Cisco WS-C3550-48-EMI Instrukcja Użytkownika Pobierz pdf (Strona 4)

Cisco Systems, Inc.

Page 4 of 19

and are serviced without compromising the priority settings administered by the network manager. Strict priority

queuing ensures that the highest priority packets will always get serviced ﬁrst, ahead of all other trafﬁc, and allows

the other three queues to be serviced using WRR scheduling. In conjunction with scheduling, the Catalyst 3550

Gigabit Ethernet ports support congestion control via Weighted Random Early Detection (WRED). WRED avoids

congestion by setting thresholds at which packets are dropped before congestion occurs.

These features allow network administrators to prioritize mission-critical and/or bandwidth-intensive trafﬁc, such

as Enterprise Resource Planning (ERP) (Oracle, SAP, etc.), voice (IP telephony trafﬁc) and CAD/CAM over less

time-sensitive applications such as FTP or e-mail (Simple Mail Transfer Protocol [SMTP]). For example, it would

be highly undesirable to have a large ﬁle download destined to one port on a wiring closet switch and have quality

implications such as increased latency in voice trafﬁc, destined to another port on this switch. This condition is

avoided by ensuring that voice 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.

The Cisco Catalyst 3550 is capable of performing rate limiting via its support of the Cisco Committed Information

Rate (CIR) functionality. Through CIR, bandwidth can be guaranteed in increments as low as 8 Kbps. Bandwidth can

be allocated 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 or when it is necessary for the network manager to control the bandwidth given to certain

users. Each Catalyst 3550 switch 10/100 port supports 8 aggregate or individual ingress policers and 8 aggregate

egress policers. Each Catalyst 3550 Gigabit Ethernet port supports 128 aggregate or individual policers and 8

aggregate egress policers. This gives the network administrator very granular control of the LAN bandwidth.

Network Scalability through High-Performance IP Routing

With hardware-based IP routing and the Enhanced Multilayer Software Image, the Catalyst 3550 switches deliver

high performance dynamic IP routing. The Cisco Express Forwarding (CEF)-based routing architecture allows for

increased scalability and performance. This architecture allows for very high-speed lookups while also ensuring the

stability and scalabilitynecessary to meet theneeds of future requirements.In addition to dynamicIP unicast routing,

the Catalyst 3550 Series is perfectly equipped for networks requiring multicast support. Multicast routing protocol

(PIM) and Internet Group Management Protocol (IGMP) snooping in hardware make the Catalyst 3550 Series

switches ideal for intensive multicast environments.

These switches offer several advantages to improve network performance when used as a stackable wiring closet

switch or as a top-of-the-stack wiring closet aggregator switch. For example, implementing routed uplinks from

the top of the stack will improve network availability by enabling faster failover protection and simplifying the

Spanning-Tree Protocol algorithm by terminating all Spanning-Tree Protocol instances at the aggregator switch.

If one of the uplinks fails, quicker failover to the redundant uplink can be achieved via a scalable routing protocol

such as Open Shortest Path First (OSPF) or Enhanced Interior Gateway Routing Protocol (EIGRP) rather than relying

on standard Spanning-Tree Protocol convergence. Redirection of a packet after a link failure via a routing protocol

results in faster failover than a solution that uses Layer 2 Spanning Tree enhancements. Additionally, routed uplinks

allow better bandwidth utilization by implementing equal cost routing (ECR) on the uplinks to perform load

balancing. This results in dynamic load balancing in a part of the network that often acts as the bottleneck. And,

routed uplinks optimize the utility of uplinks out of the wiring closet by eliminating unnecessary broadcast data

ﬂows into the network backbone.

1 2 3 4 5 6 7 8 9 ... 18 19

Brak uwag

Cisco WS-C3550-48-EMI Instrukcja Użytkownika Strona 4