Outline: ATM, Sockets Programming

• ATM (Asynchronous Transfer Mode)
  • Routing
  • QoS (Quality of Service)
• Sockets Programming
  • socket
  • connect
  • bind
  • listen
  • accept
  • read
  • write
  • read
  • close

ATM

• Asynchronous Transfer Mode -- as opposed to SONET (Synchronous Optical Network)
• originally telephone technology
• virtual circuits
• 53-byte fixed-size cells with 5-byte header
• resource reservation:
  • video
  • audio
  • best-effort

ATM Switching

• 5-byte header has a two-part identifier
• identifier is only meaningful in one direction along a single link
• when cell is received, switch:
  • uses port number and identifier as index into table containing:
    • outgoing identifier
    • outgoing port number
    • QoS indication
  • places outgoing identifier into cell header
  • routes cell to outgoing port
• table is set up at "virtual circuit setup time"

Example

ATM QoS

• Leaky bucket
• Example: 100 sources, each sending at rate r <= (0.1 + 1.5t)Mb/t
  • if t >> 1, r =~ 1.5 Mb/s
  • if t << 1, burst <= 0.1 Mb
  • therefore, traffic can be carried with no loss by a 155Mb/s link with a 10Mb buffer.
  • Maximum delay is (10Mb / 155Mb/s) =~ 0.065 s = 65ms.
• Leaky bucket and QoS reservations can be used to bound delay and eliminate or bound data loss.

Sockets: Overview

• Server listens for connections
• Server is identified by
  (ip address, port number)
• Client initiates connections
• Client is assigned a port number automatically
• Data can be exchanged in either direction
• (ipA, portA, ipB, portB) uniquely identifies a socket

socket system call

• socket

  (int domain, 

  int type, 

  
  

         int protocol)

• socket returns a file descriptor
• socket domain is

  AFINET

  for internet
• socket type is

  SOCKSTREAM

  for TCP,

  SOCKDGRAM

  for UDP
• protocol is given by

  getprotobyname("tcp")

connect system call

• connect is used by client to connect to server

• int connect(int s, /* socket */

  
  

              struct sockaddr *name,

  
  

              int namelen);

• connect returns 0 for success, -1 for failure
• s is a socket obtained by calling socket
• name is an address family and IP address obtained from gethostbyname (see homework 1)
• namelen is the size, in bytes, of the structure passed as the second argument

IP address

struct hostent * hostentry;
struct sockaddrin sin;
struct sockaddr * sap =
   (struct sockaddr *) &sin;
hostentry =
   gethostbyname("maru.ics.hawaii.edu");
if ((hostentry == NULL) ||
    (hostentry->haddrlist == NULL))
  error("gethostbyname");
bzero (&sin, sizeof (sin));
sin.sinfamily = AFINET;
bcopy(hostentry->haddrlist[0],
      &(sin.sinaddr),
      hostentry->hlength);
sin.sinport = htons(portnumber);
if (connect(s, sap, sizeof(sin)) < 0)
  error("connect");

Notes:

bind

• bind is used by server to identify port it is listening on

• int bind(int s,

           const struct sockaddr *name,

           int namelen);

• bind returns 0 for success, -1 for failure
• bind uses a special address (

  INADDRANY

  ) to specify it will accept connections from any host.
• use

  htons

  (host-to-network short) when specifying the port number to make sure the port number is stored in big-endian format.

listen

• listen is used by server to specify the maximum number of pending connections

• int listen(int s, int backlog);

• listen returns 0 for success, -1 for failure

accept

• accept is used by server to create a new socket when a new connection is requested by the client.

• int accept(int s,

             struct sockaddr *addr,

             int *addrlen);

• accept returns a new file descriptor for success, -1 for failure
• the address and addrlen pointers are optional (can be NULL), only used if the server wants to know the address of the client. If address is specified, before the call {\tt addrlen} MUST have the size of the object pointed to by address.

read

• read is used by either side to receive data sent by the other side.

• int read(int s,

           char *buf,

           int bufsize);

• read returns the number of bytes read for success, -1 for failure
• the buffer and buffer size must be specified.
• the buffer size must be the size of the area pointed to by buf
• the number of bytes read is always less than or equal to the bufsize
• after the call, the buffer does NOT contain a C string, because it lacks the terminating null character.

Notes:

write

• write is used by either side to receive data sent by the other side.

• int write(int s,

            char *buf,

            int nbytes);

• write returns the number of bytes written for success, -1 for failure. The number of bytes written will always be less than or equal to nbytes.
• the buffer and buffer size must be specified.
• the buffer size must be less than or equal to the size of the area pointed to by buf
• write will happily write NULL characters, so use

  strlen

  to compute nbytes when writing C string.

close

• all file descriptors, including sockets, should be closed when no longer needed (otherwise your program may run out of file descriptors).

• int close(int fd);

• close returns 0 for success, -1 for failure.

Homework 1

• Experiment with Unix Clients and Servers
• See web page.
• Request Unix account if needed, by sending mail to sunx@hawaii.edu
• Request account IMMEDIATELY, since may take 1-2 days to set up
• Due on Friday September 4th (because project 1 will be assigned on Friday), but can be handed in as late as Wed. (September 9th) for full credit.