mobile computing

1. MOBILE INTERNET PROTOCOL
AND TRANSPORT LAYER
S J Savitha
Assistant Professor
Computer Science and Engineering
Sri Ramakrishna Institute of technology
1

2.  TCP/IP protocol suite – top collection of protocols.
 Core protocols.
 IP is responsible for routing a packet to any host.
 Identified by IP addresses.
 In traditional IP addressing scheme, each LAN is
assigned an address.
 When a host moves to a different location, it needs
to change its IP address.
 Mobile IP – IETF(Internet Engineering Task Force).
 Mobile IP allows mobile computers to stay
connected to the internet without changing their
address.
2

3. MOBILE IP
 Mobile IP stands for Mobile Internet Protocol
 A wireless connection to the Internet
 Designed to support host mobility
 Stay connected regardless of location without
changing IP address.
 Mobile IP is a network layer solution for
homogenous and heterogeneous mobility on the
global internet which is scalable, robust , secure
and which allow nodes to maintain all ongoing
communications while moving.
3

4. 4

5. TERMINOLOGIES- MOBILE IP
 Mobile Node
A node/device that changes its point of attachment to the
Internet
 Home Agent
A router in the home network that communicates with the
mobile node
 Foreign Agent
A router in a foreign network that delivers information between
mobile node and its home agent
 Care-of-Address
Mobile Node’s current IP address
 Correspondent Node
Node/device that is communicating with the mobile node (i.e.
web server)
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6. Winter
2001
5
6.6
DATA TRANSFER TO THE MOBILE SYSTEM
Internet
sender
FA
HA
MN
home network
foreign
network
receiver
1
2
3
1. Sender sends to the IP address of MN,
HA intercepts packet (proxy ARP)
2. HA tunnels packet to COA, here FA,
by encapsulation
3. FA forwards the packet
to the MN
CN

7. Winter
2001
6
6.7
DATA TRANSFER FROM THE MOBILE SYSTEM
Internet
receiver
FA
HA
MN
home network
foreign
network
sender
1
1. Sender sends to the IP address
of the receiver as usual,
FA works as default router
CN

8. DISCOVERING THE CARE-OF ADDRESS
 Agent advertisement – Needed for mobile node to
discover mobility agent. It is an advertisement
message constructed by attaching a special
extension to an ICMP router advertisement.
 If advertisement not received or needed sooner by
mobile a solicitation may be generated. 8

9. AGENT ADVERTISEMENT
 Allows for the detection of mobility agents
 Lists one or more available care-of addresses
 Informs mobile node about special feature provided
by foreign agents, for example, alternative
encapsulation techniques
 Allows mobile nodes to determine the network
number and status of their link to the Internet
 Allows mobile node to determine whether the agent
has the functionality to serve as a HA, a FA or both.
 Flag indicates whether it is home agent or a foreign
agent.
9

10. AGENT SOLICITATION
 In case a MN(Mobile node) does not receive any
COA, then the MN should send an agent
solicitation message.
 These Solicitation message should not flood the
network.
 A MN can send up to 3 solicitation messages(one
per second) as soon as it enters a new network.
 The purpose of sending this message to search for
a foreign agent.
 If an MN does not receive any address in response
to its solicitation messages, then to avoid network
flooding, the MN should reduce the rate of sending
the solicitation messages. 10

11. TUNNELLING PROCESS
 The packet is forwarded by the home agent to the
foreign agent. When the packet comes to the
foreign agent( COA) , it delivers the packet to the
mobile node.
 Two primary functions :
 Encapsulation – data packet to reach the tunnel
endpoint.
 Decapsulation – delivering packet at that endpoint.
11

12. TUNNELLING AND ENCAPSULATION
 Tunnelling establishes a virtual pipe for the packets
available between a tunnel entry and an endpoint.
 Encapsulation refers to arranging a packet header
and data in the part of a new packet.
 The operations of encapsulation and decapsulation
takes place whenever a packet sent from a higher
protocol to lower protocol.
12

13. 13

14. PACKET DELIVERY
STEP 1 :
 If the correspondant node wants to send an IP
packet to a mobile node.CN sends the packet to the
IP address of the mobile node.
STEP 2 :
 In case MN is not present, then the packet is
encapsulated by a new header and it is tunnelled to
the COA and HA, acts as source address of a
packet. 14

15. STEP 3 :
 The encapsulated packet is routed to foreign agent
which performs decapsulation to remove the
additional header and forwards the decapsulated
packet to the MN.
STEP 4 :
 The MN after receiving the packet from CN forward
a reply packet to the CN by specifying its own IP
address along with the address of the CN.
15

16. OVERVIEW OF MOBILE IP
 Goal- Efficient packet transmission.
 A person working as a business development
executive for a company needs to take care of
many regional offices.
 How does he makes arrangements so that he
would continue to receive postal mails regardless of
his location?
 Two solutions:
 Address changing
 Decoupling mail routing from his address.
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17. FEATURES OF MOBILE IP
 Transparency
 The IP address is to be managed transparently and
there should not be any affect of mobility on any ongoing
communication.
 Compatibility
 Mobile IP should be compatible.
 Security
 Mobile IP should, as for as possible, provide users with
secure communications over the internet.
 Efficiency and Scalability
 Efficient when overhead occurs.
 Scalable to support billions of moving hosts worldwide.
17

18. KEY MECHANISMS IN MOBILE IP
 Mobile IP is associated with three basic
mechanisms.
 Discovering the care-of-address
 Registering the care-of-address
 Tunnelling to the care-of-address
18

19. DISCOVERING THE COA
 Mobile agents advertise their presence by
periodically broadcasting the agent advertisement
messages
 Mobile node receives the advertisement messages
observes whether the message from HA or FA
 If a Mobile node does not wish to wait for a periodic
advertisement , it can send out gent solicitation
messages
19

20. REGISTERING THE COA
20

21.  If a mobile node is on new network , it registers
with the foreign agent by sending a registration
request
 Request includes permanent IP address of mobile
host and HA
 When the HA receives the Registration request , it
updates the mobility binding table
 HA sends an acknowledgement to FA
 The FA updates its visitors list by inserting the entry
of the mobile node 21

22. TUNNELLING TO THE COA
 Tunnelling – forward an IP datagram from HA to
COA
 Steps :
 When a HA receives a packet addressed to a mobile
host, it forwards the packet to the COA using IP- within
–IP
 HA inserts a new IP header in front of the IP header of
any datagram
 Destination- set to the COA
 Source- set to the HA address
 After stripping out the first header , IP processes the
packet again
22

23. ROUTE OPTIMIZATION
 Mobile IP protocol-all the data packets to the mobile
node go through the home agent
 Heavy traffic between HA and CN in the network
 To overcome this problem , route optimization
needs
 Enable direct notification of the corresponding host
 Direct tunnelling from the corresponding host to the
mobile host
 Binding cache maintained at the corresponding host
Binding – The Association of the home address with a
care-of-address.
23

24.  Four Messages :
 Binding Request
 Binding Acknowledgement
 Binding Update
 Binding Warning
Binding Request :
Node sends a request to HA to know the current
location of MN.
Binding Acknowledgement
Node will return an acknowledgement after getting
binding message.
24

25. Binding update :
Message sent by HA to CN mentioning the
correct location of MN.
Message-MN IP address and COA.
Binding Warning :
If a node decapsulates a packet for a MN, but
it is not the current FN, then this node sends a
binding warning to HA of the MN.
25

26. DHCP
 Dynamic Host Configuration Protocol
 Developed based on BOOTP (Bootstrap protocol)
 Information including IP address
 IETF an extension to BOOTP
 DHCP client and server- handle roaming status and
to assign IP address
 Significance of DHCP
 Static configuration
 Temporary IP address
26

27.  DHCP- Three mechanisms for IP address allocation
:
 Automatic allocation
 Dynamic allocation
 Manual allocation
27

28. TCP –TRANSMISSION CONTROL PROTOCOL
 Most popular transport layer protocol
 TCP- de facto
 Connection-oriented protocol
 UDP – Connectionless protocol in the TCP/IP suite
 Traditional TCP- Highly inefficient and
unsatisfactory manner
 Special adaptations-wireless networks
 Developed by DARPA in 1969
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29. OVERVIEW OF TCP/IP
29

30.  Four layers of protocol :
 Application layer
 Transport layer
 Internet layer
 Network Interface layer
Application layer
 Application programmers and end users
 Messages will be passes to transport layer
Transport layer
 Converts messages into small parts and attaches certain
information.
 It passes segments to the Internet layer protocol
30

31. Internet Layer
o Attaches certain information to segments to form
packets
o TCP segment carried one or more IP packets
o The IP passes the packets to the network interface
layer
Network Interface layer
o It converts the packets to frames by adding certain
additional information such as checksum and then
transmits them on the network
31

32.  The reverse operation takes place when a frame
arrives at a host
 The network interface layer protocol removes the
information added by the corresponding network
interface layer protocol at the sender-end and passes
on the packet to IP layer
 The IP layer protocol at the destination removes the
information added by the IP layer
 The transport layer protocol at the receiver stripes
the information added by the transport layer protocol
at the sender
 Reconstructs the message and sends it to the
application layer
32

33. TERMINOLOGIES OF TCP/IP
 TCP – Transmission Control Protocol
 IP –Internet Protocol
 HTTP-Hyper Text Transmission Protocol
 SMTP-Simple Mail Transfer Protocol
 MIME-Multipurpose Internet Mail Extension
 FTP – File Transport Protocol
 SNMP- Simple Network Management Protocol
 ICMP-Internet Control Message Protocol
 ARP- Address Resolution Protocol
 RARP-Reverse Address Resolution Protocol
 BOOTP- Boot Protocol
 DNS-Domain Name System
 IGMP-Internet Group Management Protocol
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34. ARCHITECTURE OF TCP/IP
 Application Layer :
 The protocols at this layer used by applications to
communicate with other applications which possibly
running on separate hosts
 Examples :
 HTTP
 FTP
 TELNET
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APPLICATION LAYER
TRANSPORT LAYER
INTERNET LAYER
NETWORK ACCESS LAYER

35.  Transport Layer
 End-End data transfer services
 Host -to- host protocols
 To identify the end point , the concept of port number is
used
 An application or a process specifies a port number on
which it would receive a message
 Message reaches a host – demultiplexed using the port
number at the transport layer
 It provides services by making use of services of its
lower layer protocols
 It includes
 TCP (Transmission Control Protocol)
 UDP(User Datagram Protocol)
35

36.  Internet Layer
 Packs data into data packets – IP datagrams
 IP datagram contains source and destination
address(IP address)
 Responsible for routing of IP datagrams
 In a nutshell , this layer manages the addressing of
packets and delivery of packets between networks
using IP address
 Protocols includes :
 IP
 ICMP
 ARP
 RARP
 IGMP
36

37.  Network access layer
 Encoding data and transmitting
 Provides error detection and packet framing
functionalities
 ISO/OSI protocol suite – data link and physical layers
 Data link layer help to deliver protocols by use of
physical layers
 Data link layer protocols - Ethernet , Token
Ring,FDDI,X.25
 Physical layer – how data is physically sent through
network
37

38. OPERATION OF TCP
 Client-server application
 Data transmission between client and server may
span multiple networks – Sub networks
 Identification of hosts is not enough for data
delivery
 Every process is identified by port number
 Message in the form of block of data is passed to
TCP by sending application
 TCP breaks into many small parts and attaches
certain control information(TCP header)
 Data along with TCP header called segment
38

39. STRUCTURE OF TCP SEGMENT
TCP
Header
Portion of
Data
39
Control
information
TCP header includes :
1. Destination host
2.Checksum
3.Sequence number

40.  IP datagram
 Ip packet- datagram
 Datagram- variable length up to 65,536 bytes
 Two fields – header and data
40

41.  Version - IP version number Eg :IPV4 or IPV6
 Hlen – Header length as multiples of 4 bytes
 Service – priority of datagram
 Total length – allotted 16 bits to define length of
IP datagram
 Identification – To identify fragmentation that
belongs to networks
 Flags – Deals with fragmentation
 Fragment Offset – Pointer to the offset of data in
original datagram
 Time to live – total number of hops and
operation time
41

42.  Protocol – 16 bits , Example : UDP , TCP , ICMP
 Header checksum – 16 bit field to check the
integrity of the packets
 Source address – define the original source
 Destination address – defines the destination of
datagram
 Port address –
 Data encapsulation
 Facilities requests
 Destination sub-network address
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PROTOCOL PORT
TELNET 23
SMTP 25
RPC 111
DNS 53

43. ADAPTATION OF TCP WINDOW
 Flow control techniques to control congestion in a
network
 Traffic occurs when the rate at which data injected
to a host exceeds the rate at delivered to a host
 Flow control technique
 Prevents congestion in the network
 Prevents buffer overrun at the slow receivers
 If data transmissions occur at faster rate than
network infrastructure support , then packets get
built up.
 Faster rate at sender > faster rate at receiver
 Receiver uses flow control mechanism to restrict
the faster rate at sender 43

44.  Receiver indicates an advertise window , when
sender starts to send data packets
 Advertised window- set equal to the size of the
receiver buffer
 Congestion window – max number of segments
without acknowledgements
 A sender sets size to 1 and keeps on increasing
until it receives duplicate acknowledgements
 TCP detects packet loss - RTO – Retransmission
timeout and duplicate ack
 In wireless – packet loss due to mobility and
channel errors
 Wireless are vulnerable to noise
44

45. IMPROVEMENT IN TCP PERFORMANCE
 TCP designed for traditional wired networks
 Overview
 Traditional networks
 TCP in mobile networks
 TCP in Single-hop wireless networks
 TCP in multi-hop wireless networks
45

46. TRADITIONAL NETWORKS
 In wired networks - packet losses are primarily
 Congestion control mechanisms – reduces
congestions
 Important mechanisms used by TCP
 Slow start
 Congestion Avoidance
 Fast retransmit / fast recovery
RTT – Round Trip Time
RTO calculated based on RTT
46

47. SLOW START
 Slow start mechanism used when TCP session is
started
 Lowest window size and then doubled after each
successful transmission
 Rate of doubling- rate of ack come back
 Doubling size occurs at every RTT
 RTT – Time that elapses between a segment is
transmitted by a sender and ack is received
 Congestion detected – window size is reduced to
half of its current size
47

48. CONGESTION AVOIDANCE
 The CA algorithm starts when slow start stops
 When Congestion window reaches the congestion
threshold level – window size doubling is avoided
 TCP reduces its transmission rate to half the
previous value when congestion occurs
 Less aggressive than the slow start phase
48

49. FAST RETRANSMIT /FAST RECOVERY
 Sender initiates a timer after transmitting a packet
and sets timeout value(RTO)
 RTO is calculated based on RTT
 When the timer expires , it retransmits the packet
 Retransmission is not triggered by timer, triggered
by receipt of three duplicate copies of ack
 When retransmission occurs , the congestion
window size is reduced by half
49

50. TCP IN MOBILE NETWORKS
 TCP – de facto standard protocol
 The main differences between wired and wireless
networks :
 Lower bandwidth
 Bandwidth fluctuations
 Higher delay
 Intermittent disconnections
 High bit error rate
 Poor link reliability
50

51. TCP IN SINGLE-HOP WIRELESS NETWORKS
 The modifications proposed to TCP to make it
effective in single-hop wireless networks
 Indirect TCP(I- TCP)
 Fast Retransmission
 Snooping TCP(S-TCP)
 Mobile TCP (M-TCP)
 Freeze TCP
51

52. INDIRECT TCP
 Proposes by Bakre and Badrinath
 Wired part and wireless part
 Wired part – Connection between Fixed host and
base station
 Wireless part – Connection between base station
and Mobile host
 Two separate connections : fixed network and
wireless link
 Advantage - split connection of I-TCP is that it does
not need any changes to be made to standard
protocol
 Disadvantage – Does not maintain end-end
semantics of TCP 52

53. 53

54. FAST RETRANSMISSION
 Proposed by Caceres et al
 Overcomes the delay in transmissions caused due
to intermittent disconnections
 Advantage
 Reduces the time for MH to get reconnected
 Disadvantage
 Does not propose a general approach for TCP
communications in mobile wireless networks
 Example : Does not address the specific error
characteristics of the wireless medium
54

55. SNOOPING TCP
 Proposed by Balkrishnan et al – protocol that
improves the performance of TCP by modifying the
Software
 Modified software – Snoop
 Monitors every packet passes through Tcp
Connection
 If Congestion occurs , it retransmits locally and
hides the duplicate ack
 Advantage :
 Maintains TCP semantics by hiding the duplicate ack
55

56. 56

57. MOBILE TCP
 Proposed by Kevin Brown et al
 It tries to avoid the sender window
 As I-TCP , mobile host is segmented into wired and
wireless parts
 Wired part – Connection between FH and SH
(Supervisor Host)
 Wireless part – Connection between SH and MH
 SH supervises all packets transmitted to MH
 Sets full window size - MH is connected
 State transfer takes place when MH moves
 New SH can maintain TCP connection between FH
and MH 57

58. 58

59. FREEZE TCP
 The idea is to “freeze” the TCP senders before a
disconnection occurs
 “Zero Windows Advertisement” – informs the
sender that the receiver cannot receive data at that
moment
 When sender resumes its connectivity ,the receiver
can unfreeze the sender by sending the value
 Advantage – Avoidance of slow start period
 Does not require the involvement of intermediate
nodes
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