I have found tcp/ip support for ZX Spectrum 48k / 128K. So it is possible to use also with sprinter (and in future with estex?!? :)) As wrote in readme:
[...]
This software allows you to use your ZX Spectrum computer as a workstation of your TCP/IP network. It's not fully RFC-compliant, but many of incompatibilities, made for efficiency, can be turned off by configuring and re-compiling.
Low-level part of the implementation includes: PPP support NCP, LCP, IP layer, ICMP subsystem, UDP subsystem , TCP subsystem. There can be minor support of rfc 791(ip), 792, 794(icmp) and 793(tcp). 1.2 HARDWARE REQUIREMENTS
Runs on 3.5MHz 48/128k spectrum. Supports just few serial interfaces, but other ones can be easily included by re-writting low-level IO routines. 3. COMPILING * make clean * make. Result will be named tcpip.tap optionally, you may wish to do * make install which will send output to your sound-card, hopefully connected to the tape-in of your spectrum. Before it, you probably would like to write LOAD "" on your spectrum ;).

The program is written in C for Linux. (if you have a C compiler).

the file was generated after compiling sources here
http://seldon.terminus.sk/~www/software/ppp_tcpip.tar.gz
It is an implementation of web server on zx spectrum.

I know about. It's GNU GPL software wrote in assembler (c programs are crosstools under linux). I contacted with one of authors one year ago and he tell me that they stop develop this program and I may take it under General Public License (open source code). Main problem that code wrote for 3.5 MHz and we need reclock it for Sprinter speed.


Alexander Shabarshin (shaos@mail.ru)
http://www.shaos.ru

ah ok!! but... it is possible and quite easy (i think...) porting it on Estex. In .tar.gz archieve there are sources in c/c++.
But... how can is it possible to use serial port with this program with zx spectrum? how can is it possible to use internal modem with sprinter in zx mode?

Second problem - most of comments wrout on Slovack language that difference from Russian and too much difference from English. Serial port connection defined in src/arch/
print64-mrs.asm
serial-38400.asm
serial-9600.asm
serial-38400-gama.asm
we need rewrite it procedure for modem.


Alexander Shabarshin (shaos@mail.ru)
http://www.shaos.ru

Since z88dk now targets the Sprinter, ZSock could be retargetted to run on the Sprinter. It comes with a bunch of client applications such as ftp and telnet as well as an API for progamming further ones. Unfortunately, SLIP is the only working protocol - PPP still isn't finished.

I've not looked too deeply into dlls & libman, but in theory it should play along nicely..