Cross connect nodes are known which are connected to a telecommunication net- work and which usually comprise equipment fitted in standard racks to realize the functionality of the node. The size and shape of said racks are preferably predeter- mined so that in the planning and assembly phases it is possible to take into account the uses of buildings, room heights, equipment spaces, passageway dimensions and the moving of racks, for example. Moreover, the inner dimensions of said racks are predetermined to help lay out the hardware in them. According to a typical example, the standard maximum height of a rack or cabinet is 2200mm, the maximum width 600mm, and the maximum depth 300mm or 600mm Said cross connect node makes the cross connections, known as such, of the net- work electrically, usually digitally (DXC, Digital Cross Connect), by means of so- called application specific integrated circuits (ASIC) placed on a printed circuit board. The circuit boards used are normally multilayer boards that also provide buses to convey signals between the different parts and units of the node. The node is cable connected to the network via interface units usually comprising a plurality of card-like interface plug-in units, i. e. interface cards. In the interface units the signal speeds are adapted so as to be suitable for the cross connection and network.

The incoming and outgoing signals to be switched may be electric or optical. The transmission rate of digital signals is usually about 2.5Gbps, in the future even lOGbps. A plurality of interface cards are installed on a common motherboard which provides the necessary buses to convey the signals to the rest of the node, usually to the cross connecting unit. According to the prior art, the same mother- board further has a DXC plug-in unit, i. e. a cross connecting card, on it. The motherboards with their interface cards and cross connecting cards are fitted in a subrack which is further installed in said rack. To increase cross connecting capac- ity, subracks are interconnected, in accordance with the prior art, through cables and cable connectors. Motherboards usually also have a connector field for various

electric connections for power supply and to convey node alarm signals, node syn- chronization signals and network management signals, among others.

In addition to those mentioned above, also other apparatuses are fitted in a rack, such as several fan units for cooling the subracks. A rack also includes the neces- sary attachment means for the attachment of subracks. Inside the rack, space has to be reserved for cables as well.

As the demand for cross connecting capacity is continually on the rise, there can be seen in prior-art cross connect node subracks and apparatuses considerable prob- lems relating to the use of space and operation in particular. Along with the higher cross connecting capacity of a node the number of subracks has to be increased as well, whereby the electrical transmission distances between the cross connecting cards become longer and the amount of cabling increases, extending even from a rack to another. Furthermore, signal transmission usually occurs via several con- nectors, circuit board buses, and cable wires. Considerable distances cause espe- cially delays in signal transmission, which is undesirable as the transmission rates become ever higher. The great number of connectors and cables further causes interference and signal attenuation.

An object of the present invention is to eliminate the problems mentioned above. To that end, an arrangement according to the invention is characterized by that which is specified in the characterizing part of claim 1. A method according to the invention is characterized by that which is specified in the characterizing part of claim 10. A positioning board according to the invention is characterized by that which is specified in the characterizing part of claim 13.

The invention is based on the idea that a cross connecting unit is arranged in a node, which unit is connected preferably directly and via short buses to as many interface unit motherboards as possible. The cross connecting unit comprises at least one cross connecting card which is preferably in direct connection with said mother- boards and preferably constitutes a single circuit board. An essential idea is that the interface unit motherboards are fitted in the rack so that they overlap in a manner which makes possible short buses and easy connection of the cross connecting card to all the motherboards. An essential detail in the invention is the use of a special positioning board which enables easy and secure attachment of units, mutual posi- tioning of units, and fitting of units in the rack.

The invention achieves considerable advantages due to shorter delays. The compact structure of the node and optimized hardware layout in the rack bring an increase in the rack specific cross connecting capacity which is manifold compared to the prior art. Further advantages include that the quantity of connectors and cables can be considerably reduced, which speeds up assembly and adds to the reliability of the equipment.

The invention is below described in more detail with reference to the accompanying drawings where Fig. 1 shows in more detail an arrangement according to an advantageous em- bodiment of the invention in a rack of a node, especially the placement of motherboards, connector fields and cross connecting cards, viewed from the front, Fig. 2 shows a side view of a detail of Fig. 1, and Fig. 3 shows an exploded view of an arrangement according to the invention in a rack of a node, and Fig. 4 shows in a perspective the rack of Fig. 1 assembled.

Figs. 1 and 2 show a detail in an arrangement according to an advantageous em- bodiment of the invention, where a positioning board P, to be described later on, is utilized in the attachment of motherboards M1, M2, M3 and M4. In this embodi- ment, four interface units LI, L2, L3 and L4 are fitted in a rack in the node to pro- vide connection to a telecommunication network. Each interface unit preferably comprises a single-piece motherboard M1, M2, M3 and M4 and usually a plurality of parallel interface unit plug-in units Lli, L2i, L3i and L4i, or interface cards, whereby in the present example, 17 interface cards are electrically connected to each motherboard. The connectors Llc, L2c, L3c and L4c are advantageously card edge connectors arranged on the surface of the motherboard, to which each of the interface cards is electrically connected through a mating connector, advantageously a contact surface on the edge of the circuit board, said interface cards being posi- tioned substantially transversely with respect to the motherboard. The arrangement further comprises a cross connecting unit XC for realizing network cross connec- tions, said unit XC comprising in this example four card-like plug-in units XC1, XC2, XC3 and XC4, or cross connecting cards. In accordance with the invention the motherboards Ml, M2, M3 and M4 are fitted in the rack in such a manner that the cross connecting cards in the cross connecting unit XC are connectable simulta-

neously to the connectors Llx, L2x, L3x and L4x of each motherboard, which con- nectors advantageously are card edge connectors fitted on the motherboard and which connectors can be reached by a preferably single-piece cross connecting card making electrical connection therewith and being positioned substantially trans- versely with respect to the motherboard. In this arrangement, the connectors Llx, L2x, L3x and L4x of the different motherboards are arranged successively in their longitudinal direction Z, so that mating connectors, advantageously contact sur- faces, can be arranged in one longitudinal edge of the cross connecting card. The operating position of the motherboards, cross connecting cards and interface cards in the rack is substantially vertical. The connectors Llx, L2x, L3x and L4x are sub- stantially directed in the same direction in plane X. Connectors Llx and Llc and, on the other hand, connectors L4x and L4c are substantially directed in the same direc- tion in plane X. Connectors L2x and L2c and, on the other hand, connectors L4x and L4c are substantially oppositely directed in plane X. For example, the length of the cross connecting card XC1 in direction Z at least equals the combined length of connectors Llx, L2x, L3x and L4x on the different motherboards so that card XC1 extends simultaneously and directly to all these connectors without cables, wiring or the like. Thus, card XC1 extends to cover a portion of each motherboard M 1, M2, M3 and M4 in direction X, said portion comprising said connectors.

Still referring to Figs. 1 and 2, motherboards M1, M2, M3 and M4 are attached to a common positioning board P to position said motherboards and the various con- nectors with respect to each other. Said motherboards and positioning board P are substantially parallel, and the positioning board P comprises the necessary means of attachment. The motherboards and positioning board P are attached to each other through one surface. Connectors Llx of motherboard Ml, when installed in a rack, are located in the top part of the motherboard M1 and on the same side as connec- tors Llc; connectors L2x of motherboard M2 are located in the top part of the motherboard M2 and on the opposite side to connectors L2c ; connectors L3x of motherboard M3 are located in the bottom part of the motherboard M3 and on the opposite side to connectors L3c; and connectors L4x of motherboard M4 are located in the bottom part of the motherboard M4 and on the same side as connectors L4c.

Motherboard connectors Llx, L2x, L3x and L4x are directed to the same direction (direction X), and connectors in connection with the same cross connecting card are fitted successively in their longitudinal direction (direction Z). It is thus possible to minimize the space occupied by the connectors and cross connecting cards side- wise, too, (direction Y) and the cross connecting card XC1, for example, can be made a single-piece printed circuit board. Motherboards MI and M2 are positioned

overlapping on the different sides of the positioning board P so that connectors Llx and L2x are side by side in direction Z. Motherboards M3 and M4 are fitted over- lapping on the different sides of the positioning board P so that connectors L3x and L4x are side by side in direction Z. Motherboards M2 and M3 are fitted succes- sively in direction Z so that connectors L2x and L3x are side by side in direction Z.

Furthermore, interface cards Llc, cross connecting cards XC1, XC2, XC3, XC4 and interface cards L4c are lengthwise fitted successively in direction Z.

One of said motherboards, particularly circuit board M1, is fitted so as to be in- serted in the rack RI substantially in the vertical position (arrow Z), whereby con- nectors Llx of said motherboard MI are located in the top part of the motherboard MI and on the same side as connectors Llc. Motherboard M2 is fitted so as to be inserted in the rack RI substantially in the vertical position (arrow Z), whereby connectors L2x of said motherboard M2 are located in the top part of the mother- board M2 and on the opposite side to said connectors L2c. Motherboard M3 is fitted so as to be inserted in the rack R1 substantially in the vertical position (arrow Z), whereby connectors L3x of said motherboard M3 are located in the bottom part of the motherboard M3 and on the opposite side to said connectors L3c. Motherboard M4 is fitted so as to be inserted in the rack Rl substantially in the vertical position (arrow Z), whereby connectors L4x of said motherboard M4 are located in the bot- tom part of the motherboard M4 and on the same side as said connectors L4c.

In accordance with Fig. 1, connector fields CF1, CF2, CF3 and CF4 of each of the motherboards M1, M2, M3 and M4, respectively, are located on the motherboards beside connectors Llx, L2x, L3x and L4x, parallel with said connectors in direction Z, which connector fields usually comprise a plurality of electrical connectors, nor- mally D type connectors, for the node power supply, alarms, synchronization and network management control. Said connector fields CF1, CF2, CF3 and CF4 are located in each motherboard in the same part of the motherboard as connectors Llx, L2x, L3x and L4x. In Fig. 1, the connector fields may be advantageously located on the left side of the plug-in units as well. From the cabling and arrangement stand- point, the printed circuit boards, connector fields and connectors each preferably constitute continuous and separate areas.

According to an advantageous embodiment, the arrangement according to the in- vention comprises only three motherboards so that motherboard M4, for example, is left out, whereby the positioning board P can be shorter, and connectors L4x are left out of the cross connecting cards XC1, XC2, XC3 and XC4, whereby the cards can be shorter. Depending on the cross connecting capacity required, the arrangement

may also be comprised of just two motherboards M1 and M2, whereby the posi- tioning board P can be shorter, and connectors L4x and L3x are left out of the cross connecting cards XC1, XC2, XC3 and XC4, whereby the cards can be shorter. The number of cross connecting cards may also vary, as the cross connection can be backed up using one or more parallel cards.

It is obvious that the arrangement may utilize a positioning board P which is like the one described above that allows the attachment of up to four motherboards, but only motherboards MI and M4 are attached to it, so that the corresponding connectors are left out of the cross connection. The four-motherboard capacity guarantees easy expandability by just adding interface units L2 and/or L3 in the node. Moreover, the different combinations of two or three interface units can provide the considerable advantages of the invention over the prior art when the cards in the cross connecting unit are arranged and connected in accordance with the invention to shorten the buses. However, it is especially advantageous to locate two interface units in such a manner that they constitute the overlapping interface units LI, L2 or L3, L4, whereby the buses can be further shortened and at the same time the cards in the cross connecting unit can be made smaller.

It is also obvious that the positioning board P may be completely left out of the ar- rangement, whereby the motherboards are connected direct to each other or to the frame structure, by means of, say, motherboard subracks, said frame structure fixing the positions of the motherboards. The simplest and most effective way of ensuring the exact mutual positioning and immovability of connectors Llx, L2x, L3x and L4x on the motherboards M1, M2, M3 and M4 is, however, to use a positioning board P according to the invention. It especially reduces the bending and twisting forces directed to cards XC1, XC2, XC3 and XC4 as well as connectors Llx, L2x, L3x and L4x. If necessary, a motherboard may comprise a plurality of parts and the parts may be interconnected by connectors and wiring, but preferably the mother- board constitutes a single-piece circuit board in order to reduce connections and to make installation easier. The clearances and moving of the frame structure and subracks may in the course of time cause problems mentioned above. Referring to Fig. 2, it is especially easy to arrange for the mutual positioning and immovability of overlapping motherboards M2 and M3 by means of the positioning board P, since otherwise said motherboards will not be supported by or attached to each other in an overlapping manner like motherboards MI and M2 as well as mother- boards M3 and M4. The positioning board P in a simple fashion makes possible the arrangement according to the invention to position the motherboards.

A positioning board P according to the invention advantageously constitutes a single-piece planar two-sided object made of aluminum, for example, on a first sur- face of which motherboards MI and M4 are attached. On the second surface, motherboards M2 and M3 are attached according to the invention in such a manner that their connectors L2x and L3x meet the aperture (s) in the positioning board P, whereby said connectors extend right through the positioning board P. Likewise, the positioning board P has got an aperture or apertures for the connectors in the con- nector fields CF1 and CF3, whereby said connectors extend through the positioning board P. In addition, the positioning board P comprises the means required for attaching and positioning the motherboards.

Fig. 3 shows the different parts of the arrangement according to the invention in an exploded view to illustrate the layout. The embodiment described comprises three interface units LI, L2 and L3 with motherboards M1, M2 and M3 as well as a cross connecting unit XC. Each unit usually further comprises a subrack Llr, L2r, L3r and XCr to protect and support the cross connecting cards, interface cards or con- ductor fields, which subrack is also used to secure the attachment of the cross con- necting cards and interface cards. The subracks may also comprise guides and fas- tenings to make the installation and connection of cards easier. The positioning board P includes the apertures Pa required for the connectors. The positioning board P described is intended for the attachment of three motherboards so that it is about one-fifth shorter at the top end than a positioning board for four motherboards. The positioning board P with its motherboards Ml, M2, M3 and subracks Llr, L2r, L3r, XCr is fitted between ladder-like body elements B1 and B2 and attached thereto.

Said body elements B1 and B2 are fitted and attached preferably to a standard rack R1 which is located in a suitable room. The rack R1 is installed such that direction Z is upwards and substantially vertical. The assembly usually further comprises a plurality of fans F1, F2, F3 and F4 for cooling the plug-in units, which fans with their air guides Gl are also fitted in the rack Rl. The side portions of the rack Rl, between the subracks and side walls, include space and apertures for the necessary cables.

Fig. 4 shows the parts and rack R1 according to Fig. 3 assembled, where the rack R1 further includes a side wall cover, and the subracks comprise protective covers against electromagnetic radiation (EMC). In the upper part Rla of the rack Rl there is space for other equipment or expansion, comprising a motherboard for a fourth interface unit, interface cards, connectors and the subrack required.

The invention is not limited to the embodiment described above as an advantageous example, but can be modified within the scope defined by the claims attached hereto. For example, said connectors and mating connectors may vary greatly in at least their design and attachment and in that whether they are built in the card and/or motherboard.