Netware Super Library/Netware Super Library.iso/app_note/an006b/an006b.txt

Text File | 1991-01-28 | 26KB | 587 lines

Novell NetWare and AT&T ISN

 Brian Howell
 Consultant
 Systems Engineering Division

Abstract:

This application note shows the relative performance of a NetWare network
when compared to a NetWare network bridged by an AT&T  ISN.

Introduction

Purpose of Report

The purpose of this report is to show the relative performance of a Novell
NetWare network when its distance and access capabilities are enhanced by
the introduction of AT&T's Information Systems Network (ISN).

To establish the compatibility of AT&T 802.3 packets and NetWare 802.3
packets a preliminary test was conducted. NetWare network packets on an
802.3 network were passed to another NetWare network across an ISN
containing two Ethernet Bridge Interface Modules (EBIMs.)

Two Stages of Initial Testing

Initial testing was in two stages: first with one network workstation and
then with five network workstations performing a variety of common network
operations. These tests indicated that response time was significantly
longer for one workstation than it was for five workstations when identical
operations were performed. This result was opposite of what would be
expected with a typical 802.3 Carrier Sense Multiple Access/Collision
Detection (CSMA/CD) network.

Subsequent Testing and Results

Subsequent testing indicated that poor performance of a single workstation
was due to the inherent buffering design built into the EBIMs. In other
words, the performance actually increased as traffic increased. When only
one workstation was performing a given operation, the packets would be
buffered or held up until the buffer was full. When the buffer was full it
would transmit all of the buffered packets. When five workstations were all
performing the identical operations, the buffers filled faster and there
was less delay imposed by the ISN than when a single workstation was in
use. The ramifications of this design mean only that data traffic and usage
patterns should be given careful consideration when using an ISN to connect
remote NetWare networks. Special attention should be given to the amount
and type of operations that are being performed over the connections
provided by the ISN.

Description of the ISN

The Information Systems Network (ISN) is a networking product from AT&T
that consists of virtual packet switching controllers and various
communication modules (see Figure XX). The communication modules connect a
wide variety of hosts, printers and communications resources. The network
can be configured so that resources on the network can be shared by network
users. Remote concentrators extend the packet controller to users beyond
the reach of the packet controller by way of a fiber optic link or by
leased lines.

Figure 1: ISN packet controller

Packet Controller Connections

Packet controllers at different locations can be connected to create a wide
area network (WAN). The packet controllers communicate through fiber optic
links at 8.64 Mbit/s or through trunk modules that run at speeds of up to
2.048 Mbit/s. These trunk connections make communications possible across
town or across the country (see Figure XX).

Figure 2: Multinode architecture

Using AT&T's Premises Distribution System

The ISN uses AT&T's Premises Distribution System to distribute the network
to the workstation. This system is based on twisted pair wiring, fiber
optic links and modular cross-connect hardware. It makes possible a
multitude of configuration options (see Figure XX).

Figure 3: Single node architecture

Packet Description

The data transported on the ISN is broken into short packets containing a
fixed number of bits. The packets contain source and destination address
information that is appended to the data. When a user at a workstation (or
endpoint) issues a call setup request to another endpoint or resource, the
controller stores the addresses in memory. Once a call is in place, the
packets arriving at the controller have their destination addresses
replaced by the stored address and are then sent to their destination. The
virtual, or switched, connection can be taken down by one of the users and
the address is removed from memory.

Contention and Transmit Bus

Contention for the transmit and receive buses that run at 8.64 Mbit/s, is
handled by the contention bus that runs at 864 Kbit/s. Each module with a
packet to send, sends a contention code of 18 bits to the contention bus.
The code is compared with the codes of other contending modules. Based on
the value of the contention code, one module is declared the winner and
given exclusive access to the next available time slot on the transmit bus.
The contention and transmit buses of the ISN are synchronized so that the
contention bus carries a contention code in the same time that a data
packet is transmitted by the transmit bus. Modules that lose contention for
the bus back off and contend for the next available time slot.

A round robin priority algorithm allows modules that have lost contention
to raise their priority code until they win. In the ISN the short length
and high speed (8.64 Mbit/s) of the transmit and receive buses makes the
propagation delay shorter than the time that defines a single bit. The ISN
is thus able to perfectly schedule access to the transmit bus. This
technique permits a very high (80-90 percent) use of the backplane without
any serious performance degradation. Both long and short messages are
broken into a series of short packets that are interspersed in time on the
backplane buses. By sending messages a little at a time, delay in buffering
large messages is avoided. This results in much more efficient use of
transmission facilities, and it allows for shorter delays in transmission
times especially when multiple packet controllers are traversed.

Implementation

By implementing techniques described above, the ISN provides a high-speed
and versatile network that will accommodate centralized as well as
decentralized computing implementations. This maximizes the effectiveness
of the computer and peripheral resources of an organization.


Introduction to the EBIM

The Ethernet Bridge Interface Module (EBIM) is one of the many
communications modules that can be placed in the ISN controller or ISN
concentrators. Its purpose is to bridge separate Ethernet network segments.
The module conforms to the IEEE 802.3 (Carrier Sense Multiple Access with
Collision Detection) and Ethernet version 2 specifications. The EBIM
implements only the lower two levels (Physical level and Data Link level)
of the International Standards Organization's Open Systems Interconnect
(OSI) model. Devices on bridged Ethernet networks must therefore use
identical implementations of the higher level protocols.

Possible Connections

A maximum of nine EBIMs can be interconnected. Each EBIM has eight
permanent virtual circuit connections. Since each PVC requires two
connections, a total of 36 PVCs can be established. A total of 4,000 Media
Access Control (MAC) addresses can be supported across all bridged
networks. This limitation is imposed by limited memory space in the EBIM
and not by the Ethernet networks.

Up to eight interconnected Ethernet networks make up an extended network.
Five of the extended networks can be connected to allow a total of 40
Ethernet networks to communicate with each other. However, the extended
network configuration reduces the throughput because of the number of hops
or bridges that the data must traverse in order to reach its destination.


Test Configuration

AT&T ISN Configuration             Novell NetWare Configuration

AT&T ISN Model 60 E                File Server - Novell 386A

EBIM Firmware Level 2.0            Network Interface Card - NE1000

Software version 4.1.1             Operating System: SFT NetWare v2.12

Figure 4: Test configuration 1

Test Descriptions

Packet Arrival Time

Packet arrival times were measured to show the impact of an ISN on the
performance of a local network. It should be noted that the ISN is designed
to take advantage of long distance communications facilities such as
telephone trunk lines and fiber optic links. Because of the increased
capabilities the ISN adds to a network, it is not expected to perform the
same as a native CSMA/CD network. In order to assess the impact of the ISN,
a test was made on the Novell network by transmitting a file from the file
server to a workstation. A simple file copy was performed from the file
server to the hard disk of the workstation. A network protocol analyzer was
used to capture, record and measure the transmission. This was done with a
Network General Sniffer and a Novell LANalyzer. The test was performed on
one workstation and on five workstations. After taking the measurements on
the native network, the tests were redone with the same file server and
workstations with the ISN acting as a bridge between the file server and
the worksations. Figure XX shows the packet arrival time distribution.

Master Test Battery

The master test battery is a series of 11 tests that consist of 11 of the
most common network operations. The test is designed to perform a given
operation as many times as it can in the space of the test duration (20
seconds). The program counts how many times per second the operation was
performed and displays a numeric value upon completion. Again, this test
was run on the native network and then again on the network with the ISN
bridging the file server and workstations. The master test results are
shown in Figure XX.

Kbyte/s

As an additional method of showing the impact the ISN has on the
performance of the network, a protocol analyzer was used to take a reading
of the data flowing on the network for the duration of the tests. In all
cases the number shown indicates the peak load of traffic generated. The
measurements were taken in unrestricted mode and noted all traffic,
regardless of source or destination. Figure XX illustrates the measurements
for each of the operations in the master test battery.

Packet Arrival Time Distribution

Explanation

The graph shown in Figure XX displays packet arrival times in milliseconds.
It compares the percentage of the total number of packets sent and the
number that arrived within a given time frame. The operation performed is a
file transfer of a 25,184 byte file. The graph also contrasts the
percentage difference for one workstation against that of five
workstations.

Note: Appendix A lists a summary of the measurements.

Observations

Without the ISN both one and five workstations had almost 90 percent of the
packets arrive within the first four milliseconds. When the same file was
transmitted with one workstation over the ISN only 50 percent made it
within the first four milliseconds. The other 50 percent arrived within 25
to 29 milliseconds. When five workstations performed the file transfer, 50
percent arrived in the first four milliseconds and 40 percent of the
remaining packets arrived within the next five milliseconds, making
approximately 90 percent that arrived within the first nine milliseconds.

Figure 5: Packet arrival time distribution

Master Test Results

Explanation

The graph shown in Figure XX represents the number of operations per second
performed for each of the eleven operations in the test battery. The chart
shows the difference in the number of operations per second that can be
performed with and without the ISN. The numbers are included for the tests
using one workstation and five workstations. The graph represents the
average of the five workstations and indicates a per workstation number of
operations per second.

Observations

In every operation except one, the single workstation without the ISN was
able to accomplish the most operations per second. This is as expected.
However, depending on the operation being executed, the difference in
performance between one and five workstations is not as great when using
the ISN as it is when the operations are performed on a local network
without the ISN.

Figure 6: Master test results

Kbyte/s

Explanation

Figure XX, Figure XX and Figure XX are graphs that show the number of
Kbyte/s generated during the master test battery, performed first by one
workstation and then by five workstations. The first two graphs show the
difference in data traffic generated with and without the ISN.

Observations

The following two graphs show the difference in the traffic generated when
the traffic over the ISN is local rather than remote. The percentage of
difference is not the same for one workstation as it is for five
workstations.

Figure 7: Kbyte/s for one workstation

Percentage of Kbyte/s

Explanation

In the following graph 100 percent is the number of Kbyte/s that can be
generated on a native NetWare network without the ISN. (See configuration
1.) The chart compares the percentage of traffic that can be generated by
one workstation and by five workstations during the master test battery on
a network with the ISN.

Observations

The first category listed is the average percentage difference for all of
the operations executed by one workstation compared to the average
difference of five workstations performing the same operations. The chart
illustrates that one workstation connected remotely by the ISN can generate
approximately 32 percent of the traffic that a workstation can generate on
a local network. Five workstations can generate approximately
54 percent of the data that the same workstations can generate on a local
network.

Note: See Appendix A for a summary table of the number of Kbyte/s for each
of the operations in the master test battery.

Figure 8: Percentage of Kbyte/s

Average Operations Per Second

The following graph depicts the incremental changes in the performance
curve created by adding additional workstations. The operation performed
for this graph is the open/close file in multiple directories in the master
test battery. The numbers will be different for each operation performed,
but the basic curve of the graph will be the same.

Observations

The line depicting the performance curve of the operations performed on a
network without the ISN follows the same curve that a typical CSMA/CD
network follows. Initially, the degradation in performance is slight as
workstations are added. As increasing numbers of workstations and traffic
are added, the network reaches its saturation point and performance drops
off dramatically.

The line showing the performance of the workstations on the ISN network
illustrates that the curve generated by this network varies from typical
CSMA/CD networks. An important point to note is that performance actually
improves as workstations are added. This is true to a point at which the
ISN network follows the same characteristics as a typical CSMA/CD network
and performance drops off sharply. The reason performance improves is
because the buffers in the EBIMs are not waiting as long to be filled when
more workstations generate packets.

Note: See Appendix A for the summary table of the master test battery
results.

Figure 9: Performance curves

Throughput Test

The throughput test was designed to measure the maximum amount of traffic
the ISN is capable of handling.

The test was done by simulating a load on the network. During the test it
was demonstrated that the ISN could consistently transport 950 Kbit/s each
way. If that amount was exceeded, the packets were either discarded or the
workstations could not get enough packets through to complete the operation
and the application would time out. By tuning the traffic generated on the
network, it was possible to determine the maximum amount of traffic that
allowed the file transfers to complete. It was shown that the ISN is
capable of a throughput of approximately 1.9 Mbit/s (950 Kbit/s in each
direction). AT&T representatives say that for network planning purposes, a
level of 1.5 to 1.7 Mbit/s should be expected.


Conclusions

Based on the previously mentioned tests and measurements, the ISN proves to
be a viable alternative for many network implementation applications.
Because of the 182KB receive buffer and 192KB transmit buffer built into
the EBIMs, the functional performance obtained at a low load level will
seem inconsistent with the performance capabilities inherent in the EBIM
design. In fact when the EBIMs are pushed to their maximum capacity, they
approach the throughput levels on a native CSMA/CD network.

Based on these results, the ISN is a viable network alternative for
extending Novell NetWare networks beyond the reach of existing media
limitations. The ISN is another tool in the enterprise-wide implementation
of NetWare networks.


Appendix A: Raw Data Tables

Packet Arrival Time Distribution

One workstation w/EBIM        One workstation w/o EBIM

ms   Packets                  ms   Packets



0 - 4     84   51.53%         0 - 4     143  87.73%

5 - 9     0    0.00%          5 - 9     3    1.84%

10 - 14   0    0.00%          10 - 14   5    3.07%

15 - 19   0    0.00%          15 - 19   8    4.91%

20 - 24   0    0.00%          20 - 24   0    0.00%

25 - 29   79   48.47%         25 - 29   0    0.00%

>30       0    0.00%          >30       4    2.45%

          163  100.00%             163  100.00%



Five workstations w/EBIM      Five workstations w/o EBIM

ms   Packets                  ms   Packets



0 - 4     419  51.41%         0 - 4     735  90.18%

5 - 9     321  39.39%         5 - 9     17   2.09%

10 - 14   0    0.00%          10 - 14   29   3.56%

15 - 19   42   5.15%          15 - 19   7    0.86%

20 - 24   0    0.00%          20 - 24   8    0.98%

25 - 29   32   3.93%          25 - 29   8    0.98%

>30       1    0.12%          >30       11   1.35%

          815  100.00%                  815  100.00%

Note: ms = milliseconds


Kbyte/s Summary Table

                                   Five workstations   One workstation

Open/close file - mult. directories     45   68             9    31

Open/close file - single directory      45   95             9    42

Small shared file random read           40   176            8    55

Large shared file random read           18   22             4    7

Private file 128KB seq. read            45   48             9    16

Private file 128KB random read          130  341            35   128

Large block file transfer               130  414            40   192

Create/write/close/delete               120  131            35   79

Record lock/unlock                      50   132            17   55

Directory search (*.*)                  50   131            13   50

Random directory search                 60   150            12   45


File Xfer Test

               Local network                 Bridged network with ISN

               Seconds             AVG       Seconds             AVG

1,205 Bytes    0.60   0.78  0.78   0.72      2.20   2.00   1.76  1.99

5,079 Bytes    0.84   0.92  1.02   0.93      2.08   1.88   2.10  2.02

10,752 Bytes   1.08   0.91  0.98   0.99      2.31   2.36   2.22  2.30

25,184 Bytes   1.49   1.33  1.32   1.38      2.87   2.89   2.82  2.86

50,176 Bytes   1.87   1.77  1.69   1.78      3.26   2.80   2.95  3.00

108,048 Bytes  2.34   2.37  2.26   2.32      4.57   5.11   5.70  5.13

214,705 Bytes  5.07   3.64  3.54   4.08     10.71   9.81   9.59 10.04


Test Descriptions

A. Network Test Battery

The network test battery is a utility developed by Novell for benchmarking
and measuring network performance. The battery is a series of commonly
performed network operations. The name of each test describes the operation
that is being performed. Each of the operations was performed for 20
seconds except for tests eight and nine (the directory search tests), which
were performed for a duration of 10 seconds each. The numeric value to the
right of the tests indicates the number of operations per second that could
be performed within the time frame of the test duration. Each of the
individual tests is described in more detail below.

1. Open/close file (multiple directories) (no disk activity)

This test measures the number of file opens and closes the file server can
perform per second. The files opened are selected randomly within the four
levels of subdirectories. Besides testing the speed at which the file
server can do an open and close, this test also measures the time it takes
the server to traverse the hierarchical directory structure.

2. Open/close file (single directory) (no disk activity)

This test is the same as the open/close file test, except the files opened
are confined to the highest level directory. Comparing the results of this
test with the open/close file test illustrates the difference that
traversing the hierarchical directory structure makes. This test focuses
more on raw file open and close speeds.

3. Small shared file random read (4KB) (no disk activity)

This test measures the software time required to perform disk read
operations, excluding managing the disk channel. The requests are for only
1 byte of data, to minimize the packet size and the transfer time between
the file server and network adapter. The file is shared so the workstation
PC cannot do local buffering and must access the file server for every
request. This test is the best measurement of how long it takes the
operating system software to service a read request. As such, it is a
measurement of software efficiency, excluding, as much as possible, the
hardware I/O factor. Disk read is the most common file server request made.

4. Large shared file random read (4MB) (requires disk activity)

This test measures the time it takes to randomly read a large database-
type file. The requests are for only 1 byte of data, again to minimize the
packet size and the transfer time between the file server and network
adapter. Since the file is so large, only parts of it can be cached in the
server RAM, and each request probably has to go to the hard disk.

5. Create/write close/delete (requires disk activity)

This test measures the speed at which the file server can create and write
to a new file, then close and delete the file. The write is a large 16KB
request, similar to the large block file transfer test. This test is the
most disk I/O intensive of all the tests. The elevator seeking and caching
algorithms in the server make a difference with this test.

6. Private file random read (128KB) (requires disk activity)

This test illustrates the problems of local caching by the PC. A private
file is randomly read 64 bytes at a time. The MS Net-based operating
systems will read more than 64 bytes around the request and cache it
locally. However, the effort spent servicing the larger read is wasted,
because the file accessing is random and extra data read will probably not
be needed.

7. Large block file transfer (16KB) (no disk activity)

This test measures the efficiency of the server in servicing large I/O
requests. All test workstations issue 16KB read requests to the same file
at the same offset. The MS Net- based servers will service this as one
request; the NetWare-based servers will service it as 16 or 32 requests.
This test also measures the efficiency of the server in transferring data
to and from the network adapter.

8. Directory search test (no disk activity)

This test measures the number of wild card directory searches the file
server can perform per second. A search request can return several matching
directory entries. The next search nexts do not have to make a request to
the file server. NetWare does not return multiple directory entries per
search request and does not cache directory entries in the local
workstations.

9. Random directory search (multiple directories) (no disk activity)

This test shows the speed at which a search for a specific directory entry
can be performed. The test selects a random file within one of the four
directory entries and searches for it. It also randomly selects files that
do not exist to measure the time needed to discover that a file is not
there.

10. Record lock/unlock (no disk activity)

This benchmark tests the speed at which the file server can lock and unlock
records. A single physical record is locked and unlocked by the
workstation.

The file copy test consists of a NetWare copy (NCOPY) performed from a
NetWare drive on the file server to the local hard drive of the
workstation. Two files of significantly different sizes are used. The file
copy is timed from when the enter key is pressed to execute the command
until the workstation reports that the file is copied. The copies are
performed five consecutive times and the averages are listed.

C. Performance Test

The performance test is designed by Novell to measure true data throughput
or performance of a network. This test is completely end-to-end at the
application layer of the ISO model. The test is an application that sends
data to the file server and back as fast as the hardware allows. The
numeric value measures the actual data throughput listed in Kbyte/s. This
does not measure raw bandwidth or transmission capability, but data
throughput capability as seen by a network user performing a network
application. The actual operation performed by the test consisted of data
writes of records 4,096 bytes long. The writes were performed in overlaid
fashion-each record was written on top of the previous record.