User's Manual

Virtual Connect networks 103
Networks (Advanced Settings)" on page 97). Additionally, each Network or Shared Uplink Set also has a
LACP timer setting. There are three possible values: Domain-Default, Short, or Long. The domain default
option sets the LACP timer to the domain-wide default value that is specified on the Advanced Ethernet
Settings screen.
This setting specifies the domain-wide default LACP timer. VCM uses this value to set the duration of the LACP
timeout and to request the rate at which LACP control packets are to be received on LACP-supported
interfaces. Changes to the domain-wide setting are immediately applied to all existing networks and shared
uplink sets.
Using the "long" setting can help prevent loss of LAGs while performing in-service upgrades on upstream
switch firmware.
Quality of Service
QoS is used to provide different priorities for designated networking traffic flows and guarantee a certain
level of performance through resource reservation. QoS is important for the following reasons:
• It provides Service Level Agreements for network traffic and to optimize network utilization.
• Different traffic types such as management, backup, and voice have different requirements for
throughput, jitter, delays and packet loss.
• IP-TV, VOIP, and Internet expansion create additional traffic and latency requirements.
• In some cases, capacity cannot be increased. Even when possible, increasing capacity may still
encounter issues if traffic needs to be re-routed because of a failure.
Traffic must be categorized and then classified. Once classified, traffic is given priorities and scheduled for
transmission. For end-to-end QoS, all hops along the way must be configured with similar QoS policies of
classification and traffic management. VC manages and guarantees its own QoS settings as one of the hops
within the networking infrastructure.
The following diagram illustrates how VC receives traffic and categorizes it into classes. Packets can be
reordered based on priority as shown for packet number 3. Packets can also be dropped during congestion
as shown for packet number 2.
Prior to the VC 4.01 release, VC QoS support was limited apart from dynamic Max rate limiting bandwidth
control. VC Ethernet modules passed Layer 2 and Layer 3 markings in VLAN tunnel mode but in some cases
removed L2 markings in mapped mode. VC would not perform any traffic classification, marking, policing,