Abstract: The invention relates to determining a quantity to be measured from a communication system, such as a transmission delay or the phase difference of clock times. Measurement messages are transmitted (501, 502) between the two areas of the communication system in both transmission directions. Values of the time difference are calculated (503) for the measurement messages transmitted in at least one of the transmission directions, each of which values is the difference between the instant of reception measured at the reception and the instant of transmission measured at the transmission of the measurement message. The values of the time difference are used to calculate (504) an estimate of the distribution of the time difference, on the basis of which an estimate of the minimum value of the time difference is calculated (504).

Abstract: A method and apparatus for monitoring and limiting the transmission speed of a data traffic flow in a situation where the traffic flow also includes delay-critical traffic. With the sending of each protocol data unit it is determined whether the sending of the next protocol data unit should be delayed in order to meet a condition set on the transmission speed. It is also determined whether the transfer speed of delay-critical traffic meets a preset condition. If the transfer speed meets the condition, delay-critical protocol data units will not be delayed but if the condition is not met, delay-critical protocol data units will be delayed just like non-delay-critical protocol data units. Thus the transfer speed of non-delay-critical traffic adapts to variations in the transfer speed of delay-critical traffic and, furthermore, the transmission speed of the traffic flow can be monitored and limited.

Abstract: A system includes a communications device and power supply units detachably installable thereon. On an outer surface of the communications device there is an aperture arranged to enable the insertion of different power supply units in different sections of the volume inside the communications device. The volume is continuous so that instead of separate power supply units it is possible to insert, through the aperture, in the volume a physically larger power supply unit which, when installed in the volume, extends into more than one section of the volume. The communications device can be flexibly equipped e.g. with power supply units functioning as back-ups for each other, each taking up part of the volume, or with a single power supply unit, larger than the above-mentioned, taking up the volume. Therefore the volume inside the communications device can be utilized in connection with power supply units of various types.

Abstract: Determining mutual differences of transmission delays experienced by protocol data units transmitted in a communications network is based on a surprising discovery that the time difference between the receiving moments of protocol data units the temporal receiving order of which deviates from their temporal transmitting order represents the smallest possible difference between the transmission delays experienced by these protocol data units. In a method it is determined, based on an order indicator associated with a protocol data unit received at an earlier point of time and an order indicator associated with a protocol data unit received later, whether the mutual order of the protocol data units changed during transmission. If the mutual order has changed, the time difference between the receiving moments of the protocol data units is calculated, which time difference represents the smallest possible difference between the transmission delays experienced by these protocol data units.

Abstract: The invention relates to transferring of a time of day value between network elements of a data transfer network. It has been surprisingly detected that the phase reference signals available to various network elements can be utilized in the synchronization of time of day values between these network elements. In the solution according to the invention, a first network element sends to a second network element a difference variable (401, 402, 403) that indicates how much the timing phase of the time of day value maintained in the first network element differs from the timing phase of the phase reference signal available to the first network element. In the second network element that receives the message, an estimate of the time of day value is formed (404, 405) based on the difference variable and the timing phase of the phase reference signal available to the second network element.

Abstract: The invention relates to a method and arrangement for transferring synchronizing information in a data transmission system including modem connections. The arrangement according to the invention comprises a modulator (207) that is arranged to generate an analog signal (222) modulated by synchronizing information, the frequency spectrum of said signal being located in a frequency range that falls outside the data transmission bands of the modem line connected to the network element. The arrangement includes a switching circuit (208) that is arranged to connect said analog signal to a data transmission cable (206) that forms part of said modem line connected to a network element. The arrangement includes a second switching circuit (209) that is arranged to receive said analog signal from a data transmission cable that forms part of the modem line connected to the second network element.

Abstract: The invention relates to transmitting digital information between the network elements of a frame switched data network. In the present invention, it has surprisingly been discovered that the padding bits of the data field of a minimum sized Ethernet frame can be used for transmitting digital information between the elements of a data network. In that case the frame data field (109) of a minimum sized Ethernet frame contains an information unit (DIU), the size of which in bytes is smaller than the minimum size of a frame data field, as well as other digital information (DI) that is written in an area (107) of the frame data field that corresponds to the padding bits. The invention makes it possible to also utilize the data transmission capacity needed for transmitting the padding bits.

Abstract: The invention relates to transmitting time information between elements of a data network. In the present invention, it has surprisingly been discovered that in a network transmitting packet, frame or cell switched data traffic, time stamp information can be transmitted from a network element (101) to another network element (102) by using that part (113a, 113c) of the bit stream (111b) to be transmitted which is connected, in the transmitting network element (101), to the transmitted bit stream in a location that is placed, in the flowing direction of the transmitted bit stream, after a transmission buffer (103) buffering data packets, frames or cells. In an arrangement according to the invention, the random-type share of the transmission delay experienced by the time stamp information is slight, because the time stamp information does not have to queue in the transmission buffer (103) buffering data packets, frames or cells.