Transmission Control Protocol / Internet Protocol Based on Notes By

8/14/2019 Transmission Control Protocol / Internet Protocol Based on Notes By

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Netprog 2002 TCP/IPNetprog 2002 TCP/IP

TCP/IPTCP/IPTransmission Control Protocol / InternetTransmission Control Protocol / Internet

ProtocolProtocol

Based on Notes by D. Hollinger


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TopicsTopics

IPv6

TCP

Java TCP Programming


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IPv6 availabilityIPv6 availability

Generally available with (new) versions

of most operating systems. BSD, Linux 2.2 Solaris 8

An option with Windows 2000/NT Most routers can support IPV6 Supported in J2SDK/JRE 1.4


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IPv6 Design IssuesIPv6 Design Issues

Overcome IPv4 scaling problem lack of address space.

Flexible transition mechanism. New routing capabilities.

Quality of service.

Security. Ability to add features in the future.


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IPv6 HeadersIPv6 Headers

Simpler header - faster processing byrouters.

No optional fields - fixed size (40 bytes) No fragmentation fields. No checksum

Support for multiple headers more flexible than simple protocol field.


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IPv4 HeaderIPv4 Header

VERS HL

Fragment Offset

Fragment LengthService

Datagram ID FLAG

TTL Protocol Header ChecksumSource Address

Destination Address

Options (if any)

Data

1 byte1 byte 1 byte 1 byte

4 for IPv4


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IPv6 HeaderIPv6 Header

VERS PRIO

Hop Limit

Flow Label

Payload Length Next Header

1 byte1 byte 1 byte 1 byte

6 for IPv6

Source Address (128 bits - 16 bytes)

Dest. Address (128 bits - 16 bytes)


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IPv6 Header FieldsIPv6 Header Fields

VERS: 6 (IP version number) Priority: will be used in congestion control

Flow Label: experimental - sender can label asequence of packets as being in the sameflow.

Payload Length: number of bytes in

everything following the 40 byte header (up to

64Kb), or 0 for a Jumbogram (up to 4Gb).


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IPv6 Header FieldsIPv6 Header Fields

Next Header is similar to the IPv4protocol field - indicates what type of

header follows the IPv6 header.

Hop Limit is similar to the IPv4 TTL field(but now it really means hops, not time).


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Extension HeadersExtension Headers

Routing Header - source routing Fragmentation Header - supports

fragmentation of IPv6 datagrams.

Authentication Header

Encapsulating Security Payload Header


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IPv6 AddressesIPv6 Addresses

128 bits - written as eight 16-bit hexnumbers.

5f1b:df00:ce3e:e200:0020:0800:2078:e3e3

High order bits determine the type of

address.


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IPv6IPv6

Aggregate Global UnicastAggregate Global Unicast

AddressAddress

010 TLA ID NLA ID SLA ID Interface ID

3 13 32 16 64

TLA: top-level aggregation (provider)

NLA: next-level (subscriber)

SLA: site-level (subnet)

Interface ID is (typically) based on hardware

MAC address


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IPv4-Mapped IPv6 AddressIPv4-Mapped IPv6 Address

IPv4-Mapped addresses allow a host thatsupport both IPv4 and IPv6 to communicatewith a host that supports only IPv4.

The IPv6 address is based completely onthe IPv4 address.


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1Netprog 2002 TCP/IPNetprog 2002 TCP/IP

IPv4-Mapped IPv6 AddressIPv4-Mapped IPv6 Address

80 bits of 0s followed by 16 bits of ones,followed by a 32 bit IPv4 Address:

0000 . . . 0000 IPv4 AddressFFFF

80 bits 32 bits16 bits


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Works with DNSWorks with DNS

An IPv6 application asks DNS for theaddress of a host, but the host only has

an IPv4 address. DNS creates the IPv4-Mapped IPv6

address automatically.

Kernel understands this is a specialaddress and really uses IPv4communication.


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IPv4-Compatible IPv6IPv4-Compatible IPv6

AddressAddress An IPv4 compatible address allows a

host supporting IPv6 to talk IPv6 even if

the local router(s) dont talk IPv6. IPv4 compatible addresses tell endpoint

software to create a tunnel by

encapsulating the IPv6 packet in anIPv4 packet.


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IPv4-Compatible

IPv6 Address

0000 . . . 0000 IPv4 Address0000

80 bits 32 bits16 bits

80 bits of 0s followed by 16 bits of 0s,

followed by a 32 bit IPv4 Address:


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TunnelingTunneling

(done automatically by kernel when(done automatically by kernel when

IPv4-Compatible IPv6 addresses used)IPv4-Compatible IPv6 addresses used)IPv6

Host

IPv6

Host

IPv4 Routers

IPv6 Datagram

IPv4 Datagram


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IPv6 in Java 1.4IPv6 in Java 1.4

Inet6Address class :: corresponds to 0.0.0.0 (unspecified) in IPv4

::1 corresponds to 127.0.0.1 (loopback) in IPv4

::ffff:w.x.y.z IPv4-mapped address ::w.x.y.z to tunnel IPv6 packets over IPv4 routing

For details, see:http://java.sun.com/j2se/1.4/docs/guide/net/ipv6_guide/


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TCPTCP

Transmission Control ProtocolTransmission Control Protocol TCP is an alternative transport layer

protocol over IP.

TCP provides:Connection-oriented

Reliable

Full-duplexByte-Stream


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Connection-OrientedConnection-Oriented

Connection orientedmeans thata virtual connection is establishedbefore any user data istransferred.

If the connection cannot beestablished - the user program isnotified.

If the connection is everinterrupted - the user program(s)is notified.


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ReliableReliable

Reliable means that everytransmission of data is

acknowledged by the receiver. If the sender does not receive

acknowledgement within a

specified amount of time, thesender retransmits the data.


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Byte StreamByte Stream

Stream means that theconnection is treated as a stream

of bytes.

The user application does notneed to package data in individualdatagrams (as with UDP).


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BufferingBuffering

TCP is responsible for buffering dataand determining when it is time to

send a datagram.

It is possible for an application to tell

TCP to send the data it has buffered

without waiting for a buffer to fill up.


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Full DuplexFull Duplex

TCP provides transfer in both directions.

To the application program these appearas 2 unrelated data streams, althoughTCP can piggyback control and data

communication by providing controlinformation (such as an ACK) along withuser data.


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TCP PortsTCP Ports

Interprocess communication viaTCP is achieved with the use of

ports (just like UDP).

UDP ports have no relation to TCPports (different name spaces).


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TCP SegmentsTCP Segments

The chunk of data that TCP asks IPto deliver is called a TCP segment.

Each segment contains:

data bytes from the byte stream control information that identifies thedata bytes


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TCP Segment FormatTCP Segment Format

Destination Port

Options (if any)

Data

1 byte 1 byte

Source Port

Sequence Number

Acknowledgment Number

1 byte 1 byte

offset Reser. Control Window

Checksum Urgent Pointer


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TCP LingoTCP Lingo

When a client requests a connection itsends a SYN segment (a special TCP

segment) to the server port. SYN stands for synchronize. The SYN

message includes the clients ISN.

ISN is Initial Sequence Number.


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More...More...

Every TCP segment includes aSequence Numberthat refers to the firstbyte ofdata included in the segment.

Every TCP segment includes anAcknowledgement Numberthatindicates the byte number of the next

data that is expected to be received. All bytes up through this number havealready been received.


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And more...And more...

There are a bunch of control flags: URG: urgent data included.

ACK: this segment is (among other things)an acknowledgement. RST: error connection must be reset.

SYN: synchronize Sequence Numbers(setup) FIN: polite connection termination.


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And more...And more...

MSS: Maximum segment size (A TCPoption)

Window: Every ACK includes a Windowfield that tells the sender how many bytesit can send before the receiver will have to

toss it away (due to fixed buffer size).


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TCP Connection CreationTCP Connection Creation

Programming details later - for now we areconcerned with the actual communication.

A serveraccepts a connection. Must be looking for new connections! A clientrequests a connection.

Must knowwhere the server is!


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Client StartsClient Starts

A client starts by sending a SYNsegment with the following information:

Clients ISN (generated pseudo-randomly) Maximum Receive Window for client. Optionally (but usually) MSS (largest

datagram accepted). No payload! (Only TCP headers)


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Server ResponseServer Response

When a waiting server sees a newconnection request, the server sendsback a SYN segment with:

Servers ISN (generated pseudo-randomly) Request Number is Client ISN+1 Maximum Receive Window for server.

Optionally (but usually) MSS

No payload! (Only TCP headers)


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FinallyFinally

When the Servers SYN is received, theclient sends back an ACK with:

Acknowledgment Number is ServersISN+1


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SYNISN=X

SYN

ISN=X

Client Server

SYNISN=YACK=X+1

SYN

ISN=YACK=X+1

ACK=Y+1ACK=Y+1

1

2

3


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TCP 3-way handshakeTCP 3-way handshake

Client: I want to talk, and Im starting with bytenumberX.

Server: OK, Im here and Ill talk. My first bytewill be called numberY, and I know your firstbyte will be numberX+1.

Client: Got it - you start at byte numberY+1.

Bill: Monica, Im afraid Ill syn and byte yourack

1

2

3

?


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TCP Data and ACKTCP Data and ACK

Once the connection is established,data can be sent.

Each data segment includes asequence number identifying the firstbyte in the segment.

Each segment (data or empty) includesa request number indicating what datahas been received.


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BufferingBuffering

Keep in mind that TCP is part of theOperating System. The O.S. takes care

of all these details asynchronously. The TCP layer doesnt know when the

application will ask for any received

data. TCP buffers incoming data so its ready

when we ask for it.


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TCP BuffersTCP Buffers

Both the client and server allocatebuffers to hold incoming and outgoing

data The TCP layer does this.

Both the client and server announcewith every ACK how much buffer spaceremains (the Window field in a TCP

segment).


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Send BuffersSend Buffers

The application gives the TCP layersome data to send.

The data is put in a send buffer, whereit stays until the data is ACKd. The TCP layer wont accept data from

the application unless (or until) there isbuffer space.


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ACKsACKs

A receiver doesnt have to ACK everysegment (it can ACK many segments

with a single ACK segment). Each ACK can also contain outgoing

data (piggybacking).

If a sender doesnt get an ACK aftersome time limit, it resends the data.


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TCP Segment OrderTCP Segment Order

Most TCP implementations will acceptout-of-order segments (if there is roomin the buffer).

Once the missing segments arrive, asingle ACK can be sent for the wholething.

Remember: IP delivers TCP segments,and IP is not reliable - IP datagrams canbe lost or arrive out of order.


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4


TerminationTermination

The TCP layer can send a RSTsegment that terminates a connection if

something is wrong. Usually the application tells TCP to

terminate the connection politely with a

FIN segment.


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4


FINFIN

Either end of the connection can initiatetermination.

A FIN is sent, which means theapplication is done sending data. The FIN is ACKd.

The other end must now send a FIN. That FIN must be ACKd.


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4


FIN

SN=X

FIN

SN=X

App1 App2

ACK=X+1ACK=X+1

ACK=Y+1ACK=Y+1

1

2

4

FIN

SN=Y

FIN

SN=Y

3

.

.

.


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4


TCP Termination

1

2

3

4

App1: I have no more data for you.

App2: OK, I understand you are done sending.

dramatic pause

App2: OK - Now Im also done sending data.

App1: Roger, Over and Out, Goodbye,

Hastalavista Baby, Adios, Its been real ...

camera fades to black ...


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5


TCP TIME_WAITTCP TIME_WAIT

Once a TCP connection has been terminated(the last ACK sent) there is some unfinishedbusiness:

What if the ACK is lost? The last FIN will be resentand it must be ACKd.

What if there are lost or duplicated segments thatfinally reach the destination after a long delay?

TCP hangs out for a while to handle these

situations.


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5


TCP Sockets ProgrammingTCP Sockets Programming

Creating apassive mode (server)socket.

Establishing an application-levelconnection. Sending/receiving data.

Terminating a connection.


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5


Establishing a passive modeEstablishing a passive mode

TCP socketTCP socketPassive mode:

Address already determined.

Tell the kernel to accept incoming connection requestsdirected at the socket address.

3-way handshake

Tell the kernel to queue incoming connections for us.


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5


Accepting an incomingAccepting an incoming

connection.connection. Once we start listening on a socket, the

O.S. will queue incoming connections

Handles the 3-way handshake Queues up multiple connections.

When our application is ready to handle anew connection, we need to ask the O.S.for the next connection.


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5


Terminating a TCP connectionTerminating a TCP connection

Either end of the connection can callthe close() system call.

If the other end has closed theconnection, and there is no buffereddata, reading from a TCP socket returns

0 to indicate EOF.


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5


Client CodeClient Code

TCP clients can connect to a server,which:

takes care of establishing an endpointaddress for the client socket.

dont need to call bind first, the O.S. will takecare of assigning the local endpoint address(TCP port number, IP address).

Attempts to establish a connection to thespecified server.3-way handshake


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5


Reading from a TCP socketReading from a TCP socket

By default read() will block until data isavailable. Reading from a TCP socket may return

less than max bytes (whatever isavailable).

You must be prepared to read data 1byte at a time!


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5


Writing to a TCP socketWriting to a TCP socket

write might not be able to write all bytes(on a nonblocking socket).


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5


Java Sockets ProgrammingJava Sockets Programming

The package java.net provides supportfor sockets programming

Typically you import everything definedin this package with:

import java.net.*;


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6


ClassesClasses

InetAddress

Socket

ServerSocket

DatagramSocket

DatagramPacketUDPUDP


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6


Socket classSocket class

Corresponds to active TCP sockets only! client sockets

socket returned by accept();

Passive sockets are supported by a

different class: ServerSocket


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6


Socket ConstructorsSocket Constructors

Constructor creates a TCP connectionto a named TCP server.

There are a number of constructors:Socket(InetAddress server, int port);

Socket(InetAddress server, int port,

InetAddress local, int localport);

Socket(String hostname, int port);


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6


Socket MethodsSocket Methods

void close();

InetAddress getInetAddress();getpeername

InetAddress getLocalAddress(); getsockname

InputStream getInputStream();

OutputStream getOutputStream();

Lots more (setting/gettting socket options,partial close, etc.)


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6


Socket I/OSocket I/O

Socket I/O is based on the Java I/Osupport (in the package java.io).

InputStream and OutputStream areabstract classes

common operations defined for all kinds ofInputStreams, OutputStreams


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ServerSocket ClassServerSocket Class

(TCP Passive Socket)(TCP Passive Socket)Constructors:

ServerSocket(int port);

ServerSocket(int port, int backlog);

ServerSocket(int port, int backlog,

InetAddress bindAddr);


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6


ServerSocket MethodsServerSocket Methods

Socket accept();

void close();

InetAddress getInetAddress();

int getLocalPort();

throw IOException, SecurityException


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Sample Echo ServerSample Echo Server

TCPEchoServer.java, EchoClient.java,GenericClient.java

Simple TCP Echo server.

Based on code from:

TCP/IP Sockets in Java, Java OnlineTutorial

Documents

Transmission Control Protocol / Internet Protocol Based on Notes By