Quality of Service Guide QoS and QoS Policies
Edition: 01 3HE 11014 AAAC TQZZA 45
In this example, the cell site 7705 SAR is dual-homed to 7750 SR_1 and SR_2 at the
MTSO, using two disjoint Ethernet virtual connections (EVCs) leased from a
transport provider. Typically, the EVCs have the same capacity and operate in an
forwarding/standby manner. One of the EVCs—the 7750 SR—transports all the
user/mobile traffic to and from the cell site at any given time. The other EVC
transports only minor volumes of control plane traffic between network elements (the
7705 SAR and the 7750 SR). Leasing two EVCs with the same capacity and using
only one of them actively wastes bandwidth and is expensive (the mobile operator
pays for two EVCs with the same capacity).
Mobile operators with increasing volumes of mobile traffic look for ways to utilize both
of the EVCs simultaneously, in an active/active manner. In this case, using per-VLAN
shapers would ensure that each EVC is loaded up to the leased capacity. Without
per-VLAN shapers, the 7705 SAR supports a single per-port shaper, which does not
meet the active/active requirement.
• If the egress rate is set to twice the EVC capacity, then either one of the EVCs
can end up with more traffic than its capacity.
• If the egress rate is set to the EVC capacity, then half of the available bandwidth
can never be consumed, which is similar to the 7705 SAR having no per-VLAN
egress shapers.
Figure 6 VLAN Shapers for Dual Uplinks
Backhaul
Infrastructure
7750 SR_2
VPRN
Ethernet
VC-2
Ethernet
VC-1
Cell Site
7705 SAR
7750 SR_1
MTSO
VPRN
24355
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