Avaya M-ACCF/SF manual Physical Layer, Extending VLANs into the ATM Network

Chapter 1 Overview

Physical Layer

The physical layer is responsible for transmitting and receiving ATM cells over a physical medium. It is also responsible for checking the integrity of the bits being transferred over a physical media, and for making sure that they are error-free.

The ATM access module is compliant with both SONET STS-3cand SDH STM-1physical layer standards.

These standards are similar, and most devices allow you to use either framing standard on each link in the ATM network.The same framing standard must be used at each end of the link.

Many users prefer to use the same framing standard throughout their network (for example SONET STS-3c).

The physical layer is sub-divided into:

•Path — SONET and SDH are capable of carrying traffic for a number of upper layers, and ATM is only one of those layers. Each upper layer uses its own Path through the SONET/SDH layer.

•Line — A line is the whole path between one ATM device and the adjacent ATM switch or ATM end-station.

Extending VLANs into the ATM Network

You can use LAN Emulation to define and extend VLANs seamlessly through the ATM network, as shown in the example in Figure 1.17.

Traffic from one Emulated LAN (ELAN) is not seen on another ELAN as they are logically separate domains. For this reason, when you plan your network, you should consider what ELANs you require, and how the VLANs will map to these ELANs.

The ATM access module has a LEC for each of the Switch’s 16 VLANS, and each VLAN/LEC can be mapped onto an ELAN. In this way, Ethernet traffic is mapped to an ELAN by a VLAN-to-LEC association. The mapping of VLANs to ELANs is shown in Figure 1.16.

When an Ethernet device attached to a Switch generates traffic, the Switch forwards the frames to the appropriate port.

A unicast frame is only forwarded to a port if the address of the destination device is known to be on that port and the destination port is in the same VLAN as the source port. If a unicast frame is forwarded to the ATM port, the ATM port uses the destination MAC address to identify the ATM connection to use.

A broadcast or multicast frame is forwarded to all ports in the same VLAN as the source port. If a frame is received by the ATM port, the ATM port forwards it to the BUS for the associated VLAN.

24 Avaya M770 M-ACCF/SF ATM Access Modules User’s Guide