FMC Technologies Smith Meter microLoad.net, Applications Manual

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Introduction – TCP/IP and Networking with microLoad.net
AB06064 · Issue/Rev. 0.0 (5/06
)
Page 1
Introduction to TCP/IP Communications and Basic Networking
It is not necessary to become a skilled network administrator to successfully communicate with the
microLoad.net via TCP/IP. However, some basic networking knowledge will be quite helpful in
establishing and maintaining reliable communications with devices such as the microLoad.net that can be
connected via Ethernet and TCP/IP. Some of the following terms may be encountered while configuring
or maintaining your device connections:
TCP/IP (Transfer Control Protocol/Internet Protocol) is the widely accepted standard protocol for
Internet and World Wide Web communications. Many other Internet standard protocols – HTTP
for Web browsing, FTP for file transfers, etc. – use TCP/IP as the underlying control protocol.
Ethernet: A low-level protocol that implements the hardware link between two or more host
devices. TCP/IP is often used over an Ethernet connection.
MAC Address: A fixed, permanent 6-byte hardware address assigned to an Ethernet device by
the manufacturer.
IP Address: a four-byte (32 bit) number, usually displayed as 4 separate octets (8 bit numbers)
i.e. 192.168.0.1 , that uniquely identifies a host and network.
IP address ranges are grouped by class ; the first few bits determine the class. Class ‘A’ networks
have a value from 0-127 in the first octet; class ‘B’ networks start with 128-191; class ‘C’ from
192-223. The special values of 224-239 are reserved for class ‘D’ (multicast) addresses, and the
values 244-255 are reserved (class ‘E’) addresses.
Net Mask: The number of bits in the IP address that is used to specify the network address . The
remaining bits specify the host address. A Class ‘C’ network has a net mask of 24 (the first 24
bits are common to all machines on the network, the last 8 bits are the host id and are unique for
each machine on the network). Therefore, a class ‘C’ network can have up to 254 hosts (host
numbers 0 and 255 are reserved by the standard for special features such as broadcasting.) A
very large class ‘A’ network has an 8 bit net mask – leaving 24 bits to specify the host. Hence this
type of network can have a huge number of host machines -2
24
= over 16 million computers – but
there can only be 255 of those types of networks in existence since there are only 255 unique
network IDs that can be made from 8 bits. So why specify a net mask if it’s implied by the
network class? The reason for a net mask is clear when it is realized that some networks need to
have many more hosts than 255, and that there would not be very many networks if we only
allowed Class ‘A’ networks. Net masks are often written out in octet form… 255.255.255.0 is the
same as saying the net mask is 24 bits. It can also be specified with the network address using a
backslash, i.e.
192.168.0.0/24 . So, if we have a machine on that network with the IP address
192.168.0.23 (A class ‘C’ network), the network address is 192.168.0 and the host address is 23.
There are some network addresses that are reserved by the standard as ‘local network’
addresses. These network addresses are allowed only behind a router that ‘hides’ the local
network from the Internet. Many internal internet networks use these addresses: all the class ‘C’
networks starting with
192.168.xxx.xxx/24 and the class ‘A’ network 10.xxx.xxx.xxx/8 . Since most
organizations do not require a full class ‘A’ network, often a subsection of the address space is
used, i.e.
10.0.xxx..xxx/16. This is called ‘ sub-netting’ . Alternatively, sometimes two or more class
‘C’ networks are combined thus: 192 .168.0.xxx/23. This is known as ‘super-netting’ .
Gateway: a gateway address specifies where outgoing messages addressed to other networks
should be directed. This allows devices like routers, hubs and switches to be specified as the
interface to anything external to the physical network.
There is much information on TCP/IP and networking on the World Wide Web. One such example of a
more detailed description can be found at the time of this writing at
http://www.faqs.org/rfcs/rfc1180.html .
This is one of an entire series of RFCs (Request For Comments) that make up the documentation on
networking standards.