Computer Networks

Department of Computer Science

Faculty of Civil Engineering, Brno University of Technology

Computer Technology

• Networking

• Internet Services

ITU (International Telecommunication Union) - part of OSN - standards of (tele)connectivity http://www.itu.ch - ITU -T (CCITT original) - for computers communication (ISDN,…) ISO (International Organization for Standardization) - http://www.iso.ch IEEE (Institute of Electrical and Electronics Engineers) - 147countries - IEEE802 - standard. for LAN tech. (IEEE802.3 - for Ethernet)W3C (World Wide Web Consortium) standard of WWW serviceČSNI (Český normalizační institut) - member of ISOISOC - IAB - IETF, IESG - organizations in InternetIANA, NIC - IP addresses a ports support, top domain admin.

(http://www.nic.com)

Main organization for standardization

Classification of networks• area

– LAN (Local Area Network), – MAN (Metropolitan Area Network),– WAN (Wide Area Network)

• topology– bus (Ethernet),– circle (Token Ring),– star (ARCnet)

• access method– collision (stochastic) - CSMA/ CD - Ethernet,– non-collision (deterministic) - Token Ring

• node role– peer to peer, client - server

Bus topology:Ethernet

Topology with structured cabling (star):

Ethernet

Circle topology: Token Ring

HUB

Topology of network (cabling)

client -serverpeer-to-peer

Access method - CSMA with collision detecting (CSMA/CD = Carrier Sense Multiple Access/Collision Detection)

Ethernet today

• Classic – 10 MBit/s– 10Base-2, 10Base-5, 10Base-T, 10Base-FL

• FastEthernet – 100 MBit/s– 100Base-TX, 100Base-T4, 100Base-FX

• Gigabit Ethernet – 1000 MBit/s– 1000Base-SX, 1000Base-LX, 1000Base-T

•node, host = computer connected to network

•internetworking = communication between networks

•internet = connected networks

•Internet = well-known computer network

•connected servicestart-end of connection

•non-connected servicewithout connection (posted packet)

entityentity

entityentity

•With acknowledge = reliable

•Without acknowledge = non-reliable

Terminology

Layer model (what and where to do)• decomposition to the tasks maintained by separated layers• layer interface definitions

Protocol (how to do)• set of rules and technologies for communication• each layer has its own protocol• format of the data definition

LAN Microsoft: NetBEUI (non-routable)

NetWare: IPX/SPX (routable)

heterogeneous networks (WAN, LAN): TCP/IP

Architecture of networks

Layer

• Each layer uses the service of the lower layer • offers its service to the higher layer• communication partner of the n-th layer is only

the n-th layer• communication between the partners (the same

layer) is controlled by the protocol

Layer N-1

Layer N+1

Layer N

Layer N-1

Layer N+1

Layer NCommunication protocol

TCP/IP ISO/OSI

application

application presentationrelation

transport transportnetwork networknetwork interface link

physic

Four layers TCP/IPApplication - application interfaceTransport - direct connectionNetwork - routingNetwork interface - transfer of bits

Protocols TCP/IP

AL

TL

NL

PHL

Protocols TCP/IP

IGMP

transfer medium

HTTP

80

HTTP

80

FTP TELNET SMTP POP3 DNS NFS RPCother

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TCPUDP

IP

ARP RARP ICMP RIP OSPF

RTP

Ethernet, Token Ring, FDDI, Novel, X.25, ATM, (SLIP, PPP)

Protocols of TCP/IP layers

Layers has its address format

• Domain address = text address (application layer) www.seznam.cz

• IP address = logic address (network layer) 32 bits - 195.119.180.19

• MAC address = physic (real) address (net inteface) 48 bits - 00-00-64-65-73-74

Each node in the network has its own unique address

TCP/IP CommunicationTCP/IP addresses

• DNS (Domain Name System) service domain address - IP address mapping

• name servers = nodes providing DNS service

• domain address example: hp832.fce.vutbr.cz

node name . subdomain . subdomain . top level domain

• domain – specification where node is placed – top level domain:

COM, EDU, GOV, MIL, NET, ORG – v USA Non-US country code – (cz, sk, at, de, …)

– subdomain

(application layer)Domain address in TCP/IP

Domains Hierarchy

Examples:

www.atlas.czwww.rfc-editor.orgwww.altavista.com

novell

www

net

augustana

com org

nasa vutbr

cz

feefce

Unnamed root

edugov mil

indy

deint

czech

only USA

IP address

IP version 4• 32bits integer expressed as four dot separated numbers• logic (abstract) address

1001 0011 1110 0101 0001 1010 0000 10100 7 8 15 16 23 24 31

Finite number of addresses: 2 32

Example of IP address: 147.229.26.10

• new IP protocol (IP version 6) - 128 bits address - eight hexadecimal numbers colon separated CA32:F123:C210:1234:0000:0000:0000:1A11

Structure of IP address

Classes of IP addresses and network mask:

class netid hostid nodes max subnet maskA p q.r.s 16777214 255.0.0.0B p.q r.s 65534 255.255.0.0C p.q.r s 254 255.255.255.0

IP address (p.q.r.s) contains two parts (for routing)

- netid- hostid

193 12 99 0

Example: IP network address 193.12.99.0

Subnetting - dividing of the network

• goals: more nodes in the netload balancing

• hostid of IP address is divided to the two parts - subnet num - node num

• subnet mask • 32 bits integer expressed as four dot separated numbers• first continuous part of bits contain 1 - defines network part

of the IP address C

Classes of IP addresses

0 7 8 15 16 23 24 310 net node

110 net node

10 net node

A

BC

Subnet mask

Subnet mask

net node

net subnet node

Examples: determining of net and node parts of IP address

193.12.99.18 = 11000001 00001100 01100011 00010010

255.255.255.0 = 11111111 11111111 11111111 00000000

193.12.99.0 = 11000001 00001100 01100011 00000000

network part of IP address = 193.12.99.0

IP address = 195.229.26.10, subnet mask = 255.255.255.224

195.229.26.10 = 11000011 11100101 00011010 11101010

255.255.255.224 = 11111111 11111111 11111111 11100000

195.229.26.224 = 11000011 11100101 00011010 11100000

network part of IP address = 195. 229.26.224

IP address = 193.12.99.18, subnet mask = 255.255.255.0

Special IP addresses

subnet address - symbolic address of the subnet - hostid contains only 0 bits: 136.229.26.0

broadcast - message to all nodes in LAN - group IP address (hostid contains only 1 bits) example: 195.229.26.255 = 11000011 11100101 00011010 11111111

multicast - message to some group of nodes in LAN

IP address = 147.229.22.85 subnet mask = 255.255.255.192

147.229.22.85 = 1001 0011 1110 0101 0001 0110 0101 0101 255.255.255.192 = 1111 1111 1111 1111 1111 1111 1100 0000

147.229.22.64 = 1001 0011 1110 0101 0001 0110 0100 0000

network part of IP address = 147.229.22.64

Examples: determining of net and node parts of IP address

Subnetting

One net representation

Gatewaynet 193.12.x.x net 193.12.1.x

net 193.12.2.x

193.12.2.3 193.12.2.4

193.12.2.1 193.12.2.2

Applicat. layer

Transport layer

Network layer

Physic interface

layer

physic transport

frame

Application dataApplicat.

layer

Transport layer

Network layer

Physic interface layer

datagram

packet

message

TCP dataTCP header

IP header IP data

Frame dataFrame header

Node X Node YEach submitting layer adds its header (or

removes it in receiving case)

TCP/IP Communication

Passive elements (connectors, cabling, …)

Active elements - electronic equipment for network connection (signal amplifying and transformation)

physic transport

V. síťového rozhraní

node X node Y

Applic.

Transport

Network

Link bridgerepeater

router

Applic.

Transport

Network

Link

gateway

Network connecting - active elements

• Realized by IP protocol• Provides

•unified addresses – logic IP addresses•unified format of transferred data (IP datagrams)•routing between the LANs via routers•address mapping: ARP, RARP protocols•non-connected, non-reliable

service

Internet (IP) Layer

Router 1

Router 2 Router 3

A B

C D E

node knows - source (its) and target IP address, - source (its) and target MAC address (ARP)

- IP address of router of its network• node send packet to the router if the net part is different• router send packet to the router or direct to the target node• IP routing table - subnet mask, target network, gateway (router)

Data transfer between two nodes in different networks

Network layer protocols

IP Internet Protocol - packet transfer, without acknowledge, routing support

ARP Address Resolution Protocol - ARP table - determining physic address from IP address

RARP Reverse Address Resolution Protocol - automatic allocation of IP address to the connected node

ICMP Internet Control Message Protocol - transfer of reserved service information

• Data transfer between the applications

• TCP (Transmission Control Protocol) - provides:- connected service - makes connections between the nodes- acknowledging of successful data receiving

• UDP (User Datagram Protocol) - provides: - non-connected, non-reliable data transfer

Transport LayerTCP Layer

• Ports of well-known services (WWW - port no. 80)

• Other services - dynamic generated ports

Port = number of the serviceSocket = IP address + port

Ports and protocols of some services

Transport medium

HTTP

80

HTTP

80

FTP TELNET SMTP POP3 DNS NFS RPC

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IP

TCP UDP

Network interface

• Applications and services communicate directly with the transport layer

• Application implements needed mechanisms not supported in used transport layer

• The main model of TCP/IP communication:client-server.

Client actively requests the service and starts the communicationServer provides the service passively at the client request.

Application Layer

Protocols of applikation layer

FTP (File Transfer Protocol) rfc 959

Telnet - rfc 854

SMTP (Simple Mail Transfer Protocol) rfc 821

POP3 (Post Office Protocol) rfc1939

HTTP (Hypertext Transfer Protocol) rfc 2616

DNS (Domain Name System) rfc1035

DHCP (Dynamic Host Configuration Protocol)

From 1969 all information about Internet published in RFC (Request for Comments) web accessible (http://www.rfc-editor.org).

Network is inaccessible

ipconfig - default gateway determining ping to IP address - answer of gateway

Useful commands

nslookup address domain and IP address resolving

tracert address prop. of the trace to the node