DOCSIS3.0-DSID

DOCSIS3.0-DSID:

    A DSID is a 20-bit value contained in a Downstream Service Extended Header (DS EHDR) on a frame that
identifies a stream of packets to a set of CMs (ref: DS EHDR Section 6.2.5.6).

    The CM uses the DSID for purposes of downstream resequencing, filtering, and forwarding.

A DSID value communicated to the CM by the CMTS is said to be "known" by the CM.

Any DSID value not communicated to a CM is considered to be "unknown" by the CM.

The CMTS inserts a Downstream Service Extended Header (DS EHDR) on each sequenced downstream packet to
provide the DSID value and the packet’s sequence number specific to that DSID. The use of a DSID to identify a
particular packet stream sequence allows DOCSIS 3.0 CMs to filter downstream packets based on the DSID value
and resequence only those packets intended to be forwarded through the CM.

    The CMTS labels all packets of a multicast session with a DSID, and communicates that DSID to the set of CMs
that are intended to forward that session. DOCSIS 3.0 CMs will only forward multicast traffic that is labeled with a
known DSID. In order to reach all the intended recipients, the CMTS replicates a multicast packet as necessary
among the downstream channels of a MAC Domain. The CMTS inserts a DS EHDR on multicast packets to
provide the DSID which identifies the CM or set of CMs that will forward a particular replication of a multicast
session.

A DSID used to provide sequenced delivery of packets, and hence to identify a resequencing context in the CM, is
termed a Resequencing DSID. A DSID used to label multicast packets is termed a Multicast DSID. A DSID can be
used simultaneously for both purposes (e.g., sequenced multicast delivery).
The stream of packets identified by a DSID is independent of a CMTS service flow. For example, the CMTS may
transmit packets labeled with the same DSID for one or more Individual Service Flows forwarded to the same CM.
Alternatively, the CMTS may classify different IP multicast sessions each with different DSIDs to the same
"Group" Service Flow (Section 7.5.8).
A CMTS communicates DSIDs to CMs with the following messages:
• The MDD message contains a "Pre Registration DSID" intended for pre-registration downstream multicasts
Section 6.4.28.1.5;
• The REG-RSP or REG-RSP-MP message contains DSID Encodings that define an initial set of DSIDs to be
recognized by the CM (see Annex C.1.5.3.8);
• The DBC-REQ message dynamically updates the set of DSIDs recognized by the CM after registration (add,
delete, or modify), see Section 11.4.1.2.
The CMTS MUST assign DSID values uniquely per MAC Domain. This simplifies operational reporting of DSIDs
by the CMTS. DSID values are intended to be internally assigned by the CMTS, and not externally assigned by an
OSSI application.
The CM MUST report the total number of DSIDs it supports for filtering purposes (Annex C.1.3.1.30). The CM
also MUST report the number of Resequencing DSIDs (Annex C.1.3.1.31) and the number of Multicast DSIDs
supported (Annex C.1.3.1.32). The CM MUST support one DSID-Indexed Payload Header Suppression Rule on
each Multicast DSID supported. The CM MUST report at least 32 Total DSIDs, 16 Resequencing DSIDs, and 16
Multicast DSIDs. If the CM reports values larger than the minimum for any of the DSID capabilities, the Total
DSIDs may be less than the sum of the Resequencing DSIDs and Multicast DSIDs to allow for CM optimization of
resource utilization.
The CMTS MUST NOT signal a CM to add more DSIDs than the CM reports in the Total Downstream Service ID
Support capability encoding (Annex C.1.3.1.30). The CMTS MUST NOT signal a CM to add more Resequencing
DSIDs than the CM reports in the Resequencing Downstream Service ID Support capability (Annex C.1.3.1.31).
The CMTS MUST NOT signal a CM to add more Multicast DSIDs than the CM reports in the Multicast
Downstream Service ID (DSID) Support capability encoding (Annex C.1.3.1.32).