- •2 Communicating over the Network
- •2.0 Chapter Introduction
- •2.0.1 Chapter Introduction Page 1:
- •2.1 The Platform for Communications
- •2.1.1 The Elements of Communication Page 1:
- •2.1.2 Communicating the Messages Page 1:
- •2.1.3 Components of the Network Page 1:
- •2.1.4 End Devices and their Role on the Network Page 1:
- •2.1.5 Intermediary Devices and their Role on the Network Page 1:
- •2.1.6 Network Media Page 1:
- •2.2 LaNs, waNs, and Internetworks
- •2.2.1 Local Area Networks Page 1:
- •2.2.2 Wide Area Networks Page 1:
- •2.2.3 The Internet - a Network of Networks Page 1:
- •Internetwork
- •Intranet
- •2.2.4 Network Representations Page 1:
- •2.2.5 Activity - Using NeoTrace™ to View Internetworks Page 1:
- •2.3 Protocols
- •2.3.1 Rules that Govern Communications Page 1:
- •2.3.2 Network Protocols Page 1:
- •2.3.3 Protocol Suites and Industry Standards Page 1:
- •2.3.4 The Interaction of Protocols Page 1:
- •Internetwork Protocol:
- •2.3.5 Technology Independent Protocols Page 1:
- •2.4 Using Layered Models
- •2.4.1 The Benefits of Using a Layered Model Page 1:
- •2.4.2 Protocol and Reference Models Page 1:
- •2.4.3 The tcp/ip Model Page 1:
- •2.4.4 The Communication Process Page 1:
- •2.4.5 Protocol Data Units and Encapsulation Page 1:
- •2.4.6 The Sending and Receiving Process Page 1:
- •2.4.7 The osi Model Page 1:
- •2.4.8 Comparing the osi Model with the tcp/ip Model Page 1:
- •2.5 Network Addressing
- •2.5.1 Addressing in the Network Page 1:
- •2.5.2 Getting the Data to the End Device Page 1:
- •2.5.3 Getting the Data through the Internetwork Page 1:
- •2.5.4 Getting the Data to the Right Application Page 1:
- •2.5.5 Warriors of the Net Page 1:
- •2.6 Chapter Labs
- •2.6.1 Lab: Topology Orientation and Building a Small Network Page 1:
- •2.6.2 Lab: Using Wireshark™ to View Protocol Data Units Page 1:
- •2.7 Chapter Summary
- •2.7.1 Summary and Review Page 1:
- •2.8 Chapter Quiz
- •2.8.1 Chapter Quiz Page 1:
2.4.6 The Sending and Receiving Process Page 1:
When sending messages on a network, the protocol stack on a host operates from top to bottom. In the web server example, we can use the TCP/IP model to illustrate the process of sending an HTML web page to a client.
The Application layer protocol, HTTP, begins the process by delivering the HTML formatted web page data to the Transport layer. There the application data is broken into TCP segments. Each TCP segment is given a label, called a header, containing information about which process running on the destination computer should receive the message. It also contains the information to enable the destination process to reassemble the data back to its original format.
The Transport layer encapsulates the web page HTML data within the segment and sends it to the Internet layer, where the IP protocol is implemented. Here the entire TCP segment is encapsulated within an IP packet, which adds another label, called the IP header. The IP header contains source and destination host IP addresses, as well as information necessary to deliver the packet to its corresponding destination process.
Next, the IP packet is sent to the Network Access layer Ethernet protocol where it is encapsulated within a frame header and trailer. Each frame header contains a source and destinationphysical address. The physical address uniquely identifies the devices on the local network. The trailer contains error checking information. Finally the bits are encoded onto the Ethernet media by the server NIC.
2.4.6 - The Sending and Receiving Process The animation depicts the encapsulation process and protocol operation when sending a web page from a Web server to a Web client over an Ethernet network. The client requests a Web page, and the server sends the web page to the client. The Web page data is encapsulated with a TCP transport header, which creates the TCP Segment. Next, the TCP Segment is encapsulated in an IP header creating a packet. Then the Ethernet frame header and trailer encapsulate the IP packet, creating an Ethernet frame. Finally, the Ethernet frame is transmitted on the medium as bits (zeros and ones).
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This process is reversed at the receiving host. The data is decapsulated as it moves up the stack toward the end user application.
2.4.6 - The Sending and Receiving Process The animation depicts the de-encapsulation process (the reverse of the encapsulation process) and protocol operation when receiving a Web page from a Web server over an Ethernet network. The client receives the web page as bits (zeros and ones). Then the Ethernet frame header and trailer are removed (de-encapsulated) from the IP packet. Next, the IP header is removed (de-encapsulated) from the TCP segment. Finally, the TCP header is removed (de-encapsulated) from the data (actual web page), which is passed up to the Web client application to be displayed on the user's screen.
2.4.7 The osi Model Page 1:
Initially the OSI model was designed by the International Organization for Standardization (ISO) to provide a framework on which to build a suite of open systems protocols. The vision was that this set of protocols would be used to develop an international network that would not be dependent on proprietary systems.
Unfortunately, the speed at which the TCP/IP based Internet was adopted, and the rate at which it expanded, caused the OSI Protocol Suite development and acceptance to lag behind. Although few of the protocols developed using the OSI specifications are in widespread use today, the seven-layer OSI model has made major contributions to the development of other protocols and products for all types of new networks.
As a reference model, the OSI model provides an extensive list of functions and services that can occur at each layer. It also describes the interaction of each layer with the layers directly above and below it. Although the content of this course will be structured around the OSI Model the focus of discussion will be the protocols identified in the TCP/IP protocol stack.
Note that whereas the TCP/IP model layers are referred to only by name, the seven OSI model layers are more often referred to by number than by name.
2.4.7 - The O S I Model The diagram depicts the seven layers of the O S I reference model and provides a brief description and function of each layer. Layer 7. Application - The Application Layer provides the means for end-to-end connectivity between individuals using data networks. Layer 6. Presentation - The Presentation Layer provides for common representation of the data transferred between Application Layer services. Layer 5. Session - The Session Layer provides services to the Presentation Layer to organize its dialogue and to manage data exchange. Layer 4. Transport - The Transport Layer defines services to segment, transfer, and reassemble the data for individual communications between the end devices. Layer 3. Network - The Network Layer provides services to exchange the individual pieces of data over the network between identified end devices. Layer 2. Data Link - The Data Link Layer protocols describe methods for exchanging data frames between devices over a common media. Layer 1. Physical - The Physical Layer protocols describe the mechanical, electrical, functional, and procedural means to activate, maintain, and de-activate physical connections for bit transmission to and from a network device.