Data Path Processing; Downstream Data Path - Juniper G10 CMTS Hardware Manual

Data Path Processing

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Downstream Data Path

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62 JUNOSg 3.0 G10 CMTS Hardware Guide
This section describes the data path processing of the downstream and upstream traffic
flows.
Packets that enter the CMTS from the network-side interface (NSI) and are destined for the
HFC network are processed through the downstream path. Packets that enter the CMTS from
the HFC network and are destined to either the NSI or the HFC network are processed
through the upstream path. See Figure 22 on page 64 for a graphical depiction of the data
flow through the modules in a chassis.
Following is a description of the flow of a packet through the downstream data path of a
DOCSIS Module:
1. A packet is received on the Gigabit Ethernet interface of a NIC Module and is forwarded
to a DOCSIS Module over a Fast Ethernet connection.
2. If you have configured and applied a subscriber management input filter, the packet is
evaluated based on the filter configuration and is either dropped or passed.
3. If the packet is not dropped by the input filter, it is classified to an ingress logical
interface (unit) and either bridged (Layer 2) or forwarded (Layer 3), depending on the
configuration of the ingress unit, to the egress unit.
4. The packet is classified to a service flow based on its header.
5. If you have configured and applied a subscriber management or IEEE 802.1 output filter,
the packet is evaluated based on the filter configuration and is either dropped or passed.
6. If the packet is not dropped by the output filter, it is sent to QoS processing, where it is
ordered and scheduled based on its QoS parameters and the traffic scheduling policy
you have configured. If you have configured a congestion management policy, the
packet might be dropped, depending on its projected queue traversal latency.
7. The packet is transmitted to the HFC network on the physical interface associated with
the egress unit.