Theoretical and Applied Informatics
ISSN 1896–5334
Vol.22 (2010), no. 3
pp. 187–202
DOI: 10.2478/v10179-010-0009-x
A Comparison of Various Types of TNC Controllers
BARTŁOMIEJ Z IELI ŃSKI a
a
Silesian University of Technology
Institute of Computer Science
ul. Akademicka 16, 44-100 Gliwice, Poland
[email protected]
Received 23 December 2009, Revised 15 July 2010, Accepted 29 October 2010
Abstract: TNC controller allows for connection of computer or other DTE hardware to Packet Radio
network. TNC is an autonomous microprocessor system with a modem that allows control radio transceiver
directly from TNC. Nowadays there are various TNC controllers available; they are designed using 8-, 16and 32-bit microprocessors and microcontrollers. In the article, efficiency of transmission using various
types of TNC controllers is compared basing on results obtained in an experimental network. The article
also explains which factors may have influence upon TNC efficiency.
Keywords: AX.25 protocol, TNC controller, protocol performance
1. Introduction and Related Work
AX.25 protocol [9] belongs to the HDLC protocol family and is used as a data link
layer in the amateur Packet Radio network that can be considered as an example of
a simple wireless wide area network. Transmission hardware designed for Packet Radio,
namely TNC (Terminal Node Controller), may also be used as examples of protocol
converters that allow for integration of wired and wireless network segments [13]. It
can be used, among others, in some telemetry or remote control networks, including
those operating according to APRS (Automatic Position Reporting System) [12] protocol
requirements.
Packet Radio network, as a solution of radio amateurs, has never been popular, which
is acknowledged by small number of literature covering this subject. In particular, there
is lack of in-depth analysis of factors that may influence on effective network parameters,
such as throughput or transmission delays.
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RS-232 or USB
Analogue
signals
TNC controller Radio transceiver
Computer or other DTE device
Fig. 1. Typical Packet Radio station with TNC controller
In previous works, we presented an analytical efficiency estimation of AX.25 protocol [14]. This analysis allows estimate how certain protocol parameters influence on its
efficiency and – as a result – effective transmission speed observed by a user. We also developed an analytical model of TNC controller [15]. It allows estimate how presence of
TNC controller influences on time parameters of the network (e.g., effective throughput
or transmission delays). The model can also be helpful in buffer size selection.
The aforementioned works concentrate on theoretical analysis. They are useful when
it is necessary to estimate, for example, maximum achievable throughput for a given parameter set; however, they do not take into account properties of transmission hardware
and software. In fact, transmission hardware, such as TNC controllers [10], may be
built using various types of microprocessors, running at various clock frequencies. They
may also be equipped with a data memory of various capacity, thus buffer sizes may
differ between individual TNC’s. These properties may have some influence on network performance. In this paper, we describe and compare construction details of TNC
controllers; these controllers have been tested in an experimental network using various
AX.25 protocol parameters. The results show how TNC type influences on effective
transmission speed of the network.
2. TNC Controllers
TNC (Terminal Node Controller) [10] is an autonomous, microprocessor-based device used in amateur Packet Radio network. Its main purpose is a connection between
a personal computer (or another DTE-type device, such as programmable controller
or weather station) and radio receiver-transmitter operating in Packet Radio network.
A typical Packet Radio network station with TNC controller is shown on Fig. 1.
189
Microprocessor
System bus
RS-232 Asynchr.
serial port
Program
memory
Data
memory
HDLC
controller
Digital part
Modem Radio
unit
AX.25
control
Analogue part
Fig. 2. Block diagram of TNC controller
2.1. Structure of TNC controller
TNC controller consists of a two parts. In the digital one, data format processing is
run according to the requirements of Packet Radio network and operating rules of AX.25
protocol. In turn, analogue part plays a role of a modem and provides for a control over
radio transceiver directly from TNC. Block diagram of the controller is shown of fig. 2.
It might suggest that every element shown on this diagram must be a separate circuit; In
fact, using most up-to-date technologies and modern single-chip microcontrollers, entire
digital part may be implemented as a single integrated circuit (IC). However, some microcontrollers, e.g., Motorola/Freescale circuits, require attachment of external program
and data memories, while communication ports are already built-in. It depends mostly
on the architecture and capabilities of the microcontroller. On the other hand, even in
the oldest controllers, serial port and HDLC controller were usually placed in a single
IC (in most cases, Z80-SIO or 8530).
2.1.1. Digital Part of TNC
Digital part of TNC controller contains a complete microprocessor-based circuit that
plays a role of an AX.25 protocol controller. The circuit communicates with an attached
computer using asynchronous RS-232C serial port or USB, while with radio transceiver
– using HDLC controller and a modem placed already in the analogue part. Data memory is used for buffering of transmitted data and storage of TNC parameters. In order
to avoid setting them again after TNC power-on, RAM is – at least partially – battery
powered. Some more modern solutions, e.g., TNC7, store the parameters in EEPROM.
Selected construction parameters of digital part of some TNC controllers are collected
in table 1.
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From the information collected in table 1 we can see that available TNC controllers
differ very much in parameters like microprocessor type and its clock frequency (fclk ).
These properties have some influence on possible transmission rates on serial port (Rw )
and radio link (Rwl ). First of all however, processor parameters have significant influence on controller processing power, which, in turn, may influence on effective transmission speed that may be obtained. A little smaller differences may be observed in the
range of memory capacity. This parameter has large influence on circuit usage convenience, as large program memory allows for wide selection of software used or introduction of new functions. In turn, capacity of data memory is significant when using TNC
controller as a mailbox or node stations. It also seems that if the data memory sacrificed
for the transmit and receive buffers is too small, it may disable using of long frames (N1 )
and window sizes (k) that are theoretically allowed by AX.25 protocol definition.
Controller
Vendor
Microprocessor
fclk
[MHz]
ROM
[KB]
RAM
[KB]
RTC
TNC2
(prototype)
Z80
2.4576
32
16-32
–
TNC2D
Muel
Z80
4.9152
2×32
32
–
TNC2H
Symek
Z80
9.8304
2×32
19.2
–
Spirit-2 Std.
Paccomm
Z80
9.8304
2×32
32
◦
Spirit-2 H.S.
Paccomm
Z80
19.6608
2×32
32
◦
KPC-9612+
Kantronics
68HC11
16.0000
128
128-512
•
PK-96
Timewave
Z180
12.2880
64
128
◦
KAM-XL
Kantronics
68HC902
9.8304
512
512
•
DSP-232
Timewave
68340
3.6864
128
256
◦
PTC-II
SCS
68360
25.0000
256-512
512-2048
•
TNC3S
Symek
68302
14.7456
256-1024
64-2048
•
TNC31S
Symek
68302
14.7456
128-512
128-512
◦
TNC4e
HBTron
68EN302
19.6608
1024
4096
•
TNC7multi
NtG
LPC2106
58.9824
128
64
–
DLC7
NtG
S3C4530
49.1520
4096
32768
•
Legend: – not available, ◦ optionally available, • present
Tab. 1. Selected construction parameters of TNC controllers (digital part)
The most often met TNC are those compatible with TNC2 standard, using Zilog Z80
microprocessor, such as TNC2, TNC2D [3] and TNC2H [7]. They are equipped with 16
or 32 KB of RAM and 32 or 64 KB of ROM – in the second case, memory is divided into
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two switchable banks, which allows use two different software versions alternatively.
Spritit-2 controllers [5] have a large set of extensions, however, they can be configured
so that they are fully compatible with TNC2 standard. Nevertheless, they still support
higher transmission rates than typical TNC2. Besides, they can be optionally equipped
with DS1216 real time clock (RTC), placed in the socket under RAM IC.
A little more modern are PK-96 [8] and KPC-9612+ [2] controllers, in which Zilog
Z180 and Motorola/Freescale 68HC11 microcontrollers are used, respectively. In both
controllers, transmission rates are higher than in typical TNC2, but still lower than in
Spirit-2. An interesting feature is an ability of automatic setting of RS-232C transmission rate (autobaud). PK-96, similarly to Spirit-2, may be equipped with DS1216 RTC,
while KPC-9612+ already contains an RTC. An interesting and sometimes useful feature
of KPC-9612+ is capability of simultaneous operation of both radio links; one of them
can work at 0.3÷1.2 kbps, the second one – 4.8÷38.4 kbps.
Much larger capabilities are found in TNC3 and TNC31 controllers [7], using 16bit Motorola/Freescale 68302 microcontrollers. These circuits are equipped with HDLC
controllers and serial ports, thus, only external memories must be attached. The software
may be placed in EPROM or Flash; in the second case, it can be updated or replaced via
the serial port using TNC operating system commands. The operating system allows for
configuration of some TNC parameters and running various types of software, depending on user’s needs. TNC31 contains a single modem connector, while TNC3 – two ones
(both can work simultanously). Some versions are equipped with RTC. TNC4e [1] has
similar structure and capabilities, however, it additionally allows for direct connection
to an Ethernet network. In this case, it can work with up to three modems (such configuration is also possible in TNC3 when RS-232 is not used). Despite this, TNC4e is
backwards compatible with TNC3.
KAM-XL [2], DSP-232 [8] and PTC-II [6] are so-called multimode controllers, as
they can work not only in Packet Radio, but also other radio amateur communication
systems. Thus, they are equipped with DSP processors working as modems. In KAMXL, DSP-232 and PTC-IIpro both radio links may work simultaneously. DSP-232 may
be equipped with DS1216 RTC, KAM-XL and PTC-II already have an RTC. These
TNC’s use various types of Motorola/Freescale microcontrollers – 68HC902, 68340 or
68360. Each of them requires attachment of external program and data memories.
The most modern and TNC7multi and DLC7 controllers [4], both using 32-bit microcontrollers with ARM7 core. TNC7 allows build a typical end user station; its microcontroller contains 128 KB of Flash and 64 KB of RAM and partially realizes modem
functionality in software. There is unfortunately no information if any RTC can be attached to this circuit. TNC7 may be attached using RS-232 or USB; in the second case
USB may be used as a power supply. DLC7 is some kind of TNC4e successor, as it
can be directly attached to an Ethernet network. It contains two HDLC controllers up to
192
10 Mbps each and RTC, it also has large memory capacity – 4 MB of Flash and 32 MB
of RAM. In this controller, software can be updated or replaced similarly to TNC3, using
TNC operating system commands.
Some TNC controllers, e.g., KPC-9612+ or KAM-XL, allow for simple control of
some objects or devices, as they have few two-state outputs and analogue inputs. They
can be also remotely accessed from another TNC via radio link.
2.1.2. Analogue Part of TNC
Analogue part of TNC contains a modem that allows for AX.25 protocol frames
transmission using radio transceivers including those designed mainly for voice communications. For lower transmission rates, AFSK (Audio Frequency Shift Keying) modulations are used according to ITU-T V.23 or Bell 203 recommendations (1.2 kbps) and
ITU-T V.21 or Bell 103 (0.3 kbps). For transmission rates 4.8 kbps and higher FSK
modulation is used. It is sometimes called DFSK (Direct Frequency Shift Keying) as
it bypasses filters adjusted for voice transmission that limit transmission rate to about
1.2÷2.4 kbps. Selected communication parameters of TNC controllers are collected in
table 2.
The modem may be realised in several ways, e.g.:
• using an integrated circuit with a modem functionality,
• generating analogue signals from samples using ROM or microcontroller,
• using DSP (Digital Signal Processor).
Examples of integrated circuits with a modem fuctionality are Am7910 and its derivatives as well as TCM3105. They support transmission rates not exceeding 1.2 kbps and
are used mostly in TNC2, PK-96 and TNC3. As these IC’s are no longer produced,
others are used instead, such as MX604, FX604 or FX614, used in KPC-9612+ and
KPC-3+ for transmission rates up to 1.2 kbps. For higher transmission rates, MX469
(1.2÷4.8 kbps) or CMX589 (4.0÷200 kbps) can be used. FX/MX-family modems are
also used in Polish Kameleon controllers [3] that may be considered as derivative of
TNC2 standard (unfortunately, not fully compatible, despite built on basis of Z80 architecture). Transmission rate selection may be done by setting of hardware switches or by
execution of operator commands.
An interesting solution are FSK modems generating analogue signal from samples
stored in ROM. They are used in TNC2H, PK-96, Spirit-2 and TNC3 controllers. The
ROM contains samples of several various signals, which allows select an optimal wave
for a given radio transceiver. Receiver path is realised in most cases as low-pass filters built using operation amplifiers. Such circuits support wide range of transmission
rates, e.g., 4.8÷614.4 kbps; it can be easily changed by adjustment of clock frequency
193
Rw [kbps]
Controller
Rwl [kbps]
RS-232C
Additional link
Int. modem
Ext. modem
TNC2
0.3-9.6
–
0.3-1.2
◦
TNC2D
0.3-19.2
–
0.3-1.2
◦
TNC2H
0.3-38.4
–
9.6
◦
Spirit-2 Std.
4.8-57.6
–
4.8-57.6
◦
Spirit-2 H.S.
4.8-57.6
–
4.8-57.6
◦
KPC-9612+
1.2-38.4
–
0.3-38.4
–
PK-96
1.2-38.4
–
0.3-38.4
◦
KAM-XL
0.3-38.4
–
0.3-9.6
–
DSP-232
0.1-19.2
–
0.3-9.6
–
PTC-II
1.2-115.2
–
0.3-19.2
◦
TNC3S
0.15-115.2
–
–
1.2-614.4
TNC31S
0.15-115.2
–
–
1.2-614.4
TNC4e
0.15-115.2
Eth 10 Mbps
–
4.8-1228.8
TNC7multi
1.2-115.2
USB 1.2-921.6
1.2-115.2
–
DLC7
1.2-115.2
Eth 100 Mbps
–
4.8-307.2
Legend: – not available, ◦ optionally available, • present
Tab. 2. Selected communication parameters of TNC controllers (analogue part)
division degree. Such a change, however, requires also adjustment of analogue filters.
Therefore, such modems are usually made as modules already configured for a given
transmission rate, as for example those designed for TNC3 controllers. Passive elements
of analogue filters may be installed as replaceable module – such a solution is used in
Spirit-2 controllers. Modems for TNC3 may also be used in TNC4e, DLC7 and PTCIIpro controllers, however, they do not support software rate selection.
In some solutions, a microcontroller is used instead of ROM, however, signal generation method remains intact. The microcontroller allows for software transmission
rate selection, however, adjustment of analogue filter still requires replacement of some
passive elements. A good representative of this group is DM307 modem, designed for
DLC7 and supporting rates 4.8÷307.2 kbps. Although it uses the same connector as
TNC3 modems, its usage in TNC3 is doubtful because of the need of software modem
configuration. A similar construction is used in TNC7 modem, however, it is implemented in software of main microcontroller of the circuit. Passive elements of the fil-
194
ters are available in the form of replaceable modules. The modem supports rates of
1.2÷115.2 kbps, however, rates exceeding 102.2 kbps lead to unstable TNC operation.
The last group of modems is realised using DSP processors. These modems are
used only in the multimode controllers, where variety of modulation methods requires
high flexibility of a modem, ensured by DSP. These modems are usually built-in; only
PTC-IIpro allows modem replacement.
In general, possibility of modem replacement allows for higher flexibility of TNC,
because in this case the range of usable transmission rates is much wider. On the other
hand, a software-configurable built-in modem is more convenient from the user’s point
of view. In many cases it is also flexible enough if the modem supports sufficiently wide
range of the most popular transmission rates.
2.2. TNC software
Software of TNC controller is responsible for proper realisation of AX.25 protocol
that is used as a data link layer in Packet Radio network. Other functions comprise
communication with DTE (and operator) and controller parameters configuration. It
is worth notice that while realisation of AX.25 protocol should be strictly standardised
(some differences, however, can be observed), remaining functions may be implemented
more freely. Hence there are several methods of computer-to-controller communication.
Some of them are optimised for human-to-human communications (TAPR and TF command sets) and transmission between devices (KISS and HOST modes and Hayes AT
command set in TNC3). Availability of operating modes depends on hardware layer of
the controller – the widest range of software types and versions are for Z80-based controllers compatible with TNC2 standard. It is also interesting that European controllers
are usually equipped with TF software, while American ones – with TAPR.
The type of software used may have some influence on details of realisation of specific functions, especially those related to AX.25 protocol. We may therefore expect that
controller efficiency depends not only on processing power, but also on type and version
of software used.
Basic software of TNC may operate in either command or converse mode. The command mode allows for configuration of large number of parameters – including those
of AX.25 protocol, radio transceiver and TNC itself – as well as connection management. In the converse mode user data is transmitted in the way similar to Internet instant
messengers.
3. Comparison of TNC Controller Efficiency
Tests of TNC controllers efficiency were conducted in an experimental network,
containing one or two PC-class computers and two controllers. A single PC computer
195
IBM PC-class computers
TNC controllers
T ransmitting station
Receiving station
Fig. 3. Experimental Packet Radio network
is sufficient if it is equipped with two RS-232 ports or USB, depending on controllers
used in a given test. The controllers were connected with cables. This exotic – as
for circuits designed for wireless communication – configuration was chosen in order
to avoid negative influence of radio interference over transmission quality. Besides, in
such a network it was possible to set any parameter values freely, which allows for
testing cases not very common in practice. As the radio transceiver is always under full
control of TNC, lack of transceiver does not influence on transmission time. Network
configuration is shown on fig. 3.
3.1. Effective Throughput
Effective throughput tests were conducted by transmitting a file of 8 or 16 KB (depending on transmission rate) for various values of window size (k) and data field capacity (N1 ) of an AX.25 protocol information frame. The controllers operated in halfduplex Asynchronous Balanced Mode, as typical for Packet Radio communication. Dividing file size by transmission time, we get effective throughput including PC↔TNC
transmission. However, wired link effective throughput is higher than that of AX.25 protocol using half-duplex link [15]. Thus, wired link transmission time is not significant.
Measurements results of effective transmission speed for few selected TNC controllers, operating at various window sizes and maximum length data frames (N1 =
256 B) are shown on fig. 4. Transmission rate was equal to 19.2 kbps on serial port and
1.2 kbps on radio link. For comparison, the graph contains also a curve determining theoretical capabilities of AX.25 protocol. On the graph we can see that the results do not
differ very much. Some controllers (e.g., TNC2, TNC2D) can not make use of window
size 4 and above – increasing this parameter does not practically increase transmission
speed. KPC-9612 behaves similarly. Faster TNC3 and TNC7 controllers, unexpectedly,
behave worse than the others for k < 7. A more detailed analysis conducted in monitor-
196
1,2
AX.25 imm
AX.25 T2
DLC7
TNC7
TNC3
KPC-9612
PK-96
Spirit-2
TNC2D
TNC2
1,0
0,8
0,6
0,4
0,2
0,0
1
2
3
4
5
6
7
window size (k )
Fig. 4. Effective transmission speed using 1.2 kbps radio link
ing mode showed that these controllers did not request immediate acknowledgement by
setting P/F bit in AX.25 protocol control field. Thus, the recipient waits for T2 time for
possible consecutive frames and sends the acknowledgement only afterwards. However,
when k = 7, TNC3, TNC7 and DLC7 achieve higher throughput than other controllers,
close to the theoretical values. It is possible, because, for maximum window size allowed
by protocol definition, recipient does not count the T2 time.
Results of similar measurements, conducted at radio link transmission rate of
9.6 kbps, are presented on fig. 5. For comparison, the graph presents two curves showing
theoretical capabilities of AX.25 protocol. One of them (AX.25 imm) corresponds to immediate acknowledge case, the second one (AX.25 T2) – with respect to T2 time. In this
case, difference between various TNC controllers is much more visible. Depending on
controller type, maximum effective speed varies from about 1.5 kbps (TNC2D) to almost
5.5 kbps (DLC7), while theoretical maximum is about 5.9 kbps. The difference between
results for k = 6 and k = 7 are also visible for TNC3, TNC7 and DLC7 controllers.
Fig. 6 presents the results of measurements for 38.4 kbps radio link. It is the highest
transmission rate that allows for comparison of most of TNC controllers; excluded are
only the Z80-based (except Spirit-2) and the multimode ones. It is also worth notice that
the difference between Spirit-2, KPC-9612+ and PK-961 is not large. Nevertheless, they
1
PK-96 results are not shown because at 38.4 kbps it works unstable and only few measurements were
successful; this rate can be set up in software, but communication proceeds with frequent errors – probably
analogue filters are set for lower rates and do not allow for reliable transmission.
197
7,0
AX.25 imm
AX.25 T2
DLC7
TNC7
TNC3
KPC-9612
PK-96
Spirit-2
TNC2D
TNC2
6,0
5,0
4,0
3,0
2,0
1,0
0,0
1
2
3
4
5
6
7
window size (k )
Fig. 5. Effective transmission speed using 9.6 kbps radio link
all limit the effective throughput to about 5 kbps, while TNC3 allows achieve almost
8 kbps, TNC7 and DLC7 – 10 and 11 kbps, respectively. It can be easily seen that
the processing power of the microprocessor used in TNC is essential for the effective
throughput. Its significance grows up with increasing transmission rate.
3.2. Real Window Size
In order to determine exact reason of low efficiency of Z80-based TNC controllers,
additional tests were conducted. They relied on transmission of relatively large file
(64 KB), for various frame length (data field capacity N1 ) and window size (k) set to
7. All the transmitted frames were logged by the receiving TNC working in the monitor
mode. Basing on such a transmission report, we determined real window sizes that occurred during the transmission. Histograms, presenting distribution of real window sizes
for few selected controllers and transmission rates, are presented on fig. 7 to 9.
Presented results show that Z80-based TNC controllers are not able to utilize maximum window size, practically regardless of radio link transmission rate. Nevertheless,
with decreasing frame length (data field capacity), window sizes are increasing. We
may therefore assume that the controller is not able to process sufficiently large amount
of data in a sufficiently short time. Possible reasons of such behaviour are: too low
processing power of a microprocessor, low efficiency of control software (lack of opti-
198
14,0
AX.25 imm
AX.25 T2
DLC7
TNC7
TNC3
KPC-9612
PK-96
Spirit-2
TNC2D
TNC2
12,0
10,0
8,0
6,0
4,0
2,0
0,0
1
2
3
4
5
6
7
window size (k )
Fig. 6. Effective transmission speed using 38.4 kbps radio link
mization), too low capacity of memory used as transmit and receive buffers or special
limitations introduced in software.
TNC controllers based on microprocessors others than Z80, e.g., KPC-9612+, are
much more capable of full utilisation of maximum window size. Only for frames containing more than 100 data bytes we may observe efficiency decrease, however, even
for maximum length frames, window size of 7 dominates. Even better performance is
shown by TNC3 and TNC7 controllers – efficiency decrease caused by (not full) utilisation of maximum window size may be observed only for radio link transmission rates
exceeding 150 kbps.
During described tests it was shown that effective transmission speed achieved in
a given configuration depends on not only hardware – particularly microprocessor type
and its clock frequency – but also properties of software that controls TNC controller
operation. The following factors, depending exclusively on software, may have influence
over circuit performance:
• full utilisation of window size for every data field capacity of a frame,
• sufficiently high processing speed of AX.25 protocol frames,
• immediate (without delays) generation of acknowledgement of error-free information frame reception,
199
Fig. 7. Distribution of real window size for TNC2D controller at 1.2 kbps
Fig. 8. Distribution of real window size for TNC2H controller at 9.6 kbps
200
Fig. 9. Distribution of real window size for KPC-9612+ controller at 9.6 kbps
• immediate acknowledgement request by setting of P/F bit in the latest information
frame within a window.
Inability of full utilisation of window size is especially annoying in Z80-bases TNC
controllers, practically regardless of its clock frequency and memory capacity. However,
type and version of software used in TNC has some influence upon its performance.
For example, versions supporting TAPR command set utilise window size rarely – the
controller can not transmit more than 5 maximum-length frames consecutively. A little
better is TF software, which, especially in most up-to-date 2.7 version, can send up
to 7 maximum-length frames consecutively. It seems however, that such capability is
achieved at a cost of longer frames preparation for transmission.
Controllers, supporting TAPR command set, but based on other microprocessor
types, can utilise window size much better, even at higher transmission rates. Unfortunately, there is no alternative software for these controllers; it is thus hard to say if this
capability results from higher processing power of a microprocessor, or better software
quality in terms of both protocol implementation and code optimisation.
Additional factor that influences effective transmission speed is the way the recipient
treats window size less than 7. In general, if the sender does not mark the latest frame
within a window with P/F bit, TF software sends the acknowledgement only after T2
time elapses, while TAPR – immediately; however, some implementations based on
201
TAPR command set, e.g., in TimeWave and Kantronics controllers, behave similarly to
TF. In some versions of TF software T2 time may be set, in others – e.g., TNC3 – it is
calculated automatically and cannot be changed. This parameter can also be set in some
versions of TAPR software.
Some software versions – e.g., in Kantronics controllers – at the beginning of transmission, initially limit window size, and later gradually increase it up to maximum value
set. Such behaviour may be reasonable, because it allows recognise capabilities of a receiving station. However, when the transmitted information is relatively short, the transmission efficiency decreases.
4. Conclusions
In the paper we briefly described applications, structure and basic properties of various types of TNC controller. We compared their construction parameters, and afterwards we presented results of tests conducted in an experimental Packet Radio network.
They show that not only hardware properties have influence upon network efficiency,
but also – in at least equal degree – properties of software that drives TNC controller.
We pointed implementation details of AX.25 protocol, used in Packet Radio network,
that have significant influence upon effective transmission speed. These observations
may show directions of existing software modifications. It is essentially important for
TF software, a source code of which is available in Internet [11].
A more detailed comparison of properties of TNC control software may be obtained,
when there is a hardware platform for which there are many software types and versions
available. Currently – despite various types of microprocessors used in TNC controllers
– only Z80-based TNC controller family forms such a platform.
References
1. H. Baumgart: Entwicklung elektronischer Komponenten, http://www.hbtron.de/.
2. Kantronics Radio Modems/TNC’s, http://www.kantronics.com/modems.html.
3. Muel – Radiowe systemy transmisji danych, http://www.muel.internet.pl/.
4. Nachrichtentechnik Marten Güttner, http://www.nt-g.de/.
5. PacComm Packet Radio Systems, http://www.paccomm.com/.
6. SCS – the PACTOR creators – controller, http://www.scs-ptc.com/controller.html.
7. Symek Packet-Radio, http://www.symek.de/.
8. TimeWave Main Page, http://www.timewave.com/.
9. W. A. Beech, D. E. Nielsen, J. Taylor: AX.25 Link Access Protocol for Amateur Packet
Radio, Tucson Amateur Packet Radio Corporation, Tucson, 1997.
202
10. K. Dabrowski:
˛
Amatorska komunikacja cyfrowa, PWN, Warszawa, 1994.
11. H. G. Giese, P, Gülzow: ‘C’-Sources for TheFirmware for TNC-2, http://www.nordlink.
org/eng/index.htm.
12. I. Wade: Automatic Position Reporting System. APRS Protocol Reference. Protocol Version 1.0., Tucson Amateur Packet Radio Corporation, Tucson, 2000.
13. B. Zieliński: Bezprzewodowe sieci komputerowe wykorzystujace
˛ konwersj˛e protokołów,
Instytut Informatyki Politechniki Ślaskiej,
˛
Gliwice, 1998.
14. B. Zieliński: Efficiency estimation of AX.25 protocol, Theoretical and Applied Informatics, 20, 3, 2008, 199–214.
15. B. Zieliński: An analytical model of TNC controller, Theoretical and Applied Informatics,
21, 1, 2009, 7–22.
Porównanie różnych typów kontrolerów TNC
Streszczenie
W publikacji przedstawiono budow˛e kontrolerów TNC, stosowanych m. in. w radioamatorskiej sieci Packet Radio. Pokrótce opisano ich budow˛e z podziałem na cz˛eść
cyfrowa˛ i analogowa˛ oraz wskazano istotne różnice w ich implementacji. Podstawowe
parametry konstrukcyjne kontrolerów zebrano w tabeli 1. Omówiono możliwości budowy i zastosowania różnego typu modemów w poszczególnych kontrolerach.
Ze wzgl˛edu na znaczne różnice w mocy obliczeniowej kontrolerów, spowodowane
zastosowaniem różnych mikroprocesorów, przeprowadzono doświadczalne porównanie
ich wpływu na efektywna˛ pr˛edkość transmisji. Badania przeprowadzono w eksperymentalnej sieci (rys. 3), w której transmisja mi˛edzy kontrolerami odbywała si˛e przewodowo,
w warunkach idealnych, w celu unikni˛ecia wpływu zakłóceń radiowych na wydajność transmisji. Wyniki pomiarów przepustowości efektywnej, uzyskane dla kilku
wybranych pr˛edkości transmisji, przedstawiono na rys. 4–6. Wyniki te porównano
z obliczeniami analitycznymi. Okazało si˛e, że wraz ze wzrostem pr˛edkości transmisji
moc obliczeniowa kontrolera ma coraz wi˛ekszy wpływ na wydajność sieci, a pr˛edkość
efektywna jest nawet kilkukrotnie niższa niż obliczona teoretycznie dla analogicznego
zestawu parametrów.
Podczas badań okazało si˛e także, że niektóre kontrolery TNC nie sa˛ w stanie wykorzystać ustawionej wielkości okna (k). Z tego powodu przeprowadzono dodatkowe
badania w celu uzyskania rozkładu rzeczywistej wielkości okna dla różnych kontrolerów przy różnych pr˛edkościach transmisji. Wyniki te pokazano na rys. 7–9.