How Networks work

(FAQ in progress)

Have you ever wondered how the 'Net works? How you can connect to a server in Japan and talk to friends or how you get to d/l all those files off news groups(Usenet?) Well, read on and learn. The subject is utterly fasinating (to me at least)

NOTE* there is a glossary of terms at the bottom of this FAQ, refer to them for an explanation of a word, or to the computer terms FAQ.

There is 2 major types of computer networks, peer-to-peer and client+server.

comparing Client/Server VS peer-to-peer network

item

Client/Server

peer-to-peer
Access Control via user/group list of permissions(NetBIOS in the old Win3.11); automatically assigned by the ISP
Security high because access is controlled by user or group identity low because knowing the PW gives access to anybody to a shared device
performance add gateway/list of gateways
hardware cost enable/disable
host domain		 enable/disable
host domain
software cost software cost software cost
backup software cost software cost
redundancy duplicate power supply hot-swappable drive arrays, and even redundant servers are common; network OS normally is capable of using redundant devices automatically software cost


The proccess is accomplished with the aid of so called protocols. Protocols are a set of instructions on how computers can all talk to each other even if they are using different OS (Unix, Solaris, NT, Novell,ets). There are several diff sets of protocols, such as IPX/SPX(for Novell) NetBIOS(for Win for workgroups 3.11), TCP/IP, ets.
The Internet uses the TCP/IP suite of protocols.

But first, lets examine concept of the Networks reference models. The most used one is the OSI (Open System Interconnection) model. The most importain concept in OSI is the layers. Simply, networking can be broken down into series of related tasks, each leading toward a set goal. Think about how you make a phone call for example. You pick up the phone, listen for the dial tone, then dial the number of the friend you want to talk to, they pick up the phone, you talk then you say your good byes and hang up.
So, we have the Application, Presentation, Session, Transport, network, Data Link, and Physical layers.
LAYERS CORRESPONDENTING PROTOCOLS
The Application provides a set of interfaces to permit network applications as browsers, email soft, news readers access to the network services that support applications direvctly. HTTP you use a browser-Netscape or IE to access World Wide Web "pages" on web servers on ports 80, 8080 3128
NTTP Usenet, news groups, you use a news reader like SBNews to connect to a news server on port 119, NOTE: NNTP server is diff from HTTP server
FTP File Transfer Protocol, you use an FTP browser like Cute FTP to connect to an FTP server on port 21
SMTP E-mail
The Presentation layer handles data format info for the network comunuications. For outgoing messages, it converts data into a generic format that can travel across the network, for incoming messages it converts data into a format that will make sence to the receiving application. It aklso handles protocol conversion, data encription and decription, and graphics commands. PPP (Point-to-Point-Protocol),
ARPAddress Resolution Protocol a protocol in the TCP/IP suite used to associate logical (IP) to physical(MAC) address,
ICMP
The Session gets two distant computers to talk to one another across a network. Thats your computer(the client) and the server you are requesting info from.
The Transport manages the flow of the data from th sender to the recever. TCP, UDP DNS
The Network handles addressing the messages for proper delivery. It assigns and checks the IP addresses of the client nd the server, For more on IP, read the IP FAQ your ol' IP, ICMP, ARP, OSPF, RIP
Data Link ODI or NDIS model
The Physical converts the bits into proper form to be send across the network. That means either into digital if uisngf a Digital line or analog format if using old phone lines. the physical connection -modem, ethernet card,

There are several ways to attach to a network, be it LAN, WAN, the Net, ets. The most common forms of network connections are: dial up, ISDN, dedicated lease lines , T1, T2, T3.

1. dial up is the oldest and the slowest way to connect.Most ISPs still connect the majority of thier clients (you) using that way. Dial-up uses both SLIP and Point-to-Point Protocol to connect.
PPP Point-to-Point Protocol is used because it allows IP addresses to be dynamically assigned. It provides BOTH Physical and Data Link layers, thus effectevly turning a modem into a Network Interface Card (NIC), so it can support multiple protocols including IP, IPX, NetBEUI. It also supports compression and data checking, which makes it more stable faster and reliable than SLIP.

how LAN, WAN differs from Dial up networking

TCP/IP property tab

setting

modem access
(Dial Up-when you are at home)

LAN access
(using a NIC-network interface card)
IP address IP address automatically assigned by the ISP specified (get value from network admin)
WIN configuration enable/disable
WIN resolution		 disabled indicate server or enable DHCP to allow NetBIOS over TCP/IP
gateway add gateway/list of gateways none (PPP is used to connect modem to Internet) IP address of gateway used to connect LAN to Internet
DNS configuration enable/disable
host domain		 usually disabled,
unless proxy sever used by ISP		 enabled, with Host and Domain specified (get the value from the system admin)


2. ISDN, or BRI-ISDN is digital 128 kbps made up of 2 lines

3. dedicated lease lines,

4. T1 is 24X64 kbps almost equal to 1.5 Mbs, T2, T3.

5. X.25 switched 56 protocols rate at 56kbps



Thus, The Internet (InterNetWorks) is a wide area(WAN) innerconnected client/server, packet switching network type(many diff computer networks connected together with routers) using the TCP/IP suite of protocols.

So let's tie all this together. You open your browser and type the name of an http link in the window. The Session layer send a message saying Hey, here i am, I want to request a service, will you accept it? Once the distant server agrees, the Networks assigns IP numbers to the packts so they will arrive at YOUR PC, and NOT someobdy else's, and the Physical converts the bits onto an analog or digital signal and they are send on their way. Simple, NO? Yea, right!

you can also use many diff commands, to find more about the network you are on, you might wanna read the FAQ on network commands you can use for fun and knowledge network commands FAQ




Key Terms

for more complete terminology, consult the Glossary FAQ

ARP Address Resolution Protocol a protocol in the TCP/IP suite used to associate logical (IP) to physical(MAC) address

DNS Domain Name System a TCP/IP protocol used to associate (map) a computers 32 bit IP address to a name like www.microsoft.com cuz it's easier for us humans to rememeber microsoft.com than 207.123.4.56

FTP File Transfer Protocol used for remote file transfers from FTP servers. It used simple NON graphics interface and a simple DOS like dir drives naming system. Usually, a lot of the shareware, software you get resides on FTP servers.

port can be visilized as an indivigual door. just like a house has a front door, a side door, a back door, front window, side window, ets, each diff net protocol HTTP, NTTP, FTP uses a diff port to connect. there are 2 ports, one for local(your PC) and the other remote on the server you are accesing. there is about 5000 ports at least. the protocols always use the same number remote port on the server but your ports are dinamically chosen. A list of ports can be found at:

socket is the combination of the IP address plus the local and remote port. a socket is a virtual line that is established beteeen your PC and the server you are using. it can be mapped as a line streaching across the net, with your PC as the starting point and the server as the ending.

UDP User Datagram Protocol thatis connectineless TCP/IP protocol for data transport which has no error checks and is often used by trojans and viruses. Difficult to detect if you are looking for it.



This was just a small introduction on networks. I could have been much more wordy, deeply diving into all the concepts. The topic is complex and wonderfully interesting. I strongly recommand everyone using the Net to take the time and learn how it works, for it is not going away and it will become an integrated part of our lives(if it hasn't already). Thus you as the user will know what to expect.