1. ATCP is an intermediate layer between TCP and IP that monitors TCP state and takes appropriate action to improve TCP performance over multi-hop wireless networks. It aims to maintain TCP's congestion control behavior and end-to-end semantics while being compatible with standard TCP. 2. ATCP has four states - normal, congested, loss, and disconnected - that determine its behavior in response to network conditions like packet loss, congestion, or disconnections. In the loss and disconnected states, ATCP handles retransmissions to avoid reducing the congestion window unnecessarily. 3. While ATCP improves TCP throughput over ad-hoc networks, it relies on network layer feedback to detect changes and has the

1. ASSIGNMENT NO 1
ATCP Mechanism
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HANNAN
SUBMITTED BY
AQSA
rEHMAn
ROLL NO BSIT 5TH A
UOG

2. 17581556-
023
ATCP MECHANISM
Needof ATCP:
TCP is a connection-oriented transport layer protocolthat provides reliable, in-
order delivery of data to the TCP receiver. If we use TCP without any modification
in mobile ad hoc networks, we experience a serious drop in the throughput of the
connection. There are several reasons for such a drastic drop in TCP throughput
and in this section we examine these reasons
1. High Bit Error Rate (BER) affect.
2. Route Computations affect.
3. Network Partitions affect.
4. Multi path Routing affect.
Designof ATCP:
Our goal is designing ATCP was to provide a complete solution to the
problem of running TCP over multi hop wireless networks. Specifically, we
wanted to design a protocolthat has the following characteristics:
1. Improve TCP performance for connections set up in ad hoc wireless networks.

3. 2. Maintain TCP's congestioncontrolbehavior.
3. Maintain end-to-end TCP semantics.
4. Be compatible with standard TCP.
ATCP: Stands for Ad-HOC Transmission
Control Protocol
It is Ad-hoc TCP and Network layer input
component Also TCP state control It is also called End-to-end semantics and it is
Dependent on directing conventions. It is totally based on the feedback
mechanism. Sender can change its state due to any following:
1. Persist
2. Congestion control
3. Re transmit
ATCP Infrastructure:
ATCP Is intermediate layer that is layered between TCP and IP.
Functioning of ATCP layer:
The ATCP layer is only active at the TCP sender. This layer monitors
TCP state and takes appropriate action. To understand ATCP' s behavior, illustrates
ATCP's four possible states:
normal, congested, loss and disconnected.
When the TCP connection is initially established, ATCP at the sender is in the
normal state. In this state, ATCP does nothing and is invisible. Let us now examine
ATCP' s behavior under four states:
Loss Channel:

4. When the connection from the sender to the receiver is loss, it is
likely that some segments will not arrive at the receiver or may arrive out-of-order.
Thus, the receiver may generate duplicate acknowledgements acknowledgement in
responseto out of sequence segments. When TCP receives three consecutive
duplicate acknowledgement, it retransmits the offending segment and shrinks the
congestion window.
ATCP in its normal state counts the number of duplicate acknowledgement
received for any segment. When it sees that three duplicate acknowledgement has
been received, it does not forward the third duplicate acknowledgement but puts
TCP in persist mode.
After ATCP puts TCP in persist mode, ATCP enters the loss state. In the
loss state, ATCP transmits the unacknowledged segments from TCP's send buffer.
It maintains its own separate timers to retransmit these segments in the event that
acknowledgements are not forthcoming. Eventually, when a new
acknowledgement arrives (i.e., an acknowledgement for a previously
unacknowledged segment), ATCP forwards that acknowledgement to TCP which
also removes TCP from persist mode. ATCP then returns to its normal state.
Congested:
We assume that when the network detects congestion, the ECN ag is set
in acknowledgement and data packets. Let us assume that ATCP receives this
message when in its normal state. ATCP moves into its congested state and does
nothing. In other words, ATCP does not interfere with TCP's normal congestion
behavior. After TCP transmits a new segment,
ATCP returns to its normal state.
Disconnected:
Node mobility in ad hoc networks causes route even temporary
network partition. When this happens, we assume that the network generates an
ICMP Destination Unreachable message in responseto a packet transmission.
When ATCP receives this message, it puts the TCP sender into persist mode and
itself enters the disconnected state. TCP periodically generates probe packets while
in persist mode. When, eventually, the receiver is connected to the sender, it
responds to these probepackets with a duplicate acknowledgement. This removes
TCP from persist mode and moves ATCP back into normal state.

5. PROS AND CONS:
Pros:
Maintenance of end-t o-end TCP semantics.
It is Compatible with traditional TCP.
Improve the throughput of TCP ad-hoc network.
Cons:
Dependency on the network layer protocolto detect route changes and
partitions.
Addition of a thin ATCP layer to TCP.
It may re transmit change in interface function.