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I read with interest the article 'Firewalls: Gatekeepers to your Network' in the July 2001 issue of Network Magazine. The article explained in simplistic terms what a Firewall is. But in the section 'Selecting a Firewall' you stated that, technically, just two types of firewalls exist (Network layer and Application layer firewalls). But I am aware of another technology called Stateful Inspection of Firewall technology where both the network layer functions and the application functions are integrated. With this technology packets are intercepted at the network layer for best performance (as in packet filters), but then data derived from all communications layers is accessed and analyzed for improved security (compared to layers 4-7 in application-layer gateways). This technology then introduces a higher level of security by incorporating communication and application derived state and context information which is stored and updated dynamically. Please do comment on this technology.

Rakesh Raghudharan

Your article on Firewalls cleared many of my doubts. But I need to know what is the SNMP protocol? Where is it used ? Using Java can I develop this protocol ?

George Vargeese

A: The Simple Network Management Protocol (SNMP) is essentially a request-reply protocol running over UDP (ports 161 and 162), though TCP operation is possible. SNMP is an asymmetric protocol, operating between a management station (smart) and an agent (dumb). The agent is the device being managed all its software has to do is implement a few simple packet types and a generic get-or-set function on its MIB variables. The management station presents the user interface. Simple management stations can be built with UNIX command-line utilities. More complex (and expensive) ones collect MIB data over time and use GUIs to draw network maps. SNMP's packet formats are described using Abstract Syntax Notation 1 (ASN.1), one of ISO's "Open" protocols. ASN.1 basically fills the role of XDR, but does so differently. ASN.1, like all OSI standard documents, is not freely available on-line. For more information on SNMP see the FAQ on the website: www.snmp.com/protocol/

I am unclear how the communication takes place in a Bluetooth enabled transmitter and receiver. The 'hop' part of it remains a mystery. Yes, I have been reading about Bluetooth and understand that it uses spread spectrum, but I am foggy about the details. Could you please suggest a text book that can guide me?


I head a company named Bluetooth for Federal Technology in Bangalore, and would like to point out some mistakes in the figure of the Bluetooth Stack (shown in the June 2001 issue of Network Magazine).

1. Bluetooth has only one SDP and parallel to it there is the TCS layer i.e. Telephony Control Protocol Specification (Binary).

2. There is no specific layer for ACL and SCO. They are the integral part of Baseband layer.

3. There is no specific layer like Bluetooth Radio. Actually it is a dipole Antenna which is connected to Baseband layer.

4. RFCOMM instead of REFCOMM

You wrote about SCO but which layer will use SCO? For that TCS is required, and you haven't wrote any thing about TCS.

Laxmi Kant,
Senior Designer
Federal Technologies, Bangalore

I have read your article in Network Magazine. and you have given the explanation about Bluetooth protocol stacks. But there wasn’t anything regarding JINI and WAP. You have showed them as the part of Bluetooth protocol stack. I would like to know regarding it.


Bluetooth and VLSI
I am a student of PICT VLSI Design Center, based in Pune. As a part of the curriculum I want to work on Bluetooth as the major project.I have gone through latest information availabe on the Net.I want to impliment security in Bluetooth in VHDL.Can you to please suggest some functional block that can be designed as an individual's project.

Hrishikesh Belgaonkar.

Seminar on Bluetooth
I am an enginneering student and am thinking of giving my seminar on that. Can you suggest some additional material on the topic.

Swati Lohiya

I am a regular reader of Network Magazine. The Linux articles in May issue helped me a lot.I am a final year student in computer branch in R.E.C., Durgapur, West Bengal.

Laxman Rao Kondeti

More info on Bluetooth
I am a student from the IIT Madras. I have doubts regarding how communication takes place in a Bluetooth enabled transmitter and receiver.I am not able to understand the hop part of it. I have read something about the Bluetooth. I just know that it uses a spread spectrum. I do not have a clear idea of it. Could you suggest some text book for this purpose?


I am doing computer science & engineering in Tamil Nadu. Currently I am learning WAP. Can suggest any additional reference for the same.


More on security
I went through your feature on Firewalls. Can you cover some additional stuff on security.As per what I come to know of, firewalls alone aren’t sufficient for protecting corporate networks. You need to implemet additional protection for the same.Can you eloberate on that.


IDS, Security policy, etc
I read your article on Firewalls and found it very informative. Can you give more coverage to enterprise security especially on IDS, encryption, etc.


More Basics and WorkShop Wisdom
I am an engineering student doing my BE in Computer Science. I find Network Magazine very informative, especially Basics and WorkShop Wisdom very informative.Can you carry more of these in your magazine.


I am a regular reader of Network Magazine and read it from cover to cover.Can you possibly carry tutorials for CCNA, MCSE, etc. These will be handy since they will help in solving some of our concepts.


Need for security policy
I picked up the Firewalls issue of Network Magazine and liked it very much. I want to implement a security policy for my company, and would like to have more details.Can you suggest any websites where I can find more information on implementing a security policy.


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