Data Sheet

Data Sheet

After the packet goes through classification, policing, and marking, it is assigned to the appropriate

queue before exiting the switch. Cisco Catalyst 2955 Series Switches support four egress (outgoing

port) queues per port, allowing the network administrator to be more discriminating and specific in

assigning priorities for the various applications on the network. At the egress level, the switch

performs scheduling—an algorithm that determines the order in which the queues are processed.

The switches support Weighted Round Robin (WRR) scheduling, strict priority queuing or strict

priority scheduling. The WRR scheduling algorithm helps ensure that lower-priority packets are

not entirely starved for bandwidth and are serviced without compromising the priority settings

administered by the network manager. Strict priority scheduling helps ensure that higher-priority

packets will always get serviced first, ahead of other traffic in lower-priority queues.

These features allow for prioritization of mission-critical, such as motion-control traffic, critical I/O

or sensor data, video monitoring of security areas over voice (IP telephony traffic), ERP (Oracle,

SAP, etc.), and CAD/CAM, which, in turn, would be scheduled to have precedence over less time-

sensitive applications such as FTP or e-mail (SMTP). For example, it would be highly undesirable

to have a large file download destined to one port on a switch and have quality implications, such

as increased latency in industrial control traffic, destined to another port on the switch. This

condition is avoided by helping ensure that the control traffic is properly classified and prioritized

throughout the network. Other applications, such as Web browsing, can be treated as low priority

and handled on a best-efforts basis.

Cisco Catalyst 2955 Series Switches allocate bandwidth based on several criteria, including

MAC source address, MAC destination address, IP source address, IP destination address, and

TCP/UDP port number. Bandwidth allocation is essential in network environments that require

service-level agreements, or when it is necessary for the network manager to control the bandwidth

given to certain users. Cisco Catalyst 2955 Series Switches support up to six policers per Fast

Ethernet port and up to 60 policers on a Gigabit Ethernet port. This gives the network administrator

granular control of the network bandwidth.

Network Availability

To provide efficient use of resources for bandwidth-hungry applications like multicasts (common in

producer-consumer data distribution models), intelligent Cisco Catalyst 2955 Series Switches

support Internet Group Management Protocol (IGMP) snooping in hardware. Through the support

and configuration of IGMP snooping via Cisco Network Assistant, Cisco Catalyst 2955 Series

Switches deliver outstanding performance and ease of use in administering and managing

multicast applications on the LAN.

The IGMP snooping feature allows the switch to "listen in on" the IGMP conversation between

hosts. When a switch hears an "IGMP join" request from a host for a given multicast group, the

switch adds the host's port number to the group destination address (GDA) list for that group. When

the switch hears an "IGMP leave" request, it removes the host's port from the Content Addressable

Memory (CAM) table entry.

Per VLAN Spanning Tree Plus (PVST+) allows users to implement redundant uplinks while

distributing traffic loads across multiple links. This is not possible with standard Spanning-Tree

Protocol implementations. Cisco UplinkFast technology helps ensure immediate transfer to the

secondary uplink, a vast improvement over the traditional 30-to-60-second convergence time.