Routing Protocols and Transport Layer in Ad Hoc Wireless Networks

CS6003 ADHOC & SENSOR
NETWORKS
UNIT – III
Dr.A.Kathirvel, Professor and Head, Dept of CSE
Anand Institute of Higher Technology, Chennai

Unit - III
ROUTING PROTOCOLS AND
TRANSPORT LAYER IN AD HOC
WIRELESS NETWORKS
Issues in designing a routing and Transport
Layer protocol for Ad hoc networks- proactive
routing, reactive routing (on-demand), hybrid
routing- Classification of Transport Layer
solutions-TCP over Ad hoc wireless Networks.
2

Routing Protocols
for
Ad Hoc Wireless Networks
3

Issues in designing a routing protocol
Mobility
Bandwidth constraint
Error-prone shared broadcast radio channel
Hidden and Exposed terminal problems
Resource constraints
Characteristics of an ideal RP for AWN
4

Characteristics of an ideal RP
 It must be fully distributed, as centralized routing involves high
control overhead and hence is not scalable. More fault tolerant
than centralized.
 Frequent topology changes caused by mobility
 Minimum connection setup time is desired.
 Localized state maintenance
 Loop-free and free from stale routes.
 No. of packet collisions must be kept to a min
 Convergence must be quick
 Optimally use scare resources such as BW, power(computing &
battery), memory
 Provide a certain level of QoS
5

Classifications of Routing Protocols
Routing information update mechanism
use of temporal information for routing
routing topology
Utilization of specific resources
7

Table-Driven Routing Protocols
Extension of wired networks routing protocols
global topology information is maintained in the form
of table at every node
tables are updated frequently in order to maintain
consistent and accurate networks state information.
Example
Destination sequenced Distance-vector RP
Wireless RP
Cluster-Head Gateway Switch RP
Source-Tree Adaptive RP
8

DSDV
 Enhanced version of Bellman ford algorithm where each node maintains a table that
contains shortest path from first node to every other node in the networks.
 It incorporates table updates with increasing sequence number tags to prevent loops
to counter the counter to infinity problem and for faster convergence
 tables are also exchanged frequently to keep an up to date view of the n/w topology
 tables are also forwarded if a node observes a significant change in local topology
 tables update 1. Incremental update 2. Full dumps Table updates are always initiated
by the destination node with a new sequence number which is always greater than
the previous one.
 Upon receiving an updated table, a node either updates it table or holds it for some
time to select the best metric(which may be the lowest no. of hops)
 based on the sequence no. of table it may forward or reject table.
Incremental Update Full dumps
It takes a single networks data packet unit
(NDPU)
Multiple NDPUs
Used when a node does not observe a
significant change in local topology
Done either when local topology changes
significantly or when an incremental update
requires more than one NDPU
9

DSDV
 The routing table of node1 indicates that the shortest route to the destination node
(node 8) is available through node 4 and the distance to it is 3 hops.
 Reconfiguration of path
 the end node of broken link initiates a table update message with the broken links
weight assigned to infinity and with a seqno greater than the seqno stored for that
destination.
 Each node upon receiving an update with weight, quickly passes it to its neighbors
in order to propagate the broken link information to the whole n/w.
 Consider the case when node 5 moves from the current position. When the
neighbor node previous path breaks, it sets all the paths passing thro’ the broken
link with distance as infinity. For ex, when node4 knows about the link break, it
sets the path node 5 as infi and broadcasts its routing table to its neighbors. Those
neighbors detecting significant changes in their routing tables rebroadcast it to
their neighbors. In this way, the broken links information is propagated thro’ the
n/w. when node 8 receives table update mesg from 5, it informs the neighbors
about the shortest distance to node 5. This information also propagated
throughout the n/w. All nodes receiving the new update mesg with the higher
seqno. Set the new distance to node 5 in their corresponding tables.
11

DSDV
Advantages
 The availability of routes to all destinations at all times implies
that much less delay is involved in node setup.
 Existing wired n/w protocol can be applied to adhoc wireless
n/w with many fever modifications (seqno).
Disadvantages
 The updates due to broken links leads to a heavy control
overhead during high mobility. Therefore it is not scalable in
adhoc n/w which have limited BW and whose topologies are
highly dynamic.
 In order to obtain information about a particular destination a
node has to wait for a table update mesg initiated by the same
destination node.
12

Wireless Routing Protocol
 Similar to DSDV, inherits the prop. Of distributed Bellman ford algorithm
 it differs from table maintenance and in the update process
 WRP uses a set of tables to maintain more accurate information they are
 Distance Table (DT)-distance, predecessor node for a particular destination
 Routing Table (RT) - shortest distance, predecessor, successor flag
 Link Cost Table (LCT) - cost of relaying through each link
 Message Retransmit Table (MRT) - entry for every update msg that is to be retxd
and counter for each entry.
 When the link b/n 7 and 9 breaks, all nodes having a route to the D with
predecessor as node 7 delete their corresponding routing entries. Both node 9 & 7
send update msg to their neighbors indicating the cost of the link b/n node 7 &
node 9 is infi. If the nodes have any other alternate route to D 9 they udate their
table and send the changes to its neighbors. A neighbor node after receiving an
update msg, updates its routing table only if the new path is better than the
existing path.
13

WRP
Advantages
 WRP has the same advantages as that of DSDV
 In addition it has faster convergence and involves fewer table
updates
Disadvantages
 The complexity of maintenance of multiple tables demands a
larger memory and greater processing power from nodes.
 At high mobility, the control overhead involved in updating
table entries is almost the same as that of DSDV and hence is
not suitable for highly dynamic and also for very large ad hoc
wireless networks.
15

Cluster head Gateway Switch RP
CGSR employs hierarchical networks topology
unlike other table driven routing approaches that uses
flat topologies.
CGSR organizes nodes into cluster
cluster head coordinates all the nodes in cluster
cluster heads are elected dynamically by employing a
Least Cluster Change algo.
A node ceases to be a cluster head only when it
comes under the range of another cluster head, where
the tie is broken either using lowest id or highest
connectivity algo.
16

Different cluster-heads can operate on different
spreading codes on a CDMA systems
Inside a cluster, the cluster head can coordinate the
channel access based on a token-polling protocol
intercluster communication takes place via gateways
the gateways which are members of more than one
cluster can listen to multiple spreading codes.
Every member node maintains a routing table
containing the dest. Cluster head for every node in
the network.
17

In addition each node maintains a routing table which
keeps track the list of next hop nodes for reaching ever
dest. Cluster.
Each node before sending date gets token from its
cluster head it obtains the dest. Cluster head and the next
hop node from cluster member table and the routing
table respectively.
A path from any node a to any node b will be similar to
a-c1-G1-c2-G2- .. Ci-Gj.. Gn-b where Gi, cj are the ith
gateway and jth cluster head resp.
a path from node 2 to node 10 would follow 2 -1-3-7-10
19

CGSR
Advantages
clustering provides a mech. For allocating the BW.
Hence BW util. Is Better
easy to imp. Priority scheduling schemes with token
scheduling and gateway code scheduling
Disadvantages
Increase in path length and instability in the system at
high mobility when the rate of change of cluster heads
is high
power consumption at the cluster head is high
20

Source-Tree Adaptive Routing Protocol
Proposed by Garcia-Luna-Aceves and Spohn
Variation of table driven rp, with the least overhead routing
approach (LORA) as the key concept rather than the
optimum routing approach (ORA)
ORA - quick update mechanism LORA - Feasible path, not
guaranteed to be optimal, but less overhead.
STAR - Every node broadcasts its source-tree information
source tree of a node consists of the wireless links used by
the node in its preferred path to destinations
Every node, using its adjacent links and the source-tree
broadcast by its neighbors, builds a partial graph of
topology
21

Source-Tree Adaptive Routing Protocol
During initialization, a node sends an update msg to its
neighbors. Also every node is required to originate
update msg about new destination, the chances of routing
loops and the cost of paths exceeding a given threshold.
Hence, each node will have path to every dest node. Path
be sub-optimal
Absence of a reliable link layer broadcast mechanism, it
originates an update msg to all its neighbors indicate the
absence of a path to d. After getting the source tree
update from a neighbor, the node s update its source tree
and, using this it finds a path to all nodes in the network.
22

STAR
 Presence of reliable broadcast mechanism, STAR -implicit route
maintenance
 the link update mech. About the unavailability of a next hop
node triggers an update msg from a neighbor which has an
alternate source tree indicating an alternate next hop node to the
destination.
 When an intermediate node receives a Route Repair update msg,
it removes itself from the top of the route repair path and reliabl
sends it to the head of the route repair path.
Advantages
 Low overhead among all the table driven routing protocols
 use of the LORA approach in this table driven rp reduces the avg
control overhead compared to several other on demand rp
23

On Demand Routing Protocols
Execute path finding process and exchange
routing information only when a path is required
by a node to communicate with destination.
Example
DSR
AODV
TORA
LAR
ABR
SSA
24

Dynamic Source Routing
Eliminates the periodic table-update messages and
thereby reduces the BW consumed by control packets.
Beaconless & hence doesn’t require periodic message
transmission
when a source node has a data packets to be sent to the
dest. It initiates a RREQ
RREQ is flooded throughout the network
each node upon receiving RREQ can fwd it if
it has not fwd the RREQ already
it is not a dest node
25

Time to live(TTL) of packet has not exceeded
each RREQ carries a seqno generates by S node and
the path it has traversed
a node upon receiving the RREQ checks the seqno
before fwd it.
Seqno is used to avoid loop formations and to prevent
multiple transmission of the same RREQ by
intermediate nodes.
D node after receiving the first RREQ packet; sends a
RREP using the reverse path traversed by the RREQ
packet
26

This protocol uses the route cache that stores all
possible info. Extracted from source route contained in
data packet
if an intermediate node receiving a RREQ has a route
to the destination in its route cache it sends RREP with
a complete route from S to D
Optimizations:
1. Route Cache
This cache information is used by intermediate nodes
to reply to the S node when they receive a RREQ and
if they have a route to the corresponding D
27

DSR
2. Promiscuous mode
 By operating in this mode, an intermediate node learns abt the path
breaks. Info. Gained is used to update the route cache so that the
active routes maintained in route cache don’t use such links
3. During networks partition
 The affected nodes initiate RREQ packets an exponential backoff
algo. Is used to avoid frequent RREQ flooding in the network when
the D is in another dispoint set.
Route maintenance
 when an intermediate node moves away causing a wireless link to break. For
ex. If the link between node 5 & 7 fails, a route error msg is generated by a
node adjacent to path break to inform the source node. The source node
reinitiates the route establishment procedure. The cached entries at the
intermediate node and S node are removed when the route error packet is
received.
29

DSR
Advantages
 it eliminates periodical table update msg
 intermediate nodes utilize the route cache info efficiently to
reduce the ctrl overhead
Disadvantages
 route setup delay is more
 route maintenance mech doesn’t efficiently repair the path
break efficiently
 the performance of this protocol degrades rapidly with
increasing mobility
30

Adhoc Ondemand Distance Vector
 AODV uses ondemand approach, ie a route is established
only when it is required by a S node for transmitting data
packet
 it differs from DSR from the fact that DSR uses source
routing in which a data packet carries complete path to the D
 in AODV, the S node and intermediate nodes stores the next
hop info corresponding to each flow for packet txn
 uses dest. Seqno to determine an up-to-date path to the D
 a node updates its path info only if the destseqno of the
current packet received is greater than the last destseqnum
stored at the node
31

Adhoc Ondemand Distance Vector
 a RREQ carries SID,DID,S-seqno,D-seqno,BcastID and TTL
 source 1 initiates the RREQ to be flooded in the nxw for D 15
 Assuming that the Dseqno as 3 and Sseqno as 1. When the nodes
2,5 & 6 receive the RREQ, they check their route to the D. In case
a route to the D is not avail they fwd it to their neighbors. Here
nodes 3, 4 and 10 are neighbors of nodes 2,5 and 6. This is with
the assumption that the nodes 3 & 10 have routes to the D node 15
that is thro paths 10-14-15 & 3-7-9-13-15 resp.
 If the Dseqno at node 10 is 4 and is 1 at intermediate node 3 then
only node 10 is allowed to reply along the cached route to S. when
a path breaks for ex bet nodes 4 and 5, both nodes initiates RERR
msg to inform their end nodes abt the link breaks
32

AODV
 the end nodes deletes the corresponding entries from their
tables. The source node reinitiates the path finding process
with the new BcastID and the previous Dseqno
 Advantages
 routes are estab. On demand and Dseqno are used to identify
the latest path
 route set up delay is less
 disadvantages
 Multiple RREP in response to a RREQ packet can lead to a
heavy ctrl overhead
 periodic beaconing leads to unnecessary BW consumption
34

Temporally ordered Routing Algor.
Source initiated on demand routing algo which provides
loop free routes to the D
each node maintains its one-hop local topology and also
has the ability to delete partitions
distance metric used in TORA is length of path or height of
node N from the D
3 functions: establishment, maintaining and erasing routes
route estab is performed only when a node requires a path
to a D but doesn’t have any directed link
this process estab D oriented Directed Acyclic Graph
(DAG) using query/update mech.
35

Temporally ordered Routing Algor.
 When a node has a data packet to send to D node 7 it sends
query packet. This query packet is fwd by intermediate nodes 2,
3, 4, 5 & 6and reaches D node 7 or any other node which has
route to D node.
 When the query packet reaches D, it sends reply containing its
distance from D.
 Each node that receives the update packet sets its distance to a
higher value than the distance of the sender of the update
packet. By doing this, a set of directed links from the node
which originated the query to the D node 7 is created.
 When an intermediate node(5) discovers that the route to the D
is invalid, it changes its distance value to a higher value than its
neighbor and originates an update packet.
37

TORA
The neighbour node 4 that recives the update packet
reverses the link b/n 1 and 4 and forwards the update
packet. This is done to update the DAG
corresponding to D node 7.
Advantages
by limiting the ctrl packets for route reconfigurations
to a small region, TORA incurs less ctrl overhead
Disadvantages
the local reconfiguration of paths results in non-
optimal routes
38

Location Aided Routing
 Uses the location info for improving the efficiency of routing by
reducing the ctrl overhead
 availability of GPS for obtaining the position info necessary for
routing
 LAR designates two regions for selective fwd of ctrl packets
namely
1. Expected Zone
 region in which the destination node is expected to be present
given info regarding its location in the past and its mobility info
2. Request Zone
 geographic region within which the path finding ctrl packets are
permitted to be propagated
39

LAR 1 & 2
 LAR uses flooding but here flooding is restricted to a small
geographical region
 the node forward or discard ctrl packets based on two algo namely
LAR1 and LAR2
 The source node explicitly specifies the req zone in RREQ packet
 as per LAR1 the RZ is a small rectangle that includes src and dest
nodes sides of which are parallel to x and y axis when S is outside
the EZ
 when S is inside the EZ the RZ is reduced to EZ
 the src node (node 1) originates the RREQ which is broadcast to
its neigh(2,5,6)
 nodes 2 and 6 forwards the RREQ & node 5 discards the RREQ
because it is outside the RZ
40

LAR 1 & 2
 finally the RREQ reaches the dest (node 8) which orginates route
reply that contains current location and current time of the node
 the src node uses these info for route establishment
 the src node (node 1) includes the distance b/w itself and the dest
node (node 11) along with (x,y) coordinates of D in the RREQ
packet
 when the intermediate node receives this RREQ packet it
computes the distance b/w itself to D node.
 If this distance is less than the distance from S to D+* where * is a
parameter of the algo decided based on the err in location
estimation and mobility then the RREQ packet is fwd. Otherwise
RREQ is discarded
42

LAR 2
 Node 5 sends the RREQ this is received by nodes 1,2,4,7 and 6
 only nodes 4 & 7 forwards the RREQ
 other nodes 1,6,2 discards the RREQ because the distance b/w these
nodes and the D node is greater than the distance b/w S node and D
node
 once the RREQ reaches the D(node 11) it generates and send RREP
which contains the path thro which future data packets are to be
propagated
Advantages
 LAR reduces the ctrl overhead by limiting the search area for
finding a path
Disadvantages
 protocol cannot be used in place where GPS access is not possible
44

Signal-Stability based Adaptive RP
SSA is an on demand routing that uses the signal
stability as a prime factor for finding stable routes
it is beacon-based in which the signal strength of
beacon is measured for determining link stability
protocol consist of 2 parts
Forwarding Protocol(FP)-performs actual routing to
forward a pack on its way to the D
Dynamic RP(DRP)- uses an extended radio interface
that measures the signal strength from beacons - it
maintains a rt by interacting with DRP processes on
other hosts
45

Signal-Stability based Adaptive RP
Every node maintains a table that contains the beacon
count and the signal strength of each of its neighbors
if the node has received strong beacons for the past few
beacon the node classifies the link as strong/stable link
the link is otherwise classified as weak/unstable link
a src node which doesn’t have a route to the D floods the
n/w with RREQ pack
The nodes that employ SSA protocol process a RREQ
only if it is received only if it is received over a strong
link
a RREQ received thro weak link is dropped without
processing
46

SSA
 the dest. Selects the first RREQ and initiates RREP packet to notify the
selected route to the S
 when a link breaks the end nodes of the broken link notify the corresponding
end nodes of the path. A src node rebroadcasts the RREQ to find another
stable route. If no strong path is available when a link gets broken then the
new route is estab. By considering weak links also.
Advantages
 It finds more stable routes when compared to the shortest path route selection
protocols such as DSR and AODV
Disadvantages
 it puts a strong RREQ fwd condition which results in RREQ failures
 a failed RREQ reinitiates a path find process without considering stability
criteria - BW is consumed
 strong links criterion increases the path length as shortest paths may be
ignored for more stable paths
48

Zone Routing Protocol
 Hybird rp which effectively combines the adv of both proactive
and reactive
 proactive - Intra zone RP(IARP)- for nodes within a particular
zone
 Reactive - Inter zone RP(IERP) - for nodes beyond this zone
 the routing zone of a given node is a subset of the n/w within
which all nodes are reachable within less than or equal to zone
radius hops
 within routing zone each node maintains the info abt the routes
to all nodes by exchanging periodic route update packets
 IERP is responsible for finding paths to nodes which are not
within the routing zone
49

Zone Routing Protocol
 when a node S(8) has packet to be sent to node D(16) it checks
whether D is within its zone. If the dest. Belongs its own zone then it
delivers the pack directly.
 Otherwise node S bordercast(uses unicast routing to deliver pack
directly to the border nodes) the RREQ to its peripheral
nodes(2,3,5,19,14,15).
 If any peripheral finds a path to node D then it sends RREP
otherwise it rebordercast the RREQ. This process continues until D is
located.
 Nodes 10 and 14 find the info abt 16 therefore they send RREP pack
back to node 8.
 When an intermediate node in an active path detects a broken link in
the path it performs a local path reconfig. In which broken link is
bypassed by means of a shorter alternate path
51

ZRP
Advantages
reduces ctrl overhead compared to the RREQ
flooding mechanism employed in on-demand
approaches and the periodic flooding of routing info
in table driven approaches
Disadvantages
the decisions on the zone radius has a significant
impact on the performance of the protocol
52

Power Aware Routing Protocol
 Power consumption by the nodes is a serious factor to be taken
into consideration by RP for AWN
 the routes are also equally power constrained just as the nodes are
 power aware routing metrics
 singh et al. Proposed a set of routing metrics that supports
conservation of bat power
1. Minimal energy consumption per packet - min the power
consumed by a packet in traversing from S to D. The energy
consumed is the sum of energies required at every intermediate
hop in that path. The energy consumed at intermediate path is a
fun. Of distance b/w the nodes that form the link and load on the
link
53

Power Aware Routing Protocol1. q
2. Maximum n/w connectivity - balancing the routing load among
the out-set
3. Minimum variance in node power levels - to distribute the load
among all nodes in the n/w so that the power consumption pattern
remains uniform across them
4. Minimum cost per packet - in order to max the life of every node
in the n/w, this routing metric is made as a fun. Of the state of the
nodes bat. A nodes cost decreases with an increase in its bat
charge and vice versa
5. Minimize maximum node cost - min the max cost per node for a
pack after routing a number of packets or after a specific period.
This delays the failure of a node occurring due to higher
discharge because of pack forwarding
54

Transport layer
in Ad Hoc Networks
55

Transport layer, Security protocols
 The objectives of transport layer include setting up of end to
end connection, end to end delivery of data packets, flow
control and congestion control
 Example
 UDP-Simple, Unreliable, Connectionless
 TCP- Reliable, Byte stream based, Connection oriental.
 These traditional wired transport layer protocols are not
suitable for adhoc wireless n/w due to inherent problems
associated with the latter.
 The adhoc networks are highly vulnerable to security compared
to wired networks. Therefore, security protocols used in other
n/w cannot be directly applied to adhoc wireless networks.
56

Issues of designing a TL protocol
 Induced traffic
 The traffic at any given lines due to the traffic in neighboring lines is referred as
induced traffic. This induced traffic affects the throughput achieved by the transport
layer protocol.
 Induced throughput unfairness
 This refers to throughput unfairness at the transport layer due to the throughput/delay
unfairness existing at the lower layers such as the network and MAC layer.
 Separation of congestion control, flow control and reliability
 The reliability and flow control are end to end activities whereas the congestion at
time can be local activity. The performance of the transport layer protocol can be
improved if these are handled separately.
 Power and BW constraints
 The performance of a transport layer protocol is significantly affected by there
constraints.
57

Issues of designing a TL protocol
 Misinterpretation of congestion control
 Packet loss occurs in adhoc n/w due to high error rates of channel, hidden
terminal problem etc. This may lead to misinterpretation of congestion.
 Completely decoupled transport layer
 Wired n/w transport layer protocols are completely decoupled from the lower
layers. In adhoc n/w, the cross layer interaction b/n transport layers and lower
layers is important for transport layer to adopt to the changing environment.
 Dynamic topology
 Some of the deployment scenarios of adhoc wireless networks experience
rapidly changing n/w topology due to mobility of nodes. Hence, the
performance of transport layer protocol is affected by the rapid changes in n/w
topology.
58

Design goals of a TLP
Should maximize the throughput/connection
Should provide throughput fairness across contending flows
Should have mechanisms for flow control and congestion
control
Should be able to provides both reliable and unreliable
connections as per the req.
Should incur min connection set up and connection
maintenance overhead
Should minimize the resource requirements for setting up
and maintaining the connection
59

Design goals of a TLP
Should be able to adopt to the dynamics of the n/w
BW must be used efficiently
Should be aware of resource constraints such as battery
power and buffer sizes and make efficient use of them
Should make use of the information from the lower layers
for improving networks throughput
Should have well defined cross layer interaction framework
for effective scalable and protocol independent interaction
with lower layers
Should maintain end to end
60

Why does TCP not program well in AN
1.Miss interpretation of packet loss
2.Frequent path breaks
3.Effect of path length
4.Miss interpretation of congestion window
5.Asymmetric link behavior
6.Unidirectional path
7.Multipath routing
8.Network partitioning and reemerging
9.The use of sliding window based transmission.
62

Feed back based TCP (TCP-F)
 TCP-F is a feedback-based
approach. It requires the support of
a reliable link layer and routing
protocol that can provide FB to the
TCP sender about the path break.
The routing protocol is expected to
repair the broken link within a
reasonable period.
 A TCP session is setup b/n node A
and D over the path A-B-C-D
 When the intermediate link b/n
node C and node D fails, node C
originates the RFN packet and
forwards it on the reverse path to
the source node.
63

 Senders TCP stale is changed to snooze stale upon the receipt of
RFN packet.
 In snooze stale a sender stops sending anymore packet to the
destination cancels all the timers, freezes its congestion window,
freezes the retransmission timer and sets up a route failure timer.
 When route failure expires the TCP sender changes stale from
snooze stale to connected state.
 If the link CD rejoins or if any of the intermediate nodes obtains
a path to destination node a RRN packet is sent to node A and the
TCP state is updated bark to connected state.
64

Advantages
 TCP-F provides a simple FB based solution to minimize the problem arising
out of frequent path breaks in adhoc wireless networks.
 At the same time, it also permits the TCP congestion control mechanism to
respond to congestion in the n/w.
Disadvantages
 If the route to the sender is not available at the FP then additional control
packets may need to be generated for routing the RFN packet.
 TCP-F has an additional state compared to the traditional TCP state m/c, and
hence its implementation requires modifications to the existing TCP libraries.
 Congestion window used after a new route is obtained may not reflect the
achievable transmission rate to the n/w and the TCP-F receiver
65

TCP with Explicit Link Failure Notification -ELFN
 The ELFN is originated by the node detecting a path break upon
detection of a link failure to the TCP sender. This can be
implemented in two ways:
 By sending Internet Control message protocol (ICMP) destination
unreasonable (DUR) message to the sender.
 By piggy barking this information on the Route Error message
that is sent to the sender.
 Once the TCP sender receives ELFN packet it disables its
retransmission timers and enters a standby state. In this state it
periodically originates probe packets to see if a new route is
reestablished.
 Upon reception of ACK by the TCP receiver for probe packets, it
leaves the standby state, restores the retransmission timers, and
continues to function as normal.
66

TCP with Explicit Link Failure Notification -ELFN
Advantages
 TCP-ELFN improves the TCP notification performance by
decoupling the path break information from congestion
information by the use of ELFN.
 It is less dependent on routing protocol and requires only link
failure notification about the pat break.
Disadvantages
 When the n/w is temporarily partitioned the path failure may last
longer and this can lead to the origination of periodic probe
packets consuming BW and power.
 The congestion window used after a new route is obtained may
not reflect the achievable transmissions rate acceptable to the n/w
and the TCP receiver.
67

TCP-Bus
 TCP with buffering capacity and sequence information (TCP-Bus) is
similar to TCP-F and TCP-ELFN in its use of feedback information from
an intermediate node on detection of a path break. TCP-Bus was
proposed with Associativity bared routing (ABR) scheme. TCP-Bus
works as follows.
 Upon detection of a path break an upstream intermediate node (called
pivot node PN) originates explicit route disconnection notification
(ERDN) message.
 This ERDN is propagated to the TCP-Bus sender
 Upon reception of ERDN, the TCP-Bus sender stops transmissions and
freezes all times and windows.
 The packets in transit at the intermediate nodes from TCP-Bus sender to
PN are buffered until a new partial path from the PN to the TCP-Bus
receiver is obtained by PN
68

TCP-Bus
 Upon detection of a path break, the down stream node originates
the route notification (RN) packet to the TCP bus receiver
 PN attempts to final an alternate route to the TCP-Bus receiver
and availability of such partial route is to destination is intimated
to the TCP-Bus sender through an explicit route successful
notification (ERSN) packet.
 The Local Query (LQ) packet carries the sequence number of the
segment at the head of the queue buffered at the PN and REPLY
carries the sequence number of the last successful segment the
TC-Bus receiver received. This enable the TCP-Bus receiver to
understand the packets lost in transition and those buffered at the
intermediate nodes.
 The Lost packets are retransmitted by the TCP-Bus sender.
70

TCP-Bus
Advantages
Performance improvement and avoidance of fast
retransmission due to the use of buffering, seq
numbering and selective acknowledgement.
It takes advantage of ABR
Disadvantages
Increased dependency on the routing protocol and
buffering at intermediate nodes
The failure of intermediate nodes that buffer the packets
may lead to loss of packets and performance
degradation
71

Ad Hoc TCP (ATCP)
 ATCP also uses the feedback mechanism to make the sender aware
of the status of the network path. Based on the feedback information
retrieved from the intermediate nodes, the TCP sender changes its
state to the persist state, congestion control state, or the retransmit
state.
72
The major functions of the
ATCP layer is to monitor the
packets sent and received by the
TCP sender, the state of the
TCP sender, and the state of the
network.

ATCP
 The four states in the ATCP are (I) NORMAL (II) CONGESTED (III) LOSS
(IV) DISCONN
 When a TCP connection is established, the ATCP sender is in NORMAL
State. In this state, ATCP does not interfere with the operation of TCP
 When packets are lot or arrive out-of-order at the destination, it generates
duplicate ACKs. In traditional TCP, upon reception of duplicate ACKs, the
TCP sender invokes the congestion control. But the ATCP sender counts the
number of duplicate ACKs received, if it reaches three, of it puts TCP in
persists state and ATCP in loss state
 When a new ACK comes from TCP receiver. It is forwarded to TCP and the
TCP sender is removed from the persists state and then the ATCP sender
change to the NORMAL state.
 When ATCP sender is in loss state, the receipt of an ECN message charges it
to the CONGESTED State. Along with this transition, ATCP sender removes
the TCP from the persists state.
 When the n/w gets congested, the ECN flag is set in the data and the ACK
packets.
73

ATCP
 When ACTP sender receives this ECN message in the normal state, it
changes to the CONGESTED State, and permits TCP to invoke
congestion control mechanism.
 When a route failure or n/w partition occurs in the n/w, the n/w layer
details these and informs to the ATCP sender through DUR message.
 Upon reception of DUR message, ATCP puts the TCP sender in
persists state and enters into DISCONN state
 It remains in the DISCONN state until it is connected and receives
data or duplicate ACKs
 On the occurrence of any of three events, ATCP changes to the
NORMAL State.
 The receipt of DUR message in the LOSS state or CONGESTED
state causes a transition to the DISCONN state
74

ATCP
Advantages
 It maintains the end to end
semantics of TCP
 It is compatible with traditional
TCP
Disadvantages
 The dependency on the networks
layers protocol to detect the route
changes and partitions, which not
all-routing protocols may
implement.
 The addition of thin TCP layer to
the protocol stack that requires
changes in the interface functions
currently used.
75

Split TCP
 In networks, the short connections generally obtain much higher
throughput than long connections. This can also lead to unfairness
among TCP session, where one session may obtain a much higher
throughput than the other sessions.
 Split TCP provides the solution to the throughput unfairness problem by
splitting the transport layers objectives into congestion control and end
to end reliability. The congestion control is mostly a local solution. At
the same time, reliability is an end to end requirement and needs end to
end acknowledgements.
 The operation of the split TCP is shown in fig where a three stage split
connection exists b/n node 1 and node 15.
 A proxy node receive the TC packet, reads it, store it in its local buffer
and sends LACK to the source ( or the previous proxy)
76

Split TCP
 The responsibility of further delivery of packets is assigned to
proxy node. A proxy node clears a buffered packet once it
receives LACK from the immediate success or proxy for that
packet
 the split TCP maintains the end to end ACK mechanism in
addition to zone wise LACK.
 The source node clears the buffered packets only after receiving
the end to end acknowledgements.
77

Split TCP
Advantages
 improved throughput
 improved throughput fairness
 Lessened impact of mobility. Since in split TCP the path length
can be shorter than the end to end path length, the effect of
mobility on throughput is lessened.
Disadvantages
 It require modifications to TCP protocol
 The end to end connection handling of traditional TCP is
violated
 The failure of proxy nodes can lead to the throughput
degradation.
79

Application Controlled TP (ACTP)
 ACTP assigns the responsibility of ensuring reliability to the application
layer. It is more like UDP with FB of delivery and state maintenance. ACTP
stands b/n UDP and TCP It is not an extension of TCP.
 As shown in fig the application layer uses API functions to interact with the
ATCP layer. Each API function sends a packet (Send To ( ) ) to the ACTP
layer which contains information such as maximum delay the packet can
tolerate the message number of the packet and the priority of the packet. The
ATCP also maintains the delivery status through another API function. Is
ACKed <message number> and is available for application layer. A zero in
the delay field refers to the highest priority packet, which requires immediate
txn with min delay.
80

Application Controlled TP (ACTP)
Advantages
It is scalable for large n/w
throughput is not affected by path break as much as
in TCP.
It provides freedom of choosing the required
reliability level to the application layer.
Disadvantages
It is not compatible with TCP.
81

Ad hoc transport protocol (ATP)
 ATP is specifically designed for AWN and is not a variant of TCP. The major
aspects by which ATP defers from TCP are
 Coordination among multiple layers
 Rate based transmission
 Decoupling congestion ctrl and reliability
 Assisted congestion ctrl
 ATP uses information from lower layers for
 Estimation of the initial transmission rate
 Detection, avoidance and control of the congestion
 Detection of Path breaks
 The intermediate nodes attach the congestion information to every ATP packet
and the ATP receiver collects it before including it in the next ACK packet. The
congestion information is expressed in terms of the weighted average queuing
delay (DQ) and contention delay (DC) experienced by the packet.
82

ATP
 During a connection setup process or when ATP recovers from a path breaks,
the txn rate to be used is determined by a process called quick start. During
quick start process, the ATP sender propagates a probe packet to which the
intermediate nodes attach the transmission rate, which is received by ATP send
receiver, and an ACK is sent back to ATP sender. The ATP sender starts using
the newly obtained transmission rate by setting the data transmission timers.
 After congestion occurs, ATP controls it using three phases, namely, increase,
decrease, and maintain
 If R>S(1+r) then the current txn rate is increased by a factor k. where R->
new txn rate S->current txn rate r->threshold k->difference b/n new txn
rate and current txn rate
 If the new txn rate is higher than the current transmission rate but less than
the threshold then the current txn rate is maintained.
 If an ATP sender has not received any ACK packets for two consecutive
feedback periods it undergoes a multiplicate decrease of the txn rate.
83

ATP
After a third period without any ack the connection is
assumed to be lost and the ATP sender goes to the
connection initiation phase during which it periodically
generates probe packets
Advantages
Improved performance
Decoupling of the congestion control and reliability
mechanism
Avoidance of congestion window fluctuations
Disadvantages
Lack of interoperability with TCP
84

Routing Protocols and Transport Layer in Ad Hoc Wireless Networks

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Routing Protocols and Transport Layer in Ad Hoc Wireless Networks