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.

1  –  character

     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.

2  –  counters

     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

     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.