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Internet Protocols And Infra Structure Essay, Research Paper
Network: Anything reticulated or decussated at equal distances, with interstices between the intersections.
- A Dictionary of the English
SECTION : 1
1.1 WHAT IS A NETWORK?
A) What is a network?
A network is simply a collection of machines connected in some way that allows them to communicate with each other and share information. To do this the machines have to be connected in some way that allows communication, and have an agreed upon a language to talk when they do communicate.
Components of a network might include individual hosts, some form of communications hardware, a network protocol and a collection of network services.
B) Individual hosts
A network is a collection of individual machines sometimes referred to as hosts. Each host (computer) must have some unique identifier that allows other hosts to talk to it.
1.2 COMPONENTS OF A NETWORK
A) Network Protocol
In order to communicate the parties must speak the same language. Languages on computer networks are referred to as network protocols. A network protocol is simply a set of rules and formats that govern how information is sent and in what format it is sent. Some of the different network protocols used today include TCP/IP (Internet and UNIX favourite), IPX (Novell), Appletalk (MAC), DECnet and various others.
TCP/IP is quickly becoming the networking protocol and is the one I concentrate on in this subject.
B) Network services
To be of use to users the network will provide various services including file, print and device sharing, electronic mail etc.
1.3 TYPES OF NETWORKS
A) Network categories
? LAN (local area network)
All the hosts in the network are directly linked to each other. For example most of the computers on the ground floor of the IT building at CQU are part of a LAN.
? WAN (wide area network)
Much larger than a LAN and all machines are not directly connected. WANs will generally have a lower throughput than a LAN. All of the LANs on the CQU campus connect and form a WAN.
1.4 SOME MORE DEFINITIONS
Like any field of computing, networking has its own terminology. This section provides definitions for some of the terms you’ll come across.
? Packets and datagrams
Many networking protocols transmit information as packets. Information being sent across the network is divided into small (hundreds of bytes usually) chunks of data, called packets. The networking software at the sending end will break the outgoing data into packets. When the packets arrive at their destination the networking software on the receiving machine will put them all back together.
In some cases not all the packets will arrive at the destination using the same route. The packets may also arrive out of order, packet 50 might arrive before packet 49. The networking software handles all of this.
Under TCP/IP packets are often referred to as datagrams. Ethernet, on type of networking hardware, refers to packets as frames
The art of deciding which route data from one machine takes to get to another. In many cases their are multiple different possible routes that can be taken and the routing software must decide which to take.
Responsible for performing the routing for a network, a router is typically a device that connects multiple networks together. (The terms router, gateway and bridge are sometimes used interchangeably).
A device that connects two totally different types of network. For example you might have a gateway machine sitting between an IPX network and a TCP/IP network. The gateway allows the two different networks to talk to each other by converting the protocols they are using.
? Connectionless and connection oriented
Networking transport protocols will often be described as being connection oriented or connectionless. A connection oriented protocol acts like a telephone connection. The sender contacts the receiver and asks are you ready to talk? If the receiver is ready a connection is formed and communication can take place. If the receiver isn’t ready or isn’t there, no communication. Once the connection is made all the information sent down the connection will arrive at the other end.
A connectionless protocol is like the postal service in that all information is sent in individual messages (called packets or datagrams). The individual datagrams have no knowledge or interconnection. Often they are delivered using totally different routes.
? Unreliable and reliable protocols
When a protocol is called unreliable this does not imply that a large percentage of the information it sends is not arriving at the other end. Instead it means that the protocol does not check whether or not the information it just sent actually arrives at the other end.
On the other hand a reliable network protocol will send a piece of information and will wait to make sure that the information arrived at the other end (this is achieved by the receiver sending an acknowledgment back to the sender saying “yep received that piece, send me another”).
1.5 TYPES OF NETWORKING HARDWARE
There is a wide range of different networking hardware that can be used. It’s beyond the scope of this subject to examine each of these. However the following readings from the Internet have been located.
? FDDI : http://www.iol.unh.edu/training/fddi/htmls/index.html
? ISDN : http://www.acc.com/White/isdn.html
? Frame relay : http://www.acc.com/White/frame.html
? ATM : http://juggler.lanl.gov/lanp/atm.tutorial.html
? Ethernet : http://wwwhost.ots.utexas.edu/ethernet/
A) What is TCP/IP?
The Transmission Control Protocol (TCP)
The Transmission Control Protocol works with IP to provide reliable delivery. It provides a means to ensure that the various datagrams making up a message are reassembled in the correct order at their final destination and that any missing datagrams are re-sent until they are correctly received.
The primary purpose of TCP is to avoid the loss, damage, duplication, delay, or misordering of packets that can occur under IP. When IP forwards datagrams, individual datagrams may or may not arrive, and they probably will not arrive in the order in which they were sent. TCP adds the reliability that IP lacks. Also, security provisions such as limiting user access to certain machines can be implemented through TCP.
TCP provides reliability by using checksums (error detection codes) on the data, sequence numbers in the TCP header, positive acknowledgment of data received, and retransmission of unacknowledged data.
Most versions of the UNIX operating system comes with in-built support for networking. The default network protocol that UNIX systems are typically designed to talk is TCP/IP. TCP/IP is also known as the Internet Protocol Suite.
TCP/IP is the protocol used by the Internet, a network of networks spread throughout the world connecting over two million machines with over twenty million users. It is not necessary to be connected to the Internet to use TCP/IP. However being able to connect to the Internet is one of the advantages of using TCP/IP.
2.2 ISOC AND INTERNET STANDARDS
The development of Internet standards is not controlled by any one commercial organisation, even though it can be influenced by them. Instead the development of the Internet is performed by a number of different non-profit organisations including :
? The Internet Society,
A non-governmental International organisation for global cooperation and coordination for the Internet and its internetworking technologies and applications.
? The Internet Architecture Board
The Internet Architecture Board (IAB) is a body of the Internet Society responsible for overall architectural considerations in the Internet. It also serves to adjudicate disputes in the standards process.
? The Internet Engineering Task Force
The Internet Engineering Task Force (IETF) is the protocol engineering and development arm of the Internet. The IETF is a large open international community of network designers, operators, vendors, and researchers concerned with the evolution of the Internet architecture and the smooth operation of the Internet. It is open to any interested individual. (taken from http://www.ietf.org/)
? The Internet Engineering And Planning Group
The following readings are included to provide more information on these organisations.
Information on Internet organisations :
? ISOC The Internet Society SLOW SITE : http://www.isoc.org/
? IEPG the Internet engineering and planning group : http://www.iepg.org/
A) Request for comment (RFCs)
The standards used on the Internet are specified in documents called Request for Comments (RFCs). (Not all RFCs are standards). Someone proposing a new Internet standard will write and submit an RFC. The RFC will be distributed to the Internet community who will comment on it and may suggest changes. The standard proposed by the RFC will be adopted as a standard if the community is happy with it.
RFCs are assigned numbers, Figure 1 includes RFC numbers that correspond to the different protocols. If you have access to the Internet you can anonymously ftp RFCs from a number of well-known sites (including archie.au).
RFCs can and often are very technical and hard to understand unless you are familiar with the area (the RFC for ftp is about 80 pages long).
The following links might prove useful:
? Australian FTP archive of RFCs : ftp://archie.au/rfc/
? Ohio State University’s RFC archive : http://www.cis.ohio-state.edu/hypertext/information/rfc.html
? a UK based RFC archive with a search engine : http://www.connect.org.uk/techwatch/standards/index.html
2.3 TCP/IP PROOLS
A) The protocols of TCP/IP
TCP/IP is an example of a layered communications suite. The advantage of this layered approach is that the protocols at higher levels can safely assume that the lower level protocols will carry out their responsibilities.
For example TCP does not need to know anything about the hardware being used because it is hidden by the layers below it. Figure 1 displays the four different layers of TCP/IP and where some of the many protocols that make up the Internet protocol suite fit within those layers.
TCP and IP are two of the many protocols that make up the suite of Internet protocols. Figure 1 lists some of the others. Some of these protocols will be discussed in detail in the next chapter.
Other Readings On TCP/IP :
? A TCP/IP Primer SLOW SITE :
? The Linux Network Administrator’s Guide :
(a free copy of a book published by O’Reilly and Associates. Essential if you are networking using Linux.) :
The inclusion of these pages is intended to provide you with other readings on TCP/IP if you are interested.
B) IPv6 and Ipng
IPv6 is the formal name of a protocol developed by the IETF’s IPng (Next Generation Internet Protocol) working group. IPng is designed to be an evolutionary step from IPv4, the current version of IP being widely used.
In this subject we will not be examining IPv6 in any great detail but you should be aware of its existence. The following readings are included for interest.
Information on IPv6 :
? The Official IPng Page SLOW SITE : http://playground.sun.com/pub/ipng/html/ipng-main.html
? Another IPv6 Page : http://www.openvms.digital.com/openvms/announcements/ipc6-standards.html
? An Overview of IPng : http://playground.sun.com/pub/ipng/html/INET-IPng-Paper.html
= FIGURE 1 =
The four layers of TCP/IP
3.1 MOVING DOWN THE LAYERS
A) Moving Down The Layers
Each of the four layers of TCP/IP perform a different role. In order to perform this role each layer adds a small piece of control information, called a header, onto the front of each packet of information sent.
When a packet is sent it moves down the four layers. As it passes through each layer that layer appends its header information onto the front. The information is then sent. When it is received at the other end it moves up through the layers. As it moves up each layer strips off its header information and uses it to perform some task.
Figure 2 provides a representation of this.
= FIGURE 2 =
3.2 NETWORK ACCESS LAYER
A) Network access layer
The network access layer is the bottom layer of the TCP/IP protocol stack. This layer provides the ability to transmit an IP datagram from one host to another host on the same physical network. To do this the network access layer must be aware of the details of the network hardware on which it is running. This also means that for each different type of networking hardware there must be a different network access layer.
This is the layer that is responsible for translating an Internet address into a hardware address. The process will be discussed further in a later section.
3.3 THE INTERNET LAYER
A) Internet layer
The Internet layer consists of two protocols IP, the Internet protocol and ICMP, the Internet control message protocol. IP is central to the TCP/IP protocol suite. All information being sent via TCP/IP must use IP. IP performs the following tasks
? defines the size and the format of the datagram to be transmitted,
The size of the datagram depends on the type of network hardware being used. Different types of hardware can handle different size datagrams. IP will create datagrams using the MTU, maximum transmission unit for the hardware.
? defines the Internet addressing scheme,
The header for every IP datagram will contain two IP addresses. The source IP address and the destination.
? moves data between the network access layer and the transport layer
? routes datagrams for remote machine,
? fragments and re-assembles datagrams
ICMP performs a number of control, error reporting and information functions .
* example of network access layer packet being given to IP
3.4 TRANSPORT LAYER
A) Transport layer
The transport layer’s two major protocols are ;
? Transmission Control Protocol, TCP
A reliable connection oriented protocol.
? User Datagram Protocol, UDP
An unreliable connectionless protocol
Both UDP and TCP support the concept of ports. On any networked computer it is likely that there will be many different programs all using the network at the same time. This means the computer is receiving multiple datagrams for a number of different programs.
How does it know which datagram belongs to which program?
When a program wishes to send or receive information over a TCP/IP network it must connect to a port. Any information that is destined for the program must be labeled with its port number. If a program wishes to send any information it must know the port number of the receiver.
Ports are implemented by the transport protocol layer. The header for both TCP and UDP contain two 16 bit numbers that are used for the source port and the destination port. The transport layer will examine the port numbers and deliver the information to the correct program.
3.5 UDP and TCP
A) UDP and TCP
UPD delivers information with a minimum of protocol overhead and is generally used when the amount of data being transmitted is small. TCP uses considerably more overhead (a TCP header consists of 6 32-bit words while a UDP header has 2).
TCP’s extra overhead is used to ensure its reliability. Each packet of information that is sent using TCP contains a checksum. The receiver of the information will examine the checksum to determine whether or not the data has arrived unchanged. If the data is unchanged the receiver will then send an acknowledgment back to the sender (”it’s okay I received that information”). If the sender does not the acknowledgment back within a certain time the sender will resend the information.
The most common alternative is UDP (”user datagram protocol”) which is designed for applications where you don’t need to put sequences of datagrams together. It fits into the system much like TCP. There is a UDP header. The network software puts the UDP header on the front of your data, just as it would put a TCP header on the front of your data. Then UDP sends the data to IP, which adds the IP header, putting UDP’s protocol number in the protocol field instead of TCP’s protocol number. However UDP doesn’t do as much as TCP does. It doesn’t split data into multiple datagrams. It doesn’t keep track of what it has sent so it can resend if necessary. About all that UDP provides is port numbers, so that several programs can use UDP at once. UDP port numbers are used just like TCP port numbers. There are well-known port numbers for servers that use UDP. Note that the UDP header is shorter than a TCP header. It still has source and destination port numbers, and a checksum, but that’s about it. No sequence number, since it is not needed. UDP is used by the protocols that handle name lookups (see IEN 116, RFC 882, and RFC 883), and a number of similar protocols.
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