1. Ram Dantu University of North Texas, rdantu@unt.edu
Practical Networking
Ram Dantu
University of North Texas,

2. Agenda Nuts and Bolts of Internet Access, Edge, and Core Networks
LAN Design
End-user Protocols, Services and QoS
Edge and Core Networks
Performance
Bandwidth and Delay
Security

3. Performance

4. Different Types of Links
Sometimes you install your own!

5. Bigger Pipes! Sometimes leased from the phone company
STS: Synchronous Transport Signal

6. Delay in packet-switched networks
packets experience delay on end-to-end path
four sources of delay at each hop
nodal processing:
check bit errors
determine output link
queueing
time waiting at output link for transmission
depends on congestion level of router A B
propagation
transmission
nodal
processing
queueing

7. Delay in packet-switched networks
Transmission delay:
R=link bandwidth (bps)
L=packet length (bits)
time to send bits into link = L/R
Propagation delay:
d = length of physical link
s = propagation speed in medium (~2x108 m/sec)
propagation delay = d/s
Note: s and R are very different quantitites! A B
propagation
transmission
nodal
processing
queueing

8. Performance Bandwidth (throughput)
Amount of data that can be transmitted per time unit
Example: 10Mbps
link versus end-to-end
Notation
KB = bytes
Mbps = bits per second

9. Time it takes to send message from point A to point B
Latency (delay)
Time it takes to send message from point A to point B
Example: 24 milliseconds (ms)
Sometimes interested in in round-trip time (RTT)
Components of latency
Latency = Propagation + Transmit + Queue + Proc.
Propagation = Distance / SpeedOfLight
Transmit = Size / Bandwidth

10. Relative importance of bandwidth and latency
small message (e.g., 1 byte): 1ms vs. 100ms dominates 1Mbps vs. 100Mbps
large message (e.g., 25 MB): 1Mbps vs. 100Mbps dominates 1ms vs. 100ms
Consider two channels of 1Mbps and 100 Mbps respectively. For a 1 byte message, the available bandwidth is relatively insignificant given a RTT of 1 ms. The transmit delay for each channel is 8 s and 0.08 s, respectively.

11. Delay x Bandwidth Product
e.g., 100ms RTT and 45Mbps Bandwidth = 560KB of data
We have to view the network as a buffer. This may have interesting consequences:
How much data did the sender transmit before a response can be received?
Delay
Bandwidth

12. Example: Hospital Network

13. PACS Network and Remote ConnectivityW V U P
Intensive Care Unit
Operating Room T R S Q O N M F G
Out-patient
RIS
Floors
HIS
PACS Network
INTERNET A
Hospital
Distribution
PACS B C D E H I J K L X