Another typical use of per-VLAN shapers at network egress is shown in Figure: VLAN Shapers in Aggregation Site Scenario. The figure shows a hub-and-spoke mobile backhaul network where EVCs leased from a transport provider are groomed to a single port, typically a 10-Gigabit Ethernet or a 1-Gigabit Ethernet port, at the hand-off point at the hub site. Traffic from different cell sites is handed off to the aggregation node over a single port, where each cell site is uniquely identified by the VLAN assigned to it.
In the network egress direction of the aggregation node, per-VLAN shaping is required to ensure traffic to different cell sites is shaped at the EVC rate. The EVC for each cell site would typically have a different rate. Therefore, every VLAN feeding into a particular EVC needs to be shaped at its own rate. For example, compare a relatively small cell site (Cell Site-1) at 20 Mb/s rate with a relatively large cell site (Cell Site-2) at 200 Mb/s rate. Without the granularity of per-VLAN shaping, shaping only at the per-port level cannot ensure that an individual EVC does not exceed its capacity.
