|
| |
Networking Terms
ADSL: (Asymmetrical Digital Subscriber Line)
Standard in high bandwidth transmission media. DTR of 604kpbs upstream and 2,048Mpbs downstream. Trials are now being launched in the UK with ADSL by BT among other companies.
BASE 2/5/10-1000
Ethernet networking that can transmit over many cable mediums such twisted pair, co-axial cable, fibre etc. depending on the actual standard.
Bridge:
A piece of hardware that is used to connect two internal networks, LAN's, to each other which work on the same standard e.g. Ethernet>Ethernet etc.
BT: (British Telecom)
Inventors of the ISDN line and the closest thing to a commercial monopoly the UK has ever seen. Regulated by an independent watchdog called OFTEL who monitor and ensure they conform to various standards and anti-monopoly laws.
Bus:
A network backbone is present with all nodes on the network sharing a common pathway to the server to which it interacts.
CCITT (Consultative Committee for International Telegraph and Telephony)
Committee that administers and introduced standards we know today such as V.21, V.22 and X.25 digital data transmissions.
Client/Server:
The server lives to "serve" other nodes on the network e.g. the workstations that rely on the server to perform tasks, deliver software, process user accounts etc.
A typical client/server model. Many people think that servers are hardware, they are not. A server is a piece of software that configures the hardware to server clients over a distributed or contained network.
The types of protocols used are usually request/reply protocols which simplify the processes in a "connectionless" manner.In a network where nodes are connected and configured identically, this client/server model serves a network in a more efficient manner as only three layers of OSI need to be applied to implement and administer the network.
The physical and data link layers are used in order to send the data to the server and thus back to the requesting client. This is still "connectionless" as this process is handled by the hardware e.g. the Ethernet card.Layer 5, the request/reply protocol, is used to define which requests and replies are legal and no layers above this are used.
DCE (Data Communications Equipment)
Hardware devices that establish connections such as modem etc. form the group called DCE.
DTE (Data Terminal Equipment)
Devices that act as a data source.
Ethernet Address:
48-bit number, as oppose to the 32-bit IP address, which is used to identify each Ethernet network adaptor.
Ethernet:
LAN developed by Xerox® and Intel®. LAN type that connects
upto 1024 devices at a minimum of 10Mbps over fibre, twisted pair and co-axial cable.
Firewall:
Any piece of hardware, hardware firewalls are the original
and best, or software that can act as the first line (not always the first) and block certain traffic from entering or leaving the network.
They usually work on a rule base which is configured to the client's needs. Cisco has become the market leaders with their PIX, among others, series firewalls. They also have the ability to block ports etc.
FRAD: (Frame Relay Assember/Disassembler)
Packet switching network that assembles/disassembles packets leaving the network into the format required for frame relay.
Frame Relay:
Long distance, high bandwidth transmission which is similar to X.25 but differentiates as it has error checking on both ends of the line.
FTP:
FTP is the File Transfer Protocol working on port 21 usually. A client would make a request to the server to obtain or send files to the server using the GET or SEND commands. The server would usually require some kind of authentication based around a pre-setup user account or a guest account with the login
simply being "guest" and the password being the users email address.
A full list of commands can be gained by logging into a FTP server:
FTP ftp.server.com:21 and typing help after login.
Full Duplex:
The process of being able to send data two ways at the same time e.g. simultaneous 2-way data transfer e.g. the phone line.
GGP:
Gateway to Gateway Protocol. Similar to routing information protocol in that it is a vector-distance based protocol. Used in Core Gateways for interaction.
Half-Duplex:
Two way data communications technique that cannot handle simultaneous data transfer e.g. standard CB radio etc.
HTTP: (Hypertext Transfer Protocol)
The process involved with a workstation receiving data from a web server using a browser on port 80. Apache, Zeus and IIS are all examples of web server software that conform to this
protocol.
Hub:
Network hardware that allows different nodes to be connected at one common point in order for information to be relayed through different clients.
IPX®: (Internet Packet Exchange)
Novell® Netware®'s own networking standard that is used for LAN's and is almost very reliable. Although not based on TCP/IP, it is still very good and used a lot today.
ISDN: (Integrated Digital Service Network)
Developed by BT (British Telecom) in the UK, this was one of the first standards available which would prove commercial enough to the home user and good enough for businesses for video conferencing. It boasted, and still does... heh, 128Kpbs DTR upstream (via 2 64K lines using and paying for 2 phone calls in the UK... :o( ) and 64K DTR upstream.ISDN terminal adaptor cards must be used in conjunction with the digital phone lines.
LAN:
Local Area Network. A network that is comprised within the physical boundaries of a building or one area. Usually based around 10/100 Base-T architecture, LAN's conform to high bandwidth transmission rules and are now common place within all major organisations.
Mesh:
Each network node is interconnected. This is a very messy
topology which proves hard to maintain and administer for
network management staff.
MODEM: (MOdulator DEModulator)
Analogue device that connects to the standard analogue phone line to convert anaglogue>digitial and vice versa between the two connecting nodes in a PPP (Point to Point) protocol session.
NetBIOS:
Internal networking standard. This is not a protocol in itself but runs over the existing NetBEUI protocol on port 139. This
has been the subject of OOB (Out of Band) data attacks by new users to the internet. WinNuke '95 was a popular program that exploited this hole.The main hole was present in Windows '95 OSR 1, was closed down I believe in OSR 2 and was totally patched in Windows '98.
I am unsure of the exact facts but I believe those to be correct.NetBIOS is an internal networking standard meaning it does not have any routing capabilities, cannot work in conjunction with the RIP (Routing Information Protocol), so therefore cannot be used to connect to any other external entity.
Node:
Any piece of hardware on a network that has it's own
address is called a node. It is a functional piece of
equipment that requires configuration on the mask/network
it resides.
NT 4.0:
Network Operating System, allegedly, inspired (well actually probably someone's idea) and developed by Microsoft. They spent years trying to get one of their operating systems to go over on to a server and actually operate with something else other than itself, and sometimes has problems doing that.
Even when they did, they had to have it accompany in two separate packages which would interact. NT was a good idea in theory, then again so was Corel Linux.
Null Modem:
Any piece of hardware on a network that has it's own address is called a node. It is a functional piece of equipment that requires configuration on the mask/network it resides.
Cable used to serially connect two computers.
PING: (Packet InterNet Groper)
PING data is sent out to see if a host is deemed reachable, "alive", or not. PING data is set an initial TTL (Time to Live) when it is sent out. If the host is not reached in a specified TTL, the host is deemed unreachable and offline.
The number of places the PING data travels through to get to the destination is called the number of "hops".
Port:
A software controlled logical interface that expects certain types of data to arrive for processing e.g. FTP works on 21, Finger on 79, NetBIOS on 139 etc.For a more in-depth explanation of this subject, please visit http://blacksun.box.sk and download the excellent tutorial on Sendmail written by "R a v e N", very nice glossary in there which explains "ports" a little bit more in depth than me.
Ring:
Not physically a ring shape but a network topology where each computer is connected to each other and the last computer, broadcast node, is the server. Polling is used on this network topology.
RIP:
Routing Information Protocol. The protocol that is used by the Router.
RIP assumes a low cost route value in order for a message to reach it's destination from the router table held in router memory or computer memory. The lowest cost value is assigned for the message as this is equal to the fastest transmission route for the message to take.
routed and gated:
Two routing daemons used by UNIX systems administrators to
maintain the Routing Information Protocol. They can be used to select a desirable or undesirable path across a network.
Both are daemons that perform practically the same job. They are in essence, routing daemons that work as part of the gateway protocols standard.
Routing:
This is the process concerned with the transport of information, or messages, from one machine to another. A packet header is present within each message and each machine that the message enters scans and reads the packet data.
If the destination IP address of the message matches the particular machine that is scanning it, the message is retained and processed.
If the IP address does not match the machine currently scanning, the message will be 'forwarded' throughout the remainder of the network until the correct machine is found. Also, it could be forwarded to a gateway or bridge if the message is to leave that particular segment or whole network.
Simplex:
One way data transfer and I use the term "client/server",
although this is not to be mixed up with the original client/server approach it helps me explain my own point in my own words. The server delivers goods to the client and the client cannot respond.
Typically used for broadcast networks and I believe SNMP uses this type of transfer as well. TV companies use simplex transmission for analogue (wave form) broadcasts.
SMTP:
Working on port 25, this is the protocol that interfaces with the respective program in order to send mail from one sender to another recipient.
SNMP: (Simple Network Management Protocol)
Used in order to manage the network. Monitoring logs etc. are sent back to the workstation on the network that controls them via this protocol.
Socket API:
Socket Application Programming Interface. Used for creating applications that will interact and use TCP/IP standards.
Star:
Fast network topology. Each node on the network has a direct connection with the server. No common pathway, or backbone, is used and this results in high traffic bandwidth levels.
TCP/IP:
Transmission Control Protocol/Internet Protocol. Developed by ARPA, Advanced Research Projects Agency, as a means of allowing nodes on a network to interact and share resources.
Comprises of Telnet, FTP etc.
| Layer |
Name |
| 7 |
APPLICATION |
| 6 |
PRESENTATION |
| 5 |
SESSION |
| 4 |
TRANSPORT |
| 3 |
NETWORK |
| 2 |
DATA LINK |
| 1 |
PHYSICAL |
The maximum bit rate, the actual data that is to be sent in binary form are handled here. Also, the transmission methods that can be used e.g. simplex, half-duplex and duplex transmission are defined here. Simplex transmission can handle data in one way at one time, half-duplex can handle bi-directional data at one time and duplex can handle bi-directional simultaneous data transmission.
In an ideal network in an ideal world, every packet would reach it's destination in uncorrupted form and printers would never receive SKEW etc. Of course, this isn't the case and there has to be some kind of error detection inorder to detect/correct these problems. At it's most basic level, the data link level sorts the data into "frames" and sees they are all received correctly.
On a small to medium sized LAN, the sender would put the message on the network to be taken down by the recipient.
On a WAN or large scale LAN bridged to many networks... this wouldn't be possible. The message would have to overcome many "hops" in order to reach the recipient. The distance to
each recipient each time would vary depending on physical distance, network traffic, maximum bandwidth etc.The process of deciding which route to take is called "routing" and is the job of the network layer at it's most basic function.
As mentioned, the distance between sender and receiver can be somewhat of a jerky one and packets can and frequently do get lost in transit. The transport layer provides a reliable connection and a solution to secure packet transit.
A typical example would be that the transport layer receives a message from the session layer and then breaks them down into adequate sizes and then send the data off. The session layer at this point would assume the data would not be lost and the most basic of functions of this layer are complete.
Although not recognised in the DoD (Department of Defence)
protocol suite, this layer is an enhanced version of the transport layer. It allows "checkpoints" to be inserted
into particularly long transfers so in the event of a crash, the whole route does not have to be re-established and hence a
more efficient process.
Previous layers have been concerned with making sure the data gets from sender to receiver in the best possible time and condition.
The presentation layer is not concerned with this. It is concerned with structured data packets and can make easier interaction between machines which have a different data representation technique.
These are nothing more than a group of applications that work at the user interaction level to perform miscellaneous tasks based over protocols such as email, FTP etc.
Trace Route:
The process of identifying, and maybe resolving, the host name and
IP address or un-resolved host name came from. Used for IP
tracing.
CLI> windows= tracert
LINUX = traceroute
UDP: (User Datagram Protocol)
Connectionless protocol which can be unreliable as it
doesn't support error correction and detection. It is used for a simple send/reply transmission.
Found in Internet, a 7 Year old Document, worth to archive
Original by http://www.pe.net/~rlewis/Resources/james.html
The modular networking architecture of Windows 95 is based on two industry
standard models for a layered networking architecture, namely the
International Organization for Standardization (ISO) model for computer
networking, called the Open Systems Interconnect (OSI) Reference Model, and
the Institute of Electrical and Electronic Engineers (IEEE) 802 model. Windows
NT and Windows for Workgroups are also designed according to these standard
models. The ISO OSI and IEEE 802 models define a modular approach to
networking, with each layer responsible for some discrete aspect of the
networking process.
The OSI model describes the flow of data in a network, from the lowest
layer (the physical connections) up to the layer containing the user’s
applications. Data going to and from the network is passed layer to layer.
Each layer is able to communicate with the layer immediately above it and the
layer immediately below it. This way, each layer is written as an efficient,
streamlined software component. When a layer receives a packet of information,
it checks the destination address, and if its own address is not there, it
passes the packet to the next layer.
When two computers communicate on a network, the software at each layer on
one computer assumes it is communicating with the same layer on the other
computer. For example, the Transport layer of one computer communicates with
the Transport layer on the other computer. The Transport layer on the first
computer has no regard for how the communication actually passes through the
lower layers of the first computer, across the physical media, and then up
through the lower layers of the second computer.
The OSI Reference Model includes seven layers:
-
Application
-
Presentation
-
Session
-
Transport
-
Network
-
Data-Link
-
Physical
James Bond meets Number One on the 7th
floor of the spy headquarters building. Number One gives Bond a secret message
that must get through to the US Embassy across town.
Bond proceeds to the 6th floor where the message is translated into an
intermediary language, encrypted and miniaturized.
Bond takes the elevator to the 5th floor where Security checks the
message to be sure it is all there and puts some checkpoints in the message so
his counterpart at the US end can be sure he’s got the whole message.
On the 4th floor the message is analyzed to see if it can be
combined with some other small messages that need to go to the US end. Also if
the message was very large it might be broken into several small packages so
other spies can take it and have it reassembled on the other end.
The 3rd floor personnel check the address on the message and
determine who the addressee is and advising Bond of the fastest route to the
Embassy.
On the 2nd floor the message is put into a special courier
pouch(packet). It contains the message, the sender and destination ID. It also
warns the recipient if other pieces are still coming.
Bond proceeds to the 1st floor where Q has prepared the Aston
Martin for the trip to the Embassy. Bond departs for the US Embassy with the
secret packet in hand. On the other end the process is reversed. Bond proceeds
from floor to floor where the message is decoded. The US Ambassador is very
grateful the message got through safely. "Bond, please tell Number One I’ll be
glad to meet him for dinner tonight".
- · The Application layer represents the level at which
applications access network services. This layer represents the services
that directly support applications such as software for file transfers,
database access, and electronic mail.
- · The Presentation layer translates data from the
Application layer into an intermediary format. This layer also manages
security issues by providing services such as data encryption, and
compresses data so that fewer bits need to be transferred on the network.
- · The Session layer allows two applications on
different computers to establish, use, and end a session. This layer
establishes dialog control between the two computers in a session,
regulating which side transmits, plus when and how long it transmits.
- · The Transport layer handles error recognition and
recovery. It also repackages long messages when necessary into small
packets for transmission and, at the receiving end, rebuilds packets into
the original message. The receiving Transport layer also sends receipt
acknowledgments.
- · The Network layer addresses messages and translates
logical addresses and names into physical addresses. It also determines
the route from the source to the destination computer and manages traffic
problems, such as switching, routing, and controlling the congestion of
data packets.
- · The Data Link layer packages raw bits from the
Physical layer into frames (logical, structured packets for data). This
layer is responsible for transferring frames from one computer to another,
without errors. After sending a frame, it waits for an acknowledgment from
the receiving computer.
- · The Physical layer transmits bits from one computer to
another and regulates the transmission of a stream of bits over a physical
medium. This layer defines how the cable is attached to the network
adapter and what transmission technique is used to send data over the
cable.
Crossover
Cable |
 |
Loop
| |
