Chapter 1: Protocols and Layers

Chapter 1: Protocols and Layers

1. What are the differences between network layer delivery and transport layer delivery?

The network layer must be present on all systems and delivers packets hop-by-hop between adjacent intermediate systems (routers or gateways) or end systems (hosts). The transport layer can technically be absent from intermediate systems and delivers packet content end-to-end between hosts. The network layer is usually “unreliable” and connectionless but the transport layer often adds a measure of reliability (such as resending missing or errored packet content) and connections to the network layer. The network layer has the network address, while the transport layer focuses on ports and multiplexing application’s traffic on the network.

2. What are the main characteristics of a peer-to-peer process?

A peer-to-peer protocol process allows the same layers on different systems to communicate. The term “peer” means every implementation of some layer is essentially equal to all others. There is no “master” system at the protocol level. Communications between peer layers on different systems use the defined protocols appropriate to the given layer.

3. What are port addresses, logical addresses, and physical addresses?

Also called the “process address,” the port address at the transport layer has to decide which process originated the message and to which process it must deliver it. Port addresses are an important portion of the application socket in TCP/IP. The network address at the network layer is a logical address. Network (logical) addresses should be organized so that devices can be grouped under a part of that address, as are IP addresses. A physical address refers to the physical communications port. This address exists at the data link layer and is known as the MAC address on LANs.

4. What are the functions of the data link layer in the Internet model?

The data link layer organizes raw bits into a frame with header and (usually) trailer. The data link layer performs this framing, handles physical addressing (the MAC address on LANs), and error detection (error correction is another matter entirely). The data link layer handles access control and flow control on adjacent systems (those one hop away).

5. What two major types of services can be provided at the application “layer”?

The application layer can provide session support to coordinate the “dialog” between applications and internal representation conversion (presentation services) so that the data sent across the network is meaningful to the receiver.