About Global Request Manager

Overview

As the Internet is maturing, content providers, publishers, and e-business operators are looking to the Internet to be a high-performance and reliable delivery mechanism for bandwidth-intensive, rich multimedia content. Service providers and enterprises are building CDNs in order to deliver high-quality content to users quickly and efficiently.

CDNs require a number of components specifically geared toward providing premium service to users, including routing, caching, content management, and reporting services. Global Request Manager (GRM), a feature of a NetCache appliance, can direct content requests to the NetCache appliances that are the closest to the clients; no L4 switches or WCCP routers are required. NetCache appliances in a GRM deployment can also provide caching of content.

NetCache works seamlessly with other products in the Network Appliance content delivery suite that enable telcos and service providers to build robust CDNs. See Integration with other Network Appliance content delivery products for a description of how the Network Appliance ContentDirector application can be used in a GRM deployment for pushing content to NetCache appliances and how the ContentReporter application can be used to create reports of cache activity.

Advantages of directing requests to caches close to clients

A request routing scheme is necessary so that clients can find the content. In traditional caching deployments, L4 switches or WCCP routers are deployed on the network, or client browsers are manually configured to direct requests to NetCache appliances. These solutions are not ideal for CDNs, however, for the following reasons:

CDNs want to provide premium service.
In order to provided premium service, CDNs want to serve content as close to clients as possible. The reason is that the closer the device that serves the content is to the client, the faster the delivery. Additionally, the quality of the content served is likely to be higher. The content is less vulnerable to network problems because it travels a shorter distance.
CDNs typically do not want to reconfigure customer networks to deploy CDN service.
GRM provides an alternative to using L4 switches, WCCP routers, and manual configuration of client browsers to direct content requests to NetCache appliances--an alternative that is especially suited to the needs of CDNs. Often, NetCache appliances configured as GRM agents can be "dropped" into the customer environment; reconfiguration of the customer's network environment is not necessary to support GRM. Reconfiguration might be necessary if your GRM deployment is not typical, for example, if you configure GRM agent caches to fetch content from random origin servers on the Internet as well as from the CDN data centers (not the recommended approach).

Importance of serving content close to users

With the growing demand for streaming media in particular, serving content stored close to users is especially important because network congestion significantly degrades the quality of streaming media. Additionally, streaming media files, which are very large, consume a great amount of network bandwidth. NetCache appliances deployed close to users, working on behalf of the CDN content servers, can store and serve CDN content to clients. A significant amount of bandwidth is saved because the cache can fulfill multiple requests for the same content instead of the content servers at the other end of the WAN.

Standard DNS request resolution

To understand how GRM works, it is useful to understand how standard DNS resolution works. The following illustration shows how standard DNS resolution works.

The purpose of DNS is to provide the mapping between host names, which humans find convenient, and Internet addresses, which are required for routing to devices on computer networks. The previous illustration shows the path of a request issued by the client, which is described in the following table.

Stage	Description
1	When a user sends a request for content, the client queries the local DNS nameserver to try to determine the Internet location of the origin server on which the requested content is stored.
2	DNS is designed to make host information available throughout the Internet, distributed among many sites and organizations, not just in a single central site. Therefore, the local DNS nameserver must pass the DNS query up the DNS nameserver hierarchy until the query reaches a DNS nameserver that is authoritative for (that is, has knowledge of) the DNS domain to which the origin server belongs.
3	The authoritative DNS nameserver returns to the client the IP address associated with the host name in the URL.
4	The client sends the content request (the application-level request) to the IP address of the origin server.

Standard DNS has a number of limitations. The following table contrasts the limitations of standard DNS to GRM.

Standard DNS	GRM
Standard DNS nameservers have no knowledge of proximity.	The GRM returns IP addresses of caches close to clients.
Standard DNS nameservers are unaware of the availability of the Web servers whose IP addresses they return.	The GRM returns only the IP addresses of caches that are available.

Is GRM the right solution for you?

To determine whether GRM is the right solution for you, ask yourself the questions in the following table.

Questions to ask yourself	Considerations
Do you need multiple delivery points for content?	If, for example, all your content is on one Web server and clients from all over the world access that content, delivery is likely to be slow. Using a global request routing solution to serve content from multiple delivery points would result in faster access to content. Additionally, moving content close to users results in fast delivery of high-quality content. GRM is a solution for providing content from multiple locations at optimal speed. To that end, the goal of GRM is to direct clients to the closest delivery point.
Should you use transparency or a global request routing solution?	If you deliver content from multiple locations, you need to determine how content can be served to clients from the delivery point closest to the clients. To use transparency, you must have control of the networks on which clients are located so that you can deploy the L4 switches or WCCP routers needed to redirect requests to the NetCache appliances. In contrast, a global request routing solution does not require control over the networks on which the clients are located.
If a global request routing solution is appropriate, do you want to deploy one product or multiple products to provide request routing and caching services?	A NetCache appliance can provide caching services for multiple protocols plus the GRM feature--all on the same machine. The result is simpler configuration and management. Additionally, NetCache appliances configured for GRM interact seamlessly with other Network Appliance products such as ContentDirector to provide features important to content delivery.

Questions to ask yourself

Considerations

Do you need multiple delivery points for content?

If, for example, all your content is on one Web server and clients from all over the world access that content, delivery is likely to be slow.

Using a global request routing solution to serve content from multiple delivery points would result in faster access to content. Additionally, moving content close to users results in fast delivery of high-quality content.

GRM is a solution for providing content from multiple locations at optimal speed. To that end, the goal of GRM is to direct clients to the closest delivery point.

Should you use transparency or a global request routing solution?

If you deliver content from multiple locations, you need to determine how content can be served to clients from the delivery point closest to the clients.

To use transparency, you must have control of the networks on which clients are located so that you can deploy the L4 switches or WCCP routers needed to redirect requests to the NetCache appliances. In contrast, a global request routing solution does not require control over the networks on which the clients are located.

If a global request routing solution is appropriate, do you want to deploy one product or multiple products to provide request routing and caching services?

A NetCache appliance can provide caching services for multiple protocols plus the GRM feature--all on the same machine. The result is simpler configuration and management. Additionally, NetCache appliances configured for GRM interact seamlessly with other Network Appliance products such as ContentDirector to provide features important to content delivery.