As we have pointed out already there is a real need for a communication protocol to established. There is clearly a need for a standardised protocol in the global context on networking — otherwise the Internet could not exist in its current form.

Networking protocols need to be established for low level computer communication up to how application programs communicate. Each step in this protocol is called a layer.

The International Standards Organisation (ISO) defines a 7 layer model for network communication protocol. The model is more formally called the Open Systems Interconnection (OSI) model. This should exist in any network.

The advantage of breaking down the protocol into layers is twofold:

• Each layer can be regarded as a black box.
  • Well defined inputs and outputs exist, but
  • The Inner workings of the layer can be regarded as being independent
  • Thus, New versions, updates or better methods can be written without affecting the whole system.
  • Network is Future Proofed to a great extent.
  • Benefits passed on to whole network.
• Communication need only take place at the layer appropriate for the task.

The OSI model consists of 7 layers. The seven layers must be organised in the specified order:

Figure: The OSI 7 Layer Model

The function of each layer (from bottom to top) is:

Physical

– The interface between the medium and the device. The layer transmits bits (ones and zeros) and defines how the data is transmitted over the network, what control signals are used and the mechanical properties of the network (Cable size, connector for example.

Data Link

– Provides low-level error detection and correction. For example if a packet is corrupted this layer is responsible for retransmitting the packet.

Network

– Responsible for routing packets of data across the network. For example, a large email file will be divided up into packets, each packet addressed and sent out at this layer.

Transport

– An intermediate layer that higher layers use to communicate to the network layer. This layer hides the complexities of low-level networking communication from the higher levels.

Session

– The User’s (transparent) interface into the network. The layer manages the “current” connection (or session) to the network. Note: In packet-switched network a full-time network connection does exist, even though it may seem so. The Session layer keeps the communication flowing.

Presentation

– Ensures computers speak the same language. They convert text to ASCII or EBCDIC form and also encode or decode binary data for transport.

Application

– The programs you use directly may need to communicate. E.g a file transfer or email program.

Some Example Internet Protocols

• Token ring — low level network message passing.
• Telnet
• File Transfer Protocol (FTP)
• Archie — FTP search
• Simple Mail Transfer Protocol (SMTP), Post-Office Protocol version 3 (POP3), IMAP — email protocols
• Gopher – menu-based information, veronica
• WAIS – wide-area info server
• HTTP — Hypertext Transfer Protocol basis of World Wide Web

A File Server is a computer attached to a network that has the primary purpose of providing a location for the shared storage of information (such as documents, sound files, photographs, movies, images, databases, et cetera) that can be accessed by the workstations that are attached to the network. As distinguished from Timesharing or a Mainframe (where a central computer provides calculation resources for “dumb” terminals) a File Server is designed primarily to enable the rapid storage and retrieval of data where the heavy computation is provided by the workstations.

History of File Servers

In the mid-1980′s firms became increasingly interested in ways to connect a rapidly growing population of personal computers. Novell proposed an approach using software to connect each workstation to a network file server that would manage both the network and access to network resources. At the same time 3Com Corporation was creating Ethernet adapter cards building connectivity by way of a hardware approach.Novell grew upon the strength of it’s Netware and by the late 1980′s had a 50% market share of Local Area Networks. Seeing the potential growth in this arena IBM and Microsoft Corp. both introduced their own file-server strategies.Twenty years after its peak, Novell and 3Com have virtually disappeared from the Server market; today disk servers (a NAS or a SAN) supplied by one of the leading vendors such as EMC or Network Appliance are typically attached to a file server running the Microsoft Windows or Linux operating systems.Large datacenters that serve millions of customers (such as Google) run server “farms” on specialized equipment with proprietary operating systems.

Types of File Servers

A file server may be dedicated or non-dedicated. A dedicated server is generally designed specifically for use as a file server, with workstations attached for reading and writing files and databases. A workstation may share files with other workstations on the network directly however by turning on its “Server” service and then by creating a “Share” — this process creates a non-dedicated file server that is primarily being used as a workstation.File servers may also be categorized by the method of access: remote servers are frequently accessed by FTP (they run an FTP Server) or by HTTP (they run a Web Server). Servers on a LAN are usually accessed by SMB/CIFS protocol [1] (Windows, Linux, Unix and OS X) or NFS protocol [2] (Linux, Unix and OS X) protocols. Servers providing access to a shared database usually are accessed by a database device driver (they run a Database Server). Most servers provide access to printers that are attached across the network (they run a Print Spool). A single File Serving computer may be accessible by multiple means: it may run an FTP server, an HTTP server, a database server, and a print spool.

Construction of File Servers

In modern businesses the design of file servers is complicated by competing demands for storage space, access speed, recoverability, ease of administration, compatibility, security, and budget. This is further complicated by a constantly changing design environment where new hardware and technology rapidly obsoletes old equipment and yet must come online in a fashion compatible with the older machinery. To manage throughput, peak loads, and response time, server manufacturers may utilize queuing theory to model how the combination of hardware and software will respond over various levels of demand. Servers may also employ dynamic Load Balancing to distribute requests across various pieces of hardware.The primary piece of hardware equipment for servers over the last couple of decades has proven to be the disk drive. Although other forms of storage are viable (such as magnetic tape and RAM) disk drives have continued to offer the best fit for cost, performance, and capacity.

Storage

Since the crucial function of a file server is storage, hardware has been developed to operate multiple disk drives together as a team, forming a disk array. A disk array typically has cache (temporary memory storage that is faster than the magnetic disks) as well as the intelligence so that it can perform functions like RAID and virtualization. Typically disk arrays provide some level of redundancy by using mirrors and other redundant components. Disk arrays may be configured as a NAS, a SAN, or virtualized.

Security

File servers generally offer some form of system security to limit access to files to specific users or groups. In large organizations, this is a task usually delegated to what is known as directory services such as openLDAP, Novell’s eDirectory or Microsoft’s Active Directory.These servers work within the hierarchical computing environment which treat users, directories, computers, applications and files as distinct but related entities on the network and grant access based on user or group credentials. In many cases, the directory service spans many file servers, potentially hundreds for large organizations. In the past, and in smaller organizations, authentication can take place directly to the server itself. 

A File Server is a computer attached to a network that has the primary purpose of providing a location for the shared storage of information (such as documents, sound files, photographs, movies, images, databases, et cetera) that can be accessed by the workstations that are attached to the network. As distinguished from Timesharing or a Mainframe (where a central computer provides calculation resources for “dumb” terminals) a File Server is designed primarily to enable the rapid storage and retrieval of data where the heavy computation is provided by the workstations.

History of File Servers

In the mid-1980′s firms became increasingly interested in ways to connect a rapidly growing population of personal computers. Novell proposed an approach using software to connect each workstation to a network file server that would manage both the network and access to network resources. At the same time 3Com Corporation was creating Ethernet adapter cards building connectivity by way of a hardware approach.Novell grew upon the strength of it’s Netware and by the late 1980′s had a 50% market share of Local Area Networks. Seeing the potential growth in this arena IBM and Microsoft Corp. both introduced their own file-server strategies.Twenty years after its peak, Novell and 3Com have virtually disappeared from the Server market; today disk servers (a NAS or a SAN) supplied by one of the leading vendors such as EMC or Network Appliance are typically attached to a file server running the Microsoft Windows or Linux operating systems.Large datacenters that serve millions of customers (such as Google) run server “farms” on specialized equipment with proprietary operating systems.

Types of File Servers

A file server may be dedicated or non-dedicated. A dedicated server is generally designed specifically for use as a file server, with workstations attached for reading and writing files and databases. A workstation may share files with other workstations on the network directly however by turning on its “Server” service and then by creating a “Share” — this process creates a non-dedicated file server that is primarily being used as a workstation.File servers may also be categorized by the method of access: remote servers are frequently accessed by FTP (they run an FTP Server) or by HTTP (they run a Web Server). Servers on a LAN are usually accessed by SMB/CIFS protocol [1] (Windows, Linux, Unix and OS X) or NFS protocol [2] (Linux, Unix and OS X) protocols. Servers providing access to a shared database usually are accessed by a database device driver (they run a Database Server). Most servers provide access to printers that are attached across the network (they run a Print Spool). A single File Serving computer may be accessible by multiple means: it may run an FTP server, an HTTP server, a database server, and a print spool.

Construction of File Servers

In modern businesses the design of file servers is complicated by competing demands for storage space, access speed, recoverability, ease of administration, compatibility, security, and budget. This is further complicated by a constantly changing design environment where new hardware and technology rapidly obsoletes old equipment and yet must come online in a fashion compatible with the older machinery. To manage throughput, peak loads, and response time, server manufacturers may utilize queuing theory to model how the combination of hardware and software will respond over various levels of demand. Servers may also employ dynamic Load Balancing to distribute requests across various pieces of hardware.The primary piece of hardware equipment for servers over the last couple of decades has proven to be the disk drive. Although other forms of storage are viable (such as magnetic tape and RAM) disk drives have continued to offer the best fit for cost, performance, and capacity.

Storage

Since the crucial function of a file server is storage, hardware has been developed to operate multiple disk drives together as a team, forming a disk array. A disk array typically has cache (temporary memory storage that is faster than the magnetic disks) as well as the intelligence so that it can perform functions like RAID and virtualization. Typically disk arrays provide some level of redundancy by using mirrors and other redundant components. Disk arrays may be configured as a NAS, a SAN, or virtualized.

Security

File servers generally offer some form of system security to limit access to files to specific users or groups. In large organizations, this is a task usually delegated to what is known as directory services such as openLDAP, Novell’s eDirectory or Microsoft’s Active Directory.These servers work within the hierarchical computing environment which treat users, directories, computers, applications and files as distinct but related entities on the network and grant access based on user or group credentials. In many cases, the directory service spans many file servers, potentially hundreds for large organizations. In the past, and in smaller organizations, authentication can take place directly to the server itself. 

The information listed here is to assist Network Administrators in the color coding of Ethernet cables. Please be aware that modifying Ethernet cables improperly may cause loss of network connectivity. Use this information at your own risk, and insure all connectors and cables are modified in accordance with standards. The Internet Centre and its affiliates cannot be held liable for the use of this information in whole or in part.

T-568A Straight-Through Ethernet Cable

The TIA/EIA 568-A standard which was ratified in 1995, was replaced by the TIA/EIA 568-B standard in 2002 and has been updated since. Both standards define the T-568A and T-568B pin-outs for using Unshielded Twisted Pair cable and RJ-45 connectors for Ethernet connectivity. The standards and pin-out specification appear to be related and interchangeable, but are not the same and should not be used interchangeably.

T-568B Straight-Through Ethernet Cable

Both the T-568A and the T-568B standard Straight-Through cables are used most often as patch cords for your Ethernet connections. If you require a cable to connect two Ethernet devices directly together without a hub or when you connect two hubs together, you will need to use a Crossover cable instead.

RJ-45 Crossover Ethernet Cable

A good way of remembering how to wire a Crossover Ethernet cable is to wire one end using the T-568A standard and the other end using the T-568B standard. Another way of remembering the color coding is to simply switch the Green set of wires in place with the Orange set of wires. Specifically, switch the solid Green (G) with the solid Orange, and switch the green/white with the orange/white.

Ethernet Cable Instructions:

1. Pull the cable off the reel to the desired length and cut. If you are pulling cables through holes, its easier to attach the RJ-45 plugs after the cable is pulled. The total length of wire segments between a PC and a hub or between two PC’s cannot exceed 100 Meters (328 feet) for 100BASE-TX and 300 Meters for 10BASE-T.
2. Start on one end and strip the cable jacket off (about 1″) using a stripper or a knife. Be extra careful not to nick the wires, otherwise you will need to start over.
3. Spread, untwist the pairs, and arrange the wires in the order of the desired cable end. Flatten the end between your thumb and forefinger. Trim the ends of the wires so they are even with one another, leaving only 1/2″ in wire length. If it is longer than 1/2″ it will be out-of-spec and susceptible to crosstalk. Flatten and insure there are no spaces between wires.
4. Hold the RJ-45 plug with the clip facing down or away from you. Push the wires firmly into the plug. Inspect each wire is flat even at the front of the plug. Check the order of the wires. Double check again. Check that the jacket is fitted right against the stop of the plug. Carefully hold the wire and firmly crimp the RJ-45 with the crimper.
5. Check the color orientation, check that the crimped connection is not about to come apart, and check to see if the wires are flat against the front of the plug. If even one of these are incorrect, you will have to start over. Test the Ethernet cable.

Ethernet Cable Tips:

• A straight-thru cable has identical ends.
• A crossover cable has different ends.
• A straight-thru is used as a patch cord in Ethernet connections.
• A crossover is used to connect two Ethernet devices without a hub or for connecting two hubs.
• A crossover has one end with the Orange set of wires switched with the Green set.
• Odd numbered pins are always striped, even numbered pins are always solid colored.
• Looking at the RJ-45 with the clip facing away from you, Brown is always on the right, and pin 1 is on the left.
• No more than 1/2″ of the Ethernet cable should be untwisted otherwise it will be susceptible to crosstalk.
• Do not deform, do not bend, do not stretch, do not staple, do not run parallel with power cables, and do not run Ethernet cables near noise inducing components.

Basic Theory:

By looking at a T-568A UTP Ethernet straight-thru cable and an Ethernet crossover cable with a T-568B end, we see that the TX (transmitter) pins are connected to the corresponding RX (receiver) pins, plus to plus and minus to minus. You can also see that both the blue and brown wire pairs on pins 4, 5, 7, and 8 are not used in either standard. What you may not realize is that, these same pins 4, 5, 7, and 8 are not used or required in 100BASE-TX as well. So why bother using these wires, well for one thing its simply easier to make a connection with all the wires grouped together. Otherwise you’ll be spending time trying to fit those tiny little wires into each of the corresponding holes in the RJ-45 connector.