What Is A Network?

Some Coverage for exam objectives below:
Microsoft(70) 291: Server 2003 Network Infrastructure Obj. 1.2;  TCP/IP networks
Microsoft(70) 642: Server 2008 Network Infrastructure Obj. 1.1; IPv4 & IPv6 Networks
CompTIA: Network+ 2005 Edition: Objective 1.1; Network Topologies
CompTIA: Network+ 2005 Edition: Objective 2.1; MAC Address
CompTIA: Network+ 2005 Edition: Objective 2.2; OSI Model
CompTIA: Network+ 2005 Edition: Objective 2.3; OSI Network Components matchup
CompTIA: Network+ 2005 Edition: Objective 2.5; IPv4 & IPV6
CompTIA: Network+ 2005 Edition: Objective 2.7; Subnetting
CompTIA: Network+ 2005 Edition: Objective 2.10; TCP Protocols

With all that useful knowledge out of the way now, I think we're ready to continue. There is a lot of material covered here and without a doubt, this information can easily be summarized. This is my interpretation and philosophy on the topic. So if something isn't very clear, send a message to me and I'll help with it. webmaster@itjournal-stevekline.com

Network Standards - This is important because it is always good to know incase you need to provide documentation on source information or if you yourself are deciding to enter the manufacturing side of computer networking. IEEE or Institute of Electrical & Electronics Engineers have established committees dedicated to developing and defining standards for computer networking. These committees have published the standards to help companies to comply with the standard so the equipment works compatibly with existing or older equipment. Some of these standards are as follows on current IEEE Std 802-1990: IEEE Standards for Local and Metropolitan Networks documentation. You can find more for free and research at http://www.ieee802.org/dots.html

Standard	Explanation of Standard
802.1	Internetworking (routing; bridging; L3 switching)
802.2	Logical Link Control
802.3	Ethernet LAN (Carrier Sense Multiple Access w/ Collision Detection)
802.4	Token-BUS LAN
802.5	Token-RING LAN
802.6	Metropolitan Area Network (MAN)
802.7	Broadband Technical Advisory Group
802.8	Fiber-Optic Technical Advisory Group
802.9	Integrated Voice/Data Network
802.10	Network Security
802.11	Wireless Networks
802.12	Demand Priority Access LAN (100 VG-AnyLAN)

Topologies: A topology is simply nothing more than the physical layout of a network.

There are four major topologies to discuss that are in existence.

1. Bus - Becoming less common if not obsolete because these required BNC network type T connectors that went from PC to PC on a single coax cable. The T connector connected a single computer as an extra device on the coaxial cable that ran through it.

2. Ring - These are becoming less popular due to the inefficient simultaneous data transfers between devices.

3. Mesh - These networks are rare because of their cost factor, typically only used in a Wide-Area Network(WAN) incase a line fails. Other info is n=Nodes/Computers so a Full Mesh calculation is used with this formula. n(n - 1) / 2    - For Example, 48 Computers 48*47/2 comes to about 1128 connections. That's not very cheap... so therefore, not used in Local networks.

4. Star - These are the most common application of networking because they are very highly scalable. they provide no redundancy for a single point of connection failure, but with proper installation makes this a very reliable topology. This topology can be hybrid to mesh as a form of redundancy to network communication, typically a second network device is used on a pc

OSI Application Layer - TCP/IP Application Layer

In the Application layer of the OSI model you are faced with the API, GUI, and Kernel of the operating system you are working with. With that note, you face different architectures depending on the operating system you are using. This is networking, so I will not be covering any of that information here. The application layer is simply the data that the user is preparing to send over the network.
Some of the protocols typically used in this layer are HTTP, HTTPS, FTP, Telnet, POP3, DNS, SMTP, DHCP, and TFTP.

OSI Presentation Layer - TCP/IP Application Layer

The presentation layer simply crunches the application layer down to your data that can be transmitted and interpreted on the other end. The information here is also formatted in a data structure that is compatible across all systems. This is why it is important for network systems to be managed and standardized so that the data sent around the world isn't just garble to any systems involved.

Some formats supported are ASCII (American Standard Code for Information Interchange, "Az-key"), EBCDIC (Extended Binary Coded Decimal Interchange Code, "eb-see-dic"), Also general Audio/Video/Picture formats; TIFF, PICT, MIDI, MPEG, Basically anything in your GUI

OSI Session Layer - TCP/IP Application Layer

This layer is primarily responsible of establishing, managing, and terminating sessions between applications. This does not control how the electrical components work on the machine but they are generally programmed further down to interpret actions down the chains. Other layers still manage those processes. However the session layer also controls the dialogue between applications. The session layer also negotiates the transmission (Full or half duplex) and maintains the sessions transfer speeds by the acceptible mediums in between.

Some session layer examples are NFS, SQL, RPC, ASP, DNA SCP, X window system

OSI Transport Layer - TCP/IP Transport Layer

The transport layer manages your end point connections, also know as Virtual Circuits. If you have read into some CCNA material, a circuit is basically a single connection between two routers. Combining those circuits makes a single logical circuit. Since you have one network card, there's a lot of virtual circuits occuring at once. These are only used with TCP data traffic. There are two primary protocols used in the transport l

OSI Network Layer - TCP/IP Internet Layer

The network layer of the OSI Model is the communication of different networks. The most commonly used at this time and may continue for a long time is still Internet protocol version 4. However, the network layer is still in control of the logical addressing and routing between networks. Note the term "Route"

The typical hardware that is to be found on Layer 3(Network) is a Router and Switches with Layer 3 capabilities. Cisco manufactures Layer 3 switches.

OSI Data Link Layer - TCP/IP Link Layer

The data-link layer aka OSI Layer 2 or just Layer 2. This is primarily used for physical addressing of Network Interface Cards, media access, framing packets received from network layer protocols, error checking, and error correction. Typically switches and network devices operate in this particular layer of the OSI Model. There are 2 sub-layers noted as LLC and MAC.

LLC (Logical Link Control) and MAC (Media Access Control) have separate functions. The Logical link control sub-layer is responsible for creating frames out of packets from layer 3 and includes destination service access points and source service access points. This is how switches can determine their paths of forwarding frames through the ports on a switch.

The Media access control sub-layer is responsible for the physically burned in address provided by the manufacturer of the NIC. The physical ROM on the Network card has the physical address burned into it and these devices also control the way that data is processed through to the physical layer.

OSI Physical Layer - TCP/IP Link Layer

The physical layer of the OSI model speaks for itself as it controls the electrical signals used for the data transmission process. Typically binary, the 1's and 0's or On and Off signals transmit the data by the millions of bits per second.