Chapter 6: Defining Network Protocols

Lesson 1: Introduction to Protocols

This exercise is designed to help you reinforce your understanding of network protocol stacks. The following table contains two columns. In the left column are listed the seven layers of the OSI reference model. In the right column, enter the rule that applies to the layer on the left.

OSI Reference Model Rules

OSI Layers	Rules
Application layer	Initiates a request or accepts a request to send a packet
Presentation layer	Adds formatting, display, and encryption information to the packet
Session layer	Adds traffic-flow information to the packet that determines when the packet gets sent
Transport layer	Adds error-handling information to the packet
Network layer	Adds sequencing and address information to the packet
Data-link layer	Adds error-checking information and prepares packet for sending out over the physical connection
Physical layer	Sends packet as a bit stream

Because many protocols were written before the OSI reference model was developed, some protocol stacks developed earlier don't match the OSI reference model; in�those stacks, tasks are often grouped together.

Communication tasks can be classified into three groups. In this part of the exercise, the seven layers of the OSI reference model are again listed in the left column. In the right column, write in the name of one of the three groups in the following list. Your task is to identify which of these three groups maps to each of the OSI layers in the left column.

The three groups are:

• Transport services.
• Network services.
• Application-level network service users.

Matching OSI Reference Model with Communication Tasks

OSI Layers	Communication Task
Application layer	Application-level network service users
Presentation layer	Application-level network service users
Session layer	Application-level network service users
Transport layer	Transport services
Network layer	Network services
Data-link layer	Network services
Physical layer	Network services

Lesson 2: TCP/IP

Exercise 6.2 is designed to help you understand the relationship between the OSI�model and Transmission Control Protocol/Internet Protocol (TCP/IP). Because TCP/IP was developed before the OSI reference model was developed, it does not exactly match the seven OSI model layers. In this exercise, you will be mapping the four layers of TCP/IP to the seven layers of the OSI reference model. The�four layers of TCP/IP are the:

• Network interface layer.
• Internet layer.
• Transport layer.
• Application layer.

The left column lists the seven layers of the OSI reference model. In the right column, fill in the name of the corresponding TCP/IP layer.

Comparison of OSI and TCP/IP Layers

OSI Layers	TCP/IP Layers
Application layer	Application layer
Presentation layer	Application layer
Session layer	Application layer
Transport layer	Transport layer
Network layer	Internet layer
Data-Link layer	Network interface layer
Physical layer	Network interface layer

Lesson 3: NetWare Protocols

This exercise is designed to help you understand the relationship between the OSI reference model and NetWare protocols. NetWare was developed earlier than the OSI reference model and, therefore, does not precisely match the seven layers. In this exercise, you will be mapping the various components of NetWare protocols to the seven layers of the OSI reference model.

In the table that follows, the column on the left lists the seven layers of the OSI reference model. The blank columns on the right represent various components of the NetWare protocol. In the blank columns, map the following NetWare protocol components to the OSI reference model.

• IPX/SPX
• Media Access Protocol
• NetWare Core Protocol
• Routing Information Protocol
• Service Advertising Protocol

Comparison of OSI Reference Model with NetWare Protocols

OSI Layers	NetWare Protocols
Application layer	NetWare Core Protocol	Service Advertising Protocol	Routing Information Protocol
Presentation layer
Session layer
Transport layer
Network layer	IPX/SPX
Data-link layer	Media Access Protocols
Physical layer

Lesson 4: Other Common Protocols

Along with the better-known protocols, many other lesser, but still common, protocols exist. Five such protocols are listed below. In this exercise, you will be�matching each of the protocols in the list that follows with the feature that describes what it does.

Five common protocols

1. AppleTalk
2. DECnet
3. NetBEUI
4. NetBIOS
5. X.25

In each blank space on the left, fill in the letter of the protocol that uses the feature listed on the right. Note that more than one protocol can be matched to a particular feature.

_____C, D_____ A protocol that is commonly used for Microsoft-based, peer-to-peer networks

_______E______ A protocol used for packet switching

_______A______ A protocol that is commonly used for Macintosh networks

_______B______ A protocol designed by Digital Equipment Corporation (DEC)

_______D______ A protocol originally offered by IBM

_______C______ A small, fast, transport-layer protocol

_____C, D_____ A protocol that is nonroutable

1. A sending computer breaks the data into smaller sections, called _______________, that the protocol can handle.

packets

2. Several protocols can work together in what is known as a protocol ____________.

stack

3. A receiving computer copies the data from the packets to a ______________ for reassembly.

buffer

4. Protocols that support multipath LAN-to-LAN communications are known as _______________ protocols.

routable

5. The receiving computer passes the reassembled data to the ____________________ in a usable form.

application

6. To avoid conflicts or incomplete operations, protocols are _______________ in an orderly manner.

layered

7. The _______________ order indicates where the protocol sits in the protocol stack.

binding

8. Three protocol types that map roughly to the OSI reference model are application, __________________, and network.

transport

9. Application protocols work at the upper layer of the OSI reference model and provide __________ _________________ between applications.

data exchange

10. A NIC-driver protocol resides in the ______________ _______________ ________________ ( _________ ) sublayer of the OSI reference model.

Media Access Control (MAC)

11. Rules for communicating in a particular LAN environment such as Ethernet or Token Ring are called _________________ protocols.

network

12. To help the network administrator install a protocol after the initial system installation, a ______________ is included with the operating system.

utility

13. TCP/IP supports routing and is commonly used as an __________________________ protocol.

internetworking

14. NetBIOS is an IBM session-layer LAN interface that acts as an _____________________ interface to the network.

application

15. APPC (advanced program-to-program communication) is IBM's ___________________ protocol.

transport

16. NetBEUI is not a good choice for large networks because it is not _________________.

routable

17. X.25 is a protocol used for a ______________ - ________________ network.

packet switching

18. X.25 works in the ________________, ___________ - __________, and _________________ layers of the OSI reference model.

physical, data-link, and network

19. AppleTalk is a proprietary protocol stack designed for _________________ computers.

Macintosh

20. EtherTalk allows a Macintosh computer to communicate on an ___________________ network.

Ethernet