The Ericsson ARF503 Telephone Exchange

Telephone > The Ericsson ARF503 Telephone Exchange

The Crossbar System ARF503 is a Dial Switching System (Digit to Digit) working to a modified Step-by-Step principle and is composed of a Customer Stage, SL and one or two Group Selector Stage(s), GV. The Customer Stage, also called the SL-Stage, works as a combined Finder and Final Selector (Connector) Stage. The main features of the individual Selector Stages are the use of the Crossbar Switch, Figure 1, the By-Path Principle, Figure 2 and the Link Connection Principle, Figure 3.

Figure 1: The Crossbar Switch

Figure 2: The By-Path Principle

Figure 3: The Link Connection Principle

The Crossbar Switch, a Two-Dimensional Array of Contacts, consists of a frame, inside which is fitted with: a number of Vertical Selecting Bars (generally 10) and associated multi-contact arrangements; and 5 or 6 Horizontal Selecting Bars and associated Contact Groups. Each Vertical consists of 10 to 12 Spring Sets of which the appropriate one is selected by one of the 5 or 6 Horizontals. Each Spring Set has a number of Closing Contacts as determined by requirements.

The Selecting Bars can be operated by Relays. By operating the Relays, it is possible to move the Bars to close the Contacts beneath the point where two Bars cross, Figure 4. This procedure is the one that makes the routing and connection of the Telephone Call through the Telephone Exchange.

Figure 4: The Schematic Diagram of a Crossbar Switch

In Automatic Telephone Exchanges, it is important that the large number of Selectors used for establishing Speech Connections and that the Control Devices associated with each Selector should be as simple as possible. In the Crossbar System ARF503, the common setting device, the Marker, sets more than one Selector, and thus the System has been called a By-Path System, Figure 2.

The Selector Stages of the Crossbar System ARF503 are divided into two or more Partial Stages in tandem that are interconnected by means of Links. From this name Link Connection is derived, Figure 3. Each Partial Stage consists of a number of Crossbar Switches.

Figure 5 shows a simplified Trunking Diagram of a 5-Digit ARF503 Crossbar Telephone Exchange. The Exchange is equipped with First and Second Group Selectors (I-GV and II-GV). The First Group Selector, I-GV, generally connects routes to different 10,000 Line Groups in the same Exchange, trunks to other Exchanges and to Special Services. The Second Group Selector, II-GV, connects routes to the different 1,000 Line Groups of the Customers in the same Exchange, and trunks from other Exchanges.

Figure 5: Simplified Trunking Diagram for a Connection between two Customers

The Customers' Lines are assembled into Groups of 1,000 Lines. The traffic to and from such a 1,000 Group is handled by a Customer's Stage SL that is built up of four Partial Stages SLA, SLB, SLC and SLD.

When one Telephone Exchange Customer lifts his Handset, his Line Equipment calls the Marker SLM-I. The Marker connects the Customer Line through the Relay Set SR to an Idle Register REG1 and the Customer gets access to the Dial Tone. The Customer receives the Dial Tone and Dials the First Digit of the Called Customer Number (for example, 8).

When the Digit is received by REG1, the Marker GVM-I of the I-GV is called and receives from REG1 the First Digit of the Called Customer Number. By means of this Digit the Marker GVM-I know to which 10,000-Group the Called Customer Number belongs and connects the Line from SR through the First Group Selector I-GV, to another Idle Register REG2. The REG1 and SLM1 release and are ready for new Calls.

The Customer then Dials the Second Digit of the Called Customer Number (for example, 5). When the Second Digit is received by REG2, the Marker GVM-II of the II-GV is called and receives from REG2 the Second Digit of the Called Customer Number. By means of this Digit the Marker GVM-II know to which 1000-Group the Called Customer Number belongs and connects the Line from I-GV through the Second Group Selector II-GV to a Final Selector Relay Set LKR in this Group. The REG2 and the GVM-II release and are ready for new Calls.

The following Three Digits are received by REG3 connected to the Relay Set LKR. After the Marker SLM-II receives the following Three Digits from the Register REG3, it makes connection to the Called Customer's Line. The connection between the two Customers is then established, and the REG3 and the SLM-II are disconnected and become immediately ready to serve new calls.


The first Ericsson ARF503 Automatic Telephone Exchange began its operation in year 1965. At that time this installation was considered as an important technological advance because it was based on a Crossbar System, even though it yet possessed the characteristic to interwork with the Siemens F1, Step-by-Step, Automatic Telephone Exchange, which was a Strowger or Step-by-Step System.

The initial phase of installation, consisted of 3,000 lines, starting with the Customer Telephone Numbers is from 5000 to 7999. Since then, the system was expanded several times.

The first expansion was put in operation in year 1972, increasing 2,000 lines to the existing 3,000 lines of Crossbar ARF503 System. The number of Digits for the new Telephone Number changed from 4 to 5, starting from 81000 to 82999.

In Taipa and Coloane, new ARF503 Automatic Telephone Exchanges also started operation in 1974. Each of them had the capacity of 600 lines, starting with the Telephone Number from 07000 to 07599 and 08000 to 08599, respectively. These equipments substitute the existing 90 lines, from 4710 to 4799 and 4810 to 4899, in each of the Islands, respectively.

During the decade of 1970's and the beginning of the 1980's, 9,000 additional lines were installed with Telephone Numbers between 81000 to 89999, making up the Ericsson ARF503 System with a total number of 12,000 lines installed in Macauo and 1,200 lines installed in the Islands.

After the mid of 1980's, Macauo Telecommunications Company, CTM, started to deactivate gradually the use of this System by substituting it with Digital Switching Exchanges.

Telephone > The Ericsson ARF503 Telephone Exchange