J. Software Engineering & Applications, 2010, 3, 761-766
doi:10.4236/jsea.2010.38088 Published Online August 2010 (http://www.SciRP.org/journal/jsea)
761
The Design and Implement of TCP/IP Protocol
Cluster on AVR Singlechip
Rong Pan, Hai Zhao, Jialiang Wang, Dan Liu, Penghua Cai
School of Information Science and Engineering, Northeastern University, Shenyang, China.
Received June 3rd 2010; revised June 30th 2010; accepted July 6th 2010.
ABSTRACT
With the rapid development of the embedded technology, research and implement of the Internet of things will be a new
technology revolution, yet the implement of the Internet of things is on the base of the communication between the
things. For this reason, realizing the function of communication between singlechip is particularly important. Based on
the characteristics of the embedded microcontroller, we analyzed the traditional PC TCP/IP protocol, and appropri-
ately tailored TCP/IP protocol cluster on the basis of the characteristics of embedded singlechip. At last, we realized
the reduced TCP/IP protocol cluster suitable for embedded singlechip, on AVR singlechip platform.
Keywords: The Internet of Things, Webit, Embedded System, TCP/IP Protocol, Ethernet
1. Introduction
The Internet of things means a kind of net that via infor-
mation sense equipment such as FRID, infrared sensor,
GPS, laser scanner and so on, in arranged protocol, join
up between anything and the Internet to communicate
information and realize intelligent identification, tracing,
monitoring, and management. The concept of the Internet
of things is suggested in the year of 1999. It is the “In-
ternet communicated with things”. It means two aspects:
the first one is, the core and found ation of the Internet of
things is still in the Internet, which based on, extending
and expanding the Internet; the second one is, its client
side extends and expands to anything, to make the in-
formation exchanging and communication [1-3].
With the rapid development of computer and network
technology, Internet has become an important means of
information transmission, more and more embedded
equipments are necessary to achieve the Internet’s net-
work [4-5]. Relative to the PC, computing and storage
resources of embedded systems are relatively limited;
therefore to achieve all the TCP/IP protocol cluster in the
embedded singlechip is qu ite unrealistic. So th at, in ord er
to save the system resources and ensure the reliability of
the system, under the condition of improving the per-
formance of embedded system, it’s necessary to targeted
modular simplify TCP/IP protocol.
2. Adoptive Equipment and Testing Platform
Webit is an overall solution that makes the equipments
intelligent and networking. It is the new network equip-
ment system structure with the elements of Internet and
its basic idea is an independent, low-cost 3 W server
embedded in equipment, to make the equipment has in-
dependent network intelligence.
Webit is an embedded Internet product decided by
Liaoning Provincial Key Laboratory of Embedded
Technology by themselves. Webit 1.0 is successfully
pass technical appraisal and the trademark registration in
the year of 2000, and Webit 2.0 (Internet non-standard
electrical equipment access server) passed the appraising
meeting of scientific and technological achievements
held by science and technology commission of Liaoning
province in May 2001. Considering that webit is AVR 8
bit singlechip, its storage unit is very limited, therefore
it’s very important to design a kind of TCP/IP protocol
cluster suitable for the products.
The perform an ce of Webit 2.0 as follows:
 Without depending on PC system structure;
 Using Atmel AVR RISC processors;
 User-defined Web pages;
 User-defined CGI programs used to control;
 14 bit I/O interface (TTL level);
 TTL level UART supported 115200 bps;
 10 M Ethernet interface (RJ-45);
 System programming (ISP);
Overview of Ethernet controller chip RTL8019AS in
Webit:
RTL8019AS is a highly integrated Ethernet controller,
it can simply answer plug and play NE2000 compatible

The Design and Implement of TCP/IP Protocol Cluster on AVR Singlechip 762
adapter, which has two-fold and power decrease charac-
teristics. Through the three-level control characteristic,
RTL8019AS is the best ideal choice for network equip-
ment GREEN PC in all already known things. The two-
fold function can simulate send and receive the spread
between twisted-pair and all two-fold Ethernet switches.
This not only can make bandwidth stronger from 10
Mbps to 20 Mbps, but also avoid read muliaccess
agreement because of Ethernet channel fight character.
Microsoft's plug and play function can alleviate user
lower income and focus on the adapter resources, such as
the input and output, IRQ, memory address, etc. How-
ever, in special application without plug and play func-
tion of compatibility, RTL8019AS support s JUMPER
and JUMPERLESS options.
In order to provide complete plug and play solution,
RTL8019AS integrated 10BASET transceiver, and auto-
examination function between AUI and BNC interface.
In addition, 8 IRQ BUS and 16 basic addresses BUS
provide comfortable environment for large resources
situation.
RTL8019AS supports 16 k, 32 k and 64 k bytes mem-
ory BROM and the flash memory interface. It provides
the page model function, which can only support 4 M
bytes BROM under 16 k bytes of memory system space.
BROM’s useless commands are used to release BROM
memory space. RTL8019AS designed the singlechip with
the 16 k bytes SRAM, so that not only provides more
friendly function, but also saves SRAM st or age reso urces.
3. The design of Webit Reduced TCP/IP
Protocol Stack
In the AVR singlechip, due to the relatively limited re-
sources, the TCP/IP protocol cluster of complete function
cannot be achieved. So according to the characteristics of
AVR singlechip, we cutting the original TCP/IP protocol
cluster obtai ns t he red uced T C P/ IP pr ot ocol cluster.
Meanwhile, based on the architecture of TCP/IP pro-
tocol stack, we adapted the design method of network
slice model. The architecture of TCP/IP protocol cluster
after simplify contains the ARP, IP, ICMP, UDP, TCP
protocol processing model, etc. [6-8]. Each layer of the
architecture of TCP/IP protocol stack is designed as a
module of independent function, handles their data. Dif-
ferent modules can be invoked by function to turn over
datum to upper or lower processing module [9]. Figure 1
shows the simplified TCP/IP protocol architecture.
Known by Figure 1, when the AVR singlechip re-
ceives data from network, data packet processing mod-
ules will base on certain condition to choose the ARP
module of link layer or the IP protocol module of net-
work layer to process.
Likewise, when the data packets are processed by
UDP and TCP protocol modules of transp ort layer, it will
turn over processed packets to IP protocol processing mo-
Figure 1. Simplified TCP/IP protocol architecture
dule, and make encapsulation for IP first address, the first
(such as the fields like address, type of agreement, etc.)
by corresponding function calls. Then transfer the data-
gram including IP first and TCP first to the lower layer
by function call, until the data is sent smoothly. The
TCP/IP protocol processing is shown in Figure 2.
4. The Design and Implement of Simplified
Embedded TCP Protocol
First, in Webit, we format and size of the MAC and IP
address, system address configuration, and size of the
buffer were defined already. We make the address format
of MAC, IP to become fixed value in system. The system
configuration is used for setting specific value of the IP
address, the port and MAC address. In this system, for
the limited data needed the singlechip to process, so we
don’t set the buffer larger than normal.
Figure 2. The TCP/IP protocol processing

The Design and Implement of TCP/IP Protocol Cluster on AVR Singlechip 763
.DSEG
.ORG 0x60
LocalMAC: .BYTE 6
LocalIP: .BYTE 4
LocalPort: .BYTE 2
RemoteMAC: .BYTE 6
RemoteIP: .BYTE 4
RemotePort: .BYTE 2
Plugdelaytime: .BYTE 32
TCPCB: .byte 30*2
RevBuffer: .BYTE 260
4.1 The Implement of ARP Protocol
Because the embedded singlechip is normally in the ser-
vice of the passive state. So while we design and imple-
ment the ARP protocol, we don’t implement the function
of address mapping table, neither realize the function of
querying any client mapped IP into the MAC address,
only need to achieve when other client to query the local
Mac address. Packet and get feedback of the relationship
between own IP and MAC address, and send.
When the embedded singlechip receives ARP packets
from Ethernet, we according to the type of operation
codes of the packets decide type of ARP packet, if the
ARP request packet, compare destination IP address field
of ARPP packet with the local settings of IP address. If
it’s equal, local MAC address packaging to responded
ARP reply packet, if not, don't do processing, discard it.
The processing flow of ARP packet is shown in Figure
3.
4.2 The Implement of IP Protocol
The IP protocol is the core of the TCP/IP protocol cluster.
All the ICMP, UDP a nd T C P d a t a transm i t a s IP datagram
Figure 3. The ARP protocol processing
format. In the IP protocol processing modules, While
implement the IP protocol module, we firstly received
the IP date packet from the Ethernet and decide whether
the destination IP address field values in the head of da-
tagram equals local IP address, if not, discard; if consis-
tent, check such field as the version number and check-
sum of the IP datagram, etc.
After examination, confirm the packet is right, and
then decide to choose ICMP protocol, UDP protocol or
TCP to submit to upper processing, according to the type
of IP data. In addition, another function of IP protocol
module we designed and implemented is to make the
message encapsulation deliv ered from upper into IP data,
then turn over IP data encapsulation to link layer to make
data frame encapsulation and sending. The processing
flow of IP protocol is shown in Figure 4.
4.3 The Implement of ICMP Protocol
ICMP protocol is a kind of information transfer control
protocol. We think about the embedded singlechip as a
server is responded the client commonly, as a passive
device, it does not need to initiatively send back the
message. So we only implement the receiving and han-
dling the Echo Request between singlechip and other
devices in the ICMP protocol module, and also send the
Echo Reply. The implementation of ICMP protocol is as
follows: read type code of the first byte of ICMP data
packets, and check the ICMP packet types. If the type
code is 8, the type of packets will be modified to 0, fill
each field of packets to make the encapsulation of Echo
Reply packets needed to be sent back, finally calls Sen-
dIP function, make ICMP data packets into IP datagram
encapsulation to send. If the packets’ type code isn’t 8,
discard the packet. The processing flow of ICMP proto-
col is shown in Figure 5.
Figure 4. The IP protocol processing

The Design and Implement of TCP/IP Protocol Cluster on AVR Singlechip 764
Figure 5. The ICMP protocol processing
4.4 The Implement of UDP Protocol
UDP protocol provides reliable, connectionless commu-
nication between applications, it transmits datum to the
IP layer and sends out, but does not guarantee they can
reach the destination.
When the UDP protocol modules receive packets, first
locate the port fields of UDP packets, save the remote
and purpose port of the UDP packets, then the compare
the objective port of the packet with the port of local
regulations, if not equal, discard it; if equal, call the cor-
responding function. Finally, set the source port, objec-
tive port, data length, checksum field in the header of
UDP packet, add datum to be sent, make encapsulation
and sending by IP layer. The processing flow of UDP
protocol is shown in Figure 6.
4.5 The Implementation of TCP Protocol
Due to the limited resources of singlechip, and to handle
TCP packet better, so while implementing the TCP pro-
tocol module, we reduced the common TCP/IP protocol,
and did not implement the sliding window protocol, flow
control and congestion control mechanisms. Meanwhile,
we set two TCP connection control block in the TCP
protocol modules, and adopt the response mode with
single window. When receiving TCP packets, first locate
mark field of TCP packets, if the TCP packet is required
to build a new connection, check whether still exist sp are
TCP connection control block in the system. If present,
this spare control block will be used as the control block
for this connection, and establish connections. Con-
versely, if there is no spare TCP connection control block,
and do nothing.
When the mark field of the TCP packets is another
type, search whether exist TCP connection control block
corresponding to the TCP packets. If present, judge ac-
cording to the mark field of the value of SYN, FIN, ACK
and so on, then choose corr esponding fun ction to process
packets. If don't exist TCP connection control block cor-
responding to the TCP packets, don’t do anything. Cons-
Figure 6. The UDP protocol processing
truction and closing the connection of the TCP protocol
are through the “three handshakes” and “four times spe-
cific wave”. Setting the mark field in the TCP packets to
different control bits is the specific approach. The proc-
essing flow of TCP protocol is shown in Figure 7.
5. Testing
In order to test whether the TCP/IP protocol realized can
achieve the desired objective, we carried on a series of
tests.
The Ping command is the most frequently used in net-
Figure 7. The TCP protocol processing

The Design and Implement of TCP/IP Protocol Cluster on AVR Singlechip 765
work. This command sends a network message and re-
quests response via ICMP protocol. Therefore, through
the Ping command we can determine whether the current
network is connected correctly, and test whether the con-
dition of network connections is available. So, for the
testing of ARP, IP, and ICMP protocol, we can finish the
testing through Ping command. The process of test is:
first, connect Webit and PC, do the network configura-
tion through WebitNetIfConfig function, make configu-
ration of suitable IP address (in this test set IP of Webit
as 192.168.180.94). Fin ally, input “ping 192.16 8.180.94”
on the PC. The running test of Figure 8 shows that the
network is connected, network equipment is available. It
states:
1) ARP module is normal, and can properly achieve
the address mapping;
2) The IP protocol modules work normally, and can
correctly analyze that this is an ICMP messages;
3) ICMP protocol modules work normally, and can
correctly return responses message.
The response condition of ICMP packet is listed in the
Table 1. The test is mainly by sending ping date packet
to singlechip to verify the success rate of date sending.
As the test date of the table shows, as the request packet
sending to the singlechip is smaller, so the request can be
effectively handle d by serv e r.
For the testing of TCP protocol, we can choose to
write a simple Telnet-Server program based on TCP/IP
protocol. Users can access on PC, according to system
cue, users can input some simple commands to obtain
relevant information. Testing method is: input “telnet
192.168.180.94” on PC. The result is: the system shows
that the connection is established successfully, and the
associated tip. Input something according to cue, and
then obtain appropriate information. Finally, the test
shows that TCP protocol modules in the TCP/IP protocol
cluster are correct, and the network layer protocol is cor-
rect.
In addition, we also test the established time of TCP
Figure 8. The test results of ARP, ICMP and IP protocol
Table 1. Response of ICMP packet
Size Request
packets Reply packets Success rate
Response
of
ICMP 128 Byte 50 50 100%
Table 2. The established time of TCP
Meanvalue Standard
deviation Maximum
The established
time of TCP 2.314 /ms 0.53 /ms 2.437 /ms
many times.
As the test results listed in the Table 2, the average
established time of TCP is about 2.314 ms, it means that
server can quickly respond according to external request.
In the process of test, while singlechip server accepting
the connection request, it has well reliability. Mean while,
it means after implementing the reduced TCP/IP protocol
on the AVR singlechip, it can well meet the requirement
of non-PC devices be connected to Internet.
For the testing of UDP protocol, we write a program
according to the realized UDP protocol that creates two
UDP Sockets, one is to achieve the function of sending
UDP data, and the other is used to achieve the function
of receiving UDP data, in order to test the correctness of
the UDP protocol. The procedure of testing is:
1) Initialize the equipment;
2) Create the UDP Sockets (S1 and S2) through We-
bitUdpCreateSocket;
3) S1 sends UDP data to S2 through the function of
WebitUdpSendTo, S2 receives data form S1 through the
function of WebitUdpReceiveFrom, and output the re-
ceived data to the serial port;
4) Close the two created Sockets (S1 and S2) through
WebitUdpDestroySocket command.
Finally, the testing results show that S2 received data
form S1 successfully; this means the UDP protocol of
TCP/IP protocol cluster is correct.
6. Conclusions
This paper expounds the implement principle, method
and technology of the TCP/IP protocol on WEBIT plat-
form. In implement of the TCP/IP protocol we bring in
the programming ideas of network layer and reduced
TCP/IP system structure which adapt to the characteris-
tics of singlechip [10]. At the same time, the paper also
make certain explore and try in embedded singlechip and
network applications finally, the feasibility of this proto-
col is confirmed in simulation experiment system, so it’s
significant and full of reference value for embedded In-
ternet system design and development.
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