An Introduction to the Ericsson Transport Network Architecture ...

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82 Fig. 3 Time Space Switch structure SS Speach Store single or redundant connection to the rest of the system to suite different availability needs. The CP is described in another article in this issue of Ericsson Review. The UPs handle - Communication between the CP and the Hardware (HW) - Maintenance and Control of the Device/- Switch plane - Alarm from the Device/Switch plane. The UPs are equipped with so-called Flash-PROMs, which means that one part of the program memory can be write-protected and one part can be updated. This makes it possible to use central, loadable software (SW) -an advantage in future upgradings of the system - and still have nonvolatile storage of the programs. Program-load and inventory are two important features of the processor block. New UP programs can be loaded either from the CP through the SNI interfaces or through a special test port, located at the board front. Programs are loaded without disturbing traffic in progress. Thanks to the Flash-PROMs, the program will be kept during power-off, for example when shifting the board between two magazines. The product number, revision state and individual serial number of each board are stored during production tests at the factory and can be read by the CP. Another function handled by the UP is the reading of the physical board position in the magazine and the magazine ID. This information will be sent to the CP on request to give a complete picture of the system's functional and physical configuration. The control system is based on an open architecture using object-oriented system design and language. Motorola type MC 68 302 computers are used as UPs. Sun or Stratos UNIX machines can be chosen as CP, depending on reliability requirements. Switching The switching network performs all connections necessary for communication between the Devices. The Switch provides two types of function for the Devices: cross-connection of transmission signals and switching of control information. 128 STM-1 equivalent ports, corresponding to 8196 2 Mbit/s signals, is the maximum capacity of the present AXD 4/1 Switch. The AXD 4/1 is based on column switching, which allows all types of VC-n switching (n = 1,2,3 or 4) using the basic switching element of one SDH column, i.e. 9 x 64 kbit/s = 576 kbit/s. These columns are then combined to form the VC-ns that are to be cross-connected. The SDH and PDH signals that have pre-defined crossconnections are: VC-4, VC-3, VC-2, VC-12, VC-11 and 140, 34, 2, 45 and 1.5 Mbit/s. A number of VC-ns, or columns, can be grouped together to form other cross-connections, e.g. concatenated VC-2s. Different types of connection can be established in the AXD 4/1 Switch, regardless of the hierarchical level or mix of the connections: - Simplex, one way signals - Duplex, bidirectional signals - Broadcast, multi-destination signals. In the AXD 4/1 Switch, the number of destinations in a broadcast connection - as ERICSSON REVIEW No. 3, 1992
83 well as the number of simultaneous broadcast connections - is unlimited. This means that an AXD 4/1 Switch is suitable for services on leased or switched circuits from 1.5 Mbit/s up to 140/155 Mbit/s. SNI-4 column, the basic switching entity An SNI-4 column, 9 x 64 kbit/s, is the smallest possible switchable entity. The bandwidth of one SNI-4 column is regarded as sufficiently small for internal applications too. Each external signal terminated by the AXD 4/1 and each standard tributary of that signal is mapped into an integer number of columns. As a maximum, a whole STM-1 channel (155 Mbit/s) including overhead (OH) can be switched. To be able to provide connections that use a number of columns, the integrity of the frame of columns is guaranteed, i.e. the time sequence integrity. Non-blocking, full connectivity Switch matrix The Switch matrix is designed to provide circuit-switched connections without any internal congestion and to ensure full connectivity between any input and any output port, independently of the hierarchical level of the cross-connected signals and of the mix of hierarchies (CEPT, NAS, SDH, simplex, broadcast). The Switch is a Time-Space-switch (TS) consisting of a number of Speech Stores (SS), arranged in rows and columns: one row for each input and one column for each output, Fig. 3. Every time a signal is to be fed to a certain output, it can be chosen from among the signals stored in one of the SS (n) associated exclusively with that output. The choice is made through the use of Control Stores (CS) associated with that same output. No switch action will affect connections already established. Characteristics of the TS structure Since no internal routing is necessary and only one T-stage is involved, the TS switch has the following characteristics: - No rearrangement of established connections is needed to permit the set-up of a new connection, capable of being used for broadcast also - The delay introduced by the switch is minimised. This results in a switch with short set-up time and very low transmission delay, which is necessary in a large network with stringent service requirements. Multicolumn switching Multiconnection switching is characterised by the connection of a number of columns executed at the same time. The number of columns that can be connected in a multiconnect switching operation has no upper limit. As an extreme, the whole switch can be reconfigured at the same time. Internal communication The AXD 4/1 Switch is capable of handling packet-oriented signals. This function is used both for internal control communication and to handle Embedded Communication Channels (ECC) in SDH signals. A special communication protocol is developed to handle the internal communication - the Basic Communication Protocol (BCP). BCP is a self-addressing protocol that uses the tree-structure of the integrated control paths to give reliable internal communication. Information is carried in 'packet format'. The packet-handling equipment and the circuit switch are triplicated, so as to fulfil general requirements for failure immunity and fault detection capability. The supervision of internal communication is handled by BCP functionality and by the triplication. Devices All types of equipment connected to the Switch are called Devices. The most common types are Termination Access Units (TAU), which terminate transmission signals. The Central Processor, too, is connected as a Device. In addition to the termination of signals, i.e. line signal access and multiplexing, a Device terminates the switching network. Majority vote is used to terminate the signals from the triplicated Switch. This is the basic function that forms a single fault-tolerant system.
Page 1: ERICSSON REVIEW 3 1992 An Introduct
Page 4 and 5: An Introduction to the Ericsson Tra
Page 6 and 7: 60 Fig. 3 AXD 155 system integratio
Page 8 and 9: Control and Operation of SDH Networ
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
Page 16 and 17: Fig. 4 Control System Architecture
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 30 and 31: 84 Fig. 4 AXD 4/1 Devices Devices o
Page 32 and 33: 86 The control signals, which come
Page 34: 88 Fig. 8 Protection Switch Unit st

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