Internet technologies and their applications in BASs - Intelligent Buildings and Building Automation - page 98

IP is documented in RFC 791 and is the primary Network Layer protocol in
the Internet protocol suite. Along with the Transmission Control Protocol
(TCP), IP represents the heart of the Internet protocols. IP has two primary
responsibilities: providing connectionless, best-effort delivery of datagrams
through an internet, and providing fragmentation and reassembly of data-
grams to support data links with different maximum-transmission unit
sizes.
IP addressing: As with any other Network Layer protocol, the IP address-
ing scheme is integral to the process of routing IP datagrams through an
internet. Each IP address has specific components and follows a basic for-
mat. These IP addresses can be subdivided and used to create addresses for
sub-networks, as discussed in more detail later in this section. Each host on
a TCP/IP network is assigned a unique 32-bit logical address that is divided
into two main parts: the network number and the host number. The network
number identifies a network and must be assigned by the Internet Network
Information Center (InterNIC) if the network is to be part of the Internet.
An Internet service provider (ISP) can obtain blocks of network addresses
from the InterNIC and can itself assign address space as necessary. The host
number identifies a host on a network and is assigned by the local network
administrator.
IP address format: The 32-bit IP address is grouped 8 bits at a time,
separated by full stops ('dots'), and represented in decimal format (known
as dotted decimal notation ). Each bit in the octet has a binary weight (128,
64, 32, 16, 8, 4, 2, 1). The minimum value for an octet is 0, and the max-
imum value for an octet is 255. Figure 6.3 illustrates the basic format of an
IP address.
IP address classes: IP addressing supports five different address classes: A,
B, C, D and E. Only classes A, B, and C are available for commercial use. The
left-most (high-order) bits indicate the network class. The high-order bits in
each class are fixed. Figure 6.4 illustrates the format of the commercial IP
address classes.
The class of address can be determined easily by examining the first octet of
the address and mapping that value to a class range in the following table. In

32 b its

Network Host

8 bits 8 bits 8 bits 8 bits

Dotted
Decimal
Notation

172 16 122 204

Figure 6.3 An IP address consists of 32 bits, grouped into four octets.