Operation Manual

Product Description
6
Interim Local
Management
Interface (ILMI)
There is a MIB in the User-Network Interface (UNI) specification, ILMI,
which includes sufficient “managed objects” to allow you to control and
configure ATM nodes and terminals. As you will recall, the UNI simply
consists of ATM Forum-developed specifications which define the procedures
and protocols between a user and the ATM network.
ILMI is a link-level management and configuration protocol defined across
the UNI. It plays a vital role in the autoconfiguration of many ATM
parameters including, in particular, ATM addresses. The address registration
mechanisms of the ILMI allow ATM switches to allocate address prefixes to
ATM end systems, while ATM end systems supply the ATM switch with
their unique 48-bit MAC addresses.
Address Registration Using ILMI. One of the most useful features of
ILMI is address registration. This means that your switch can automatically
re-register its ATM addresses if the link goes down — and is reinstated.
Without ILMI address registration, if a link goes down the switch will
remove the addresses from its local Address Table.
The bottom line is that, with ILMI, you do not need to manually configure
ATM end systems with ATM addresses. This is very significant, not only
because ATM addresses are a very user-unfriendly 20 bytes of hexadecimal
symbols but, just as importantly, they allow network administrators to
control the allocation of addresses.
Two Modes Of Ethernet Switching
There are two popular methods to forward information: store-and-forward
and cut-through. Although your switch employs store-and-forward as the
default, you can also choose cut-through.
Store-and-forward Store-and-forward means that your switch stores the entire packet and then
forwards it.
Store-and-forward switching, performed at the MAC layer, allows your
switch to temporarily store packets until network resources, typically a
congested port, are available. Frames which are incorrect, an invalid CRC for
example, are discarded. Store-and-forward switching, therefore, ensures data
integrity, thus preventing network error conditions from being generated
throughout the network.
Store-and-forward mode is implemented when packets are converted to cells
on each ATM transmission.
Cut-through In a cut-through system, the device starts to forward the incoming packet
while the packet is still being received on the inbound link.
Cut-through switching requires software that can both look at the start of the
packet and determine which outbound link is to be used to forward the
packet. Cut-through does not check for errors before forwarding a packet.