ECHO! Echo! echo. (echo)
Python, 299 295 265 263
from threading import*
from socket import*
a='',7;S=socket
u=S(2,2);u.bind(a)
def U():
 while 1:u.sendto(*u.recvfrom(4**8))
Thread(None,U).start()
def C(c,x):
 while c.send(c.recv(1)):1
s=S(2,1);s.bind(a);s.listen(1)
while 1:Thread(None,C,args=s.accept()).start()

handles both udp and tcp.
@MorganThrapp helped saving 33 (!) chars