ATM and LAN integration
1. LAN EmulationLAN Emulation (LANE) is a layer 2 bridging protocol that operates at the media access control (MAC) sublayer.
And LANE is defined in an Asynchronous Transfer Mode (ATM) standard.
LANE encapsulates network layer packets, such as IP packets, in ATM cells.
Or it reconstructs network packets from ATM cells.
After protocols are processed at an Ethernet level, a LAN switch, which has LANE capability, maps the protocol to an ATM cell.
While the cells are transferred across an ATM network, only the ATM and physical layer information is processed.
Layers higher than the ATM layer are transparent to the ATM network, and their information is processed only once it is received on a different section of the LAN.
By operating at such a low layer, LANE enables ATM networks to function as connectionless Ethernet LAN segments.
LANE also allows existing LANs to use an ATM backbone by specifying how nodes in a mixed network environment should communicate with one another.
Using an ATM backbone allows connectivity between connection-oriented ATM networks and connectionless networks, such as Ethernet or Token Ring networks, that the IP protocol requires for data transmission.
LANE provides functionality that classical IP over ATM transmission does not offer.
With LANE, devices do not need to discover the MAC address of destination devices because the LAN Emulation Server (LES) registers client MAC addresses and maps them to ATM addresses.
Additionally, LANE provides broadcast functions and accommodates multiple protocols, so it is not restricted to IP network traffic.
The LANE 2.0 specification supports redundancy, replicated services, and MultiProtocol over ATM (MPOA) for larger networks, such as campus and enterprise networks.
A LANE 2 a LAN emulated user-to-network interface (LUNI) has been defined in which LAN emulation clients (LE clients or LECs) interact with an LAN emulation service.
LECs are LAN devices that have an interface to the ATM network.
The interaction between LECs and an LE service has the following distinct phases:
initialization
registration
address resolution
data transfer
initialization
During initialization, LECs acquire the ATM addresses of the LE services on a network.
Each instance of an LE service has its own ATM address.
Additionally, each LEC is associated with a particular emulated LAN (ELAN) and having been associated with an ELAN the LEC gives a declaration as to whether or not it wants to receive address resolution requests for frames with unregistered destinations.
registration
During registration, the LE service is informed of the MAC addresses that the LEC services.
This function is vital as the LEC, which may be a host on an Ethernet or Token Ring LAN segment, is the point of access for all of that segments clients to the emulated LAN.
address resolution
During address resolution, the LE clients can determine the ATM address that is associated with a particular MAC address.
It is also used to obtain the ATM address of an LE service using a particular multicast MAC address.
data transfer
During data transfer, LE Service Data Units (LE-SDU) are formatted into ATM Adaption Layer (AAL) 5 frames.
These frames transfer data from the source to the destination. The main components of LE service are a
LAN Emulation Configuration Server (LECS)
LES
Broadcast and Unknown Server (BUS)
Question
Which of the following do you think is a typical setup for the LE service components – LECS, LES, and BUS?
Options:
Three separate servers linked to a high-speed connection
Three server software components installed on a single router
Three servers positioned on an Ethernet network with three mirror servers on the ATM network
Answer
The three LE service components are typically installed on a single router or switch device.
Option 1 is incorrect. Although LECS, LES, and BUS are often depicted as three separate servers, they are software components that can be installed on a single device. Although they may be implemented in a distributed manner, it is typically not the case.
Option 2 is correct. LECS, LES, and BUS are all software components of the LE service. In order for LE to function correctly, these components need to be set up on a single hardware device – for example, a single router or switch.
Option 3 is incorrect. LECS, LES, and BUS are software components that are typically installed on a single device, and only one instance of the LE service is implemented per ELAN.
2. LAN Emulation Configuration ServerThe LECS assigns an LEC to an ELAN.
An LECS can carry out these functions for a set of ELANs through its configuration database, which determines the ELAN to which a device belongs.
The assignment to an ELAN can be based on either a physical (ATM) address or logical (MAC) address.
Each ELAN has one instance of an LE service and at least one LEC.
Each LEC registers with the LECS when it joins an ATM network.
The LECS supplies each LEC an ATM address for a specific LES.
In this way, each Token Ring or Ethernet segment has an associated LEC that handles data transfers to a particular ELAN within the ATM switch cloud.
An LECS detects failures in LE service components that may result in failure or a loss in connectivity between nodes on an ELAN.
You can also use an LECS to monitor network performance by querying the status and throughput of each LES.
You can use these results to load balance traffic.
The LECS database processes the following entry types:
an ELAN name paired with an LEC MAC address
an LEC ATM template paired with the ELAN name
an LES ATM address paired with the ELAN name
the default ELAN name
3. LAN Emulation ServerThe LES component of LANE provides address-resolution functions.
It also provides joining and address-registration functions to LECs in its ELAN.
An LES forwards address-resolution information to other LESs in control frames over a LANE Network-to-Network Interface (LNNI) using virtual channel connection (VCC).
The LNNI allows for the efficient deleting of cached registration data by handling notification of an LES failure on a network.
The LANE 2.0 specification caters for multivendor interoperability because it specifies the requirements and procedures needed for LES failure detection and cache register deletion whereas LANE 1 did not.
Because LESs process LANE Address Resolution Protocol (ARP) requests, they can convert MAC addresses to ATM addresses.
This conversion enables nodes on a network to communicate with one another.
In this way, the LES on the LEC’s ELAN resolves the physical (MAC) address of the ATM interface card on each LEC into an ATM address.
The Broadcast Unknown Server (BUS) component of LANE sequences and distributes broadcast information regarding ELAN members.
Its main purpose is to distribute data that has a multicast address, or a unicast address where the ATM address is unknown.
Question
What type of traffic do you think BUS handles?
Options:
Multicast
Broadcast
Unicast flooding
Unknown traffic
Answer
BUS handles multicast, broadcast, unicast flooding, and unknown traffic.
Option 1 is correct. BUS handles multicast traffic, which means it can transmit a single message to a select group of recipients. A simple example of multicasting is sending an e-mail message to a mailing list. Teleconferencing and videoconferencing also use multicasting but require more robust protocols and networks.
Option 2 is correct. BUS handles broadcast traffic, which means it can simultaneously send the same message to multiple recipients. Broadcasting sends a message to everyone on the network, whereas multicasting sends a message to a select list of recipients.
Option 3 is correct. BUS handles unicast flooding traffic, which is the communication that takes place over a network between a single sender and a single receiver.
Option 4 is correct. BUS handles unknown traffic, either from an unknown source or destination, by directing it to the appropriate destination.
SummaryLAN Emulation (LANE) is a bridging protocol that operates at the media access control (MAC) sublayer. By operating at such a low layer, LANE enables Asynchronous Transfer Mode (ATM) networks to function as connectionless LAN segments. LANE has three main components – LAN Emulation Configuration Server (LECS), LAN Emulation Server (LES), and Broadcast and Unknown Server (BUS).
The LECS component of LANE assigns a LAN Emulation Client (LEC) to an Emulated LAN (ELAN). Each ATM switch cloud typically has one LECS, and this LECS supplies an LES address to particular LECs on a network. The LECS also assists with network monitoring tasks.
The LES component of LANE provides address resolution functions. An LES forwards address resolution information to other LESs using control frames over an LANE Network-to-Network Interface (LNNI) control VCCs. The BUS component of LANE handles all multicast traffic and traffic that uses the broadcast MAC address.
Table of Contents | Top of page |
| Learning objective |
| 1. LAN Emulation |
| 2. LAN Emulation Configuration Server |
| 3. LAN Emulation Server |