User Guide

AB-Access Config & User Guide 5.5 Axxcelera Broadband Wireless
July 27, 2004 Company Confidential Page 12 of 129
3 AB-Access Overview
3.1 Topologies
There are three topologies that are available with the AB-Access units CLIP, 1483 Bridging,
and Native ATM. There are several configuration variations within these topologies but all will be
referred by these names with an extension.
3.1.1 CLIP (RFC 1577)
CLIP stands for Classical IP and is a routed topology. The AP or SU acts as a standard
Layer 3 IP router, which means when data comes into the unit it analyzes the IP header and sends it
out one of its interfaces based on the information in the header and its routing tables. It is important
to note that only IP traffic can be passed over the units in this configuration.
3.1.2 1483 Bridging (RFC 1483)
1483 Bridging is a Layer 2 bridge, which will pass any valid Ethernet frame regardless of
protocol. 1483 is also referred to as MPoA (Multi-protocol over ATM). The basic concept of how the
bridge works is simple. It has two tables one for the terrestrial interface and one for the wireless
interface. The terrestrial table stores all source MAC address it has learned from the terrestrial
interface. It learns the MAC addresses by storing the source MAC address of any packet that has
originated from a device on its terrestrial interface. If a packet is received that has a destination MAC
address that is already in the table it will be discarded. The reason for this is if the destination MAC
address is in the table it must mean that the device with that MAC address is on the terrestrial side
of the radio. The wireless table works in the same manor except it learns the source MAC address of
packets that have been received from the wireless interface. It is important to note that all broadcast
packets will be sent over the link. It is also important to note that the implementation of 1483 bridging
that the AB-Access system uses is LLC/SNAP encapsulation and we do not support the VC
multiplexing implementation.
3.1.3 Native ATM
Native ATM is a mode where both the AP and the SU act as an ATM switch. In this mode
ATM cells are simply passed through the switching layer of the radio at layer 2. It is important to note
that the AB-Access radio only supports PVC and not SVC.
3.1.4 PPPoA (RFC 2364)
PPPoA is no longer supported.