Lecture - 9 - waitaki

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Oct 26, 2013 (3 years and 7 months ago)

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TELE202 Lecture 9 Internet Protocols (1)
1

Lecturer Dr Z. Huang

Overview


Last Lecture

»
Congestion control

»
Source: chapter 12


This Lecture

»
Internet Protocols (1)

»
Source: chapter 15


Next Lecture

»
Internet Protocols (2)

»
Source: chapter 15


TELE202 Lecture 9 Internet Protocols (1)
2

Lecturer Dr Z. Huang

TCP/IP


Transmission Control Protocol


Internet Protocol


TCP/IP refers to an entire suite of
networking protocols, developed for
use on the Internet

»
TCP and IP are two of the most important









TCP/IP reference model

TELE202 Lecture 9 Internet Protocols (1)
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Lecturer Dr Z. Huang

TCP/IP and Internet


Internet is different from ‘internet’


A brief history

»
1969 ARPA funded ARPANET

»
1973 Ethernet (Bob Metcalfe’s PhD Thesis)

»
1977 packet switching funded by ARPA

»
1979 Internet Research Group for TCP/IP

»
1982/1983 TCP/IP as a core protocol

»
1983 BSD4.2 Unix with TCP/IP from UCB

»
1986 BSD4.3, performance improvements

»
1988 BSD4.3, slow start, congestion avoidance

»
1993 BSD4.4, multicasting


Size

»
1969
-

4 sites

»
1981
-

200 sites

»
1996
-

100,000th network added in Internet

»
1997
-

16M computers

»
1998
-

30M computers

»
2000
-

50M computers

»
How many computers in Internet today?


Internet Activities Board

»
Internet Engineering Task Force

»
Internet Research Task Force

»
Network Information Center

»
RFC: technical reports on protocols

TELE202 Lecture 9 Internet Protocols (1)
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Lecturer Dr Z. Huang

IP
-

Internet Protocol


Unreliable connectionless protocol

»
A datagram service

»
Not guaranteed delivery


best effort delivery

»
Packets are not guaranteed to arrive in order
or via the same route


Packets may be duplicated

»
Routing decisions may be made for each
packet

»
Reliability is the responsibility of next layer
up (e.g. TCP)


Uses the packet
-
switching technique


IP takes care of network differences

»
Make sure IP packets can be transferred
through different networks

»
Use data link layer protocols, e.g. Ethernet,
or other network layer protocols, e.g. X.25, as
vehicles to transfer IP packets

»
IP packets are encapsulated into data link
layer frames or other network packets


Ethernet hdr

IP packet

TELE202 Lecture 9 Internet Protocols (1)
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Lecturer Dr Z. Huang

IP operation


The following figure illustrates how
an IP packet is transferred from one
LAN to another LAN through X.25

TELE202 Lecture 9 Internet Protocols (1)
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Lecturer Dr Z. Huang

Interface with higher layer


Interface with higher layer, e.g. TCP

»
Functions to be performed

»
Form of primitive implementation dependent


e.g. subroutine call

»
Send


Request transmission of data unit

»
Deliver


Notify user of arrival of data unit


Parameters for send and deliver

»
Source address

»
Destination address

»
Protocol

»
Type of service indicators

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Identification

»
Don’t fragment identifier

»
Time to live

»
Data length

»
Option data

»
Data


TELE202 Lecture 9 Internet Protocols (1)
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Lecturer Dr Z. Huang

IP packet format










Version (4 bits)

»
version of IP that created the packet

»
Currently IPv4, shortly IPv6


Header length (4 bits)

»
number of 32
-
bit words in the packet header

»
Minimum 5, maximum 15


Service type (3 bits)

»
allows the host to tell the subnet what kind of
service it desires (reliability and speed)


Total datagram length (16 bits)

»
length of the entire IP packet. Max 64KB.

TELE202 Lecture 9 Internet Protocols (1)
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Lecturer Dr Z. Huang

IP packet fields


Identification, flags, fragment offset

»
used for breaking up a packet received from
the next higher layer protocol and
reassembling it if the packet is too big


Time to live (8 bits)

»
Decremented by routers to prevent looping.

»
Normally set to 30

»
Packet is discarded when it reaches 0.


Protocol (8 bits)

»
Specifies the next higher protocol. Used at
destination to give data to appropriate entity.

»
6, to TCP; 17, to UDP; 1, to ICMP


Header checksum (16 bits)

»
Error correction for the packet header. IP
only worries about errors at its level.


Source and destination IP addresses

»
32 bit fields for the addresses


Options

»
record route, timestamp, packet routing,
security


Padding

»
makes header end at a 32 bit boundary

TELE202 Lecture 9 Internet Protocols (1)
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Lecturer Dr Z. Huang

IP packet fields


Data

»
data provided by higher layer.

»
Integer multiple of 8 bits long (octet)

»
Max length of an IP datagram (header plus
data) 65,535 octets


Type of services

»
Precedence: 3 bits, 8 levels

»
Reliability: 1 bit, normal or high

»
Delay: 1 bit, normal or low

»
Throughput: 1 bit, normal or high






Options

»
Security


Attach a security label

»
Source routing


A sequence of router addresses
specifying the route

»
Route recording


Record the sequence of routers visited

»
Stream identification: reserve resources for
real
-
time applications

»
Timestamping:add a timestamp when goes by

TELE202 Lecture 9 Internet Protocols (1)
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Lecturer Dr Z. Huang

Fragmentation


Different networks allow different
maximum frame sizes.

»
Maximum Transfer Unit (MTU).

»
If IP receives a packet larger than the MTU
of an underlying network, IP must break up
the packet into fragments to transmit it.


The identification, flags, and
fragment offset fields are used in this
process

»
Identification: packet’s identification value

»
Flag field contains a more
-
fragments bit
(mfb), indicating there are more fragments
following

»
Fragment offset field: offset of the fragment
in the packet’s data field

TELE202 Lecture 9 Internet Protocols (1)
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Lecturer Dr Z. Huang

Re
-
assembly


When to re
-
assemble

»
At destination


Results in packets getting smaller as data
traverses internet

»
Intermediate re
-
assembly


Need large buffers at routers


Buffers may fill with fragments


All fragments must go through same
router, which inhibits dynamic routing


IP re
-
assembles at destination only


Dealing with failure

»
Re
-
assembly may fail if some fragments get
lost

»
Need to detect failure


Re
-
assembly time out

»
Assigned to first fragment to arrive

»
If timeout expires before all fragments arrive,
discard partial data


Use time
-
to
-
live field of the first
fragment as the packet life time

»
Let the time
-
to
-
live field continue to
decrement per second

»
If time
-
to
-
live runs out, discard partial data


TELE202 Lecture 9 Internet Protocols (1)
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Lecturer Dr Z. Huang

IP Addresses


An IP address has four bytes

»
Dotted decimal notion e.g.139.80.32.92


IP addresses are divided into classes


Class A

»
0nnnnnnn xxxxxxxx xxxxxxxx xxxxxxxx

»
8
-
bit network address

»
24
-
bit node ID address

»
126 networks of 16 million hosts


Class B

»
10nnnnnn nnnnnnnn xxxxxxxx xxxxxxxx

»
16
-
bit network address

»
16
-
bit node ID address

»
16,384 networks of 64K hosts


Class C

»
110nnnnn nnnnnnnn nnnnnnnn xxxxxxxx

»
24
-
bit network address

»
8
-
bit node ID address

»
2 million networks of 254 hosts

TELE202 Lecture 9 Internet Protocols (1)
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Lecturer Dr Z. Huang

IP Addresses


Class D is multicast address

»
1110xxxx xxxxxxxx xxxxxxxx xxxxxxxx


Class E is reserved for future use

»
11110xxx xxxxxxxx xxxxxxxx xxxxxxxx


Example: 139.80.32.92

»
Which class? Convert it into binary code:


10001101.01010000.00100000.01011100

TELE202 Lecture 9 Internet Protocols (1)
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Lecturer Dr Z. Huang

Internet Domains and Names


IP domain

»
Hierarchical

»
Domains are not geographical

»
Domains can have subdomains

»
Example: edu, com, org, gov, nz, co.nz


IP name

»
ws1.cs.mit.edu

»
vax2.dunedin.xyz.co.nz


IP name is different from IP address!


Examples

»
mary.otago.ac.nz
-

139.80.32.92

»
microsoft.co.nz
-

202.37.145.231


There is a mapping between IP name
and IP address


Domain Name System (DNS)

»
Provide DNS servers to map an IP Name into
an IP address

»
A distributed database for name
-
address
pairs
-

no DNS server knows everything

»
A hierarchical system distributed among
DNS servers


Try ‘nslookup’ to get the IP address
for a text name

»
Example: nslookup atlas.otago.ac.nz

TELE202 Lecture 9 Internet Protocols (1)
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Lecturer Dr Z. Huang

Summary


TCP/IP reference model


TCP/IP protocol suite


Internet Protocol

»
Datagram service

»
Packet switching

»
Interface with higher layer

»
IP packet format

»
Fragmentation and re
-
assembly

»
IP addresses and classes

»
Internet domains and names