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Lecture 3: Networking and Internetworking

Haibin Zhu, PhD.

Assistant Professor

Department of Computer Science

Nipissing University

© 2002

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Contents

3.1 Introduction3.2 Types of network3.3 Network principle

IP routing

3.4 Internet protocols TCP IP

3.5 Case study: Ether Net ATM

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Basic terminology:

Communication subsystem A collection of hardware and software components that provide

the communication facilities for a distributed system.

Host - devices that use a network for communication Node - any computer or switching device on a network Subnet - (CDK’s definition) set of interconnected nodes

that employ same technology to communicate among themselves. (Not a standard definition of subnet - which usually denotes an

organization of IP addresses and a physical location for routing.)

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What are the network issues?

PerformanceScalabilityReliabilitySecurityMobilityQuality of serviceMulticasting

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Performance:

Message transmission time: =latency (the delay that occurs after a send op is

executed before data starts to arrive at the dest) + length/data transfer rate (the speed data can be

transfered) (assuming no message fragmentation)

Total system bandwidth: Total volume of traffic that can be transferred across

the network in a given time

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Figure 3.1 Network types and comparison

Range Bandwidth (Mbps) Latency (ms)

LAN 1-2 kms 10-1000 1-10WAN worldwide 0.010-600 100-500MAN 2-50 kms 1-150 10Wireless LAN 0.15-1.5 km 2-11 5-20Wireless WAN worldwide 0.010-2 100-500Internet worldwide 0.010-2 100-500

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3.3 Network Principles

Packet transmission Let a computer have an enough buffer Avoid undue delay

Switching schemesProtocolsRouting

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Switching schemes:

Broadcast Direct addressing

Circuit switching Dialing 705-495-1431

Packet switching Store-and-forward

Frame relay Fast packet switching based on a method of

routing.

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Protocols:

CDK: … a well-known set of rules and formats to be used

for communication between processes including two parts of specification:The sequence of messages that must be exchangedThe format of the data in the messages

What is the difference between a protocol layer and a protocol suite? Each layer presents an interface to the layers above

it that extends the properties of the underlying communication system.

A suit is a complete set of protocol layers.

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Figure 3.2Conceptual layering of protocol software

Layer n

Layer 2

Layer 1

Message sent Message received

Communicationmedium

Sender Recipient

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Figure 3.3 Encapsulation as it is applied in layered protocols

Presentation header

Application-layer message

Session header

Transport header

Network header

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Figure 3.4 Protocol layers in the ISO Open Systems Interconnection (OSI) model

Application

Presentation

Session

Transport

Network

Data link

Physical

Message sent Message received

Sender Recipient

Layers

Communicationmedium

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Figure 3.5OSI protocol summary

Layer Description ExamplesApplication Protocols that are designed to meet the communication requirements of

specific applications, often defining the interface to a service. HTTP, FTP, SMTP,CORBA IIOP

Presentation Protocols at this level transmit data in a network representation that isindependent of the representations used in individual computers, which mayDiffer. Encryption is also performed in this layer, if required.

Secure Sockets(SSL),CORBA DataRep.

Session At this level reliability and adaptation are performed, such as detection offailures and automatic recovery.

Transport This is the lowest level at which messages (rather than packets) are handled.Messages are addressed to communication ports attached to processes,Protocols in this layer may be connection-oriented or connectionless.

TCP, UDP

Network Transfers data packets between computers in a specific network. In a WANor an internetwork this involves the generation of a route passing throughrouters. In a single LAN no routing is required.

IP, ATM virtualcircuits

Data link Responsible for transmission of packets between nodes that are directlyconnected by a physical link In a WAN transmission is between pairs ofrouters or between routers and hosts. In a LAN it is between any pair of hosts.

Ethernet MAC,ATM cell transfer,PPP

Physical The circuits and hardware that drive the network. It transmits sequences ofbinary data by analogue signalling, using amplitude or frequency modulationof electrical signals (on cable circuits), light signals (on fibre optic circuits)or other electromagnetic signals (on radio and microwave circuits).

Ethernet base- bandsignalling, ISDN

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Figure 3.6Internetwork layers

Underlying network

Application

Network interface

Transport

Internetwork

Internetwork packets

Network-specific packets

MessageLayers

Internetworkprotocols

Underlyingnetworkprotocols

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Packet assembly and delivery:

assembly Transport layer usually handles assembly and

reassembly Packets consist of a header and a data. If the data > MTU (maximum transfer unit), it must be

divided into multiple packets. A transport address is the network address of host +

port number.Delivery

Two approaches to delivery in the network layerDatagram deliveryVirtual circuit packet delivery

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Routing

Hosts Linksor local networks

A

D E

B

C

1

2

5

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Routers

decide the route for each packet

update knowledge of the network

Routing in a wide area network

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Figure 3.8Routing tables for the network in Figure 3.7

Routings from D Routings from E

To Link Cost To Link CostABCDE

336

local6

12201

ABCDE

4456

local

21110

Routings from A Routings from B Routings from C

To Link Cost To Link Cost To Link CostABCDE

local1131

01212

ABCDE

1local

214

10121

ABCDE

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local55

21021

Hosts Linksor local networks

A

D E

B

C

12

5

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6Routers

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Link-state algorithm:

keep a distance vector for destinations in routing table

send a summary of routing table to neighbors using RIP (router information protocol)

read tables from neighbors and update as needed

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Figure 3.9 Pseudo-code for RIP routing algorithm

Send: Each t seconds or when Tl changes, send Tl on each non-faulty outgoing link.Receive: Whenever a routing table Tr is received on link n:

for all rows Rr in Tr {if (Rr.link <> n) {//Rr.link ==n means that the local will not use it a route(it is a go and return route)//the neighbour’s link might be used as a possible route for the local

Rr.cost = Rr.cost + 1; //if the local use this linkRr.link = n; //if the local use this linkif (Rr.destination is not in Tl) add Rr to Tl; // add new destination to Tlelse for all rows Rl in Tl {

if (Rr.destination = Rl.destination and (Rr.cost < Rl.cost or Rl.link = n)) Rl

= Rr;// Rr.cost < Rl.cost : remote node has better route// Rl.link = n : remote node is more authoritative

}}

}

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Details:

t is typically 30 secondswhen a faulty link is detected, cost is set tocosts can be based on bandwidth rather than

hopsslow convergence and loops are a problem

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3.4 Internet Protocols

TCP(Transport Control Protocol) abstractionTCP

Ports and sockets TCP protocol

IP Addressing IP protocol IP routing IPv6Firewall

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Figure 3.12TCP/IP layers

Messages (UDP) or Streams (TCP)

Application

Transport

Internet

UDP(User Datagram Protocol) or TCP packets

IP datagrams

Network-specific frames

MessageLayers

Underlying network

Network interface

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Figure 3.13 Encapsulation in a message transmitted via TCP over an Ethernet

Application message

TCP header

IP header

Ethernet header

Ethernet frame

port

TCP

IP

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TCP abstractions:

abstraction of a stream of bytes a connection is established before messages

are sentassumes one process is the client and one is

the server in establishing a connectionmessages are sent using handles rather than

source-destination addresses

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TCP

Transport services Use ports

Additional mechanisms Sequencing (segment number) Flow control (segment number + ack + win-size) Retransmission (no ack, retransmit) Buffering (discard + retransmit ) Checksum (if checksum not the same, drop)

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Ports:

A message destination specified by a small integer (16 bits) any process can send a message to it

Internet protocols use the combination (IP address, local port)

IANA (Internet Assigned Numbers Authority) ports: well-known ports: 1 - 1023 registered ports: 1024 - 49151 dynamic or private ports: 49152 - 65535

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UDP

A transport-level replica of IPEncapsulated with an IP packetSource + dest. port numbersNo guarantee of deliveryOnly checksum added as optionalUp to 64KB packetFast

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Figure 3.14 The programmer's conceptual view of a TCP/IP Internet

IP

Application Application

TCP UDP

IP-Internet Protocol

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IP Addressing:

UniversalEfficient

Rate of growth Address space allocation

Lend itself to the development of a flexible and efficient routing scheme

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Internet address structure, showing field sizes in bits

7 24

Class A: 0 Network ID Host ID

14 16

Class B: 1 0 Network ID Host ID

21 8

Class C: 1 1 0 Network ID Host ID

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Class D (multicast): 1 1 1 0 Multicast address

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Class E (reserved): 1 1 1 1 unused0

Reserved

>255

All others

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Figure 3.16 Decimal representation of Internet addresses

octet 1 octet 2 octet 3

Class A: 1 to 127

0 to 255 0 to 255 1 to 254

Class B: 128 to 191

Class C: 192 to 223

224 to 239 Class D (multicast):

Network ID

Network ID

Network ID

Host ID

Host ID

Host ID

Multicast address

0 to 255 0 to 255 1 to 254

0 to 255 0 to 255 0 to 255

0 to 255 0 to 255 0 to 255

Multicast address

0 to 255 0 to 255 1 to 254240 to 255 Class E (reserved):

1.0.0.0 to 127.255.255.255

128.0.0.0 to 191.255.255.255

192.0.0.0 to 223.255.255.255

224.0.0.0 to 239.255.255.255

240.0.0.0 to 255.255.255.255

Range of addresses

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Figure 3.17 IP packet layout

dataIP address of destinationIP address of source

header

up to 64 kilobytes

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Figure 3.18 IPv6 header layout

Source address(128 bits)

Destination address(128 bits)

Version (4 bits) Priority (4 bits) Flow label (24 bits)

Payload length (16 bits) Hop limit (8 bits)Next header (8 bits)

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Firewalls

A system designed to prevent unauthorized access to or from a private network. Service control Behavior control User control IP address filtering TCP gateway Application-level gateway

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Figure 3.20 Firewall configurations

Internet

Router/Protected intraneta) Filtering router

Internet

b) Filtering router and bastion

filter

Internet

R/filterc) Screened subnet for bastion R/filter Bastion

R/filter Bastion

web/ftpserver

web/ftpserver

web/ftpserver

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Figure 3.21 IEEE 802 network standards

IEEE No. Title Reference

802.3 CSMA/CD Networks (Ethernet) [IEEE 1985a]

802.4 Token Bus Networks [IEEE 1985b]

802.5 Token Ring Networks [IEEE 1985c]

802.6 Metropolitan Area Networks [IEEE 1994]

802.11 Wireless Local Area Networks [IEEE 1999]

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3.5 Network Case study

Ethernet CSMA/CD (Carrier Sensing Multiple Access/ Collision Detection

) http://www.erg.abdn.ac.uk/users/gorry/course/lan-pages/csma-cd.html

Package broadcasting Package layout

Preamble(7)+S(1)+Dest. Addr(6) + Source Addr.(6) + Length(2)+ data(46-1500)+checksum(4)

http://media.pearsoncmg.com/aw/aw_kurose_network_2/applets/csmacd/csmacd.html

http://www2.rad.com/networks/2001/ethernet/csma.htm

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Figure 3.22 Wireless LAN configuration

LAN

Server

WirelessLAN

Laptops

Base station/access point

Palmtop

radio obstruction

A B C

DE

Hidden stations, Fading, Collision maskingCSMA/CA (Collision Avoidance)http://www.pcworld.com/howto/article/0,aid,15531,00.asp

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ATM (Asynchronous Transfer Mode)

Cell relay: http://www.webopedia.com/TERM/c/cell_relay.html http://www.kevinboone.com/compdict/

compdict_ATM_cell_relay.html

Virtual channel: A logical unidirectional association between two

endpoints of a link in the physical path from source to destination.

Virtual path: A bundle of virtual channels that are associated with a

physical path between two switching nodes.

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Figure 3.23 ATM protocol layers

Physical

Application

ATM layer

Higher-layer protocols

ATM cells

ATM virtual channels

MessageLayers

ATM adaption layer

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Figure 3.24 ATM cell layout

VPI in VPI out

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VPI = 3

VPI = 5

VPI = 4

Virtual path Virtual channels

VPI = 2

VPI : virtual path identifier

VP switch VP/VCswitch

VP switch

Host

Host

Figure 3.25 Switching virtual paths in an ATM network

Flags DataVirtual channel idVirtual path id

53 bytes

Header: 5 bytes

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Summary

Network Principle Packet transmission Switching Protocols Routing

Network Protocols TCP IP Addressing IP Protocol IP routing Firewall

Case Study Ethernet ATM