3.4.2.1 Availability Parameters 

The following are suggested parameters for HTTP availability that can identify if a service 

has failed: 

Parameter Name 

General Description 

RequestException 

Any errors that occur in making a request such as failure 

to connect to a server or DNS lookup failures 

ReplyStatus 

Use to capture the status code. 5xx reply status indicate a 

server error 

ServiceErrorHeader 

Use to capture service error headers that indicate failure in 

a backend component that service delivery depends on. 

These headers are required as backend component failures 

will return valid HTTP responses that cannot be detected 

as an error. These headers must be agreed with the Service 

Provider so that they can be detected in HTTP responses 

from the service 

Table 3: Availability Parameters 

Although, there are other parameters that could also be monitored such as the IP address of 

the client making the request, the ones that are identified above are key parameters for 

analysing the performance availability of HTTP. 

3.5 Parameter Capture 

Having defined base performance and availability parameters, the next issue is where to 

capture these parameters to give an accurate reflection of the end user experience. The 

options available include  

Monitor on the server side 

Monitor between the browser and server by using a proxy: The implications of 

where to place such a proxy have been discussed already.