|Title of Invention||
A LAN TRAINER LAB APPARATUS
|Abstract||A LAN Trainer Lab Apparatus comprises a LAN emulator unit having nodes, delay generators , carrier sensing blocks, collision detecting blocks, bit error generator, frame error generator, token generator& grant block, expansion ports; an intelligent network interface unit, being a PC plug-in card based on hardware and software, connected to the LAN emulator unit; PC software for allowing two independent applications, each with its own window, for accessing the network interface unit and also for controlling experiments via LT-shell, being a graphical user interface.|
|Full Text||This invention relates to a LAN trainer lab apparatus.
Today, Local Area Networks (LANs) are in widespread use throughout the world for interconnecting computers in offices, factories and homes. Hence, there is a strong demand for professionals trained in the operation, programming and design of LANs.
There are many types of LANs [Tanenbaum 96]. First, the way in which the computers (or nodes) are interconnected may vary. This is referred to as the Topology. All the nodes may be connected to a single wire in a Bus topology. All nodes may be connected to a single central node in a Star topology. Each node may be connected to two neighbours in a ring topology. Commonly used LAN topologies are shown in Fig 1.
Second, all the nodes on a LAN need to follow certain Protocols or conventions regarding how and when they may transmit and receive data. These protocols are referred to as the Medium Access Control (MAC) protocol or Access Method. Many MAC protocols are in common use; CSMA/CD (Carrier Sense Multiple Access / Collision Detection) in the Ethernet LAN, token passing in the FDDI LAN (Fiber Distributed Data Interface), CSMA in radio-based LANs, to name a few.
LANs are subject to electrical and other noise that may cause corruption and/or loss of data. To ensure reliable data communication, ARQ (Automatic Repeat Request) protocols are used. These protocols check the received data for correctness, and in case of error request retransmission of the data.
Given the above and other complexities in LANs, theoretical study is not sufficient for a competent networking professional. Practical experience is essential.
Using currently available equipment, it is practical to equip a lab with only one specific LAN e.g. Ethernet using bus topology. Students in such a lab can get practical exposure to only this specific LAN. To provide students with experience with a variety of different LANs is prohibitively expensive. Furthermore, as new LAN technologies evolve, further expense would be required to introduce these into the lab.
We have devised an innovative apparatus, the LAN Trainer that provides practical experience with a range of LAN technologies at a very affordable cost. The LAN Trainer, consisting of a Network Interface Unit that can be plugged into a few inexpensive PCs, a LAN Emulation Unit and a PC software enables a user to experiment with LANs having various topologies, LAN sizes, a range of data transmission rates,. MAC protocols, ARQ protocols and other networking protocols. The user can introduce errors in data to study the efficacy of the protocols.
By virtue of its software-intensive design, the LAN Trainer can be field-upgraded at a minimal cost to new LAN technologies in the future.
The LAN Trainer Lab Apparatus, according to this invention, comprises a LAN emulator unit having nodes, delay generators, carrier sensing blocks, collision detecting blocks, bit error generator, frame error generator, token generator & grant block, expansion ports; an intelligent network interface unit, being a PC plug-in card based on hardware and software, connected to the LAN emulator unit; PC software for allowing two independent applications, each with its own window, for accessing the network interface unit and also for controlling experiments via LT-shell, being a graphical user interface.
Fig. 2 shows the components of LAN Trainer. Several of these components can be connected together for LANs of various sizes.
This invention will now be described in further detail by reference to the accompanying drawings wherein
Fig. I illustrates some commonly used LAN topologies
Fig. 2 illustrates components of one of the preferred embodiments of the LAN Trainer
Fig. 3 illustrates a view of one of various possible front panels of the I.AN Trainer Emulator Unit
Fig. 4 illustrates the block diagram of the LAN Trainer Emulator Unit
Fig. 5 illustrates the node architecture
between frames or packets may be corrupted in a controlled fashion.
Thus, without cables, the LAN Emulator Unit mimics the topology and behaviour of several LANs under diverse operating conditions. Several Emulator Units may be connected in series to increase the total number of nodes and total effective distance covered by the LAN.
The block diagram of the LAN Emulator Unit hardware is shown in Fig 4. The building blocks of LAN Emulator Unit are
These are the blocks that simulate the actual node operation depending on the Topology selected. Fig 5 shows various conditions of the nodes in different topologies. It allows data to be transmitted in both forward & reverse direction. When the node wants to transmit depending on the topology selected the node architecture changes according to the topology. Ex: In ring topology the path is cut open to transmit the TX data and does not allow, the incoming data in the ring to pass until data transmission is completed.
This block delays the data by selected number of bits. The data signal propagates down the cable at a constant velocity close to the speed of light. Therefore the propagation delay is directly proportional at cable length. By
Fig. 6 illustrates the block diagram of the NIU card hardware
and Fig. 7 illustrates a block diagram of the NRJ card software.
LAN Emulator Unit (LEU)
The LAN Emulator Unit consists of several blocks (as shown in Fig 4) that makes it funnctionally and behaviounally equivalent to a LAN. It is composed of standard integrated circuits and custom field-programmable gate arrays (FPGA) to give such flexibility to the unit. By means of control buttons and jumper wires, the unit may be made to emulate a variety of LANs. Specifically, the user may select:
1. Topology: Using a control button [A] and also by wiring up the nodes using jumpers [B] the student selects bus, ring, star and other topologies.
2. Data Rate: Using a control button [C] a data rate in a wide range such as 8 Kbps to 1 Mbps is selected.
3. Propagation Delay: Using control button [D], the signal propagation delay is selected. In a LAN, the data signal propagates down the cable at a constant velocity, close to the speed of light. Hence, the propagation delay and the cable length are directly proportional. Thus, the LAN Emulator Unit can be configured for a range of cable lengths.
4. Bit Error Rate: Using a control button [E], error may be inserted into the data at a controlled rate, e.g. 1 in 10 bits to I in 10^ bits. This mimics the data errors due to electromagnetic interference (EMI) that is normal in any operational LAN.
5. Frame Error Rate: Analogous to Bit Error Rate, the boundary marker
delaying the data the propagation delay is introduced in the transmission line and hence the various cable length emulation by the LAN Trainer.
Carrier Sensing block
This block senses the carrier for the presence of data. When the data is absent for more than a specified time then it gives out a data absence signal. It generates a data presence signal as soon as the data is sensed in the carrier. This signal is used by NIU when emulating the CSMA or CSMA/CD protocol.
Collision Detection biock
While a data is getting transmitted from a node and if presence of any other data (other than the transmitted data) is sensed on the carrier then this block generates a collision detection signal to alert all the nodes in the network so that they can take appropriate action. This signal is used in CSMA/CD protocol.
Bit Error Generator
This block introduces bit errors in the data to mimic the data errors due to electromagnetic interference (EMI) that is normal in any LAN operation. It uses a PRBS code as reference to introduce errors according to the bit error selected.
Frame Error Generator
This block corrupts the boundary markers in frames or packets in a controlled fashion. It uses a comparator to identify the boundary markers and corrupt according to the error rate selected.
Token Generator & Grant block
This block generates a token and grants it to the node that requires the token.
This token is passed in a ring until a node grabs it. The node that grabs the token have to release it as soon as it completes its job and the token again continue to go in a ring. This block also generates multiple tokens, false token, etc. to study the concept of Token Management. The token generation by this block can be suspended and this allows the token generation by the upper software layer.
Two ports. Expansion IN & Expansion OUT, are provided so that trainer units can be cascaded. The nodes in all the trainer units when cascaded are connected according to the topology selected. All the required signals to connect nodes in various topologies are available in these ports. These ports also does functions like token passing to the next trainer unit when they are connected, looping back to the first node, etc. automatically.
Network Interface Unit (NIU)
The NIU is a PC plug-in card that can be plugged into the PC bus. It is connected to the LAN Emulation Unit via a multi-core data cable. Each NIU has 2 independent channels and acts as two nodes on the LAN. Hence a LAN Emulation Unit with, say, three PC plug-in cards can act as a 6-node LAN. The NIU card is based both on hardware and software.
The functional block diagram of the NIU hardware is shown in Fig 6. The heart of the NIU is the digital signal processor (DSP). This is interfaced, on one side, via its two high-speed serial ports to the LAN Emulation Unit through line drivers. On the other side, it is connected to the PC bus.
The Interrupt Controller unit maps five events to three interrupts. The events are carrier sense for nodes 0 & 1, Token Grant for nodes 0 & 1, Collision detection. They are mapped in such a way that the interrupts are used effectively depending on the topology selected.
The NIU card software (DSP software) block diagram is shown in Fig 7. A protocol module [A] implements each LAN protocol. The specific protocol is selected by the control module [B] under command from the application
software on the PC. The interface to the PC and the LAN Emulation Unit is through bi-directional queues [C] and the corresponding drivers [D]. This DSP software can be resident in an EPROM on the NIU or can be downloaded from the PC.
Implementation of the protocols in software, together with the facility for downloading of new software is the key to the ability of the LAN Trainer to adapt even to new LAN designs in the future.
The PC Software performs the following functions:
1. Allows two independent applications, each with its own window, to
access the single NIU. This is done by means of a Windows DLL
(dynamic link library). Together with the 2-channel ability of the NIU
card, this allows one PC to act as 2 independent nodes in the LAN.
2. Control of the experiment via a simple, easy to use graphical user
interface referred to as LT-Shell. LT-Shell is available even for
experiments developed by the user.
The LAN Trainer is constructed with the following facilities to operate for learning, teaching, and developing LAN concepts.
Jumpers & Control Switches
Each block (nodes, delay generators, etc.) have input & output ports terminated
with posts. These posts are connected using patch cords thereby interconnecting the blocks and forming a network in required topologies. This allows nodes and other blocks to be added or bypassed by the user.
Control switches are provided to select the topology of operation by the nodes, data rate, bit errors, frame errors, number of bits to be delayed between each node, operation of the LAN Emulation unit in Master or Slave mode when they are cascaded, etc.
Downloadable DSP Software
This software emulates the required MAC protocols - ALOHA, CSMA, CSMA/CD, Token Bus/Ring, etc. This also allows implementing the protocol using PC software by the user. This facility along with PC software and the LEU/NIU hardware units provides a development platform to the user and to adapt new LAN designs in furture.
This software consists of experiment codes, DLL and a library (LT-Shell). The DLL allows two independent applications to access single NIU. The library allows all controls & communication between the DSP software and the PC software that can be upgraded as and when new features are required to emidate new LAN technologies. This structure of PC software together with downloadability of DSP software and hardware combination allows user to implement new protocols, analyze the protocol behaviours implement upper layers of networking and do behavioural analysis.
These are the ports through which LAN Emulator Units can be cascaded to increase the number of nodes and the effective distance in the network thereby emulating the real-life LAN conditions. Addition of nodes in the network increases the traffic and therefore behaviour of the protocol will be more realistic. When these units are cascaded, one among them will be assigned
master and the remaining will become slaves. These ports also does functions like token passing to the next trainer unit when they are connected, looping back to the first node, etc. automatically.
Front Panel Block Diagram
The diagram on the front panel clearly shows the functioning and configurations of the LAN with all necessary user interfaces like jumpers, switches, LED displays, etc. This allows quick understanding and easy operation of the system. All default values are clearly indicated on the panel. The front panel diagram is shown in Fig 3.
Steps to Operate the Trainer
• Plug in the NIU card into the PC.
• Connect NIU card and the LAN Emulator unit through the cable provided.
• Configure the Emulator imit to the required topology using jumpers and switches and other parameters for operation.
• Download the DSP software to the NIU card separately or before the PC software starts operating.
• Run the compiled experiments (application programs) and study the
. functioning & behaviour of the emulated LAN (Or)
• Use the source code to alter, develop new concept, etc. and study the
Some of the salient aspects of this invention are compiled in the following
1. Multi-protocol, multi-t(HX)logy LAN Emulation with a single hardware unit.
2. The above LAN Emulation of LANs spanning several kilometers but
using cables of about one meter.
3. The above LAN Emulation with provision for emulation of future LAN designs without hardware change.
4. The above LAN Emulation providing realistic operational conditions including bit-errors, frame-errors and channel efficiency.
5. Implementation of protocol in software together with the facility for downloading the software to NIU PC plug-in card.
6. Modularity of the LAN Emulator unit
a) To configure & work in different topologies and protocols
b) To add or bypass one or more blocks in the network loop by using jumpers and control switches.
7. Ability to interconnect several LAN Emulator units to increase the number of nodes and the effective distance in the Network and thereby increasing the traffic for real-life LAN conditions emulation.
8. PC software capability together with 2 channel ability of NIU card to allow one PC to act as two independent nodes in the LAN.
9. A LAN Trainer comprising of LAN Emulation Unit, NIU PC plug-in card and PC software to emulate and study the behaviour of various LAN Topologies and protocols under various operating conditions like propagation delays, errors involved in a networic, etc.
The terms and expressions in this specification are of description and not of limitation there being no intention in the use of such terms and expressions of excluding any equivalents of the features illustrated and described but it is understood that various other embodiments of this invention are possible without departing from the scope and ambit thereof.
1. A LAN Trainer Lab Apparatus comprising a LAN emulator unit having nodes, delay generators, carrier sensing blocks, collision detecting blocks, bit error generator, frame error generator, token generator & grant block, expansion ports; an intelligent network interface unit, being a PC plug-in card based on hardware and software, connected to the LAN emulator unit PC software for allowing two independent applications, each with its own window, for accessing the network interface unit and also for controlling experiments via LT-shell, being a graphical user interlace. 7
2. A LAN Trainer Lab apparatus as claimed in claim 1 wherein the nodes simulate the actual node operation depertding on the topology selected and allow data to be transmitted in both forward and reverse directions.
3. A LAN Trainer Lab Apparatus as claimed in Claim 1 or Claim 2 wherein the delay generators delay the data by selected number of bits thereby emulating several kilometers of LAN implementation.
4. A LAN Trainer Lab Apparatus as claimed in any one of the preceding Claims wherein the carrier sensing blocks sense the carrier for the presence of data, giving out a data absent signal whenever the data is absent for more than a specified time and giving out a data presence signal whenever the data is sensed in the carrier.
5. A LAN Trainer Lab Apparatus as claimed in any one of the preceding Claims wherein the collision detection block generates a collision detecting signal for alerting all the nodes in the network.
6. A LAN Trainer Lab Apparatus as claimed in any one of the preceding Claims wherein the bit error generator introduces bit errors, using a PRBS code as reference in the data, to mimic data errors due to electromagnetic interference.
7. A LAN Trainer Lab Apparatus as claimed in any one of the preceding Claims wherein the frame error generator corrupts the boundary markers in frames or packets, in a controlled manner, said frame error generator
in frames or packets, in a controlled manner, said frame error generator employing a comparator for identifying the boundary markers and corrupting according to the error rate selected.
8. A LAN Trainer Lab Apparatus as claimed in any one of the preceding
Claims wherein the token generator & grant block generate a token and
grant it to the node that requires the token, said token being passed in a
ring until a node grabs it, the node grabbing the token releasing the same
on completion of its job, the token again continuing to go in a ring.
9. A LAN Trainer Lab Apparatus as claimed in any of the preceding Claims
wherein the token generator & grant block generates multiple tokens,
false tokens, the said generator & grant block being capable of
suspending the token generation.
10. A LAN Trainer Lab Apparatus as claimed in any of the preceding Claims wherein the expansion ports comprise expansion IN and expansion OUT ports for cotmecting several LAN Emulator Units.
11. A LAN Trainer Lab apparatus as claimed in any one of the preceding Claims comprising jumper and control switches, downloadable DSP software and front panel diagram.
12. A LAN Trainer Lab Apparatus substantially as herein described with
reference to, and as illustrated in, Figs. 2 to 7 of the accompanying
|Indian Patent Application Number||556/MAS/1999|
|PG Journal Number||13/2008|
|Date of Filing||13-May-1999|
|Name of Patentee||INDIAN INSTITUTE OF TECHNOLOGY|
|Applicant Address||IIT P.O., CHENNAI - 600 036,|
|PCT International Classification Number||H04L 12/28|
|PCT International Application Number||N/A|
|PCT International Filing date|