UNIT IV MOBILE NETWORK AND TRANSPORT LAYERS Mobile IP – Dynamic Host Configuration Protocol-Mobile Ad Hoc Routing Protocols–Multicast routing-TCP over Wireless Networks – Indirect TCP – Snooping TCP – Mobile TCP – Fast Retransmit / Fast Recovery – Transmission/Timeout Freezing-Selective Retransmission – Transaction Oriented TCP- TCP over 2.5 / 3G wireless Networks

1. 2/12/2016
IT 2404 Mobile Communication
By
Dr T Gnanasekaran
1

2. Mobile IP – Dynamic Host Configuration Protocol- Mobile
Ad Hoc Routing Protocols–Multicast routing- TCP over
Wireless Networks – Indirect TCP – Snooping TCP –
Mobile TCP – Fast Retransmit / Fast Recovery –
Transmission/Timeout Freezing-Selective Retransmission –
Transaction Oriented TCP- TCP over 2.5 / 3G wireless
Networks
2/12/2016 2
UNIT IV
MOBILE NETWORK AND TRANSPORT
LAYERS

3. Mobile IP
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4. Mobile IP Uses
 Enable computers to maintain Internet connectivity
while moving from one Internet attachment point to
another
 Mobile – user's point of attachment changes
dynamically and all connections are automatically
maintained despite the change
 Nomadic - user's Internet connection is terminated
each time the user moves and a new connection is
initiated when the user dials back in
 New, temporary IP address is assigned
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5. 2/12/2016 5

6. 2/12/2016 6

7. 1.Server X transmits an IP datagram destined for mobile node A, with A's home address in
the IP header. The IP datagram is routed to A's home network.
2.At the home network, the incoming IP datagram is intercepted by the home agent. The
home agent encapsulates the entire datagram inside a new IP datagram, which has the A's
care-of address in the header, and retransmits the datagram. The use of an outer IP
datagram with a different destination IP address is known as tunneling.
3.The foreign agent strips off the outer IP header, encapsulates the original IP datagram in a
network-level Protocol Data Unit (PDU) (for example, a LAN Logical Link Control
[LLC] frame), and delivers the original datagram to A across the foreign network.
4.When A sends IP traffic to X, it uses X's IP address. In our example, this is a fixed address;
that is, X is not a mobile node. Each IP datagram is sent by A to a router on the foreign
network for routing to X. Typically, this router is also the foreign agent.
5.The IP datagram from A to X travels directly across the Internet to X, using X's IP address.
To support the operations illustrated in Figure 1, Mobile IP includes three basic
capabilities:
Discovery: A mobile node uses a discovery procedure to identify prospective home
agents and foreign agents.
Registration: A mobile node uses an authenticated registration procedure to inform
its home agent of its care-of address.
Tunneling: Tunneling is used to forward IP datagram from a home address to a care-
of address.2/12/2016 7

8. Operation of Mobile IP
 Mobil node is assigned to a particular network – home
network
 IP address on home network is static – home address
 Mobile node can move to another network – foreign
network
 Mobile node registers with network node on foreign
network – foreign agent
 Mobile node gives care-of address to agent on home
network – home agent
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9. Capabilities of Mobile IP
 Discovery – mobile node uses discovery procedure to
identify prospective home and foreign agents
 Registration – mobile node uses an authenticated
registration procedure to inform home agent of its care-of
address
 Tunneling – used to forward IP datagrams from a home
address to a care-of address
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10. Discovery
 Mobile node is responsible for ongoing discovery
process
 Must determine if it is attached to its home network or a
foreign network
 Transition from home network to foreign network can
occur at any time without notification to the network
layer
 Mobile node listens for agent advertisement messages
 Compares network portion of the router's IP address with
the network portion of home address
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11. Agent Solicitation
 Foreign agents are expected to issue agent advertisement
messages periodically
 If a mobile node needs agent information immediately, it
can issue ICMP router solicitation message
 Any agent receiving this message will then issue an agent
advertisement
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12. Move Detection
 Mobile node may move from one network to another
due to some handoff mechanism without IP level
being aware
 Agent discovery process is intended to enable the agent to
detect such a move
 Algorithms to detect move:
 Use of lifetime field – mobile node uses lifetime field as a
timer for agent advertisements
 Use of network prefix – mobile node checks if any newly
received agent advertisement messages are on the same
network as the node's current care-of address
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13. Co-Located Addresses
 If mobile node moves to a network that has no foreign
agents, or all foreign agents are busy, it can act as its
own foreign agent
 Mobile agent uses co-located care-of address
 IP address obtained by mobile node associated with mobile
node's current network interface
 Means to acquire co-located address:
 Temporary IP address through an Internet service, such as
DHCP
 May be owned by the mobile node as a long-term address
for use while visiting a given foreign network
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14. Registration Process
 Mobile node sends registration request to foreign agent
requesting forwarding service
 Foreign agent relays request to home agent
 Home agent accepts or denies request and sends
registration reply to foreign agent
 Foreign agent relays reply to mobile node
2/12/2016 14

15. Registration Operation Messages
 Registration request message
 Fields = type, S, B, D, M, V, G, lifetime, home address,
home agent, care-of-address, identification, extensions
 Registration reply message
 Fields = type, code, lifetime, home address, home agent,
identification, extensions
2/12/2016 15

16. Registration Procedure Security
 Mobile IP designed to resist attacks
 Node pretending to be a foreign agent sends registration
request to a home agent to divert mobile node traffic to itself
 Agent replays old registration messages to cut mobile node
from network
 For message authentication, registration request and
reply contain authentication extension
 Fields = type, length, security parameter index (SPI),
authenticator
2/12/2016 16

17. Types of Authentication Extensions
 Mobile-home – provides for authentication of
registration messages between mobile node and home
agent; must be present
 Mobile-foreign – may be present when a security
association exists between mobile node and foreign
agent
 Foreign-home – may be present when a security
association exists between foreign agent and home
agent
2/12/2016 17

18. Tunneling
 Home agent intercepts IP datagrams sent to mobile node's
home address
 Home agent informs other nodes on home network that
datagrams to mobile node should be delivered to home
agent
 Datagrams forwarded to care-of address via tunneling
 Datagram encapsulated in outer IP datagram
2/12/2016 18

19. Mobile IP Encapsulation Options
 IP-within-IP – entire IP datagram becomes payload
in new IP datagram
 Original, inner IP header unchanged except TTL
decremented by 1
 Outer header is a full IP header
 Minimal encapsulation – new header is inserted
between original IP header and original IP payload
 Original IP header modified to form new outer IP header
 Generic routing encapsulation (GRE) – developed
prior to development of Mobile IP
2/12/2016 19

20. DHCP
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21. 2/12/2016 21

22. Ad Hoc Routing Protocols
 An ad hoc routing protocol is a
convention, or standard, that controls how
nodes decide which way to route packets
between computing devices in a mobile ad
hoc network
2/12/2016 22

23. Three categories of ad hoc routing
protocols
1. Flat routing
2. Hierarchical routing
3. Hybrid (both proactive and reactive) routing
4. Geographic position assisted routing
Again they are fall into two sub categories
1. Proactive protocols
2. Reactive protocols
2/12/2016 23

24. Table-driven (proactive) routing
This type of protocols maintains fresh lists of destinations
and their routes by periodically distributing routing tables
throughout the network.
Examples of proactive algorithms are:
1. Optimized Link State Routing Protocol (OLSR)
2. Destination Sequence Distance Vector (DSDV)
Advantage is that they can give QOS guarantees related t
connection setup, latency and other real time requirements
Disadvantage of proactive scheme are their overhead in
Lightly loaded networks, the algorithm generates a lot of
unnecessary traffic and drains the batteries of mobile
device
2/12/2016 24

25. On-demand (reactive) routing
This type of protocols finds a route on demand by flooding
The network with Route Request packets.
Advantage of scalability if there light traffic and low mobility,
mobile device utilizes longer low power periods, they wake up
for data transmission or route discovery.
The main disadvantages of such algorithms are:
 High latency time in route finding.
 Excessive flooding can lead to network clogging.
Examples of on-demand algorithms are:
1. Ad hoc On-demand Distance Vector
2. Dynamic Source Routing
3. Flow State in the Dynamic Source Routing
4. Power-Aware DSR-based
2/12/2016 25

26. Hybrid (both proactive and reactive)
routing
This type of protocol combines the advantages of proactive and
reactive routing. The routing is initially established with some
proactively prospected routes and then serves the demand from
additionally activated nodes through reactive flooding. The choice of
one or the other method requires predetermination for typical cases.
The main disadvantages of such algorithms are:
Advantage depends on number of other nodes activated.
Reaction to traffic demand depends on gradient of traffic volume.
Examples of hybrid algorithms are:
1.ZRP (Zone Routing Protocol) ZRP uses IARP as pro-active
2.IERP as reactive component.
2/12/2016 26

27. Hierarchical routing protocols
With this type of protocol the choice of proactive and of reactive
routing depends on the hierarchic level in which a node resides.
The routing is initially established with some proactively
prospected routes and then serves the demand from additionally
activated nodes through reactive flooding on the lower levels.
The choice for one or the other method requires proper
attributation for respective levels.
The main disadvantages of such algorithms are:
Advantage depends on depth of nesting and addressing scheme.
Reaction to traffic demand depends on meshing parameters.
Examples of hierarchical routing algorithms are:
1. CBRP (Cluster Based Routing Protocol)
2. FSR (Fisheye State Routing protocol)
2/12/2016 27

28. Geographic routing
Geographic routing (also called geo routing or position-based
routing) is a routing principle that relies on geographic position
information.
It is mainly proposed for wireless networks and based on the idea
that the source sends a message to the geographic location of the
destination instead of using the network address.
The idea of using position information for routing was first
proposed in the 1980s in the area of packet radio networks and
interconnection networks.
Geographic routing requires that each node can determine its own
location and that the source is aware of the location of the
destination.
With this information a message can be routed to the destination
without knowledge of the network topology or a prior route
discovery.
2/12/2016 28

29. 29
Multicasting And Multicast
Routing Protocols
2/12/2016

30. 30
In unicast routing, the router forwards
the received packet through
only one of its interfaces.
Introduction: Unicasting
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31. 31
Multicasting
In multicast routing,
the router may forward the
received packet
through several of its interfaces.
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32. 32
Multicasting versus multiple unicasting
Emulation of multicasting through
multiple unicasting is not
efficient and may
create long delays,
particularly with a large group.
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33. 33
Application of Multicasting
 Access to Distributed Databases
 Information Dissemination: e.g. multicast software
updates to customers
 News Delivery
 Teleconferencing, Web Seminars
 Distant Learning
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34. 34
Multicast Routing
Objectives
 Every member receives EXACTLY ONE copy of the packet
 Non-members receive nothing
 No loops in route
 Optimal path from source to each destination.
Terminology
 Spanning Tree: Source is the root, group members are the
leaves.
 Shortest Path Spanning Tree: Each path from root to a
leaf is the shortest according to some metric
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35. 35
Multicast Trees
 Source-Based Tree:
 For each combination of (source , group), there is a
shortest path spanning tree.
 Approach 1: DVMRP; an extension of unicast distance
vector routing (e.g. RIP)
 Approach 2: MOSPF; an extension of unicast link state
routing (e.g. OSPF)
 Group-Share Tree
 One tree for the entire group
 Rendezvous-Point Tree: one router is the center of the
group and therefore the root of the tree.
 CBT and PIM-SP protocols.
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36. 36
Multicast routing protocols
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37. 37
Distance Vector Multicast Routing
Protocol - DVMRP
 No pre-defined route from source to destination. Tree
is gradually created by successive routers along the
path.
 Uses shortest path (fewest hops)
 Prevent loops: apply Reverse Path Forwarding (RFP)
 Prevent Duplication: apply Reverse Path Broadcasting
(RPB)
 Multicast with dynamic membership: apply Reverse
Path Multicasting (RPM) with pruning, grafting, and
lifetime.
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38. 38
Reverse Path Forwarding
In reverse path forwarding (RPF),
the router forwards only
the packets that have traveled the
shortest path from the source
to the router; all other
copies are discarded. No Loops
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39. 39
Reverse Path Broadcasting
Prevent Duplication in RPF
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40. 40
RPF versus RPB
 The router with the shortest path to the source becomes the
designated parent of a network
 A Router forwards packets only to its designated child networks
2/12/2016

41. 41
RPB creates a shortest path
broadcast tree from the source
to each destination.
It guarantees that each destination
receives one and only
one copy of the packet.
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42. 42
Figure 14-8
RPF, RPB, and RPM
RPM adds pruning and grafting to RPB
to create a multicast shortest
path tree that supports
dynamic membership changes.
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43. 43
MOSPF
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44. 44
Unicast tree and multicast tree
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45. 45
Core-Based Tree
CBT
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46. 46
Figure 14-10
Shared-group tree with rendezvous router
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47. 47
Figure 14-11
Sending a multicast packet to
the rendezvous router
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48. 48
In CBT, the source sends the
multicast packet (encapsulated in a
unicast packet) to the core router.
The core router decapsulates the
packet and forwards it
to all interested hosts.
2/12/2016

49. TCP for Wireless Networks
2/12/2016 49

50. Outline
 Motivation
 TCP mechanisms
 Indirect TCP
 Snooping TCP
 Mobile TCP
 Fast retransmit/recovery
 Transmission freezing
 Selective retransmission
 Transaction oriented TCP
Adapted from J. Schiller, “Mobile Communications”, Chapter 10
2/12/2016 50

51. Motivation
 Transport protocols typically designed for
 Fixed end-systems
 Fixed, wired networks
 TCP congestion control
 Packet loss in fixed networks typically due to
(temporary) overload situations
 Routers discard packets as soon as the buffers are full
 TCP recognizes congestion only indirectly via missing
acknowledgements
 Retransmissions unwise, they would only contribute to
the congestion and make it even worse
 Slow-start algorithm as reaction
2/12/2016 51

52. TCP Slow Start
 Sender calculates a congestion window for a
receiver
 Start with a congestion window size equal to one
segment
 Exponential increase of the congestion window up
to the congestion threshold, then linear increase
 Missing acknowledgement causes the reduction of
the congestion threshold to one half of the current
congestion window
 Congestion window starts again with one segment
2/12/2016 52

53. TCP Fast Retransmit/Recovery
 TCP sends an acknowledgement only after
receiving a packet
 If a sender receives several acknowledgements for
the same packet, this is due to a gap in received
packets at the receiver
 However, the receiver got all packets up to the gap
and is actually receiving packets
 Therefore, packet loss is not due to congestion,
continue with current congestion window (do not
use slow-start)
2/12/2016 53

54. Influences of mobility on TCP
 TCP assumes congestion if packets are dropped
 typically wrong in wireless networks, here we often
have packet loss due to transmission errors
 furthermore, mobility itself can cause packet loss, if
e.g. a mobile node roams from one access point (e.g.
foreign agent in Mobile IP) to another while there are
still packets in transit to the wrong access point and
forwarding is not possible
 The performance of an unchanged TCP degrades
severely
 however, TCP cannot be changed fundamentally due
to the large base of installation in the fixed network,
TCP for mobility has to remain compatible
 the basic TCP mechanisms keep the whole Internet
together2/12/2016 54

55. Indirect TCP I
 Indirect TCP or I-TCP segments the connection
 no changes to the TCP protocol for hosts connected to the wired
Internet, millions of computers use (variants of) this protocol
 optimized TCP protocol for mobile hosts
 splitting of the TCP connection at, e.g., the foreign agent into 2 TCP
connections, no real end-to-end connection any longer
 hosts in the fixed part of the net do not notice the characteristics of
the wireless part
mobile host
access point
(foreign agent) wired Internet
“wireless” TCP standard TCP
2/12/2016 55

56. I-TCP socket and state migration
mobile host
access point2
Internet
access point1
socket migration
and state transfer
2/12/2016 56

57. Indirect TCP II
 Advantages
 no changes in the fixed network necessary, no changes for the
hosts (TCP protocol) necessary, all current optimizations to TCP
still work
 transmission errors on the wireless link do not propagate into the
fixed network
 simple to control, mobile TCP is used only for one hop between,
e.g., a foreign agent and mobile host
 therefore, a very fast retransmission of packets is possible, the
short delay on the mobile hop is known
 Disadvantages
 loss of end-to-end semantics, an acknowledgement to a sender
does not any longer mean that a receiver really got a packet,
foreign agents might crash
 higher latency possible due to buffering of data within the foreign
agent and forwarding to a new foreign agent
2/12/2016 57

58. Snooping TCP I
 Transparent extension of TCP within the foreign agent
 buffering of packets sent to the mobile host
 lost packets on the wireless link (both directions!) will be retransmitted
immediately by the mobile host or foreign agent, respectively (so called
“local” retransmission)
 the foreign agent therefore “snoops” the packet flow and recognizes
acknowledgements in both directions, it also filters ACKs
 changes of TCP only within the foreign agent (+min. MH change)
„wired“ Internet
buffering of data
end-to-end TCP connection
local retransmission correspondent
hostforeign
agent
mobile
host
snooping of ACKs
2/12/2016 58

59. Snooping TCP II
 Data transfer to the mobile host
 FA buffers data until it receives ACK of the MH, FA detects packet loss via
duplicated ACKs or time-out
 fast retransmission possible, transparent for the fixed network
 Data transfer from the mobile host
 FA detects packet loss on the wireless link via sequence numbers, FA
answers directly with a NACK to the MH
 MH can now retransmit data with only a very short delay
 Advantages:
 Maintain end-to-end semantics
 No change to correspondent node
 No major state transfer during handover
 Problems
 Snooping TCP does not isolate the wireless link well
 May need change to MH to handle NACKs
 Snooping might be useless depending on encryption schemes
2/12/2016 59

60. Mobile TCP
 Special handling of lengthy and/or frequent disconnections
 M-TCP splits as I-TCP does
 unmodified TCP fixed network to supervisory host (SH)
 optimized TCP SH to MH
 Supervisory host
 no caching, no retransmission
 monitors all packets, if disconnection detected
 set sender window size to 0
 sender automatically goes into persistent mode
 old or new SH reopen the window
 Advantages
 maintains semantics, supports disconnection, no buffer forwarding
 Disadvantages
 loss on wireless link propagated into fixed network
 adapted TCP on wireless link
2/12/2016 60

61. Fast retransmit/fast recovery
 Change of foreign agent often results in packet loss
 TCP reacts with slow-start although there is no congestion
 Forced fast retransmit
 as soon as the mobile host has registered with a new foreign
agent, the MH sends duplicated acknowledgements on purpose
 this forces the fast retransmit mode at the communication
partners
 additionally, the TCP on the MH is forced to continue sending
with the actual window size and not to go into slow-start after
registration
 Advantage
 simple changes result in significant higher performance
 Disadvantage
 further mix of IP and TCP (to know when there is a new
registration), no transparent approach
2/12/2016 61

62. Transmission/time-out freezing
 Mobile hosts can be disconnected for a longer time
 no packet exchange possible, e.g., in a tunnel, disconnection
due to overloaded cells or mux. with higher priority traffic
 TCP disconnects after time-out completely
 TCP freezing
 MAC layer is often able to detect interruption in advance
 MAC can inform TCP layer of upcoming loss of connection
 TCP stops sending, but does not assume a congested link
 MAC layer signals again if reconnected
 Advantage
 scheme is independent of data and TCP mechanisms
(Ack,SN) => works even with IPsec
 Disadvantage
 TCP on mobile host has to be changed, mechanism depends
on MAC layer2/12/2016 62

63. Selective retransmission
 TCP acknowledgements are often cumulative
 ACK n acknowledges correct and in-sequence receipt of
packets up to n
 if single packets are missing quite often a whole packet
sequence beginning at the gap has to be retransmitted (go-
back-n), thus wasting bandwidth
 Selective retransmission as one solution
 RFC2018 allows for acknowledgements of single packets,
not only acknowledgements of in-sequence packet streams
without gaps
 sender can now retransmit only the missing packets
 Advantage: much higher efficiency
 Disadvantage
 more complex software in a receiver, more buffer needed at
the receiver
2/12/2016 63

64. Transaction oriented TCP
 TCP phases
 connection setup, data transmission, connection release
 using 3-way-handshake needs 3 packets for setup and
release, respectively
 thus, even short messages need a minimum of 7 packets!
 Transaction oriented TCP
 RFC1644, T-TCP, describes a TCP version to avoid this
overhead
 connection setup, data transfer and connection release can
be combined
 thus, only 2 or 3 packets are needed
 Advantage
 efficiency
 Disadvantage
 requires changed TCP
 mobility no longer transparent2/12/2016 64

65. References
 Book: Wireless Communications and Networks by
William Stallings
 PPT: WilliamStalling.com/StudentsSupport.html.
 http://www.wirelesscommunication.nl/reference/abo
ut.htm
65

66. THANK YOU
2/12/20162/12/2016 66