Cisco 2950SX 24 - Catalyst Switch - Stackable Manual do Utilizador descarregar pdf (Página 3)

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The Cisco Catalyst 2950 Series offers superior and highly granular QoS to ensure that network trafﬁc is classiﬁed

and prioritized, and that congestion is avoided in the best possible manner. The Cisco Catalyst 2950 Series can

classify, reclassify, police (determine if the packet is in or out of predetermined proﬁles and affect actions on the

packet), and mark or drop the incoming packets before the packet is placed in the shared buffer. Packet classiﬁcation

allows the network elements to discriminate between various trafﬁc ﬂows and enforce policies based on Layer 2 and

Layer 3 QoS ﬁelds.

To implement QoS, ﬁrst,the CiscoCatalyst 2950 Series switches identify trafﬁc ﬂows, or packet groups, and classify

or reclassify these groups using either the Differentiated Services Code Point (DSCP) ﬁeld or the 802.1p

class-of-service (CoS) ﬁeld, or both. Classiﬁcation and reclassiﬁcation can be based on criteria as speciﬁc as the

source/destination IP address, source/destination Media AccessControl (MAC)address, or the Layer 4 Transmission

Control Protocol/User Datagram Protocol (TCP/UDP) port. At the ingress, the Cisco Catalyst 2950 Series can also

perform policing and marking of the packet.

Afterthepacket goes throughclassiﬁcation,policing,and marking, it isthenassignedto the appropriatequeuebefore

exitingthe switch.The Cisco Catalyst2950 Seriessupports four egress (outgoing port)queues per port, which allows

the service provider to be more discriminating and speciﬁc in assigning priorities for the various applications. At the

egress, the switch performs Weighted Round Robin (WRR) or strict priority scheduling to determine the order in

which the queues are processed. The WRR queuing algorithm ensures that the 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 ensures that the highest-priority packets are always serviced ﬁrst, ahead of all

other trafﬁc.

In terms of rate limiting, the Cisco Catalyst 2950 Series is capable of allocating 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 requiring service-level agreements (SLAs),

or when it is necessary for the network manager to control the bandwidth given to certain subscribers. The Cisco

Catalyst 2950 Series supports up to 6 policers per Fast Ethernet port and up to 60 policers on a Gigabit Ethernet

port. Trafﬁc policing can be done in 1-Mbps increments on Fast Ethernet ports and 8-Mbps increments on Gigabit

Ethernet ports, giving the network manager very granular control of network bandwidth.

In addition, the Cisco Catalyst2950 Series provides key voice andvideo service features with voice VLAN(auxiliary

VLAN) for VoIP services and hardware-based Internet Group Management Protocol (IGMP) snooping, allowing the

switch to “listen in” on the IGMP conversation between hosts and routers. When a switch hears an IGMP join

request from a host for a given multicast group, the switch adds the host port number to the Group Destination

Address (GDA) list forthat group. And, when the switchhears an IGMP leave request, itremoves the host port from

the list. Together with the superior QoS and rate-limiting features mentioned previously, service providers can build

a ﬂexible network with the Cisco Catalyst 2950 Series to provide voice, video, and data services all in one network

architecture.

Service Availability through Resiliency Enhancements and Network Redundancy

The Cisco Catalyst 2950 Series provides a rich set of resiliency enhancement features to ensure quick failover

recovery and create a high-availability network. The IEEE 802.1w Rapid Spanning Tree standard allows the service

provider to achieve subsecond spanning tree convergence times to maximize network stability and reliability. The

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