Technology Overview
Technology: IP Overview
IP
Internet Protocol is the language computers on the Internet use to talk to one
another.
IP Packet
To send a message using IP, the computer adds extra information, known as the IP
header, in front of the message, creating an
. The IP header contains the
address of the computer meant to receive the message, as well as the address of the
sender. It is like regular mail: the IP header is the envelope, with the recipient
address and the sender addresses on it, and the message itself is inside. In this case
the addresses are numbers, like "67.34.22.199". The IP packet is sent to the
Internet, over Ethernet, DSL, or PPP.
The computers that make up the Internet itself look at the destination address in the
IP header, and forward the packet on, from one to another, until it gets to where it is
going, just as the Post Office forwards envelopes from one sorting office to the next
until it is finally sent out for delivery.
TCP
IP is unreliable: packets can get lost due to faults or overloads in the network. If a
packet does get lost the sender has no way of knowing. TCP (Transmission Control
Protocol) is designed to fix this. Nearly everything that happens on the Internet –
web browsing, e-mail, instant messaging, etc – uses TCP.
TCP adds its own header to the message, saying how much data it has already sent
and how much it has received from the other end. The combination of TCP header
and the actual message is then wrapped in IP and sent to the network, hopefully to
reach the addressed computer - usually after passing through many, many
forwarding computers on the way.
When the recipient computer receives the TCP message it sends an acknowledgment
back. If the original sender sees that acknowledgment, then all is well: the next
message can be sent.
If the sender does not get an acknowledgment within a reasonable time, it sends the
message again, repeating this until it knows the message has got through, or until it
eventually gives up and assumes that the network is broken.
In reality, TCP acknowledges many messages at a time, while simultaneously
sending its own messages. For example, a TCP header might say "I have received all
your messages up to number 97, and here is my message number 38".
ICMP and Ping
ICMP (Internet Control Message Protocol), like TCP, uses IP to communicate from
one computer to another. Unlike with TCP, these messages do not carry information
of interest to users; instead they let the computers find out about one another.
One important type of ICMP message is called echo request. When one computer
wants to check that it can reach another, it sends it echo request ICMP packet, which
asks ”r;are you there?” When the other end receives that, it sends back a reply,
called an echo response, meaning ”yes, I am here”. This process is called a ping. By
sending a series of pings it is possible to learn a lot about the state of the network.
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Summary of Contents for XTT 5000
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Page 55: ...Throughput Testing L2 BERT Diagram Home Layer 2 BERT Where do you want to go next Home 49...
Page 58: ...XTT 5000 User s Manual Throughput Stream Results Throughput Test Setup Working Desktop Home 52...
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Page 67: ...Throughput Testing Throughput Aggregate Results Throughput Stream Results Home 61...
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Page 147: ...Save Features 141 RFC2544 NE Applications IP Test Setup Monitor Setup Loopback Test Setup Home...
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