Patent GB-1344452-A (GB)
Title: Switching networks
IPC: H04Q3/68
Filed: 1971-04-19
Abstract: 1344452 Automatic exchange systems INTERNATIONAL STANDARD ELECTRIC CORP 19 April 1971 [1 April 1970] 25229/71 Heading H4K [Also in Division H1] In a switching network having separate multi-stage line and group (trunk) switching units, the two types of unit are interconnected by plug-in cables rather than by a conventional IDF. The arrangement is such that on expansion of the network half the existing cables retain their positions while the other half are simply displaced on to the new units. Trunking.-The network utilizes up to 64 line selection units LSU of which one is shown in Fig. 2 and up to 4 group selection units BSU of which a partly equipped one is shown in Fig. 3. An LSU comprises thirty-two 16 Î 8 A switches and eight, 32 x 16 B switches thus providing full availability between 512 inlets and 128 outlets. An LSU is identified by a 6 bit binary code l 5 / 0  where the subscripts denote the bit positions in the identifying code number. Thus for the LSU shown it has the decimal number 0 and the binary number 000000, that is l 5  = 0, l 4  = 0, l 3  = 0, l 2  = 0, l 1  = 0 and l 0  = 0. In like manner each B switch is identified by a 3 bit code b 2/0  and each switch outlet by a 4 bit code nb 3/0 . Each outlet from the line selection network is thus identified by a unique 13 bit binary number l 5  l 4  l 3  l 2  l 1  l 0  b 2  b 1  b 0  nb 3  nb 2  nb 1  nb 0  ... (1). A BSU comprises eight selection blocks BS0-BS7 of CD switches and eight 16 Î 16 E switches thus providing full availability between 2048 inlets and the same number of outlets. The selection blocks each consist of sixteen 16 x 16 C switches and sixteen 16 Î 16 D switches. An inlet to the group selection network is uniquely identified by a binary number g 1  g 0  bg 2  bg 1  bg 0  c 3  c 2  c 1  c 0  sc 3  sc 2  sc 1  sc 0  ... (2) where g 1/0  denotes the particular BSU, bg 2/0  the selection block BS<SP>1</SP>, c 3/0  the C switch identity and sc 3/0  the identity of the inlet on the C switch. Grading is effected by setting up an equation of the type: which means that in the code number of an outlet B and inlet C to be interconnected the bits l, and sc, are equal, l 0  and sc 0  are equal and so on. This particular example is only valid for an exchange having four line selection units and one group selection unit which itself contains just two selection blocks. Its significance is that the 16 outlets of a B switch are equally distributed on both selection blocks (bg 0  = 0 or 1 in accordance with the value of nb 2 ) and that, of the 8 outlets going to one block, these are then distributed on only four C matrices. This doubling of links between any particular pair of B and C switches is typical of a small exchange and tends to be eliminated during exchange growth. Certain portions of the above equality would be maintained throughout the growing period of the exchange thus ensuring that rearrangement of plug-in BC links is kept to a minimum and that at least half the network is always available for traffic. BC linking.-The switches are mounted on equipment racks in a manner governed by the grading equation and adjacent outlets are strapped to plug-connections on the racks so that it becomes possible to effect BC linking by preformed lengths of multiconductor cable having plug connections at their ends. In Fig. 5 the eight B switches of a single LSU are mounted on a common subframe AB of a line selector rack BB while the sixteen C switches of a group selector block BS are mounted on a subframe AC of a group selector rack BC. In the AB subframe the 16 outlets of each switch are arranged in pairs disposed vertically whereas in the AC subframe the outlets form a single column. The leftmost AB column represents the first B switch in the LSU shown in Fig. 2, i.e. b 2 b 1 b 0  = 000, the values of the three bits b 2  b 1  b 0  being shown below the columns. The rows in a column correspond to the 1st and 2nd, 3rd and fourth &c. outlets of a B switch as represented by the bits nb 3  nb 2  nb 1  while distinction is made between the pairs of outlets with the two value 0 and 1 of the bit nb 0 . By comparing the rotation in Fig. 3 with that in the AC subframe the identities of the C switches and of their outlets is similarly ascertainable. A multiconductor strap ca0 connects the first two outlets of the first four B switches to a plug connector bcb 0  on the subframe AB. From there via pluggable cable form ca and plug connector bcc0, connections are made to the first inlets of the first eight C switches of the first group selector block BSO. Other groups of B switch outlets and C switch inlets are similarly connected in a highly symmetrical manner to plug connectors on their respective frames so that BC linking is simply effected by standard lengths of plugable cable forms extending between the two racks.