1. Introduction to Computer Networks
Foundation
Ilam University
Mozafar Bag-Mohammadi

2. Statistical Multiplexing Inter-Process Communication
Outline
Introduction
Statistical Multiplexing
Inter-Process Communication
Network Architecture
Performance Metrics

3. Introduction
Building a network to support diverse ranges of applications
Distributed computing.
Multimedia.
Telecommunication.
E-commerce, etc.
What kind of technology do we need?
Hardware.
Software.

4. First Step What is computer Network?
Different views.
Differences from other networks, Its generality.
What is requirements? Different perspective:
Network provider
Network designer
Application programmer

5. Design goals Connectivity Scalability Simplicity Efficiency
For designers.
Most importantly for users.
Efficiency
cost
performance
Support for common user services.

6. Building Blocks Nodes: PC, special-purpose hardware…
hosts
switches, routers and gateways
Links: coaxial cable, optical fiber…
point-to-point
multiple access …

7. Switched Networks A network can be defined recursively as...
two or more networks connected by two or more nodes
two or more nodes connected by a link, or

8. Strategies Circuit switching: carry bit streams
Connection oriented.
Original telephone network
Dedicated resource.
Packet switching: store-and-forward messages
Connectionless (IP) or connection oriented (ATM)
Shared resource.
Packet switching is the focus of computer Networks.

9. Addressing and Routing
Address: byte-string that identifies a node
usually unique
Routing: process of forwarding messages to the destination node based on its destination address
Types of addresses
unicast: node-specific
broadcast: all nodes on the network
multicast: some subset of nodes on the network

10. Multiplexing (resource sharing)
Time-Division Multiplexing (TDM)
Frequency-Division Multiplexing (FDM) L1 L2 L3 R1 R2 R3
Switch 1
Switch 2

11. Statistical Multiplexing
On-demand time-division
Schedule link on a per-packet basis
Packets from different sources interleaved on link
scheduling
fairness, quality of service
Buffer packets that are contending for the link
Buffer (queue) overflow is called congestion …

12. Packet Switching A node in a packet switching network incoming links
outgoing links
Memory

13. Inter-Process Communication
Turn host-to-host connectivity into process-to-process communication regardless where the process are.
Give a unified view and fill gaps between what applications expect and what the underlying technology provides.
Host
Host
Application
Host
Channel
Application
Host
Host

14. IPC Abstractions Request/Reply (Client-server)
Guarantee delivering data, and might protect privacy and integrity.
distributed file systems (NFS)
digital libraries (web)
File Transfer (FTP)
Stream-Based- sequence or stream of bits.
Video on demand:
sequence of frames. Delay constrained, but can be fetched before hand.
For example, a 1/4 NTSC with 352x240 pixels and 24 bit color. (352 x 240 x 24)/8=247.5KB
Assuming 30 frame per second => 7500KBps = 60Mbps
Video Conferencing-
tightly delay bounded. VIC From Berkeley.
Both application can tolerate packet loss.

15. Reliability in the network?
What Goes Wrong in the Network?
Bit-level errors (electrical interference), a bit is corrupted or a burst error.
Packet-level errors (congestion)
Messages are delayed
Messages are deliver out-of-order
Packet loss
Third parties eavesdrop
Link and node failures

16. Performance Metrics Bandwidth (throughput) Latency (delay)
data transmitted per time unit
link versus end-to-end
notation
KB = 210 bytes
Mbps = 106 bits per second
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 (light speed)
Transmit = Size / Bandwidth

17. Bandwidth versus Latency
Relative importance
Latency bounded- sending 1-byte by client, 1ms vs 100ms dominates sending a message on a 1Mbps or 100Mbps link
Bandwidth Bounded- sending 25MB image: 1Mbps vs 100Mbps dominates 1ms vs 100ms delayed channel.
Infinite bandwidth
RTT dominates
Throughput = TransferSize / TransferTime
TransferTime = RTT + 1/Bandwidth x TransferSize
1-MB file to 1-Gbps link the same as 1-KB packet to 1-Mbps link.

18. Delay x Bandwidth Product
Amount of data “in flight” or “in the pipe”
Example: 100ms x 45Mbps = 560KB
We are usually more interested in 2 times of this value
Since it take RTT to hear from receiver.

19. Host-to-host connectivity
Layering
Use abstractions to hide complexity and decompose to manageable components.
Abstraction naturally lead to layering
Alternative abstractions at each layer
Application programs
Request/reply
Message stream
channel
channel
Host-to-host connectivity
Hardware

20. Layering Advantages Disadvantages
Modularity – protocols easier to manage and maintain
Abstract functionality –lower layers can be changed without affecting the upper layers
Reuse – upper layers can reuse the functionality provided by lower layers
Disadvantages
Information hiding – inefficient implementations

21. Protocols
Building blocks of a network architecture, or layer abstraction.
Each protocol object has two different interfaces
service interface: operations on this protocol
peer-to-peer interface: messages exchanged with peer
Term “protocol” is overloaded
specification of peer-to-peer interface
module that implements this interface

22. Interfaces Host 1 Host 2 Service High-level High-level object
Protocol
Protocol
Peer-to-peer
interface

23. Protocol Machinery Protocol Graph
Nodes are protocols and edge are depends on.
most peer-to-peer communication is indirect
peer-to-peer is direct only at hardware level
Digital
library
application
Video
RRP
MSP
HHP
File
Host 1
Digital
library
application
Video
RRP
MSP
HHP
File
Host 2

24. Protocol 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

25. ISO OSI Reference Model
ISO – International Standard Organization
OSI – Open System Interconnection
Started to 1978; first standard 1979
ARPANET started in 1969; TCP/IP protocols ready by 1974
Goal: a general open standard
allow vendors to enter the market by using their own implementation and protocols

26. ISO Architecture Telnet, FTP, TFTP MSB, integer Manage TCP streams
End host
End host
Telnet, FTP, TFTP
MSB, integer
Manage TCP streams
Message, P2P(process)
Packet, routing
Frame, CRC
Raw bit pipe
Application
Application
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
The last 3 protocols are implemented in all elements in the
Network.

27. Encapsulation
A layer can use only the service provided by the layer immediate below it
Each layer may change and add a header to data packet
data
data
data
data
data
data
data
data
data
data
data
data
data
data

28. OSI Model Concepts Service – says what a layer does
Interface – says how to access the service
Protocol – says how is the service implemented
a set of rules and formats that govern the communication between two peers

29. Physical Layer (1)
Service: move the information between two systems connected by a physical link
Interface: specifies how to send a bit
Protocols: coding scheme used to represent a bit, voltage levels, duration of a bit
Examples: coaxial cable, optical fiber links; transmitters, receivers

30. Datalink Layer (2) Service:
framing, i.e., attach frame separators
send data frames between peers
others:
arbitrate the access to common physical media
ensure reliable transmission
provide flow control
Interface: send a data unit (packet) to a machine connected to the same physical media
Protocols: physical layer addresses, implement Medium Access Control (MAC) (e.g., CSMA/CD)…

31. Network Layer (3) Service:
deliver a packet to specified destination
perform segmentation/reassemble
others:
packet scheduling
buffer management
Interface: send a packet to a specified destination
Protocols: define global unique addresses; construct routing tables

32. Transport Layer (4) Services:
provide an error-free and flow-controlled end-to-end connection
multiplex multiple transport connections to one network connection
split one transport connection in multiple network connections
Interface: send a packet to specified destination
Protocols: implement reliability and flow control
Examples: TCP and UDP

33. Session Layer (5) Service: Interface: depends on service
full-duplex
access management, e.g., token control
synchronization, e.g., provide check points for long transfers
Interface: depends on service
Protocols: token management; insert checkpoints,

34. Presentation Layer (6)
Service: convert data between various representations
Interface: depends on service
Protocol: define data formats, and rules to convert from one format to another

35. Application Layer (7) Service: any service provided to the end user
Interface: depends on the application
Protocol: depends on the application
Examples: FTP, Telnet, WWW browser

36. Internet Architecture
Defined by Internet Engineering Task Force (IETF). Developed in mid 60s in the ARPANET project.
No assumption about the network tech. …
FTP
HTTP NV
TFTP
TCP
UDP IP
NET 1 2 n

37. Internet Architecture
Hourglass Design, IP is the focal point. Delivery is separated from end-to-end process channel.
No restrict layering
Application vs Application Protocol (FTP, HTTP)
Network IP
TCP
UDP
Application

38. OSI vs. TCP/IP
OSI: conceptually define services, interfaces, protocols
Internet: provide a successful implementation IP
LAN
Packet
radio
TCP
UDP
Telnet
FTP
DNS
Application
Application
Presentation
Session
Transport
Transport
Network
Internet
Datalink
Host-to-
network
Physical
OSI
TCP