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Cisco MGX 8220 Installation and Configuration
Release 5.0, Part Number 78-6430-03 Rev. D0, November 2003
Chapter Cisco MGX 8220 System Overview
Traffic Management
Traffic management is provided by the Cisco MGX 8220 Connection Congestion Management
(ACCM) feature. This feature is a v ir tu al so ur ce /v ir tu al d es ti na ti on rat e-based closed loop feedback
scheme between nodes based on ForeSight and the ATM Forum Available Rate specification.
Periodically the round trip d ela y (RTD) of a cel l to the far end and back is cal cu lat ed f or e ach ac tual
connection. The RTD is used to dete rm ine how frequently the ForeSight ra te a djustment cells are sent
to the far end. Based on available b an d w id th an d cu rren t acc ess rate, every few microseconds a
ForeSight cell is transmitted t o the far end with any rate adjustm e nt s th at a re necessary to make better
use of the available bandwidth (rate is adjusted up, down, or fast down). The Cisco MGX 8220 MIB
includes rate (MIR, P I R, and QIR) and adjustm e nt (up%, down%, and fa s t -d ow n%) objects.
ATM Local Management Interface
ATM local management interface (ATM LMI) operates between the Cisco MGX 8220 shelf and the
Cisco BPX 8600 series. The ATM LMI is used to communicate change of status of semi-permanent
connections. The ATM LMI pr o t o co l conforms to the prot o c o l s p e c ifie d in ITU-TS Recomme ndation
Q.2931, Sept. 1994. The ATM LMI also supports optional proprietary extensions to the ATM LMI for
the reporting of node information and BNI queue configurations.
The two end points of the ATM LMI signaling are an ATM LMI process in the BCC in the Cisco
BPX 8600 series and an ATM LMI process in the ASC in the Cisco MGX 8220 shelf. The ATM LMI
PDUs are transported over an AAL 5 co nnec tion (VPI=3/VCI=31) between t he B N I o n th e Ci s co
BPX 8600 series side and the BNM on the Cisco MGX 8220 side. The ATM LMI process in the Cisco
BPX 8600 series can support ATM LMI connections for up to 16 Cisco MGX 8220 shelves.
The Cisco ATM LMI extension (which must b e specifically enabled) uses a no de update status message,
which is sent (Cisco BPX 8600 to Cisc o MGX 8220 shelf or Cisco MGX 8220 shel f to Ci sco BPX8600)
whenever a change in node name, node IP address, major alarm status, or minor alarm status occurs.
The message can optionally contain Qbin status, thereby allowing Cisco MGX 8220 to configure the
BNI port egress queues.
Cisco MGX 8220 Shelf
Physically, the Cisco MGX 8220 shelf consists of cards in a 19-inch rack-mounted shelf.
The shelf can be powered either from a -48V DC source or from a 220–240V AC source. The DC
version includes DC power entry modu les that can be moun te d in the shel f. The A C vers i on requ ir es an
external rack-mounted, AC power module. Both versions require a rack-mounted cooling assembly.
Multiple Cisco MGX 8220 shelves can be mounted in the same rack sharing power and cooling
assemblies. For more information on the shelf a nd power options, see Chapter2, “Common Equipment
Description.”
The Cisco MGX 8220 shelf contai ns 16 slots. Each slot can accommodate a front card and a back card.
Six slots are reserved for common eq u ipm en t m o dule s. The common equipment modules a re th e co re
modules required for the system to operate. Service modules (SMs) occupy the other 10 slots and
provide communication and transfer capab ilit y.
The front row of the shelf is used for function modules. These cards perform the more complex
functions within the unit (for example, Frame Relay to ATM conversion).
The back row is used for line modules. T hese cards provide interfaces to one or mor e transmission lines
connected to the Cisco MGX 82 20 sh el f (fo r exam ple, the trunk line to the Cisco BPX s w i tc h o r an
RS-232 line to a control terminal).