data stream provides end-to-end transport
services. The Internet is often represented by a cloud. The
transport layer sends data packets from the sending source to
the receiving destination through the cloud. End-to-end
control, provided by sliding windows and reliability in
sequencing numbers and acknowledgments, is the primary duty of
the transport layer when using TCP. The transport layer also
defines end-to-end connectivity between host applications.
Transport services include all the following services: TCP
and UDP - Segmenting upper-layer application data
- Sending segments from one end device to another end
device
TCP only - Establishing
end-to-end operations
- Flow control provided by
sliding windows
- Reliability provided by sequence
numbers and acknowledgments
The Internet is often
represented by a cloud. The transport layer sends data packets
from the sending source to the receiving destination through
the cloud. The cloud deals with issues such as “Which of
several paths is best for a given route?” Interactive Media
Activity Checkbox: The Transport Layer After completing
this activity, the student will be able to identify the
protocols used in the transport layer. Web Links
Transport Layer http://searchnetworking.techtarget.com/
sDefinition/0,,sid7_ gci213212,00.html
Content
9.1 Introduction to TCP/IP 9.1.4
Internet layer The purpose of the Internet layer is to
select the best path through the network for packets to travel.
The main protocol that functions at this layer is the Internet
Protocol (IP). Best path determination and packet switching
occur at this layer. The following protocols operate at the
TCP/IP Internet layer: - IP provides connectionless,
best-effort delivery routing of packets. IP is not concerned
with the content of the packets but looks for a path to the
destination.
- Internet Control Message Protocol (ICMP)
provides control and messaging capabilities.
- Address
Resolution Protocol (ARP) determines the data link layer
address, MAC address, for known IP addresses.
- Reverse
Address Resolution Protocol (RARP) determines IP addresses when
the MAC address is known.
IP performs the following
operations: - Defines a packet and an addressing scheme
- Transfers data between the Internet layer and network
access layers
- Routes packets to remote hosts
Finally, as a clarification of terminology, IP is
sometimes referred to as an unreliable protocol. This does not
mean that IP will not accurately deliver data across a network.
Calling IP an unreliable protocol simply means that IP does not
perform error checking and correction. That function is handled
by upper layer protocols from the transport or application
layers. Interactive Media Activity Drag and Drop: The
Internet Layer After completing this activity, the student
will be able to identify the protocols used in the Internet
layer. Web Links Internet Layer
http://www.pku.edu.cn/academic/research/
computer-center/tc/html/TC0300.html
Content
9.1 Introduction to TCP/IP 9.1.5
Network access layer The network access layer is also
called the host-to-network layer. The network access layer is
the layer that is concerned with all of the issues that an IP
packet requires to actually make a physical link to the network
media. It includes the LAN and WAN technology details, and all
the details contained in the OSI physical and data-link layers.
Drivers for software applications, modem cards and other
devices operate at the network access layer. The network access
layer defines the procedures for interfacing with the network
hardware and accessing the transmission medium. Modem protocol
standards such as Serial Line Internet Protocol (SLIP) and
Point-to-Point Protocol (PPP) provide network access through a
modem connection. Because of an intricate interplay of
hardware, software, and transmission-medium specifications,
there are many protocols operating at this layer. This can lead
to confusion for users. Most of the recognizable protocols
operate at the transport and Internet layers of the TCP/IP
model. Network access layer functions include mapping IP
addresses to physical hardware addresses and encapsulation of
IP packets into frames. Based upon the hardware type and the
network interface, the network access layer will define the
connection with the physical network media. A good example of
network access layer configuration would be to set up a Windows
system using a third party NIC. Depending on the version of
Windows, the NIC would automatically be detected by the
operating system and then the proper drivers would be
installed. If this were an older version of Windows, the user
would have to specify the network card driver. The card
manufacturer supplies these drivers on disks or CD-ROMs.
Interactive Media Activity Drag and Drop: The Network
Access Layer After completing this activity, the student will
be able to identify the protocols used in the network access
layer. Web Links Network Access Layer
http://www.pku.edu.cn/academic/research/
computer-center/tc/html/ TC0200.html
Content
9.1 Introduction to TCP/IP 9.1.6
Comparing the OSI model and the TCP/IP model The
following is a comparison of the OSI model and the TCP/IP model
noting the similarities and differences: Similarities of the
OSI and TCP/IP models: - Both have layers
- Both
have application layers, though they include very different
services
- Both have comparable transport and network
layers
- Packet-switched, not circuit-switched,
technology is assumed
- Networking professionals need
to know both models
Differences of the OSI and
TCP/IP models: - TCP/IP combines the presentation and
session layer into its application layer
- TCP/IP
combines the OSI data link and physical layers into one layer
- TCP/IP appears simpler because it has fewer layers
- TCP/IP transport layer using UDP does not always
guarantee reliable delivery of packets as the transport layer
in the OSI model does
The Internet is developed by
the standards of the TCP/IP protocols. The TCP/IP model gains
credibility because of its protocols. In contrast, networks
typically are not built on the OSI protocol. The OSI model is
used as a guide for understanding the communication process.
Interactive Media Activity Drag and Drop: Comparing the
TCP/IP and OSI Model After completing this activity, the
student will be able to identify the differences between the
TCP/IP model and OSI model. Web Links Introduction to
TCP/IP http://www.snnug.com/meetings/tcpip.htm
Content
9.1 Introduction to TCP/IP 9.1.7
Internet architecture While the Internet is complex,
there are some basic ideas in its operation. In this section
the basic architecture of the Internet will be examined. The
Internet is a deceptively simple idea, that when repeated on a
large scale, enables nearly instantaneous worldwide data
communications between anyone, anywhere, at any time. LANs are
smaller networks limited in geographic area. Many LANs
connected together allow the Internet to function. But LANs
have limitations in scale. Although there have been
technological advances to improve the speed of communications,
such as Metro Optical, Gigabit, and 10-Gigabit Ethernet,
distance is still a problem. Focusing on the communication
between the source and destination computer and intermediate
computers at the application layer is one way to get an
overview of the Internet architecture. Placing identical
instances of an application on all the computers in the network
could ease the delivery of messages across the large network.
However, this does not scale well. For new software to function
properly, it would require new applications installed on every
computer in the network. For new hardware to function properly,