Metrics (networking)
Encyclopedia
Metrics is a property of a route
in computer networking, consisting of any value used by routing algorithms to determine whether one route should perform better than another. The routing table stores only the best possible routes, while link-state or topological databases may store all other information as well. For example, Routing Information Protocol
uses hopcount (number of hops) to determine the best possible route.
A Metric can include:
In EIGRP, metrics is represented by an integer from 0 to 4294967295. In Microsoft Windows XP routing it ranges from 1 to 9999.
A Metric can be considered as :
A survey of routing metrics can be found here.
To calculate the availability of a service expressed in this format, you need to do the following calculation:
98% availability on 24/7/52
You can then deduce how many full hours/days per year the service can be unavailable before the supplier is in breach of their Service Level Agreement. In this example, 8736 (hours) - 8561 (hours) = 175 hours (or around 7.3 days).
Routing
Routing is the process of selecting paths in a network along which to send network traffic. Routing is performed for many kinds of networks, including the telephone network , electronic data networks , and transportation networks...
in computer networking, consisting of any value used by routing algorithms to determine whether one route should perform better than another. The routing table stores only the best possible routes, while link-state or topological databases may store all other information as well. For example, Routing Information Protocol
Routing Information Protocol
The Routing Information Protocol is a distance-vector routing protocol, which employs the hop count as a routing metric. RIP prevents routing loops by implementing a limit on the number of hops allowed in a path from the source to a destination. The maximum number of hops allowed for RIP is 15....
uses hopcount (number of hops) to determine the best possible route.
A Metric can include:
- measuring link utilisation (using SNMP)
- number of hops (hop countHop countIn computer networking, hop count refers to the number of routers through which data must pass between source and destination. Each router along the data path constitutes a hop, as the data is moved from one Layer 3 network to another...
) - speed of the path
- packet loss (router congestion/conditions)
- latencyLagLag is a common word meaning to fail to keep up or to fall behind. In real-time applications, the term is used when the application fails to respond in a timely fashion to inputs...
(delay) - path reliability
- path bandwidthBandwidth (computing)In computer networking and computer science, bandwidth, network bandwidth, data bandwidth, or digital bandwidth is a measure of available or consumed data communication resources expressed in bits/second or multiples of it .Note that in textbooks on wireless communications, modem data transmission,...
- throughput [SNMP - query routers]
- loadLoad (computing)In UNIX computing, the system load is a measure of the amount of work that a computer system performs. The load average represents the average system load over a period of time...
- MTUMaximum transmission unitIn computer networking, the maximum transmission unit of a communications protocol of a layer is the size of the largest protocol data unit that the layer can pass onwards. MTU parameters usually appear in association with a communications interface...
In EIGRP, metrics is represented by an integer from 0 to 4294967295. In Microsoft Windows XP routing it ranges from 1 to 9999.
A Metric can be considered as :
- additive - the total cost of a path is the sum of the costs of individual links along the path,
- concave - the total cost of a path is the minimum of the costs of individual links along the path,
- multiplicative - the total cost of a path is the product of the costs of individual links along the path.
A survey of routing metrics can be found here.
Service Level Metrics
Service Level Metrics are concerned with the end user's experience of using the product.Availability
The availability of a computer network (or an individual service) may be expressed using the notation hh/d/ww. For a 24 hour service, seven days a week, available all year around, this would be expressed 24/7/52 (where the 52 stands for the number of weeks in a year). Service providers usually express that a service will be available for a percentage of this time.To calculate the availability of a service expressed in this format, you need to do the following calculation:
98% availability on 24/7/52
Multiply 24 hours per day by 7 days per week by 52 weeks per year = 8736 hours per year
Find 98% of the hours per year = 8736 * 98 / 100 = 8561.28 hours guaranteed
You can then deduce how many full hours/days per year the service can be unavailable before the supplier is in breach of their Service Level Agreement. In this example, 8736 (hours) - 8561 (hours) = 175 hours (or around 7.3 days).