Manual:Connection oriented communication (TCP/IP) 1 Manual:Connect ion oriented communicati on (TCP/IP) Connection oriented communicat ion (TCP/IP) The connection-oriented communication is a data communication mode in which you must first establish a connection with remote host or server before any data can be sent. It is similar with analog telephone network where you had to establish connection before you are able to communicate with a recipient. Connection establishment included operations such as dial number, receive dial tone, wait for calling signal etc. TCP session establishment and termination Process when transmitting device establishes a connection-oriented session with remote peer is called a three-way handshake . As the result end-to-end virtual (logical) circuit is created where flow control and acknowledgment for reliable delivery is used. TCP has several message types used in connection establishment and termination process (see Figure 2.1.).
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5/12/2018 Connection Oriented Communication (TCPIP) - slidepdf.com
Manual:Connection oriented communication (TCP/IP) 2
Connection establishment process
1. The host A who needs to initialize a connection sends out a SYN (Synchronize) packet with proposed initial
sequence number to the destination host B.
2. When the host B receives SYN message, it returns a packet with both SYN and ACK fags set in the TCP header
(SYN-ACK).
3. When the host A receives the SYN-ACK, it sends back ACK (Acknowledgment) macket.4. Host B receives ACK and at this stage the connection is ESTABLISHED.
Connection-oriented protocol services are often sending acknowledgments (ACKs) after successful delivery. After
packet with data is transmitted, sender waits acknowledgement from receiver. If time expires and sender did not
receive ACK, packet is retransmitted.
Connection termination
When the data transmission is complete and the host wants to terminate the connection, termination process is
Manual:Connection oriented communication (TCP/IP) 3
The host A starts transmit with window size of 1000, one 1000byte frame is transmitted. Receiver (host B) returns
ACK with window size to increase to 2000. The host A receives ACK and transmits two frames (1000 bytes each).
After that receiver advertises an initial window size to 2500. Now sender transmits three frames (two containing
1,000 bytes and one containing 500 bytes) and waits for an acknowledgement. The first three segments fill the
receiver's buffer faster than the receiving application can process the data, so the advertised window size reacheszero indicating that it is necessary to wait before further transmission is possible.
The size of the window and how fast to increase or decrease the window size is available in various TCP congestion
avoidance algorithms such as Reno, Vegas, Tahoe etc.
Ethernet networking
CSMA/CD
The Ethernet system consists of three basic elements:
• the physical medium used to carry Ethernet signals between network devices,• medium access control system embedded in each Ethernet interface that allow multiple computers to fairly
control access to the shared Ethernet channel,
• Ethernet frame that consists of a standardized set of bits used to carry data over the system.
Ethernet network uses Carrier Sense Multiple Access with Collision detection (CSMA/CD) protocol for data
transmission. That helps to control and manage access to shared bandwidth when two or more devices want to
transmit data at the same time. CSMA/CD is a modification of Carrier Sense Multiple Access. Carrier Sense
Multiple Access with Collision Detection is used to improve CSMA performance by terminating transmission as
soon as collision is detected, reducing the probability of a second collision on retry.
Before we discuss a little more about CSMA/CD we need to understand what is collision, collision domain and
network segment. A collision is the result of two devices on the same Ethernet network attempting to transmit data at
the same time. The network detects the "collision" of the two transmitted packets and discards both of them.
Manual:Connection oriented communication (TCP/IP) 5
1. Any host on the segment that wants to send data “listens” what is happening on the physical medium(wire) an is
checking whether someone else is not sending data already.
2. Host A and host C on shared network segment sees that nobody else is sending and tries to send frames.
3. Host A and Host C are listening at the same time so both of them will transmit at the same time and collision will
occur. Collision results in what we refer to as "noise" - a change in the voltage of the signals in the line (wire).4. Host A and Host B detect this collision and send out “ jam” signal to tell other hosts not to send data at this time.
Both Host A and Host C need to retransmit this data, but we don't want them to send frames simultaneously once
again. To avoid this, host A and host B will start a random timer (ms) before attempting to start CSMA/CD
process again by listening to the wire.
Each computer on Ethernet network operates independently of all other stations on the network.
Half and Full duplex Ethernet
Ethernet standards such as Ethernet II and Ethernet 802.3 are passed through formal IEEE (Institute of Electrical and
Electronics Engineers) standardization process. The difference is that Ethernet II header includes Protocol type field
whereas in Ethernet 802.3 this field was changed to length field. Ethernet is the standard CSMA/CD access method.
Ethernet supports different data transfer rates Ethernet (10BaseT) – 10 Mbps, Fast Ethernet (100Base-TX) – 100
Mbps Gigabit Ethernet (1000Base-T) – 1000 Mbps through different types of physical mediums (twisted pairs
(Copper), coaxial cable, optical fiber). Today Ethernet cables consist of four twisted pairs (8 wires). For example,
10Base-T uses only one of these wire pairs for running in both directions using half-duplex mode.
Half-duplex data transmission means that data can be transmitted in both directions between two nodes, but only one
direction at the same time. Also in the Gigabit Ethernet is defined (Half-duplex) specifications, but it isn’t used in
practice.
Full-duplex data transmission means that data can be transmitted in both directions using different twisted pairs for
each of direction at the same time. Full Duplex Ethernet, collisions are not possible since data is transmitted andreceived on different wires, and each segment is connected directly to a switch. Full-duplex Ethernet offers