Internet technologies and their applications in BASs - Intelligent Buildings and Building Automation - page 99

No. of Bits 7 24

Host Host Host

Class A 0 Network

128 64 32 16 8 4 2 1

16

14

1 0 Network Network Host Host

Class B

8

21

1 1 0 Network Network Network Host

Class C

Figure 6.4 IP address formats A, B, and C for commercial use.

an IP address of 172.31.1.2, for example, the first octet is 172. Because 172
falls between 128 and 191, 172.31.1.2 is a Class B address. Table 6.1 sum-
marizes the range of possible values for the first octet of each address class.
IP subnet addressing: IP networks can be divided into smaller networks
called sub-networks (or subnets). Subnetting provides the network admin-
istrator with several benefits, including extra flexibility, more efficient use
of network addresses and the capability to constrain broadcast traffic (a
broadcast will not cross a router). Subnets are under local administration.
As such, the outside world sees an organization as a single network and
has no detailed knowledge of the organization's internal structure. A given
network address can be broken up into many sub-networks. For example,
172.16.1.0, 172.16.2.0, 172.16.3.0, and 172.16.4.0 are all subnets within
network 172.16.0.0. (All 0s in the host portion of an address specify the
entire network.)

6.2.2 TCP and UDP

Transmission Control Protocol (TCP): The TCP provides reliable transmis-
sion of data in an IP environment. TCP corresponds to the Transport Layer
of the OSI Reference Model. Among the services TCP provides are stream

Table 6.1 The range of possible values existing for the first octet of each address
class

Address class First octet in decimal High-order bits

Class A 1-126 0

Class B 128-191 10

Class C 192-223 110

Class D 224-239 1110

Class E 240-254 1111