TCPIP Architecture

1
TCP/IP Architecture

• The Transmission Control Protocol/Internet
  Protocol (TCP/IP) networking model consists of
  only four layers, instead of the seven in the
  Open Systems Interconnection (OSI) reference
  model.
• The TCP/IP model is defined in Request for
  Comments (RFC) 1122, "Requirements for Internet
  HostsCommunication Layers."

2
The OSI Reference Model and the TCP/IP Stack
3
TCP/IP Protocols
4
The Point-to-Point Protocol (PPP) Frame
5
PPP Connection Establishment Phases

• Link dead. The two computers begin in a state
  where there is no communication between them,
  until one of them initiates a physical layer
  connection.
• Link establishment. After a physical layer
  connection is established, the computers use Link
  Control Protocol (LCP) to negotiate the
  parameters they will use during the rest of the
  PPP session.
• Authentication. If required, the two computers
  exchange PPP frames that perform a user
  authentication sequence.
• Link quality monitoring. If required, the two
  computers exchange link quality protocol messages
  after the authentication process is complete.

6
PPP Connection Establishment Phases (Cont.)

• Network layer protocol configuration. The
  computers perform a separate exchange of messages
  by using the appropriate network control
  protocols for each network or internet layer
  protocol they agreed to use.
• Link open. When the network control protocol
  negotiations are complete, the PPP connection is
  fully established, and the exchange of packets
  containing application data can begin.
• Link termination. When the two computers have
  finished communicating, they sever the PPP
  connection by exchanging LCP termination
  messages, after which the systems return to the
  link dead state.

7
The IP Datagram Format
8
IP Addressing

• The Source IP Address and Destination IP Address
  fields in every IP header identify the computer
  that created the datagram and its final
  recipient.
• IP addresses are 32-bit values that identify both
  a particular network interface and the network to
  which that interface is connected.

9
IP Routing

• Routing is the process by which IP passes
  datagrams from system to system until they reach
  their final destination.
• A router is a device that connects TCP/IP
  networks and maintains information about the
  other routers in its immediate vicinity.

10
Fragmentation

• Fragmentation occurs during the routing of
  packets through an internetwork.
• When a router receives a packet that is too large
  to be transmitted over another network, the
  router splits the datagram into fragments and
  encapsulates each fragment in a separate packet.
• Datagrams can be fragmented, and their fragments
  fragmented, as many times as necessary on the way
  to their destination.
• The fragments are reassembled when they all reach
  the system identified by the Destination IP
  Address field in their IP headers.

11
Address Resolution Protocol (ARP)

• A computer with an IP address of a router or
  computer that it must resolve generates an ARP
  Request message containing that IP address and
  broadcasts it to the local network.
• All the other TCP/IP systems on the network
  receive the message and compare the enclosed IP
  address with their own.
• The computer using the requested IP address then
  generates an ARP Reply message containing the
  hardware address of its network interface adapter
  and returns it to the sender as a unicast (that
  is, a transmission addressed to a single
  destination).

12
Internet Control Message Protocol (ICMP)

• ICMP, as defined in RFC 792, is another
  internet-layer TCP/IP protocol, but it does not
  carry application data as IP does.
• ICMP has two functions it carries request and
  reply data for diagnostic programs such as Ping,
  and it provides error reporting services for
  intermediate systems.
• Because IP is an end-to-end protocol, it is
  designed so that only the destination system
  reads the contents of the datagram and processes
  the data.
• If an error that occurs during transmission
  prevents the packet from reaching its
  destination, the destination system has no way of
  knowing about the problem or its cause.

13
Converting a Binary Address to Decimal
14
Two LANs Connected by Routers
15
Binary IP Address and Subnet Mask Values
16
IP Address Classes
17
IP Addressing Rules

• The network identifier cannot have a first-byte
  value of 127.
• This value is reserved for loopback and
  diagnostic functions.
• The network identifier and host identifier bits
  cannot all be 1s.
• If all bits were set to 1, the address would be
  interpreted as a broadcast rather than an
  individual host.
• The network identifier and host identifier bits
  cannot all be 0s.
• If all bits were set to 0, the address would be
  interpreted to mean "this network only."

18
IP Address Ranges for Private Networks
19
Calculating Subnet Masks

• You have a Class C network address, such as
  192.168.24.0, and you want to create 10 subnets
  supporting 12 hosts each.
• You can borrow 4 bits from the 8-bit host
  identifier to create a 4-bit subnet identifier
  NNNNNNNN NNNNNNNN NNNNNNNN SSSSHHHH
• Because 24 2 14, the subnet identifier can
  support 10 subnets, and the 4-bit host identifier
  permits up to 14 hosts per subnet.
• To compute the subnet mask, add the number of
  network and subnet identifier bits and mask them
  all, resulting in 11111111 11111111
  11111111 11110000
• The values of the first three bytes of the mask
  are 255.255.255, and the fourth byte now is
  11110000, which becomes 240 in decimal form.
• Therefore, the subnet mask you should use on this
  network is 255.255.255.240.

20
Binary Conversion Values for 8-Bit Numbers
21
Lining Up Bit Values with Conversion Values
22
Adding the Conversion Values
23
Example Subnet and Host Identifier Values

• First three bytes
• 11000000 10101000 00011000
• 192 168 24 192.168.24
• Fourth byte, possible values
• 0001 0001 0001 10000001 0010 0001 10010001
  0011 0001 10100001 0100 0001 10110001
  0101 0001 11000001 0110 0001 11010001
  0111 0001 1110

24
Example IP Address Values for the First Subnet
25
Subnet Mask for Class B Network Example
26
TCP Services

• Guaranteed delivery
• Packet acknowledgment
• Data segmentation
• Flow control
• Error detection
• Application identification

27
The TCP Message Format
28
TCP Connection Establishment

• A Transmission Control Protocol (TCP) connection
  is actually two separate connections, with one
  running in each direction.
• To establish each one of the connections, a
  computer transmits a TCP message with the SYN
  control bit activated.
• The other computer then replies by sending a
  message with the ACK control bit activated.
• To streamline the process into three steps
  instead of four, the client sends its SYN message
  and the server replies with a message containing
  both the ACK and SYN bits.
• The server acknowledges the clients connection
  request and issues its own connection request
  using just one message.
• The client then replies to the server with an ACK
  message, and both of the connections are
  complete.

29
The TCP Three-Way Handshake
30
TCP Packet Acknowledgment

• The TCP packet acknowledgment and error
  correction systems rely on the values of the
  Sequence Number and Acknowledgment Number fields
  in the TCP header.
• During the three-way handshake, when the server
  replies to the clients SYN message, the SYN/ACK
  message that the server generates contains its
  own initial sequence number (ISN) in the Sequence
  Number field and also a value in its
  Acknowledgment Number field.
• This acknowledgment number value is the
  equivalent of the clients ISN plus 1.
• The function of this field is to inform the other
  system of what value is expected in the next
  messages Sequence Number field.

31
TCP Packet Acknowledgment (Cont.)

• When the systems begin to send data, they
  increment their sequence number values by 1 for
  each byte of data they transmit.
• The same message numbering process also occurs
  simultaneously in the other direction.

32
TCP Checksum Computation and Error Correction
33
TCP Flow Control
34
The TCP Termination Process
35
The UDP Message Format