1 DDCMP =title DDCMP The DDCMP module is a data link control procedure that ensures a reliable data communication path between communication devices connected by data links. DDCMP has been designed to operate over full-duplex and half-duplex synchronous and asynchronous channels in both point-to-point and multipoint modes. It can be used in a variety of applications such as distributed computer networking, host/front end processing, remote terminal concentration, and remote job entry-exit system operation. The hierarchical relationship of the entities that constitute the DDCMP module: DDCMP Port Link Logical station The DDCMP entity is the top-level entity in the hierarchy of entities belonging to the DDCMP module. 2 character =title Characteristic Attributes DNA VERSION Version number of the DDCMP architecture specification to which the implementation conforms. You cannot modify this characteristic. 2 ddcmp link =title DDCMP LINK The DDCMP link entity defines the attributes of a link to a communications port that uses the DDCMP protocol. 3 character =title Characteristic Attributes DEAD TIMER Default: 10000 Value: 1-65535 Specifies the delay, in milliseconds, between polls of one of the set of dead tributaries. This attribute is supported only if the characteristic protocol is set to control. DELAY TIMER Default: 0 Value: 0-65535 Specifies the minimum delay, in milliseconds, between polls. You can use this timer to limit the effect of a fast control station on slower tributaries. A value of 0 means that no delay is added. This attribute is supported only if the characteristic protocol is set to control. PHYSICAL LINE Default: No Name Value: local-entity-name Name of the Physical layer entity that the link operates over. A value for this characteristic must be set before the link entity is enabled. You can modify this characteristic only when the entity is disabled. PROTOCOL Default: Point Protocol mode used by the local station. You cannot modify this characteristic. The value of this characteristic is a copy of the protocol argument specified when the DDCMP link entity is created. The default value is point and is the only permissible value. RECEIVE BUFFERS Default: 4 Value: 1-255 Number of receive buffers reserved for the link. You can modify this characteristic only when the entity is disabled. Also, you can only increase the characteristic value. RETRANSMIT TIMER Default: 3000 Value: 1-65535 Maximum time, in milliseconds, to wait between sending a message and receiving a valid response. If this time expires, the local station takes error recovery action. On full-duplex point-to-point links, the timer is started immediately when a message is sent. SCHEDULING TIMER Default: 200 Value: 50-65535 Time, in milliseconds, between the recalculation of tributary polling priorities. This attribute is supported only if the characteristic protocol is set to control. STREAM TIMER Default: 6000 Value: 0-65535 Time, in milliseconds, for which a tributary or the remote station on a half-duplex, point-to-point link can hold the line. This characteristic is not supported if the characteristic protocol is set to tributary. 3 counters =title Counter Attributes NAKS RECEIVED INDICATING MESSAGE HEADER FORMAT ERROR Number of NAK messages received that report errors in message headers sent from the local station. NAKS RECEIVED INDICATING RECEIVE OVERRUN Number of NAK messages received that report a receive overrun at the remote station. PDUS RECEIVED WITH MESSAGE HEADER FORMAT ERROR Number of times the local station detected an error in a message header. RECEIVE OVERRUNS Number of times the local station detected a receive overrun. SELECTION ADDRESS ERRORS Number of times that the controller of a multipoint link received a message with an address other than that of the currently selected station. This counter is supported only if the characteristic protocol is set to control. STREAMING TRIBUTARIES Number of times that the remote station or a tributary station exceeded the maximum transmission interval without releasing the line, or failed to release the line after sending a message with the select flag set. This counter is present only on half-duplex, point-to-point links, or when the local station is a controller of a multipoint link. This counter is not supported if the protocol characteristic is set to tributary. TRANSMIT UNDERRUNS Number of times the local station detected a transmit underrun. 3 status =title Status Attributes PHYSICAL PORT Name of the port entity in the Physical layer returned when the port is opened. If this is null, the port is not open. STATE State of the DDCMP link. The value of this attribute is determined by the enable and disable commands. OFF - The entity is disabled. ON - The entity is enabled. In addition the link is disabled and its state set to off if the Physical layer port that the link uses is deleted. 2 logical =title DDCMP LINK LOGICAL STATION The DDCMP Link Logical Station entity manages a link to a remote station. The link name is the DDCMP link associated with the logical station and the station name refers to the logical station. 3 Character =title Charateristics Attribute ACTIVE BASE Default: 255 Value: 0-255 Base priority to which an active tributary is reset after it has been polled. This characteristic is supported only if the characteristic protocol of the owning ddcmp link entity is set to control. ACTIVE INCREMENT Default: 0 Value: 0-255 Value to be added to the active tributary priority each time the scheduling timer expires. This characteristic is supported only if the characteristic protocol of the owning ddcmp link entity is set to control. ADDRESS Default: 1 Value: 1-255 Data link address of the remote station or tributary. You can modify this characteristic only when the entity is disabled. BABBLE TIMER Default: 6000 Value: 1-65535 Time, in milliseconds, for which a selected tributary or remote station is allowed to transmit. This characteristic is not used on full-duplex links. This characteristic is not supported if the characteristic protocol of the owning ddcmp link entity is set to tributary. BUFFER SOURCE Default: Implementation_specific Value: see below Source of the receive buffers. CLIENT SUPPLIED - Buffers are provided by the client entity. COMMON POOL - Buffers are assigned from the common buffer pool. This characteristic is supported only if the characteristic protocol of the owning ddcmp link entity is set to control. You can modify this characteristic only when the entity is disabled. DEAD THRESHOLD Default: 8 Value: 0-255 Number of times that an active, inactive, or dying tributary is polled before its status attribute polling substate is changed to dead because of receive timeouts. This characteristic is supported only if the characteristic protocol of the owning ddcmp link entity is set to control. DYING BASE Default: 0 Value: 0-255 Base priority to which a dying tributary is reset after being polled. This characteristic is supported only if the characteristic protocol of the owning ddcmp link entity is set to control. DYING INCREMENT Default: 16 Value: 0-255 Value to be added to a dying tributary's priority each time the scheduling timer expires. This characteristic is supported only if the characteristic protocol of the owning ddcmp link entity is set to control. DYING THRESHOLD Default: 2 Value: 0-255 Number of times an active or inactive tributary is polled before its status attribute polling substate is changed to dying because of receive timeouts. This characteristic is supported only if the characteristic protocol of the owning ddcmp link entity is set to control. HOLDBACK TIMER Default: 0 Value: 0-13000 Maximum time, in milliseconds, that the local station can delay acknowledging a received message if there is no data to send. The value of this characteristic is linked to the retransmit timer used on the remote station. A suggested value is between 10% and 20% of that timer. However, the actual values you can use may be limited by the communications product. The default value indicates that no holdback is used and the local station must acknowledge immediately. INACTIVE BASE Default: 0 Value: 0-255 Specifies the priority to which an inactive tributary is reset after it has been polled. This characteristic is supported only if the characteristic protocol of the owning ddcmp link entity is set to control. INACTIVE INCREMENT Default: 64 Value: 0-255 Value to be added to an inactive tributary's priority each time the scheduling timer expires. This characteristic is supported only if the characteristic protocol of the owning ddcmp link entity is set to control. INACTIVE THRESHOLD Default: 8 Value: 0-255 Number of times an active tributary is polled before its status attribute polling substate is changed to inactive because of no data response. This characteristic is supported only if the characteristic protocol of the owning ddcmp link entity is set to control. MAXIMUM BUFFERS Default: 4 Value: Implementation specific Maximum number of buffers that a tributary can use from the common buffer pool. A value of 0 means that there is no limit to the number of buffers that can be used. This characteristic is supported only if the buffer source characteristic is set to common pool. This characteristic is supported only if the characteristic protocol of the owning ddcmp link entity is set to control. You can modify this characteristic only when the entity is disabled. Also, you can only increase the characteristic value. MAXIMUM TRANSMIT Default: 4 Value: 1-255 Maximum number of messages that a tributary or a remote half-duplex station can send at one time. The value of this characteristic must be greater than or equal to that of transmit window on the selected station. This characteristic is not supported if either of the following conditions is true: o The characteristic protocol of the owning ddcmp link entity is set to tributary. o The communications link is full-duplex and point-to-point. You cannot modify this characteristic. POLLING STATE Default: Automatic Value: see below Specifies the effect of the local station's polling algorithm on the state of a tributary. The value of this characteristic is reflected in the value of the status attribute polling substate. ACTIVE - The state is locked to active. AUTOMATIC - The state varies according to the operation of the polling algorithm. DEAD - The state is locked to dead. DYING - The state is locked to dying. INACTIVE - The state is locked to inactive. This characteristic is supported only if the characteristic protocol of the owning DDCMP link entity is set to control. TRANSMIT TIMER Default: 0 Value: 0-65535 Time, in milliseconds, that the local station waits between data transmissions. This characteristic is supported only if the characteristic protocol of the owning ddcmp link entity is set to control. TRANSMIT WINDOW Default: 1 Value: 1-255 Maximum number of data messages that the local station can send without receiving an acknowledgment. This characteristic applies only when the remote station is a control station or on a half-duplex, point-to-point link. The value of this characteristic must be less than or equal to the equivalent of the maximum transmit characteristic on the control station or remote station. 3 Counters =title Counter Attributes BUFFERS TEMPORARILY UNAVAILABLE Number of times the local station could not service messages from the remote station because there were no receive buffers available. BUFFERS TOO SMALL Number of times the local station could not service messages from the remote station because the receive buffers were not large enough. INCOMPLETE REPLIES TO SELECT Number of selection intervals that were not properly terminated that is, by a message with the Select bit set in the header, during which a transmission was received or an attempt at transmission was detected. This counter is supported only if the protocol characteristic of the owning ddcmp link entity is set to control, or when the link is a half-duplex, point-to-point link. LOCAL REPLY TIMEOUTS Number of times the local station failed to receive an acknowledgment before the reply timer expired. LOCALLY INITIATED STATE CHANGES Number of times that the station protocol state changed through action of the local station. NAKS RECEIVED INDICATING BUFFER TOO SMALL Number of times the remote station reported that it could not service a message because the receive buffer was not large enough. NAKS RECEIVED INDICATING BUFFERS TEMPORARILY UNAVAILABLE Number of times the remote station reported that it could not service a message because no receive buffer was available. NAKS RECEIVED INDICATING DATA FIELD BLOCK CHECK ERROR Number of times the remote station reported that a block check error was detected in the data field of an incoming message. NAKS RECEIVED INDICATING HEADER BLOCK CHECK ERROR Number of times the remote station reported that a block check error was detected in the header block of an incoming message. NAKS RECEIVED INDICATING REP RESPONSE Number of times the remote station reported that it did not receive all the messages sent from the local station. NAKS SENT WITH REP RESPONSE Number of times that the local station detected that not all of the messages sent from the remote station were received correctly. NO REPLIES TO SELECT Number of times that the select timer expired for any of the following reasons: o No valid control message was received. o No valid header to a data message was received. o No valid header to a maintenance message from the selected station was received. o No transmission from the remote station was received. This counter is supported only if the protocol characteristic of the owning ddcmp link entity is set to control, or when the link is a half-duplex, point-to-point link. PDUS RECEIVED WITH DATA FIELD CHECK BLOCK ERROR Number of messages received with a check error in the data field. PDUS RECEIVED WITH HEADER BLOCK CHECK ERROR Number of messages received with a check error in the header block. RECEIVE ERROR THRESHOLDS REACHED Number of times that the receive error threshold has been reached. REMOTE REPLY TIMEOUTS Number of times the local station received a REP message and sent an acknowledgment in return. This sequence indicates that all messages sent from the remote station have been correctly received. REMOTELY INITIATED STATE CHANGES Number of changes in the station protocol state caused by action of the remote station. SDU OCTETS RECEIVED Number of data octets received from the remote station. SDU OCTETS SENT Number of data octets sent to the remote station. SDUS RECEIVED Number of data messages received from the remote station not including retransmissions. SDUS SENT Number of data messages sent to the remote station not including retransmissions. SELECTION ERROR THRESHOLDS REACHED Number of times that the selection error threshold has been reached. This counter is not supported if the characteristic protocol of the owning ddcmp link entity is set to tributary. SELECTION INTERVALS Number of times that the local station selected the remote or a tributary station. The counter does not appear if the link uses the tributary protocol. In addition, the counter appears only when the local station is the control station for a number of tributaries, or is operating over a half-duplex, point-to-point link. This counter is supported only if the protocol characteristic of the owning ddcmp link entity is set to control, or when the link is a half-duplex, point-to-point link. SEND ERROR THRESHOLDS REACHED Number of times that the send error threshold has been reached. STRTS RECEIVED WHILE IN MAINTENANCE Number of times that the local station received a STRT protocol message while in the Maintenance state. 3 status =title Status Attributes POLLING SUBSTATE State of a tributary as determined by the polling algorithm. This attribute applies only when the value of the link's protocol characteristic is set to control. The value of this attribute is affected by the value of the characteristic polling state. If the characteristic polling state is set to automatic, the value of this status attribute reflects the current state of the polling algorithm. For all other values of the polling state characteristic, the values of both attributes are the same. ACTIVE - The tributary is active and responds with data when selected. DEAD - The tributary did not respond when selected within the appropriate timeout period, when already in the Dying or Inactive state. The tributary will be ignored until the station reinitializes. DYING - The tributary, currently in the Inactive or Active state, has not responded within the appropriate timeout period when selected. INACTIVE - The tributary has not sent any data when selected by the control station. However, the tributary has responded with an appropriate message when selected. PROTOCOL STATE State of the data link protocol with the remote station. HALTED - The protocol is stopped and no messages are being exchanged with the remote station. RUNNING - The protocol is on line and is exchanging messages with the remote station. STARTING - There is an attempt to initialize the protocol between the local and remote stations. This uses the STRT and STACK PDUs. MAINTENANCE - The protocol is off line and dealing with maintenance messages only. STATE Operational state of the local logical station. OFF - The station is disabled. ON - The station is enabled. 2 port =title DDCMP PORT A DDCMP port entity represents an access point to the Data Link layer service offered by ddcmp. Ports are created and deleted automatically when a client of DDCMP uses the link. 3 status =title Status Attributes CLIENT Name of the client entity. LINK Name of the DDCMP link that the client is using. LOGICAL STATION Name of the DDCMP link logical station supplied by the client when the port was opened. STATE State of the port. OPEN - The port is assigned to a client. OPEN DISABLED - The port is assigned to a client, but the link or logical station entity used by the port is disabled. CALL ATTACHED - The port is assigned to a client and the link is associated with the current call on the line. Applies only when the link operates over a switched line. TYPE Type of port. NORMAL - For normal data communications. SERVICE - For service operations. This is the value that modules