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Basic Communications Systems Class 10. Today’s Class Topics Asynchronous Transfer Mode (ATM) Cell Switching Classes of Service Providing Integrated Voice.

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Presentation on theme: "Basic Communications Systems Class 10. Today’s Class Topics Asynchronous Transfer Mode (ATM) Cell Switching Classes of Service Providing Integrated Voice."— Presentation transcript:

1 Basic Communications Systems Class 10

2 Today’s Class Topics Asynchronous Transfer Mode (ATM) Cell Switching Classes of Service Providing Integrated Voice and Data Security Concepts Viruses Firewalls Management

3 ATM Features 53-byte cells Connection Oriented Design (SVC, PVC) Scaleable Bandwidth (25, 100, 155, 622 Mbps) Hub Backplane Design (Star / Non-Blocking) LAN and WAN convergence Adaptive to traffic demands (ABR, CBR, VBR) Low latency

4 ATM Market 1. Major Success: Large Carrier Networks AT&T and MCI have stated that they will convert their backbones to ATM within the next few years 2. Moderate Success: Corporate Backbones Some large corporations utilize ATM to interconnect switched LANs and provide in-house video and audio services 3. Not much Success: Desktop ATM to the desktop has not been very popular

5 How ATM Works? A sender must set up an ATM Virtual Channel to a destination before sending data Two Types: Permanent Virtual Channel, Switched Virtual Channel Switched Virtual Channel is set up by sending SETUP message using Q.93B All data going over Virtual Channel follows same path ATM devices transmit all data in fixed-length 53-byte ATM cells ATM Cell = 5-byte header, 48-bytes data Cell header contains Virtual Channel ID # ATM Switches forward data cells along established Virtual Channels. Each Virtual Channel has Quality-of-Service parameters (priority, delays, etc.) associated with it.

6 How ATM Works? ATM Cell-Switching ATM Switch ATM Switch Cell Header 5 bytes Cell Data (48 bytes) Cell Header 5 bytes Cell Data (48 bytes) Cell Header 5 bytes Cell Data (48 bytes) Cell Header 5 bytes ATM cells flow continuously

7 How ATM Works? Why 53 Bytes? 5 byte 48 byte payload header 64 Bytes 32 Bytes / 2 = 53 Byte compromise European Community United States and Japan

8 ATM Feature : QOS 1. ATM’s distinguishing feature: It can provide tighter guarantees on QOS parameters than other services: 1. Both constant bit-rate and variable bit-rate services 2. Guaranteed Max/Avg/Min Bandwidth 1. Implemented via Burst Length and Burst Ratio (max to avg) 3. Guaranteed end-to-end delay 4. Guaranteed cell loss rate

9 ATM in the LAN, WAN, and Telco ATM in the Building/Campus Backbone ATM in the Carrier Network ATM Access to the Carrier Network ATM to the Desktop

10 How ATM Works? Video Server ATM SVC - Switched Virtual Connection (a temporary logical connection between two endpoints) A virtual connection that has been established dynamically in response to a signaling request message.

11 How ATM Works? Call Set-up Example: ATM Switch Port 1 Port ) SETUP Message 2.) Switch sends CALL PROCEEDING to caller, SETUP to called device 3.) Device replies with CONNECT message 4.) Switch sends CONNECT msg caller acks

12 How ATM Works? ATM PVC - Permanent Virtual Connection (a permanent logical connection between two endpoints) A virtual channel connection that has been established by manual methods in advance of its need.

13 ATM Classes of Service (COS) Every time a Virtual Circuit (VC) is set up, the customer specifies a CLASS OF SERVICE desired for that VC. Desired Bandwidth and Class of Service determines the price (cost per minute) for using a particular VC. ATM has Classes of Service that are functionally equivalent to Leased Line service Frame Relay service Internet service

14 ATM Classes of Service (COS) Continuous Bit Rate (CBR)  Performs like a leased line. Most expensive. Variable Bit Rate (VBR)  Like Frame Relay. Customer specifies CIR. Customer must stay within CIR. Network guarantees performance. Medium expensive. Available Bit Rate (ABR)  Customer sends data as fast as he wants. However, if network gets busy, flow control messages are sent back to customer site and customer equipment must slow down. Unspecified Bit Rate (UBR)  No performance guarantees. Cheapest ATM service type.

15 Congestion Management CBR, VBR guarantee service levels If network is too heavily loaded, new connection requests will be rejected (busy signal) – ABR guarantees service level if flow control messages from network are obeyed If network is too heavily loaded, current connections are told to throttle back – UBR provides no service guarantee

16 How ATM Works? Adaptive to traffic demands (ABR, VBR, CBR) Constant Bit Rate Traffic e.g. Voice, Video Variable Bit Rate Traffic e.g. LAN Traffic Available Bit Rate Traffic e.g.

17 Constant Bit Rate

18 Packet Switching via ATM

19 Voice/Data Integration So, ATM can carry: Voice, Audio or Video at pre-reserved fixed bandwidths Packetized Data by using whatever bandwidth is dynamically available at any given moment Prioritized Data by assigning appropriate priority level to data packets It will provide the appropriate quality of service (QOS) for each of these over the same transmission facilities

20 Data Communications and Computer Networks Chapter 13 Introduction While computer systems today have some of the best security systems ever, they are more vulnerable than ever before. This vulnerability stems from the world-wide access to computer systems via the Internet. Computer and network security comes in many forms, including encryption algorithms, access to facilities, digital signatures, and using fingerprints and face scans as passwords.

21 Data Communications and Computer Networks Chapter 13 Basic Security Measures The basic security measures for computer systems fall into eight categories: External securityOperational security SurveillancePasswords AuditingAccess rights Standard system attacksViruses

22 Data Communications and Computer Networks Chapter 13 External Security Protection from environmental damage such as floods, earthquakes, and heat. Physical security such as locking rooms, locking down computers, keyboards, and other devices. Electrical protection from power surges. Noise protection from placing computers away from devices that generate electromagnetic interference.

23 Data Communications and Computer Networks Chapter 13 Operational Security Deciding who has access to what. Limiting time of day access. Limiting day of week access. Limiting access from a location, such as not allowing a user to use a remote login during certain periods or any time.

24 Data Communications and Computer Networks Chapter 13

25 Data Communications and Computer Networks Chapter 13 Surveillance Proper placement of security cameras can deter theft and vandalism. Cameras can also provide a record of activities. Intrusion detection is a field of study in which specialists try to prevent intrusion and try to determine if a computer system has been violated.

26 Data Communications and Computer Networks Chapter 13 Passwords and ID Systems Passwords are the most common form of security and the most abused. Simple rules help support safe passwords, including: Change your password often. Pick a good, random password (minimum 8 characters, mixed symbols). Don’t share passwords or write them down. Don’t select names and familiar objects as passwords.

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28 Data Communications and Computer Networks Chapter 13 Passwords and ID Systems Many new forms of “passwords” are emerging: Fingerprints Face prints Retina scans and iris scans Voice prints Ear prints

29 Data Communications and Computer Networks Chapter 13 Auditing Creating a computer or paper audit can help detect wrongdoing. Auditing can also be used as a deterrent. Many network operating systems allow the administrator to audit most types of transactions. Many types of criminals have been caught because of computer-based audits.

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31 Data Communications and Computer Networks Chapter 13 Access Rights Two basic questions to access right: who and how? Who do you give access right to? No one, group of users, entire set of users? How does a user or group of users have access? Read, write, delete, print, copy, execute? Most network operating systems have a powerful system for assigning access rights.

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33 Data Communications and Computer Networks Chapter 13 Viruses Many different types of viruses, such as parasitic, boot sector, stealth, polymorphic, and macro. A Trojan Horse virus is a destructive piece of code that hides inside a harmless looking piece of code. Sending an with a destructive attachment is a form of a Trojan Horse virus.

34 Data Communications and Computer Networks Chapter 13 Viruses Signature-based scanners look for particular virus patterns or signatures and alert the user. Terminate-and-stay-resident programs run in the background constantly watching for viruses and their actions. Multi-level generic scanning is a combination of antivirus techniques including intelligent checksum analysis and expert system analysis.

35 Data Communications and Computer Networks Chapter 13 Standard System Attacks Denial of service attacks, or distributed denial of service attacks, bombard a computer site with so many messages that the site is incapable of answering valid request. In bombing, a user sends an excessive amount of unwanted to someone. Smurfing is a nasty technique in which a program attacks a network by exploiting IP broadcast addressing operations. Ping storm is a condition in which the Internet Ping program is used to send a flood of packets to a server.

36 Data Communications and Computer Networks Chapter 13 Standard System Attacks Spoofing is when a user creates a packet that appears to be something else or from someone else. Trojan Horse is a malicious piece of code hidden inside a seemingly harmless piece of code. Stealing, guessing, and intercepting passwords is also a tried and true form of attack.

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38 Data Communications and Computer Networks Chapter 13 Basic Encryption and Decryption Cryptography is the study of creating and using encryption and decryption techniques. Plaintext is the the data that before any encryption has been performed. Ciphertext is the data after encryption has been performed. The key is the unique piece of information that is used to create ciphertext and decrypt the ciphertext back into plaintext.

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40 Data Communications and Computer Networks Chapter 13 Monoalphabetic Substitution-based Ciphers Monoalphabetic substitution-based ciphers replace a character or characters with a different character or characters, based upon some key. Replacing: abcdefghijklmnopqrstuvwxyz With: POIUYTREWQLKJHGFDSAMNBVCXZ The message: how about lunch at noon encodes into EGVPO GNMKN HIEPM HGGH

41 Data Communications and Computer Networks Chapter 13 Polyalphabetic Substitution-based Ciphers Similar to monoalphabetic ciphers except multiple alphabetic strings are used to encode the plaintext. For example, a matrix of strings, 26 rows by 26 characters or columns can be used. A key such as COMPUTERSCIENCE is placed repeatedly over the plaintext. COMPUTERSCIENCECOMPUTERSCIENCECOMPUTER thisclassondatacommunicationsisthebest

42 Data Communications and Computer Networks Chapter 13 Polyalphabetic Substitution-based Ciphers To encode the message, take the first letter of the plaintext, t, and the corresponding key character immediately above it, C. Go to row C column t in the 26x26 matrix and retrieve the ciphertext character V. Continue with the other characters in the plaintext.

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44 Data Communications and Computer Networks Chapter 13 Transposition-based Ciphers In a transposition-based cipher, the order of the plaintext is not preserved. As a simple example, select a key such as COMPUTER. Number the letters of the word COMPUTER in the order they appear in the alphabet C O M P U T E R

45 Data Communications and Computer Networks Chapter 13 Transposition-based Ciphers Now take the plaintext message and write it under the key C O M P U T E R t h i s i s t h e b e s t c l a s s i h a v e e v e r t a k e n

46 Data Communications and Computer Networks Chapter 13 Transposition-based Ciphers Then read the ciphertext down the columns, starting with the column numbered 1, followed by column number 2. TESVTLEEIEIRHBSESSHTHAENSCVKITAA

47 Data Communications and Computer Networks Chapter 13 Public Key Cryptography Very powerful encryption technique in which two keys are used: the first key (the public key) encrypts the message while the second key (the private key) decrypts the message. Not possible to deduce one key from the other. Not possible to break the code given the public key. If you want someone to send you secure data, give them your public key, you keep the private key. Secure sockets layer on the Internet is a common example of public key cryptography.

48 Data Communications and Computer Networks Chapter 13 Data Encryption Standard Created in 1977 and in operation into the 1990s, the data encryption standard took a 64-bit block of data and subjected it to 16 levels of encryption. The choice of encryption performed at each of the 16 levels depends on the 56-bit key applied. Even though 56 bits provides over 72 quadrillion combinations, a system using this standard has been cracked. Larger keys is the answer to better security.

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50 Data Communications and Computer Networks Chapter 13 Digital Signatures – Verifying the Sender Document to be signed is sent through a complex mathematical computation that generates a hash. Hash is encoded with the owner’s private key. To prove future ownership, the hash is decoded using the owner’s public key and the hash is compared with a current hash of the document. If the two hashes agree, the document belongs to the owner. The U.S. has just approved legislation to accept digitally signed documents as legal proof.

51 Data Communications and Computer Networks Chapter 13 Public Key Infrastructure The combination of encryption techniques, software, and services that involves all the necessary pieces to support digital certificates, certificate authorities, and public key generation, storage, and management. A certificate, or digital certificate, is an electronic document, similar to a passport, that establishes your credentials when you are performing transactions.

52 Data Communications and Computer Networks Chapter 13 Public Key Infrastructure Applications that could benefit from PKI: World Wide Web transactions Virtual private networks Electronic mail Client-server applications Banking transactions

53 Firewalls Firewalls are filters that can be placed between internal networks and the public Internet Watches all data packets going in both directions Filters packets by IP subnet, TCP port, etc. Acts as proxy web server, such that internal users must pass all web requests to firewall for inspection before they are passed to outside Acts as auditor by recording all packet activity in and out of the organization

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56 Data Communications and Computer Networks Chapter 13 Security Policy Design Issues What is the company’s desired level of security? How much money is the company willing to invest in security? If the company is serious about restricting access through an Internet link, what about restricting access through all other entry ways? The company must have a well-designed security policy.


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