After you click the “send” button, your computer’s email browser will convert the message into packets. A packet is a piece of your message transmitted through a packet switching network. A packet switching network uses protocols agreed upon by various network specialists that allow individual packets to transfer through different routers along various paths to the packet’s destination. It is easier and faster to ship small packets of information through the Internet than to send large ones that use up too much bandwidth and delay delivery. This explains why large files take a few minutes to download. A large file will consist of numerous packets and your computer cannot open the file until all the packets arrive. A typical packet will contain from 1,000 to 1,500 bits. Some files can contain as much as 2Mb (2,000,000 bytes) or more of data. Therefore, the size of your message will determine the number of packets sent over the Internet to its destination.
Most packets split into three parts: a header, the body, and footer.
Header
Body
Footer
Destination Address
Source Address
Length
Synchronization
Packet Number
Data
FCS – Frame Check Sequence
The header contains instructions about the data in the packet:
- Destination address – the IP address of the recipient
- Source address – your computer’s IP address
- Length of packet – the number of bits in this packet
- Synchronization - helps match packets at its destination
- Packet number – the receiving computer will wait to receive all packets before assembling the message
The body contains the actual data of the message. A packet has a fixed length and if the amount of data is greater than what the body can hold then the email program will create more packets until the entire message fits into packets. However, if the body does not contain enough data then the email program will add blank data to the body of the message to make it the right size.The footer contains the Frame Check Sequence (FCS). A FCS, also known as the cyclic redundancy check, is a technique used by email programs to detect data transmission errors. Transmitted messages divide into predetermined lengths and are divided by a fixed divisor. According to the calculation, the remainder is added onto the packet and sent with the message. When the message reaches its destination, the computer recalculates the remainder and compares it to the transmitted remainder. An error occurs when the numbers do not match.
For more information contact the Help Desk at extension 3103.
Send mail to help.desk@ctcd.edu with questions or comments about this web site.
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