Data unit sending means and control method

Details Data unit sending means and control method Data unit sending means and control method

2000-05-25

2004-11-09

Yao, Kwang Bin (Department: 2667)

Multiplex communications

Communication over free space

Having a plurality of contiguous regions served by...

C370S469000

Reexamination Certificate

active

06816471

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a data unit sending means and a method for controlling a data unit sending means.
In the field of communications, the concept of packet exchange is well known. A data packet is a given length of data whose structure is determined by a given protocol, i.e. a set of rules governing the exchange, manipulation and interpretation of such packets. Depending on the protocol, different names are used, such as frame, packet, etc. A more generic term is protocol data unit (PDU), and the following description shall use the term data unit for simplicity.
The process of sending data via a packet exchange typically comprises a plurality of protocols, which are arranged in a hierarchy. A schematic example of such a hierarchy is shown in FIG.
6
. The example of
FIG. 6
shows three layers, a higher layer referred to as L
3
, a layer below L
3
referred to as L
2
_ARQ, and a lowest layer L
1
. In fact, the terms L
3
, L
2
_ARQ and L
1
refer to protocols associated with these layers. As an example, L
3
can be the internet protocol IP, L
2
_ARQ may be the radio link protocol RLP known from GSM, and L
1
can be any suitable physical layer protocol. In accordance with the concept of layering, data units associated with a higher layer are passed to a lower layer, e.g. from L
3
to L
2
-ARQ in example of
FIG. 6
, where the lower layer protocol embeds the higher layer data units. The term “embedding” may refer to encapsulation or segmentation. In the case of encapsulation, a higher layer data unit is placed into one lower layer data unit, whereas in the case of segmentation, the higher layer data unit is segmented into smaller pieces of data, each piece being placed into a lower layer data unit.
One of the important aspects of protocol layering is that in a data communication, i.e. in a process where a given amount of data is being sent from a source to a destination, the overall path that is associated with a highest layer comprises sublinks associated with the lower layer protocols, where the endpoints of a protocol of a given layer are called peers of said protocol. This concept is well known in the art and does not need to be described further here. Reference is made e.g. to the book “TCP/IP, The Protocols” by W. R. Stevens, Edison Wesley 1996.
PROBLEM UNDERLYING THE INVENTION
Specific problems in connection with the transmission of data occur in radio networks, due to the fact that radio links typically have a poorer transmission quality than fixed lines. For the purpose of explanation,
FIG. 3
shows the architecture for a generic cellular communication system. This system consists of a core network (CN)
100
, and a part referred to as a radio access network (RAN)
110
. The radio access network is divided into controller nodes
101
and base transceiver stations (BTS)
102
. The hierarchy of the network is such that the core network is connected to several controllers and the controllers are connected to several base stations. The base stations
102
communicate with mobile stations (MS)
103
.
A typical problem that will occur when sending data in the up-link direction (i.e. from a mobile station
103
to a base transceiver station
102
) or in the down-link direction (from the base transceiver station
102
to a mobile station
103
) is that errors are introduced over the radio interface. Such errors are typically due to changes in the transmission quality, e.g. because the mobile station
103
moves around. Another potential situation for data loss is a handover of a communication between a given mobile station
103
and a given base transceiver station
102
to another base transceiver station, when the mobile station moves into another cell. Both situations, namely a specific error condition or a handover lead to the necessity of a link reset, in the course of which all data in the send buffer of the sending peer of the radio link is purged to thereby establish a “clean slate”, such that communication may begin anew in a state unambiguously defined for both sender and receiver.
Due to the error characteristics of the radio interface, a so-called ARQ protocol (ARQ=Automatic Repeat reQuest) can optionally be executed between the mobile station and the radio access network to reduce the residual error rate. An ARQ protocol comprises the function of acknowledging the correct receipt of data units by the receiving peer, where the sending peer implements mechanisms for retransmitting such data units that were not correctly received. In this way, the complete transmission of data is secured. It may be noted that the use of an ARQ mechanism can be an option associated with a specific mode, i.e. that not every data unit needs to be sent with the ARQ mechanism activated. As an example, in connection with known protocols there are known a so-called numbered mode (or I-mode) in which ARQ is activated, and a so-called unnumbered mode, in which no acknowledgment and consequently no retransmission occurs. The first mode is advantageous for data where secure transmission is a priority, the second mode is advantageous for data where delay sensitivity is a priority and data loss is not so much of a problem, such as real-time voice-over-Internet data.
In the following, two known types of solutions for securing user data from being lost in case of a handover of a ARQ protocol communication between different network nodes will be described.
According to a first solution, a protocol state transfer is enacted, i.e. when a handover is performed, the whole state including state variables and buffers is moved from the ARQ entity in the RAN (i.e. the peer) to the new network node. Using this mechanism, the ARQ entity in the mobile station does not need to know when a handover occurs. Such a solution is described e.g. in R. Cohen, B. Patel and A. Segall, “Handover in a Micro-Cell Packet Switched Mobile Network”, ATM Journal of Wireless Networks, Volume 2, no. 1, 1996, pages 13-25, or in S. Powel Ayanoglu, T. F. La Porta, K. K. Sabdani, R. D. Gitlin, “AIRMAIL: A link layer protocol for wireless networks”, ATM/Baltzer Wireless Networks Journal, Volume 1, 1995, pages 47-60.
The benefits of this solution are that no unnecessary re-transmission of user data over the radio interface occurs, and the ARQ protocol in the mobile station can be unaware of the handover, which makes the implementation less expensive.
The disadvantage of this solution is, that it is limited to handle intra-system handover. This means that both network nodes between which the handover is executed must operate in accordance with the same protocol. If a core network is connected to multiple radio access networks of different type, which do not use exactly the same ARQ protocol, this solution cannot be used, because an inter-system handover is necessary. Such situations will become more common in the future.
A different solution for securing user data is that of providing an additional ARQ protocol. In this case, one ARQ protocol is run between the mobile station and the radio access network (the base station controller node) and takes care of errors encountered of the radio interface. The second ARQ protocol is run between the mobile station and the core network. In case of data loss due to resetting the link between the mobile station and the base station controller (be it due to an error condition or a handover), this second ARQ protocol will perform a re-transmission. As an example, in GPRS (General Radio Packet Service) the first ARQ protocol is called RLC (Radio Link Control Protocol) and the second ARQ protocol is called LLC (Link Layer Control Protocol).
Although such an arrangement enables the handling of inter-system handovers, it has disadvantages. First of all, additional radio resources are consumed due to the overhead introduced by the second ARQ protocol. As an example, in GPRS the overhead per transmitted L
3
data unit introduced by the LLC protocol is in the order of 7 bytes. Compared to the size of a Van Jacobson compressed TCP acknowledgment, which is under

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