Understanding the network.pdf - Back to Home

Packets and frames are often used as mutually exclusive terms. For the purposes of
this discussion, we'll use the term "packet" to indicate a transmission frame
containing data, and "frame" to discuss the transmission format.
The frame contains the network data and node addresses of the sender and the
receiver. Think of a network packet as an envelope. The letter (data) is inside. The
recipient's address is on the outside, and so is the sender's address, in case the
packet gets lost or cannot be delivered.
NOTE
Computer networks use two types of addresses to deliver network data. The
transmission protocol address or node address is used to distinguish each of the
different nodes connected to the transport medium segment. The transport protocol,
known as Ethernet, uses a 48-bit address called the Media Access Control (MAC)
address for this purpose. The MAC address is the machine address: the physical
identifier for the host on a segment. It needs to be unique only on a given segment.
Theoretically, two hosts could have the same transport layer address, provided they
were not connected to the same network segment. There is a distinction between a
transport address and a network address.
The network protocol address or host/end-station address is used as a unique
identifier throughout the entire network, which may consist of more than one
transport medium segment. Unlike transport medium addresses, every host or
node on the network must have a unique network protocol address. For example,
the network protocol called Internet Protocol (IP) uses a statically assigned 32-bit
address. Alternatively, AppleTalk dynamically assigns a network address to every
host on its network. Network protocols are used to exchange data between different
networks; they will be explained in the next section.
Figure 1.5 illustrates the conceptual difference between network segments and the
network as a whole.