8/6/2019 Chapter Summary 2

1/2

CHAPTER SUMMARY

1. There are many types of data networks, including Local Area Networks (LAN) and Wide AreaNetworks (WAN). The components used to build networks are:

a. the mediab. end devices that send and receive messages (e.g., computers, VoIP phones) andc. Intermediary devices (e.g., hubs, switches, routers) that move messages among different

parts of the network.

2. Most organizations have many LANs that are connected to WANs, and to the Internet, whichitself is a series of WANs.

3. Understanding the way Network layers work together to transfer messages is critical because it isthe foundation other concepts will be built upon throughout the course. A set of functions mustbe performed inside each computer or device to move messages through the network. These

functions are organized into a set of layers. The idea of layers implies a stack, with one layer ontop of another.

4. A Network Model defines these layers and the functions that each performs. The OSI model , andthe TCP/IP model are two different models for organizing the layers and their functions, but theyare similar in many ways. Each layer has its own language or "protocol" that has rules abouthow that layer will operate. Layers also have standards to ensure that any two computers thatuse the same protocol will be able to communicate.

5. The OSI model is the formal reference model, while the TCP/IP model was developed to reflectthe implementation of the TCP/IP protocol stack. The TCP/IP model is more important because itis the one most commonly used in practice, as a result of the popularity of the Internet. It is alsothe most concrete.

6. Each protocol has a protocol data unit (PDU) that is like a grammar or a paper form that theprotocol uses to communicate. This "form," called a PDU, is added to the message at each layerin the stack.

7. Every device has a set of addresses - i.e., there are different addresses for different layers in theprotocol stack.

a. Layer 2 addresses (M AC address) which are used to move messages to the correct enddevice .

b. Layer 3 addresses (IP address) which are used to move message between different parts ofthe network and to identify the correct end device. IP addresses have two parts:

y the network (e.g., the IP number assigned to google.com) andy the specific computer within that part of the network (e.g., a specific web server or

e-mail server within the Google network).

c. Layer 4 addresses (TCP port numbers) are used to move the message to correct Applicationlayer conversation at the end device (e.g., the Web browser or e-mail software on yourcomputer).

8/6/2019 Chapter Summary 2

2/2