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AL121
Advance Information
8 Port 10/100 Mbit/s Dual Speed Fast Ethernet Switch
Product Description
The AL121 is an eight-port 10/100 Mbit/s dual speed Ethernet switch. A low-cost and scalable
solution for up to 32-ports is achieved through the use of low-cost buffer memory and Allayer's
proprietary RoX-II architecture. In addition, the AL121 also supports port-based VLAN and
multiple port aggregation trunks.
Figure 1
System Block Diagram
Supports seven 10/100 Mbit/s Ethernet ports
with RMII and one 10/100 Mbit/s Ethernet
port with MII/RMII interface
Capable of trunking up to 800 Mbit/s link
with link fail-over
Full- and half-duplex mode operation
Supports 1K MAC address tables
Scalable design for stackable switch imple-
mentation
RoX-II expansion link supports 6.4 Gbit/s
throughput
Flexible prioritized queueing for multimedia
and data traffic
Gigabit Ethernet ready with AL1022
Layer 3/4 switching with AL3000 on RoX-II
IEEE 802.3x flow control for full-duplex
operation
Optional backpressure flow control support
for half-duplex operation
IGMP frame trapping
Supports 64 IP multicast groups
RMON and SNMP support with the
AL300A management (MIB) device
0.25 micron, 2.5V / 3.3V CMOS technology
2.5V and 3.3V operation
Packaged in 272-pin BGA
10/100 MAC
10/100 MAC
10/100 MAC
10/100 MAC
10/100 MAC
10/100 MAC
10/100 MAC
10/100 MAC
High Speed
Switch Fabric
Switch
Controller
Address
Control
Address
Table
Buffer
Manager
EEPROM
Interface
Management
Information
Expansion
Interface
AL121 Advance Information
2/2000
Reference Only / Allayer Confidential
2
AL121 Overview
The AL121 is an eight-port 10/100 ethernet switch chip with RoX-II expansion interface. The
RoX-II interface is a 3.2 Gbit/s interface (6.4 Gbit/s full-duplex). The RoX-II Bus can support up
to four switch chips and one management or router chip. Various combinations can be used for
different configurations. The maximum port configuration will be 32-port 100 Mbit/s ports or 24-
port 10/100 Mbit/s plus two Gigabit Ethernet ports, or eight gigabit ports. Higher port count
stacking configurations can be achieved with additional bridges and crossbar devices.
The RoX-II interface supports an external management device, the AL300A. SNMP and RMON
are supported through this management device. The RoX-II interface also supports Layer 3 and
Layer 4 switching provided by the AL3000. Because the AL3000 has all the AL300A functions
integrated, there is no need for the AL300A if the AL3000 is already on the RoX-II bus.
The AL121 also supports trunking applications. The chip provides two optional load balancing
schemes, explicit and dynamic. With trunking, it is possible to group up to eight full-duplex links
together to form a single 1600 Mbit/s link. The device also supports the current IEEE 802.3ad
specification.
Data received from the MAC interface is stored in the external memory buffer. The AL121
utilizes cost effective SGRAM to provide 8 Mbit or 16 Mbit of buffer memory.
The AL121 provides two flow control methods. For half-duplex operations, an optional jamming
based flow control (also known as backpressure) is available to prevent loss of data. With this
method of flow control, the switch will generate a jam signal when the receive-buffer is full. In the
full-duplex mode, the AL121 utilizes IEEE 802.3x as the flow control mechanism.
All ports support multiple MAC addresses.
For managed switch applications, the AL121 supports network management through the network
management option. When the management option is enabled, network statistics for each port are
gathered and sent across the RoX-II bus. The management information base chip on the bus will
collect and store the data for the network management agent. Access to the statistic counters is
provided via the CPU interface of the AL300A.
The AL121 operates only in the store and forward mode. The entire frame is checked for errors
and any frames with errors are automatically filtered and are not forwarded to the destination port.
The device also provides 64 IP multicast group addresses for IP multicast applications.
The switch is initialized and configured by an external EEPROM. For an unmanaged switch
design, there is no need for a CPU. A parallel interface can be utilized to reprogram the EEPROM
for field reconfiguration.
The device supports port based VLAN for workgroup and segment switching applications.
The device also provides two levels of security for intrusion protection. Security can be
implemented on a per-port basis.
Other features include port monitoring and broadcast storm filtering to reduce broadcast traffic
through the switch.
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