A Fundamental Look at Networking Services
Most of us take it for granted that we can connect to the Internet and find resources across a wide array of networks. In this article we are going to introduce the basic networking services that make it all possible.
Network Layer Protocols - IP
There are many protocols in the TCP/IP (Transmission Control Protocol and the Internet Protocol) suite. The two most noteworthy are IP and TCP.
Let’s begin by discussing IP as it is the key addressing and routing protocol that allows packets to find their way through the Internet.
IP is a connectionless protocol. It is a simple design for a packet or datagram structure that is very efficient and easy for routers to process. Most of the traffic that moves through the Internet are IP datagrams.
Every node that connects directly to the Internet needs a unique IP address. However, these addresses are limited. Nodes that maintain a constant Internet presence, or web site, have to have a static IP address that is allocated indirectly from the Internet governing bodies through authorized registrars who keep track of IP addresses and domain names. When a home or business user logs onto the Internet, the ISP that they pay for access to the Internet will provide a leased or dynamic IP address that is allocated from the bank of addresses that the ISP themselves lease from the Internet registrars.
The commonly used Internet Protocol address is IP version 4, or IPv4. It is a 32 bit dotted decimal address. For many years now it has been accepted that the limited number of potential IPv4 addresses would be used up, and the number of users that could access the Internet would be finite, or limited.
IP addressing also allows for subnetting, which is an excellent way to limit network connections and control the assignment of IP addresses. Subnetting is the process of logically breaking a larger network into smaller networks. IP addresses are always used in combination with a subnet mask, which is a numeric value that can identifies which part of the IP address represents the network and which part of the IP address represents the actual node. Connection problems in an IP addressed network can often be traced to an improper subnet mask value.
To address the problem of a limited number of IPv4 addresses, the next generation of IP addresses, IPv6, was established. The backbone routers and switches that manage Internet traffic are prepared to read IPv6 addresses. However, the ISPs themselves have hesitated to update their allocation practices, and we are still currently using IPv4 addresses.
Another significant development, NAT, or network address translation, has made the deployment of IPv4 addresses more efficient, and reduced the threat of running out of IPv4 addresses. NAT is the process of modifying IP address information in IP packet headers while in transit across a traffic routing device.
Transport Layer Protocols – TCP , UDP
TCP, or Transport Layer Protocols, employs several critical features as it manages packet transmissions. First, it helps control session layer communications by setting up a two way communication between the sending and receiving nodes. It ensures that a connection will be maintained until the higher layer session or application protocols decide to end the connection.
Next it can setup acknowledgements and sliding window protocols which will allow for flow control and optimizing the data exchange between the nodes. It also establishes sequencing values so that packets can be routed throughout the network or Internet and still be reassembled in order at the receiving node. There are many other advantages that the TCP protocol provides, and you will want to review the textbook TCP descriptions carefully.
TCP also provides socket communications, and TCP can manage multiple connections by maintaining not only a node address, but also a TCP port designation for each connection.
Ports are logical values assigned to processes. When you combine a protocol and a port, for example 172.16.0.1:80, you create a socket with the node addressed 172.16.0.1 that designates port 80, which designates a specific process or protocol type for the specific connection. In this example, the packet would be sent to TCP port 80 ( port 80 is reserved for the HTTP protocol which allows for Internet web browsing ) on node 172.16.0.1
In a protocol stack, middle and lower layer protocols need to work ‘transparently’ or independently of the applications or services that work at higher layers. It is critical that TCP sessions can perform accurately regardless of the application or service that they are supporting.
You should know that protocols that operate at the transport layer and above are connection oriented protocols, used by connection oriented services. However the one exception is UDP (User Datagram Protocol), which is connectionless and used for large multimedia streaming services. These high end packet delivery services cannot afford the overhead to error control and process retransmissions, so lost or damaged packets are merely forgotten.
Application Layer Protocols – DHCP
It’s important to understand where protocols work in the TCP/IP stack. Dynamic Host Configuration Protocol, DHCP, and File Transfer Protocol, FTP, are higher layer protocols that work in the Application layer of the OSI model or the TCP/IP stack. They not only engage a connection or session between two nodes, but they also provide an actual application service.
Email protocols like POP3 or SMTP also work at the application layer. One thing to remember about application layer protocols is that they are dependent on lower layer protocols, specifically session and transport layer services, to establish and maintain connections. However, they need to work independently of the lower layer protocols, and just trust the network services to perform their connection oriented transport services properly.
The next trends in network computing, including the Internet, are web based applications and services. Users are now able to logon to remote network servers through the Internet, and receive access to web based applications and services just as if they were working in a LAN. These computing services are completely dependent on TCP transport services for managing the underlying connections and sessions
Understanding how computers connect is a fundamental skill that helps all of us when we are connecting to the Internet or setting up a simple home network. The protocols and services that are used for both home networks and Internet services all come from the TCP/IP protocol suite. When troubleshooting you can refer back to the terms in this article to help you define and explain the connections that your computers are using.
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