The listing, Unix Network Programming Paperback has ended.
Great book, I've read it cover to cover. But why buy it when the author has newer versions out? Because (1) it is more concise and (2) it has info not in the other editions. I recommend you read this one cover-to-cover and buy the others as more detailed reference. His 3 other books (Advanced Programming in the Unix Environment, Unix Net. Prog.,2nd Ed., Vol.1; Unix Net. Programming, 2nd Ed., Vol.2) are far more detailed and worth having, but each is very thick. AND, the author died without finishing Unix Network Programming, 2nd Ed., Vol.3 (Applications). You have to buy this older edition to get the applications. It's easier to read 1 book 700 pp. long than to read 3 books, each 700 pp. long. Time is money.