Difference between Router ,Repeater , Hub , Bridge , Switch ?
Repeater
• Forwards every frame it receives
• it is a generator, not an amplifier(i.e it removes noise & regenerates signal )
• Bi-directional in nature
• Useful in increasing ethernet size/length
• Maximum of 5 Repeaters in an Ethernet
• A repeater connects segments of a LAN.
• A repeater forwards every bit;
it has no filtering capability.
Function of a repeater
1)Right to lift transmission
2)Lift to right transmission
Bridge
• connect similar/dissimilar LANS
• Designed to store and forward frame
• Protocol independent
• Transparent to End Stations
• Operates in Layer-1 & Layer-2
• *uses a table for filtering/routing
• *does not change the Mac address in the frame
Routers
• *connects independent LANs or WANs to create an internetwork (internet).
• not transparent to end stations
• Acts on a network layer frame
• isolates LAN to subnets to manage & control traffic
• *A router is a three-layer
(physical, data link, and network)
device.
• A router changes the physical addresses
in a packet.


configuration of email architecture
First scenario: When the sender and the receiver of an email are on the same system, we need only two user agents.
Second scenario: When the sender and the receiver of an email are on different systems, we need two UAs and a pair of MTAs (client and server).
Third scenario: When the sender is connected to the mail server via a LAN or a WAN, we need two UAs and two pairs of MTAs (client and server).
Fourth scenario: When both sender and receiver are connected to the mail server via a LAN or a WAN, we need two UAs, two pairs of MTAs (client and server), and a pair of MAAs (client and server). This is the most common situation today.
Push vs. pull
client push massage to server
Server pull massage from client
UA:
The user agent (UA) provides service to the user to make the process of sending and receiving a message easier Email address


Some examples of command-driven user agents are mail, pine, and elm
Some examples of GUI-based user agents are Eudora, Outlook, and Netscape.

Format of an email:
Envelope ,massage (header ,body)
Email address:
Local part (address of the mailbox in the mail server )
Domain name(the domain name of the mail server)
SMTP
The actual mail transfer requires message transfer agents (MTAs). The protocol that defines the MTA client and server in the Internet is called Simple Mail Transfer Protocol (SMTP).
URL:


WEB DOCUMENTS:
The documents in the WWW can be grouped into three broad categories: static, dynamic, and active. The category is based on the time the contents of the document are determined
Dynamic document:
Using CGi (program)
using server-site script (run the script(s) inside the HTML document )
Active document:
using Java applet
using client-site script
The Hypertext Transfer Protocol (HTTP) is a protocol used mainly to access data on the World Wide Web. HTTP functions like a combination of FTP and SMTP.
File Transfer Protocol (FTP) is the standard mechanism provided by TCP/IP for copying a file from one host to another.



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