Installation Manual

TSUNAMI MULTIPOINT

2-1

Point-to-Multipoint Network Model

When we talk about the PMP network, one should look at the Subscriber Unit (SU)

and the Base Station Unit (BSU) as an integrated transmission and switching medium

with physical ports or access points that interface to end user devices. Each Base

Station Unit or SU represents one such physical port or access point. Packets received

by a SU are transmitted to the Base Station Unit and emerge out from it as a single

data stream. Packets flowing into the Base Station Unit are broadcasted to the SUs,

which select only packets destined for their local networks based on a set of filtering

criteria.

Figure 2-2: Model of the PMP network

Bridging and Address Filters

Depending on the transmission mode selected, the PMP network can function either

as a "bridge" or as an "IP gateway" to the end user. In Bridging mode, the PMP

network provides a direct physical connection between a SU and its Base Station Unit

for the exchange of Ethernet frames between the two entities. To conserve wireless

bandwidth, the SU uses some simple filtering criteria in hardware and software to

prevent traffic destined for local network to be sent uplink. If the destination Ethernet

address is not in the hardware table, the packet is given to software, which provides

further filtering by matching the destination address with local addresses stored in its

ARP table. The size of the ARP table is set to 512.

In the downlink direction, the outbound traffic is filtered in the SU via a

"Programmable Hash Filter". If the destination Ethernet address of a downlink packet

BSU

port

LAN traffic

LAN

traffic

PMP Network