WO2006074612A1

WO2006074612A1 - A method for realizing the high layer signaling transmission in the ieee 802.16 system

Info

Publication number: WO2006074612A1
Application number: PCT/CN2006/000057
Authority: WO
Inventors: Jianjun Wu; Jiang Li
Original assignee: Huawei Technologies Co., Ltd.
Priority date: 2005-01-13
Filing date: 2006-01-13
Publication date: 2006-07-20
Also published as: CN100455106C; CN1805595A

Abstract

A method for realizing the high layer signaling transmission in the IEEE 802.16 system includes that the transmission terminal sets the identification for the high layer signaling to be transmitted and transmits it to the receiving terminal. The method of the present invention can complete the high layer signaling transmission between the terminal and the base station in the IEEE 802.16 system, thereby realizing the high layer signaling transmission between the terminal and the core network, the access of the terminal to the core network and the operation and the management from the core network to the terminal.

Description

Method for implementing high-level signaling transmission in IEEE 802.16 system

The present invention relates to a method of implementing high level signaling transmission between a terminal and a core network in an IEEE 802.16 system. Background of the invention

The IEEE 802.16 standard defines the air interface specification for Wireless MAN, which can be divided into two parts: fixed broadband wireless access air interface standard and mobile broadband wireless access air interface standard, of which 802.16, 802.16a, 802.16d belongs to the fixed wireless access air interface standard, and 802.16e belongs to the mobile broadband wireless access air standard. The IEEE 802.16 standard defines different physical layer technologies for different frequency bands. The standard is intended for residential, small office/home office (SOHO, Small Office Home Office), remote workers, and small business users (SME, Small Enterprise). ) Market and so on. '

The IEEE 802.16 standard Media Access Control (MAC) technology supports a poor user environment and can support hundreds or thousands of users on each channel while supporting both continuous mode and burst mode services.

Since the IEEE 802.16 standard only specifies the protocol standard of the air interface portion between the terminal and the access network base station in the wireless network architecture, the terminal can transmit a message with the access network according to the IEEE 802.16 standard. However, in order to access the terminal of the IEEE 802.16 system to the core network and implement the operation and management of the core network to the terminal, the problem of transmitting high-level signaling between the terminal and the core network is inevitably involved. In this case, the base station needs to be able to forward the received high layer signaling from the terminal or core network to the core network or the terminal without parsing the received high layer signaling and Processing, while the current IEEE 802.16 The standard does not have any provisions for this aspect, so it is impossible to achieve high-level signaling transmission between the terminal and the core network. Here, the high layer signaling refers to non-access stratum signaling that implements operation and management of the terminal by the core network. Summary of the invention

In order to solve the above technical problems, the present invention provides a method for implementing high layer signaling transmission between a terminal and a core network in an IEEE 802.16 system.

The method for implementing the high-level signaling transmission in the IEEE 802.16 system includes: the sending end sets an identifier for the high-level signaling to be sent, and sends the identifier to the receiving end; the receiving end identifies the received information according to the identifier. High-level signaling.

The method of the present invention can be implemented by adding a MAC management message specifically for encapsulating high layer management signaling between the terminal and the core network based on the IEEE 802.16 standard protocol.

The sending end of the present invention sets the identifier for the high layer signaling to be sent: encapsulating the high layer signaling into a preset signaling delivery message;

The signaling delivery message includes: a management message type field for identifying the signaling delivery message type and a signaling message field carrying the higher layer signaling.

The sending according to the present invention is: transmitting the signaling delivery message on a basic connection established when the terminal accesses the base station.

The signaling delivery message of the present invention further includes: an encoding field.

The method of the present invention can also pass high layer signaling as a general service data packet on the air interface between the terminal and the base station.

The high-level signaling of the present invention is a high-level signaling sent by the terminal to the core network; the transmitting end is a terminal; and the receiving end is a base station;

After the method receives the high layer signaling, the method further includes: the base station will receive the high Layer signaling is forwarded directly to the core network through a network connection between the base station and the core network.

The method of the present invention further includes: the high layer signaling is a high layer signaling that is sent by the core network to the terminal; the sending end is a base station; and the receiving end is a terminal;

The method further includes: before the base station sets the identifier for the high layer signaling, the core network sends the high layer signaling sent to the terminal to the base station through a network connection between the core network and the base station.

The identifier set for high layer signaling according to the present invention is a connection identifier assigned by the base station in the connection establishment process initiated by the terminal.

Before the sending end sets the identifier for the high layer signaling, the method further includes the terminal initiating the connection establishing process, where the connection establishing process includes:

a terminal sends a connection establishment request message to the base station, and makes a special indication in the message, indicating that the service flow created by the current connection establishment request is used to carry the high layer signaling;

After receiving the connection establishment request message, the base station creates a service flow, allocates a special connection identifier to the service flow, and encapsulates the service flow creation result and the allocated connection identifier in the connection establishment response message. Sending to the terminal, and recording the assigned connection identifier at the same time, indicating that the service flow identified by the connection identifier is used to carry the high layer signaling;

c. After receiving the connection establishment response message, the terminal stores the connection identifier therein, and makes a special record, indicating that the service flow identified by the connection identifier is used to carry the high-level signaling.

The high-level signaling of the present invention is a high-level signaling sent by the core network to the terminal; the transmitting end is a base station; and the receiving end is a terminal;

The method of the present invention further includes: the high layer signaling is a high layer signaling sent by the terminal to the core network; the sending end is a terminal; the receiving end is a base station; After receiving the high layer signaling, the method further includes: the base station forwards the received high layer signaling directly to the core network through a network connection between the base station and the core network.

The identifier set for high layer signaling according to the present invention is a connection identifier assigned by the base station in the connection establishment procedure initiated by the base station.

Before the sending end sets the identifier for the high layer signaling, the method further includes: the base station initiates a connection establishment process, where the connection establishment process includes:

A. The base station allocates a special connection identifier, sends a connection establishment request message of the connection identifier to the terminal, and gives a special indication in the message, indicating that the service flow created this time is used to carry the high layer signaling;

B. After receiving the connection establishment request message, the terminal creates a service flow, encapsulates the service flow creation result in a connection establishment response message, and sends the result to the base station; then stores the received connection identifier, and makes a special record. The connection identifier is used to identify the service flow carrying the higher layer signaling.

C. After receiving the connection establishment response message, the base station performs special recording on the allocated connection identifier, and indicates that the monthly service flow identified by the connection identifier is used for carrying high layer signaling.

The connection establishment request message of the present invention includes: a quality of service requirement parameter required for high layer signaling;

The creating a service flow is: creating the service flow according to a quality of service requirement parameter required for high layer signaling carried in the connection establishment request message.

The special indication of the present invention is: a reserved value of the transaction identifier field in the connection establishment request message and the connection establishment response message, or a newly added higher layer signaling bearer indication field in the connection establishment request message.

It can be seen that the method for implementing high-level signaling transmission between the terminal and the core network in the IEEE 802.16 system according to the present invention controls the base station to receive by defining a new signaling delivery message or establishing a special connection identifier. High-level signaling packets to be transferred The high-level signaling transmission can be completed between the terminal and the core network in the IEEE 802.16 system, and the terminal-to-core network access and the core network-to-terminal operation and management are realized. BRIEF DESCRIPTION OF THE DRAWINGS

1 shows a terminal initiated service flow establishment process according to a preferred embodiment of the present invention;

2 shows a service flow establishment process initiated by a base station according to a preferred embodiment of the present invention;

FIG. 3 is a flow chart of a method for transmitting high layer signaling between a terminal and a core network according to the present invention. Mode for carrying out the invention

The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

In order to realize the transmission of the high layer signaling between the terminal and the core network, the general idea of the present invention is to set a special identifier for the high layer signaling for the transmission by the terminal and the base station, and the base station will receive the received high layer signaling by identifying the identifier set by the terminal. The forwarded core network is not processed; the terminal knows that the currently received data is the high layer signaling from the core network by identifying the identifier set by the base station.

Figure 3 shows the flow of the method of the present invention, which mainly includes the following steps:

In the uplink direction: a. The terminal sets an identifier for the high-level signaling sent to the core network, and sends the identifier to the base station. b. The base station sends the received high-level signaling to the core network through a network connection between the base station and the core network.

In the downlink direction: c. The core network sends high-level signaling to the terminal through the core network and the base station. The network connection is sent to the base station; d. The base station sets an identifier for the received high layer signaling, and sends the identifier to the terminal.

Preferred embodiments of the present invention will be described in detail below.

Example 1

In order to implement high-level signaling transmission between the terminal and the core network of the IEEE 802.16 system, the method in this embodiment adds a MAC management message, which is called a signaling transfer message, based on the IEEE 802.16 standard protocol. ), specifically for encapsulating high-level management signaling between the terminal and the core network. The Signal Transfer Message includes at least: a Management Message Type field, a Transaction ID field, and a Signal Message field.

The Management Message Type field is used to identify the type of the Signal Transfer message, and the length is 8 bits. The terminal and the base station identify that the currently sent data is high layer signaling. The IEEE 802.16 standard indicates the different types of messages by setting different values on the Management Message Type field included in various types of messages transmitted between the base station and the terminal. Therefore, in the method described in this embodiment, The terminal or the base station may define any reserved value that is not defined by the IEEE 802.16 standard to represent the Signal Transfer Message.

The Transanction ID field is used to identify the number of the message itself and is 8 bits in length. The terminal or the core network may identify the Signal Transfer Message sent or received by the value of the field, and implement the targeted processing during the information interaction between the terminal and the core network.

The Signal Message field is used to carry high layer signaling passed between the terminal and the core network, and the length of the field is variable.

The terminal or the base station encapsulates the high-level signaling message that needs to be transmitted into the above-mentioned Signal Transfer Message, and implements high-level signaling transmission between the terminal and the base station. The Signal Transfer Message may be carried on a basic connection between the terminal and the base station, and the basic connection is identified by a Basic CID, which is used to carry a management message between the base station and the terminal, The terminal is allocated by the base station when accessing the network. Therefore, the transmission of the Signal Transfer Message does not need to establish a new service flow, which greatly saves the air interface overhead between the terminal and the base station, and also accelerates the transmission speed of the high layer signaling.

The transmission process of high-level signaling between the terminal and the core network will be described in detail below: In the uplink direction, after receiving the Signal Transfer Message from the terminal, the base station identifies the message as a Signal Transfer Message by using the Management Message Type field. Extracting the high layer signaling in the Signal Message field, and then encapsulating the high layer signaling into an IP data packet, and then sending the network packet to the core network through the network connection between the access network and the core network; the core network will receive the The IP packets are processed to obtain high-level signaling from the terminal.

In the downlink direction, after receiving the IP data packet containing the high layer signaling message from the core network, the base station inserts the high layer signaling message carried by the base station into the Signal Message field of the Signal Transfer Message, and then passes between the base station and the terminal. The basic connection on the air interface is sent to the terminal; the terminal will parse the received Signal Transfer Message to obtain high-level signaling from the core network.

It can be seen from the above analysis that the method described in this embodiment can implement high-level signaling transmission between the terminal and the core network.

Those skilled in the art can understand that the Signal Transfer Message can be further enhanced by adding a Code field in the Signal Transfer Message and defining different values of the field to indicate different types of signaling messages that the base station does not need to process. Scalability. For example, in the current IEEE 802.16e draft, the pre-authentication method in the handover process is not specifically described, and the pre-authentication should be performed at the terminal to switch to the target base station. Before, a complete authentication process is completed between the mobile station and the target base station, not just a key distribution process. Therefore, it is necessary for the terminal to initiate the pre-authentication process to the target base station, in which the serving base station does not process the message after receiving the message from the mobile station or the target base station, but forwards the complete message content to the target base station or The mobile station, the serving base station is relatively relayed during the authentication process. Obviously, the forwarding process of the above service base station can be implemented by adding a description of the Code field in the Signal Transfer Message. At this time, the Signal Message field defined by the present invention will be used to encapsulate an authentication request message sent by the mobile station to the target base station during the pre-authentication process or an authentication response message sent by the target base station to the mobile station. When the serving base station receives the Signal Transfer Message from the mobile station or the target base station, and detects that the Signal Transfer Message carries the pre-authentication message through the Code field, the message will not be processed and forwarded to the corresponding Target base station or mobile station.

Example 2:

In order to implement the transmission of the high layer signaling between the terminal and the core network, the method in this embodiment first transmits the high layer signaling as a general service data packet on the air interface between the terminal and the base station, and then the base station The forwarding of the high layer signaling to the core network is completed. In order to ensure that the base station and the terminal perform special processing different from the general data packet for the high-level signaling data packet transmitted in the air interface, the terminal and the base station need to assign a special connection identifier to the service flow when creating the service flow. (CID), used to identify the currently transmitted data packet as high-level signaling transmitted between the terminal and the core network. The above establishment process with a special CID service flow may be initiated by the terminal or by the base station.

As shown in FIG. 1 , the service flow establishment process initiated by the terminal includes the following steps: Step 101: The terminal sends a connection establishment request (DSA) that carries the service shield quantity (QoS) requirement parameter required for the high layer signaling to be transmitted through the air interface. – REQ) message to the base station, initiates a connection setup operation, and makes a special indication in the message, indicating the connection establishment request The created service flow is used for the transmission of higher layer signaling.

In this step, the special indication can be implemented in the following two ways: The first method does not need to modify the DSA-REQ/RSP message defined by the current protocol, and sets the Transaction ID field of the DSA_REQ/RSP message to be special. Value to indicate that the CID allocated during this DSA-REQ/RSP process will be used to carry high layer signaling. For example, you can define Transaction ID = 0x0000 as the Transaction ID that is used when the high-level signaling CID bearer is established between the terminal and the base station. In this way, the terminal and the base station can determine whether the service flow currently requested to be used for transmitting the high layer signaling by detecting the value of the Transaction ID field. Of course, the Transaction ID field can also be set to any other reserved value without departing from the scope of the present invention.

The second method needs to modify the DSA-REQ message defined by the current protocol, and adds a high-level signaling indication indication (Signal Indication) field, which is 1 bit long, and is used to indicate whether the service flow currently established by the request is used for transmission. High-level signaling. For example, you can set the Signal Indication field to 1, indicating that the server that is currently requesting to establish a high-level signaling, and 0 for transmitting general service data, and vice versa.

Step 102: After receiving the DSA-REQ message, the base station creates a service flow according to the QoS parameters carried in the protocol and the service flow creation rule specified by the protocol, and allocates a special CID to the created service flow, and then creates a service flow. And the CID encapsulation is sent to the terminal through the air interface in a connection establishment response (DSA-RSP) message; at the same time, the base station makes a special record on the allocated CID, which is marked on the one hand and then sent by the terminal to the base station, and is forwarded by the base station to The high-level signaling of the core network is carried by the CID. On the other hand, the high-level signaling sent by the core network to the base station and forwarded by the base station to the terminal is also carried by the CID, that is, the uplink and downlink high-level signaling transmission. Use the same CID bearer.

Step 103: After receiving the DSA-RSP message, the terminal stores the CID carried therein, and makes a special record, indicating that the data packet carried on the CID is not a general service. The data packet, but the high-level signaling that needs to be processed, so that the terminal can perform corresponding processing.

After the above steps are completed, the high-level signaling between the terminal and the core network can be carried on the assigned special CID and transmitted using the created service flow. Specifically, in the uplink direction, the terminal carries the high-level signaling data packet (usually the manner of the IP data packet) sent to the core network on the allocated special CID, and then sends the signal to the base station; the base station receives the data packet. Then, the high-level signaling data packet carried on the CID is directly forwarded to the core network through the back-end network connection. In the downlink direction, the core network first sends a high-level signaling data packet (usually an IP data packet mode) sent to the terminal to the corresponding base station, and after receiving the high-level signaling data packet, the base station performs the high-layer signaling. The data packet is carried on the same special CID as the corresponding uplink direction, and is sent to the terminal through the air interface. After receiving the data packet, the terminal processes the high layer signaling carried on the CID.

The service flow establishment process initiated by the base station from the core network to the terminal direction is as shown in FIG. 2, and includes the following steps:

Step 201: The base station allocates a special CID for the transmission of the downlink high-level signaling, and sends a DSA-REQ message carrying the QoS requirement parameter required by the high-level signaling transmission and the special CID to the terminal through the air interface, and initiates a connection establishment operation. And make a special indication in the DSA-REQ message, indicating that the service flow created this time is used for the transmission of high-level signaling.

The special indications described in this step can be implemented in the same manner as the special instructions described in step 101.

Step 202: After receiving the DSA-REQ message, the terminal creates a service flow according to the QoS requirement parameter carried in the protocol and the service flow creation rule specified by the protocol, and encapsulates the service flow creation result in the DSA-RSP message, and passes the air interface. Sending to the base station; At the same time, storing the CID carried in the DSA-REQ message, and making a special record, indicating that the data packet carried on the CID is a higher layer signaling instead of a general service data packet, so that the terminal performs corresponding processing. Step 203: After receiving the DSA-RSP message, the base station performs special recording on the received special CID, and indicates on the one hand that the higher layer signaling sent by the core network to the base station and forwarded by the base station to the terminal is carried by the CID. The high-level signaling that is sent by the terminal to the base station and forwarded by the base station to the core network is also indicated, and is also carried by the CID, that is, the uplink and downlink high-level signaling uses the same CID bearer.

After the above steps are completed, the high-level signaling between the terminal and the core network can be carried on the assigned special CID and transmitted using the created service flow. Specifically, in the downlink direction, the base station carries the high-level signaling data packet (usually in the form of an IP data packet) received from the core network side to the terminal, and sends the data to the terminal through the air interface; After the high-level signaling data packet, the high-level signaling carried on the CID will be processed. In the uplink direction, for the high-level signaling sent by the terminal side to the core network, the terminal carries the high-layer signaling on the same CID as the corresponding downlink direction, and sends it to the base station through the air interface; after receiving the CID, the base station receives the CID. The higher layer signaling packets (usually in the form of IP packets) are forwarded to the core network through the back end network connection.

The service flow creation process described in steps 101 to 103 and steps 201 to 203 above respectively describes the establishment process of two types of CIDs. Both of these methods are used to establish a CID direction in the way that the base station performs special recording on the CID. The two directions are used, that is, the uplink and downlink high-level signaling use the same CID bearer. The advantage of this is that high-level signaling from the core network to the terminal or from the terminal to the core network can be carried on the same CID connection without the need to initiate connection or service flow establishment for signaling in different directions. The process, while saving air interface overhead, also speeds up signaling.

Example 3:

In order to implement the high-level signaling between the terminal and the core network, the method described in this embodiment is similar to the method described in Embodiment 2, that is, the high-level signaling is also regarded as a general service data packet at the terminal and the base station. Passed between the air interfaces, but the difference is that this embodiment The method respectively establishes different service flows in the uplink and downlink directions, and is used for transmitting high-layer signaling, and does not affect each other.

The method described in this embodiment includes a service flow establishment process initiated by the terminal and a service flow establishment process initiated by the base station.

The service flow establishment process initiated by the terminal includes the following steps:

Step 301: The terminal sends a DSA-REQ message carrying the QoS requirement parameter required for the high layer signaling to be transmitted to the base station, initiates a connection establishment operation, and makes a special indication in the message, indicating that the connection establishment request is created. Service flow for high-level signaling transmission;

In this step, the special indication may be the same as the special indication described in step 101;

Step 302: After receiving the DSA-REQ message, the base station creates a service flow according to the QoS parameters carried therein and the service flow creation rule specified by the protocol, and allocates a special uplink CID, and then creates a service flow result and The allocated uplink CID is encapsulated in the DSA-RSP message and sent to the terminal through the air interface. At the same time, the base station makes a special record for the allocated uplink CID, indicating that the terminal is sent to the base station by the terminal and forwarded by the base station to the upper layer of the core network. The signaling is carried by the uplink CID, so that the base station performs corresponding processing on the data packet carried on the uplink CID;

Step 303: After receiving the DSA-RSP message, the terminal stores the uplink CID carried in the terminal, and performs special recording on the CID, indicating that the data packet carried on the uplink CID is not a general service data packet, but needs to be processed. High-level signaling, so that the terminal can handle it accordingly.

The service flow establishment process initiated by the base station from the core network to the terminal direction includes the following steps:

Step 401: The base station allocates a special downlink CID for transmission of downlink high-level signaling. 57 transmitting, by using an air interface, a QoS requirement parameter required for high-level signaling transmission and a DSA-REQ message of the downlink CID to the terminal, initiating a connection establishment operation, and giving a special indication in the DSA_EQ message, indicating the created Service flows are used for the transmission of higher layer signaling;

Step 402: After receiving the DSA-REQ message, the terminal creates a service flow according to the QoS requirement parameter carried in the protocol and the service flow creation rule specified by the protocol, and encapsulates the service flow creation result in the DSA-RSP message through the air interface. Sending to the base station; At the same time, the terminal stores the received downlink CID, and makes a special record for the downlink CID, indicating that the data packet carried on the downlink CID is higher layer signaling, instead of a service data packet, so that the terminal Carry out corresponding processing;

Step 403: After receiving the DSA-RSP message, the base station performs special recording on the downlink CID, and indicates that the high-level signaling that is sent by the core network to the base station and forwarded by the base station to the terminal is carried by the downlink CID, so that the base station performs Processing accordingly.

After the above steps 301 to 303 and steps 401 to 403 are completed, the high layer signaling between the terminal and the core network can be carried on the two allocated uplink and downlink CIDs, and the two service flows created separately are used for transmission. That is, in the uplink direction, the terminal carries the high-level signaling (usually in the form of an IP packet) sent to the core network on the established uplink CID, and transmits it to the base station through the air interface; after receiving the uplink, the terminal uplinks the uplink The high layer signaling packets carried on the CID are forwarded to the core network through the network connection at the back end. In the downlink direction, the base station carries the high-level signaling data packet (usually in the form of an IP data packet) that is received from the core network side to the terminal, and is sent to the terminal through the air interface; the terminal receives the After the high layer signaling data packet, the high layer signaling carried on the downlink CID will be processed. This enables high-level signaling to be transferred between the terminal and the core network.

Claims

Claim

A method for implementing high-level signaling transmission in an IEEE 802.16 system, wherein the transmitting end sets an identifier for the high-level signaling to be sent, and sends the identifier to the receiving end; the receiving end identifies the received according to the identifier. The information is for high layer signaling.

The method according to claim 1, wherein the sending end sets the identifier for the high layer signaling to be sent: encapsulating the high layer signaling into a preset signaling delivery message;

The method according to claim 2, wherein the sending is: transmitting the signaling delivery message on a basic connection established when the terminal accesses the base station.

4. The method of claim 2, wherein the signaling delivery message further comprises: an encoding field.

The method according to claim 1, wherein the high-level signaling is a high-level signaling sent by the terminal to the core network; the transmitting end is a terminal; and the receiving end is a base station;

The method further includes: after receiving the high layer signaling by the base station, the base station forwards the received high layer signaling directly to the core network through a network connection between the base station and the core network.

The method according to claim 5, wherein the method further comprises: the high layer signaling is a high layer signaling sent by the core network to the terminal; the sending end is a base station; and the receiving end is a terminal ;

The method according to claim 5 or 6, wherein the identifier set for the higher layer signaling is a connection identifier allocated by the base station in the connection establishment process initiated by the terminal.

The method according to claim 7, wherein before the sending end sets the identifier for the high layer signaling, the method further includes the terminal initiating the connection establishing process, where the connection establishing process includes:

The method according to claim 1, wherein the high-level signaling is a high-level signaling that is sent by the core network to the terminal; the transmitting end is a base station; and the receiving end is a terminal;

The method according to claim 9, wherein the method further comprises: the high layer signaling is a high layer signaling sent by the terminal to the core network; the sending end is a terminal; ;

The method according to claim 9 or 10, wherein the identifier set for higher layer signaling is a connection identifier allocated by the base station in a connection establishment procedure initiated by the base station.

12. The method according to claim 11, wherein the transmitting end is high layer signaling Before the setting of the identifier, the method further includes: the base station initiates a connection establishment process, where the connection establishment process includes:

A. The base station allocates a special connection identifier, sends a connection establishment request message carrying the connection identifier to the terminal, and gives a special indication in the message, indicating that the service flow created this time is used to carry the high layer signaling. ;

C. After receiving the connection establishment response message, the base station performs special recording on the allocated connection identifier, and indicates that the service flow identified by the connection identifier is used to carry the high layer signaling.

The method according to claim 8 or 12, wherein the connection establishment request message comprises: a quality of service requirement parameter required for high layer signaling;

The creating a service flow is: creating the service flow according to a service mean requirement parameter required for high layer signaling carried in the connection establishment request message.

The method according to claim 8 or 12, wherein the special indication is: a reservation value of a transaction identifier field in a connection establishment request message and a connection establishment response message, or a new addition in a connection establishment request message The higher layer signaling bearer indication field.