Protocol - A written specification that defines what tasks a service or device should perform. Each protocol defines messages, often in the form of headers, plus the rules and processes by which these messages are used to achieve some stated purpose.

All communication, whether face-to-face or over a network, is governed by predetermined rules called protocols.

A delineation of networking protocols and standards into different categories, called layers, along with definitions of which sets of standards and protocols need to be implemented to create products that can be used to create a working network.

Theses rules, or protocols, that work together to ensure successful communication are grouped into what is known as a protocol suite.

An international, nonprofit organization for the advancement of technology related to electricity. IEEE maintains the standards of defining many LAN protocols.

The organizations that standardize networking protoocls are the Institute of Electrical and Electronics Engineers (IEEE) and the Internet Engineering Task Force (IETF)

A model that consists of various layers that enable the development and explanation of technology to be done on a modular basis. This allows interoperability among different technologies among the different layers.

The IT industry uses layered models to describe the complex process of network communication.

Transmission Control Protocol/Internet Protocol - A network model defined by the IETF that has been implemented on most computers and network devices in the world.

The TCP/IP model is a protocol model because it describes the functions that occur at each layer of protocols within the TCP/IP suite.

The process by which a device adds networking headers and trailers to data from an application for the eventual transmission of the data onto a transmission medium.

The process of adding control information as it passes through the layered model is called encapsulation.

A process by which an end device, after it receives data over some transmission medium, examines the headers and trailers at each successive higher layer, eventually handing the data to the correct application. Sometimes called deencapsulation.

Decapsulation is the process of removing the extra information and sending only the original application data up to the destination application layer.

A generic term from OSI that refers to the data, headers, and trailers about which a particular networking layer is concerned.

The generic term for data at each level is protocol data unit (PDU), but a PDU is different at each layer.

International standardization program created by ISO and ITU-T to develop standards for data networking that facilitate multivendor equipment interoperability.

The OSI model describes the entire communication process in detail, and the TCP/IP model describes the communication process in terms of the TCP/IP protocol suite and the way it functions.

Know the details of the OSI model to understand the entire network communication process

Know the TCP/IP model to understand how the process is implemented in current networks

The Open Systems Interconnections (OSI) model, known as the OSI model, provides an abstract description of the network communication process.

An international standards body that defines many networking standards. Also, the standards body that created the OSI model.

[OSI] Developed by the International Organization for Standardization (ISO) to provide a road map for nonproprietary protocol development, the OSI model did not evolve as readily as the TCP/IP model.

In networking, this term is used in several ways. With Ethernet hub and switch hardware, port is simply another name for interface, which is a physical connector in the switch into which a cable can be connected. With TCP and UDP, a port is a software function that uniquely identifies a software process on a computer that uses TCP or UDP. With PCs, a port can be a physical connector on the PC, like a parallel or USB port.

This is because the transport layer adds port numbers to its segment header information to ensure that the destination host knows which application process is to receive the packet.  

The format of the message, such as how much data to put into each segment

The way intermediary devices share information about the path to the destination

The method to handle update messages between intermediary devices

The process to initiate and terminate communications between hosts

HTTP

Hypertext Transfer Protocol

TCP

Transport Protocol

IP

Internetwork Protocol

Defines common terms that describe the network functions to those working in the industry and allows greater understanding and cooperation

Segments the process to allow technologies performing one function to evolve independently of technologies performing other functions

Fosters competition because products from different vendors can work together

Provides a common language to describe networking functions and capabilities

Assists in protocol design, because protocols that operate at a specific layer have defined information that they act upon and a defined interface to the layers above and below

A protocol model provides a model that closely matches the structure of a particular protocol suite

The hierarchical set of related protocols in a suite typically represents all the functionality required to interface the human network with the data network

provides a common reference for maintaining consistency within all types of network protocols and services

not intended to be an implementation specification or to provide a sufficient level of detail to define precisely the services of the network architecture

Primary purpose of a reference model is to aid in clearer understanding of the functions and process involved

The Open Systems Interconnection (OSI) model is the most widely know internetwork reference model

defines the four communication functions that protocols perform

is an open standard

1.  Creation of data at the application layer of the originating source end device

2.  Segmentation and encapsulation of data as it passes down the protocol stack in the source end device.

3.  Generation of the data onto the media at the network access layer of the stack.

4.  Transportation of the data through the internetwork, which consists of media and any intermediary devices.

5.  Reception of the data at the network access layer of the destination end device

6.  Decapsulation and reassembly of the data as it passes up the stack in the destination device.  you learn more about the encapsulation and decapsulation processes in the next section

7.  Passing this data to the destination application at the application layer of the destination end device.

Data -> Application layer PDU

Segment -> Transport layer PDU

Packet -> Internetwork layer PDU

Frame -> Network access layer PDU

Bits-> PDU used for the physical transmission of binary data over media.

1. An end user, using an em-mail application, creates data.  The application layer coeds the data as e-mail and sends the data to the transport layer

2.  The message is segmented, or broken into pieces, for transport.  The transport layer adds control information in a header so that it can be assigned to the correct process and all segments put into proper order at the destination.  The segment is sent down to the internetwork layer.

3.  The internetwork layer adds IP addressing information in an IP header.  The segment is now an addressed packet that can be handled by routers en route to the destination.  The internetwork layer send the packet down to the network access layer.

4.   The network access layer creates an Ethernet frame with local network physical address information in the header.  This enables the packet to get to the local router and out to the web.  The frame also contains a trailer with error-checking information.  After the frame is created, it is encoded into bits and sent onto the media to the destination.

5.  At the destination host, the process is reversed.  The frame is decapsulated to a packet, then to a segment, and then the transport layer puts all segments into the proper order.

6.  When all data has arrived and is ready, it is sent to the application layer, and then the original application dta goes to the receiver's e-mail application.  The message is successful.

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When juxtaposed, you can see that the functions of the application, presentation, and seesion layers of the OSI model are combined into one application layer in the TCP/IP model.

The bulk of networking functions reside at the transport and the network layers, so they remain individual layers.  TCP operates at the transport layer, and IP operates at the INternet layer.

The data link and physical layers of the OSI model comibine to make the network access layer of the TCP/IP model.

Addressing of data happens in three different layers of the OSI model.  The PDU at each layer adss address information for use by the peer layer at the destination.

Physical - Timing and Synchronization Bits

Data Link - Destination and Source Physical Addresses

Network -Destination and Source Logical Network Addresses

Transport - Destination and Source Process Number (Ports)

Upper Layers - Encoded Application Data

During encapsulation, address identifiers are added to the data as it travels down the protocol stack on the source host.

The first identifier, the host physical address, is contained in the header of the Layer 2 PDU, called a frame.

The Layer 2 address is unique on the local network and represents the address of the end device on the physical media.  This address comes from codes placed on the NIC by the manufacturer.

In Ethernet, this address is called the MAC address.

Physical address and MAC address are often used interchangeable.

After a frame is successfully received by the destination host, the Layer 2 address information is removed as the data is decapsulated and moved up the protocol stack to Layer 3.

Layer 3 protocols are primarily designed to move data from one local network to another local network within an internetwork.

Layer 3 addresses must include identifiers that enable intermediary network devices to locate hosts on different networks.

At the boundary of each local network, an intermediary network device, usually a router, decapsulates the frame to read the destination host address contained in the header of the packet, the Layer 3 PDU.  Routers use the network identifier portion of this address to determine which path to use to reach the destination host.  When the path is determined, the router encapsulates the packet in a new frame and sends it on its way toward the destination end device.  When the frame reaches its final destination, the frame and packet headers are removed and the data moved up to Layer 4.

At Layer 4, information contained in the PDU header does not identify a destination host or a destination network.  What it does identify is the specific process or service running on the destination host device that will act on the data being delivered.

A user can send and receive many types of traffic over a single network interface, and using port numbers for each segment keeps traffic for web pages separate from em-mail traffic and so on.  The segment contains both source and destination ports in case the receiver needs to contact the sender.

Question 1

Which OSI layer is associated with IP addressing?

C = 3

IP addressing is a concern of the OSI network layer (Layer3).  Physical addressing happens at OSI Layer 2

Question 2

The elements of communication include a message source, a message destination, and a ___________, or medium to transport the message.

Question 3

Which type of addressing is found at the OSI Layer 2? (Choose two).

B = Physical

C = MAC 

A MAC address is the physcial address burned on to the OSI Layer 2 network interface card.  Logical addressing happens at OSI Layer 3.

Question 4

When a server responds to a web request, what occurs next in the encapsulation process after the web page data is formatted and separated into TCP segments?

D = The server adds the source and destination IP address to each segment header to deliver the packets to the destination.

Encapsulating into TCP segments occurs at OSI Layer 4, so the next encapsulation is at OSI Layer 3, which includes adding source and destination IP addresses to the segment headers and converting them into packets.  Then the physical addressing is added and the data is converted to bits.

Question 5

Which term describes a specific set of rules that determine the formatting of messages and the process of encapsulation used to forward data?

B =Protocol

A protocol describes a specific set of rules for communication, including message formatting and encapsulation.

Question 6

A limited-use protocol owned by a company is considered to be _________________.

Question 7

Which one of the following is associated with Layer 4 of the OSI model?

B = TCP

TCP has control features pertaining to OSI Layer 4, FTP is an application (Layer 7), and IP and TFTP are network layer protocols (Layer 3).

Question 8

The device that connects a device to the media is called a/an ______________.

Question 9

Which of the following terms defines dividing data streams into smaller pieces suitable for transmission?

C = Segmentation

Segmentation, which occurs at OSI Layer 4, is the correct answer.

Question 10

A device that moves data between networks is a ________________________.

Question 11

Which of the following is the process for interweaving multiple data streams onto one shared communication channel or network medium?

B = Multiplexing

Multiplexing is the correct term.

Question 12

Which of the following is associated with the network layer?

A = IP address

IP addressing is an OSI Layer 3 fucntion.  All others are OSI Layer 2 functions.

Question 13

Which of the following is the correct "top down" order of the OSI model?

B = Application, presentation, session, transport, network, data link, physical

The correct order is application, presentation, session, transport, network, data link, physical.

Question 14

Question 14 Which layer of the OSI model is concerned with end-to-end message delivery over the network?

B = Transport

End-to-end message delivery is the concern of OSI Layer 4, the transport layer.

Challenge Question 1

Which layers of the OSI model are combined into other layers of the TCP/IP model? (Choose all that apply)

B = Presentation

D = Data Link

F = Physical

G = Session

The OSI presentation and session layers are combined

into the application layer of the TCP/IP model. The OSI

data link and physical layers are combined into the

network access layer of TCP/IP. The transport and

network layers have parallell layers in TCP/IP.

Challenge Question 2

Which of the following are true about LANs and WANs? (Choose two).

C = WANs connect groups of networks using TSPs

E =Hosts on a LAN use physical addressing to communicate.

LANs are connected by WANs.  WANs connect networks through telephone service providers (TSP).  Logical addressing is used between networks, and physical addressing, or MAC addresses, are used inside LANs.