Atm Addressing; Local Area Network Emulation (Lane) - Cisco RJ-45-to-AUX Brochure

Variable bit rate−real time (VBR−RT)—Typically used for connections that carry VBR traffic in
which a fixed timing relationship exists between either VBR video or voice compression.
Variable bit rate−non real time (VBR−NRT)—Used to carry VBR traffic in which no timing
relationship exists for data traffic where a guarantee of bandwidth or latency is needed. This type of
connection is used in Frame Relay where the committed information rate (CIR) of the Frame Relay
connection is mapped into a bandwidth guarantee within the ATM network.
Unspecified bit rate−real time (UBR−RT)—Does not offer any service guarantees whatsoever. This
type of connection is typically for the bursty or unpredictable traffic patterns from LAN protocols
served by ATM routers.

ATM Addressing

ATM devices must have unique ATM addresses in order to connect to other ATM devices. The device at the
other end of your circuit must know your address. ATM uses both private and public types of addresses.
Because the ATM standard has adopted the subnetwork model of addressing, the ATM layer is responsible for
mapping Network layer addresses to the ATM addresses.
Currently, two types of ATM addressing plans are used. The ATM UNI address format defined by ITU−T
uses telephone−type E.164 addresses. This format is used to connect an endpoint to a telephone carrier's
network. One drawback to this type of address is that E.164 addresses are available only from large telephone
carriers, which prevents the addresses from being assigned to competitors and private businesses.
The ISO has defined a second address type that uses a Network Service Access Point (NSAP) format. This
format is used to connect an ATM endpoint to a private network. The ATM Forum has now used this method
to incorporate the E.164 address of the public networks into the address of customers using NSAP addresses.
The ATM Forum is also working on a method for the phone carriers to use NSAP−based addressing on their
networks. Let's take a look at the components of an NSAP address, as shown in Figure 8.5:
Figure 8.5: The format of an ATM NSAP address.
Authority and format identifier (AFI)—Used to indicate which standard is being used for the ATM
address. An AFI of 47 indicates a British Standards Institute address (used by Cisco on all its ATM
devices); an AFI of 39 indicates an ISO address and an E.164 address.
Initial domain identifier (IDI)—Indicates the address allocation and administrative authority.
Domain specific part (DSP)—Contains the actual routing information.
End−system identifier (ESI)—Places the end system's MAC address in the frame.
NSAP selector field (SEL)—Identifies the LANE components.

Local Area Network Emulation (LANE)

In a LAN environment, broadcast support is an inherent part of the networking technology. Legacy networks
have native broadcast support to perform address mapping resolution. In contrast, ATM networks are
Non−Broadcast Multiple Access (NBMA) networks with no such support. The LANE standard was created
by the ATM Forum in 1994 to provide connectivity for ATM networks to legacy Ethernet and Token−Ring
networks.
LANE provides these broadcast services by making an ATM interface look like an Ethernet or Token Ring
interface. LANE gives ATM devices MAC addresses, just like Ethernet or Token Ring devices. Because the
ATM interfaces can use the same frame format as legacy devices, LAN−based applications can run without
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