ACL filter tcp port

Question

Dear Expert,
I study the ACL to filter (stop) the tcp port from below URL
http://www.cisco.com/en/US/tech/tk648/tk361/technologies_configuration_example09186a0080100548.shtml
In the section of "Allow Only Internal Networks to Initiate a TCP Session", grateful if someone would enlighten me the usage of "established"
interface ethernet0
ip access-group 102 in
access-list 102 permit tcp any any gt 1023 established
What is different if the ACL is changed to following:
access-list 102 permit tcp any any gt 1023
rdgs

Answer 1

Dear Jennifer,
Great helpful.
Gratful if you would comment on following configuration which I digest your advice
interface serial 0/0
description 45M DS3 from HK to US
ip access-group 105 in
interface fastethernet 0/0
Description Internat VLAN 100 for xxx department
ip address 102.168.100.0 255.255.255.0
ip access-group 101 in
access-list 101 remark -- only allow Web service from internal to outside --
access-list 101 permit tcp 192.168.100.0 0.0.0.255 any http
access-list 105 remark -- allow return traffic if destination tcp port great than 1023 --
access-list 105 permit tcp any 192.168.100.0 eq http 0.0.0.255 gt 1023 established
! it should embed the partial function of "permit tcp any eq http 192.168.100.0 0.0.0.255 gt 1023" but the
! traffic should be permit only if it initiates from 192.168.100.0/24. If the traffic is initiate from outside,
! the acl 105 would deny it.
access-list 115 remark -- allow in/return traffic for tcp port great than 1023 --
access-list 115 permit tcp any eq http 192.168.100.0 0.0.0.255 gt 1023
! the traffic is permit no matter it is initiate from internal or external
access-list 125 remark -- allow return traffic for all tcp port --
access-list 125 permit tcp any eq 80 192.168.100.0 0.0.0.255 any established
! include the function of ACL 105, also support tcp port range from 1 to 1023 
access-list 135 remark -- allow in/return traffic for all tcp port --
access-list 135 permit tcp any eq 80 192.168.100.0 0.0.0.255 any
! include the function of ACL 115, also support tcp port range from 1 to 1023
If so, I would like to modify the ACL to support more services, grateful if you would comment on it.
access-list 101 remark -- only allow Internet services from internal to outside --
access-list 101 permit tcp 192.168.100.0 0.0.0.255 any http
access-list 101 permit tcp 192.168.100.0 0.0.0.255 any smtp
access-list 101 permit tcp 192.168.100.0 0.0.0.255 any pop
access-list 101 permit tcp 192.168.100.0 0.0.0.255 any imap
access-list 101 permit tcp host 192.168.100.120 eq imap any estanlished
access-list 101 permit tcp 192.168.100.0 0.0.0.255 any telnet
access-list 145 remark --- return and in traffic ---
access-list 145 permit tcp any 192.168.100.0 0.0.0.255 gt 1023 established
access-list 145 permit tcp any host 192.168.100.120 imap