Explain TCP operations

Exam: Cisco 300-101 - Implementing Cisco IP Routing (ROUTE v2.0)


One topic of importance under the exam number 300-101 route is “explain TCP operations”. We will discuss the topic in details so that you can get a better idea of how to go about preparation of this section for the CCNP exam.

TCP is nothing but transmission control protocol. It is vital that all devices that implement the networking protocol do it in a consistent manner. If this is not done the devices will not behave the way they are expected to. The TCP is a protocol that performs a lot of functions.

IPv4 and IPv6 (P)MTU

MTU is maximum transmission unit. The IPv6 MTU path discovery will allow a host to dynamically discover and adjust to the differences that you will find in the MTU size of every link in a given path. When it comes to IPv6 it will allow a host to dynamically discover and also adjust to differences in the MTU size. In IPv6 the fragmentation is taken care of by the source of a packet when MTU path of one particular link along with the given data path is not big enough to accommodate the size of the packets.

A device that is originating IPv6 traffic will MTU cache that will MTU values that are received in the ICMPv6 (internet control message protocol). The minimum MTU at the IPv4 layer is 68 bytes. Both the IPv6 and the IPv4 tunnels are used to connect the large regional IPv6 networks.

This is done because it is very tricky to build a cross continent native IPv6 network. As both IPv4 and IPv6 have MTU differences you will often come across fragmentation problem. In some situations these problems are almost unavoidable. Fragmentation can be harmful and leads to a lot of problems in the network.

MSS

The full form of MSS is maximum segment size. We will now explain the same in details. It is a parameter that is used in TCP protocol. It will specify the largest amount of data that can be specified in octets. The default TCP maximum segment size is about 536. As the maximum segment size is controlled by the TCP option the host can change the value later. It must be kept in mind that each direction of the data flow is allowed to use different MSS.

In order to avoid fragmentation the host must specify the maximum segment size as equal to the largest IP datagram that the host can manage. This must be excluding the size of the TCP header size and the IP header size. If you reduce the value of MSS considerably then it will definitely reduce the IP fragmentation but it will also lead to overhead. In case of a personal computer the MSS option is set by the operating system itself.

Latency

Latency is basically the interval between the response and the stimulation. It is one of the factors that affect the speed of a network. The network can suffer from a low latency to a high latency. If there is too much latency in the network it will prevent the data from filling the network pipe as a result the effective bandwidth will reduce. The impact of the latency on the network can be a few seconds and it can be a long one too. Using the network tools like the ping test and the traceroute the latency can be measured. It will measure the time that is taken by the packet to travel from the source to the destination and back.

The latency in network depends on two factors. One is the length of the route that the packets have to travel between the receiver and the sender. Secondly it depends on the interaction TCP reliability and the congestion control protocol. The latency in network is caused by routing and switching, queuing and buffing and lastly by data protocols.

Windowing

It is a flow chart mechanism that is used in computer networking to manage the amount of data that can be sent without getting an acknowledgement. In TCP windowing is also termed as sliding windows. This is a method that is followed by the TCP to control the packets that are flowing between computers or networks.

In TCP it is essential that the host receives and acknowledges the receipt of all the data that was transmitted. However, with the help of windowing the multiple packets of data can be confirmed with a single acknowledgement. The receiving system sends window announcements to the transmitting system. This is nothing but an acknowledgement of the data receipt and the current buffer size.

Bandwidth-delay product

The Bandwidth-delay product is also known as the BDP. This is used to determine the amount of data that can be transited in a network. It is a product of the available latency and bandwidth. The BDP is very important from the point of view of TCP. The rate of the data transmission is controlled by the BDP in a TCP.

Global synchronization

The TCP Global synchronization is a common phenomenon that you will often notice in a computer network. It happens when the TCP/IP flow during the congestion period. This happens as each of the senders will reduce the rate of transmission at the same time when the loss occurs. This happens when the TCP routers are handling a multiple TCP streams and when there is a lot of traffic.

Congestion is a natural method that is followed by the TCP to recover the dropped packets. The sender will reduce the rate of sending the data for some time and will again increase the rate in sometime this is also called slow start algorithm.

All the senders will use the same time delay before they increase he rates. This pattern that each sender follows of increasing and decreasing the pattern of transmission rates is called the global synchronization. This leads to the inefficient use of the bandwidth as a result large number of packets are dropped that should be retransmitted.


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