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Networking Fundamentals: Understanding Communication Networks, Study notes of Computer Systems Networking and Telecommunications

University of California - DavisComputer Systems Networking and Telecommunications

An overview of communication networks, discussing the difference between circuit and packet switching, connection oriented and connectionless networks, and multiplexing. It also covers fundamental issues in networking, such as latency, bandwidth, loss rate, and number of end users, and the importance of reliability and real-time communication. The document also introduces network components, types of networks, and the concept of switched and broadcast communication networks.

Typology: Study notes

Pre 2010

Uploaded on 09/17/2009

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koofers-user-8cb 🇺🇸

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Chuah, Fall 2004 1
Lecture 1: Overview
§Introduction to Networking
-Circuit vs. packet switching
-Connection oriented vs. connectionless
-Multiplexing
§Fundamental Issues in Networking
Readings: Chapter 1.1-1.2
Chuah, Fall 2004 2
What is a Communication Network?
(End-system Centric View)
§Network offers a service: move information
-Bird, fire, messenger, post, telegraph, telephone, Internet …
§What distinguish different types of networks?
-The services they provide
§What distinguish the services?
•Latency
•Bandwidth
•Loss rate
•Number of end users/systems
•System interface (how to invoke the service)
•Others
¢reliability, real-time, etc.
Chuah, Fall 2004 3
What is a Communication Network?
(Infrastructure Centric View)
§Communication medium: electron, photon
§Network components
-Links –carry bits from one place to another (or maybe
multiple places): fiber, copper, satellite, …
-Interfaces –attach devices to links
-Switches/routers –interconnect links: electronic/optic,
crossbar/Banyan
-Hosts –communication endpoints: workstations, PDAs,
cell phones, toasters
§Protocols –rules governing communication
between nodes
-TCP/IP, ATM, MPLS, SONET, Ethernet, X.25
§Applications: Web browser, X Windows, FTP, ...
Chuah, Fall 2004 4
Network Components (Examples)
Fibers
Coaxial Cable
Links Interfaces Switches/routers
Ethernet card
Wireless card
Large router
Telephone
switch
pf3
pf4
pf5

Partial preview of the text

Download Networking Fundamentals: Understanding Communication Networks and more Study notes Computer Systems Networking and Telecommunications in PDF only on Docsity!

Chuah, Fall 2004 1

Lecture 1: Overview

ß Introduction to Networking

  • Circuit vs. packet switching
  • Connection oriented vs. connectionless
  • Multiplexing

ß Fundamental Issues in Networking

Readings: Chapter 1.1-1.

Chuah, Fall 2004 2

What is a Communication Network?

(End-system Centric View)

ß Network offers a service: move information

  • Bird, fire, messenger, post, telegraph, telephone, Internet …

ß What distinguish different types of networks?

  • The services they provide

ß What distinguish the services?

  • Latency
  • Bandwidth
  • Loss rate
  • Number of end users/systems
  • System interface (how to invoke the service)
  • Others ¢ reliability, real-time, etc.

Chuah, Fall 2004 3

What is a Communication Network?

(Infrastructure Centric View)

ß Communication medium: electron, photon

ß Network components

  • Links – carry bits from one place to another (or maybe

multiple places): fiber, copper, satellite, …

  • Interfaces – attach devices to links
  • Switches/routers – interconnect links: electronic/optic,

crossbar/Banyan

  • Hosts – communication endpoints: workstations, PDAs,

cell phones, toasters

ß Protocols – rules governing communication

between nodes

  • TCP/IP, ATM, MPLS, SONET, Ethernet, X.

ß Applications: Web browser, X Windows, FTP, ...

Chuah, Fall 2004 4

Network Components (Examples)

Fibers

Coaxial Cable

Links Interfaces Switches/routers

Ethernet card

Wireless card

Large router

Telephone switch

Chuah, Fall 2004 5

Types of Networks

ß Information type

  • Data vs. telecommunication networks

ß Application type

  • Special purpose (e.g., airline reservation network,

banking network) vs. general purpose network (e.g.,

Internet)

ß Geographical distance: LAN, MAN, WAN

ß Right to use: private vs. public

ß Technologies

  • terrestrial vs. satellite
  • wired vs. wireless, protocols

Chuah, Fall 2004 6

ß Communication networks can be classified based on

the way in which the nodes exchange information:

A Taxonomy of Communication

Networks

Communication Network

Switched Communication Network

Broadcast Communication Network

Chuah, Fall 2004 7

ß Broadcast communication networks

  • Information transmitted by any node is received by every

other node in the network

  • examples: usually in LANs (Ethernet, WLAN)
  • Challenge: coordinate the access of all nodes to the shared

communication medium (Multiple Access Problem)

ß Switched communication networks

  • Information is transmitted to a sub-set of designated nodes
    • examples: WANs (Telephony Network, Internet)
  • Challenge: how to forward information to intended node's)
    • this is done by special nodes (e.g., routers, switches)

running routing protocols

Broadcast vs. Switched

Communication Networks

Chuah, Fall 2004 8

Switched Networks

  • two or more nodes connected by a link, or - two or more networks connected by two or more nodes

ß A network can be defined recursively as...

Chuah, Fall 2004 13

Packet Switched Networks

ß Data entering network is divided into chunks called

“packets”

ß Each packet is passed through the network from node to

node along some path ( Routing )

ß Store-and-forward approach: packets buffered before

transmission

Chuah, Fall 2004 14

Packet Switching: Store -and-Forward

R R R

L

ß Packets move one hop at a time

  • Entire packet must arrive at router before it can be

transmitted on the next link

  • Wait turn at the next link

ß Example:

  • Packet size L, link rate = R, takes L/R seconds to transmit

entire packet

  • End-to-end transmission delay = 3L/R
  • If L is large, e.g., 7.5Mbits, R=1.5 Mbps,

delay = 15 sec

Chuah, Fall 2004 15

Resource Sharing in Packet Switching

ß Packets traversing network share resources with other

packets

  • On demand resource use: statistical resource sharing

ß Aggregate resource demand can exceed amount of

bandwidth available

  • Congestion => packets queue, wait for link use => queuing delay, packet loss

Header Data Trailer

ß How to tell different users apart?

  • Packets have the following structure
  • Packet header & trailer control information, e.g., src/dest address, checksum

Chuah, Fall 2004 16

Packet Switching: Message Segmenting

Now break up the message into 5000

packets

ß Each packet 1,500 bits

ß 1 msec to transmit packet on

one link

ß pipelining: each link works in

parallel

ß Delay reduced from 15 sec to

5.002 sec

Chuah, Fall 2004 17

Statistical Multiplexing

ß Time division, but on demand rather than fixed ß Reschedule link on a per -packet basis ß Packets from different sources interleaved on the link ß Buffer packets that are contending for the link ß Buffer buildup is called congestion ß This is packet switching, used in computer networks

Chuah, Fall 2004 18

Why Statistically Share Resources

ß Efficient utilization of the network

ß Example scenario

  • Link bandwidth: 1 Mbps
  • Each call requires 100 Kbps when transmitting
  • Each call has data to send only 10% of time

ß Circuit switching

  • Each call gets 100 Kbps: supports 10 simultaneous calls

ß Packet switching

  • Supports many more calls with small probability of contention
    • 35 ongoing calls: probability that > 10 active is < 0.0017!

Chuah, Fall 2004 19

Circuit Switching vs Packet Switching

Effect of congestion Call blocking Queuing delay

When can congestion occur At setup time On every packet

Call setup Required Not Needed

Each packet follows the same route Yes No

Store-and -forward transmission No Yes

Potentially wasted bandwidth Yes No

Bandwidth available Fixed Dynamic

Dedicated “copper” path Yes No

Item Circuit-switched Packet-switched

Chuah, Fall 2004 20

Packet-Switching vs. Circuit-Switching

ß Most important advantage of packet-switching

over circuit switching is its ability to exploit

statistical multiplexing:

  • efficient bandwidth usage; ratio between peek and

average rate is 3:1 for audio, and 15:1 for data traffic

  • great for bursty data

ß However, packet-switching needs to deal with

congestion:

  • more complex routers
  • harder to provide good network services (e.g., delay

and bandwidth guarantees)

ß In practice they are combined:

  • IP over SONET, IP over Frame Relay