Application-Level Implementation of TCP Team Alaska San Jose State University Fall 2007 CMPE207 Dr....

Application-Level Implementation of TCP

Team AlaskaSan Jose State UniversityFall 2007

CMPE207Dr. Frank Lin

Chris NelsonRuchir Sutaria

Kimsi SinghGagandeep Singh

Team Alaska – Fall 2007 Slide 2

Team Members

Gagandeep Singh

- Server Application- Concurrency Expert

Kimsi Singh

- Client Applications- Test Expert

Chris Nelson

- Team Leader- Documentation- Connection Establishment/ Termination

Ruchir Sutaria

- Seq/Ack Numbering- Flow Control Guru

Slide Prepared/Presented by: C. Nelson


Agenda

Project Management Code Control

Documentation

Design Overview Protocol Code

Concurrent Server

Client Test Applications

Test Overview Test Cases

Test Results



Project Management

SourceForge.net:

http://cmpe207-alaska.sourceforge.net

CVS repository for code control

Wiki pages for documentation and tasks

Google Groups:

http://groups.google.com/group/cmpe207-alaska-developers

Archive of team e-mail discussions



Project Management

Our main project wiki page...



Project Management

Tracking our tasks and progress...



Project Management

Tracking our discussions...



Project Management

Tracking our code...



Design Overview

General Concept: Create an Additional Layer

cmpe207server.cpp (Application) cmpe207client.cpp (Application)

CMPE207 Protocol (Application) CMPE207 Protocol (Application)

UDP Protocol (Transport Layer) UDP Protocol (Transport Layer)

IP Protocol (Network Layer) IP Protocol (Network Layer)

Data Link Layer Data Link Layer

Physical Layer



Design Overview

Create an API

extern int cmpe207_socket (int type);

extern int cmpe207_bind (int sockfd, cmpe207_sockaddr *myaddr, int addrlen);

extern int cmpe207_listen (int sockfd, int queue_size);

extern int cmpe207_accept (int sockfd, cmpe207_sockaddr *claddr, int addrlen);

extern int cmpe207_send (int sockfd, const char* buf, int len, int flags);

extern int cmpe207_recv (int sockfd, char* buf, int len, int flags);

extern int cmpe207_close (int sockfd);

extern int cmpe207_connect (int sockfd, cmpe207_sockaddr *myaddr, int addrlen);



Design Overview

Control Structures

socket_blocks: Array of socket control blocks1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 ...

/* Socket control block */typedef struct {

int socket_desc; //Socket descriptorshort inuse; //In-use flag (TRUE or FALSE)cmpe207_sockaddr local_addr; //Local address, port, UDP portcmpe207_sockaddr remote_addr; //Remote address, port, UDP portint udp_sockfd; //UDP socket descriptorshort state; //Connection stateint listen_queue_size; //Listen queue size

// Send sequence variables...uint32_t snd_una; //send unacknowledgeduint32_t snd_nxt; //to keep track of sender seq nouint16_t send_window; //Send windowuint16_t snd_wl1; //Seg seq num used for last windowuint16_t snd_wl2; //Seg ack num used for last win updateuint16_t ISS; // initial send seq number

// Receive sequence variables...uint32_t rcv_nxt; //recv nextuint16_t rec_window; //Receive windowuint16_t IRS; //initisl recv seq number

// Current segment variables...uint32_t seg_ack; //ACK Numberuint32_t seq_nbr; //Sequence Numberuint32_t seg_len; //segment length uint32_t seg_wnd; //segment window

// Time variables...uint32_t last_data_snd; //time of last data senduint32_t last_ack_snd;uint32_t last_data_rcvd;uint32_t last_ack_rcvd;

} cmpe207_control_block;



Design Overview

Packet Header StructureByte 0 20 28 48... ... up to 999

IP HeaderUDP

Header 207 Header 207 Data

/* CMPE207 Packet Header */typedef struct { uint16_t src_port; /* 16-bit source port */ uint16_t dest_port; /* 16-bit destination port */ uint32_t seq_nbr; /* 32-bit sequence number */ uint32_t ack_nbr; /* 32-bit ack number */ uint16_t f_flag : 1, /* Fin flag */ s_flag : 1, /* Sync flag */ r_flag : 1, /* Reset flag */ p_flag : 1, /* Push flag--off except for close */ a_flag : 1, /* Ack flag */ u_flag : 1, /* Urgent flag--always off */ offset : 10; /* Offset--always 0x05 */ uint16_t window; /* 16-bit window field */ uint16_t chksum; /* 16-bit checksum field */ uint16_t urgptr; /* 16-bit urgent pointer--unused */ } cmpe207_pkt_hdr;



Design Overview

Internal Functions

int cmpe207_pack (char *udp_data, cmpe207_pkt_hdr *header, char *data_207, int data_207_length);

int cmpe207_unpack (char *udp_data, unsigned int udp_data_size, cmpe207_pkt_hdr *header, char *data_207, unsigned int data_207_size);

header data_207

udp_data

header data_207

udp_data



Design Overview

Screenshot of cmpe207_unpack()...



Design Overview

Screenshot of cmpe207_scb_print()...



Design Overview

Flow Control

Basic sequencing in cmpe207_connect, cmpe207_accept, cmpe207_send, cmpe207_receive and cmpe207_close

Cumulative Ack with no sequence increment for Ack packet

Timeouts and retransmission

Window Management

Slide Prepared/Presented by: R. Sutaria


Design Overview

Basic Sequencing

Whenever data sent Seq nbr of segment Length of data sent Segment window length Send unack ,Send next, Last

data send and send window are set based on values in the TCB

Whenever data received Checks for flags Check valid range Store the incoming window

length Recv nxt, seq nbr, last data

recvd and last ack recvd set based on the received header values



Design Overview

Timeouts, Retransmission, and Window Management

The timeout done using select() function.

Retransmission based on state and the window size

Window size is dynamic

Have the capability to transmit large chunks of data.

Done by splitting the packet according to window size



Design Overview

The cmpe207_send function will split the data and send it to the receiver. This provides us a mechanism to send large chunks of data.


2000 Bytes Data

500 Bytes

500 Bytes

500 Bytes

500 Bytes

Advertised window size = 500Data Packet Size = 2000


Design Overview

THE SERVER Key Elements

Implements the 207 – Protocol API (discussed earlier)

In addition, has its own API (For logging any data)

- Server_Accept()

- Server_Read()

- Server_Write()

- Server_Close()

Concurrent (Can handle upto 10 clients at a given time)

Multi-Threaded

Slide Prepared/Presented by: G. Singh


Design Overview

THE SERVER (Multi - Threading)

master

slave1 slave2 slave3

Socket



Design Overview

THE SERVER (Multi - Threading)

Socket

master

slave1

Request

Data



Design Overview

THE SERVER (Our Approach) CRUX:

Issue: Race Condition - recvfrom() function, as only ONE socket, but multiple threads

Solution: The main thread always yields to the slave thread, except in SYN_RECEIVED state

Issue: Shared Memory Solution: Every Thread given its own routine

to execute



Design Overview

THE SERVER Features Targeted:

RobustnessPerformanceReliability



Test Cases

INTERACTIVE TEST APPLICATION

Includes 25 Test Cases; 25 Cases have been implemented

Plan to include 25 more, before submission

Slide Prepared/Presented by: K. Singh


Test Cases

Test Cases: Five chosen test cases

All Flags UP (ALL_FLAGS_UP) No Acknowledgment after the received data

(NO_ACK_OF_RECEIVED_DATA) Reset after the data sent (RST_AFTER_DATA_SENT) Malformed Header (MALFORMED_HEADER) SYN_ATTACK



Test Cases

(ALL_FLAGS_UP) SERVER in Listen State

Clearly a false packet

Listen State

All flags set, including SYN

PKT



Test Cases EXPECTED RESULT Packet should be ignored! Also, THREE WAY HANDSHAKE should not

proceed…

ACTUAL RESULT

Server Proceeded with the Handshake.

Failed the Test.



Test Cases(NO_ACK_OF_RECEIVED_DATA)

The Server waits for an ACK but does not get an ACK!

Server

ACK

Client receives converted data

Client



The Expected Behavior is:

1) Slave Socket times out and closes.

2) Server remains in the listening mode

Actual result:

Server passed this test.

Test CasesSlide Prepared/Presented by: K. Singh


Test Cases(RST_AFTER_DATA_SENT)

Sends Data

RST



Test Cases

EXPECTED RESULT Slave socket expected to receive this RST and

respond with an RST and Finally close. Server is expected to continue in the listening

mode.

ACTUAL RESULT

Server Failed the Test



Test CasesMALFORMED_HEADER

Header of 18 bytes instead of 20 bytes ( Corrupted header).

ALL Flags : OK

EXPECTED BEHAVIOUR

Slave Socket is expected to ignore the packet.

Actual Behavior = Expected Behavior

Server passes the test.



Test Cases SYN_ATTACK Client Keeps Sending SYN even after getting a

SYN_ACK from the Server

SYNSYN

SYNSYN



Different implementations come up with different solutions to this problem. Bottomline: Server should not be fooled.

Our Approach:

If Server receives 5 SYN packets from the same IP address and port in SYN_RECEIVED , it sends an RST and goes back to the LISTEN state.

Test Cases



Test ResultsSlide Prepared/Presented by: K. Singh


References

http://cmpe207-alaska.sourceforge.net

http://www.ietf.org/rfc/rfc793.txt

http://www.50states.com/maps/alaska.gif

http://www.wunderground.com/data/wximagenew/h/hinzmanb/88.jpg

http://maps.google.com


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