1. Introduction and Foundation
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2. Introduction & Foundation
About the Book
Computer Networks: A Systems Approach
- Peterson& Davie (5th Edition)
Core Concepts and Fundamental Principles
- standards change
- technology evolves
How network works & how packet header are formatted
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3. Most other Computer Network books
Organized according to layered model given by ISO (International Standards Organization)
OSI (Open Systems Interconnection) Architecture
End host
End host
Application
Application
Partitioning of network functionality into 7 layers
Not a Protocol Graph
- A reference model for a protocol graph
Presentation
Presentation
Session
Session
Transport
Transport
Network
Network
Network
Network
Data link
Data link
Data link
Data link
Physical
Physical
Physical
Physical
One or more nodes
within the network
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4. Introduction & Foundation
Expectations
This class IS about...
Principles and Concepts
General-Purpose Computer Networks
Internet Perspective
Network Software
Designing and Building a System
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5. Introduction & Foundation
Perspective
Network users: services that their applications need, e.g., guarantee that each message it sends will be delivered without error within a certain amount of time
Network designers: cost-effective design e.g., that network resources are efficiently utilized and fairly allocated to different users
Network providers: system that is easy to administer and manage e.g., that faults can be easily isolated and it is easy to account for usage
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6. Introduction & Foundation
Requirements
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7. Connectivity: Building Blocks
Nodes: PC, special-purpose hardware…
hosts
switches
Data Links: coax cable, optical fiber…
point-to-point
multiple access …
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8. Indirect Connectivity: Switched Networks
Nodes forwards data received on one link out on another
A network can be defined recursively as...
two or more nodes connected by a link, or
two or more networks connected by two or more nodes
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9. Introduction & Foundation
The Cloud
The Cloud c
point-to-point
multiple-access link
Switched network
Any other network
covered in the book
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10. Introduction & Foundation
LANs, MANs, WANs
Local Area Network (LAN) – < 1 km
Metropolitan Area Network (MAN) – tens of km
Wide Area Network (WAN) – can be worldwide
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11. Introduction & Foundation
Switching Strategies
Circuit switching: dedicated circuit; dedicated circuit; send/receive a bit stream
Original telephone network
Packet switching: store-and-forward messages, send/receive messages (packets)
Computer networks, Internet
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12. Packet-Switched Networks
Nodes in such a network send discrete blocks to each other. We call each block of data either a packet or a message. These blocks of data corresponds to application data such as
A file
A piece of
An image
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13. Addressing and Routing
Address: byte-string that identifies a node
usually unique
Routing: process of forwarding messages to the destination node based on its address
Types of addresses
unicast: node-specific
broadcast: all nodes on the network
multicast: some subset of nodes on the network
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14. Introduction & Foundation
Multiplexing
Cost-Effective Resource Sharing:
Must share (multiplex) network resources (nodes and links) among multiple users.
Two Common Multiplexing Strategies:
Time-Division Multiplexing (TDM)
Frequency-Division Multiplexing (FDM) L1 L2 L3 R1 R2 R3
Switch 1
Switch 2
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15. Statistical Multiplexing
On-demand time-division rather than fixed
Schedule link on a per-packet basis
Packets from different sources interleaved on link
Buffer packets that are contending for the link
Buffer (queue) overflow is called congestion …
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16. Inter-Process Communication
Application programs running on the hosts connected to the network must be able to communicate in a meaningful way.
Turn host-to-host connectivity into process-to-process communication.
Fill gap between what applications expect and what the underlying technology provides.
Host
Application
Channel
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17. Introduction & Foundation
IPC Abstractions
Network supports common process-to-process channels.
Request/Reply
distributed file systems
digital libraries (web)
Client: process requests access (read/write) to a file
Server: process that supports access to the file
Examples:
FTP (File Transfer Protocol)
NFS (Network File System)
Stream-Based
video: sequence of frames
1/4 NTSC(standard TV image)
= 352x240 pixels (resolution)
24-bits color for each pixel
for each frame:
(352 x 240 x 24)/8,= 247.5KB
frame rate: 30 fps
total  7500KBps = 60Mbps
video applications
on-demand video
video conferencing
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18. Introduction & Foundation
The vic Unix video application
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19. What Goes Wrong in the Network?
Bit-level errors (electrical interference)
Packet-level errors (congestion)
Link and node failures
Messages are delayed
Messages are out-of-order
Third parties eavesdrop
The key problem is to fill in the gap between what
applications expect and what the underlying
technology provides.
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20. Introduction & Foundation
Performance Metrics
Bandwidth (throughput)
data transmitted per time unit
Link(physical) versus end-to-end(logical)
notation
KB = 210 Bytes (or 103 =1,000 Bytes)
Mbps = 220 bits per second (or 106 =1,000,000 bits per seconds)
Latency (delay)
time to send message from point A to point B
one-way versus round-trip time (RTT)
components
Latency = Propagation + Transmit + Queue
Propagation = Distance / c Speed of Light over that wire
Transmit = Size / Bandwidth
3.0  108 m/s (Vacuum)
2.3  108 m/s (Cable)
2.0  108 m/s (Fiber)
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21. Bandwidth versus Latency
Relative importance
1-byte message: latency dominates bandwidth
1ms  100ms (RTT) is important
& 1Mbps  100Mbps (Bandwidth) is not
25MB image: bandwidth dominates latency
1Mbps  100Mbps (Bandwidth) is important
& 1ms  100ms(RTT) is not
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22. Perceived Latency (Response Time) Versus RTT
10,000
5000
2000
1000
500
1-MB object, 1.5-Mbps link
200
1-MB object, 10-Mbps link
Perceived latency (ms)
100
2-KB object, 1.5-Mbps link
2-KB object, 10-Mbps link 50
1-byte object, 1.5-Mbps link
1-byte object, 10-Mbps link 20 10 5 2 1 10
100 R
TT (ms)
Chapter 1, Figure 9
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23. Delay x Bandwidth Product
Amount of data “in flight” or “in the pipe”
Example: 100ms x 45Mbps = 560KB
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24. Introduction & Foundation
Network Architecture
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25. Layering Use abstractions to hide complexity
Abstraction naturally lead to layering
Can have alternative abstractions at each layer
e.g. at Process-to-process channels layer
Application programs
Request/reply
Message stream
channel
channel
Host-to-host connectivity
Hardware
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26. Introduction & Foundation
Protocols
Building blocks of a network architecture
Each protocol object has two different interfaces
service interface: defines operations on this protocol
peer-to-peer interface: defines messages exchanged with peer
Term “protocol” is overloaded
specification of peer-to-peer interface
module that implements this interface
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27. Introduction & Foundation
Interfaces
Host 1
Host 2
Service
High-level
High-level
object
interface
object
Protocol
Protocol
Peer-to-peer
interface
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28. Introduction & Foundation
Protocol Machinery
Protocol Graph
collection of protocols and their dependencies
most peer-to-peer communication is indirect
peer-to-peer is direct only at hardware level
Host 1
Host 2
File
Digital
Video
Digital
File
Video
library
library
application
application
application
application
application
application
RRP
MSP
RRP
MSP
HHP
HHP
RRP - Request/Reply Protocol
MSP - Message Stream Protocol
HHP – Host-to-Host Protocol
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29. Introduction & Foundation
Machinery (cont)
Multiplexing and Demultiplexing (demux key)
Encapsulation (header/body)
Host 1
Host 2
Application
Application
program
program
Data
Data
RRP
RRP
RRP
Data
RRP
Data
HHP
HHP
HHP
RRP
Data
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30. Internet Architecture
Evolved out of experiences with ARPANET
(Advanced Research Projects Agency)
Defined by IETF (Internet Engineering Task Force)
Hourglass Design
Application vs Application Protocol (FTP, HTTP)
Application …
FTP
HTTP NV
TFTP
TCP
UDP IP
NET 1 2 n
Application Protocol
HTTP – Hypertext Transport Protocol
TFTP – Trivial File Transfer Protocol
End-to-end Protocol or Transport Protocol
TCP- Transmission Control Protocol
UDP – User Datagram Protocol
Offers channel abstraction to application programs
Supports the interconnection of multiple network technologies into a single logical internetwork
Network
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31. Standard Architectures
Open Systems Interconnect (OSI) Architecture
International Standards Organization (ISO)
International Telecommunications Union (ITU)
ISO, usually in conjunction with ITU, publishes a series of protocol specification based on the OSI architecture
a “Reference Model” for a protocol graph
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32. OSI Architecture (Open Systems Interconnection)
Partitioning of network functionality into 7 layers
Not a Protocol Graph
A reference model
for a protocol graph
End host
End host
The transport layer and higher layers typically run only on the end hosts
but not on the intermediate switches or routes
Application
Application
Presentation
Presentation -
Session
Session
The unit of data exchanged is commonly called message rather than a packet or frame
Implements process-to-process channel
Transport
Transport
The unit of data exchanged is typically called a packet rather than a frame
Handles routing among nodes within a packet-switched network
Network
Network
Network
Network
Collects a stream of bits into a larger aggregate called a frame
Data link
Data link
Data link
Data link
Handles raw bits over a communication link
Physical
Physical
Physical
Physical
One or more nodes
within the network
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