Computer Networking

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From OST

1 Computer Networking
2 Seven Layers of Networking (OSI Model)
3 Ethernet
4 Hubs and Switches
- 4.1 HUBS
- 4.2 SWITCHES
5 Routers
6 Virtual LANS
7 References

Computer Networking

Computer Networking is the process of linking many computer users together to communicate. Computer Networks can be classified in five different categories depending on the size of the network. The categories are (beginning with smallest to largest): Personal area network (PAN), Local Area Network (LAN), Campus Area Network (CAN), Metropolitan area network (MAN), or Wide area network (WAN).

Seven Layers of Networking (OSI Model)

The seven layers of networking is sometimes referred to the OSI Model, Open System Interconnection. Networking is broken down by traveling through several layers or protocols. This process is broken down into seven layers; Application Layer, Presentation Layer, Session Layer, Transport Layer, Network Layer, Data Link Layer, and Physical Layer. When a person communicates to another person on a network the information passes through these layers. It begins at the Application Layer, works its way through to the Physical Layer and then back up to the Application Layer.

(7) Application Layer- This layer is where the end-user (computer user) begins the communication process. At this layer user authentication is identified and protocols like FTP, TELNET, E-MAIL, and other file transfer protocols begin with the user starting the process.

(6) Presentation Layer - This layer is where encryption occurs. This layer converts the file and/or information into a language (format) that the remaining layers can read and handle without any compatibility problems.

(5) Session Layer - This layer is where the communication is coordinated. Applications are managed in this layer. This layer manages the exchange of information by creating and terminating all communication between the application layer at both ends.

(4) Transport Layer - This layer is responsible for ensuring the data completes it's transmission to the other user. It's also responsible for flow control and error recovery.

(3) Network Layer - This layer is where the routing and switching takes place. Packet sequencing, addressing, congestion control, and internetworking happen at this layer. Logical paths are created at this level to allow users to communicate to each other. This layer utilizes IP addresses.

(2) Data Link Layer - This layer is where packets (information) is broken into bits through encoding and decoding. At this layer you have two sections; Media Access Control (MAC), and Logical Link Control (LLC). The MAC section is where packets (information) is gathered and gets permission to transmit the data. The MAC section is where your computer's MAC address is located to allow proper delivery to a specific system (computer). The LLC section controls synchronization, flow control, and error checking.

(1) Physical Layer - This layer is where your hardware such as ethernet cable, Network Interface Cards, etc., provide the transmission through electrical impulse, light, and radio waves. This layer is the hardware means of sending and receiving data (information).

Some ways to remember the seven layers are:

All People Seem To Need Data Processing

Ethernet

Ethernet is part of the Physical Layer (Layer 1) on the OSI model. It uses frames to transport information within a Local Area Network. Ethernet began around 1980 and is referred to as IEEE 802.3 [1]. The first form of ethernet was in the form of a coaxial cable called 10base5 or "thicknet". 10base5 could transport frames for a length of 500 meters and a rate of 10 megabits per second [2]. The next standard to evolve was called "thinNet, cheapNet" or 10base2. 10base2 could transports frames for a length of 185 meters and at a rate of 10 megabits per second [3]. 10base5 and 10base2 used terminators called N connectors for 10base5 and BNC connectors for 10base2. If these terminators were not in place the frames would not be broadcasted. Ethernet has now evolved into fast ethernet branching into gigabit to 10gigabit ethernet. Fast ethernet transports frames at 100 megabits per second utilizing twisted pair cable, gigabit (one gigabit per second) utilizing fiber (cat5 copper cabling) to 10gigabit (10 gigabits per second) utilizing copper twisted pair [4]. The basis of fast ethernet began with 10baseT which is four wires, two twisted pairs, in a cat-3 or cat-5 cable. 10baseT has a RJ-45 connector that plugs into ports on a Hub/Switch (Data Link Layer-Layer 2) and/or Router (Network Layer-Layer 3).

Hubs and Switches

Hubs and Switches are part of the Data Link Layer (Layer 2) of the OSI model. In a sense, hubs and switches are like train stations in a network. They allow for information to be guided to a specification destination. Information is sent in the form of a frame (a segment of information) at this level. The source and destination for the frames are done by locating MAC addresses for devices. A MAC address is a Media Access Control address. In other words, it is series of numbers and letters used as a identifier on a device. Devices being computers, servers, printers, etc. The MAC address is usually broadcasted in a frame by network adapters and/or Network Interface Cards. Hubs were initially used first in ethernet networking. Eventually Switches, became more efficient in ethernet networking.

HUBS

Hubs are devices that connect other devices on a network by broadcasting frames to these devices. Hubs utilize MAC addresses for directing the frames to devices connected on an ethernet network. Hubs contain more than two ports (plug-ins for the ethernet cable) and broadcast frames through all it's ports. They do not make any decisions, they just pass information along through all its ports. As a result, frames can collide amongst each other. For example, if a person prints a huge file, that file is broadcasted to all devices connected to that hub causing a lot of frames traveling back and forth amongst each other. In a big network a lot of collisions will occur causing a network to be slow and sluggish. Collisions are confined to collision domains, which are limited to all the devices that are connected to the same hub and devices. A major problem with using a hubs on a network is the risk of experiencing a broadcast storm. A broadcast storm happens when information is repeated amongst hubs causing an infinite loop. Some indicators of knowing you are experiencing a broadcast storm is by noticing the lights on your hub are all lit and do not blink. Also, you are unable to send any frames.

SWITCHES

Switches are very similar to hubs with the fact that they forward frames. The difference between switches is that they forward frames to specific ports. They do not forward or broadcast frames to all ports. Switches utilize a built in operating system to construct a MAC address table to record which device is dedicated to which port on the switch. Now, there are three types of switches. An Ethernet Switch which is a layer 2 switch that uses MAC addresses to forward frames to specific devices. A Layer 3 Switch that uses MAC addresses to forward frames to specific devices with routing capabilities. Basically, a layer 3 switch has a built-in router in the switch. Routers are a layer 3 device on the OSI model. A Multilayer Switch is a switch with a built in router but has increased capabilities which allow it to control TCP and UDP. TCP is Transmission Control Protocol which is used in file transferring and e-mail in a connection oriented protocol [5]. UDP is User Datagram Protocol which is like TCP but utilizes a connectionless protocol; meaning, "there is no effort made to setup a dedicated end-to-end connection" [6]. TCP and UDP are in the Transport Layer (Layer 4) in the OSI Model. When a frame is sent through a network containing switches, the switches utilized the MAC address table to construct direct paths to devices by finding matches between MAC addresses, devices, and ports. This causes a faster network with less collisions. Now, if there is no match then the frames are sent to all the ports on the switch.

Routers

As stated above routers work on layer three of the OSI model. They work on this level because of the fact that they route IP addresses, and not MAC addresses like a switch does. Routers are used mainly for routing traffic to the "outside" world. Outside referring to outside of your network. We use routers to connect a network to another network. The main network routers connect to is the Internet. As stated Routers work with IP addresses and routing tables.

Routing tables basically tell what each address of the nodes on the network have as well what interface the network uses. This in turn helps the router to route traffic. When a nodes sends a request for information from another node the request goes to the router. The router then looks at the routing table to determine where the request needs to go and sends it to the node which has it. If the information is located on another network it sends the request to the appropriate router which in turn sends the request to the appropriate node on its network.

Routers come in different variations and preferences depending on what you need it to do. They could also be routers with switches built in, they could be wireless routers, which have different variations as well. You can also get wireless routers which serve as a wireless access point (WAP). Before purchasing a router it is wise to research what exactly the router is going to be used for. You do not want to get a router that does everything except what the specific need is. For instance if you need a router which serves as a WAP with an 8-port switch, you do not want to get a router which has no wireless abilities with only 4-ports and no switch capabilities.

Routing can be done in two different ways, classful and classless. Classful routing is done with the whole IP address and netmask in place, ie. 10.1.1.24 255.255.0.0, which in turn depends on what class the IP address belongs too. Class being class A, class B, or class C addressing schemes. Classless routing is done with the IP address and bits used for the network address part of the IP address, ie. 10.1/16.

This is a basic image of a network routing scheme.

Virtual LANS

Virtual LANS are VLANS (virtual local area networks). VLANS are virtual separations on a switch that produce more than one local area network. For Example, on a switch you can have more than one local area network through the use of VLANS. VLANS allow a single switch to act as multiple LANS. Without VLANS a switch can only support one LAN.

VLAN's can be named or numbered. The default VLAN is VLAN 1. If you do not specify a VLAN when connecting a device (eg. computer), that device will be connected to the default VLAN; VLAN 1. In order for VLAN's on a single switch to communicate to each other you need a link to a router to route the communication to the VLAN's on the switch. For instance, if you have a switch with four VLAN's you need four links, one for each VLAN. If you have two switches with four VLAN's you need links for all the VLAN's on both switches to a router. There's a process to connect VLANS, this process is called TRUNKING.

TRUNKS are links for more than one VLAN. The links for the TRUNKS have to be on a port on the switch that do not belong to a VLAN. You can connect all VLAN's on a single switch to a router through the use of a trunk. The problem with this is, you have a bandwidth issue, causing a slower speed of network traffic. The best solution for this today is utilizing a layer 3 switch. A layer 3 switch is a switch that has routing capabilities. It has a built-in router. This allows for every VLAN to have its own link without any external links.