A Carrier Sense Multiple Access with Collision Detection CSMA/CD Local Area
Network LAN provides high-speed communications channels for connecting
computers and other digital devices located within a moderate-sized
geographic area. Like other LANs, the CSMA/CD LAN falls between
long-distance, low-speed networks that carry data for hundreds or thousands
of kilometers, and specialized, high-speed intercommunications that are
generally limited to tens of meters. The CSMA/CD LAN is intended primarily
for use in such areas as office automation, distributed data processing,
terminal access, distributed systems, and other situations that require
economical connection to a local communication medium with sporadic traffic
at high-peak data rates.
The entities that constitute the CSMA-CD module are listed below. The
indentation indicates the hierarchical relationships between the entities.
CSMA-CD
Port
Station
The CSMA/CD module incorporates the functions and operations defined in
the Ethernet Specification V2.0 and the ISO 8802-3 IEEE 802.3 CSMA/CD
Access Method and Physical Layer specification as well as parts of the ISO
8802-1 IEEE 802.1 Addressing, Internetworking, and Network Management and
the ISO 8802-2 IEEE 802.2 Logical Link Control specifications. To this,
the CSMA-CD module adds features often needed by users of the Data Link.
A typical such Data Link user is the Network Layer.
The CSMA-CD entity is the top-level entity in the hierarchy of entities
belonging to the CSMA-CD module.
1 – character
VERSION
Version number of the CSMA/CD Data Link architecture specification
to which the implementation conforms. You cannot modify this
characteristic.
2 – port
A CSMA-CD Port entity represents an access point to the service offered by the CSMA-CD module. A client transmits and receives data through a port. Ports are created and deleted by client use of open and close service interface procedures.
2.1 – counters
Unless stated otherwise, counts include both normal and multicast traffic
and all protocol types, service access points SAPs, and protocol identifiers.
MULTICAST OCTETS RECEIVED
Number of multicast data octets that were successfully received and
made available to the port user. The count is the number of octets in
the CSMA/CD user data field and does not include MAC medium access
control, a sublayer of the CSMA/CD Data Link layer headers. Comparing
this count to the octets received count yields the gross percentage
of bandwidth that was consumed over time by multicast PDUs received
by the port.
MULTICAST OCTETS SENT
Number of multicast data octets that were successfully sent through the
port. The count is the number of octets in the MAC user data field,
including any padding or length fields; it does not include MAC
headers. Comparing this count to the octets sent count yields the
gross percentage of bandwidth that was consumed over time by multicast
PDUs transmitted by the port.
MULTICAST PDUS RECEIVED
Number of multicast PDUs that were successfully received and made
available to the port user. Counted PDUs passed address and protocol
filtering and were received without errors. Comparing this count to the
PDUs received count yields a gross percentage of CSMA/CD usage for
multicast pdus received by this port.
MULTICAST PDUS SENT
Number of multicast PDUs that were successfully sent through the port.
Comparing this count to the PDUs sent count yields a gross percentage
of CSMA/CD usage for multicast PDUs sent by this port.
OCTETS RECEIVED
Total number of MAC user data octets that were successfully received
and made available to the port user. Counted frames passed address and
protocol filtering for both individual and multicast MAC addresses and
were received without errors. The count is the number of octets in the
CSMA/CD user data field plus any padding, Ethernet length fields, or
logical link control LLC header fields; it does not include MAC
headers. Adding the octets received count to the protocol overhead
calculated from the pdus received count yields the amount of CSMA/CD
bandwidth consumed by frames received by the port.
OCTETS SENT
Total number of user data octets that were successfully sent through
the port. The count is the number of octets in the MAC user data field
including any padding or length fields; it does not include MAC headers.
Adding the octets sent count to the protocol overhead calculated from
the PDUs sent count yields the amount of CSMA/CD bandwidth consumed
over time by frames sent by the port.
PDUS RECEIVED
Total number of PDUs that were successfully received and made available
to the port user. Counted PDUs passed address and protocol filtering
and were received without errors. The count provides a gross
measurement of incoming CSMA/CD usage by the port.
PDUS SENT
Total number of PDUs that were successfully sent through the port. The
count provides a gross measurement of outgoing CSMA/CD usage by the
port.
UNAVAILABLE USER BUFFERS
Number of times that no user buffer was available at the port for an
incoming frame that passed all filtering for the port. Used in
conjunction with the PDUs received count, this counter can indicate
the rate of user buffer receive problems.
2.2 – status
CLIENT
Name specified by the data link user when the port was opened.
ETHERNET PROTOCOL TYPES
Set of Ethernet protocol types that are currently recognized for this
port.
LENGTH PRESENT
The data link adds a length field on transmit frames, and assumes the
presence of a length field and attempts to remove it on received
Ethernet frames. When false, the data link does not add and remove
length fields. This attribute is irrelevant for ISO 8802-3 formatted
frames, which always have a length field.
TRUE - The data link adds and removes length fields.
FALSE - The data link does not add and remove length fields.
LLC SAP ADDRESSES
Set of individual and group logical link control LLC service access
point SAP addresses that are currently recognized for this port.
LLC SERVICE
Type of LLC logical link control PDU processing that is required on
the port as defined by the user when the port was opened.
CLASS 1 - The data link provides class 1, type 1 service.
USER-SUPPLIED - The user is responsible for handling the LLC protocol.
MAC ADDRESSES
Set of individual and multicast MAC medium access control addresses
that are currently recognized for this port.
RECEIVE MODE
Type of receive mode that is currently enabled for the port.
NORMAL - The port receives only those frames that meet the
normal address and protocol filtering requirements
requested by the user.
PROMISCUOUS - The port receives all frames regardless of format and
MAC address.
SNAP PROTOCOL IDENTIFIERS
Set of subnetwork access protocol SNAP identifiers that are currently
recognized for this port.
STATION
Name of the station associated with this port as specified by the user
when the port was opened.
3 – station
A CSMA-CD station entity manages a CSMA/CD controller. Wherever Phase IV DECnet manages a line, DECnet-Plus manages a station. Each station corresponds to a particular logical link control LLC, medium access control MAC, and physical attachment. The station name refers to the station managed by this command.
3.1 – character
STATION BUFFERS
Number of receive buffers reserved for the station. You can modify
this characteristic only when the entity is disabled.
3.2 – counters
Unless stated otherwise, counts include both normal and multicast traffic and
all protocol types, service access points SAPs, and protocol identifiers.
ALIGNMENT ERRORS
Number of times a received frame did not contain an integral number of
octets.
CARRIER CHECK FAILURES
Number of times the data link did not sense the receive carrier signal
or detected an error in the receive carrier signal during transmission
of a frame.
COLLISION DETECT CHECK FAILURES
Number of times the collision detect test signal was not sensed after
a transmission. If this count approximates the number of frames sent,
either the collision detect circuitry is not working correctly or the
test signal is not implemented.
DATA OVERRUNS
Number of times the hardware lost one or more consecutive, partially
complete, incoming frames because it could not keep up with the
incoming frame rate. Used in conjunction with pdus received, this
count provides a measure of hardware resource and bandwidth failures.
EXCESSIVE COLLISIONS
Number of times a transmission failed because the maximum allowable
number of retransmission attempts all culminated in collisions.
FRAME CHECK ERRORS
Number of times a received frame containing an integral number of
octets failed the frame check sequence FCS.
FRAME SIZE ERRORS
Number of times the user requested transmission of a frame outside the
range of valid frame sizes.
FRAMES TOO LONG
Number of times a received frame exceeded the maximum length allowed
by CSMA/CD medium access control.
INITIALLY DEFERRED PDUS SENT
Number of times a PDU was deferred by the station access algorithm on
the first attempt at transmission, but was then transmitted
successfully without collision. Used in conjunction with PDUs sent,
this count measures the rate of CSMA/CD contention with no collisions.
LATE COLLISIONS
Number of times a collision was detected after the allotted time for
collisions had expired.
MULTICAST OCTETS RECEIVED
Number of multicast data octets that were successfully received. The
count is the number of octets in the CSMA/CD user data field and does
not include MAC headers. Comparing this count to the octets received
count yields the gross percentage of bandwidth that was consumed over
time by multicast frames received by the local system.
MULTICAST OCTETS SENT
Number of multicast data octets that were successfully sent. The count
is the number of octets in the MAC user data field, including any
padding or length fields; it does not include MAC headers. Comparing
this count to the octets sent count yields the gross percentage of
bandwidth that was consumed over time by multicast frames
transmitted by the local system.
MULTICAST PDUS RECEIVED
Number of multicast PDUs that were successfully received. Comparing
this count to the pdus received count yields a gross percentage of
CSMA/CD usage for multicast PDUs received by this system.
MULTICAST PDUS SENT
Number of multicast PDUs that were successfully sent. Comparing this
count to the pdus sent count yields a gross percentage of CSMA/CD
usage for multicast PDUs sent by this system.
MULTIPLE COLLISIONS PDUS SENT
Number of times a PDU was successfully transmitted on the third or
later attempt by the station access algorithm after normal collisions
on previous attempts. Used in conjunction with pdus sent, this count
provides a measure of CSMA/CD media contention at a level where there
are collisions and the backoff algorithm no longer works efficiently.
OCTETS RECEIVED
Total number of MAC user data octets that were successfully received
from frames that passed address and protocol filtering for both
individual and multicast MAC addresses. The count is the number of
octets in the CSMA/CD user data field plus any padding, Ethernet
length fields, or LLC header fields; it does not include MAC
headers. Adding the octets received count to the protocol overhead
calculated from the pdus received count yields the amount of CSMA/CD
bandwidth consumed by frames received by the local system.
OCTETS SENT
Total number of user data octets that were successfully sent. The
count is the number of octets in the MAC user data field including any
padding or length fields; it does not include MAC headers. Adding the
octets sent count to the protocol overhead calculated from the pdus
sent count yields the amount of CSMA/CD bandwidth consumed over time
by frames sent by the local system.
PDUS RECEIVED
Total number of PDUs that passed address and protocol filtering and
were received without errors. The count provides a gross measurement
of incoming CSMA/CD usage by the local system; this information can be
used in conjunction with other counters to approximate the average
receive frame size or to determine the ratio of errors to successful
receives.
PDUS SENT
Total number of PDUs successfully sent. The count provides a gross
measurement of outgoing CSMA/CD usage by the local system; this
information can be used in conjunction with other counters to
approximate the average transmit frame size or to determine the ratio
of errors to successful transmissions.
RECEIVE DATA LENGTH ERRORS
Number of times a frame was received with a length field value that was
invalid for the number of octets actually received by medium access
control.
SEND DATA LENGTH ERRORS
Number of times the user requested transmission of an 802.3 frame with
a length field value that was not valid for the number of octets
actually passed.
SINGLE COLLISION PDUS SENT
Number of times a PDU was successfully transmitted on the second
attempt by the station access algorithm after a normal collision
occurred on the first attempt. Used in conjunction with pdus sent,
this count provides a measure of CSMA/CD media contention at a level
where there are collisions, but the backoff algorithm still works
efficiently.
STATION FAILURES
Number of times that the station self-testing procedures reported
failure.
UNAVAILABLE STATION BUFFERS
Number of times a complete, fully received PDU was discarded because
no station buffer was available. Used with pdus received, this count
provides a measure of receive problems related to the station buffer.
UNAVAILABLE USER BUFFERS
Number of times no user buffer was available for an incoming frame that
passed all filtering for the port. Used in conjunction with the pdus
received count, this counter can indicate the rate of user buffer
receive problems.
UNRECOGNIZED INDIVIDUAL DESTINATION PDUS
Number of times a received PDU with an individual destination MAC
address was discarded because there was no port with the correct
Ethernet protocol type, SNAP protocol identifier, or link logical
control SAP address enabled.
UNRECOGNIZED MULTICAST DESTINATION PDUS
Number of times a received PDU with a multicast destination MAC
address was discarded because there was no port with the correct
Ethernet protocol type, SNAP protocol identifier, or link logical
control SAP address enabled.
3.3 – status
ADDRESS FILTERS
All individual MAC addresses currently enabled by any of the ports on
the station.
COMMUNICATION PORT
DECnet-Plus device name for the station.
HARDWARE ADDRESS
Individual medium access control MAC address that was assigned during
manufacture of the communications hardware that is associated with the
station.
MAC ADDRESS
Current MAC address if any of the station. For more information about
the MAC address, refer to the enable command.
RECEIVE MODE
Current receive mode for the station. Some stations may not support
all modes.
NORMAL - The station receives only those frames individual and
multicast that meet the normal format, protocol, and
access control requirements.
ALL MULTICAST - The station receives all individual-addressed frames
that meet the normal format, protocol, and address
requirements, and all multicast-addressed frames
regardless of their format, protocol, and address
types.
PROMISCUOUS - The station receives all frames individual and
multicast regardless of format, Ethernet protocol
type, SNAP identifier, LLC SAP address, or MAC
address.
STATE
Operational state of the station.
OFF - The station is disabled.
ON - The station is enabled and available for use.
FAILED - Either an attempt to enable the station failed during
the self-test or the station was on and the data link
determined that the station would now fail the
self-test.
INITIALIZING - The station is currently being initialized and tested
by the data link.