Chapter 72: Virtual ports
Overview
Purpose
A 7750 SR can act as a Broadband Network Gateway (BNG), fairly distributing bandwidth among the subscriber host sessions by accounting for the packet encapsulation overhead and ATM bandwidth expansion for each type of broadband session. In this way, subscriber packets are less likely to be dropped downstream in the DSLAM DSL port. Furthermore, the BNG shapes the aggregate rate of each subscriber and the aggregate rate of all subscribers destined to a given DSLAM to prevent congestion of the DSLAM.
In the BNG application, when a set of per FC queues are applied to each subscriber host context, the host per FC queue packet rate is overridden by the rate provided in the Radius access-accept message. This rate represents the ATM rate that will be seen on the last mile and includes the encapsulation offset and the per packet expansion due to ATM segmentation into cells at the BSAN.
In order to enforce the aggregate rate of each destination BSAN, a virtual port must be configured. Virtual ports are scheduling nodes that operate like port schedulers, with the exception that multiple virtual ports can be created on the egress context of an access/hybrid Ethernet port. A virtual port and a port scheduler cannot exist simultaneously on a single port.
Virtual ports can be configured on a port that is a member of a LAG. When a virtual port is created, modified, or deleted on the primary port of a LAG, this action is replicated on all other ports within the LAG. These actions can only be performed on the primary port. When a port is added to a LAG, it must have the same virtual ports defined as the existing ports on the LAG. The name of a virtual port is local to the port on which it is applied, but must be the same for all member ports of a LAG.
Virtual ports are supported on Ethernet ports on IOM3/IMM on the 7750 SR, 7750 SR-c4, and 7450 ESS.
Virtual ports are not supported on the 7750 SR-1 and the 7450 ESS-1, HSMDA Ethernet ports, or VSM MDA.
Virtual port statistics can be collected and displayed for all queues forwarding to a virtual port configured on an egress of an Ethernet port. This is only supported on an 7750 SR or 7450 ESS equipped with a 2 x XP MDA IOM-3. The collected data is available on the Statistics tab of the Egress Scheduling Virtual Port properties form.
SLA Profiles
A subscriber host queue with the port-parent option enabled can be scheduled within the context of a port scheduler policy associated with a port or a virtual port. To specify that a subscriber host queue with the port-parent option enabled be scheduled within the context of a virtual port, the Scheduler Type parameter must be set to Virtual port when configuring an SLA Profile.
See To configure an SLA profile for more information.
Subscriber Profiles
The subscriber aggregate rate is adjusted to account for the fixed offset and per packet variable expansion of the last mile for the specific session used by the subscriber host. The adjustment is based on the average frame size.
See To configure a subscriber profile for more information.
Contents
Workflow to configure and manage virtual ports
To configure a virtual port using the navigation tree