Cisco Cisco IOS Software Release 12.1(7)CX
Feature Overview
4
DOCSIS 1.1 for Cisco uBR7200 Series Universal Broadband Routers
Cisco IOS Release 12.1(7)CX1
DOCSIS 1.1 Quality of Service
The DOCSIS 1.1 QoS framework is based on the following objects:
•
Service class—A collection of settings maintained by the CMTS that provide a specific QoS service
tier to a cable modem that has been assigned a service flow within a particular service class.
tier to a cable modem that has been assigned a service flow within a particular service class.
•
Service flow—A unidirectional sequence of packets receiving a service class on the DOCSIS link.
•
Packet classifier—A set of packet header fields used to classify packets onto a service flow to which
the classifier belongs.
the classifier belongs.
•
PHS rule—A set of packet header fields that are suppressed by the sending entity before transmitting
on the link, and are restored by the receiving entity after receiving a header-suppressed frame
transmission. Payload Header Suppression increases the bandwidth efficiency by removing repeated
packet headers before transmission.
on the link, and are restored by the receiving entity after receiving a header-suppressed frame
transmission. Payload Header Suppression increases the bandwidth efficiency by removing repeated
packet headers before transmission.
In DOCSIS 1.1, the basic unit of QoS is the service flow, which is a unidirectional sequence of packets
transported across the RF interface between the cable modem and CMTS. A service flow is characterized
by a set of QoS parameters such as latency, jitter, and throughput assurances.
transported across the RF interface between the cable modem and CMTS. A service flow is characterized
by a set of QoS parameters such as latency, jitter, and throughput assurances.
Every cable modem establishes a primary service flow in both the upstream and downstream directions.
The primary flows maintain connectivity between the cable modem and CMTS at all times.
The primary flows maintain connectivity between the cable modem and CMTS at all times.
In addition, a DOCSIS 1.1 cable modem can establish multiple secondary service flows. The secondary
service flows either can be permanently created (they persist until the cable modem is reset or powered
off) or can be created dynamically to meet the needs of the on-demand traffic being transmitted.
service flows either can be permanently created (they persist until the cable modem is reset or powered
off) or can be created dynamically to meet the needs of the on-demand traffic being transmitted.
Each service flow has a set of QoS attributes associated with it. These QoS attributes define a particular
class of service and determine characteristics such as the maximum bandwidth for the service flow and
the priority of its traffic. The class of service attributes can be inherited from a preconfigured CMTS
local service class (class-based flows), or they can be individually specified at the time of the creation
of the service flow.
class of service and determine characteristics such as the maximum bandwidth for the service flow and
the priority of its traffic. The class of service attributes can be inherited from a preconfigured CMTS
local service class (class-based flows), or they can be individually specified at the time of the creation
of the service flow.
Each service flow has multiple packet classifiers associated with it, which determine the type of
application traffic allowed to be sent on that service flow. Each service flow can also have a Payload
Header Suppression (PHS) rule associated with it to determine which portion of the packet header will
be suppressed when packets are transmitted on the flow.
application traffic allowed to be sent on that service flow. Each service flow can also have a Payload
Header Suppression (PHS) rule associated with it to determine which portion of the packet header will
be suppressed when packets are transmitted on the flow.