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Attributes and Technologies...^1
Network
Attributes and Technologies
Victor S. Frost
Dan F. Servey Distinguished Professor Electrical Engineering and Computer Science University of Kansas 2335 Irving Hill Dr. Lawrence, Kansas 66045 Phone: (785) 864-4833 FAX:(785) 864- e-mail: [email protected] http://www.ittc.ku.edu/
Network Characterization
Network impairments
¾ The physical environment impacts
network protocols
Network performance criteria
Basic networking technologies
¾ Circuit Switching
¾ Packet Switching
¾ Virtual Circuit Switching
Attributes and Technologies...^3
Network Impairments
Propagation Delay:
¾ The Speed of Light Limitation Propagation delay = Distance (m)/(Speed of Light m/s) ¾ Example: 3000 km fiber link Speed of light in fiber = 0.66(3x10 8 m/s) Propagation delay = 3000x10^3 m/ 0.66(3x10 8 m/s)= 15ms Speed of light in free space= 1.0(3x10 8 m/s) Speed of light in coax= 0.88(3x10^8 m/s)
Clocking time
Section 3.1.
Packet
Source Destination
Clocking time = L/C = 1 ms
Example: Distance = 3000km, Data rate = 1 Mb/s, Packet size = 1000 bits
Propagation time = 10 ms
Network Impairments: Propagation Delay
Satellite Networks
¾ 500ms
Terrestrial Networks
PAN: Personal Area Networks [BAN: Body Area Network]
¾ 3 m or 10ns
DAN.: Desk Area Networks
¾ 3 m or 10ns
LAN: Local Area Networks
¾ 3 Km or 10us
Attributes and Technologies...^7
Network Impairments:
Error Environment
Random, bit errors
are independent
Bursty, bit errors are
correlated and come
in groups,
Good StateGood State Very LowVery Low Error RateError Rate
Bad StateBad State Very HighVery High Error RateError Rate
Good StateGood State Very LowVery Low Error RateError Rate
Bad StateBad State Very HighVery High Error RateError Rate
BER= 10 -12^ BER= 10 -
Network Impairments:
Error Environment
Random, bit errors
are independent
Bursty, bit errors are
correlated and come
in groups,
Good StateGood State Very LowVery Low Error RateError Rate
Bad StateBad State Very HighVery High Error RateError Rate
Good StateGood State Very LowVery Low Error RateError Rate
Bad StateBad State Very HighVery High Error RateError Rate
BER= 10 -12^ BER= 10 -
Attributes and Technologies...^9
Network Impairments:
Example: Impact of delay and errors:
¾ Link rate 600 Mb/s
¾ Free Space
¾ Link distance 3000 km 10ms
¾ Packet size:
- Payload 48 bytes
- Overhead 5 bytes
- Total 53 bytes ( 424 bits )
Network Impairments:
424 bits/(600Mb/s) = .7us/packet 10ms/(0.7us/packet) = 14,285 packets in flight
Question: How do you cope with packets in error?
Attributes and Technologies...^13
Network Impairments and
Application Types
Non Real time (elastic) applications ¾ Can tolerate delay variance ¾ Can not tolerate errors
- E-mail
- Telnet
- FTP
- www ¾ Require accurate delivery of information ¾ Does not require ‘timely’ delivery of data
Network Performance Criteria
Response time T (^) R : The time to “correctly” transmit a packet from Source to destination. “correctly” implies Response time includes acknowledgments
Source Host
Network Interface Card
Network
Destination Host
Network Interface Card
Examine key components of delay
Attributes and Technologies...^15
Network Performance Criteria:
Response Time
Time from source applications to NIC
Waiting time in NIC to enter the network: buffering time
Time to transmit the packet: clock the packet into the network
Time for the network to deliver the packet to the destination’s NIC
Time for destination’s NIC to generate an acknowledgment
Time for the acknowledgment to reach the source host: repeating the above steps
Network Performance Criteria:
Response Time Dependencies
State of the network ¾ Current topology ¾ Active nodes ¾ Active links
State of the other users ¾ Congestion Errors
State of source/destination host Link speeds
Message sizes
Message priorities
Attributes and Technologies...^19
Network Performance Criteria
Throughput in b/s, packets/sec,
cells/sec
Normalized throughput
S =^ R C
where
R = Average error free rate (b/s) passing a reference point in the network
S = % time the network is carrying error free packets-goodput
C = Link Capacity (b/s)
Network Performance Criteria
Channel (or link) utilization:
¾ The % time the channel (or link is busy)
Channel Efficiency
¾ The % time the channel is carrying user
information (impact of overhead)
Let D = #user data bits / packet H = # network overhead bits / packet then Channel efficiency = S( D D + H
)
Attributes and Technologies...^21
Network Performance Criteria
Channel Capacity, Smax, is the maximum
obtainable throughput over the entire range
of input traffic intensities, i.e., offered load.
Offered Load
Throughput Ideal Case 1
1
s max
Network Performance Criteria:
Other Throughput Metrics
Maximum lossless throughput
Peak throughput
Full load throughput
Transfer from local to remote host memory as fast as possible
Attributes and Technologies...^25
Network Performance Criteria: Case Study
With DS
Access
Lines
Network Performance Criteria
Blocking Probability
¾Packet
¾Call Will derive & apply blocking formulas later
Fairness
Security
Reliability
Attributes and Technologies...^27
Network Performance Criteria
Reliability: The reliability of a network
can be defined as the probability that the functioning nodes are connected to working links. Reliability = 1 - Network Failure
Here lets assume all nodes are working
and analyze simple ring and tree networks
Network Performance Criteria
4 links
5 links:
every node has two paths
Tree Network
Topology
Ring Network
Topology
NE=Network Element
NE
NE
NE NE
NE
NE
NE (^) NE
NE
NE
Attributes and Technologies...^31
Network Performance Criteria
But
(1-p) 4 = 1 - 4p + 6p^2 - 4p^3 + p^4
Prob[network failure] =
4p - 6p^2 + 4p^3 - p^4
Assuming p is small then
for 5 node tree network the Prob[network failure] ≈ 4p
Network Performance Criteria
Reliability for a 5 node ring network
Ring network has 5 links
Ring network can have one link failure and
still be working, note one more link can fail
Let q = 1 - p=probability of link good
Prob[network good]=Prob[all good or one
failed and 4 good] = q 5 + 5p q^4
So Prob[network failure] =
1 - q^5 - 5p q^4
∑= =
5 1 Prob[linkjfailedandallotherlinksgood]5pq^4 j
Attributes and Technologies...^33
Network Performance Criteria
Expanding Prob[network failure] =
10p^2 q^3 + 10p^3 q 2 + 5p^4 q +p^5
The dominant term (assuming p small)
is 10p^2 q^3
Network Performance Criteria
Tree Ring
p 4p 10p^2 q^3
10 -5^ 4x10-5^10 - 10 -7^ 4x10-7^10 -
Network Failure Probabilities
Attributes and Technologies...^37
Network Performance
Perspective: User-Oriented
Minimum application response time
(Delay guarantee)
Maximum application throughput
(Throughput (b/s) guarantee)
Low loss (Maximum packet loss guarantee)
Highly reliable (Availability guarantee)
Very flexible
Secure
Low cost
Network Performance Perspective:
Network Manager/Provider
Maximum throughput for all users
Effective congestion control
Power = Throughput/Delay
Easy of management
Highly reliable
Fairness
Ease of billing
Low cost
Attributes and Technologies...^39
Network Performance Perspective: Network Designer/Developer/Vendor
Simple design
Robust
Scales
¾ Number of users ¾ Geographical distribution ¾ Speed
Efficient use of resources, CPU, links and
memory
Evolvable
Network Performance:
What Can the Network Guarantee?
Quality of Service (QoS)-
Absolute/Contractual performance guarantees Examples: ¾ Sustainable rate ¾ Peak rate ¾ Packet delay (average and standard deviation) ¾ Packet/Cell loss rate
Network must reserve resources to provide
QoS
ATM is designed to provide QoS
