QoS on Frame Relay (Per-PVC Queuing)
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Alcatel-Lucent
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OmniAccess 5740 Unified Services Gateway CLI Configuration Guide
QOS ON FRAME RELAY (PER-PVC QUEUING)
Frame Relay provides an unreliable, connection-oriented service to the user. It
means that a Virtual Circuit (VC) has to be established before any data can be
sent, but network does not give any guarantee that the data will be delivered to
the destination.
One of Frame Relay's main benefits is that it makes a pool of bandwidth available
to many VCs. However, there is a danger that some applications consume all of
the available bandwidth leaving nothing or only small amount of bandwidth to
other applications. To prevent this, FR interface has to be configured with QoS.
The purpose of QoS is to provide fair access to the network's bandwidth by all the
user applications and ensure that the key applications are not starved of required
bandwidth.
Consider an interface with available bandwidth as 64 Kbit/s. Application A needs
much of the bandwidth most of the time and application B needs only a small
amount of the bandwidth every now and then.
In this scenario, without QoS on the interface, application A will consume all the
available bandwidth leaving nothing or only small amount of bandwidth to
application B. With QoS applied on the interface, you can allocate 48 Kbit/s
bandwidth to application A, and 16 Kbit/ bandwidth to application B. This
arrangement provides guaranteed access and required bandwidth for both the
applications.
QOS ON FR AND FR SUB INTERFACE
QoS can be configured on FR and FR sub interface (Serial Interface with Frame-
Relay encapsulation).
On meshed FR networks, FR provides a mechanism to allow a physical interface
(i.e., FR) to be partitioned into multiple virtual interfaces (i.e., PVC). The actual
bandwidth of the physical interface is shared by all the virtual interfaces. This
allows packets to be received on a physical interface and to be sent out from the
same physical interface, but it will be forwarded to different sub-interface. Packets
on each virtual interface will be distinguished based on the DLCI number. So, the
total sum of the packets received on the interface/sub-interface will always be less
than or equal to the bandwidth capacity of the FR interface. The sub-interface will
always use the physical interfaces’ resource to send and receive the packets. One
of the examples is credit limit.
Note: Currently, maximum 16 sub-interfaces can be created on a FR interface. So, there will
be 17 PVCs (including the main interface) on a FR interface.
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