From Mycomputer Notes

Revision as of 18:16, 5 April 2006

Introduction to TCP/IP

In this chapter we learn about the Transmission Control Protocol/Internet Protocol (TCP/IP). We will compared the TCP/IP Model to the OSI Model, we will discribe and identified each Layer of the TCP/IP model We will discuss the type of IP Addresses (Class A, Class B, Class C, Class D).

The TCP/IP model was created by the US Department of Defense (DoD)because it wanted a network that could survive under any conditions. The DoD wanted any packet to to reach its destination every single time and under any comdition; from any point to any point. Under this conditions the TCP/IP model was created and since then it has become the standard on which the Internet has grown.

For those who one to read a bit more about this topic outside this Wiki you can read the article from Wikepedia[1]

TCP/IP Model

Application Layer

The application layer handles high level protocols an issues of :

Representation

Encoding

Dialog Control

The TCP/IP protocol suites combines all applications related issues into a single layer and ensures that this data is properly packaged to the next layer. Besides Internet and transportation protocols TCP/IP also includes common protocols to support common applications like email, file transfer and remote loging:

• HTTP
• TFTP
• FTP
• NFS
• SMTP
• Telnet
• SNMP
• DNS

Transport Layer

The transport layer provides transport services from the source host to the destination host. The transport layer creates a logical connection the sending and receiving host. The Transport protocol (TCP or UDP) segments and re assambles upper layer applications into the same data streams between end points . This layer provides end to end transport services. The tranport layer user two protocols:

UDP

Its primary duty is to transport data from source to destination.

TCP

Provides end-to-end control by sliding windows and reliability in sequencing numbers and acknowledgments.

Services Provided by both Protocols

Internet Layer

All upper and lower layer communications travel through the TCP/IP protocol stack (Application, Transport, Internet and Network ). The purpose ot the Internet layer is to send packet from a device using the correct protocol that functions at this layer. Best path determination and packet switching occur at this layer. Protocols that operates at this layer are:

• IP
• ICMP
• ARP
• RARP

Internet Protocol (IP)

Provides connectionless , best effort delivery routing of packets. IP is not concerned with the content of the packet. Instedad, It looks for a way to moved the packets to their destination. IP performs the folowing operations:

• Defines a packet and addressing scheme.
• Transferring data between the Internet Layer and the network access layer.
• Routing packets to remote hosts.

Internet Control Message Protocol (ICMP)

Provides control and messaging capabilities

Address Resolution Protocol (ARP)

Determines the data link layer addresses (MAC) for known IP addresses.

Reverse Address Resolution Protocol (RARP)

Determines IP addresses when data link layer addresses (MAC) are known.

Network Access Layer

This layer is concerned with all the issues that an IP packer requires to make a physical link to the network medium.(LAN & WAN technologies) Network Access Functions included mapping IP addresses to physical hardware addresses adn encapsulating IP packets into frames. Based on the hardware type of the network interface, the network access layer define the connection with the physical network medium. Technologies that work in this layer are:

• Ethernet
• Fast Ehternet
• SLIP and PPP
• FDDI
• ATM
• ARP
• RARP

The OSI Model and TCP/IP Model

Similarities

• Both have layers.
• Both have Application Layers but the services are different.
• Both have comparable transport and network layers.
• Packet switched (not circuit switched technology is assumed.

Differences

• TCP/IP combines (Presentation & Session) = Application Layer
• TCP/IP combines (Data Link & Physical ) = Networks Access Layer
• TCP/IP appears simplier because it has fewer layers.
• The TCP/IP transpoer layer using UDP does not always guarantee reliable delivery of packets, as the transport layer in the OSI Model.
• TCP/IP protocols sre the standard around which the Internet developed, so the TCP/IP modek gains credibility because of the protocols. On the other hand the OSI Model is used as a guide to understand the communication process and does not have a OSI Protocol

Internet Addresses

Inside the pc an ip address is stored as a 32 bits sequence of 1s and 0s. To make and IP address easier to understand and used we write it as a four decimal numbers separated by periods (i.e 192.168.1.2) this was of written the address is called dotted decimal format.

IP Addressing Format

We remember that the Internet Protocol is the one responsible for forwarding packets from the Network on which they originate to the destination network. This addressing scheme, therefore, must include an indentifier for both the source and destination networks. When the packet arrives at a router connectred to the destination network, IP must then located the particular computer connected to that network. Since an IP address has two parts, one part identifies the network to which the system is connected and a second part identifies that particular systems on the network. The router that receives the packet for its network will delivery it to the host that is identified on the IP address.

Class of IP Address

When the IP scheme (IPv4)was implemented it was thought that the number of IP addresses was going to be enough. The assumption was that there would be a relatively small number of large networks, possibly with millions of computers, a significanlty large number of medium-sized networks, with perhaps thousands of computers. But the prediction was more of a great number of networks having several hundred or fewers machines. To accommodate different-sized networks and ot aid inclassifying them, IP addresses are divided into groupings called classes.

IP Addressing Format

Obtainning an IP Address

Over here I will be reviewing how network devices obtain IP Addresses. For a Network to function properly an IP addresses must be assigned (to each host) according to a specific logic, hierarchy.

IP addresses can be assigned either statically or dynamically.

STACTICT IP ASSIGNATION

• Each device must be configured with an IP address.
• Record of IP assignement are need it.
• Not all operating systems identify duplicate addresses.

Devices that are best with static IP address are:

1. Web Server
2. Network Printers
3. Aplication Servers
4. Routers.