Chapter 4 FCIP over IP/MPLS Core

Using FCIP Tape Acceleration

•TCP window size

•TCP maximum bandwidth

•TCP minimum available bandwidth

•Round Trip Time (RTT)

TCP Window Size

TCP uses a sliding window to control the flow of data from end to end. The TCP maximum window size (MWS) is the maximum amount of data the sender allows to be outstanding without acknowledgment at one time. The minimum MWS is 14 KB; the maximum is 32 MB.

The sender can use a larger window size to allow more outstanding data and to make sure that the pipe remains full. However, sending too much data at once can overrun intermediate routers, switches, and end devices. The TCP congestion control manages changes to the window size.

You cannot configure the TCP window size directly. This value is automatically calculated from the product of the maximum bandwidth x RTT x 0.9375 + 4 KB. In SAN-OS 1.3 and later, the RTT can dynamically adjust up to four times the configured value in the FCIP profile according to network conditions. The TCP sender dynamically changes the maximum window size accordingly.

TCP Maximum Bandwidth

The TCP maximum bandwidth is the maximum amount of bandwidth an FCIP link consumes from the point of view of the TCP sender. The maximum bandwidth settings for an FCIP link can be asymmetric. Set the TCP maximum bandwidth to the maximum amount of bandwidth you want the FCIP link to consume. Set it no higher than the bandwidth of the slowest link in the FCIP link path. For example, if the FCIP link is mapped over a dedicated DS3 WAN link, set the maximum bandwidth to 45 Mbps.

The TCP maximum bandwidth value is used as the bandwidth value in the bandwidth-delayproduct calculation of the TCP MWS.

Observe the following guidelines when selecting a value for TCP maximum bandwidth:

•Set the TCP maximum bandwidth value no higher than the maximum path bandwidth available to the FCIP.

•If deploying FCIP over a shared link with critical traffic, lower the maximum bandwidth to a level that allows the other traffic to coexist with minimal retransmissions. Quality of service (QoS) should be considered in these situations.

•When using the Cisco MDS 9000 software compression, set the maximum bandwidth value as though compression is disabled. The Cisco MDS 9000 uses a dynamic moving average feedback mechanism to adjust the TCP window size according to the compression rate.

TCP Minimum Available Bandwidth

The value should represent the minimum amount of bandwidth in the FCIP path that you expect to be always available. This value determines the aggressiveness of FCIP—a higher value is more aggressive, a lower value is less aggressive. A value that is too high can cause congestion and packet drops for any traffic traversing the shared network links.

Bandwidth allocation strongly favors the FCIP traffic when mixed with conventional TCP traffic, which recovers from drops more slowly. To cause FCIP to behave more fairly, use a lower value for the min-available-bwparameter. FCIP starts at a lower rate and increments the send rate every RTT, just like classic TCP slow-start.

Data Center High Availability Clusters Design Guide

 

OL-12518-01

4-9

 

 

 

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Cisco Systems OL-12518-01 manual TCP Window Size, TCP Maximum Bandwidth, TCP Minimum Available Bandwidth
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OL-12518-01 specifications

Cisco Systems OL-12518-01, also known as the Cisco Management Services for Wireless LAN Controller, is a key component for businesses seeking to enhance their wireless networking capabilities. This product offers a comprehensive management solution designed to ensure high performance and security of wireless networks.

One of the main features of OL-12518-01 is its centralized management interface, which simplifies the deployment and operation of multiple access points across an organization. This centralized approach allows network administrators to manage all wireless devices from a single pane of glass, significantly improving operational efficiency and reducing the potential for human error.

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A significant characteristic of OL-12518-01 is its scalability. As businesses grow, their network requirements can change dramatically. The Cisco Management Services solution is designed to scale easily alongside the organization’s needs, allowing for the addition of more access points and the integration of advanced features seamlessly. This adaptability makes it suitable for both small businesses and large enterprises, ensuring consistent wireless connectivity across diverse spaces.

Moreover, OL-12518-01 features robust analytics and reporting capabilities. It provides valuable insights into network performance and user behavior, enabling administrators to make informed decisions about resource allocation and troubleshooting. With real-time monitoring tools, IT staff can quickly identify and resolve issues, minimizing downtime and enhancing overall user experience.

In summary, Cisco Systems OL-12518-01 is a powerful wireless LAN management solution that combines centralized management, advanced security features, scalability, and comprehensive analytics. These characteristics make it an ideal choice for organizations aiming to optimize their wireless networking performance while ensuring security and reliability in their operations. By investing in OL-12518-01, businesses can achieve a robust wireless infrastructure that meets their current and future needs.
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