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CS-328A Networking Primer

Internet Programming

TCP/IP

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OSI Network Model

7

6

5

4

3

2

1

ApplicationLayer

Presentation Layer

SessionLayer

TransportLayer

NetworkLayer

Data LinkLayer

Physical Layer

Provides the interface to a set of network-wide services.Provides such services as: file transfer access and management, document andMessage interchange, job transfer, etc.

Provides a syntax independent message interchange service.Provides for data representation conversion and syntax negotiation.

Provides the control structure for communication between applications.Establishes, manages, and terminates sessions between applications.

Provides a message transfer facility independent of underlying network.Provides for end-to-end message transfer.Deals with connection management, fragmentation, flow control, error control.

Breaks data into information packets.Provides a virtual packet carrying end-to-end connection.Deals with routing, addressing, call setup, buffering, and flow control.

Breaks data into information frames.Provides a data link that is free of undetected transmission errors.Deals with framing, data transparency, error control, flow control

Deals with bits. Provides a virtual bit pipe.Provides for the transmission of bit streams over physical medium.Deals with mechanical, electrical, functional, & procedural aspects of medium.

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LANs

• Local Area Networks– Layers 1 and 2 of the OSI model

– A collection of peer computers connected together with a common wire protocol

• Ethernet

• Token Ring

– for the purpose of local communications

• Printer sharing

• File sharing

– Usually connected together in the same geographical area • Each host identified by its Media Access Control (MAC) address

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2 Peers Connected Together

PC NIC PCNIC

S S

R R

Crossover Cable

Peer Connections like this are ok for connecting two computers together, connecting additional computers together requires the creation of a Local Area Network (LAN)

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LAN

HUB

STAR Topology

ethernet

ethernet

ethernet

ethernet

ethernet

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Ethernet (CSMA/CD)

• Polite Human Communication– Listen before speaking, if someone else is speaking wait for them

to finish

– While speaking, if someone else starts speaking, stop speaking• This collision detection

• Carrier Sense Multi Access w/Collision Detection– Carrier Sense is how you tell if someone else is already talking

– While sending, listen to the receive if you hear someone a collision is occurring so hold off and try later

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Ethernet Cable

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An internetwork

WAN

LAN

LAN

LANLAN LAN

LA

LAN

LAN

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Internetworks

• A network of networks

• Hubs let you build LANs

• To join LANs into a WAN requires a device that works at the Network Layer of the OSI model to bridge the multiple networks– This is usually an IP Router

• Could also be a Switch or a Bridge

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TCP/IP

• Transmission Control Protocol and Internet Protocol (TCP/IP)– software suite that enables a single, standards

based approach to communications for a heterogeneous wide area network

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Layering

• Network protocols are usually developed in layers

• TCP/IP protocol suite is a combination of a set of protocols operating at the various layers

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TCP/IP Layers

Application

Transport

Network

Linkdevice driver and interface card ARP/RARP

IP, ICMP,IGMP

TCP, UDP

Telnet, FTP, SMTP....

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Link Layer

• Handles all of the details of physically connecting a machine to the network– network card– device driver for the card– operating system

• Protocols– Address Resolution Protocol (ARP)– Reverse Address resolution Protocol (RARP)

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NetworkLayer

• handles the movements of packets around the network

• routing takes place in the network layer

• protocols– Internet Protocol (IP)– Internet Control Message Protocol (ICMP)– Internet Group Management Protocol (IGMP)

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Transport Layer

• provides a flow of data between two hosts for the application layer

• Transmission Control Program (TCP)– Reliable Delivery System

• User Datagram Protocol (UDP)– also known as Unreliable Datagram Protocol

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Application Layer

• handles details of the particular application

• common applications:– Telnet for remote login– File Transfer Protocol (FTP)– Simple Mail Transfer Protocol (SMTP)– Simple Network Management (Protocol)– Ping– DateTime

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TCP and UDP

• TCP– reliable data flow

• receipt acknowledgement• packet sizing• timeouts• checksuming

– connection based• telephone metaphor

– call another host– caller knows if

answered

• UDP– sends datagrams

(packets) fast– no guarantees– connectionless

• mailbox metaphor– datagram is a letter– put letter into

mailbox– hope someone picks

it up

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TCP Frame• 16 bit Source Port number

• 16 bit Destination Port Number

• 32 bit Sequence Number

• 32 bit Acknowledgement Number

• 4 bit Data Offset

• 6 bit reserved

• 1 bit Urgent Flag (URG)

• 1 bit Acknowledgement Field is valid (ACK)

• 1 bit Push Function (PSH)

• 1 bit Reset connection (RST)

• 1 bit Synchronized sequence numbers (SYN)

• 1 bit No more data from sender (FIN)

• 16 bit Window field (# of bytes sender is willing to accept)

• 16 bit checksum (one’s complement sum of all 16 bit words in the header and data)

• 16 bit urgent pointer (add to sequence # of this segment, this pointer to last octet of urgent data

• options -

• padding

• data

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TCP Connection - Establish

• TCP establishes a connection between two hosts by performing a 3-way handshake, this will establish a virtual connection between the two hosts Host 1 Host 2

Send SYN seq=x

Receive SYN segment

Send SYN seq=y, ACK x+1

Receive SYN + ACK segment

Send ACK y+1

Receive ACK Segment

Network Messages

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TCP Connection - Closing

Send FIN seq=x

Receive FIN segment

Send ACK x+1

Receive FIN + ACK segment

Send ACK y+1

Receive ACK Segment

Network Messages

Send FIN ,ACK seq=x+1Receive ACK segment

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Client/Server and TCP/IP

FTP Client

FTP Server

TCPTCP

IP IPIP

Ethernet driver

Ethernet driver

Ethernet

FTP Protocol

TCP Protocol

IP Protocol

Ethernet Protocol

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IP Routing and protocol conv.

FTP Client

FTP Server

TCPTCP

IP IP

Ethernet driver

Token ring Driver

Ethernet

FTP Protocol

TCP Protocol

IP Protocol IP Protocol

IP

Router

Ethernet driver

Token ring driver

Token Ring

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A Clearer Picture

User Process

User Process

User Process

User Process

TCP UDP

IPICMP IGMP

Hardware Interface

ARP RARP

Application

Transport

Network

Link

media

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Internet Addresses (IPv4)

• 32 bit number– written as 4 decimal numbers seperated by

periods (dotted decimal notation)

• Five classes of internet addresses– class A thru class E

• netid are issued by InterNIC (Internet Network Information Center) also registers domain names

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Class A

00

7 bits7 bits

netidnetid

24 bits24 bits

hostidhostid

0.0.0.00.0.0.0 thru 127.255.255.255 thru 127.255.255.255

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Class B

128.0.0.0 thru 191.255.255.255128.0.0.0 thru 191.255.255.255

1010 netidnetid

14 bits14 bits 16 bits16 bits

hostidhostid

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Class C

192.0.0.0 thru 223.255.255.255192.0.0.0 thru 223.255.255.255

110110

21 bits21 bits 8 bits8 bits

netidnetid hostidhostid

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Class D

224.0.0.0 thru 239.255.255.255224.0.0.0 thru 239.255.255.255

1110

28 bits

multicast group id

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Class E

240.0.0.0 thru 247.255.255.255240.0.0.0 thru 247.255.255.255

1111011110

27 bits27 bits

reserved for future usereserved for future use

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IPv6 (IPng)

• 128 bit number– written as 8 decimal numbers separated by colons

• 3 types of addresses– Unicast - a packet sent to a unicast address is delivered to the interface

identified by that address

– Anycast - an identifier for a set of interfaces(typically belonging to different nodes). A packet sent to an anycast address is delivered to one of the interfaces identified by the address (the “nearest” identified by the routing protocol’s measure of distance)

– Multicast - An identifier for a set of interfaces ( typically belonging to different nodes). A packet sent to a multicast address will be delivered to all interfaces identified by that address.

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IPv6 Text representation of Addresses

• Preferred form:– x:x:x:x:x:x:x:x

• where each x represents a 4 hexadecimal digit 16-bit piece of the address– FEDC:BA89:7654:3210:FEDC:BA98:7654:3210

– 1080:0:0:0:8:800:200C:417A

– note - leading zeros are not required

– note- pieces consisting of all zero bits may be shown as ::

• Alternative form– sometimes used in mixed IPv4 and IPv6 environments

• x:x:x:x:x:x:d.d.d.d– where x represents high order 6 pieces of IPV6 address and the 4 d’s represent the

IPv4 address

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IPv4 to IPv6 transition

0000…………………………………………0000 0000 IPv4 address

80 bits 16bits 32 bits

0000…………………………………………0000 FFFF IPv4 address

80 bits 16bits 32 bits

IPv4-compatible IPv6 address (special IPv6 unicast address that contain the IPv4 address)

IPv4-mapped IPv6 address

For tunneling IPV6 packets through an IPv4 infrastructure use:

For nodes that are IPv4 only (do not support IPv6) use:

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Domain Name System (DNS)

• Distributed database– provides translation between IP addresses and

hostnames (and vice-versa)

• Most TCPIP Applications can use either way of identifying a host (i.e. by host name or IP address)

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Encapsulation

user data

user dataApp.Hdr

user dataApp.HdrTCP Hdr

user dataApp.HdrTCP HdrIP Hdr

user dataApp.HdrTCP HdrIP Hdrethernet hdr

ethernet trailer

ethernet frame

Application

Transport

Network

Link

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Ports and Sockets

• mean the same thing, part of a buffering scheme

• implemented at transport layer (TCP/UDP)

• 16 bit number in the TCP or UDP header (32767 connection possible)

• ports 1 thru 1023 reserved for “well known ports”

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Well Known Ports

• ports used for common TCP/IP applications– TCP port 7 - Echo– TCP port 20 - FTP-Data– TCP port 21 - FTP-Commands– TCP port 23 - telnet– UDP port 67 - BOOTP (Server)– UDP port 68 - BOOTP (Client)– UDP port 69 - TFTP– etc

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Java and sockets

• supports both TCP and UDP sockets– also multicast under RMI

• provided both ends of a TCP application connection (i.e. client and server facilities)

• java.net

• also provides URL connections

• can be used to implement almost any existing internet protocol.

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Java Sockets

• create a socket

• create an input stream

• create an output stream

• connect the inputstream to the socket

• connect the output stream to the socket

• reading and writing the stream transfers data between the two hosts (local and remote)