Describe the properties and characteristics of TCP/IP. Explain common TCP and UDP ports, protocols, and their purpose.
Compare and contrast various Wi-Fi networking standards and encryption
answer
1. TCP/IP Properties and Characteristics
An understanding of TCP/IP is important for anyone working on the Internet or on home or corporate networks. This section describes TCP/IP and how it works. TCP/IP is actually a suite of protocols. A protocol is a set of rules that end points in a telecommunication connection use when they communicate. Each end point uses the protocol to send or receive messages in a network. All TCP/IP protocols operate at the network (Internet) and transport layers. Connection and addressing are key concepts in defining the operation of the transport layer. Connection refers to the establishment of a virtual circuit between the communicating applications. This circuit is used to send data in both directions. Once all data has been sent, the virtual circuit is removed. Addressing refers to the use of logical identifiers for establishing and maintaining connections. Data sent between two connected devices may take many different paths over a network. This can occur because network devices and paths may be added, removed, or become faulty. The sending device determines the path that data should take by using the logical destination address and information about network conditions. Data arriving at the destination is in turn received by the transport layer and is then passed to the appropriate application.
Transmission Control Protocol/Internet Protocol (TCP/IP) was created during the 1970s by the U.S Department of Defense. It is the most commonly used network today. Its popularity can be attributed to two major factors. First, the emergence of the Internet as a major communications infrastructure has created a high demand for TCP/IP. Second, the explosion of microcomputers onto the networking scene has created a huge base of potential TCP/IP users. Although the microcomputer market is currently dominated by other networking protocols, the momentum of the Internet is gradually causing a shift towards TCP/IP.
1.1. TCP/IP Overview
The design of the network allowed for a simple robust network which could survive partial failure of some computers or some connections without losing all data. This was a major concern in the design of the arpanet and in the original design of tcp/ip. This is known as the hourglass model which means that a network has many types of physical media (fiber, satellite etc) but a small set of protocols. In the modern internet the osi model is rarely used by network engineers, it is more of an academic tool. In the design of tcp/ip, the osi model was not followed. Tcp/ip has its own model which is the tcp/ip protocol suite. This model is described a later section.
The entire suite of tcp/ip protocols are named after two of the most common protocols – tcp and ip. The tcp/ip protocols were developed in the 1970s and 1980s and were included in the unix operating system. The protocols were designed to be very modular.
Tcp/ip is a suite of data communications protocols that is used to connect hosts on the internet. Tcp/ip can also be used as a communications protocol in a private network (an intranet or an extranet).
1.2. TCP/IP Layers
Furthermore, it determines if resources at the intended communication partner are sufficient for the requested service, also ensuring that the requested service is available. If a connection request is accepted, the application layer is responsible for setting up and tearing down the required network resources for the session. Data from different applications is separated. The Application Layer defines the types of messages and/or data the partners are using and the syntax for the message. Finally, the Application Layer is responsible for translating data between the network and the semantics of the application. This involves a number of complex operations to prepare the data for transfer between systems.
The top layer in the TCP/IP protocol suite is the Application Layer. The Application Layer is the network support to the end user. This is where the interface between the human network users and the network itself is accomplished. The Application Layer has a couple of specific responsibilities it handles. It is responsible for identifying and authenticating the desired communication partner, ensuring that only authorized entities can use the network.
The internet protocol suite is organized into layers. Each layer has a particular responsibility and is designed to provide abstraction from the layers above and below. TCP/IP has four layers.
1.3. IP Addressing
The IP protocol has two primary versions in use today. These are known as IPv4 and IPv6. The current and most widely used version of IP is IPv4. This version operates on a 32-bit addressing system, and will still be widely used for years to come. Despite this, there is a growing concern that the pool of available IPv4 addresses has almost been depleted due to the vast expansion of the internet over the last decade. This exhaustion of addresses has led to an increasing implementation of the next version of IP, known as IPv6. This version operates on a 128-bit binary addressing system. This expanded address space is sufficient to meet the demand, and will support the future of the internet. At present, there are few hosts using IPv6, however, in years to come, the transition from IPv4 will take place, and eventually IPv6 will become the prevalent version of IP.
The IP address serves several purposes. Its most important function is that it identifies an address of a host, or possibly an entire network. Other IP functions are used for host or network interface identification and location addressing. The addressing structure of IP is hierarchical. The network identifier is used as a reference to the network, and the host identifier is used to reference devices on that network. This is imperative to allow for the smooth operation of routing data across networks. IP addressing can run over several types of network. The most common is connection to a LAN. This allows the use of MAC addressing to map IP addresses to physical addresses. Hosts can also connect to IP over WAN links, or even using a point to point dial up link. Connection to different types of network can affect the method used to encapsulate data, but this does not affect the addressing of hosts and networks using IP.
1.4. TCP/IP Protocols
The most important protocol in the internet layer is the Internet Protocol (IP). It provides the addressing structure using IP addresses and is used for the routing of packets across the network. IP does not guarantee to deliver packets to the destination. Its successor, IPv6, is designed to replace it.
– Link layer – Internet layer – Transport layer – Application layer
TCP/IP protocols are a set of protocols developed to allow cooperating computers to share resources across a network. They do this by providing an addressing structure and an array of services. The addressing structure is used to uniquely identify each machine on a network, and the array of services is used to facilitate the transfer of data between machines. The set of protocols can be divided into the following layers:
1.4.1. TCP (Transmission Control Protocol)
1.4.2. UDP (User Datagram Protocol)
1.4.3. ICMP (Internet Control Message Protocol)
1.5. Common TCP/IP Ports
– FTP data transfer (command is port 21) – 20. FTP data transfer and commands use two separate connections. – DNS name server (UDP) – 53, concurrent with TCP often. – Remote login – 23. Telnet is not a secure protocol. – E-mail – SMTP – 25. The Simple Mail Transfer Protocol is used to send e-mail between servers. The newer protocol for sending mail between two servers and on the client side retrieving it is known as ESMTP. It is upward compatible with SMTP and uses port 25. – E-mail retrieval – 110. Post Office Protocol or POP3 is an older e-mail protocol that sends mail to a client. The newer protocol, Internet Message Access Protocol or IMAP, is similar to HTTP as it keeps mail on the server and is thus more flexible and useful for multiple clients. Both protocols use different port numbers (110, 143) and for this reason are known as POP and IMAP with the number indicating the port, ex. IMAP4.
Many common TCP/IP protocols have well-known port numbers. These port numbers are included in the headers of data segments to tell the upper-layer protocols which protocol data unit should get which TCP/IP process. Here are a few examples of common port numbers:
1.5.1. Port 80 (HTTP)
1.5.2. Port 443 (HTTPS)
1.5.3. Port 25 (SMTP)
1.5.4. Port 53 (DNS)
1.5.5. Port 110 (POP3)
1.6. Purpose of TCP/IP
TCP and IP were developed in a Department of Defense research project, and the goal was a network that could survive a nuclear war. This objective has had a profound effect on the design of the protocols and the structure of the internet. The principal design feature is that the internet only provides a best-effort delivery service. Although this approach may seem surprising in light of the critical importance placed on data delivery by applications, it is rooted in the military origins of the protocols. Given that a nuclear attack would certainly disrupt the existing form of the internet, a system was needed that would allow the network to survive even complete annihilation and rebuilding. Out of this grew the idea of a virtual network built on top of the existing physical network. The virtual network would hide the underlying physical network, providing a uniform service to the user across a wide variety of underlying network technologies. If part of the underlying network were to be destroyed, the virtual network could be rerouted over the remaining fragments. Today, the best-effort delivery service and the design of a virtual network have turned out to be extremely beneficial for internetworking, even though the original motivation has long since passed.
The ultimate goal of TCP is the delivery of data, and the purpose of TCP/IP is to provide end-to-end delivery of data, known as a domestic or local area network (LAN), or to another network, which presumably would be a commercial network on a larger scale. LANs are generally owned, controlled, and operated by a single person or organization. Examples of LANs would be the network in a home or office, or the network comprising an apartment within a building. A commercial network would usually interconnect a large number of hosts in a fairly extensive geographic area, such as a single building, a campus, or a metropolitan area. The TCP/IP internet, or internetwork, is a network of networks, which provides a global service to millions of users worldwide. Thus, TCP/IP can be used for many different purposes, which accounts for the great variety of environments in which it operates.