architecture - university of california, berkeleyee122/sp04/architecture.pdfnetwork architecture...

Network Architecture� Introduction� Layering Example� Internet Layers – First Look� Layering Step by Step� Downside of Layering� Interconnecting Networks� The Internet

TOC – Architecture

Introduction� Issues:

� Inter-operability� Extensibility

� Applications & Technologies� Scalability

� Internet Solution:� Layered Architecture� End-to-End Principle� Hierachical Addressing & Naming

TOC – Architecture �� Introduction

Layer: Example…

TOC – Architecture – Layer Example ��

FAX SYSTEM

SECRETARYJohn

SECRETARYMary

Prof. A Prof. B

Please fax letterto Prof. B, Urgent

Here is a letter from Prof. A

Here is my review of paper 554.I believe its main result is wrong.Here is a counterexample.


COVERTo: Prof. BFr: Prof. AUrgent



Layer: Example…

TOC – Architecture – Layer Example ��

FAX SYSTEM

SECRETARYJohn

SECRETARYMary

Prof. A Prof. B

Please fax letterto Prof. B, Urgent

Here is a letter from Prof. A

INTERFACE

FUNCTIONS

HEADER

SERVICE - SECY

SERVICE - FAX


Layer: Example

TOC – Architecture �� Layer Example

FAX SYSTEM

SECRETARYJohn

SECRETARYMary

Prof. A Prof. B• Secretaries implement functions that transform a simple service into a more complex one(E.g., add MULTIPLEXING)• They follow rules of communication:

PROTOCOL• They use the header as control information•Note: Encapsulation (adding header) and Decapsulation(removing header)




Internet Layers - Intro

TOC – Architecture – Internet Layers: Intro

� Browsing� Services� Names� Examples� Specifications� Encapsulation� Functions

Browsing� Name � IP Address � Connect; Get; Close � Supervise Connection� Forward Packets Across Many Links� Transmit Packets on Each Link� Transmit Bits on Each Medium

TOC – Architecture – Internet Layers: Intro �� Browsing

1

2

3

4

5

H H

R R

� DSN Servers� End hosts 5� End hosts 4� Routers 3� Link/LAN 2� Transceivers 1

Services

TOC – Architecture – Internet Layers: Intro �� Services

1

2

3

4

5

Signals

Bits

Packets: End to End

Connection

Application

Packets

Names

TOC – Architecture – Internet Layers: Intro �� Names

1

2

3

4

5

Signals

Bits

Packets: End to End

Connection

Application

Packets

Physical

Link

Network

Transport

Application

Examples

TOC – Architecture – Internet Layers: Intro �� Examples

1

2

3

4

5

Signals

Bits

Packets: End to End

Connection

Application

Packets

Physical

Link

Network

Transport

Application

Fiber-1Gbps; Cat5-100Mbps;Wireless; SONET

Ethernet; ADSL; …

IP; ATM; …

TCP; UDP; …

DNS; HTTP; TFTP; RTP

Specifications

TOC – Architecture – Internet Layers: Intro �� Specification

N

N - 1

N + 1

• Interfaces: Formats, …• Functions: Service Provided

Typically: State Machine

Encapsulation

TOC – Architecture – Internet Layers: Intro �� Encapsulation

N + 1

N

N - 1

H

Data Unit that N Delivers

Header: Control Info of N

Examples of H:AddressesError Control CodesFraming Delimiters

Functions

TOC – Architecture �� Internet Layers: Intro – Functions

APP

TRAN

NET

LINK

PHY Modulation; Demodulation

Framing; Error Coding;Local Addressing; Switching

Global Addressing; Routing;Forwarding

Multiplexing; Flow Control;Congestion Control

Set Up Connections; Presentation; …

Layers Step By Step� Physical� Data Link� Network� Transport� Application� DNS

TOC – Architecture – Layers Step By Step

Physical

��

��

In the beginning were two computers…

TOC – Architecture – Layers Step By Step – Physical

��

Physical

ModemRS232-CInterface

Interface wires

Modem RS232-CInterface

Interface wires

Synchronous unreliable bit pipe

Physical Medium

Physical Medium � Virtual Bit Pipe

1011011Example: Manchester Encoding

TOC – Architecture – Layers Step By Step �� Physical

Data Link Control Layer

Data Link Protocol

��

��

PhysicalInterface

PhysicalInterface


Data LinkControl

Data LinkControl

Asynchronous reliable bit pipe

Physical Link

FH Data

Bit Stream

�� !� " ��#��$� % ��&�'� &��#�

��( ��

% ��'��#��( ��

)*��+�% , " )�

TOC – Architecture – Layers Step By Step – Link

Data Link Control Layer What about a broadcast system?

� Example: Satellite, ethernet, 802.11� Individual transmissions can interfere and destroy

many frames� A multiaccess protocol is required to try and avoid

these collisions or the link will be too unreliable� Example: TDM, CSMA� Makes the bit-pipe provided by the physical layer look

“intermittent” to the DLC� Protocol must interface with Physical and DLC layers� By convention the Multiaccess Control Layer (MAC) is

considered a “sub-layer” of the DLC

TOC – Architecture – Layers Step By Step – Link

Data Link Control Layer What about a broadcast system?

PhysicalInterface

PhysicalInterfaceMultiaccess

Medium

PhysicalInterface

MAC MAC

MACDLC

DLC

DLC

Need Addresses…Burned into NICs

TOC – Architecture – Layers Step By Step �� Link

Network Layer: Routing

A B

" �� -� ��# ��./��

Routing information must be contained in a message unlessit is part of a circuit…Network addressing and protocol required to accomplishdelivery over multiple hops

C D

E

TOC – Architecture – Layers Step By Step – Network

Network Layer: Complexity

A B

��-��. �� #��*��

��#��# ��#��

C D

E

Topology discoveryLink State monitoringForwardingBuffer management


Network Layer: Routers/Switches

A B

& ��% ��0�� , ��0��

% ��#��( ��

C D

E

R S


Network Layer

PhysicalInterface

PhysicalInterface


Data LinkControl

Data LinkControl


Physical Link

Network NetworkAsynchronous path

FH Data

PhysicalInterface


Data LinkControl


Physical Link

NetworkAsynchronous path

FH Data

PH Data PH Data

)*��+�12�� 3

TOC – Architecture – Layers Step By Step �� Network

Transport Layer

A B

C D

E

a b c

APP

x y z

APP

��1��

��-��. ��

TOC – Architecture – Layers Step By Step – Transport

Transport Layer

PhysicalInterface

PhysicalInterface


Data LinkControl

Data LinkControl


Physical Link

Network NetworkAsynchronous routed path

FH Data

PhysicalInterface


Data LinkControl


Physical Link

NetworkAsynchronous routed path

FH Data

Transport Transport

PH Data PH Data

TH Data

End Node Subnet Node End Node

)*��+��2��4 5 2

TOC – Architecture – Layers Step By Step �� Transport

Application Layer

)*��+�6 ��7��#��

PhysicalInterface

PhysicalInterface


Data LinkControl

Data LinkControl


Physical Link


FH Data

PhysicalInterface


Data LinkControl


Physical Link


FH Data

Transport Transport

PH Data PH Data

TH Data


Application ApplicationData

TOC – Architecture – Layers Step By Step �� Application

Network Directory Servers

A B

8 ��#��

��1��5 " %

C D

E

R S

X

TOC – Architecture � Layers Step By Step – DNS

Encapsulation

PhysicalInterface

PhysicalInterface


Data LinkControl

Data LinkControl


Physical Link


TH Data

PhysicalInterface


Data LinkControl


Physical Link


Transport Transport

PH TH Data


PH TH Data

FH PH TH Data FH PH TH Data

)��9 ��

Application Application

Data

TOC – Architecture – Layers Step By Step – Encapsulation

The downside of layering

� Efficiency� Suboptimal network behavior

� TCP and wireless links

� Redundant Implementation� Fragmentation and reassembly� Multiple address spaces

� Confusion in actual networks� Layer 2 , Layer 4 and Layer 4-7 switches� What layer does the function “security” belong to?� Network devices (such as routers) may run application

protocols

TOC – Architecture �� Downside

Inter-Connecting NetworksIP1 | IP4 | Data

A

B

TOC – Architecture �� Interconnecting

R

PCKT=

IP1E1

IP2E2

IP3E3

IP4E4

E1 | E2 | PCKT

E3 | E4 | PCKT

Destination – Next HopIP4 E4

“A”- Addresses

“B”- AddressesGlobal Address

Router R sees network B as a direct link

The Internet� Overview� Minimal Router State� Layering� End-to-End Argument� Success� Caveats

TOC – Architecture - Internet

Overview� Interconnect networks with different

� Speeds, Reliability, Cost � Go across multiple networks� Internet Service = Best Effort datagram service:

� Try hard to deliver each packet� Anything more, e.g. voice grade service, would

� Preclude many networks from joining the internet� Require great amounts of co-ordination and

compliance monitoring� Create an endless clamoring for even other kinds of

guarantees such as video grade service

TOC – Architecture - Internet �� Overview

Case for minimal router state� Adding connection state to routers creates problems

in the presence of failures…� How to clean up the “bad state”?

� Scaling router state with number of transport connections would be very expensive

� Adding connection state in only some routers might not be good enough� What if many congested routers did not implement state

� So: The internet provides datagram service. Under this constraint, the internet is designed to support as many different types of applications as possible.

TOC – Architecture - Internet �� Minimal State

Layering� Almost Any kind of

application can write directly on IP� Including new transport

protocols� IP cannot be avoided� As long as the routers

speak IP, any application that can make do with datagram service can be written and implemented on the end devices.� No co-ordination, standards

activity etc. is required!!

Network

IP

TCP UDP

Application

BGP HTTP RTP TFTP

TCP UDP

IP

Ethernet FDDI Token Etc.

TOC – Architecture - Internet �� Layering

End-to-End Argument(Saltzer, Reed and Clark 1984)� Implement a network function at the end

hosts unless it cannot be implemented correctly in this manner.

OR� “Don’t implement a function at the lower

levels of the system unless it can be completely implemented at this level”(Peterson and Davie)

TOC – Architecture - Internet �� E2E Argument

Success

TOC – Architecture - Internet - Success

4/1-4/16 2002•1,224,733 IP addresses, •2,093,194 IP links, •932,000 destinations, •70% of globally routable network prefixes; •10,999 ASes (84% of ASes),•34,209 peering sessions

TOC – Architecture - Internet �� Success

Success

Caveats

� Internet is actually a lot more complicated and messy than today’s lecture would suggest

� The end-to-end argument is being subverted and under attack

� The internet does a poor job of supporting high performance traffic such as voice and video

� The phone network is hardly going away…� We will deal with these issues in much more detail

towards the end of the course

TOC – Architecture �� Internet - Caveats

architecture - university of california, berkeleyee122/sp04/architecture.pdfnetwork architecture...

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