power enters the switch through the power supplies. several types of power supplies are available, depending on the power needs for your system and the power type available on your site. all power supplies provide a 3.3 v circuit (shown as a dash-dot line) to the components on the backplane and a 12 v circuit (shown as a solid line) that is carried over the backplane to the fans, supervisor engine, and switching modules. power supplies that support poe (1300 w ac,
2800 w ac, 4200 w ac or 1400 w dc) also provide a –48 v circuit (shown as a dashed line) to poe-enabled switching modules, which is then available to the powered device connected to the switching module.
the supervisor engine ii-plus ts has internal dc-to-dc converters that use the 12 v circuit to provide poe to powered devices connected to the supervisor engine only. if your system has a supervisor engine ii-plus ts in slot 1, you still need a poe-enabled power supply to provide poe to the other slots.
all catalyst 4500 series switches support dual power supplies, configurable as combined mode or redundant mode. in combined mode, the switch has available the combined rated wattage of both power supplies, less some expected efficiency loss. in redundant mode, one power supply provides power to the system and the other supply is on standby should there be a failure in either the power supply or the input voltage source it is connected to.
power over ethernet
the cisco catalyst 4500 series switches support the cisco pre-standard and 802.3af standard for poe on 10/100 or 10/100/1000 ports, enabling customers to support telephones, wireless base stations, video cameras, and other appliances. poe makes it possible to place devices in unique locations without having to provide new outlets and costly electrical circuits. poe also enables businesses to isolate critical devices on a single power system so that the entire system can be supported by uninterruptable power supply (ups) backup.
all new cisco catalyst poe line cards can support 15.4 w of power per port simultaneously. not only do the cards support the ieee standard, including the optional power classifications, but the cisco pre-standard power implementation is also supported to help ensure backward compatibility with existing cisco powered devices. the cards are compatible with any chassis and supervisor engine. most importantly, the catalyst 4500 series switch has the power supplies and accessories to support 15.4 w per port on every port simultaneously in any fully loaded chassis. (this requires an external power shelf or a 4200 w dual-input power supply.)
poe over-subscription
with the advent of powered devices requiring as much as 15.4 w and the different combinations of power supplies and chassis port densities, it becomes quite possible to over-subscribe the poe capacity of the power supplies. this temporary over-subscription typically occurs when a power supply configured in combined mode fails or when the user has not kept track of the powered devices and plugs in one too many. the best practice is to design a poe system in which all devices receive the power needed at all times. when a power supply is over-subscribed—more power is being drawn from it than it can supply—the power supply shuts down. there are several ways to predictably manage a temporary poe over-subscription:
1. configure unused ports to never receive poe. this prevents a user from inadvertently plugging a powered device into a port and causing problems for other powered devices.
2. configure ports to be in static mode. this is for ports that have highestpriority, such as phones for executives or wireless access points. if ports need to be disabled because of a power shortage, auto ports are disabled before static ports.
3. configure the maximum wattage on ports to be less than the default, based on the maximum power consumption of the powered device. this disallows devices demanding unexpected amounts of power and also stretches the finite resources of the power supplies. for example, the default port wattage is 15.4 w. by configuring a maximum of 7 w, twice as many poe powered devices can be supported with the same power supply.
poe line cards
the cisco catalyst 4500 series offers line cards, power supplies, and accessories required to deploy and operate a standards-based poe internetwork. poe provides –48 v dc power over standard category 5 unshielded twisted-pair (utp) cable up to 100 meters when an ieee 802.3af-compliant or cisco pre-standard powered device is attached to the poe line card port. instead of requiring wall power,attached devices such as ip phones, wireless base stations, video cameras, and other ieee-compliant appliances can use power provided by the poe line cards. this capability gives network administrators centralized control over power and eliminates the need to install outlets in ceilings and other out-of-the-way places where a powered device may be installed.
although references to “poe,” “inline-power,” and “voice” power supplies and line cards are synonymous, there are only two versions: cisco prestandard and ieee 802.3af compliant. every cisco catalyst 4500 series chassis and poe power supply supports the ieee 802.3af standard and the cisco prestandard power implementation ensuring backward compatibility with existing cisco powered devices. all ieee 802.3af-compliant line cards can distinguish an ieee or cisco prestandard powered device from an unpowered network interface card (nic),ensuring that power is applied only when an appropriate device is connected.all poe line cards can distinguish an ieee or cisco prestandard powered device from an unpowered network interface card (nic) to ensure power is applied only when an appropriate device is connected. with a cisco poe network, administrators can depend on a robust network that is safe to deploy and simple to maintain.
deploying poe on the cisco catalyst 4500 series
when the switch is properly configured, implementing poe is easy when it is used with a cisco powered device that supports cisco discovery protocol. all poe line cards automatically detect an attached powered device the moment it is installed.also, the switch returns unused port power to the system power budget for use by other devices because it supports the ieee802.3af optional power classifications.
the cisco catalyst 4500 series offers internal power supplies and external power devices for multiple deployment scenarios. these scenarios include small and large deployments in ac or dc environments for data-only configurations, and scalability of up to 15.4 w per port for poe configurations.
the switches share a common power supply form factor. each cisco catalyst 4500 series chassis is designed for 1 + 1 power protection while meeting the needs of poe demands. in addition to power resiliency, the cisco catalyst 4500 series includes 1 + 1 supervisor-engine redundancy (cisco catalyst 4507r and catalyst 4510r only) and software-based fault tolerance. integrated resiliency in both hardware and software minimizes network downtime, helping ensure workforce productivity, portability, and customer success.
all available cisco catalyst 4500 series power supplies can be used for data-only deployments, which typically require just a few hundred watts. for deployments that dictate support for poe power, cisco offers several options.
the cisco catalyst 4500 series offers several internal supplies: 1000 w ac (data only), 1400 w ac (data only), 1300 w (data and poe), 1400 w dc (data and poe), 2800 w (data and poe), and 4200 w ac (data and poe). when more than
4200 w of redundant data and poe are required for a cisco catalyst 4500 series chassis in an ac-powered environment, cisco offers an external ac power shelf that houses two 2500 wac power supplies. when two power shelves are combined, they can produce 7500 w—the remaining 2500 w supply can be used for n + 1 protection.
the cisco catalyst 4500 series has two dc power options; one is optimized for data-only deployments in service provider central offices (part number pwr-c45-1400dc), and the other is used for high-power poe deployments (part number pwr-c45-1400dc-p).
cisco catalyst 4500 series external ac power shelf and
1400 w dc power supply with integrated power entry module
the external ac power shelf must be used in conjunction with the 1400 w dc power supply. in addition to providing power for the chassis, fans, and non-poe line cards, the 1400 w dc power supply contains a power entry module (pem).the pem is used to pass additional power to the chassis backplane, power demanded by the poe line cards. the chassis power trace used for poe is independent from the one used by the supervisor engine(s), fan tray, and backplane components. the 1400 w dc power supply can accept up to 7500 w dc for data and poe applications. up to 1400 w can be dedicated for data (supervisor engine, fan tray, etc.), while the remaining power is passed through via the pem and is used for poe.
when only one external ac power shelf is used (with two 2500 wac power supplies), it provides the 1400 w dc power supply with 5000 w of dc power in total. when two ac power shelves are strapped together, the switch can provide up to 7500 w of dc power (3 + 1 redundant).
cisco catalyst 4500 series service provider dc power supply
the triple-input 1400 w dc power supply is optimized for service provider or central-office deployments. by providing multiple inputs, the service provider dc power supply enables central-office technicians to customize the output power to meet their application needs. many central-office deployments require only a fraction of the 1400 w available in the service provider power supply. low current inputs mean technicians can connect the supply to smaller fuses and breakers. the service provider power supply makes it possible to deploy a cisco catalyst 4503
with a single 15a circuit. likewise, it is possible to deploy a fully populated cisco catalyst 4510r with two 20a and one 15a circuits rather than a single 60a connection, which often requires rack rewiring.
management flow
figure 1-22 shows management and status information flow through the system.
each system component has an eeprom that identifies it to the supervisor engine over a serial connection on the backplane, which also passes along information like temperature, fan speed, power draw per slot and port, and port activity. led status information is also sent to the supervisor engine, which makes it available to an administrator through a terminal connection or management software.
all catalyst 4500 series switches support:
1 hardware-based multicast-protocol independent multicast (pim).
2 internet group management protocol (igmp).
3 cisco group management protocol support standards-based and cisco technology-enhanced efficient multimedia networking.
4 simple network management protocol (snmp).
5 ciscoworks, which can manage critical network characteristics such as availability, responsiveness, resilience, and security.
6 cisco netflow services. the cisco netflow services card for the supervisor engine iv and v support statistics capture in hardware for flow-based and vlan-based statistics monitoring. this data can be exported, collected, and analyzed for virus detection and mitigation, network-traffic accounting,usage-based network billing, network planning, network monitoring, and data-mining capabilities. cisco netflow services is integral to the supervisor engine v-10ge.
switching traffic flow
figure 1-23 shows switching traffic flow through the system.
frames flow into the switch through interfaces on the switching modules. each switching module connects to a mux/buffer on the backplane that supports a connection of up to 6 gbps up (tx) to the supervisor engine and 6 gbps from (rx) the supervisor engine. when a frame reaches the supervisor engine, it is examined and either sent out of an interface in one of the other slots, or out of the uplink on the supervisor engine.
over-subscription
switching modules that have 24 or 48 gigabit ethernet (1000base-t) ports over-subscribe on a catalyst 4500 switch by grouping the ports with an additional mux/buffer on the switching module, which creates a single, nonblocking, full-duplex gigabit ethernet connection to the internal switch fabric. for each group of ports, frames received are buffered and sent to the common gigabit
ethernet link to the internal switch fabric. if the amount of data received for a port begins to exceed buffer capacity, flow control sends pause frames to the remote port to temporarily stop traffic and prevent frame loss.
each port in the group shares the bandwidth of a gigabit ethernet link. however,each port operates independently so that flow control, or configuration of one port, does not block or degrade the performance of another port in that group. switching modules that have up to six 1000base-t ports do not use over-subscription.
the amount of over-subscription can be controlled by varying the number of ports used at 1000 mbps. all ports can use cisco gigabit etherchannel technology or ieee 802.3ad for high-speed interconnection applications. all over-subscribed ports use the standard ieee 802.1x flow control (pause frame) mechanism to control gigabit ethernet host traffic.
supervisor redundancy
the cisco catalyst 4507r and catalyst 4510r switches support 1+1 supervisor-engine redundancy for integrated resiliency. redundant supervisor engines help minimize network downtime. with the support of stateful switchover (sso), the secondary supervisor engine serves as a backup to immediately take over after a primary supervisor failure. during the switchover, layer 2 links are maintained transparently without the need to renegotiate sessions. as a result,business-critical applications such as voice-over-ip (voip) calls are not dropped. the nonstop forwarding (nsf) aware feature in cisco ios software is also supported, providing the ability to interface with nsf-capable devices and to continue forwarding packets as routing information is updated upon a supervisor-engine switchover.