Here is something that may help.
The OSI model is just used for that, a model. It does help to know the PDU (Protocol Data Unit) at each layer. I believe that is what you are referring to.
When you start your Internet browser and type in
www.google.com, the application will build the data to send to google.com (The Get request, as defined in the RFC for HTTP: rfc 2616, section: 9.3). A host (Computer, PC, etc) operates at all layers of the OSI model. It helps you to understand how 2 devices inter-operate nothing more nothing less. Getting back to the example, the host will build the HTTP data, but before it can send the data it need the data, it needs to establish a 3 way handshake first. I assume you know the basics here so I will not cover it. Frames are not packets, frames are not cells, yes people use them interchangeably, but they are unfortunately incorrect in assuming frames are packets, etc. let me explain why. So after a host establishes a 3 way handshake with a webserver, the host now can send the GET request that it built (Typically this data is stored in a buffer). The data is is passed from Layer 7 to layer 6 and headers are added (if needed), then down to layer 5, layer 5 adds the headers and passes the data to layer 4, layer 4 adds its headers and passes the segment down to layer 3, layer 3 adds its headers and passes the packet to layer 2, layer 2 add its headers and passes the frame down to layer 1 and these is where the frame is converted to a signal to be put in the medium (transmitted).
The adding of the headers and trailers is called encapsulation
A TCP/IP Ethernet Network:
Layer 7 PDU: Data
Layer 6 PDU: Data
Layer 5 PDU: Data
Layer 4 PDU: Segment
Layer 3 PDU: Packet
Layer 2 PDU: Frame
Layer 1 PDU: Bit
http://www.infocellar.com/networks/osi-model.htmBilly
