1 hdlc =title HDLC The HDLC module implements one of the protocols in the Data Link layer. The HDLC High-level Data Link Control protocol is intended to cover a wide range of applications; for example, one-way, two-way alternate or two way simultaneous data communication between data stations which are usually buffered, including operations on different types of data circuits; for example multipoint/point-to-point, duplex/half-duplex, and switched/non-switched. This implementation uses HDLC to offer reliable communication at the Data Link layer for point-to-point synchronous data lines over a wide area network link. The HDLC module typically runs as a Data Link module under the CLNS Network protocol. The hierarchical relationship of the entities that constitute the HDLC module: HDLC Port Link Logical Station You must install the WAN device drivers before you can refer to these entities. The HDLC entity is the top-level entity in the hierarchy of entities belonging to the HDLC module. 2 character =title Characteristics Attribute VERSION Version of the HDLC architecture specification to which the implementation conforms. You cannot modify this characteristic. 2 Link =title HDLC Link An HDLC link entity is associated with a port of the supporting physical layer module. It contains attributes common to local HDLC operations for all logical stations on the line. 3 character =title Characteristic Attribute ACKNOWLEDGE TIMER Default: 3000 Value: 1-60000 Time, in milliseconds, to wait for an acknowledgment before using error recovery procedures. The value of this characteristic corresponds to the T1 parameter of HDLC. You can modify this characteristic only when the entity is disabled. HOLDBACK TIMER Default: 0 Value: 1-60000 Maximum time to wait before sending an acknowledgment supervisory frame if no other frames carry the acknowledgment. A value of zero means that the frame will be sent immediately if no I-frame can be sent. You can modify this characteristic only when the entity is disabled. LINK TYPE Operational mode of the HDLC link. The value of this characteristic is a copy of the link type argument specified when the entity is created. You cannot modify this characteristic. MAXIMUM DATA SIZE Default: 1500 Value: 262-65532 Maximum number of bytes that users of the data link can specify. This number applies to both transmit and receive frames. The value of this characteristic must be greater than or equal to the value of the minimum data size characteristic. You can modify this characteristic only when the entity is disabled. MAXIMUM UNSEQUENCED PDUS Default: 1 Value: 1-127 Maximum number of unsequenced I-frames that a primary or secondary station can send in a single transmission. This characteristic is not used if the link type characteristic is balanced. MINIMUM DATA SIZE Default: 576 Value: 262-65532 Minimum number of bytes that users of the data link can specify. This number applies to both transmit and receive frames. The value of this characteristic must be less than or equal to the value of the maximum data size characteristic. You can modify this characteristic only when the entity is disabled. PHYSICAL LINE Default: None Value: Local-entity-name Local entity name of the the Physical layer entity over which the HDLC protocol is to operate. This characteristic must have a value before the HDLC link is enabled. You can modify this characteristic only when the entity is disabled. PREFERRED CRC TYPE Default: Either Value: 16-bit, 32-bit or Either CRC types available for negotiation. If the value of this characteristic is either, the station will try to use 32-bit but will use 16-bit if that is all that the remote station supports. PREFERRED LOCAL STATION ADDRESS Default: 2 Value: 1-253 Address proposed for the local logical station during negotiation. If there is no negotiation, the value of this characteristic is the value that is used. If negotiation is necessary, the value of this characteristic must be between 2 and 253. You can modify this characteristic only when the entity is disabled. PREFERRED MAXIMUM DATA SIZE Default: 1500 Value: 262-65532 Default size, in octets, of frames that the station receives and transmits. This value is used only if the link initialization does not specify a buffer value. The value of this characteristic must lie between those of the maximum data size and minimum data size characteristics. You can modify this characteristic to a lower value only when the entity is disabled. PREFERRED WINDOW SIZE Default: 2 Value: 1-127 Window size to be offered during negotiation for both receive and transmit frames. The value of this characteristic must be compatible with that for the sequence modulus characteristic. PROFILE Simple name that can be used when the HDLC protocol is dependent on network subscription time commitments pertinent to the Data Link layer. The value of this characteristic is a copy of the profile argument specified when the entity is created. You cannot modify this characteristic. RECEIVE BUFFERS Default: 4 Value: 1-128 Number of receive buffers reserved for the link. This characteristic can only be set to a lower value when the entity is disabled. RETRY MAXIMUM Default: 10 Value: 1-255 Maximum number of times that a frame will be retransmitted before the local station assumes that a fatal error has occurred. This characteristic can be modified only when the entity is disabled. SEQUENCE MODULUS Default: 128 Value: 8 or 128 Whether modulo-8 or modulo-128 sequence numbering is allowed on the HDLC link. The value 8 means that only normal sequence numbering is allowed. The value 128 means that both extended and normal sequence numbering are supported for negotiation. 3 counters =title Counter Attributes BUFFER UNAVAILABLE ERRORS Number of times that the Physical layer reported that no buffer was available to hold a message. This counter is not supported in all implementations. CRC ERRORS RECEIVED Number of frames received that had a bad CRC. TIMES PDU RECEIVE OVERRUN Number of times a physical line indicated an overrun condition to the Data Link layer. This counter is not supported in all implementations. TIMES PDU TRANSMIT FAILED Number of times that an attempt to send a frame failed. UP TRANSITIONS Number of times that the entity's status attribute state has changed from off to on. 3 status =title Status Attributes ACTUAL SEQUENCE MODULUS Sequence number modulus in use on the link. Until negotiation is complete, this attribute has the value 128. However, if the value of the characteristic sequence modulus is 8, the modulus always appears as the value 8. INTERFRAME DELAY Time required between frames to enable the local station to successfully receive them. LINE TYPE Defines whether the underlying physical line is switched or nonswitched. This status affects the subset of port states that are related to a given link. MAXIMUM PDU SIZE Maximum frame size in octets that can be used on the link. Until negotiation is complete, the value of this status attribute is the same as the characteristic preferred maximum data size. NEGOTIATED CRC TYPE CRC mode that has been negotiated with the remote station. This mode will not be used until the station is next enabled. Until negotiation is complete, the value of this is 16-bit. PHYSICAL PORT Name of the port in the Physical layer associated with the communications link. RESPONSE ADDRESS Address that the remote station puts in response frames. STATE State of the HDLC link. This reflects the last enable or disable command issued. OFF - The link is disabled. ON - The link is enabled. WINDOW SIZE Maximum number of I-frames that can be outstanding before an acknowledgment must be received. Until negotiation is complete, the value of this status attribute is the same as the characteristic preferred window size. 2 logical =title HLDC Link Logical Station The HDLC Link Logical Station entity controls the characteristics of an HDLC Logical Station. There is one station for each remote termination of a line associated with the HDLC link. The link name is the link entity within the HDLC module and the logical station name refers to the logical station. 3 Counters =title Counter Attributes DATA OCTETS RECEIVED Total number of octets received in the I-field of I-frames and UI-frames. This total excludes protocol ID information in UI-frames and frame retransmissions. DATA OCTETS SENT Total number of octets sent in the I-field of I-frames and UI-frames. This total excludes protocol ID information in UI-frames and frame retransmissions. DATA PDUS RECEIVED Total number of I-frames and UID-frames received. This number does not include frames that had to be retransmitted. DATA PDUS SENT Total number of I-frames and UID-frames sent. This number does not include frames that had to be retransmitted. FRMRS GENERATED Number of FRMRs frame rejects sent. FRMRS RECEIVED Number of FRMRs frame rejects received. INVALID MODE COMMANDS Number of command frames SABME, SABM, SNRME, SNRM,SARM, and SIM received that are not applicable to this station. NEGOTIATION FAILURES Number of times that the XID negotiation with the remote station has failed. POLLS RECEIVED Number of frames received with the poll bit set. REJS RECEIVED Number of REJ frames rejects received. REJS SENT Number of REJ frames rejects sent. RNRS RECEIVED Number of RNR receive not ready supervisory frames received from the remote station. RNRS SENT Number of RNR receive not ready supervisory frames transmitted. TIMES ACKNOWLEDGE TIMER EXPIRED Number of times that the acknowledge timer has expired. TIMES STATION HALTED Number of times the station halt event has occurred. TIMES STATION INITIALIZING Number of times the station initialized event has occurred. TIMES STATION INOPERATIVE Number of times the entity's status attribute state became inoperative. TIMES STATION MAINTENANCE Number of times the entity's status attribute state became maintenance. TIMES STATION RESETTING Number of times that the station reset event has occurred. TIMES STATION RUNNING Number of times that the station running event has occurred. TIMES STATION SETUP FAILED Number of times the station setup failure event has occurred. UNKNOWN UI PDUS RECEIVED Number of UI-frames the local station received whose protocol ID does not match that of any open port. XIDS RECEIVED Number of XID identification command or response frames received. 3 status =title Status Attributes COMMAND ADDRESS Address the local station uses when sending command frames to the remote station. MAINTENANCE MODE Whether the station is in maintenance mode. When set to true, the station will be used exclusively for maintenance operations. When set to false, the station operates in normal fashion. The limit command sets the value of this attribute to true, and the unlimit to false. PROTOCOL STATE State of the data link protocol. ERROR - A protocol error occurred. For instance, the logical station received an invalid frame. HALTED - The protocol could not start. For example, there is no client. INITIALIZING - The protocol is being initialized. INOPERATIVE - The protocol cannot be started because no contact has been established with the remote station. MAINTENANCE - The logical station is in maintenance mode. RESETTING - The protocol is resetting after an error. RUNNING - The protocol is running and capable of exchanging frames with the remote station. REMOTE VERSION Version number of the HDLC protocol that the remote station is using. This is received as part of an XID message from the remote station. STATE State of the logical station. OFF - The logical station is off because of a disable command. ON - The logical station is on because of an enable command. 2 PORT =TITLE HDLC Port The HDLC Port entity represents one end of an HDLC connection. The entity maintains information about that link. Ports are created and deleted automatically when a client of HDLC uses the link. 3 status =title Status Attributes CLIENT Name of the client using the port. LOGICAL STATION hdlc link logical station entity that the port is operating over. PROTOCOL ID Protocol ID that the port is using. For sequenced ports, this value is decided during negotiation. For unsequenced ports, the value is sent in every UI-frame. STATE State of the port. OPEN - The port is assigned to a client. If the communications line is unswitched, data transfer can begin. For switched lines, an association must be made with the line before data transfer can begin. OPEN DISABLED - The port is associated with a client, but the link or logical station associated with it is disabled. TYPE Type of port. SEQUENCED - The port can send and receive sequenced and unsequenced data. UNSEQUENCED - The port can send and receive unsequenced data only.