However, some applications, commonly those that use remote procedure calls RPC , do require a discrete session layer. Whether the data to be exchanged between a user application instance and server application instance requires the use of a presentation layer or session layer, data to be transmitted across an internetwork will be handled by a transport protocol.
The transport protocol is primarily responsible for data multiplexing—that is, ensuring that data transmitted by a node is able to be processed by the appropriate application process on the recipient node.
The transport protocol is commonly responsible for providing guaranteed delivery and adaptation to changing network conditions, such as bandwidth changes or congestion. Some transport protocols, such as UDP, do not provide such capabilities. Applications that leverage UDP either implement their own means of guaranteed delivery or congestion control, or these capabilities simply are not required for the application.
The components mentioned previously, including transport, session, presentation, and application layers, represent a grouping of services that dictate how application data is exchanged between disparate nodes. These components are commonly called Layer 4 through Layer 7 services, or L4—7 services, or application networking services ANS. L4—7 services rely on the packet routing and forwarding services provided by lower layers, including the network, data link, and physical layers, to move segments of application data in network packets between nodes that are communicating.
With the exception of network latency caused by distance and the speed of light, L4—7 services generally add the largest amount of operational latency to the performance of an application. This is due to the tremendous amount of processing that must take place to move data into and out of buffers transport layer , maintain long-lived sessions between nodes session layer , ensure data conforms to representation requirements presentation layer , and exchange application control and data messages based on the task being performed application layer.
Figure shows an example of how L4—7 presents application performance challenges. Figure The performance challenges caused by L4—7 can generally be classified into the following categories: latency, bandwidth inefficiencies, and throughput. These are examined in the following three sections. L4—7 latency is a culmination of the latency components added by each of the four layers involved: application, presentation, session, and transport.
Given that presentation layer, session layer, and transport layer latency are typically low and have minimal impact on overall performance, this section focuses on latency that is incurred at the application layer.
By default, TCP uses a cumulative acknowledgement scheme that forces the sender to either wait for a roundtrip to learn if any packets were not received by the recipient or to unnecessarily retransmit segments that may have been correctly received. SACK allows the receiver to inform the sender about all segments that have arrived successfully, so the sender only needs to retransmit the segments that have actually been lost.
BIC TCP then sets the maximum window size value to the size of the window just before the packet loss event occurred. Because packet loss occurred at the maximum window size, the network can transfer traffic without dropping packets whose size falls within the minimum and maximum window size values. If BIC TCP does not register a packet loss event at the updated maximum window size, that window size becomes the new minimum. If a packet loss event does occur, that window size becomes the new maximum.
These compression technologies reduce the size of transmitted data by removing redundant information before sending the shortened data stream over the WAN.
By reducing the amount of transferred data, WAAS compression can reduce network utilization and application response times. When a WAE uses compression to optimize TCP traffic, it replaces repeated data in the stream with a much shorter reference, then sends the shortened data stream out across the WAN.
The receiving WAE uses its local redundancy library to reconstruct the data stream before passing it along to the destination client or server. The WAAS compression scheme is based on a shared cache architecture where each WAE involved in compression and decompression shares the same redundancy library.
LZ compression operates on smaller data streams and keeps limited compression history. DRE operates on significantly larger streams typically tens to hundreds of bytes or more and maintains a much larger compression history.
Large chunks of redundant data is common in file system operations when files are incrementally changed from one version to another or when certain elements are common to many files, such as file headers and logos. Cisco WAAS uses application-intelligent software modules to apply these acceleration features. In a typical Common Internet File System CIFS application use case, the client sends a large number of synchronous requests that require the client to wait for a response before sending the next request.
Compressing the data over the WAN is not sufficient for acceptable response time. If all these requests are sent over a ms round-trip WAN, the response time is at least 70 seconds x 0. Each WAAS device uses optimization policies to match specific types of the traffic to an application and to determine whether that application traffic should be optimized and accelerated.
The following WAAS application accelerators are available:. You must choose one or the other to operate on WAAS peer devices because they cannot operate simultaneously on the same device and both peers must use the same accelerator. You must enable the accelerator on both of the peer WAEs at either end of a WAN link for all application accelerators to operate. File Services include the following features:. The Edge WAE is a client-side, file-caching device that serves client requests at remote sites and branch offices.
The device is deployed at each branch office or remote campus, replacing file and print servers and giving local clients fast, near-LAN read and write access to a cached view of the centralized storage. By caching the data most likely to be used at these sites, Edge WAEs greatly reduce the number of requests and the volume of data that must be transferred over the WAN between the data center and the edge.
Data returned from the data center is distributed by the Edge WAE to the end user who requested it. The Core WAE is a server-side component that resides at the data center and connects directly to one or more file servers or network-attached storage NAS. The data center Core WAEs can provide load balancing and failover support. Core WAEs can be arranged in logical clusters to provide scalability and automatic failover capabilities for high-availability environments.
The WAAS software includes the following print services options:. Note The legacy print services feature is no longer supported. Legacy print services users must migrate to another print services option. These services eliminate the need for a separate hardware print server in the branch office. The WAAS software allows you to configure a virtual blade, which allows you to add services running in their own operating environments to your WAAS system.
You can install an operating system and applications to work with your WAAS system and provide additional services for the users on your network. The default administrator username is admin and the password is default. Ensure that your web browser is set to use Unicode UTF-8 character encoding.
Click Cancel to proceed to the Central Manager login screen. This happens because the Central Manager uses a self-signed certificate. Click on the link Continue to this website not recommended. You can permanently install the certificate to avoid this error in the future. To install the certificate in Internet Explorer 8, click the red Certificate Error button in the address bar and choose View Certificates.
Click Install Certificate , then click Next. Select Automatically select the certificate store based on the type of certificate and click Next , click Finish , then click Yes on the security warning, click OK on the acknowledgement, and click OK on the Certificate dialog. The certificate installation procedure differs depending on the browser. When you log into the Central Manager the first time, you are prompted to install Google Chrome Frame.
Choose a language, click Get Google Chrome Frame , and follow the prompts to download and install the plug-in. If you do not want to install the plugin, click the link to continue without installing Google Chrome Frame. The number of concurrent sessions is unlimited by default. To change the number of permitted concurrent sessions, set the System.
Note A user must log off the Central Manager to end a session. If a user closes the browser or connection without logging off, the session is not closed until after it times out in 10 minutes by default, up to a possible maximum of minutes. If the number of concurrent sessions permitted also is exceeded for that user, there is no way for that user to regain access to the Central Manager GUI until after the timeout expires.
Note After an upgrade, downgrade, or new installation, you must first clear the cache in your browser, close the browser, and restart the browser session to the WAAS Central Manager. In the Devices and AppNav Clusters menus, a small target icon appears when you hover over a device or cluster name. Place your cursor over the target icon to open a pop-up that shows the device or cluster status see Figure Figure Devices Context Menu.
Menus contain different functions when a particular device, device group, AppNav Cluster, or location is selected than when you are in the global context. Some menu options contain submenus. Hover over the triangle to the right of the menu option name to open the submenu. Table Menu Descriptions. In the global context, allows you to go to the dashboard for your WAAS network. In a context other than global, this menu is named with the entity name and allows you to activate devices, view users, assign groups or devices, or view the dashboard or home screen of the entity.
Allows you to configure WAAS services and settings. Allows you to see network traffic and other charts and reports to monitor the health and performance of your WAAS network. Allows you to manage and schedule reports for your WAAS network. Contains troubleshooting tools.
Allows you to manage user accounts, passwords, secure store, licenses, and virtual blades, update the WAAS software, and view system logs and messages.
Table Taskbar Icon Descriptions continued. Deletes a WAAS element, such as a device, and device group. Create or Add.
Advanced Search. Filters the information in a table to make it easier to locate a specific item. View All. The commands and data entered by you are transferred to the centralized server and you get the results from the central station. This facilitates keeping all your data at a central place while allowing you to work from different stations. Each of the components has its own advantages to keep your WAN, a step ahead of others. The data center WAE performs the following actions:.
If the data center WAE has optimization disabled, then an optimized connection will not be established and the traffic passes over the network unoptimized. Note If unoptimized traffic reaches a WAE, the WAE forwards the traffic in pass-through mode without affecting the performance of the application using the passed-through connection.
Cisco WAAS contains the following services that help optimize traffic over your wide area network:. TFO protects communicating clients and servers from negative WAN conditions, such as bandwidth constraints, packet loss, congestion, and retransmission. The receive window size determines the amount of space that the receiver has available for unacknowledged data.
Windows scaling allows TCP endpoints to take advantage of available bandwidth in your network and not be limited to the default window size specified in the TCP header.
Increasing TCP's initial window size provides the following advantages:. With an initial window of at least two segments, the receiver generates an ACK response after the second data segment arrives, eliminating the wait on the timeout. This increased buffer helps the two WAEs participating in the connection keep the link between them full, increasing link utilization.
Selective Acknowledgement SACK is an efficient packet loss recovery and retransmission feature that allows clients to recover from packet losses more quickly than the default recovery mechanism used by TCP.
By default, TCP uses a cumulative acknowledgement scheme that forces the sender to either wait for a roundtrip to learn if any packets were not received by the recipient or to unnecessarily retransmit segments that may have been correctly received.
SACK allows the receiver to inform the sender about all segments that have arrived successfully, so the sender only needs to retransmit the segments that have actually been lost. When your network experiences a packet loss event, BIC TCP reduces the receiver's window size and sets that reduced size as the new value for the minimum window. BIC TCP then sets the maximum window size value to the size of the window just before the packet loss event occurred.
Because packet loss occurred at the maximum window size, the network can transfer traffic without dropping packets whose size falls within the minimum and maximum window size values.
If BIC TCP does not register a packet loss event at the updated maximum window size, that window size becomes the new minimum. If a packet loss event does occur, that window size becomes the new maximum.
These compression technologies reduce the size of transmitted data by removing redundant information before sending the shortened data stream over the WAN. By reducing the amount of transferred data, WAAS compression can reduce network utilization and application response times. When a WAE uses compression to optimize TCP traffic, it replaces repeated data in the stream with a much shorter reference, then sends the shortened data stream out across the WAN.
The receiving WAE uses its local redundancy library to reconstruct the data stream before passing it along to the destination client or server. The WAAS compression scheme is based on a shared cache architecture where each WAE involved in compression and decompression shares the same redundancy library. LZ compression operates on smaller data streams and keeps limited compression history. DRE operates on significantly larger streams typically tens to hundreds of bytes or more and maintains a much larger compression history.
Large chunks of redundant data is common in file system operations when files are incrementally changed from one version to another or when certain elements are common to many files, such as file headers and logos. Even though TFO optimizes traffic over a WAN, protocol messages between branch office clients and remote servers can still cause slow application response time. To resolve this issue, each WAAS device contains application proxies that can respond to messages locally so that the client does not have to wait for a response from the remote server.
The application proxies use a variety of techniques including caching, command batching, prediction, and resource prefetch to decrease the response time of remote applications.
Cisco WAAS uses application-intelligent software modules to apply these acceleration features. In a typical Common Internet File System CIFS application use case, the client sends a large number of synchronous requests that require the client to wait for a response before sending the next request. Compressing the data over the WAN is not sufficient for acceptable response time.
If all these requests are sent over a ms round-trip WAN, the response time is at least 70 seconds x 0. Each WAAS device uses application policies to match specific types of traffic to an application and to determine whether that application traffic should be optimized and accelerated. For more information, see the "File Services for Desktop Applications" section.
Secure NFS traffic is not accelerated. The SSL accelerator also provides secure management of the encryption certificates and keys. Microsoft Outlook clients are supported. The video accelerator automatically splits one source video stream from the WAN into multiple streams to serve multiple clients on the LAN. The Windows print accelerator supports Windows and Windows Server print servers.
To enable or disable application accelerators, see the "Enabling and Disabling the Global Optimization Features" section on page You must enable the accelerator on both of the peer WAEs at either end of a WAN link for all application accelerators to operate. By fulfilling the client's request locally, the WAE minimizes the traffic sent over the WAN and reduces the time it takes branch office users to access files and many desktop applications, allowing enterprises to consolidate their important information into data centers.
Note WAAS version 4. The new transparent mode requires no core, edge, or connectivity configuration. You configure the legacy mode the same as in WAAS version 4. These two modes are mutually exclusive. We recommend using the new transparent mode if you have no need to interoperate with WAAS 4. This provides users with faster first-time file access, and makes more efficient use of available bandwidth.
This service accelerates print traffic between clients and a Windows print server located in the data center. This option requires no configuration but does require that the CIFS accelerator and Windows print acceleration be enabled. For more information, see the "Enabling and Disabling the Global Optimization Features" section on page You can install a Windows print server in a virtual blade on the branch WAE, which allows you to manage printing by using standard Windows print server functionality.
For more information, see Chapter 14, "Configuring Virtual Blades. All three of these services eliminate the need for a separate hardware print server in the branch office.
The WAAS software allows you to configure a virtual blade, which allows you to add services running in their own operating environments to your WAAS system.
You can install an operating system and applications to work with your WAAS system and provide additional services for the users on your network. The default administrator username is admin and the password is default. For information on creating accounts and changing passwords, see Chapter 7, "Creating and Managing Administrator User Accounts and Groups.
Ensure that your web browser is set to use Unicode UTF-8 character encoding. The number of concurrent sessions is unlimited by default. To change the number of permitted concurrent sessions, set the System.
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