Question

I am studying the CCNA 200-125 books written by WENDELL ODOM.

Here it talks about the Link layer in TCP/IP model.

Figure 1-11 shows four steps, in the first step Larry encapsulates the IP packet between an Ethernet header and Ethernet trailer, creating an Ethernet frame.

Larry encapsulates the IP packet, what does this mean?

Is it like compressing a file into a zip and compressing the IP packet into a frame?

I've read the previous pages about the upper layer, it seems that every layer has a header.

Does this IP package include all the headers of the upper layer? like TCP, HTTP and IP

As it mentions, the link layer includes a large number of protocols and standards, are all the protocols be encapsulated?

Why Ethernet headers exist at the beginning of the message and Ethernet trailers exist at the end?

Thanks.

TCP/IP Link Layer (Data Link Plus Physical) The TCP/IP model's original link layer defines the protocols and hardware required to deliver data across some physical network. The term link refers to the physical connections, or links, between two devices and the protocols used to control those links Just like every layer in any networking model, the TCP/IP link layer provides services to the layer above it in the model. When a host's or router's IP process chooses to send an IP packet to another router or host, that host or router then uses link-layer details to send that packet to the next host/router Chapter 1: Introduction to TCP/IP Networking 29 Because each layer provides a service to the layer above it, take a moment to think about the IP logic related to Figure 1-10. In that example, host Larry's IP logic chooses to send the IP packet to a nearby router (R1), with no mention of the underlying Ethernet. The Ethernet network, which implements link-layer protocols, must then be used to deliver that packet from host Larry over to router R1. Figure 1-11 shows four steps of what occurs at the link layer to allow Larry to send the IP packet to R1 1 NOTE Figure 1-11 depicts the Ethernet as a series of lines. Networking diagrams often use this convention when drawing Ethernet LANS, in cases where the actual LAN cabling and LAN devices are not important to some discussion, as is the case here. The LAN would have cables and devices, like LAN switches, which are not shown in this figure. Key Topic Larry 1.1.1.1 R1 IP Packet IP Packet Encapsulate 4 De-encapsulate Ethernet Header Eth Trailer Ethernet Header Eth. Trailer IP Packet IP Packet 2 Transmit 3 Receive Figure 1-11 Larry Using Ethernet to Forward an IP Packet to Router R1 Figure 1-11 shows four steps. The first two occur on Larry, and the last two occur on Router R1, as follows: Step 1. Larry encapsulates the IP packet between an Ethernet header and Ethernet trailer, creating an Ethernet frame. Larry physically transmits the bits of this Ethernet frame, using electricity flow ing over the Ethernet cabling Step 2. Step 3. Router R1 physically receives the electrical signal over a cable, and re-creates the same bits by interpreting the meaning of the electrical signals. Step 4 Router R1 de-encapsulates the IP packet from the Ethernet frame by removing and discarding the Ethernet header and trailer By the end of this process, the link-layer processes on Larry and R1 have worked together to deliver the packet from Larry to Router R1 general reason, but headers NOTE Protocols define both headers and trailers for the same exist at the beginning of the message and trailers exist at the end. The link layer includes a large number of protocols and standards. For example, the link layer includes all the variations of Ethernet protocols, along with several other LAN stan- dards that were more popular in decades past. The link layer includes wide-area network 30 CCENT/CCNA ICND1 100-105 Official Cert Guide (WAN) standards for different physical media, which differ significantly compared to LAN standards because of the longer distances involved in transmitting the data. This layer also includes the popular WAN standards that add headers and trailers as shown generally in Figure 1-11-protocols such as the Point-to-Point Protocol (PPP) and Frame Relay. Chapter 2,"Fundamentals of Ethernet LANS," and Chapter 3, "Fundamentals of WANS," further develop these topics for LANS and WANS, respectively In short, the TCP/IP link layer includes two distinct functions: functions related to the physical transmission of the data, plus the protocols and rules that control the use of the physical media. The five-layer TCP/IP model simply splits out the link layer into two layers (data link and physical) to match this logic

Answer 1

Encapsulation means taking data from one protocol and translating it into another protocol, so the data can continue across a network. Headers and trailers are added to the packet.
It does not mean compressing the IP Packet to frame but it means that some extra information like headers and trailers are added to the packet so that the message in the packet is safe.
All the headers of the upper layer are present in the IP Package and when this whole package reaches the destination, it removes the headers and trailers of each layer one by one and finally delivers the actuall message to the user.
Ethernet Header is added so that the IP Package knows the destination and source addresses. Ethernet Trailer is added to check the redundancy in the message.