DATA TRANSMISSION SYSTEM WITH SLIDING-WINDOW DATA FLOW CONTROL

Abstract: The invention relates to a digital data transmission system with a non-transparent circuit-switched data connection (V.110) between a transmitting (A) and a receiving party (B), whose nominal data transmission rate may vary during a call. The data connection uses a sliding-window data flow control protocol involving transmission of data frames in a preset order, checking the order of received data frames based on this order information, acknowledgement of properly received data frames and retransmission of incorrect or missing data frames. The transmissing party (A) may temporarily group the data frames, whereby the resulting "wrong" order of frames inside the group or between groups may cause unnecessary retransmissions. In the invention this is eliminated so that the receiving party (B), upon detection of a missing data frame, delays the transmission of a retransmission request for a period of time that will ensure that the missing frame has not been sent later.

Description: Data transmission system with sliding-window data flow control Field of the invention The invention relates to a data transmission sys¬ tem with sliding-window flow control on a non-transparent data connection whose nominal data transmission rate may vary during the connection. Background of the invention In non-transparent asynchronous data transmission on a circuit-switched connection, data is transmitted from a transmitting party A to a receiving party B in frames or "packets". Besides actual user data, the frames comprise both error-detecting and error-correcting bits to enable the receiving party to detect and possibly correct trans¬ mission errors. Each frame is also numbered or the order of the frames is indicated by means of another kind of identifier. The correctness of each received frame is tested at the receiving end. If the frame is found cor- rect, the receiving party acknowledges receipt by trans¬ mitting the frame number. If a frame is not found correct (eg due to a transmission error) , it will not be further processed (but is "discarded") . A negative acknowledgement (eg a retransmission request) is sent for example in case of discontinuity in frame numbering. Let us assume that the correct frame numbering is, for example 1,2,3,4,5. However, if frame 3 is followed by frame 5, frame 4 is missing and a negative acknowledgement will be sent for frame 4. Once the transmitting end receives a negative ac- knowledgement or no acknowledgement at all, it retransmits the frame a predetermined number of times. The total num¬ ber of repetitions is limited, so that endless transmis¬ sion loops are avoided in a very bad connection. On such a connection user data throughput varies with the quality of the connection. Deterioration in the quality of the connection results in an increase in the number of incorrect and lost frames, and consequently the number of repetitions. The frames have to be stored (buffered) at the transmitting end until they have been acknowledged so that they are available should retransmission be needed. To limit the amount of necessary buffering, a flow control protocol based on a sliding window may be used in the acknowledgement. In accordance with the flow control pro- tocol the transmitting party A may send a plurality of data frames before requiring acknowledgement from the re¬ ceiving party. A window represents a sliding sequence of successive frames that have been sent but have not yet been acknowledged (a transmission window) . The maximum number of unacknowledged frames equals window size WS. Party B is also prepared to receive WS frames in a recep¬ tion window, which is a sliding sequence of successive frames that may be acceptably received. The frames that fit into said window but have not arrived in the correct order are gathered into the reception window. Let us assume that frames 1,2,5,6,7 are received. After frames 1 and 2 the window is slid forward, whereas 5, 6 and 7 are stored in the reception window where they wait for the missing frames 3 and 4. Once frames 3 and 4 arrive, the reception window is slid over 3,4,5,6 and 7. When the re¬ ceiving end acknowledges one or more frames, the reception and transmission windows are slid forward a corresponding number of frames. By means of a sliding window the nominal data transmission capacity of a transmission channel may be better utilized and a higher throughput may be achieved than in a case when the transmitting end A does not send a new frame until it has received an acknowledgement of the previous frame from the receiving end. Usually the receiving end B assumes that the frames arrive in the right order, defined by said frame number or another kind of identifier. If a frame is miss¬ ing, for example frame N, which is deduced from the re¬ ception of frame N+M (M>0) immediately after frame N-l, in conventional systems party B immediately informs party A about the absence of the frame. As a result, party A re¬ transmits frame N and sometimes also starts the transmis¬ sion sequence from number N even if some later frames had been sent and received. Sometimes the frames may arrive to party B in the wrong order. If frame N has been delayed on the transmis¬ sion path and party B receives frame N+M (M>0) immediately after frame N-l, it immediately informs party A about the missing frame N. This results in unnecessary retransmis¬ sion of frame N, which may cause congestion in the net- work. Such a situation may arise in a data transmission system where several frames are sent temporarily grouped together, or if a plurality of semi-independent parallel traffic channels is used. If a frame is missing from a certain group, it may have been moved to another group. A retransmission request for such a delayed frame may, how¬ ever, be sent or placed in a queue to be sent from party B before the arrival of the next group actually containing the "missing" frame N. If the retransmission request ar- rives to the party after it has transmitted the group actually containing frame N, party A assumes that party B has not received the frame and retransmits it . This loads the transmission system and may even mix up the trans¬ mission protocol. An example of data transmission according to the above type is non-transparent asynchronous data transmis¬ sion on a circuit-switched connection in the European di¬ gital mobile communication system GSM. Herein the sliding- window flow control is Radio Link Protocol RLP in accord- ance with the GSM specification 04.22. The most significant factor limiting transmission capacity in mobile communication systems is the traffic channel at the radio interface. Eg the GSM system cannot at present support user data transmission rates higher than 9.6 kbits/s, which is the maximum user data transmis¬ sion rate for one full-speed GSM traffic channel. One solution that enables also higher user data transmission rates in mobile communication systems is dis¬ closed in the applicant's copending Finnish Patent Ap- plications 942190 and 945817 (unpublished on the priority date of the present application) . Herein two or more par¬ allel traffic channels (subchannels) on the radio path are allocated for one high-speed data connection. A high-speed data signal is divided into these parallel subchannels at the transmitting end for transmission over the radio path, and reassembled at the receiving end. This allows the offering of data transmission services where the transmis¬ sion rate may be even eightfold, depending on the number of allocated traffic channels, compared with the transmis- sion rate of the conventional (single-channel) transmis¬ sion rate. In the GSM system, for instance, a total user data transmission rate of 19.2 kbits/s is achieved by two parallel subchannels each supporting rate-adapted 9.6 kbits/s as in the existing non-transparent 9.6 kbits/s bearer services of the GSM system. Consequently, a non-transparent circuit-switched data connection may comprise a plurality of parallel traf¬ fic channels at the radio interface, and the number of traffic channels may vary during the connection. The frames to be sent are divided into N parallel channels in groups of N frames, where N may change during the connec¬ tion. Thus, the above problems of receiving frames in the wrong order are especially obvious on such a multi-channel transmission connection. Disclosure of the invention The object of the invention is to alleviate or eliminate the above problems. This is achieved with a digital data transmission system comprising a transmitting party, a receiving party, a non-transparent circuit-switched data connection between the transmitting and receiving parties, and a data flow control protocol involving transmission of data frames in a preset order on the data connection, checking the order of received data frames, based on order information in- eluded in the frames, acknowledgement of properly received data frames, and retransmission of erroneous or missing data frames. In accordance with the invention, the system is characterized in that the transmitting party (A) is temporarily capable of grouping the data frames, and that the receiving party (B) , upon detecting a missing data frame based on order information included in two in succession received data frames, is arranged to send a retransmission request for the missing data frame with a delay ensuring that the missing frame has not been sent later. In accordance with the invention, a receiving party B in a data transmission system using a sliding-win¬ dow flow control protocol, delays the transmission of a retransmission request for a missing frame for the dura- tion of a delay D, by means of which party B may ensure that the missing frame has not been moved to be sent later in the same group or in the next groups. If the missing frame is received later in the same group or in the next groups within said delay, no retransmission request is sent. If the missing frame is not received within said delay, i.e. it is not found in the next groups either, a retransmission request is sent after the delay has ex¬ pired. This eliminates unnecessary retransmissions due to the wrong frame order, and resulting loading or conges- tion. This results in a higher throughput on the data con- nection. If grouping is not being used, retransmission is not delayed unless a delay is needed for another reason. A temporary feature in data transmission may be that a sequence of N frames is sent rapidly in succession, for instance when N simultaneous and parallel traffic channels have been allocated to a data connection to in¬ crease the data transmission rate. According to an embodi¬ ment of the invention, the number of retransmissions may in this case be significantly decreased as the receiving party does not send a retransmission request until, for example, N subsequent frames have been received after the frame was found missing. The retransmission request is sent when frame M+N has been received after the missing frame M, where N is the number of parallel channels (other frames may be missing between M and MjN) . Brief description of the drawings The invention will be described below with reference to accompanying drawing in which Figure 1 illustrates a part of a mobile commun- ication system to which the invention may be applied on a single-channel non-transparent connection. Figure 2 illustrates a part of a mobile commun¬ ication system to which the invention may be applied on a multi-channel non-transparent connection. Figure 3 is a flow chart illustrating a manner in accordance with the invention of delaying the transmission of a retransmission request when the receiving party ob¬ serves a missing frame. Preferred embodiments of the present invention The present invention may be employed in all digital data transmission systems using sliding-window flow control with an adjustable window size on a non- transparent data connection whose nominal data transmis¬ sion rate may vary during the connection. The present invention is especially suited for data transmission applications in digital mobile commun¬ ication systems of the TDMA or CDMA type, such as the European digital mobile communication system GSM, DCS1800 (Digital Communication System) , a mobile communication system according to the EIA/TIA Interim Standard IS/41.3, etc. The invention will be described below by using the GSM mobile communication system as an example without being limited to it. The basic structural parts of the GSM system are shown in Figure 1, but in this application there is no need to describe their properties or other sections of the system in greater detail . As to a more detailed description of the GSM system, reference is made to the GSM specifications and the book "The GSM System for Mobile Communications", M. Mouly & M. Pautet, Palaiseau, France, 1992, ISBN: 2-9507190-0-7. A mobile services switching centre MSC estab¬ lishes incoming and outgoing calls. The MSC performs sim¬ ilar tasks as an exchange in the public switched telephone network (PSTN) . Moreover, the MSC performs functions typ¬ ical of mobile telephone traffic only, such as subscriber location management, in cooperation with the subscriber registers of the network (not shown) . Mobile stations MS communicate with the MSC via base station systems (BSS) . The base station system BSS consists of a base station controller BSC and base transceiver stations BTS. The GSM system is a time division multiple access (TDMA) system where traffic on the radio path is time divided and occurs in successively repeating TDMA frames, each of which consists of a plurality of time slots. A short information packet is sent in each time slot as a radio frequency burst of finite duration and consisting of a group of modulated bits. Time slots are mainly used to convey control channels and traffic channels. Speech or data is transmitted on the traffic channels. Signalling between a base station and a mobile station takes place on the control channels. The channel structures used at the radio interface of the GSM system are described in more detail in the GSM specifications 05.02. In accordance with the specification, one time slot from one of the carrier waves is designated to a mobile station MS as a traffic channel (Single Slot Access) at the beginning of a call. The mobile station MS synchronizes with the time slot to transmit and receive radio frequency bursts. In the GSM system a data connection is estab¬ lished between a terminal adaptation function TAF 31 of a mobile station MS and an interworking function IWF 41 (usually in connection with the mobile services switching centre MSC) in a fixed network. The data connection is a circuit-switched connection that reserves one (or more) traffic channels from the radio interface for the whole duration of the connection. In the GSM network, the data connection is a V.110 speed-adapted, to V.24 interfaces adaptable digital connection. The herein described V.110 connection is a digital transmission channel originally designed for ISDN technology (Integrated Services Data Network) that adapts to the V.24 interface and offers a chance to transmit also V.24 statuses (control signals) . The CCITT recommendation for a V.110 speed-adapted connec- tion is described in the CCITT Blue Book V.110. The CCITT recommendation for the V.24 interface is presented in the CCITT Blue Book V.24. The terminal adaptation function TAF adapts a data terminal (not shown) connected to a mobile station MS to the V.110 connection, which is established in Figure 1 over a circuit-switched connection using one traffic channel chl. The interworking function IWF adapts the V.110 connection to another V.110 network, such as ISDN or another GSM network, or to another transit net¬ work, such as the public switched telephone network PSTN. Data is transmitted between the terminal adapta- tion function TAF and the interworking function IWF in frames or "packets" using sliding-window flow control with an adjustable window size. This sliding-window flow con¬ trol is Radio Link Protocol (RLP) according to the GSM specification 04.22. Data transmission between the inter¬ working function IWF according to the protocol will be de¬ scribed below under the assumption that the interworking function IWF is the transmitting party A and the terminal adaptation function TAF is the receiving party B. Is should, however, be noted that data transmission takes place similarly even in the opposite direction, TAF-IWF. In non-transparent asynchronous data transmission on a circuit-switched connection, data is transmitted from a transmitting party A to a receiving party B in frames or "packets". An example of such frames is disclosed in the GSM specification 04.22. Besides actual user data, the frames comprise error-detecting bits to enable the re¬ ceiving party to detect transmission errors. Each frame is also numbered or the order of the frames is indicated by means of another kind of identifier. Party A stores, i.e. buffers, the transmitted frame until receipt from party B of an acknowledgement of successful receipt of the frame. Party B tests the correctness of each received frame. If the frame is found correct, the receiving party acknow- ledges receipt by transmitting the frame number. If the frame is not found correct (eg due to a transmission error) , it will not be further processed (but is "dis¬ carded") . A negative acknowledgement (eg a retransmission request) is sent for example in case of discontinuity in frame numbering. Let us assume, for example, that a cor¬ rect frame numbering is 1,2,3,4,5. However, if frame 3 is followed by frame 5, frame 4 has been left out and a neg¬ ative acknowledgement will be sent for frame 4. Once party A receives a negative acknowledgement, or no acknowledge- ment at all, party A retransmits the frame until an acknowledgement is received or the maximum number of re¬ transmissions is reached. The total number of repetitions is limited so that endless transmission loops are avoided in a very bad connection. The transmitting party A may transmit a plurality of data frames and buffer them before requiring acknow¬ ledgement from the receiving party B. This sliding se¬ quence of successive frames that have been sent but not yet acknowledged, is called a sliding transmission window. The maximum number of unacknowledged frames equals window size WS. In the same way the receiving party B is prepared to receive WS frames in a reception window, which is a sliding sequence of successive frames that can be accept¬ ably received. The frames that fit into said window but have not arrived in the correct order are gathered into the reception window. Let us assume that frames are re¬ ceived in the order 1,2,5,6,7. After frames 1 and 2 the window is slid forward, whereas frames 5, 6 and 7 are stored in the reception window where they wait for the missing frames 3 and 4. Once frames 3 and 4 arrive, the reception window is slid over 3,4,5,6 and 7. When the re¬ ceiving end acknowledges one or more frames, the reception and transmission windows are slid forward a corresponding number of frames . By means of a sliding window the nominal data transmission capacity of the transmission channel may be better utilized and a higher throughput may be achieved than when the transmitting end A does not send a new frame until it has received an acknowledgement of the previous frame from the receiving end. Usually the receiving party B assumes that the frames arrive in the right order, defined by said frame number or another kind of identifier. As stated above, the processing performed by the transmitting party and various transmission delays in a multi-channel data connection, for example, may change the order of the received frames. In this case, an immediate retransmission request for a missing frame used in a mobile communication system in accordance with the GSM specifications, for instance, causes unnecessary loading and decrease in throughput, and even congestion. This is eliminated by means of an arrangement in accordance with an embodiment of the invention, where the receiving party B delays the transmission of a retrans¬ mission request for a missing frame for the duration of delay D, so that party B may make sure that the missing frame has not been sent later. The retransmission request may also be delayed until the reception of a frame whose number is E times higher (E>0, typically E=N, where N = the number of parallel channels) . If the missing frame is found in the next received group, no retransmission re¬ quest is sent. If the missing frame is not found in the next group, a retransmission request is sent with delay D. This eliminates unnecessary retransmissions due to the wrong frame order, and the resulting loading or conges- tion. The result is a higher throughput on the data con¬ nection. If grouping is not being used, retransmission is not delayed unless a delay is needed for another purpose. A temporary feature in data transmission may be that a sequence of N frames is sent rapidly in succession, for instance when N simultaneous and parallel traffic channels have been allocated to a data connection to in¬ crease the data transmission rate. The number of retrans¬ missions may in this case be significantly decreased as the receiving party does not send a retransmission request until, for example, N later frames, i.e. a new group of frames, have been received after the frame was found miss¬ ing. The applicant's copending Finnish Patent applica¬ tions 942190 and 945817 disclose a procedure where a mo- bile station MS that needs higher-rate data transmission than one traffic channel (9600 bits/s) can offer, is as¬ signed two or more time slots in the same TDMA frame. The maximum user data transmission rate of a multi-channel data connection is the number of parallel traffic channels x the user data transmission rate 9600 bits/s of one traf¬ fic channel. In this way the user rate 19200 bits/s, for instance, may be supplied on two traffic channels as a minimum. This procedure is presented in this application as one example of a manner of embodying high-rate data transmission based on ε. plurality of parallel traffic channels in a radio system. Regarding the details of this procedure, reference is made to said patent applications. It must, however, be noted that as to the invention, the only essential requirement is that it is possible to establish a multi-channel transmission connection, and the invention is solely directed at the adjustment of delay D at the receiving end B, as the transmission capacity of such a multi-channel connection is changed by increasing or decreasing the number of traffic channels. Figure 2 illustrates the architecture of the GSM network that embodies a data transmission service using such a group of multiple parallel traffic channels. Figure 2 is identical to Figure 1 except that in Figure 2 a circuit-switched non-transparent connection comprising N parallel traffic channels chl-chn, where N=l,2,..., exists between the terminal adaptation function TAF and the interworking function IWF. In a mobile station the network termination 31 operates as a divider that divides a high- rate data signal DATA IN received from data terminal equipment into parallel traffic channels chl-chn, and as a combiner that combines low-rate partial signals received from parallel traffic channels chl-chn into a high-rate data signal DATA OUT. Correspondingly, at the other end of a multi-channel data connection, the interworking function IWF operates as a divider that divides an incoming high- rate data signal DATA IN into parallel traffic channels chl-chn, and as a combiner that combines low-rate partial signals received from parallel traffic channels chl-chn into a high-rate data signal DATA OUT. On a multi-channel data connection, a temporary feature of the data connection is that N frames are sent rapidly in succession via N parallel traffic channels, i.e. in a group of N frames. Moreover, the grouping may change during the data connection as the transmission ca- pacity of the data connection changes. Changing the nom¬ inal transmission capacity may involve changing the number of radio channels allocated to the connection or changing the nominal transmission rate of one or more traffic chan¬ nels. Traffic channels are typically allocated and deal- located, i.e. added to or removed from a data connection, by the mobile services switching centre MSC, preferably its call control unit 42, which then signals the informa¬ tion on the allocated traffic channels to the mobile sta¬ tion MS, preferably to its call control 32. From the point of view of the invention, the procedure for allocating traffic channels to a data connection, or the unit or function participating in the allocation, is not essen¬ tial. As far as the invention is concerned, it is only es¬ sential that the receiving party B (IWF or TAF) is either directly or indirectly provided with information on delay D being used, for example information on the grouping of frames used by the transmitting party A at each specific time, or information permitting the deduction of the frame grouping used, for example the number of traffic channels allocated to the data connection. In the example shown in Figure 2, the call control unit 42 transmits information on the nominal transmission capacity used at each specific time to IWF and the call control unit 32 to TAF. IWF and TAF will adapt delay D according to the transmission capa- city in use. Alternatively the parties to the data trans- mission may negotiate, for example, about the length of the delay time. Figure 3 shows a flow chart illustrating an ex¬ ample of a procedure with which the delay according to the invention may be realized in a terminal adaptation func¬ tion TAF or an interworking function IWF. In Figure 3, FN is a frame number obtained from a received frame; FC is a frame counter; and D is a delay according to the invention, i.e. D frames. In the example of Figure 3 it is assumed that the correct frame transmis¬ sion and reception order conforms to the frame numbering. In step 300, the data connection is initialized or the transmitting party changes the grouping. The re¬ ceiving party B receives information on the grouping or information based on which it may deduce the grouping and delay D, such as the number of traffic channels. In step 301, a frame is anticipated and in step 302, frame FN is received. In step 303, it is checked to see if the frame contains information indicating that this is the last frame of the data connection. If yes, recep¬ tion is ended in step 304. Information regarding the end of a connection may alternatively be received by other means than in a data frame. If the frame is not the last one, the next step is 305. In step 305, it is checked to see if the frame number FN of the received frame is the reading of the frame counter FC increased by one. If FN is not FC+1, frame FN was not received in the right order. In this case frame FN is added to the list of unacknowledged frames. This list includes all frames that have been received but have not been acknowledged to the transmitting party A as they have arrived in the wrong order. Step 313 is followed by step 314. In step 314, it is checked to see if the frame number FN is higher than the sum of the frame counter FC and delay D according to the invention. If FN > FC+D, the duration of D frames has elapsed since FC+1 should have been received. Consequently, the next step is 315, where party B sends a retransmission request for frame FC+1 to party A. Thereafter follows step 301, where a new frame is anticipated. If FN ≤ FC+D, the delay according to the invention has not yet elapsed, and therefore the next step is 301, where a new frame is anticipated. If the frame number FN = FC+1 in step 305, i.e. the frame was received in the right order, the next step is 306, where the frame counter is increased by one. Then party B sends an acknowledgement of frame FC (equal to FN) to party A. Next, in step 308, a check is made to see if frames exist on the list of unacknowledged frames. If not, the process returns to step 301 to anticipate a new frame. If yes, the next step is 309. In step 309, a check is made to see if frame FC+1 is on the list of unacknowledged frames. If not, the process returns to step 301 to anticipate a frame. If yes, the next step is 310. In step 310, the frame counter FC is increased, and then party B sends an acknowledgement of frame FC+1 to party A in step 311 and removes frame FC+1 from the list of unacknowledged frames in step 312. Thereafter the pro¬ cess returns to step 309. Delay D may also be defined as a number of re¬ ceived frames. For example, a fixed delay time D = 30 ms may be defined as a period of time during which seven TDMA frames are received, i.e. the retransmission request will be delayed for seven TDMA frames. The delay is measured by counting the received TDMA frames. Instead of a frame counter, a timer, for in¬ stance, may also be used to measure the delay time D from the instant when a missing frame should have been re- ceived. The timer is started when the missing frame is de¬ tected. If the missing frame is not received before the timer expires, (within delay D) , a retransmission request is sent to party A. If the missing frame is received be- fore the timer expires (within delay D) , an acknowledge¬ ment is sent to party A. It should, however, be noted that as to the basic idea of the invention it is irrelevant whether the sending of a retransmission request is delayed by a frame counter, a timer, or another means. Even though the invention has been explained with reference to certain embodiments, it will be understood that the description is intended for an example only and changes and modifications may be made to the presented embodiments without departing from the spirit and scope of the invention set forth in the appended claims.

Claims: Claims 1. Digital data transmission system comprising a transmitting party (A) , a receiving party (B) , a non- transparent circuit-switched data connection between the transmitting and receiving parties, and a data flow con¬ trol protocol involving transmission of data frames in a preset order on the data connection, checking the order of received data frames, based on order information included in the frames, acknowledgement of properly received data frames, and retransmission of erroneous or missing data frames, c h a r a c t e r i z e d in that the trans¬ mitting party (A) is temporarily capable of grouping the data frames, and that the receiving party (B) , upon de- tecting a missing data frame, based on order information included in two in succession received data frames, is arranged to send a retransmission request for the missing data frame with a delay ensuring that the missing frame has not been sent later. 2. System as claimed in claim 1, c h a r a c ¬ t e r i z e d in that said delay is such that the receiv¬ ing party (B) receives a sufficient number of data frames in order to ensure that the missing data frame is not re¬ ceived later in the same group or in one of the next groups. 3. System as claimed in claim 1 or 2, c h a r ¬ a c t e r i z e d in that the transmitting party (A) sends the data frames in groups of N frames, and that said delay is in the order of N frames, eg N frames. 4. System as claimed in claim 1, 2 or 3, c h a r a c t e r i z e d in that the data transmission system is a multiple access mobile communication system where a data connection comprises one traffic channel (chl) or a plurality of traffic channels (chl-chn) on the radio path, and that said grouping involves sending data frames via N parallel traffic channels, and that said delay is in the order of N frames, eg N frames. 5. System as claimed in claim 1, c h a r a c ¬ t e r i z e d in that said delay is dependent on the grouping of the data frames used by the transmitting party. 6. System as claimed in claim 1, c h a r a c ¬ t e r i z e d in that said delay is defined as a number of received frames. 7. System as claimed in claim 1, c h a r a c ¬ t e r i z e d in that the delay is defined by counting the received frames. 8. System as claimed in any of the claims 1 to 5, c h a r a c t e r i z e d in that the transmitting party is a terminal adaptation function (TAF) in a mobile sta¬ tion and the receiving party is an interworking function (IWF) in a mobile communication network. 9. System as claimed in any of the claims 1 to 5, c h a r a c t e r i z e d in that the transmitting party is an interworking function (IWF) in a mobile communica¬ tion network and the receiving party is a terminal adapta¬ tion function (TAF) in a mobile station.

Inventors: AHOPELTO JUHA-PEKKA, KANERVA MIKKO, KARI HANNU, VAINIKKA JARI, AHOPELTO, JUHA-PEKKA, KANERVA, MIKKO, KARI, HANNU, VAINIKKA, JARI
Applicants: AHOPELTO JUHA PEKKA, KANERVA MIKKO, KARI HANNU, NOKIA TELECOMMUNICATIONS OY, VAINIKKA JARI, AHOPELTO, JUHA-PEKKA, KANERVA, MIKKO, KARI, HANNU, VAINIKKA, JARI
Application year: 1996
Main classification: H04L29
IPC codes: H04L12, H04L29