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Cisco SCE 8000 10GBE Software Configuration Guide
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Chapter 14 Value-Added Services (VAS) Traffic Forwarding
How VAS Traffic Forwarding Works
VAS Traffic Forwarding and SCA BB
When VAS traffic forwarding is enabled, in addition to all its basic functions, the SCA BB application
classifies each flow as either a VAS flow or as a standard flow (non-VAS flow). This classification is
made on the first packet of the flow (for example, TCP SYN packet). The classification must be
performed on the very first packet because the classification is used to select the routing of the packet to
a VAS server or to the subscriber or network.
The VAS traffic forwarding rules table is configured using the SCA BB console. These rules map certain
traffic to the VAS server groups. When a flow is classified as a VAS flow, the VAS server group for this
flow is selected. If the group includes more than one VAS server, traffic is forwarded so that the
subscriber load is shared between the servers on the same group.
The mapping of traffic portions per package to VAS server groups is also done using the SCA BB
console.
VLAN Tags for VAS Traffic Forwarding
The traffic is routed between the Cisco SCE platform and the VAS servers by VLANs. There is a unique
VLAN tag for each Cisco SCE platform and VAS server combination.
Before the traffic is forwarded to the VAS servers, the Cisco SCE platform adds the VLAN tags to the
original traffic. When the traffic returns to the Cisco SCE platform, the Cisco SCE platform removes the
VLAN tag it previously added, and then forwards the traffic on its original link.
The VLAN tag for each VAS server is user-configured. To preserve consistency of the traffic flow, the
VAS feature requires a unique VLAN tag be configured for each Cisco SCE platform and VAS server
combination.
The VLAN tag has 12 bits, divided as follows:
•
The lower six bits identify the VAS server.
•
The higher six bits identify the Cisco SCE platform.
For example, 0x171 = 1011 10001 = SCE 11, VAS 17
Observe the following for the six bits that identify the Cisco SCE platform:
•
These six bits must be the same for all VAS servers attached to a specific Cisco SCE platform.
•
These six bits must be different for VAS servers attached to different Cisco SCE platforms.
The Cisco SCE platform enforces that the user-configured VLAN tags retain this format, that is, the
lower bits match the VAS server number for which the VLAN tag is configured and the higher bits match
the higher bits previously configured for other VAS servers on this Cisco SCE platform. However, the
Cisco SCE platform cannot determine the configuration of other Cisco SCE platforms, and therefore, it
is important that the configured Cisco SCE ID (higher bits) be unique for each Cisco SCE platform.
The use of VLAN tags is an integral part of the VAS feature, and therefore, requires that the VAS device
be able to work in 802.1q trunk while preserving the VLAN information.
Service Flow
The Cisco SCE platform classifies a flow to a VAS server group based on the subscriber package and the
TCP/UDP ports of the flow. It then selects one server within this group to handle the flow.
