Background: Know: MTTF, availability, Recognize:
The profitability of telecommunications companies depends on their ability to provide a useful service to their customers. Vodafone in Australia has recently announced losses that may see them exit the market because of percieved problems with the quality of their service if their customer numbers keep declining.
The role of the telecommunications engineer is to design networks that fulfill the needs of the customer. Factors that need to be considered include cost, serviceability and maintainability. Service levels specify the qualities of the service offered to customers by a service provider. These qualities may vary in cost to meet the requirements of the customer in terms of speed and reliability. In order to ensure that a specified level of service is being provided the quality must be measurable and measurements provided to prove that the advertised service level is provided.
Some of the metrics that customers might want to have reported to them are service availability, physical access to the system, reliable billing, fast fault rectifictation, performance levels including bandwidth, latency, jitter, packet loss, availabilty and volume. See Akamai Network Performance Comparison for examples of latency and packet loss.
The average throughput of the network, for example 100Mb/s or 1Gb/s.
Delay between two points in the network. The causes of latency include:
- Speed of light - not adjustable by the service provider
- Equipment switching and processing delays - may vary between equipment vendors and models
- Queuing and shaping delays - include delays due to congestion and under-dimensioning
Variation in latency may be caused by congestion.
The percentage of packets lost.
The availability of the service - see the "Measuring availability in 9s" wiki page
The volume of data that is allowed to be transferrred withing a given period - for example 100GByte per month.
Service levels may be subject to contracts between the supplier and customer - see the Service Level Agreements.wiki page.
Examples of Service Levels defined in the SLA for AT&T Broadband - Business Edition are
F. Network Availablity - 99.9%
G. Installation Interval - 5 business days for AT&T provided Service installation
H. Network Latency - 40 milliseconds (ms)
I. Data Delivery (Packet Loss) - 99.9%
I. 24 Hour Service Restoration
Many network performance monitoring tools have been developed to measure service levels - see the Stanford list of network monitoring tools at http://www.slac.stanford.edu/xorg/nmtf/nmtf-tools.html.
Measuring availability in 9s http://tele9752.wikia.com/wiki/XxNE
Network performance http://en.wikipedia.org/wiki/Latency_vs_Bandwidth