Transcript EECS 122 Communications Networks

TOC: Introduction
Network Examples
Network Components
Ethernet
Interconnected LANs
Internetwork
Types of Networks
Internet
Packets
Transport
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Introduction: Network Examples
UCB
Backbone:



Teleglobe
Global Crossing
Williams
Regional: Palo Alto
Types of Networks
Internet
Packets
Transport
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Network Examples: UCB
SODA
E3
BACKBONE
2nd Floor
Cory
E1
E2
1st Floor
Cory
REGIONAL
LOCAL
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CAMPUS
EVANS
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Network Examples: Backbone
Teleglobe Communications Corporation – Fiber + Satellite
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Network Examples: Backbone
Global Crossing Corporation
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Network Examples: Backbone
Williams Communications
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Network Examples: Regional
Palo Alto Network
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Introduction: Network Components
Links: carry bits from one place to another
(or maybe to many other places)
Interface: attaches device to link
Switch/router: interconnect links
Host: communication endpoint (workstation,
PDA, cell phone, toaster, tank) – connected
to links
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Network Components:
Links
Fibers
Cat5 Unshielded
Twisted Pairs
Coaxial Cable
Wireless
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Network Components:
NIC
Ethernet Network Interface Card
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Network Components
Telephone Switch
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Large Router
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Introduction: Ethernet
Ethernet is a Local Area Network (LAN)
• Architecture: Switch and/or Hub
• System View: Services
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Ethernet: Architecture
Switch and/or Hub:
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Ethernet: System View
Ethernet is a broadcast-capable, multi-access
LAN
Provides a “Link” service between nodes
Abstract view:
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Introduction: Interconnected LANs
LANs interconnected by routers
LAN2
LAN1 R1
LAN3
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R3
R2
R4
Internet
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Introduction: Internetwork
Provides message delivery between multiple
networks that may belong to different
organizations:
ISP 1
Subnet 1
ISP 2
Subnet 2
Example:
Subnet 1 = network of LANs of previous slide
ISP 1 = Sprint, ISP 2 = MCI
Subnet 2 = UCB network
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Introduction: Types of Network
Classification 1: Size, Information, Application
Classification 2: Use, Protocols, Technologies
Switching
Broadcast vs. Switched
 Characteristics
 How to switch
 Taxonomy

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Types of Network: Classification 1
Geographical distance

Local Area Networks (LAN): Ethernet, Token ring,
FDDI
Metropolitan Area Networks (MAN): DQDB, SMDS
 Wide Area Networks (WAN): X.25, ATM, frame relay
 Caveat: LAN, MAN, WAN may mean different
things: Service, network technology, networks

Information type

Data networks vs. telecommunication networks
Application type

Special purpose networks: airline reservation

General purpose network: Internet
network, banking network, credit card network,
telephony, CATV
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Types of Network: Classification 2
Right to use
Private: enterprise networks
 Public: telephony network, Internet

Protocols:
Proprietary: SNA, AppleTalk
 Open: IP

Technologies
Terrestrial vs. satellite
 Wired vs. wireless

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Types of Network:
Broadcast vs. Switched
Broadcast Network:
Switched Network:
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Types of Network:
Characteristics
Broadcast



One to all
Examples: some LANs (Hub-Ethernet, 802.11)
Problem: coordinate the access of all nodes to
the shared communication medium (Multiple
Access Problem)
Switched



One to subset
Examples: WANs (Telephony Network, Internet)
Problem: how to forward information to
intended node(s)
 This is done by special nodes (e.g., routers,
switches) running routing protocols
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Types of Network:
How to Switch?
Circuit-Switched:
1.
2.
3.
Set up circuit between two devices
Exchange information
Release circuit
Packet-Switched:

Send packets with source and destination
addresses
Vircuit-Circuit Switched:
1.
2.
3.
4.
Select path from source to destination (Virtual
Circuit)
Assign a “label” to that path
Send packets with that label
Release Virtual Circuit
{Note: Some VCs are permanent.}
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Types of Network:
Taxonomy
Based on the way in which the nodes
exchange information:
Switched
Circuit
Telephone
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Virtual
Circuit
MPLS
ATM
Frame Relay
Broadcast
Packet
Sw.-Ethernet
Internet
Hub-Ethernet
CATV
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Introduction: The Internet
Overview
Scale
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Internet: Overview
A global network of networks all
using a common protocol (IP, the
Internet Protocol)
Focus of this class
A challenge to understand:


large scale (10’s of millions of users, 10’s
of thousands of networks)
heterogeneity, irregular topology,
decentralized management
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Internet: Scale
• Data from www.nw.com
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Introduction: Packets
Illustration
Main Ideas
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Packets: Illustration
B
1
A | B | ...
2
3
A
B  port 2
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Packets: Main Ideas
The switches have no memory of
packets: scalability
The network is independent of the
applications: flexibility
The packet formats and addresses are
independent of the technology:
extensibility
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Introduction: Transport
Acknowledgments
Link Sharing
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Transport: Acknowledgments
The destination sends back an
acknowledgment for every correct
packet it gets.
The source uses these ACKs to
- Retransmit unacknowledged packets
- Adjust the rate of its transmissions.
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Transport: Link Sharing
Shared links
The sources base their
transmissions on when
they get acknowledgments.
The scheme regulates the
sharing of common links
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