Introduction
While studying for CompTIA Network+, I totally couldn't understand a difference between Network Metrics and Routing Metrics. Both terms have "Metrics", which confused me.
Once I understood why each one existed, everything fell into place. So I decided to write it down.
Difference between two Metrics
As a premise, two Metrics are used for different purposes.
Network Metrics：
→ Indicator for measuring performance of network
→ System managers use it for surveillance or troubleshooting
Routing Metrics：
→ Value for selecting the best path
→ Routers use it automatically
Network Metrics
Indicator for measuring performance of network
In a CompTIA Network+, 4 metrics are particularly important.
1. Bandwidth
Keyword：Width of road
Meaning：Maximum amout of data that can be sent at one time
Unit：bps・Mbps・Gbps
Good condition：Higher is better
Wide road → It enables many vehicles to drive at the same time
Large Bandwidth → It enebles large amounts of data to be sent at once
2. Latency
Keyword：Period of time signal reaches
Meaning：the time it takes for data to travel from sender to receiver
Unit：ms（milliseconds）
Good condition：Lower is better (Under 20ms is preferable)
Example：
Online video games → 1ms（5G）
4G communication → 30〜50ms
Connection to servers overseas → over 100ms
3. Jitter
Keyword：Variation in delay
Meaning：Latency becomes inconsistent rather than remaining constant
Unit：ms
Good condition：Lower is better
Latency is stable（Low Jitter）：
→ 10ms・10ms・10ms・10ms
Latency is unstable（High Jitter）：
→ 10ms・50ms・5ms・80ms
In case of high Jitter：
・Video call and online video game are lagged
・Quality of voice through VoIP become worse
4. Packet Loss
Keyword：Data loss
Meaning：Portion shows that data don't reach to the destination
Unit：%
Good condition：Lower is better (0% is preferable)
Calculation for Packet Loss
In case that 95 packets are reached even if 100 packets are served：
→ Packet Loss = 5%
In case of high Packet Loss：
・Delay to load Web pages
・Disturb video call
・Fail to download files
Summary table
| Metrics | Meaning | Unit | Good condition |
|---|---|---|---|
| Bandwidth | Maximum amount of data transfer | Mbps・Gbps | Higher is better |
| Latency | Delay time for signal | ms | Lower is better |
| Jitter | Variation in travel time | ms | Lower is better |
| Packet Loss | Data loss | % | Lower is better |
Understanding with highway
Bandwidth = Width of road（The number of lanes）
Latency = Arrival time
Jitter =Bariation of required time
Packet Loss = The proportion for car going missing on the way
Relationships between each metric
Even if bandwidth is bigger, it makes you feel slow due to high latency
Even if latency is lower, call will be low quality due to high jitter
Even if above all is good condition, it makes you feel slow for resending due to high packet loss
Routing Metrics
** It is a value used by routing protocol to prioritize available routes. It works as cost or score for specific route. **
In a nutshell, ** score for network route**.
Why is it needed
Problem：
When multiple routes exists to the same destination, it becomes difficult to determine which one is optimal.
Solution：
Attach value (metric) on each route
→ Give priority to the route having lower value
→ Router can select the best route automatically
Meaning of cost and score
cost：
→ Lower is better
→ Image of the cost for going through the way
score：
→ Evaluation value
→ It changes whether higher or lower is better depending on context
In CompTIA Network+ exam, it is enough to remember *cost ( lower is better) *.
Practical image
In case that there are three routes to the destination：
Route A：Metric = 10 ← Lowest value = Top priority
Route B：Metric = 50
Route C：Metric = 100 ← Highest value = Bottom priority
Router selects Route A which has the lowest metric value
Understanding with a car navigation
Route A：Highway（The distance is long but fast）→ cost 10
Route B：Public road（The distance is short but slow） → cost 50
Route C：Mountain path（The distance is long and slow） → cost 100
A car navigation ( Router ) select Route A which has the lowest cost
Kinds of routing metrics
Used value differs from each protocols.
| Metrics | Meaning | Used protocol |
|---|---|---|
| Hop Count | The number of router that it go through | RIP |
| Bandwidth | Maximum speed on the route | OSPF |
| Latency | Delay time for overall route | EIGRP |
| Cost | Weigh set up by system managers | OSPF |
Organize two metrics table
| Item | Network Metrics | Routing Metrics |
|---|---|---|
| Purpose | Measure the performance | Select routes |
| Use case | Monitoring・Troubleshooting | Route selection by Router |
| Representative indicator | Bandwidth・Latency・Jitter・Packet Loss | Hop Count・Cost・Bandwidth・Latency |
| User | Network administrator | Router（auto） |
Conclusion
Firstly, I couldn't distinguish the difference between each metric.
Once I understood the difference, the purpose behind each metric became clear.
Network Metrics = Measure performance
Routing Metrics = Select route
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