2. Introduction to Computer Networks Introduction to Computer Networks

3. How Networks Send Data This lesson introduces the concept of packets as the basic building blocks of network data communications.

4. The Function of Packets Data usually exists as rather large files. However, networks cannot operate if computers put large amounts of data on the cable at the same time.Data usually exists as rather large files. However, networks cannot operate if computers put large amounts of data on the cable at the same time. Large continuous streams of data slow down the network.Large continuous streams of data slow down the network.

5. The Function of Packets In order for many users at once to transmit data quickly and easily across the network, the data must be broken into small, manageable chunks.In order for many users at once to transmit data quickly and easily across the network, the data must be broken into small, manageable chunks. This way, users each get their share of access to the network. These chunks are called packets, or frames.This way, users each get their share of access to the network. These chunks are called packets, or frames. When the network operating system at the sending computer breaks the data into packets, it adds special control information to each frame.When the network operating system at the sending computer breaks the data into packets, it adds special control information to each frame.

6. Packet Structure Header: 1. An alert signal to indicate that the packet is being transmitted. 2. The source address. 3. The destination address. 4. Clock information to synchronize transmission.Header: 1. An alert signal to indicate that the packet is being transmitted. 2. The source address. 3. The destination address. 4. Clock information to synchronize transmission. Trailer : contains an error- checking component called a cyclical redundancy check (CRC). The CRC is a number produced by a mathematical calculation on the packet at its source.Trailer : contains an error- checking component called a cyclical redundancy check (CRC). The CRC is a number produced by a mathematical calculation on the packet at its source. Data: From 0.5 kilobytes (KB) to 4 KB.Data: From 0.5 kilobytes (KB) to 4 KB.

7. Example: Packets in Printing (1) A large print job must be sent from a computer to a print server.A large print job must be sent from a computer to a print server. 1. The sending computer establishes a connection with the print server.1. The sending computer establishes a connection with the print server.

8. Example: Packets in Printing (2) 2. The sending computer breaks the large print job into packets.2. The sending computer breaks the large print job into packets. Each packet contains the destination address, the source address, the data, and control information.Each packet contains the destination address, the source address, the data, and control information.

9. Example: Packets in Printing (3) 3. The network interface card (NIC) in each computer examines the receiver's address on all frames sent on its segment of the network.3. The network interface card (NIC) in each computer examines the receiver's address on all frames sent on its segment of the network. until it detects a frame addressed specifically to it.until it detects a frame addressed specifically to it.

10. Example: Packets in Printing (4) 4. The destination computer is the print server. The packets enter through the cable into the NIC.4. The destination computer is the print server. The packets enter through the cable into the NIC. 5. The network software processes the frame stored in the NIC's receive buffer.5. The network software processes the frame stored in the NIC's receive buffer.

11. Example: Packets in Printing (5) 6. the network operating system in the receiving computer reassembles the packets back into the original file and moves the file into the computer's memory.6. the network operating system in the receiving computer reassembles the packets back into the original file and moves the file into the computer's memory. From there the file is sent to the printer.From there the file is sent to the printer.