Network

Yes. I know. I hear you. I understand. I comprehend. I got ya. Roger that. Word.
You are sick of, and do not want to hear about the F#$@%$^ Open Systems Interconnect Reference Model. And so am I. Unfortunately for both of us, The Network+ test loooves the 0SI model, so you must Memorize it. Commit to it. Live it. Just Do It. Have it Tattooed on the Back of your Skull. Here, in all of it's (sic) glory, is a study jam for the OSI Model.

Other N+ stuff is also in this study jam- so if you just can't take it anymore, scroll past all this OSI stuff and read on-----

Intro

the one millionth picture you have seen of the OSI model The OSI model layers are stacked on top of each other like a Dagwood sandwich. The operating system sits on top of the Application layer. The actual network cable is below the Physical layer. Data passes through each layer in the stack, on the way up and/or on the way down. The diagram at left shows the OSI model and the often-repeated mnemonic to remember the proper order.

7. The Application Layer

The application layer is all about messaging, network access, file transfers and other application services. When you see Application layer, think supporting user applications, databases and e-mail. "Devices" at this layer include application interfaces and gateways. Protocols at this layer include X.400, HTTP, FTP, SMTP, DHCP, NFS, NIS & NIS +, DNS, NDS, SMB & X-Windows.

6. The Presentation Layer

The Presentation layer deals with presenting data to the layers immediately above and below itself. It translates data between the computer and the network format. Services include character set conversion, protocol conversion and data compression. The redirector operates at this level. "Devices" at this level include application interfaces and gateways. Protocols and standards include ASCII, EBCDIC and SNA

5. The Session Layer

The Session layer allows the establishment of a session. A session establishes the connection between communicating devices. This provides synchronization, security authentication, and network naming. Again,. devices at this level include application interfaces and gateways. Protocols that function at this layer include RPC, XNS and LDAP.

4. The Transport Layer

The transport layer is all about connectivity. It is responsible for packet handling. Repeat after me : "Ensures packets are delivered error free, in sequence, without losses." This layer deals with fragmentation and reassembly. Remember that the protocols at this layer are almost all connection-oriented . Error and flow control are dealt with at this layer (ACK). The devices most commonly accused of being at this level are gateways. Protocols calling this level home are TCP, UDP, NFS, SNMP, SMTP, NetBEUI, SPX & TFTP.

3. The Network Layer

The network layer is responsible for addressing, makes routing decisions, forwards datagrams further away then a single link, manging network net traffic problems, (QoS) Quality of Service and (TOS) Type of Service (that unused flag in the packet header is going to come into play as soon as Corporate America figures out how to charge extra money for it. Someone will hack their Unix TCP/IP stack to increase packet service type within 2-12 hours immediately afterwards.) Devices at this layer include Routers, Brouters, and gateways. Protocols include IP, IPX, ICMP, ARP, RARP, NetBEUI, and DLC. Routing Protocols -finally something interesting- at this level include RIP, OSPF, EGP, IGMP, BGP, IGRP, & EIGRP.

2. The Data Link Layer

The International Standards Layer felt that the Data Link Layer was not as mind numbingly interesting as some of the other layers, so they decided to break it down into two sublayers. They called these layers the Logical Link Control (LLC) and the Media Access Control (MAC) .The Logical Link Control sublayer is in charge of establishing and maintaining links between communicating devices. The MAC sublayer is responsible for framing data. Ethernet and Token Ring protocols operate in the Data Link layer, as do CSMA/CD, FDDI, SLIP, PPP,ATM, and their ilk. Devices at this layer include switches, bridges and intelligent hubs.

1. The Physical Layer

The Physical layer transmits data over a physical medium. Cable specifications, pinouts, and transmission techniques are defined at this level. The physical level is mostly concerned about putting data on the pipe. Devices at this level include hubs. switches, repeaters, cables, connectors, receivers, multiplexers, and other hardware. Most network problems- or at least the ones i run into have to do with this layer, so start your troubleshooting here. Make sure one of your (L)users (big shout out to Vic Vega) is not picking his/her nose with the UTP cable and wondering why they cannot log in.

Wrapup

Well, now that wasn't so bad, now was it? Hello? Wake up, it's over. Now either read on, or go take that Network + exam , and be done with this OSI propaganda. Oh yeah, if you haven't already taken your Net Ess and TCP/IP exam, well, I have some bad news for you....

Other Network+ Exam Stuff

UART Who You UART

UART-Universal Asyncronous Reciever/Transmitter -A chip used to manage serial port communications. 85xx chips max out at 9600 Bps. 164xx and 165xx UARTs max out at 115,200 bps. Nuff said.

The Network+ Troubleshooting Model

Identify the exact issues
Re-create the problem
Isolate the cause
Formulate the correction
Implement the correction
Test
Document the problem and solution
Give Feedback

802s Blues

802.1

Internetworking

The F$^&%$#@# OSI Reference Model And other Network + Stuff

Other Network+ Exam Stuff

The F$^&%$#@# OSI Reference Model
And other Network + Stuff