Lecture 1 Introduction

Advanced Computer Network
Dan LI
CS Department, Tsinghua University
2012/11/23
1
About Me

Research area




Office


4-104, FIT Building
Homepage


Internet architecture design
Cloud computing and data center networks
Green networking
http://www.netlab.edu.cn:8080/netlab/teacher/lidan/
lidan.html
Email

[email protected]
2012/11/23
2
Teaching Assistant



Yirong Yu
1th year master student
Research direction



Future Internet architecture
Transport layer design
Email

2012/11/23
[email protected]
3
About You

Whether I pronounce your name correctly

The name you like to be called

Make sure about your registration for the
course
2012/11/23
4
Administrative Trivia


You are NOT required to buy any books
Reference materials



Computer Networks, Andrew. S. Tanenbaum
Reading list of papers
Course Web page



http://www.netlab.edu.cn:8080/netlab/teacher/lid
an/FIA.htm
Web learning system
Check it periodically to get the latest information
2012/11/23
5
Course Goals

Graduate Course


Research driven
Understand




How does the Internet work?
What are the Internet’s design principles and
architectures?
What are the current Internet research efforts?
Where is the future Internet architecture heading to?
2012/11/23
6
Course Goals (Cont.)

Appreciate what is good networking research





Real and important problem
Sound solution
Valid research methodology
Attractive presentation
Apply what you learned into a course project
2012/11/23
7
Course Format

9 lectures


Paper presentation and discussion


Please read at least 1 paper for every lecture topic
after the lecture
Two times
Course Project
2012/11/23
8
Course Schedule








Week 1: Introduction
Week 2: Local Area Network and Ethernet
Week 3: Data center network
Week 4: Internetworking & IPv6
Week 5: Intra-domain routing
Week 6: Inter-domain routing
Week 7: Multicast
Week 8: TCP and congestion control (1)
2012/11/23
9
Course Schedule (Cont.)








Week 9: TCP and congestion control (2)
Week 10: P2P and overlay network
Week 11: Mobile & wireless network
Week 12: Network security
Week 13: Future Internet
Week 14: Paper presentation and discussion
Week 15: Course project report
Week 16: Examination
2012/11/23
10
Paper Presentation & Discussion

Tell the whole story of a research paper



Prepare slides
30-minute presentation



Background, motivation, solution, evaluation,
conclusion
Rehearsal one week before presentation
10-minte discussion
Everyone gives a score for your presentation
2012/11/23
11
Course Project

Two options

A survey paper on a certain topic


A paper on novel research idea


Problem definition, solution design, evaluation
Report two times



Problem, existing solutions, comparison
First time: problem, motivation and basic idea
Second time: solution, evaluation,
documentation
Try to publish
2012/11/23
12
Class Disciplines

Keep your mobile phones silent

Do not need to take notes

Ask questions
2012/11/23
13
Grading

Class participation
20%
Presentation
30%
Course project
50%
More important is what you realize/learn
than the grade
2012/11/23
14
Review on Computer Networks

Networking Taxonomy

Internet Overview

Internet Layering Architecture

Important Issues in Future Internet Design
2012/11/23
15
Networking Review

What is a network?



A system of lines/channels that interconnect
nodes
E.g., railroad, highway, telephony network,
computer network
What is a computer network?


2012/11/23
A form of communication network —
moves information
Nodes are general-purpose computers
16
A Taxonomy of Communication
Networks
Communication
Network
Switched
Communication
Network
Broadcast
Communication
Network
2012/11/23
17
Broadcast vs. Switched

Broadcast communication networks


Information transmitted by any node is received by
every other node in the network
Problem: coordinate the access of all nodes to the
shared communication medium (Multiple Access
Problem)
A
2012/11/23
B
C
D
18
E
Broadcast vs. Switched (Cont.)

Switched communication networks

Information is transmitted to a sub-set of
designated nodes


Example: WAN
Problem: how to forward information to intended
node(s)
A’
A
B’
B
2012/11/23
19
Multiplexing in Switched Network

Need to share network resources
D
A’
A
B
C



Conversation 1: A->B
Conversation 2: C->D
How?


Con. 1 gets the forwarding resource of A’ sometimes
Con. 2 gets the forwarding resource of A’ sometimes
2012/11/23
20
Taxonomy of Switched
Communication Networks
Switched
Communication
Network
Circuit-Switched
Communication
Network
2012/11/23
Packet-Switched
Communication
Network
21
Circuit Switching


Source first establishes a connection (circuit)
to the destination
Source sends the data over the circuit


Then the connection is torn down
Example: telephony network


2012/11/23
Early versions: human-mediated switches
Later versions: end-to-end electrical connection
22
Timing in Circuit Switching
Host 1
Node 1
Node 2
Host 2
processing delay at Node 1
propagation delay
between Host 1
and Node 1
Circuit
Establishment
Data
Transmission
propagation delay
between Host 2
and Node 1
DATA
Circuit
Termination
2012/11/23
23
Circuit Switching

A node (switch) in a circuit switching network
incoming links
2012/11/23
Node
24
outgoing links
Circuit Switching (Cont.)

What about many connections?

Many wires


E.g., those big 200-pair cables you sometimes see
A more practical approach is to multiplex
multiple circuits over a single “fast” wire
2012/11/23
25
Circuit Switching:
Multiplexing/Demultiplexing




Time divided in frames and frames divided in slots
Relative slot position inside a frame determines which
conversation the data belongs to
Needs synchronization between sender and receiver
In case of non-permanent conversations

Needs to dynamically bind a slot to a conservation
2012/11/23
26
A Taxonomy of Communication
Networks
Switched
Communication
Network
Circuit-Switched
Communication
Network
2012/11/23
Packet-Switched
Communication
Network
27
Packet Switching


Data divided into multiple packets
At each node the entire packet is received, stored,
and then forwarded to the next node

Store-and-Forward Networks
incoming links
Node
Memory
2012/11/23
28
outgoing links
Packet Switching (Cont.)


Data from any conversation can be
transmitted at any given time
How to tell them apart?

2012/11/23
Use meta-data (header) to describe packet
29
Packet-Switching vs. CircuitSwitching

Advantage of packet-switching over circuit
switching


Disadvantage



Efficient bandwidth usage
More complex routers
Harder to provide good network services (e.g., delay
and bandwidth guarantees)
In practice they are combined

IP over SONET, IP over Frame Relay
2012/11/23
30
A Taxonomy of Communication
Networks
Packet-Switched
Communication
Network
Datagram
Network
2012/11/23
Virtual Circuit
Network
31
Datagram Packet Switching

Each packet is independently switched


No pre-allocated (reserved) path in advance


Outgoing link of the packet is determined by the
switching node in per-packet granularity
The paths for packets from the same
conversation can be different
Example: IP networks
2012/11/23
32
Timing of Datagram Packet
Switching
Host 1
transmission
time of Packet 1
at Host 1
Node 1
Packet 1
Packet 2
Packet 3
Host 2
Node 2
propagation
delay between
Host 1 and
Node 2
Packet 1
processing
delay of
Packet 1 at
Node 2
Packet 2
Packet 3
Packet 1
Packet 2
Packet 3
2012/11/23
33
A Taxonomy of Communication
Networks
Packet-Switched
Communication
Network
Datagram
Network
2012/11/23
Virtual Circuit
Network
34
Virtual-Circuit Packet Switching

Hybrid of circuit switching and packet
switching





Data is transmitted as packets
All packets from one conversation are sent along
a pre-established path (=virtual circuit)
Guarantees in-sequence delivery of packets
within a virtual circuit
However: Packets from different virtual
circuits may be interleaved
Example: ATM networks
2012/11/23
35
Virtual-Circuit Packet Switching (Cont.)

Communication with virtual circuits takes
place in three phases



2012/11/23
VC establishment
Data transfer
VC disconnect
36
Timing of Virtual-Circuit Packet Switching
Host 1
Node 1
Host 2
Node 2
propagation delay
between Host 1
and Node 1
VC
establishment
Packet 1
Packet 2
Data
transfer
Packet 3
Packet 1
Packet 2
Packet 3
Packet 1
Packet 2
Packet 3
VC
termination
2012/11/23
37
Circuit Switching vs. Virtual-Circuit
Packet Switching

Both establish a path before data transfer


Guarantee in-sequence packet delivery
Difference


Whether using packet (header)
Resource multiplexing


2012/11/23
The reserved slot for a circuit in circuit switching
cannot be used by other circuits
But no slot reservation in virtual-circuit packet
switching
38
Today’s Lecture

Networking Taxonomy

Internet Overview

Internet Layering Architecture

Important Issues in Future Internet Design
2012/11/23
39
The Simplest Network
Node Link
2012/11/23
Node
40
More than Two Nodes

… But what if we want more hosts?
Wires for everybody!

Scalability?
2012/11/23
41
Small Network
LAN
2012/11/23
42
Grow bigger
WAN
2012/11/23
43
And bigger
Today’s Internet
2012/11/23
44
The Internet


Public, global-scale, general-purpose,
heterogeneous-technologies, computer
network
Internet Protocol


Open standard: Internet Engineering Task Force
(IETF) as standard body ( http://www.ietf.org )
Technical basis for other types of networks


Intranet: enterprise IP network
Driven by the research community
2012/11/23
45
History of the Internet

ARPANET





1969, built by DARPA
Started as a research project for the military, < 100
computers , 56 kbps
Mid of 70’s, using TCP/IP
1983, ARPANET and MILNET split
NSFNET




2012/11/23
NSF builds NSFNET in 1986
Links 6 Supercomputer centers
1.5 Mbps, 10,000 computers
Replaces ARPANET as the backbone of Internet
46
History of the Internet (Cont.)

1990


1994


Birth of WWW
2005



NSF backbone dismantled, multiple private backbones
1994


NSFNET moves to 45 Mbps, 16 mid-level networks
Backbones run at 10 Gbps
>300 millions users from allover the world
2011


Backbone speed reaches 100s Gbps
>2 billion users in the world, among which 0.48 billion from
China
2012/11/23
47
Services Provided by the Internet

Shared access to computing resources


Shared access to data/files


FTP, NFS (1980’s)
Communication medium over which people
interact



Telnet (1970’s)
Email (1980’s), on-line chat rooms (1990’s)
Instant messaging, IP Telephony (2000’s)
A medium for information dissemination


2012/11/23
WWW (1990’s)
Audio, video (2000’s): peer-to-peer systems
48
Technological Requirements of Internet







Cost
Evolvability
Manageability
Security
Deployment
Accountability
Scalability
2012/11/23
49
Today’s Lecture

Networking Taxonomy

Internet Overview

Internet Layering Architecture

Important Issues in Future Internet Design
2012/11/23
50
Layering




Layering is a particular form of modularization
The system is broken into a vertical hierarchy of
logically distinct entities (layers)
The service provided by one layer is based solely
on the service provided by the layer below
Rigid structure
2012/11/23
51
Why Layering?
Application
Transmission
Media

Telnet
FTP
NFS
Coaxial
cable
Fiber
optic
HTTP
Packet
radio
Without layering



2012/11/23
Each new application has to be re-implemented for
every network technology
Each new network tech requires changes on all apps.
High cost
52
Why layering? (Cont.)

Solution: introduce an intermediate layer that
provides a unique abstraction for various network
technologies
Application
Telnet
FTP
NFS
HTTP
Intermediate
layer
Transmission
Media
2012/11/23
Coaxial
cable
Fiber
optic
53
Packet
radio
Pros. & Cons.

Advantages




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


2012/11/23
Information hiding
Inefficient implementations
54
Design Issues in Each Layer






2012/11/23
Addressing
Error Control
Flow Control
Congestion Control
Fragmentation
Routing
55
ISO/OSI Reference Models
• Seven layers
– Lower three layers are implemented everywhere
– Next four layers are implemented only at hosts
Host A
Application
Presentation
Session
Transport
Network
Datalink
Physical
2012/11/23
Router
Network
Datalink
Physical
Physical medium
56
Host B
Application
Presentation
Session
Transport
Network
Datalink
Physical
Logical Communication

Layers interacts with corresponding layer on
peer
Host B
Host A
Application
Presentation
Session
Transport
Network
Datalink
Physical
2012/11/23
Router
Network
Datalink
Physical
Physical medium
57
Application
Presentation
Session
Transport
Network
Datalink
Physical
Physical Communication

Communication goes down to physical
network, then to peer, then up to relevant
layer
Host A
Host B
Application
Presentation
Session
Transport
Network
Datalink
Physical
2012/11/23
Router
Network
Datalink
Physical
Physical medium
58
Application
Presentation
Session
Transport
Network
Datalink
Physical
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
2012/11/23
59
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
Term “protocol” is overloaded


2012/11/23
specification of peer-to-peer interface
module that implements this interface
60
OSI Model Concepts
Layer k+1
Layer k+1
Service provided by layer k
Protocol
Layer k-1

Layer k-1
Service and Protocol
2012/11/23
61
Physical Layer

Service


Interface


Specify how to send and receive a bit
Protocol



Move the information between two systems
connected by a physical link
Make sure the correct transmission
Coding scheme used to represent a bit, voltage levels,
duration of a bit
Examples

2012/11/23
Coaxial cable, optical fiber links
62
Data Link Layer

Service

Transform a raw transmission facility into a line appearing
free of undetected transmission erros to the upper layer


Others (optional)




Arbitrate the access to common physical media
Ensure reliable transmission
Provide flow control
Interface


Framing, i.e., attach frames separator
Send/receive a data unit (packet) to/from a machine
connected to the same physical media
Protocol

Layer addresses, mechanisms for Medium Access Control
(MAC) (e.g., CSMA/CD)…
2012/11/23
63
Layer-2 Technologies

Ethernet




InfiniBand



Dominate LAN technology
Listen to wire before transmission
Avoid collision with active transmission
Primarily used in high-performance computing
Features: QoS, failover, Scalable
Fabre channel



2012/11/23
Primarily used for storage networking
Gigabit-speed network technology
With active transmission
64
Network Layer

Service



Deliver a packet to specified destination
Perform segmentation/reassemble (fragmentation/
defragmentation)
Others



Interface


Packet scheduling
Buffer management
Send/receive a packet to a specified destination
Protocol


2012/11/23
Define global unique addresses
Construct routing tables
65
Internet Protocol (IP)
host
router
router
host
router
router
router


Data communication across a packet-switched internetwork
Best effort delivery


router
Characterized as unreliable
Lack of reliability results in

Data corruption, data packet loss, duplicate arrival, out-of-order
packet delivery
2012/11/23
66
IPv4
IPv4 Header
Ver
ToS
IHL
Identifier
TTL
Total Length
Fragment
Offset
F
Protocol
Header Checksum
20 bytes
Source Address
Destination Address
Header size can vary
if options are used
Options and Padding


IPv4 address is too short
Many fields are useless
2012/11/23
67
IPv6
IPv6 Header
Ver
Traffic
Class
Flow Label
Payload Length
Next
Header
Hop
Limit
Source Address
(128 bits)
Destination Address
(128 bits)

Extension headers can be added after
the addresses
2012/11/23
68
Routing

Router Operation

When packet arrives at router



Examine header to determine intended destination
Look up in table to determine next hop in path
Send packet out appropriate port
How to generate the
routing table?
Router
2012/11/23
69
Routing (Cont.)

Graph model:



Represent each router as node
Direct link between routers represented by edge
Edge “cost” c(x,y) denotes measure of difficulty
of using link
E
3
C
1
1
F
2
6
1
A
2012/11/23
3
4
B
70
D
Transport Layer

Service




Interface


How to send/receive a segment by user’s requirements
Protocol


Provide an error-free and flow-controlled end-to-end
connection
Multiplex multiple transport connections to one network
path
Split one transport connection in multiple network paths
Implement reliability, flow control and congestion control
Examples

TCP and UDP
2012/11/23
71
Transport Layer (Cont.)

7
7
6
6
5
5
Transport
Transport
IP
IP

IP
Datalink
2
2
Datalink
Physical
1
1
Physical
2012/11/23
Lowest level endto-end protocol
72

Header generated
by sender is
interpreted only by
the destination
Routers view
transport header
as part of the
payload
UDP(User Datagram Protocol)

“Best effort” service, UDP segments may be



Connectionless

No handshaking between UDP sender and receiver
Each UDP segment handled independently of others

No flow control, no error control, no retransmission

Streaming multimedia apps:



Lost
Delivered out of order to app
Unreliable
Applications

Loss tolerant
Rate sensitive

Client can get the query result quickly


2012/11/23
DNS, SNMP
73
TCP (Transmission Control Protocol)


UDP provides just integrity and demulplexing
TCP adds…






2012/11/23
Connection-oriented
Reliable
Ordered delivery
Byte-stream
Flow control
Congestion control
74
Top Three layers


Session and Presentation are seldom
mentioned
Application layer

Service


Interface


Depends on the application
Examples

2012/11/23
Depends on the application
Protocol


Any service provided to the end user
FTP, Telnet, WWW browser
75
ISO/OSI Layers






Physical – sends individual bits
Data link – sends frames, handles access
control to shared media
Network – delivers packets, using routing
Transport – demultiplexes, provides
reliability & flow control
Session & Presentation – seldom used
Application – what end user gets, e.g., HTTP
(web)
2012/11/23
76
TCP/IP Reference model
• OSI: conceptually define services, interfaces, protocols
• Internet: provide a successful implementation
Application
Presentation
Session
Transport
Network
Datalink
Physical
OSI (formal)
2012/11/23
Application
Transport
Internet
Net access/
Physical
Internet (informal)
77
Telnet
FTP
TCP
DNS
UDP
IP
LAN
Packet
radio
OSI VS. TCP/IP
•
OSI
•
•
•
•
2012/11/23
• TCP/IP
Bad timing
Bad technology
Bad implementations
Bad politics
•Service, interface, and
protocol not distinguished
•Not a general model
•Host-to-network “layer” not
really a layer
•No mention of physical and
data link layers
•Minor protocols deeply
entrenched, hard to replace
78
Current Model
email WWW phone...
SMTP HTTP RTP...
Applications
TCP UDP…
IP
ethernet PPP…
CSMA async sonet...
Technology
copper fiber radio...


This is “Hourglass” philosophy of Internet
Idea

2012/11/23
If everybody just supports IP, can use many different
applications over many different networks
79
The “Curse of the Narrow Waist”

IP over anything, anything over IP



Has allowed for much innovation both above and
below the IP layer of the stack
An IP stack gets a device on the Internet
Drawbacks:



2012/11/23
difficult to make changes to IP
But…people are trying (GENI)
Only a small amount of information available
about lower levels (wireless)
80
Today’s Lecture

Networking Taxonomy

Internet Overview

Internet Layering Architecture

Important Issues in Future Internet Design
2012/11/23
81
Important issues





Multicast
P2P
Cloud computing
Data center networking
Green network
2012/11/23
82
Multicast- Efficient Data Distribution
Src
2012/11/23
Src
83
P2P Networks

Client/server service model -> P2P service
model




Reduce the server burden
Client not only downloads, but also uploads to
other clients
Make better use of the end-system capability
Applications


2012/11/23
File sharing
Multimedia streaming
84
Cloud Computing

A new Internet service model


Users share computers and data


In the cloud
Elasticity and Multiplexing


The other extreme is P2P
Cost saving
Technologies



2012/11/23
Data center
Long-distance transport
Mobile + cloud
85
Commercial clouds
2012/11/23
86
Data Center Networking



The core of cloud computing
Interconnect hundreds of thousands of
computers and provide the routing service
A new environment of networking


Quite different from Internet
Technologies



2012/11/23
Interconnection topology
Routing
Transport
87
Green Network
Beautiful
But, wasteful
2012/11/23
88
Test
2012/11/23
89