Concept of Network and TCP_I

1. Concept of Network and TCP/IP Model
Broadband Faculty
Advanced Level Telecom Training Centre (ALTTC)
Bharat Sanchar Nigam Limited (BSNL)

2. Concept of Network and TCP/IP Model 2
Agenda
• Internet
• Comparison of TCP/IP & OSI
• Data Encapsulation
• TCP-IP Protocol Suite
• TCP/IP Protocol Documents
• TCP-IP Protocol Suite (IPv4 vs IPv6)

3. Concept of Network and TCP/IP Model 3
What is Internet?
• Internet is network of networks, with different
hardware/software technologies
• Also known by the name TCP/IP Internet
• Name TCP/IP is taken from the names of the one of
the transport layer protocols (Transport Control
Protocol) and the network layer protocol (Internet
Protocol)
• TCP/IP is backbone of the Internet

4. Concept of Network and TCP/IP Model 4
TCP/IP and OSI
• OSI is made of seven layers.
• TCP/IP protocol is made of five layers.
PHYSICAL
DATA LINK
NETWORK
TRANSPORT
APPLICATION
PHYSICAL
DATA LINK
NETWORK
TRANSPORT
SESSION
PRESENTATION
APPLICATION
OSI Model TCP/IP Model

5. Frame Head Trailer
Frame
Concept of Network and TCP/IP Model 5
Data Encapsulation
Data
Data
Data
TCP Header
TCP Segment
UDP Header
UDP Message
TCP-UDP Data
IP Header
IP Datagram
IP Header TCP-UDP Data
Application
TPT Layer
NW Layer
Data Link

6. D
P
N
T
A
Concept of Network and TCP/IP Model 6
TCP/IP Protocol Suite..
ICMP IGMP
RARP
ARP
FTP
SMTP
TELNET
HTTP
TFTP
NFS
SNMP
DNS
TCP UDP
IP
Protocols defined by the underlying networks

7. Concept of Network and TCP/IP Model 7
Applications using TCP
• File Transfer Protocol (FTP)
– Provides the ability to upload and download files between hosts
on the network.
• Simple Mail Transport Protocol (SMTP)
– Provides the ability to send mail between users on the network.
• TELNET
– Provides the ability to login into a remote host and administer
the machine.
• Hyper Text Transfer Protocol (HTTP)
– Provides the ability to supply web pages between a browser and
the server.

8. Concept of Network and TCP/IP Model 8
Applications using UDP
• Trivial File Transfer Protocol (TFTP)
– Provides simplex file transfer for network booting of devices.
• Network File System (NFS)
– Provides the ability for sharing directories between hosts on the
network.
• Simple N/w Management Protocol (SNMP)
– Provides the ability to supply network management services on
the network.
• Domain Name Service (DNS)
– Provides mapping between domain name and IP address and
vice versa.

9. Concept of Network and TCP/IP Model 9
TCP Details
• Provides application programs access to the network
using a reliable connection-oriented transport layer
service
• TCP sends and receives data reliably using sequence
numbers and acknowledgements
• TCP is a byte oriented protocol i.e. every byte in each
packet is assigned a sequence number
• Data stream handed over to TCP is called an unstructured
stream
• TCP divides this data stream into segments for
transmission to remote network

10. TCP Header..
Octet +0 Octet +1 Octet +2 Octet +3
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
SOURCE PORT DESTINATION PORT
SEQUENCE NUMBER
ACKNOWLEDGEMENT NUMBER
HELEN
U
R
G
A
C
K
P
S
H
R
S
T
S
Y
N
F
I
N
WINDOW SIZE
CHECKSUM URGENT POINTER
OPTIONS AND PADDING
10
Concept of Network and TCP/IP Model

11. Concept of Network and TCP/IP Model 11
TCP Header…
• Source & Destination Port (16 Bits)
– Can run number of applications using same transport by multiplexing through port
numbers
– Port numbers are used to identify a unique application in a machine
– 65536 (0-65535) port numbers can be defined
– Theoretically it is possible to run 65535 simultaneous applications in a host
– The first 1024 ports, port numbers 0-1023 known as well known port numbers, are
assigned and are reserved for standard applications and are controlled by IANA
– The remaining ports, 1024-65535, are dynamic and can be used freely by
applications
– Source port is randomly generated by the source machine

12. Concept of Network and TCP/IP Model 12
Well known port numbers
PORT DESCRIPTION
20 File Transfer-Data
21 File Transfer-Control
23 Telnet
25 SMTP
53 Domain Name Server
69 Trivial File Transfer
80 WWW
123 Network Time Protocol
179 Border Gateway Protocol

13. Concept of Network and TCP/IP Model 13
TCP Header…
• Sequence Number (32 Bits)
– Helps in establishing TCP connections, along with SYN bit, called as Three
Way Handshake
– Helps in maintaining account of amount of data being transferred
– Identifies where the encapsulated data fits within a data stream from the
sender
– Sequence number is incremented, in the system, every 4 microsecond
• Acknowledgement Number (32 Bits)
– Helps in maintaining account of amount of data being transferred
– Identifies the sequence number expected from the other end of data
transmission unit

14. Concept of Network and TCP/IP Model 14
Seq/Ack numbers relation
• During TCP Connection Establishment / Three way
handshake
– Acknowledgement Number Sent = Sequence Number Received+1
• During Data Transfer
– Acknowledgement Number Sent = Sequence Number Received + Data
Received in Bytes

15. Three-Way-Handshake
Receiver
Sender 0 1
0-Closed; 1-Listen; 2-SYN-Sent; 3-SYN-Received; 4-Established
AN-00000
000B
0
1
SN-95426
2
AN- 95427
000B
1
1
SN-16780 3
AN-16781
000B
1
0
SN-95427
4
15
Concept of Network and TCP/IP Model

16. Data Transfer
AN- 95428
100B
1
0
SN-16781
5
AN- 95427
000B
1
1
SN-16780
AN-00000
000B
0
1
SN-95426
AN-16781
000B
1
0
SN-95427
Receiver
Sender
0 1
0-Closed; 1-Listen; 2-SYN-Sent; 3-SYN-Received; 4-Established; 5-Data Transfer
2
3
4
AN-16881
200B
1
0
SN-95428
5
AN- 95628
150B
1
0
SN-16881
5
AN-17031
250B
1
0
SN-95628
5
AN- 95878
300B
1
0
SN-17031
5
16
Concept of Network and TCP/IP Model

17. Closing a TCP Connection
Receiver
Sender
6-Finish; 0- Closed
0 0
6
SN - 95880
AN -17334
0B
1
1
0 SN - 17334
AN - 95881
0B
0
1
0
WAIT
SN - 17334
AN - 95881
0 B
1
1
0
6
SN - 95881
AN -17334
0B
0
1
0
17
Concept of Network and TCP/IP Model

18. Concept of Network and TCP/IP Model 18
TCP Header….
• Header Length (4 Bits)
– Sometimes called Data Offset
– Indicates the length of header in 32-bit words
– Identifies the beginning of data
– Typical value is 5 unless there are options
• Flags (6 Bits)
– Urgent (URG)
– Acknowledgement (ACK)
– Push (PSH)
– Reset (RST)
– Synchronisation (SYN)
– Finish (FIN)

19. Concept of Network and TCP/IP Model 19
TCP Header…..
• Window Size (16 Bits)
– Indicates the size of the sliding window
– Specifies the number of octets, starting with the octet
indicated by the acknowledgement number, that the
sender of the segment will accept from its peer at the
other end of the connection before the peer must
stop transmitting and wait for an acknowledgement
– A default window size is 4096 bytes
– Used for flow control by using Sliding window
mechanism

20. Concept of Network and TCP/IP Model 20
Flow Control
• Sender retains a copy of transmitted data until it receives an
acknowledgment from the remote network.
• If no acknowledgment is received, within a specified time, the data
is retransmitted by using adaptive retransmission algorithm.
– TCP records the time of the transmission and sequence number of the
segment.
– TCP again records the time of the acknowledgement received.
– Using this delta, TCP builds a sample round-trip delay time and uses this to
build an average time for a packet to be sent and to receive an
acknowledgement
• TCP will time out after a number of unsuccessful retransmissions

21. Concept of Network and TCP/IP Model 21
Sliding Window-Flow Control
Moves to right when
ack is received.
Moves to right when
data is sent.
Moves to right or left to fix
the size of the window.
Window Size
Sent and ack
Sent but not ack
Can be sent
Can’t be sent

22. Concept of Network and TCP/IP Model 22
TCP Header…..
• Checksum(16 Bits)
– Used for error detection
– Covers both header and the encapsulated data
• Urgent Pointer(16 Bits)
– Used only when urgent flag is set
– Points to the last octet of urgent data
• Options
– One of the important options is MSS (Maximum Segment
Size)
• Informs the receiver of the largest segment the sender is willing to
accept, without causing fragmentation

23. Concept of Network and TCP/IP Model 23
TCP Header……
• Padding
– Consists of 1-3 octets, each equal to zero, to force
the length of TCP header to be in multiples of four
octets.

24. Concept of Network and TCP/IP Model 24
User Datagram Protocol
• Provides unreliable connectionless service
• Transfers data without establishing a session
• Used for services that have an inbuilt reliability
• Does not use end to end error checking and correction
• Does not order the packets; may loose or duplicate a
packet
• Runs faster than TCP due to less overheads

25. Concept of Network and TCP/IP Model 25
UDP Header..
Octet +0 Octet +1 Octet +2 Octet +3
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
SOURCE PORT DESTINATION PORT
MESSAGE LENGTH CHECKSUM

26. Concept of Network and TCP/IP Model 26
UDP Header...
• Source Port (16 Bits)
– Identifies the sending process.
• Destination Port (16 Bits)
– Identifies the receiving process.
– Some fixed, pre-assigned port numbers used for services on the Internet.
• 7 for UDP; 69 for TFTP
• Message length (16 Bits)
– Indicates the size of the UDP header and its data in bytes.
– Minimum size is 8, if carries no data.
• Checksum (16 Bits)
– Covers the UDP header and UDP data.
– Optional; If not used, set to all zeros.

27. Concept of Network and TCP/IP Model 27
Internet Protocol.
• Provides best-effort or connectionless delivery service.
• No error checking or tracking
• If reliability is important, IP must be paired with a reliable
protocol like TCP
• Transmits blocks of data called datagrams each of which
is transported separately
• Responsible for IP addressing
• Datagrams may travel along different routes and may
arrive out of sequence or duplicated.

28. IP Header..
Octet +0 Octet +1 Octet +2 Octet +3
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
VER HLEN TOS TOTAL LENGTH
IDENTIFICATION D
F
M
F FRAGMENT OFFSET
TIME TO LIVE PROTOCOL HEADER CHECKSUM
SOURCE ADDRESS OF HOST
DESTINATION ADDRESS OF HOST
OPTIONS PADDING
28
Concept of Network and TCP/IP Model

29. Concept of Network and TCP/IP Model 29
IP Header…
• Version (4 Bits)
– Identifies the IP version to which the packet belongs
• Header Length (4 Bits)
– Indicates the length of IP header in 32 bit words.
– Minimum length is 20 octets.
– Options may increase the size up to a maximum of 24 octets.
• Type of Service (8 Bits)
– Used for specifying special handling of packet.
– Has two sub-fields:
• Precedence
• TOS

30. Concept of Network and TCP/IP Model 30
IP Header….
0
C
R
T
D
P
P
P
Reliability
0-Normal
1-Maximise
Precedence
000-Routine
001-Priority
010-Immediate
011-Flash
100-Flash Override
101-CRITIC/ECP
110-Internetwork Control
111-Network Control
Delay
0-Normal
1-Minimise
Throughput
0-Normal
1-Maximise
Cost
0-Normal
1-Minimise
Reserved:
Always set to ‘0’
0 = No TOS
0
0
0
0
0
0
0

31. Concept of Network and TCP/IP Model 31
IP Header…..
• Total Length (16 Bits)
– Specifies total length of the packet, including header, in octets
– Largest decimal number =216= 65535, the maximum possible
size of an IP packet is 65535 octets
– Total length - header length = Packet’s data payload
• Identification (16 Bits)
– Each datagram is identified by a identification number set by the
source.
– Normally incremented by 1 for each datagram sent.

32. Concept of Network and TCP/IP Model 32
IP Header……
• Flags (3 Bits)
– First bit is not used.
– Second bit is Don’t Fragment (DF) bit
– Third bit if More Fragment (MF) bit
• Maximum Transmit Unit (MTU) is the size of the largest packet,
including IP Header, that can be transmitted or received through a
data link
• Default MTU is 576 bytes, which can be handled by any network
without fragmentation

33. Concept of Network and TCP/IP Model 33
IP Header……
• Fragment Offset (13 Bits)
– The fragmentation occurs at the routers, if the original packet
length exceeds the MTU of a data link
– Used only in the cases when a datagram is fragmented on its
way
– Specifies the offset, in units of eight octets, from the beginning
of header to the beginning of the fragment
– Each fragment is marked, by router, with the same identifier
number

34. Concept of Network and TCP/IP Model 34
Fragmentation..
172.16.2.0 172.16.3.0
MTU-1500 MTU-1500
MTU-576
Data
TCP
IP
1500 B
Data
TCP
IP
512 B
Data
512 B
Data
476 B
Data
TCP
IP Data Data
Data
TCP
IP
IP IP IP
DF=0; MF=1; Offset=0 DF=0; MF=1; Offset=64 DF=0; MF=0; Offset=128

35. Concept of Network and TCP/IP Model 35
Fragmentation
• Only the receiver host reassembles the datagram
• The destination machine starts a reassembly timer
for about 60-120 seconds.
• If not all fragments were received, then hosts discard
the packets and sends a time exceeded ICMP
message to the source machine
• If a single fragment is lost during a transmission, the
entire packet must be resent

36. Concept of Network and TCP/IP Model 36
IP Header……
• Time to live-TTL (8 Bits)
– Assigns a life to an IP datagram
• Protocol (8 Bits)
– Specifies the protocol that runs on the top of IP.
– TCP-6; EGP-8; UDP-17; OSPF-89
• Header Checksum (16 Bits)
– Error detection field for IP header
– As each router decrements the TTL, the checksum is
calculated by each router

37. Concept of Network and TCP/IP Model 37
IP Header…….
• Source Address of Host (32 Bits)
– IP Address of the Originating Machine
• Destination Address of Host (32 Bits)
– IP Address of the Destination Machine
• Options
– Security:
• Specifies how secret the datagram is
– Strict Source Routing(SSR):
• Gives the complete path to be followed
– Loose Source Routing(LSR):
• Gives the list of routers not to be missed

38. Concept of Network and TCP/IP Model 38
IP Header……..
– Record Route:
• Makes each router to append its IP address.
– Time Stamp:
• Makes each router to append its IP address and time
stamp.
• Padding
– Ensures that the header ends on a 32 bit
boundary by adding zeros after the option field.

39. Concept of Network and TCP/IP Model 39
Underlying Networks Protocols
• Ethernet
• Token Ring
• FDDI
– Fiber Distributed Data Interface
• HDLC
– High-level Data Link Control
• Frame Relay
• PPP
– Point-to-Point Protocol
• ATM
– Asynchronous Transfer Mode

40. Concept of Network and TCP/IP Model 40
Socket Connection..
• Ports along with an IP address, known as socket
connection, allow any application in any machine on
an internet to be uniquely defined.
• Multiple applications can run simultaneously on a
host by making use of separate socket connection for
each application.

41. Concept of Network and TCP/IP Model 41
Socket Connection-Multiplexing
DATA
DATA
3753-53
2764-21
DATA
DATA
DATA 3753-53
2764-21
DATA
A.B.C.D-E.F.G.H
A.B.C.D-E.F.G.H
A.B.C.D-E.F.G.H
DATA 3753-53
2764-21
DATA A.B.C.D-E.F.G.H
TRAILER
TRAILER HEADER
HEADER
D
P
N
T
DNS
FTP
2764 3753
TCP UDP
IP
A.B.C.D
DNS
FTP
21 53
TCP UDP
E.F.G.H
1. A.B.C.D(2764) – E.F.G.H(21) 2. A.B.C.D(3753) – E.F.G.H(53)

42. Concept of Network and TCP/IP Model 42
Socket Connection-Demultiplexing
D
P
N
T
DNS
FTP
2764 3753
TCP UDP
IP
A.B.C.D
DNS
FTP
21 53
TCP UDP
E.F.G.H
53- 3753
21- 2764
DATA
DATA
DATA 53- 3753
21- 2764
DATA
E.F.G.H-A.B.C.D
E.F.G.H-A.B.C.D
DATA
DATA
E.F.G.H-A.B.C.D
DATA 53- 3753
21- 2764
DATA E.F.G.H-A.B.C.D
TRAILER
TRAILER HEADER
HEADER
1. A.B.C.D(2764) – E.F.G.H(21) 2. A.B.C.D(3753) – E.F.G.H(53)

43. Concept of Network and TCP/IP Model 43
Internet Control Message Protocol
• Internet Control Message Protocol is a mechanism used
by hosts and routers to send notification of datagram
problems back to the sender.
• Sends error messages only to the source and not to
intermediate routers.
• Sole function is to report problems, not to correct them.
• An important use of ICMP is echo/reply to test whether a
destination is reachable and responding.

44. Concept of Network and TCP/IP Model 44
Internet Control Message Protocol
• Echo request/reply (PING; Packet INternet Gropher)
– Destination unreachable
0-Network unreachable
1-Host unreachable
2-Protocol unreachable
3-Port unreachable
4-Fragment needed but DF bit is set
5-Source route failed
6-Destination network unknown

45. Concept of Network and TCP/IP Model 45
Internet Control Message Protocol
7-Destination host unknown
8-Source host isolated
9-Communication with destination network administratively
prohibited
10-Communication with destination host administratively prohibited
11-Network unreachable for type of service
12-Host unreachable for type of service
– Time exceeded message format
• 0-TTL exceeded
• 1-Fragment reassembly time exceeded

46. Concept of Network and TCP/IP Model 46
Internet Group Message Protocol
• Internet Group Message Protocol provides allows for
multicast to operate on an internetwork.
– Multicast is one-to-many communication.
– A message sent can be simultaneously received by
a group of hosts.
• Special type of Class-D IP addresses, starting with
1110, are reserved as multicast addresses.

47. Concept of Network and TCP/IP Model 47
Address Resolution Protocol
• Address Resolution Protocol is used to translate 32
bits IP addresses to 48 bits Ethernet addresses.
• A host’s physical address is determined by
broadcasting its IP address to all machines.
• The machine with matching IP address, in broadcast
message, sends its hardware address to the machine
originating broadcast.

48. Concept of Network and TCP/IP Model 48
ARP Operation
Request
Ignored
Request
Ignored
ARP
Response
Accepted
Give me MAC address of 129.1.1.4
That’s
Me
Here is my MAC address
129.1.1.1 129.1.1.4
129.1.1.2 129.1.1.3
08-00-39-00-2F-C3
08-00-10-99-AC-54
08-00-5A-21-A7-22
08-00-39-00-2F-AB

49. Concept of Network and TCP/IP Model 49
Reverse Address Resolution Protocol
• Reverse Address Resolution Protocol is used to get
the 32 bits Source IP address, knowing the 48 bits
Hardware address.
• It is reverse of ARP, hence named Reverse Address
Resolution Protocol.
• A diskless workstation broadcasts RARP-Request to
find its IP Address at the time of boot up.

50. Concept of Network and TCP/IP Model 50
RARP Operation
Give me my IP address RARP Response
Diskless
work
station
RARP
Server
08-00-39-00-2F-C3 08-00-10-99-AC-54
08-00-5A-21-A7-22
223.1.2.1
223.1.2.2
223.1.2.3
08-00-39-00-2F-AB

51. Concept of Network and TCP/IP Model 51
IPv4 vs IPv6
• Some independent protocols of version 4 are part of
ICMPv6.
– RARP protocol is dropped from the suite.
– ARP and IGMP are combined with ICMPv6.
ICMP IGMP
RARP
ARP
IPv4
ICMP
IPv6

52. IPv6 Base Header
Octet +0 Octet +1 Octet +2 Octet +3
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
VER PRI FLOW LABEL
PAYLOAD LENGTH NEXT HEADER HOP LIMIT
SOURCE ADDRESS
(128 Bits)
DESTINATION ADDRESS
(128 Bits)
PAYLOAD (0-65535 Bytes)
(EXTENSION HEADERS + DATA PACKETS FROM UPPER LAYERS)
52
Concept of Network and TCP/IP Model

53. Concept of Network and TCP/IP Model 53
TCP/IP Protocol Documents
• TCP/IP technical documents are known as Request
For Comments (RFCs).
• Once issued, RFC do not change.
– Updated by new RFCs.
– RFCs can be obsoleted but their numbers are
never used again.
• A major source for RFCs is the Internet Engineering
Task Force and are accessible on site www.ietf.org

54. Concept of Network and TCP/IP Model 54