- •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:
2.5 Network Addressing
2.5.1 Addressing in the Network Page 1:
The OSI model describes the processes of encoding, formatting, segmenting, and encapsulating data for transmission over the network. A data stream that is sent from a source to a destination can be divided into pieces and interleaved with messages traveling from other hosts to other destinations. Billions of these pieces of information are traveling over a network at any given time. It is critical for each piece of data to contain enough identifying information to get it to the correct destination.
There are various types of addresses that must be included to successfully deliver the data from a source application running on one host to the correct destination application running on another. Using the OSI model as a guide, we can see the different addresses and identifiers that are necessary at each layer.
2.5.1 - Addressing in the Network The diagram depicts functions and addressing at each layer of the O S I model. Layers 5, 6, and 7 are grouped together and referred to as Upper Layers. - Upper Layers - Encoded Application Data - Transport - Destination and Source Process Number (ports) - Network - Destination and Source Logical Network Addresses - Data Link - Destination and Source Physical Addresses - Physical - Timing and Synchronization Bits
2.5.2 Getting the Data to the End Device Page 1:
During the process of encapsulation, address identifiers are added to the data as it travels down the protocol stack on the source host. Just as there are multiple layers of protocols that prepare the data for transmission to its destination, there are multiple layers of addressing to ensure its delivery.
The first identifier, the host physical address, is contained in the header of the Layer 2 PDU, called a frame. Layer 2 is concerned with the delivery of messages on a single local network. The Layer 2 address is unique on the local network and represents the address of the end device on the physical media. In a LAN using Ethernet, this address is called the Media Access Control (MAC) address. When two end devices communicate on the local Ethernet network, the frames that are exchanged between them contain the destination and source MAC addresses. Once 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.
2.5.2 - Getting the Data to the End Device The diagram depicts two PC's connected by a cloud labeled "Network". The PDU header contains device address fields: the destination device address, source device address, and the data from the source device. These are Layer 2 device hardware addresses.
2.5.3 Getting the Data through the Internetwork Page 1:
Layer 3 protocols are primarily designed to move data from one local network to another local network within an internetwork. Whereas Layer 2 addresses are only used to communicate between devices on a single local network, Layer 3 addresses must include identifiers that enable intermediary network devices to locate hosts on different networks. In the TCP/IP protocol suite, every IP host address contains information about the network where the host is located.
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. Once 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.
2.5.3 - Getting the Data through the Internetwork The diagram depicts an IP phone labeled "Source end device" (IP address 209.165.202.130), which is connected through three routers to a PC destination device (IP address 209.165.200.230). In addition to the Layer 2 addresses, the PC and IP Phone PDU's also contain the Layer 3 IP source and destination addresses, each of which consists of a network portion and a host (device) portion. A PDU is shown above the diagram with a destination IP network address of 209.165.200 and device (host) address of .230 for the PC. (These two combined create the PC IP address). The IP phone has a source network address of 209.165.202 and device (host) address of 130. (These two combined create the IP phone IP address). The IP address of the router interface for the source network is 209.165.202.145, and the IP address of the router interface for the destination network is 209.165.200.226.