Network Architecture for CyberspaceJoel Crichlow, Ph.D

Network Architecture

Layers

Protocols

Standards

ISO/OSI Reference Model◦ International Organization for Standardization/Open

Systems Interconnection TCP/IP

◦ Transmission Control Protocol/Internet Protocol

ISO/OSI

Physical Layer

Digital-to-Analog Conversion

Analog-to-Digital Conversion◦ Modulation/Demodulation - modem

Transmission Media

Multiplexing

Circuit Switching and Packet Switching

Errors◦ Error correcting codes◦ Error detecting codes

Transmission Media

Twisted pair Coaxial cable Optical fibers Wireless Transmission

MultiplexingFrequency Division Multiplexing (FDM)

MultiplexingTime Division Multiplexing (TDM)

user 1

Channel

4

Channel

3

Channel

2

Channel

1

user 3

user 4

user 2

Circuit Switching and Packet Switching Circuit Switching

◦ Complete end-to-end path for exclusive use throughout the duration of session

Message Switching◦ Store-and-forward

Packet Switching

Data Link Layer

Link management◦ Efficient and reliable transmission of information from

one node (host or PSN) in the network to a neighboring node

Frames◦ Constructed from packets received from upper layer

Frames Flag – Begin, End

Bit stuffing◦ For example, if the flag is 01111110, then no sequence of 6 ‘1’ bits is allowed, a

‘0’ bit is inserted (stuffed) after every sequence of five ‘1’ bits

FLC - kind of frame, sequence number and acknowledgement indication

CRC – polynomial code

Network Layer

Connection Oriented Service◦ Set up connection then transfer data

Connectionless Service◦ Transfer data without setting up connection◦ Acknowledged, Unacknowledged

Virtual Call◦ Virtual Circuit for all packets in right sequence

Datagram◦ Each packet handled independently

Routing

Flow Control

Routing Shortest Path

Best Route◦ number of hops◦ distance (usually km)◦ bandwidth◦ traffic◦ communication cost

Static Routing

Dynamic Routing

Distance vector Routing

Route

to

Preferred out line Distance in hops

A A 0

B B 1

C B 2

D G 2

E E 1

F E 2

G G 1

Table at Router A

Path vector routing Current path vector for router A

Route to Preferred outline Path

A A A

B B A-B

C B A-B-C

D G A-G-D

E E A-E

F E A-E-F

G G A-G

Dynamic routing

Link State routing◦ Determine the delay along the link to neighbors◦ Send this information to all the other routers◦ Use this information to establish the shortest path to

every other router

Flow control and congestion

Too much traffic can overwhelm the system Finite bandwidth, finite memory Processing overhead Dropped packets Re-sends

Transport Layer

Process-to-Process Network-wide Addressing

◦ Name Servers Service

◦ Connection oriented◦ Connectionless◦ Integrity of delivered messages◦ Flow control

Session Layer

Application-oriented flavor◦ Different characteristics may determine different

procedures◦ Distributed computation vs multimedia transfer

Session management◦ Multiple transport connections◦ Multiple sessions over single transport connection

Presentation Layer

Data Integrity◦Data formats◦Conversions

Security and Privacy◦Encryption

Application Layer

The User Layer Useful Open? Friendly?

TCP/IP

ISO/OSI?

Five Layers

TCP - Transmission Control Protocol◦ Connection Oriented

UDP – User Datagram Protocol◦ Connectionless

IP – Internet Protocol◦ Datagram service

Local Area Networks

Range◦ Limited

Topologies◦ Bus, Ring, Star, …

IEEE Standards◦ Widespread use

M M M

P P P P

Bus

C

C

C

CC

Ring

C

C

C

C

Star

Wireless Computing

Base Station Adhoc Networks WiFi Bluetooth

WiFi

(a) WiFi with base station; (b) WiFi without base station

Bluetooth

Bluetooth topology: (a) 1 piconet, (b) A scatternet of 3 piconets

Conclusion We looked at:

ISO/OSI Reference Model

TCP/IP

Local Area Networks

Wireless Computing