Okay, there are the books you need:

"Advanced Programming in the UNIX Environment"
by W. Richard Stevens 1992 Addison-Wesley
ISBN 0-201-56317-7

"TCP/IP Illustrated Volume 2"
by Gary R. Wright, W. Richard Stevens 1995 Addison-Wesley
ISBN 0-201-63354-X

"UNIX Network Programming Volume 1"
by W. Richard Stevens 1998 Addison-Wesley
ISBN 0-13-490012-X

"UNIX Network Programming Volume 2"
by W. Richard Stevens 1999 Addison-Wesley
ISBN 0-13-081081-9

Unfortunately, the author (Stevens) was killed in a car crash a year or two ago, so this former font of practical information is no more.

Cheers