This is the second lecture of Advanced Computer Network . The Book is :Computer Networks 4th Ed - by : Andrew S. Tanenbaum

1. 5/2/2014
Characteristics of WANs
Covers large geographical areas
Circuits provided by a common carrier
Consists of interconnected switching nodes
Traditional WANs provide modest capacity
• 64000 bps common
• Business subscribers using T1 service – 1.544 Mbps
common
Higher-speed WANs use optical fiber and transmission
technique known as asynchronous transfer mode (ATM)
• 10s and 100s of Mbps common

2. 5/2/2014
Wide Area Networks
Alternative technologies
• Circuit switching
• Packet switching
• Frame relay
• Asynchronous Transfer Mode (ATM)

3. 5/2/2014
Characteristics of LANs
Like WAN, LAN interconnects a variety of devices
and provides a means for information exchange
among them
Traditional LANs
• Provide data rates of 1 to 20 Mbps
High-speed LANS
• Provide data rates of 100 Mbps to 10 Gbps

4. 5/2/2014
Differences between LANs and WANs
Scope of a LAN is smaller
• LAN interconnects devices within a single
building or cluster of buildings
LAN usually owned by organization that owns the
attached devices
• For WANs, most of network assets are not owned
by same organization
Internal data rate of LAN is much greater

5. Example Networks
The Internet
Connection-Oriented Networks: ATM
Ethernet
Wireless LANs: 802:11
5/2/2014

6. Architecture of the Internet
Overview of the Internet
5/2/2014

7. ATM Virtual Circuits
5/2/2014
ATM cell

8. The ATM Reference Model
5/2/2014

9. Ethernet
Architecture of the original Ethernet
5/2/2014

10. Wireless LANs
(a) Wireless networking with a base station.
(b) Ad hoc networking.

11. Modems
(a) A binary signal
(b) Amplitude modulation
(c) Frequency modulation
(d) Phase modulation
The Local Loop: Modems, ADSL, and Wireless

12. Digital Subscriber Lines
Bandwidth versus distanced over category 3 UTP for DSL.

13. Digital Subscriber Lines
Operation of ADSL using discrete multitone modulation
A typical ADSL equipment configuration.

14. Wireless Local Loops

15. Frequency Division Multiplexing

16. Wavelength Division Multiplexing

17. Time Division Multiplexing
The T1 carrier (1.544 Mbps)

18. Time Division Multiplexing
Multiplexing T1 streams into higher carriers

19. 5/2/2014
Techniques Used in Switched Networks
Circuit switching
• Dedicated communications path between two
stations
• E.g., public telephone network
Packet switching
• Message is broken into a series of packets
• Each node determines next leg of transmission for
each packet

20. Circuit Switching
(a) Circuit switching.
(b) Packet switching.

21. 5/2/2014
Data sent out of sequence
Small size (packets) of data at a time
Packets passed from node to node between source
and destination
Used for terminal to computer and computer to
computer communications
Packet Switching

22. Message Switching
(a) Circuit switching (b) Message switching (c) Packet switching

23. Packet Switching
A comparison of circuit switched and packet-switched networks.

24. 5/2/2014
Effect of Packet Size on Transmission
Effect of Packet Size on Transmission time

25. Propagation and Transmission Delay
Propagation Delay = Distance/Propagation speed
Transmission Delay = Message size/bandwidth bps
Latency = Propagation delay + Transmission delay +
Queueing time + Processing time

26. 5/2/2014
Performance comparison
Circuit switching Packet switching

27. 5/2/2014
Variable vs. Fixed-Length Packets
No Optimal Length
 if small: high header-to-data overhead
 if large: low utilization for small messages
Fixed-Length Easier to Switch in Hardware
 simpler
 enables parallelism

28. 5/2/2014
Network Criteria
Performance
 Depends on Network Elements
 Measured in terms of Delay and Throughput
Reliability
 Failure rate of network components
 Measured in terms of availability/robustness
Security
 Data protection against corruption/loss of data due to:
• Errors
• Malicious users