APPENDIX / BASIC TCP/IP DESCRIPTION A-3
the Internet Protocol Address, the IP Address or the
Internet Address. These terns are interchangeable.
Each packet sent across the internet contains the IP
address of the source of the packet and the IP
address of its destination.
For routing efficiency, the IP address is considered in
two parts: the prefix which identifies the physical
network, and the suffix which identifies a computer on
the network. A unique prefix is needed for each
network in an internet. For the global Internet,
network numbers are obtained from Internet Service
Providers (ISPs). ISPs coordinate with a central
organization called the Internet Assigned Number
Authority (IANA).
2.3 IP Address Classes
The first four bits of an IP address determine the class
of the network. The class specifies how many of the
remaining bits belong to the prefix (aka Network ID)
and to the suffix (aka Host ID). The first three
classes, A, B and C, are the primary network classes.
Class
First 4
Bits
Number
of Prefix
Bits
Max # of
Networks
Number
of Suffix
Bits
Max # of
Hosts Per
Network
Range
0000 to
A
0xxx 7 128 24
16,777,216
127.255.255.255
128.0.0.0 to
B
10xx 14 16,384 16 65,536
191.255.255.255
192.0.0.0 to
C
110x 21
2,097,152
8 256
223.255.255.255
224.0.0.0 to
D
1110 Multicast
239.255.255.255
240.0.0.0 to
E
1111
Reserved for future use
255.255.255
When interacting with mere humans, software uses
dotted decimal notation; each 8 bits is treated as an
unsigned binary integer separated by periods. IP
reserves host address 0 to denote a network.
140.211.0.0 denotes the network that was assigned
the class B prefix 140.211.
2.4 Netmasks
Netmasks are used to identify which part of the
address is the Network ID and which part is the Host
ID. This is done by a logical bitwise-AND of the IP
address and the netmask. For class A networks the
netmask is always 255.0.0.0; for class B networks it is
255.255.0.0 and for class C networks the netmask is
255.255.255.0.
2.5 Subnet Address
All hosts are required to support subnet addressing.
While the IP address classes are the convention, IP
addresses are typically subnetted to smaller address
sets that do not match the class system. The suffix
bits are divided into a subnet ID and a host ID. This
makes sense for class A and B networks, since no
one attaches as many hosts to these networks as is
allowed. Whether to subnet and how many bits to
use for the subnet ID is determined by the local
network administrator of each network.
If subnetting is used, then the netmask will have to
reflect this fact. On a class B network with
subnetting, the netmask would not be 255.255.0.0.
The bits of the Host ID that were used for the subnet
would need to be set in the netmask.
2.6 Directed Broadcast Address
IP defines a directed broadcast address for each
physical network as all ones in the host ID part of the
address. The network ID and the subnet ID must be
valid network and subnet values. When a packet is
sent to a network’s broadcast address, a single copy
travels to the network, and then the packet is sent to
every host on that network or subnetwork.
2.7 Limited Broadcast Address
If the IP address is all ones (255.255.255.255), this is
a limited broadcast address; the packet is addressed
to all hosts on the current (sub)network. A router
will not forward this type of broadcast to other (sub)
networks.
2.8 ICMP
Internet Control Message Protocol is a set of
messages that communicate errors and other
conditions that require attention. ICMP messages,
delivered in IP datagrams, are usually acted on by
either IP, TCP or UDP. Some ICMP messages are
returned to application protocols.
A common use of ICMP is “pinging” a host. The Ping
command (Packet INternet Groper) is a utility that
determines whether a specific IP address is
accessible. It sends an ICMP echo request and waits
for a reply. Ping can be used to transmit a series of
packets to measure average round-trip times and
packet loss percentages.
3.0 LINK LAYER
3.1 ARP
The Address Resolution Protocol is used to translate
virtual addresses to physical ones. The network
Summary of Contents for DS Series
Page 5: ...1 2 INTRODUCTION END OF INTRODUCTION SECTION ...
Page 8: ...HARDWARE INTERFACE 2 3 Figure 2 3 Figure 2 2 Figure 2 1 ...
Page 13: ...2 8 HARDWARE INTERFACE END OF HARDWARE INTERFACE ...
Page 19: ...3 6 MODBUS RTV PROTOCAL DESCRIPTION END OF MODBUS RTU PROTOCAL DESCRIPTION ...
Page 23: ...5 2 MODBUS FUNCTION FORMATS END OF MODBUS FUNCTION FORMATS ...
Page 29: ...6 6 PHOENIX AC DRIVE FUNCTION FORMATS END OF PHOENIX AC DRIVE FUNCTION FORMATS ...
Page 31: ...7 2 EXCEPTION RESPONSE END OF EXCEPTION RESPONSE ...
Page 37: ...9 2 PARAMETER CONVERSION END OF PARAMETER CONVERSION ...
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