Rec. G.821 therefore defines how to deal with higher bit rates. The G.821 parameters - after rather animated discussions- have not been found to be the solution to new requirements imposed on quality parameters. For example, they are still based on BER. A draft, Rec. G.82x, defines new quality parameters for bit rates higher than 64 kbit/s. The G.82x parameters will be used within SDH when the recommendation has been approved. The G.82x parameters are based on Errored Blocks (EB) instead of BER. One EB is a block that contains one or more errored bits. The following parameters were defined in the G.82x draft of June, 1992: ES ESR Errored Seconds ES Ratio s= 1 EB during 1 s The ratio of ES to the total number of seconds in available time during a specified measurement interval SES Severely Errored Seconds ss Y % EB during 1 s. (Y > 30 provisionally) SESR SES Ratio BBER Background Block Error Ratio The ratio of SES to the total number of seconds in available time during a specified measurement interval The ratio of errored blocks to the total number of blocks excluding all blocks during SES and unavailable time
Page 1: ERICSSON REVIEW 3 1992 An Introduct
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Page 6 and 7: 60 Fig. 3 AXD 155 system integratio
Page 10 and 11: 64 These functions and a number of
Page 12 and 13: 66 to the OS upon detection of a se
Page 14 and 15: 68 BOX 3 The SDH NE MANAGEMENT ORGA
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Page 18 and 19: 72 Fig. 6 Software Architecture CSA
Page 20 and 21: 74 Functional requirements Certain
Page 22 and 23: 76 Fig 10 SMUX Control System Hardw
Page 24 and 25: AXD 4/1, a Digital Cross-Connect Sy
Page 26 and 27: 80 Fig. 2 AXD 4/1, System Architect
Page 28 and 29: 82 Fig. 3 Time Space Switch structu
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Page 32 and 33: 86 The control signals, which come
Page 34: 88 Fig. 8 Protection Switch Unit st

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