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TCP/IP Lecture Extra
TCP/IP

Developed by DARPA (Defense Advanced
Research Projects)
 TCP is a connection-oriented transport
protocol that sends data as an unstructured
stream of bytes.
 By using sequence numbers and
acknowledgment messages, TCP can provide
a sending node with delivery information
about packets transmitted to a destination
node.
TCP/IP Continued

Where data has been lost in transit from source to
destination, TCP can retransmit the data until either a
timeout condition is reached or until successful
delivery has been achieved.
 TCP can also recognize duplicate messages and will
discard them appropriately.
 If the sending computer is transmitting too fast for the
receiving computer, TCP can employ flow control
mechanisms to slow data transfer.
 TCP can also communicate delivery information to
the upper-layer protocols and applications it supports.
TCP/IP versus OSI
TCP/IP Applications
SMTP (Simple Mail Transport Protocol)
 FTP (File Transfer Protocol)
 TELNET

Other things about TCP
Heaving processing burden on source
and destination hosts
 It adds to network traffic
 Error correction of TCP adds to network
delay

Internet Protocol

IP Basics
– Connectionless
– Unreliable
IP Datagrams
 Hop by Hop

– Traceroute example
– http://www.visualware.com/visualroute/inde
x.html
IP Addressing

Hierarchical Addressing
– At the local computer level
– At the gateway
– Loopback address
IP Addressing Continued

Network Mask
– Tells the router where to go

Subnet Part
– Allows the message to be routed to the host
computer

Subnet Mask
– Generally listed as 255.255.255.0 but it can be
manipulated to expand on the number of
computers that can use one IP Address.
Other Facts about IP address

Rule 1: A prefix length of 0 matches
anything
•

Rule 2: A prefix length of 32 is an exact
match
•

A prefix of 0.0.0.0/0, or 0/0, is the shortest
possible IP address prefix and matches
any IP address. We'll see later how this
prefix can used to construct default routes
to handle routing in cases where no other
information is available.
A prefix length of 32 bits, the width of a
complete IP address, is the longest
possible address prefix and matches one
IP address exactly. 32 bit prefixes are
used to construct host routes, which
specify routing behavior for a single IP
address.
Rule 3: Prefix lengths of 8, 16, and 24
match whole bytes
•
Any prefix length that's a multiple of 8
matches on byte boundaries. For example,
a prefix of 172.30/16 matches any IP
address that begins with 172.30 in the first
two bytes, and ends with anything in the
last two bytes. Similarly, an 8 bit prefix
matches the first byte exactly and a 24 bit
prefix matches the first three bytes exactly.
Routers
Source/Destination on the Same Subnet
 Source/Destination Different Subnets
 Router Forwarding to Another Router
 Border Routers

Router Forwarding Tables

Next hop
 Simple match
– Masks – tell how long the match should be

Longest Match Selection
– The longer the prefix the better the match

Metric-based selection
– Used when two routers are tied when using
longest match

Default Router
– 0.0.0.0