Juniper Networks G10 CMTS manual Data Path Processing, Downstream Data Path

Data Path Processing

•Data Path Processing

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•	This section describes the data path processing of the downstream and upstream traffic
•	flows.
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•	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.
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•Downstream Data Path

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•	Following is a description of the flow of a packet through the downstream data path of a
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	DOCSIS Module:
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•	1. A packet is received on the Gigabit Ethernet interface of a NIC Module and is forwarded
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		to a DOCSIS Module over a Fast Ethernet connection.
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•	2. If you have configured and applied a subscriber management input filter, the packet is
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		evaluated based on the filter configuration and is either dropped or passed.
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•	3.	If the packet is not dropped by the input filter, it is classified to an ingress logical
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		interface (unit) and either bridged (Layer 2) or forwarded (Layer 3), depending on the
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		configuration of the ingress unit, to the egress unit.
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•	4. The packet is classified to a service flow based on its header.
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•	5.	If you have configured and applied a subscriber management or IEEE 802.1 output filter,
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		the packet is evaluated based on the filter configuration and is either dropped or passed.
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•	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
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	you have configured. If you have configured a congestion management policy, the
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	packet might be dropped, depending on its projected queue traversal latency.
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•	7. The packet is transmitted to the HFC network on the physical interface associated with
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	the egress unit.
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62 JUNOSg 3.0 G10 CMTS Hardware Guide