Step by step Configuration of Cisco L2 Switch and Basic Switch Management
Lesson - Networking and the OSI Reference Model
Networking and the OSI Reference Model Networking:Is the interconnection of workstations, peripherals(such as printers, hard drives, scanners, etc), and other devices. It is not important what type of computer is used in a network, what is important is that all devices speak the same language, or protocol, which is a formal description of a set of rules and conventions that govern how devices on a network exchange information
The OSI Reference Model:Is a descriptive network scheme; its standards ensure greater compatibility and interoperability between various types of network technologies. It illustrates how information travels through networks. It describes how information or data makes its way from application programs(such as spreadsheets) through a network medium(such as wires) to another application program located on another computer on a network.
The OSI Reference Model divides the problem of moving information between computers over a network medium into seven layer for smaller and more manageable problems.
7 Application – Network processes to applications
6 Presentation – Data representation
5 Session – Inter host communication
4 Transport – end to end connections
3 Network – Addresses and best path, Routers
2 Data link – Access to media, Switches
1 Physical - Binary Transmission
Layers 1 through 3 – control the physical delivery of messages over the network, often called media layers.
Layers 4 through 7 – provide for the accurate delivery of data between computers on the network, often called host layers
Peer to Peer Communication
Each layer’s protocol exchanges information called protocol data units (PDUs), between peer layers. This peer-layer protocol communication is achieved by using the services of layers below the communicating layer. The layer below any current layer provides its services to the current layer. Each lower-layer service takes upper-layer information as part of the lower-layer PDUs it exchanges with its layer peer.
For Example in TCP/IP:1. The transport layer of TCP (Host A) communicates with the peer (Host B) TCP function using segments.2. Thus, the TCP segments become part of the network-layer packets(also called datagrams) exchanged between IP peers.
3. In turn, the IP packets must become part of the data link frames exchanged between directly connected devices.4. Ultimately, these frames must become bits as the data is finally transmitted by the physical layer protocol using hardware.
Data Encapsulation:
Is the process in which data is wrapped in a particular protocol header before network transit.
For example, A user sending e-mail message
1. Build the data – e-mail messages, alphanumeric in characters are converted into data
2. Package the data for end to end transport - Data is packaged into segments to ensure that hosts at both ends of the e-mail system can reliably communicate.
3. Append network address in header – data is put into packet or datagram that contains a network header with source and destination logical address.
4. Append local address in data-link header – Each network device must put the packet into frame. The frame allows connection to the next directly connected network device.
5. Convert to bits for transmission – the frames must be converted into a pattern of ones and zeros for transmission on the medium usually a wire.
Networking Devices
1. Repeater – exist on Layer 1, extend the distance of a network so that signals will be more recognizable to devices receiving them.
2. Hub – acts as multiple repeaters, also called concentrators. Data arriving at one port gets sent out on all ports
3. Bridge – operate at layer 2, more intelligent than hubs, control broadcast to the network and maintain address table, used primarily to connect segments of a network
4. Router – operate at layer 3, used to connect separate networks and access the internet. It provides end to end routing by passing data packets and routing traffic between different networks based on network protocol or layer 3 information.
Difference between Router and Bridge
a. Bridging occurs at layer 2, the data link layer, whereas routing occurs at layer 3, network layer of the OSI Reference Model.
b. Bridges use physical or MAC addresses to make data forwarding decisions. Routers uses layer 3 information, IP Addresses to make forwarding decisions
c. Mac addresses are assigned by Manufacturer and hard coded into the NIC. Ip addresses are usually assigned by the Network Administrator.