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Data Path – Ingress
Incoming packets are validated according to:
•
Correct Packet Format; Ethernet frame format as per IEEE 802.3 including:
•
802.3
•
802.1Q
•
Multiple stacked VLAN
•
Ethernet frame encapsulating MPLS payload (e.g. According to the Martini draft)
•
Packet Size
•
Minimum – 64 Bytes
•
Maximum – 1600 Bytes
•
Valid CRC
The network processor processes only valid frames and discards the invalid frames. The first stage of
processing is packet classification. Frame classification is used to identify:–
•
The service to which this frame belongs. Frame destination or set of destinations depends on
the service type. This is defined in the provisioning process.
•
Identify the frame priority. This will determine the precedence and delay with which it will be
forwarded to the ISA–PR port card. Frames will be classified into one of three available CoS
(Class of Service) queues defined as high, medium or low.
For further information with regard to service definitions and QoS mechanisms in the ISA–PR, please refer
to 3.7 on page 245 and 4.35 on page 507.
Following frame classification, the network processor performs frame editing. Frame editing refers to the
appending or swapping of a tag for identification purposes. The following functions are currently
supported.
•
Append MPLS tag to identify the service and priority to which the frame belongs. This
information is used by other network elements in network – always
•
Strip Martini header – optional
•
Append, Swap or Strip VLAN – optional
The network processor forwards validated and edited frames to the port card (ISA–PR) for transmission
to the destination access cards. Payload information is passed between the access card and port card
via two 1Gbps backplane channels.
Data Path – Egress
The first part of the egress process takes part on the port card. For further details, please refer to and
4.35 on page 507.
Frames that have been designated for delivery to client ports are delivered from the port card to the
relevant access card over two 1Gbps backplane channels.
The network processor handles the buffering of frames until they can be forwarded over the appropriate
Ethernet interface. Delivery of frames is according to bandwidth availability and frame priority.
Prior to emitting a frame network processor applies frame editing as follows:
•
Strip MPLS tag, which has been used to identify the service and priority to which the frame
belongs at the ring – always
•
Append Martini header – optional
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