Tag Archives: 1.1e

1.1.e Explain TCP operations

1.1.e [vii] Options

A TCP segment consists of a segment header and a data section. The TCP header contains 10 mandatory fields, and an optional extension field.

Options have up to three fields:

1. Option-Kind (1 byte)

2. Option-Length (1 byte)

3. Option-Data (variable)

The ACL IP Options Selective Drop feature allows a router to filter IP options packets, thereby mitigating the effects of these packets on a router and downstream routers, and perform the following actions:

● Drop all IP options packets that it receives and prevent options from going deeper into the network. ● Ignore IP options packets destined for the router and treat them as if they had no IP options. The following example shows how to configure the router (and downstream routers) to drop all options packets that enter the network:

Router( config)# ip options drop

show ip traffic command can be used to verify the actual IP options drop statistics.

Adam, Paul (2014-07-12). All-in-One CCIE V5 Written Exam Guide (Kindle Locations 1157-1166).  . Kindle Edition.



1.1.e Explain TCP operations

1.1.e [vi] Global synchronization

Global synchronization happens when multiple TCP hosts reduce their transmission rates in response to packet dropping, then increase their transmission rates once again when the congestion is reduced.

WRED avoids the globalization problems that occur when tail drop is used as the congestion avoidance mechanism on the router.

Adam, Paul (2014-07-12). All-in-One CCIE V5 Written Exam Guide (Kindle Locations 1144-1147).  . Kindle Edition.



1.1.e Explain TCP operations

1.1.e [v] Bandwidth delay product

Bandwidth-delay product refers to the product (or multiplication) of a data link’s capacity (in bits per second) and its end-to-end delay (in seconds). The result, an amount of data measured in bits (or bytes), is equivalent to the maximum amount of data on the network circuit at any given time, i.e., data that has been transmitted but not yet acknowledged.

In wide area networks (WANs), where the end-to-end delay-bandwidth product becomes a significant factor, TCP uses the network buffers to sustain a steady-state throughput that matches the available network capacity.

Adam, Paul (2014-07-12). All-in-One CCIE V5 Written Exam Guide (Kindle Locations 1138-1143).  . Kindle Edition.


1.1.e Explain TCP operations

1.1.e [iv] Windowing

Flow control allows us to deal with a situation when a sending computer tries to transmit information at a faster rate than the destination computer can receive and process it. This can happen if the receiving computers have a heavy traffic load in comparison to the sending computer, or if the receiving computer has less processing power than the sending computer.

Sliding-window flow control is best utilized when the buffer size is limited and pre-established. During a typical communication between a sender and a receiver the receiver allocates buffer space for n frames ( n is the buffer size in frames). The sender can send and the receiver can accept n frames without having to wait for an acknowledgement. The receiver acknowledges a frame by sending an acknowledgement that includes the sequence number of the next frame expected. This acknowledgement announces that the receiver is ready to receive n frames , beginning with the number specified. Both the sender and receiver maintain what is called a window. The size of the window is less than or equal to the buffer size.

Sliding window flow control has a far better performance than stop-and-wait flow control. For example in a wireless environment data rates are low and noise level is very high, so waiting for an acknowledgement for every packet that is transferred is not very feasible. Therefore , transferring data as a bulk would yield a better performance in terms of higher throughput.

Adam, Paul (2014-07-12). All-in-One CCIE V5 Written Exam Guide (Kindle Locations 1132-1137).  . Kindle Edition.