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This section describes the mechanical design of the MGX 8250, including chassis, power options, midplane, cabling, and EMI.
The MGX 8250 has a universal chassis design that provides a double shelf with both upper and lower single-height service bays capable of accepting up to 24 I/O service modules. The MGX 8250 is also easily field-adaptable to provide for up to 12 double-height service modules like the Route Processor Modules (RPM) or the Processor Switch Modules (PXMs).
The chassis is 17.72 inches wide, 29.75 inches high (28 inches high without the rack unit (RU) gap filler), 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:
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The physical layout of the MGX 8250 switch chassis is shown in Figure 2-1.
The MGX 8250 chassis supports the PXM1. There are two double-height slots in positions seven and eight that are reserved for the redundant Processor Switch Module (PXM). PXM1 combines a 1.2 GBps switching fabric with an R4700 microprocessor to provide switch control and local ATM switching on the same card.
The MGX 8250 chassis and midplane provide upper and lower service bays to accommodate processor switch modules, narrowband and broadband service modules, and service resource modules at the front of the unit, and interface cards at the rear of the unit. There are a total of 32 single-height slots, which can also be viewed as 16 double-height slots.
The MGX 8250 chassis supports up to 32 single-height front cards (or a number between 12 and 24 for a mix of single-height and double-height front cards). The MGX 8250 supports up to 32 back cards. Each double-height service module is capable of supporting two back cards, and each single-height front card is capable of supporting a single-height back card. Four back card slots are dedicated to the Service Resource Modules and can be used to provide bulk distribution to the service module slots. The final four back cards are dedicated to the redundant PXM modules. Each PXM has a user interface (UI) back card, and a back card with broadband ports.
There are an additional four single-height slots in positions 15 and 16, and 31 and 32 that are reserved for the Service Resource Module (SRM). The SRM enables 1:N redundancy for the service modules, BERT testing, and built-in M13 grooming. The remaining slots in positions 1-6, 9-14, 17-22, and 25-30 are used for the service modules.
Combinations of single-height and double-height service modules can coexist in a single MGX 8250 chassis subject to configuration rules. The single-height slots are easily converted into double-height slots by removing a slot partition. There are seven field-removable slot partition inserts, one for each adjacent pair of service bays (slots 1-2, 3-4, 5-6, 9-10, 11-12, and 13-14).
All back cards for all slots are single-height (Figure 2-2). The partition between the upper and lower bays in the back of the chassis is not removable.
The following rules and guidelines are to assist the user in installing single-height and double-height service modules in an MGX 8250 chassis. Rules must be followed while guidelines are instituted for better performance.
The center guides that partitions 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.
The removal of center guides must be done starting from the left side and working toward the right side of the chassis (assuming the user is facing the chassis). This means it is not possible to convert slots 11 and 12 into double-height slots without converting slots 9 and 10 into double-height slots.
Center guides can be removed from the chassis either by 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 PXMs.
In the initial MGX release, 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.
The weights of the individual components of the MGX 8250 are in Table 2-1:
| Component | Weight (lbs.) | Weight (kgs) |
|---|---|---|
Exhaust Plenum | 7.66 | 3.47 |
Fan Tray Assembly | 9.5 | 4.31 |
Center Guide Module | 1.32 | 0.60 |
Card Cage/Backplane w/ All (7) | 59 | 26.76 |
MGX 8250 Single-Height Front Card | 1.74 | 0.79 |
MGX 8250 Single-Height Back Card | 0.74 | 0.34 |
MGX Double-Height Card | 4.8 | 2.18 |
MGX 8250 Door | 7.10 | 3.22 |
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 141 pounds.
(4.8 * 2) + (24 * 1.74) + (4 * 1.74) + (32 * 0.74) + 59 = 141 pounds.
The following modules (for complete information about the modules, refer to Chapters 4 and 5) are supported on the MGX 8250 (see Table 2-2):
| Service Module | Back Cards | Height (in.) | Width (in.) | Weight |
|---|---|---|---|---|
AX-FRSM-8T1 | AX-RJ48-8T1 | 7.25 | 15.83 | 1.74 lbs. (0.79kgs) |
AX-FRSM-8E1 | AX-RJ48-8E1 | 7.25 | 15.83 | 1.74 lbs. (0.79kgs) |
AX-FRSM-2CT3 | AX-BNC-2T3 | 7.25 | 15.83 | 1.74 lbs. (0.79kgs) |
AX-FRSM-2T3E3 | AX-BNC-2T3 | 7.25 | 15.83 | 1.74 lbs. (0.79kgs) |
AX-AUSM/B-8-T1 | AX-RJ48-8T1 | 7.25 | 15.83 | 1.74 lbs. (0.79kgs) |
AX-AUSM/B-8-E1 | AX-RJ48-8E1 | 7.25 | 15.83 | 1.74 lbs. (0.79kgs) |
AX-CESM-8T1 | AX-RJ48-8T1 | 7.25 | 15.83 | 1.74 lbs. (0.79kgs) |
AX-CESM-8E1 | AX-RJ48-8E1 | 7.25 | 15.83 | 1.74 lbs. (0.79kgs) |
AX-CESM-T3E3 | AX-2-T3E3 | 7.25 | 15.83 | 1.74 lbs. (0.79kgs) |
MGX-VISM-8T1 | AX-RJ48-8T1 | 7.25 | 15.83 | 1.74 lbs. (0.79kgs) |
MGX-VISM-8E1 | AX-RJ48-8E1 | 7.25 | 15.83 | 1.74 lbs. (0.79kgs) |
AX-FRSM-HS1/B | MGX-12IN1-4S (4xV.35) | 7.25 | 15.83 | 1.74 lbs. (0.79kgs) |
AX-FRSM-HS2 | AX-SCSI2-2HSSI | 7.25 | 15.83 | 1.74 lbs. (0.79kgs) |
MGX-SRM-3T3 | MGX-BNC-3T3-M | 7.25 | 15.83 | 1.74 lbs. (0.79kgs) |
PXM1-2-T3E3 | MGX-BNC-2T3E3 | 15.65 7.0 (BC) | 15.83 4.125 (BC) | 4.8 lbs. (2.18kgs) |
PXM1-4-155 | MGX-SMFIR-4-155 MGX-SMFLR-4-155 MGX-MMF-4-155 | 15.65 7.0 (BC) | 15.83 4.125 (BC) | 4.8 lbs. (2.18kgs) |
PXM1-1-622 | MGX-SMFIR-1-622 MGX-SMFLR-4-155 | 15.65 7.0 (BC) | 15.83 4.125 (BC) | 4.8 lbs. (2.18kgs) |
MGX-RPM-64M | MGX-RJ45-FE MGX-MMF-FE MGX-RJ45-4E MGX-MMF-FDDI MGX-SMF-FDDI | 15.65 7.0 (BC) | 15.83 4.125 (BC) | 4.8 lbs. (2.18kgs) |
Figure 2-4 shows the dimensions of a double-height front card and Figure 2-5 the two single-height back cards.
The MGX 8250 switch 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.
Table 2-3 provides the optical specifications for the different interfaces.
| Back Card | Light Source Type/Wavelength | Tx Power Min/Max | Rx Power Min/Max | Connector Type | Range |
OC-3 MMF | LED / 1310 nm | -22 / -15 dBm | -31 / -10 dBm | SC | 2 km |
OC-3/STM-1 SMF IR | Laser Diode / 1310 nm | -15 / -8 dBm | -28 / -8 dBm | SC | 15 km |
OC-3/STM-1 SMF LR | Laser Diode / 1310 nm | -5 / 0 dBm | -34 / -10 dBm | SC | 40 km |
OC-12/STM-4 SMF IR | Laser Diode / 1310 nm | -15 / -8 dBm | -28 / -8 dBm | SC | 15 km |
OC-12/STM-4 SMF LR | Laser Diode / 1310 nm | -5 / 0 dBm | -28 / -8 dBm | SC | 40 km |
OC-12/STM-4 SMF ER | Laser Diode / 1550 nm | -3 / +2 dBm | -28 / -8 dBm | SC | 50+ km |
STM-16 SMF IR | Laser Diode / 1310 nm | -5 / 0 dBm | -18 / 0 dBm | SC | 15 km |
STM-16 SMF LR | Laser Diode / 1310 nm | -5 / 0 dBm | -26 / -10 dBm | SC | 40 km |
STM-16 SMF ER | Laser Diode / 1550 nm | -4 / +1 dBm | -26 / -9 dBm | SC | 50+ km |
As the optical transceivers in the PXM1 interfaces are compliant with ITU-T G.957, the dispersion tolerance according to G.957 are:
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:
All MGX single mode optical interfaces (OC3, OC12 and OC48) are terminated with the UPC (Ultra Physical Contact) 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
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).
Ethernet (10BaseT) is a distance of 100 meters to the first repeater.
DS3 per ANSI T1.102 is a distance of 450 feet to the DSX-3 cross-connect.
HSSI per ITU-T V.12 (ANSI/EIA/TIA-612) is a distance of 50 feet (15 meters) between load and generator.
The MGX 8250 can be powered either by an AC power system or by a nominal 48 VDC power system. The following are the available power options:
The AC power system consists two major components: an AC power supply tray and multiple power supply modules.
The power supply tray has two options: one with one AC cord and another with two AC cords.
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 watts 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. Since there is only one AC cord, you do not have redundancy for the AC cord itself.
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.
| AC Power Tray Type | No. of Power Modules Minimum | No. of Power Modules Maximum | Notes |
MGX-AC2-2 | 2 | 6 | Even no. of modules |
MGX-AC1-1 | 1 | 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.
In the DC system, the 48 VDC is supplied through either one or two Power Entry Modules (PEMs). The PEMs will be plugged into the midplane through the same connectors as the AC power supply. Each PEM has a circuit breaker for protection.
DC Power Range:
There are two DC PEM modules per MGX 8250 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 7" x 10" x 1.5" (W x L x H).
The following chart details the AC power cords available by regions.
Power cord with AS 3112 plug (Australia) |
Power cord with CEE 7/7 plug (Continental Europe) |
Power cord with BS 1363 plug (Great Britain) |
Power cord with CEI 23-16/VII plug (Italy) |
Power cord with NEMA L6-20 Twistloc (North America) |
The power consumption of the different modules is defined in Table 2-6.
| Service Module | Back Cards | Power Consumption |
|---|---|---|
AX-FRSM-8T1 | AX-RJ48-8T1 | 29.30 watts |
AX-FRSM-8E1 | AX-RJ48-8E1 | 29.30 watts |
AX-FRSM-2CT3 | AX-BNC-2T3 | 49.20 watts |
AX-FRSM-2T3E3 | AX-BNC-2T3 | 45.25 watts |
AX-AUSM/B-8-T1 | AX-RJ48-8T1 | 28.22 watts |
AX-AUSM/B-8-E1 | AX-RJ48-8E1 | 25.75 watts |
AX-CESM-8T1 | AX-RJ48-8T1 | 29.10 watts |
AX-CESM-8E1 | AX-RJ48-8E1 | 29.10 watts |
AX-CESM-T3E3 | AX-2-T3E3 | 32.45 watts |
MGX-VISM-8T1 | AX-RJ48-8T1 | 60.10 watts |
MGX-VISM-8E1 | AX-RJ48-8E1 | 60.10 watts |
AX-FRSM-HS1/B | MGX-12IN1-4S (4xV.35) | 35.00 watts |
AX-FRSM-HS2 | AX-SCSI2-2HSSI | 56.56 watts |
MGX-SRM-3T3 | MGX-BNC-3T3-M | 25.24 watts |
PXM1-2-T3E3 | MGX-BNC-2T3/E3 | 71.50 watts |
PXM1-4-155 | MGX-SMFIR-4-155 | 105.85 watts |
PXM1-4-155 | MGX-MMF-4-155 | 78.00 watts |
MGX-RPM-128M/B | MGX-RJ45-4E | 104.43 watts |
MGX-RPM-128M/B | MGX-RJ45-FE | 107.46 watts |
MGX-RPM-128M/B | MGX-MMF-FDDI | 126.72 watts |
The current requirements are configuration-dependent. For general planning purposes:
The total power consumption is dependent on the configuration of the switch.
A fully loaded, AC-powered MGX 8250 node dissipates up to 9560 BTUs. A DC-powered MGX 8250 node dissipates up to 8200 BTUs.
The MGX 8250 does not use switches or magnetic conductors. Instead, it uses circuit breakers. These circuit breakers are compliant to the European approvals VDE as per IEC 950 specifications.
The MGX 8250 uses miniature circuit breakers instead of fuses. The circuit breakers are as follows:
The cooling system consists of the following components:
The fan tray contains nine fans. Only eight of the nine fans need to be operational to provide enough cooling capacity. The fan trays are front loadable.
The PXMs provide a variety of system environmental monitoring and logging functions. The PXM is capable of reading the speed of these fans to determine if they are operating below the configured threshold. Upon failure of any of the fans, an alarm is generated. The temperature monitor circuit monitors the MGX 8250 shelf air-intake temperature in units of one degree Celsius.
Figure 2-6 shows the fan tray on the MGX 8250.
MGX 8250 environmental specifications are listed as follows:.
Ambient Temperature Range:
In operation +41 to +104F (+5 to +40C)
In short-term operation +35 to +122F (+1.7 to +50C) (up to or less than 72 consecutive hours and 15 days in one year)
In storage -40 to +140F (-40 to +60C)
Relative Humidity Range:
In operation 20-55%
In short-term operation 20-80%
In storage 5-95%
Altitude Range: 200 feet below the mean sea level to 10,000 feet above the mean sea level taking into account the function of temperature and humidity.
Shock: Withstands 10 G, 10 ms. at 1/2 sine wave. Vibration: Withstands 1/4 G, 20 to 500 Hz.
Maximum Heat Gain: 5 kw or 17,070 Bus/hour (50% to 75% of this value in typical configurations).
Minimum Floor Void: None. The restriction on floor void is solely dependent upon the cabling. There are no critical distances to be considered.
To maintain correct airflow and to reduce Radio Frequency Interference (RFI) and Electromagnetic Interference (EMI), all unused back card slots must be covered with the blank faceplates provided by Cisco Systems. If a front door option is ordered, there is no need to order or install blank front faceplates.
Front side EMI is obtained by either installing Cisco-provided blank cards or by installing an EMI-tight front door, which can be ordered as an option. There are different faceplates to accommodate double-height and single-height slots.
The card cage holds the midplane PCB, which provides interconnectivity between cards. The card cage also provides alignment rails for card insertion. Removable center guides divide the card cage into two bays. Three bulkheads are provided between slots 6 and 7, 8 and 9, and 14 and 15 for center guide support.
The MGX 8250 has a midplane design that increases flexibility and minimizes service disruptions by allowing front cards to be replaced without disrupting cabling at the rear of the chassis. In backplane architectures, the design reduces the flexibility to change interfaces and increases the risk of causing accidental operational outages due to cables coming loose when cards are being swapped.
Components of the backplane include:
The switching fabric of the MGX 8250 resides on the Processor Switch Module (PXM). The PXM supports eight cell buses. The cell bus provides a high-speed cell data path between the PXM switch fabric and the service modules. The cell bus consists of a collection of independently controlled bus lanes. Figure 1 shows the MGX 8250 back plane cell bus capacity. 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 also provides some additional functionality, including:
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. Note: bandwidth can be allocated in any proportion. For example, if a cell bus runs on single-speed mode, one slot can use 1 Mbps while the other can get all the remaining bandwidth. A cell bus in the lower service bay operates in excess of bidirectional 160 Mbps. Each cell bus services six slots and will provide 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.
Each cell bus operates independently of every other cell bus with the PXM providing the 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-2T3E3, FRSM-T3E3), 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.
The distribution of the eight fully redundant cell buses is as follows:
Figure 2-7 shows the interconnection of the cell bus lanes on the midplane.
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 as well as 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 may also be required to break out traffic to the DS0 level in order to provide more advanced grooming/pooling capabilities.
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 modules 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.
This is the core card bus that connects the PXM and SRM cards.
The BERT bus is used by the SRM-3T3/B to distribute T1 signals to the service modules. The SRM can support BERT on only 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 Nx64K port per MGX 8250 at any given time and 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 (via the BERT bus) and back to the service module (via the BERT bus). On the service module, the data that is transmitted 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. It also reports the number of errors for bit error rate calculation purposes.
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Caution BERT is a disruptive test. Activation of this test will stop the data flow on all the channels configured on the port under test. BERT testing requires the presence of an SRM-3T3/B card in the service bay in which the card under test is located. |
The following cables are required for minimum configuration of one MGX 8250 shelf:
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.
Additionally, 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. Run three wires 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.
SM Cable: Table 2-7 summarizes the type of interfaces provided by the different service modules:
| Service Module | Interface |
8 T1s ports | RJ-48 connector |
8 E1s ports | RJ-48 or SMB connector |
T3/E3 ports | BNC connector |
HSSI ports | SCSI-II connector (according to ANSI/TIA/EIA-613) |
Ethernet ports | RJ-45 connector |
Fast Ethernet ports | RJ-45 connector |
FDDI ports | SC connector |
PXM1 OC-3 multimode ports | SC connector |
PXM1 OC-3 single mode ports (IR and LR) | SC connector |
PXM1 OC-12 single mode ports (IR and LR) | SC connector |
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 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 long/wide.
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 (CPE, for example).
Posted: Mon Oct 2 17:00:59 PDT 2000
Copyright 1989-2000©Cisco Systems Inc.
