1. CSTP FS01CS423 (cotter)1 Protocols 2 References: RFC’s 791, 793, 768, 826

2. CSTP FS01CS423 (cotter)2 Lecture Outline TCP Header TCP Functions Introduction to Sockets

3. CSTP FS01CS423 (cotter)3 TCP Protocol Functions Connection Oriented Sequence Numbers Flow Control Reliable Data Transfer Congestion Control

4. CSTP FS01CS423 (cotter)4 TCP Header 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source Port | Destination Port | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sequence Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Acknowledgment Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Data | |U|A|P|R|S|F| | | Offset| Reserved |R|C|S|S|Y|I| Window | | | |G|K|H|T|N|N| | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Checksum | Urgent Pointer | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Options | Padding | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | data | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

5. CSTP FS01CS423 (cotter)5 TCP - Connection control 2-way Handshake 3-way Handshake System ASystem B syn syn i syn j ack i+1 data i+1 ack j+1 data

6. CSTP FS01CS423 (cotter)6 Segment Sequence Numbers 32 bit field (2^32 numbers) suggest timer based initialization (4 microsec.) wrap-around at 4.55 hrs.

7. CSTP FS01CS423 (cotter)7 TCP Window Identify how much data a receiving site can hold (buffer size) in bytes. Example: –Window size is 4096 bytes –Assume packet size is 512 bytes (with 40 additional bytes for TCP and IP headers). –Initial sequence number is 123000

8. CSTP FS01CS423 (cotter)8 TCP Window System ASystem B seq 123000 ack 124536 credit 4096 ack 126584 credit 4096 seq 123512 seq 126072 seq 124536 seq 125048 seq 125560 seq 124024

9. CSTP FS01CS423 (cotter)9 TCP Window (recv failure) System ASystem B seq 123000 ack 124536 credit 4096 ack 125048 credit 4096 seq 123512 seq 126072 seq 124536 seq 125048 seq 125560 seq 124024

10. CSTP FS01CS423 (cotter)10 TCP-Reliable Data Transfer Lost Packet Retransmission –Go-Back-N –Selective Repeat Round Trip Time Calculation –time from send to ack –RTT = X * old_RTT + (1 - X)*new_RTT –Karn’s Algorithm (don’t time retransmissions)

11. CSTP FS01CS423 (cotter)11 TCP - Flow Control 0123456701234567 Packets sent ack. window (8)

12. CSTP FS01CS423 (cotter)12 TCP - Congestion Control Window-size backoff –multiplicative decrease –additive increase

13. CSTP FS01CS423 (cotter)13 Sockets Introduction IP Addresses 134.193.2.254 134.193.2.250

14. CSTP FS01CS423 (cotter)14 Sockets Introduction Ports 134.193.2.254 134.193.2.250 123789

15. CSTP FS01CS423 (cotter)15 Sockets Introduction Socket App 1 App 2App 3 1 23 134.193.2.254

16. CSTP FS01CS423 (cotter)16 Internet Ports 16 bit fields (64k ports possible) Duplicate sets for TCP and UDP Well-known Ports ( 1-255 reserved) –ftp: 21telnet:23finger: 79 –time:37echo:7SNMP: 161 BSD usage conventions –1 - 1024 Privileged Ports –1025 - 5000General Applications (arbitrary ports) –5000 +Site Specific services

17. CSTP FS01CS423 (cotter)17 Basic Socket Functions Server Socket ( ) –Create a socket of a particular type Bind ( ) –Bind that socket to a specific port Listen ( ) –Wait for an incoming message Accept ( ) –Create a new socket and return new socket ID to server

18. CSTP FS01CS423 (cotter)18 Basic Socket Functions Server Read ( ) –Read an incoming message Write ( ) –Send a message to client Close ( ) –Close the socket

19. CSTP FS01CS423 (cotter)19 Basic Socket Functions Client Socket ( ) –Create a socket of a particular type Connect ( ) –Establish a connection to a remote Port/Socket Read ( ) / Write ( ) –Send and receive messages to/from remote socket Close ( ) –Close the socket

20. CSTP FS01CS423 (cotter)20 Socket Interaction Client Server Wait for connection requests and accept when one arives accept ( ) Create a Socket socket ( ) Bind address to socket bind ( ) Put socket in listen state listen ( ) Create a Socket socket ( ) Bind address to socket bind ( ) Make a connection request connect ( )

21. CSTP FS01CS423 (cotter)21 Additional Socket Functions Byte ordering functions –DEC / Intel vs Internet / 68000 Name resolution functions –host / protocol / service –by name / address / port Other Stuff

22. CSTP FS01CS423 (cotter)22 Information Byte Ordering Convert from host to network order htons ( )/* used to convert a short integer */ htonl ( )/* used to convert a long integer */ Convert from network to host order ntohs ( ) ntohl ( )

23. CSTP FS01CS423 (cotter)23 Host Name Lookup Convert Domain name to IP address hostent *hptr gethostbyname (char *newname) struct hostent { char *h_name; /* official host name */ char **h_aliases;/* other aliases */ int h_addrtype;/* address type */ int h_length;/* address length */ char**h_addr_list;/* list of addresses*/ }; #define h_addrh_addr_list[0]

24. CSTP FS01CS423 (cotter)24 Port Number Lookup Used for well-known services servent *sptr getservbyname(char *service) struct servent{ char *s_name;/* official service name */ char**s_aliases;/* other aliases */ int s_port;/* port for this service */ char *s_proto;/* protocol to use */ };

25. CSTP FS01CS423 (cotter)25 Protocol Number Lookup Used to convert protocol name to official number protoent *pptr getprotobyname ( char *protocol) structprotoent{ char *p_name;/* official protocol name */ char**p_aliases;/* list of aliases allowed */ short p_proto;/* official protocol number */ };

26. CSTP FS01CS423 (cotter)26 Socket Address Structure connect (sd, (struct sockaddr far *) &addr_Loc, sizeof(addr_Loc)); struct sockaddr_in { u_shortsin_family; /* address family */ u_shortsin_port;/* address port */ struct in_addrsin_addr;/* IP address (union) */ charsin_zero[8];/* filler */ };

27. CSTP FS01CS423 (cotter)27 Course Review: Evolution of C / S Architecture –how did we get to Client Server? Objectives of C/S Architecture –What problem is C/S trying to solve? C / S transport (specifically Internet model) –How do the lower protocol layers work? Socket Concepts –How do sockets (in general) work?

28. CSTP FS01CS423 (cotter)28 Next Step: Client/Server in Windows CSTP Windows Support Environment Windows Operating Environment Windows Programming Environment Sockets