Chapter 3: Network Management
1. Intro
a.
b.
c.
d.
e.
f.
Network map of the world https://www.submarinecablemap.com/#/
https://www.akamai.com/us/en/solutions/intelligent-platform/visualizing-akamai/
http://internettrafficreport.com/
https://www.internetexchangemap.com/
Any mid-size business will have 100’s or 1000’s of switches and routers.
It is expensive and difficult to maintain networks.
2. Quality of Service
a. Network quality of service: To measure the performance of the network
i. Speed: in bits per second. kbps, Mbps, Gbps, Tbps. On a 56kbps modem,
a 4MB photo will take about 12 minutes to download. A HD movie will
take about 6 days.
1. Rated Speed and Throughput: Promised vs speed that you actual
receive.
2. Shared speed: Aggregate and individual throughput. Individual
throughput = aggregate throughput/ number of users.
ii. Availability: percentage of time, network is up.
iii. Errors: percentage of incorrect bits or packets. When network is
overloaded, error rates soar.
iv. Latency: Time delay in receiving packets (in milliseconds). At 125ms,
telephone conversations become difficult.
v. Jitter: Average variability in the latency between successive packets.
1. Ok for most everything but apps like VOIP and video can be
problematic. You may have observed jitters when you see video
slowing down or fast forwarding on its own.
3. Multiplexing
a. Combining multiple signals to take advantage of single transmission line.
b. Why? No need to separate lines for each connection. A single trunk line can carry
signals from multiple devices. Cost effective. Besides not everyone transmits all
the time or even at the same time.
4. Service level agreements
a. For commercial clients, ISPs provides service level agreements that guarantees a
minimum level of service, failing which they have to pay a penalty.
b. SLA guarantees are expressed as worst-case. For example, speed no less than
100mpbs or latency no more than 125ms, or 99.99% uptime.
5. Network design.
a. Networks are critical. You don’t want a university network to go down right
before the exam or even worst during the exam.
b. Network analysis and design are a critical component of setting up a network.
c. Traffic Analysis:
i. How much traffic must flow over each networks many individual
transmission links.
ii. Two site analysis: Say a company has two sites A and B and they need to
communicate at 1Gbps. Then you need a transmission line that can
support 1Gbps.
iii. Three site analysis: Now say there are three sites, A, B, and C. Say A
wants to communicate with B @50Mbps, B wants to communicate with C
@ 100Mbps, and A wants to communicate with C @ 200Mbps. Then the
network will be designed with A & B with 250Mbps link, B&C with
300Mbps link.
iv. Four site analysis: Again, estimate traffic requirements for each pair (there
will be 4C2 pairs or 4!/2!2! = 6pairs. Then just add the max traffic flowing
through each pair and calculate the network requirements.
A
B
C
D
10Mbps
100Mbps
1Gbps
100Mbps
100Mbps
1Gbps
Link: 1.11Gbps
Link: 1.3 Gbps
Link: 2.1Gbps
d. Reliability: Reliability is achieved through redundancy. Redundancy does not
mean just adding a spare line. Redundant lines are also used and included in
capacity planning.
6. Leased lines
a. Point to point links between two sites can be through leased lines from telephone
companies. Leased lines are always on.
Line
Transmission Speed
T1
1.544 M b p s
T3
44.7 M b p s
O C-3
155.58 M b p s
O C-12
622.02 M b p s
O C-48
2.488 M b p s
O C-192
9,953 M b p s
7. Spikes and momentary traffic increase: Traffic spikes last for maximum of a second or
two but can wreak havoc. They cause delays and create latency. Some packets and frame
even get dropped. Spikes can be handled in the following three ways:
a. Add more capacity: Expensive
b. Prioritize Traffic: Voice and Video go through, everything else waits.
c. Give QoS guarantee: e.g. reserved seats in the stadium. Everyone else gets served
on capacity basis.
8. Traffic shaping: Preventative measure to avoid spiking. Edge routers maintain an Access
Control List that specify what to do with different types of traffic. For example,
temporarily block YouTube while traffic normalizes.
9. Centralized network management: Centralized operations to manage and troubleshoot the
networks. They allow network visibility, send commands to individual routers and
switches, and monitor alarms. These software are expensive but well worth the cost.
Alternate is employees travelling to individual nodes to troubleshoot.
10. Ping: Oldest network visibility tool. Send a ping, the device responds. If no response,
something is wrong with the network. Ping helps in diagnosing reachability and latency
problems
11. Traceroute: Shows latency of each hop between routers along the route. High latency
indicates trouble.
12. Simple Network Management Protocol (SNMP):
a. SNMP manager runs on a computer and allows control of managed devices like
switches, routers, access points, firewalls, servers, and PCs.
b. SNMP agent: SNMP manager negotiates with SNMP agent which are installed on
every hosts.
13. Network visualization software: Takes SNMP data and displays it as maps. Helps in
finding root causes of the problems.
14. SDN : Software defined networks: Cloud computing approach to facilitate network
management instead of individual and manual network management.
15. Designing network using Visio.