Table Of Contents
Configuration Guidelines for Populating Cards in the MGX 8250
Physical Characteristics of Modules
Card Dimensions (Front and Back)
AC Power Cords Available for Different Regions
System Power Current Requirements
Heat Dissipation for a Fully Loaded MGX 8250
Physical Architecture
This chapter describes the mechanical design of the MGX 8250, which includes the chassis, power options, midplane, cabling, and EMI.
The MGX 8250 chassis design provides a double shelf with 32 upper and lower single-height service bays (See Figure 2-1). These service bays accommodate the following modules:
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Processor switch modules (PXM)
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Figure 2-1 MGX 8250 Chassis
Chassis
This section describes the types and positions of the cards for the front and the rear of the chassis. This section also describes the basic dimensions of the cabinet.
Front
The front of the chassis has 32 single-height slots, which can be converted to 16 double-height slots.
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Rear
The rear of the chassis supports up to 32 single-height back cards. All rear back cards are single-height (see Figure 2-2). The partition between the upper and lower bays in the back of the chassis cannot be removed.
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Figure 2-2 Rear of the MGX 8250 Chassis
Mounting
The MGX 8250 is a rack-mount unit that can be fitted to a standard 19-inch rack or a 23-inch rack using optional 23-inch adapters.
Chassis Dimensions
The chassis is 29.75 inches high (28 inches high without the rack unit (RU) gap filler), 17.72 inches wide, and 21.5 inches deep. It can be mounted in either a 19-inch, a 23-inch EIA/RETMA, or ETSI telco rack.
Other relevant dimensions include:
Configuration Guidelines for Populating Cards in the MGX 8250
The following guidelines are to assist you in installing single-height and double-height service modules in an MGX 8250 chassis.
Removing the Center Guides
The center guides that partition the top and the bottom bays can be removed two slots at a time. This means that the partition for slots 1 and 2 can be turned into double-height slots at the same time.
Center guides must be removed from the left side of the chassis toward the right side of the chassis. This means it is not possible to convert slots 11 and 12 into double-height slots without first converting slots 9 and 10 into double-height slots.
Center guides can be removed from the chassis starting with slots 1 and 2 at the far left of the chassis or starting with slots 9 and 10 just to the right of the PXM.
Creating Double-Height Slots
Slots 9 and 10 do not support 1:N redundancy in bulk distribution mode and therefore should be the first double-height slots created.
Cards that do not require such features (such as RPM) should use slots 9 and 10.
Figure 2-3 shows an enclosure with cards and center guide modules installed.
Figure 2-3 Installed Cards and Center Guides
Component Weights
The weights of the individual components of the MGX 8250 are in Table 2-1:
For example, the weight of an MGX 8250 card cage with 2 PXMs, 24 service modules cards, 4 SRMs and 32 back cards, and no door would be:
(4.8 * 2) + (24 * 1.74) + (4 * 1.74) + (32 * 0.74) + 59 for a total of 141 pounds.
Physical Characteristics of Modules
The modules in Table 2-2 are supported on the MGX 8250. See "Processor Switch Module" and "Service Modules" for information on the functionality of these modules.
Card Dimensions (Front and Back)
Figure 2-4 shows the dimensions of a double-height front card and Figure 2-5 shows the two single-height back cards.
Figure 2-4 Double-Height Card Dimensions
Figure 2-5 Single-Height Card Dimensions
Optical Specifications
The optical transceivers in the PXM1 interfaces are compliant with ITU-T G.957. The dispersion tolerances according to G.957 are:
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The modulation used in all PXM1 optics is direct build-in electroabsortion modulator in standard temperature range (0 - 70°C).
The type of laser sources for the different PXM1 interfaces are:
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All MGX single mode optical interfaces (OC3, OC12, and OC48) are terminated with the ultra physical contact (UPC) polish type. Note that this does not apply to multimode fiber. The UPC polish includes an extended polishing cycle at the end-face surface for a better surface finish, resulting in back reflection as low as -55 dB.
Table 2-3 provides the optical specifications for the different interfaces.
Interface Ranges
The cable distance ranges for the various interfaces are as follows.
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DS1 per ANSI T1.102 states distance of 655 feet. This means a compliant pulse (per pulse mask template) to the DSX-1 (cross-connect).2.
Ethernet (10BASE-T) is a distance of 100 meters to the first repeater.3.
DS3 per ANSI T1.102 is a distance of 450 feet to the DSX-3 cross-connect.4.
HSSI per ITU-T V.12 (ANSI/EIA/TIA-612) is a distance of 50 feet (15 meters) between load and generator.Power
The MGX 8250 can be powered either by an AC power system or by a nominal 48 VDC power system. This section contains information on the following topics:
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AC Power
The AC power system consists of two major components: an AC power supply tray and multiple power supply modules.
The power supply tray has two options—a single AC cord and another with two AC cords.
MGX-AC1-1
The MGX-AC1-1 is for systems requiring a single AC power supply that will be powered from a single AC power source. MGX-AC1-1 provides up to 1200 watts of load-shared redundant power. If additional power is needed, additional power supplies, providing an additional 1200 watt each, can be added.
The one-AC cord version uses 1:N power-supply redundancy. If you have three 1200W power modules, you can support up to 2400W of power; the third module is redundant. Because there is only one AC cord, you do not have redundancy for the AC cord itself.
MGX-AC2-2
MGX-AC2-2 is for systems requiring redundant AC power supplies that will be powered from two AC power sources.
The two-AC cord power tray supports 1:1 power-supply redundancy. If you have four 1200W power supplies, you can support only 2400W of power. The two-AC cord power tray has two AC cords; therefore, both the AC cord and the power modules are redundant.
The quantity of AC power modules is determined by the type of power tray and by the customer's overall power requirements. Table 2-4 shows the minimum and maximum number of power modules for each type of power tray.
Table 2-4 Minimum and Maximum Number of Power Modules
MGX-AC2-2
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Even no. of modules
MGX-AC1-1
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4
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The AC power module converts 220V 50/60 cycle AC into 48 VDC. The DC power is supplied to the chassis through cables and connectors on the midplane.
AC Power Cords Available for Different Regions
The following table details the AC power cords available by regions.
DC Power
In the DC system, the 48 VDC is supplied through either one or two power entry modules (PEMs). The PEMs are plugged into the midplane through the same connectors as the AC power supply. Each PEM has a circuit breaker for protection.
DC Power Range
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Power Entry Modules
There are two DC PEM modules per shelf. Each PEM accepts one battery feed and provides 60A of battery power to the shelf. The PEMs are redundant; therefore, a loss of one PEM will not disturb the system.
Both PEMS are located inside the air-intake plenum, which is located at the bottom of the shelf. The battery feed is connected to each PEM via a terminal block, similar to the BPX PEM. The output of each PEM is connected to the backplane through a power cable with power D-Sub connectors attached.
The dimension of each PEM is approximately 1.5 inches x 7 inches x 10 inches x (H x W x D).
Module Power Consumption
The power consumption of the different modules is defined in Table 2-6.
System Power Current Requirements
The current requirements are configuration-dependent, use the following values for general planning purposes:
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Circuit Breakers
The MGX 8250 uses circuit breakers instead of switches or magnetic conductors. These circuit breakers are compliant to the European approved VDE IEC 950 Specifications.
The circuit breakers are as follows:
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Cooling
The MGX 8250 contains it own plemum fan cooling system.
Components
The cooling system consists of the following components:
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The fan tray contains nine front loadable fans. Eight of the nine fans must be operational to provide enough cooling capacity.
Monitoring
The PXMs provide a variety of system environmental monitoring and logging functions. The PXMs monitor the fan speed. An alarm is generated if any fan drops below the configured threshold.
A temperature monitor circuit reads the shelf air-intake temperature in units of one degree Celsius.
Figure 2-6 MGX 8250 Fan Tray
Heat Dissipation for a Fully Loaded MGX 8250
A fully loaded, AC-powered MGX 8250 node dissipates up to 9560 Btus. A DC-powered MGX 8250 node dissipates up to 8200 Btus.
Environmental Requirements
MGX 8250 environmental specifications are listed below.
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Electromagnetic Interference
To maintain correct airflow and to reduce radio frequency interference (RFI) and electromagnetic Interference (EMI), observe the following procedures.
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Card Cage Midplane
The MGX 8250 has a midplane design that increases flexibility and minimizes service disruptions. Front cards can be replaced without disrupting cabling on the rear cards or chassis.
Midplane Key Benefits
The midplane design provides the following benefits.
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Midplane BUS Components
The components of the midplane bus are cell buses, a distribution bus, a service redundancy bus, a local bus, and a BERT bus.
Cell Buses
The switching fabric of the MGX 8250 resides on the processor switch module (PXM). The PXM supports eight cell buses that provide a high-speed cell data path between the PXM switch fabric and the service modules. The cell bus is a collection of independently controlled bus lanes.
Figure 2-7 shows the MGX 8250 back plane cell bus interconnections.
Figure 2-7 MGX 8250 Cell Bus Lane Interconnection
Operation
Each cell bus operates independently of every other cell bus. The PXM provides arbitration and control functions. The total switching capacity of all the cell bus switching interfaces is approximately
2.2 GBps. Although any service module can be used in any slot, the upper service bay is engineered for high-capacity cards (FRSM-2CT3, FRSM-2T3/E3, FRSM-T3/E3), while the lower service bay is better suited for the low-capacity cards (FRSM-8, CESM-8, AUSMB-8). Any cell bus based service module can be deployed in any slot.The MGX 8250 midplane supports eight cell buses, which support 2.2 GBps full duplex total capacity. The cell buses are connected on a per-slot basis on the MGX 8250 chassis. Each cell bus on the bottom service tray has OC-3 net capacity; cell buses on the top shelf are capable of running at OC-6.
Cell Bus to Slot Distribution
The distribution of the eight fully redundant cell buses is as follows:
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Figure 2-7 shows the interconnection of the cell bus lanes on the midplane.
To facilitate communication between PXMs, a cell bus slave is added to each PXM. Each cell bus is fully redundant and has a minimum bidirectional bandwidth capacity 160 Mbps. The cell bus provides the following additional functionality.
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Upper Service Bay
A cell bus in the upper service bay can operate in excess of bidirectional 310 Mbps bandwidth. Each cell bus on the upper service bay services two slots, sharing 160 Mbps or 310 Mbps bidirectional bandwidth across the two slots.
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Lower Service Bay
A cell bus in the lower service bay operates in excess of bidirectional 160 Mbps. Each cell bus services six slots and provides 160 Mbps of shared bandwidth capacity to six single-height service modules. The bandwidth on the lower service bay is also allocated based on usage and, in case the bandwidth is not being used by any other service module, the entire available bandwidth could be used up by any one service module.
Distribution Bus
The MGX 8250 backplane supports the same distribution bus employed in the MGX 8220. This is used in conjunction with the SRM-3T3 to provide M13 circuit breakout and distribution capability and T1/E1 1:N service module redundancy. In bulk mode the service modules have 1:N redundancy without using the separate T1 redundancy bus.
The distribution system is also augmented with a T3 distribution mechanism, so that a future SRM could break out an OC-12 into DS3 streams, which in turn could be routed to individual DS3 speed service modules.
The TDM distribution buses for the upper and lower service bays are independent. In the future, the SRM could also be required to break out traffic to the DS0 level in order to provide more advanced grooming/pooling capabilities.
Service Redundancy Bus
A redundancy bus supports T1/E1 service module redundancy. The service modules have access to the redundant bus, and the service redundant logic on the SRM is responsible for sending control signals to each service module to use the redundant bus. This redundancy bus carries traffic from the back card of a failed service module to the front card of an active secondary card module.
Local Bus
The local bus is the core card bus that connects the PXM and SRM cards. Local buses carry traffic between common cards to create one logical card (common cards include PXMs and SRMs). Local bus A connects to the SRM in slots 15 and 31; local bus B connects to SRMs in slots 16 and 32.
BERT Bus
The BERT bus is used by the SRM-3T3/B to distribute T1 signals to the service modules. The SRM only supports BERT on one line or port at a time. BERT is capable of generating a variety of test patterns, including all ones, all zeros, alternate one zero, double alternate one zero, 223-1, 220-1, 215-1, 211-1, 29-1, 1 in 8, 1 in 24, DDS1, DDS2, DDS3, DDS4, and DDS5.
The BERT bus is used to provide the BERT operation to the individual service modules. This bus is also used to drive special codes such as fractional T1 loopback codes, and so on, onto the T1 line. The BERT function is initiated on only one logical T1/E1 N x 64K port per MGX 8250 at any given time. This is controlled by the PXM. The SRM-3T3 ensures that the BERT patterns are generated and monitored (if applicable) at the appropriate time slots.
The data path then for that particular port (n x 64K) is from the service module to the SRM-3T3/B (using the BERT bus) and back to the service module (using the BERT bus). On the service module, the transmitted data is switched between the regular data and the BERT data at the appropriate timeslots as needed. Similarly, in the receive direction, the received data is diverted to the BERT logic for comparison during appropriate time slots.
The BERT logic is self synchronizing to the expected data, and reports the number of errors for bit error rate calculation purposes.
Caution
Cable Management
The MGX 8250 includes cable management hardware to allow the convenient routing of the various system cables.
Required Cables
The following cables are required for minimum configuration of one MGX 8250 shelf:
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For systems sold in the United States, the AC power is supplied through either one or two standard IEC power cords. Systems sold elsewhere receive power through either one or two terminal blocks on the AC power tray. Power cords for different countries can be ordered through Cisco.
Additional Cables
The system also requires the following cables under different configurations.
DC Cable—For DC systems, the wiring is connected from a 48 VDC power source to one or two DC power entry modules. Three wires can be run from the DC terminal block located on the front panel of the power module to a source of 48 VDC. All wires must be six AWG in size.
Service Module Cables—Table 2-7 summarizes the type of interfaces provided by the different service modules.
Cable Management
A cable management system (see Figure 2-8 and Figure 2-9) is available to route both copper and fiber back card cables to the sides of the card cage. A cable routing bracket is mounted above and below the back cards and is attached to the card cage. The bracket separates the copper and the fiber cables. The fiber routing has a 1.5-inch controlled radius. The bracket routes cables out to each side of the card cage.
The cable routing bracket is 3.10 inches high x 19.00 inches wide.
Figure 2-8 Cable Management Assembly at Back Enclosure
Figure 2-9 Routing Data Cables at the Cooling Assembly
Copper-based data cables from the back cards go up or down to the cable manager and pass through the channels, then run to either the left or right side of the rack. Fiber optic cables pass over the sheet metal portion. The cables subsequently go to the related equipment (for example, CPE).
