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How VAS Traffic Forwarding Works
VAS Data Flow
VAS data flow is slightly more complex than the basic data flow. It is received and transmitted in the
same manner as the basic non-VAS SCE platform flow, but before it is transmitted to its original
destination, it flows through the VAS server.
The flow steps are:
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Load Balancing
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VAS servers can be grouped logically according to their service type. Consider, for example, a system
that requires both FTP caching and virus filtering. A single VAS server for each service might not have
enough capacity. Let us say that the system requires five VAS servers, three to provide FTP caching, and
two to provide virus filtering. Defining two VAS Server Groups, FTP caching and virus filtering, permits
load sharing across the servers for each Server Group.
The VAS Server Group to which the flow should be attached is determined by the package of the
subscriber. The selection of a specific VAS server from the VAS servers within this group is based on
the current load on each VAS server. The system tries to create an equal subscriber load for all the VAS
servers belonging to the same group.
In some cases, a VAS server may be used by more than one SCE platform. Remember that the SCE
platform performs load balancing only on the traffic that it sends to the VAS server; it is not aware how
much of a load the VAS server may be bearing from a different SCE platform. It is the responsibility of
the user to allocate available VAS servers to the SCE platforms in a way that ensures proper total load
on each VAS server.
Cisco SCE 2000 and SCE 1000 Software Configuration Guide
12-8
A subscriber packet is received at the SCE platform port 1 (S).
The SCE platform classifies the flow as VAS flow.
The SCE platform adds a VLAN tag to the packet.
The VLAN tag is used by the Ethernet switch to route the packet to the proper VAS server.
Note that at this point the packet has a VLAN tag, which is indicated by the red line.
The packet is sent to the VAS subscriber port from SCE platform port 4 (N).
The VAS server processes the packets and either drops the packet or sends it back to the SCE
platform; from the VAS network port to the SCE platform subscribers port 3 (S).
Note that the VAS server passes the VLAN tag transparently. This is important to enable the Ethernet
switch (not shown) to route the packet back to the proper SCE platform.
The SCE platform receives the packet on port 3 (S), drops the VLAN tag, and passes the packet
towards the network through port 2 (N).
Load Balancing and Subscribers, page 12-9
Load Balancing and Subscriber Mode, page 12-9
Chapter 12
Value Added Services (VAS) Traffic Forwarding
OL-7827-12
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