Enterprise Internets Copyright 1997 Prentice-Hall
Wide Area Networks (WANs) <ul><li>WAN Technologies </li></ul><ul><ul><li>Ordinary telephone line and telephone modem.  </l...
Local versus Enterprise Internets <ul><li>LANs and Local Internets </li></ul><ul><ul><li>Run on customer premises </li></u...
Carriers <ul><li>You have the right to lay wires on your own premises </li></ul><ul><li>You do not have the right-of-way t...
<ul><li>Local Telephony </li></ul><ul><ul><li>U.S. divided into 161 Local  Access and Transport Areas (LATAs) </li></ul></...
Transmission Carriers in the U.S. <ul><li>Domestic Inter-LATA Carriers (U.S.) </li></ul><ul><ul><li>Domestic means within ...
Transmission Carriers Between Countries <ul><li>International Carriers </li></ul><ul><ul><li>Called International Common C...
Point of Presence (POP) POP at LEC Switching Office Trunk Line The POP provides interconnection between LEC subscribers an...
Connecting to IXCs and ICCs POP at LEC Switching Office Trunk Line IXC Switching Office IXC Switching Office ICC Switching...
POP <ul><li>All competitors can interconnect their customers into an integrated system </li></ul><ul><li>The key to compet...
Circuit <ul><li>End-to-End Connection Between Stations </li></ul><ul><ul><li>May Pass through Several Switches </li></ul><...
Circuit Speeds <ul><li>Voice Grade Circuits </li></ul><ul><ul><li>Ordinary telephone line, except point-to-point </li></ul...
Circuit Speeds <ul><li>64 kbps Circuits </li></ul><ul><ul><li>Digital line:  low error rate </li></ul></ul><ul><ul><li>If ...
Circuit Speeds <ul><li>T1 Circuits </li></ul><ul><ul><li>1.544 Mbps </li></ul></ul><ul><ul><li>Designed to multiplex 24 di...
Circuit Speeds <ul><li>Fractional T1 Circuits </li></ul><ul><ul><li>Many firms need between 64 kbps and T1 speeds </li></u...
Circuit Speeds <ul><li>T3 Circuits </li></ul><ul><ul><li>44.7 Mbps in U.S. </li></ul></ul><ul><ul><li>For firms needing ve...
Circuit Speeds <ul><li>E Series Circuits </li></ul><ul><ul><li>Used in Europe, other areas </li></ul></ul><ul><ul><li>Crea...
Circuit Speeds <ul><li>Higher-Speed Digital Lines (SONET/SDH) </li></ul><ul><ul><li>Single world-wide standard for very hi...
Types of Traditional Telephone Circuits <ul><li>Dial-Up Service (Any-to-Any) </li></ul><ul><li>Leased Lines </li></ul><ul>...
Leased Line Service Customer Premises A Customer Premises B Switching Office Switching Office Switching Office Trunk Line ...
Leased Lines <ul><li>Limited to 2 points </li></ul><ul><li>Cheaper than dial-up on high-volume routes </li></ul><ul><li>Co...
Data Networks <ul><li>Data Networking Alternatives </li></ul><ul><ul><li>Use the telephone network and modems (slow) </li>...
Circuit-Switched Data Networks <ul><li>Switched for any-to-any communication </li></ul><ul><li>Just dial the number of the...
Circuit-Switched Data Networks <ul><li>Dedicated Capacity </li></ul><ul><ul><li>Circuit is maintained during the duration ...
Circuit-Switched Data Networks <ul><li>ISDN </li></ul><ul><ul><li>Usually circuit-switched </li></ul></ul><ul><ul><li>Both...
Packet-Switched Data Networks <ul><li>Messages are Broken into Small Pieces (Packets) </li></ul><ul><ul><li>Flow through t...
Packet Switches <ul><li>Packet Switched Networks have Switches </li></ul><ul><ul><li>Route the packets through the network...
Packet Switching is Efficient <ul><li>Packets from several stations multiplexed over trunk lines between switches </li></u...
Error Checking in Packet-Switched Data Networks <ul><li>The Process </li></ul><ul><ul><li>Sender transmits the packet </li...
Error Checking in Packet-Switched Data Networks <ul><li>Considerations in </li></ul><ul><ul><li>Adds delay (latency) every...
Reliable Packet-Switched Data Networks <ul><li>Check for Errors at Each Hop </li></ul><ul><ul><li>Have reduced throughput ...
Unreliable Packet-Switched Data Networks <ul><li>No Error Check at Each Packet Switch </li></ul><ul><ul><li>Check only onc...
Unreliable Service <ul><li>Most Packet Switched Networks Today are Unreliable </li></ul><ul><ul><li>Little Need:  Error ra...
Connectionless Service <ul><li>Routing Decision for each packet at each switch </li></ul><ul><ul><li>Places a heavy load o...
Connection-Oriented Service <ul><li>Routing decision is made once, at start of connection </li></ul>2 1 6 5 4 7 3 Decision...
Connection-Oriented Service <ul><li>First decision establishes a path (virtual circuit) </li></ul><ul><ul><li>All subseque...
Connection-Oriented Packet-Switched Data Networks <ul><li>All Commercial Packet Switched Networks are Connection-Oriented ...
Connections in Packet-Switched Data Networks <ul><li>Permanent Virtual Circuits (PVCs) </li></ul><ul><ul><li>Established f...
Connections in Packet-Switched Data Networks <ul><li>Switched Virtual Circuits </li></ul><ul><ul><li>Established at call s...
OSI Layering <ul><li>Connectionless Service </li></ul><ul><ul><li>OSI Layer 3 (Networking) </li></ul></ul><ul><ul><li>Rout...
Packet-Switched Services <ul><li>Offered by Carriers </li></ul><ul><li>X.25 </li></ul><ul><ul><li>Old, slow, and not suffi...
X.25 Packet-Switched Data Networks <ul><li>Oldest packet switched network service (1970s) </li></ul><ul><li>Low speed (max...
Frame Relay Packet-Switched Data Networks <ul><li>Software upgrade to X.25 switches </li></ul><ul><li>Uses PVCs </li></ul>...
ATM (Asynchronous Transfer Mode) <ul><li>Offers very high speeds </li></ul><ul><ul><li>622 Mbps, 2.5 Gbps to 40 Gbps </li>...
ATM <ul><li>Speeds are beyond most corporate needs today </li></ul><ul><li>High costs </li></ul><ul><li>Seen as the next g...
Pricing Packet Switched Services <ul><li>Customer Premises Equipment </li></ul><ul><li>Access Line to Point of Presence </...
Customer Premises Equipment <ul><li>Access Device </li></ul><ul><ul><li>Has link to internal system (often a LAN) </li></u...
Modular Routers <ul><li>CSU/DSUs are removable expansion boards </li></ul>Router Switching Circuitry Port 1 CSU/DSU (T1) P...
Elements of a Packet Switched Network Customer Premises A LEC Switching Office POP at LEC Office Leased Access Line to POP...
Elements of a Packet Switched Network Switched Data Network Trunk Line Network Switching Office POP Customer Premises B Le...
Pricing of Frame Relay <ul><li>Speed of the Access Line from Site to Network </li></ul><ul><ul><li>Determines maximum tran...
Pricing of Frame Relay <ul><li>In Some Frame Relay networks, two speeds </li></ul><ul><ul><li>Committed Information Rate (...
Pricing of Frame Relay <ul><li>Additional price per PVC </li></ul><ul><ul><li>Usually small compared to the access line ch...
Calculations <ul><li>Situation </li></ul><ul><ul><li>You have four sites </li></ul></ul><ul><ul><li>You want any one to be...
Calculations <ul><li>PVCs </li></ul><ul><ul><li>If you have N sites, there are N(N-1)/2 possible connections </li></ul></u...
Pricing of Frame Relay <ul><li>May Depend on Distance </li></ul><ul><ul><li>But often a flat monthly rate throughout the c...
Leased Lines vs. Packet-Switched Data Networks <ul><li>Leased Lines </li></ul><ul><ul><li>Point-to-point, inexpensive for ...
Circuit-Switched  vs. Packet-Switched Services <ul><li>Circuit Switched Networks (ISDN, Switched 56) </li></ul><ul><ul><li...
Virtual Private Network Corporate Site A  VPN Server Corporate Site B Tunnel Internet Extranet Remote Access for Intranet ...
VPN  advantage <ul><li>Virtual Private Network (VPN) </li></ul><ul><ul><li>Transmission over the Internet with added secur...
VPN issues <ul><li>VPN Problems </li></ul><ul><ul><li>Latency and Sound Quality </li></ul></ul><ul><ul><ul><li>Internet ca...
ISP-Based PPTP Remote Access VPN <ul><li>Remote Access VPNs </li></ul><ul><ul><li>User dials into a remote access server (...
VPN and PPTP <ul><li>Point-to-Point Tunneling Protocol </li></ul><ul><ul><li>Available in Windows since Windows 95 </li></...
IPsec in Tunnel Mode Tunnel Only Between Sites Hosts Need No Extra Software Secure Tunnel Tunnel Mode IPsec Server IPsec S...
IPsec in Transfer Mode End-to-End (Host-to-Host) Tunnel Hosts Need IPsec Software Secure Tunnel Transfer Mode IPsec Server...
IPsec alternatives <ul><li>IP Security (IPsec) </li></ul><ul><ul><li>Tunnel mode: sets up a secure tunnel between IPsec se...
Security at the internet layer <ul><li>IP Security (IPsec) </li></ul><ul><ul><li>At internet layer, so protects informatio...
Common IPsec configuration <ul><li>IP Security (IPsec) </li></ul><ul><ul><li>Security associations: </li></ul></ul><ul><ul...
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    1. 1. Enterprise Internets Copyright 1997 Prentice-Hall
    2. 2. Wide Area Networks (WANs) <ul><li>WAN Technologies </li></ul><ul><ul><li>Ordinary telephone line and telephone modem. </li></ul></ul><ul><ul><li>Point-to-Point Leased lines </li></ul></ul><ul><ul><li>Public switched data network (PSDN) </li></ul></ul><ul><ul><li>Send your data over the Internet securely, using Virtual Private Network (VPN) technology </li></ul></ul>VPN PSDN
    3. 3. Local versus Enterprise Internets <ul><li>LANs and Local Internets </li></ul><ul><ul><li>Run on customer premises </li></ul></ul><ul><ul><li>Organization controls transmission lines </li></ul></ul><ul><li>Enterprise Internets Span Sites </li></ul><ul><ul><li>Organization does not have right of ways between sites </li></ul></ul><ul><ul><li>Organization must turn to a transmission carrier </li></ul></ul><ul><ul><li>Carriers have legal rights to rights-of-way between customer premises </li></ul></ul><ul><ul><li>Carriers are regulated </li></ul></ul>Hong Kong New York London
    4. 4. Carriers <ul><li>You have the right to lay wires on your own premises </li></ul><ul><li>You do not have the right-of-way to lay wires outside your premises </li></ul><ul><li>For services beyond your premises, you must turn to a carrier </li></ul><ul><li>Carriers have rights of way. To compensate for this power, they are regulated </li></ul>
    5. 5. <ul><li>Local Telephony </li></ul><ul><ul><li>U.S. divided into 161 Local Access and Transport Areas (LATAs) </li></ul></ul><ul><ul><li>In each LATA, there is a main carrier--the local telephone company. </li></ul></ul><ul><ul><li>This company formerly had a monopoly on intra-LATA service. </li></ul></ul><ul><ul><li>This firm is the local exchange carrier (LEC) </li></ul></ul><ul><ul><li>CAP - Competitive Access Providers </li></ul></ul><ul><ul><li>Refer to last class meeting for details </li></ul></ul>Transmission Carriers in the U.S. LATAs LEC
    6. 6. Transmission Carriers in the U.S. <ul><li>Domestic Inter-LATA Carriers (U.S.) </li></ul><ul><ul><li>Domestic means within a country </li></ul></ul><ul><ul><li>Inter-LATA service (between LATAs) </li></ul></ul><ul><ul><li>Carriers are called inter-exchange carriers (IXCs). </li></ul></ul><ul><ul><li>Competition has long existed in this arena. </li></ul></ul>IXC
    7. 7. Transmission Carriers Between Countries <ul><li>International Carriers </li></ul><ul><ul><li>Called International Common Carriers (ICCs) </li></ul></ul><ul><ul><li>Each pair of countries negotiates on what ICCs to allow, like we saw last class meeting. </li></ul></ul><ul><ul><li>When you call internationally, you use one ICC, not two--one at each end. </li></ul></ul>ICC
    8. 8. Point of Presence (POP) POP at LEC Switching Office Trunk Line The POP provides interconnection between LEC subscribers and CAP subscribers. The POP is located at a LEC switching office.
    9. 9. Connecting to IXCs and ICCs POP at LEC Switching Office Trunk Line IXC Switching Office IXC Switching Office ICC Switching Office The POP also links LEC and CAP subscribers to IXCs and ICCs.
    10. 10. POP <ul><li>All competitors can interconnect their customers into an integrated system </li></ul><ul><li>The key to competition </li></ul><ul><ul><li>Without it, new competitors could not get a critical mass of customers </li></ul></ul><ul><ul><li>With a POP, even a small customer base is no problems, because these customers can reach any other telephone customers in the world. </li></ul></ul><ul><li>Trunk lines connect carrier switching offices </li></ul>
    11. 11. Circuit <ul><li>End-to-End Connection Between Stations </li></ul><ul><ul><li>May Pass through Several Switches </li></ul></ul><ul><ul><li>May Go Through Multiple Transmission Media </li></ul></ul><ul><ul><li>Maintained throughout the call </li></ul></ul><ul><li>May flow through multiple carriers </li></ul><ul><ul><li>LEC, ICC, etc. </li></ul></ul>Wire Wire Satellite
    12. 12. Circuit Speeds <ul><li>Voice Grade Circuits </li></ul><ul><ul><li>Ordinary telephone line, except point-to-point </li></ul></ul><ul><ul><li>Analog line: high error rate </li></ul></ul><ul><ul><li>Requires modem </li></ul></ul><ul><ul><li>Worst of all, slow: Under ~35 kbps </li></ul></ul>Analog
    13. 13. Circuit Speeds <ul><li>64 kbps Circuits </li></ul><ul><ul><li>Digital line: low error rate </li></ul></ul><ul><ul><li>If you digitize an analog telephone system, it generates 64 kbps in data </li></ul></ul><ul><ul><li>Used to be sufficient for linking people from home </li></ul></ul><ul><ul><li>Used to be sufficient for linking branch offices </li></ul></ul><ul><ul><li>Sometimes, 56 kbps </li></ul></ul><ul><ul><li>Use to be the most widely used digital circuit </li></ul></ul><ul><ul><ul><li>Inexpensive. In range of most demand. </li></ul></ul></ul>Digital 64 kbps 56 kbps
    14. 14. Circuit Speeds <ul><li>T1 Circuits </li></ul><ul><ul><li>1.544 Mbps </li></ul></ul><ul><ul><li>Designed to multiplex 24 digital voice lines </li></ul></ul><ul><ul><li>Can be used as a single high-speed data pipe </li></ul></ul><ul><ul><li>Sufficient for many uses to connect sites </li></ul></ul><ul><ul><li>Also called DS1 for the signaling format </li></ul></ul><ul><ul><li>Very widely used: In the critical speed range for many “high speed” corporate uses and not too expensive </li></ul></ul>T1 1.544 Mbps DS1
    15. 15. Circuit Speeds <ul><li>Fractional T1 Circuits </li></ul><ul><ul><li>Many firms need between 64 kbps and T1 speeds </li></ul></ul><ul><ul><li>128 kbps, 256 kbps, 384 kbps, 768 kbps common </li></ul></ul><ul><ul><li>Each vendor only offers some options </li></ul></ul><ul><ul><li>Different vendors offer different options </li></ul></ul><ul><ul><li>768 kbps usually is the fastest offering </li></ul></ul>Fractional T1 128 kbps 256 kbps 384 kbps 768 kbps
    16. 16. Circuit Speeds <ul><li>T3 Circuits </li></ul><ul><ul><li>44.7 Mbps in U.S. </li></ul></ul><ul><ul><li>For firms needing very high speeds </li></ul></ul><ul><ul><li>Uncommon now but increasing </li></ul></ul><ul><li>Other T-Series Speeds </li></ul><ul><ul><li>There are faster T-series circuits, but they are rarely used. </li></ul></ul><ul><ul><li>There are T2 circuits, but they are not offered </li></ul></ul>T3 44.7 Mbps
    17. 17. Circuit Speeds <ul><li>E Series Circuits </li></ul><ul><ul><li>Used in Europe, other areas </li></ul></ul><ul><ul><li>Created by CEPT (Conference of European Postal and Telecommunications Authorities) </li></ul></ul><ul><ul><li>E1: 2.048 Mbps (faster than T1) </li></ul></ul><ul><ul><li>E3: 34.4 Mbps </li></ul></ul>E Series 2.048 Mbps 34.4 Mbps
    18. 18. Circuit Speeds <ul><li>Higher-Speed Digital Lines (SONET/SDH) </li></ul><ul><ul><li>Single world-wide standard for very high speeds </li></ul></ul><ul><ul><li>In U.S., called SONET (Synchronous Optical Network) </li></ul></ul><ul><ul><li>In Europe, elsewhere called SDH (Synchronous Digital Hierarchy) </li></ul></ul><ul><ul><li>OC circuit designations. Multiples of 51.84 Mbps </li></ul></ul><ul><ul><li>OC3: 156 Mbps </li></ul></ul><ul><ul><li>OC12: 622 Mbps </li></ul></ul><ul><ul><li>Defined up to a few Gigabits per second </li></ul></ul>SONET SDH
    19. 19. Types of Traditional Telephone Circuits <ul><li>Dial-Up Service (Any-to-Any) </li></ul><ul><li>Leased Lines </li></ul><ul><ul><li>Point-to-point only </li></ul></ul><ul><ul><li>Cheaper for high volumes of use </li></ul></ul>Leased Line Switched Dial-Up Service Seattle Washington, D.C.
    20. 20. Leased Line Service Customer Premises A Customer Premises B Switching Office Switching Office Switching Office Trunk Line Trunk Line Local Loop Local Loop Leased Lines May Pass Through Multiple Switches, Even Multiple Carriers
    21. 21. Leased Lines <ul><li>Limited to 2 points </li></ul><ul><li>Cheaper than dial-up on high-volume routes </li></ul><ul><li>Companies can build enterprise networks from meshes of leased lines between sites </li></ul>See this document for price example Leased Line Corporate-owned Switch
    22. 22. Data Networks <ul><li>Data Networking Alternatives </li></ul><ul><ul><li>Use the telephone network and modems (slow) </li></ul></ul><ul><ul><li>Lease lines, add own switching (complex) </li></ul></ul><ul><li>Data Networks </li></ul><ul><ul><li>Optimized for data transmission </li></ul></ul><ul><ul><li>Customer only has to connect to the data network </li></ul></ul><ul><ul><li>Carrier handles transmission, switching, management </li></ul></ul><ul><ul><li>Shown as cloud to indicate lack of need to know details </li></ul></ul><ul><ul><li>Two types: circuit-switched and packet-switched </li></ul></ul>Data Network
    23. 23. Circuit-Switched Data Networks <ul><li>Switched for any-to-any communication </li></ul><ul><li>Just dial the number of the party being called </li></ul><ul><li>Very flexible </li></ul>
    24. 24. Circuit-Switched Data Networks <ul><li>Dedicated Capacity </li></ul><ul><ul><li>Circuit is maintained during the duration of the call </li></ul></ul><ul><ul><li>Capacity is always available </li></ul></ul><ul><ul><li>You must pay for this constant capacity </li></ul></ul><ul><ul><li>Most data transmission is burst, with long silences between transmission </li></ul></ul><ul><ul><li>Utilization of the line may be as low as 5% </li></ul></ul><ul><ul><li>So circuit-switched services is inherently expensive </li></ul></ul>
    25. 25. Circuit-Switched Data Networks <ul><li>ISDN </li></ul><ul><ul><li>Usually circuit-switched </li></ul></ul><ul><ul><li>Both voice and data </li></ul></ul><ul><ul><li>Two 64 kbps B channels to the desktop </li></ul></ul><ul><ul><li>Sometimes can combine into a 128 kbps circuit </li></ul></ul><ul><ul><li>About twice as expensive as a telephone line </li></ul></ul><ul><ul><li>Needs a terminal adapter to connect computer, phone </li></ul></ul><ul><ul><li>Reasonably inexpensive, reasonably fast, popular </li></ul></ul>ISDN Seen previously
    26. 26. Packet-Switched Data Networks <ul><li>Messages are Broken into Small Pieces (Packets) </li></ul><ul><ul><li>Flow through the network more easily than long messages, like sand in an hourglass </li></ul></ul>Packet
    27. 27. Packet Switches <ul><li>Packet Switched Networks have Switches </li></ul><ul><ul><li>Route the packets through the network </li></ul></ul>2 1 6 5 4 7 3 Switch
    28. 28. Packet Switching is Efficient <ul><li>Packets from several stations multiplexed over trunk lines between switches </li></ul><ul><ul><li>No costly dedicated transmission capacity </li></ul></ul>1 2 Trunk Line
    29. 29. Error Checking in Packet-Switched Data Networks <ul><li>The Process </li></ul><ul><ul><li>Sender transmits the packet </li></ul></ul><ul><ul><li>Sender maintains the packet in memory </li></ul></ul><ul><ul><li>Receiver checks the packet for errors </li></ul></ul><ul><ul><li>If there is an error, asks for a retransmission </li></ul></ul><ul><ul><li>Sender retrieves from memory, retransmits </li></ul></ul>2 1
    30. 30. Error Checking in Packet-Switched Data Networks <ul><li>Considerations in </li></ul><ul><ul><li>Adds delay (latency) every time it is done </li></ul></ul><ul><ul><li>Places a heavy load on the switch, lowering throughput </li></ul></ul><ul><ul><li>Not often needed, because there are very few errors on modern transmission lines. </li></ul></ul>
    31. 31. Reliable Packet-Switched Data Networks <ul><li>Check for Errors at Each Hop </li></ul><ul><ul><li>Have reduced throughput </li></ul></ul><ul><ul><li>Have latency (delays) </li></ul></ul>2 1 3 4 5 Error Check Error Check Error Check Error Check Error Check
    32. 32. Unreliable Packet-Switched Data Networks <ul><li>No Error Check at Each Packet Switch </li></ul><ul><ul><li>Check only once, at receiving host </li></ul></ul><ul><ul><li>Low latency, load on switches </li></ul></ul>2 1 3 4 5 Error Check No Error Checks at Switches
    33. 33. Unreliable Service <ul><li>Most Packet Switched Networks Today are Unreliable </li></ul><ul><ul><li>Little Need: Error rates are low with modern lines, switches </li></ul></ul><ul><ul><li>Reduces delays: critical for some applications </li></ul></ul><ul><ul><li>Low load on the switches for high throughput </li></ul></ul><ul><ul><li>Better to check once, on the receiving host, than at every switch </li></ul></ul>
    34. 34. Connectionless Service <ul><li>Routing Decision for each packet at each switch </li></ul><ul><ul><li>Places a heavy load on switches </li></ul></ul><ul><ul><li>Unnecessary work: subsequent packets usually travel same path, because conditions rarely change between packets </li></ul></ul>See some Verizon services 2 1 6 5 4 7 3 Decision Decision Decision Decision
    35. 35. Connection-Oriented Service <ul><li>Routing decision is made once, at start of connection </li></ul>2 1 6 5 4 7 3 Decision Decision Decision Decision
    36. 36. Connection-Oriented Service <ul><li>First decision establishes a path (virtual circuit) </li></ul><ul><ul><li>All subsequent packets follow the virtual circuit </li></ul></ul>2 1 6 5 4 7 3 Virtual Circuit
    37. 37. Connection-Oriented Packet-Switched Data Networks <ul><li>All Commercial Packet Switched Networks are Connection-Oriented </li></ul><ul><ul><li>Reduces loads on the switches for higher throughput </li></ul></ul><ul><ul><li>Lower latency because of less work at each switch </li></ul></ul><ul><li>When marketers say “packet switched,” they now automatically include the concept of connection orientation </li></ul>
    38. 38. Connections in Packet-Switched Data Networks <ul><li>Permanent Virtual Circuits (PVCs) </li></ul><ul><ul><li>Established for long durations </li></ul></ul><ul><ul><li>Set up weeks or months ahead of time </li></ul></ul><ul><ul><li>If your firm has four sites, need 6 PVCs </li></ul></ul><ul><ul><li>Makes packet switched networks like network of leased lines </li></ul></ul>Site 1 Site 3 Site 4 Site 2 PVC
    39. 39. Connections in Packet-Switched Data Networks <ul><li>Switched Virtual Circuits </li></ul><ul><ul><li>Established at call setup </li></ul></ul><ul><ul><li>Only available in some packet switched networks </li></ul></ul><ul><ul><li>Will provide the any-to-any flexibility of circuit-switched data networks AND the efficiency of connection-oriented packet switching </li></ul></ul>
    40. 40. OSI Layering <ul><li>Connectionless Service </li></ul><ul><ul><li>OSI Layer 3 (Networking) </li></ul></ul><ul><ul><li>Routing across a series of packet switches </li></ul></ul><ul><ul><li>Alternative Routing </li></ul></ul><ul><li>Connection-Oriented Service </li></ul><ul><ul><li>OSI Layer 2 (Data Link) </li></ul></ul><ul><ul><li>Reduces network to a single path </li></ul></ul><ul><ul><li>Loses flexibility of alternative routing after virtual circuit is established </li></ul></ul>
    41. 41. Packet-Switched Services <ul><li>Offered by Carriers </li></ul><ul><li>X.25 </li></ul><ul><ul><li>Old, slow, and not sufficiently cheaper than frame relay </li></ul></ul><ul><li>Frame Relay </li></ul><ul><ul><li>Speeds in main range of user demand </li></ul></ul><ul><ul><li>Attractive prices </li></ul></ul><ul><ul><li>Dominates the market today </li></ul></ul><ul><li>ATM </li></ul><ul><ul><li>High speeds and costs </li></ul></ul>
    42. 42. X.25 Packet-Switched Data Networks <ul><li>Oldest packet switched network service (1970s) </li></ul><ul><li>Low speed (maximum around 64 kbps) </li></ul><ul><li>Mature: easy to implement </li></ul><ul><li>Uses PVCs </li></ul><ul><li>Reliable service, so latency in transmission </li></ul><ul><li>Mostly replaced by Frame Relay </li></ul>
    43. 43. Frame Relay Packet-Switched Data Networks <ul><li>Software upgrade to X.25 switches </li></ul><ul><li>Uses PVCs </li></ul><ul><li>Unreliable, so much faster on same switches </li></ul><ul><li>Good speed range: 56 kbps - 40 Mbps: Meets most corporate needs (most under 2 Mbps) </li></ul><ul><li>Priced aggressively to kill leased lines (succeeding) </li></ul><ul><li>Best-selling packet switched network service </li></ul>See more here .
    44. 44. ATM (Asynchronous Transfer Mode) <ul><li>Offers very high speeds </li></ul><ul><ul><li>622 Mbps, 2.5 Gbps to 40 Gbps </li></ul></ul><ul><li>Connection-oriented (PVCs), unreliable </li></ul><ul><li>Quality of Service (QOS) guarantees critical traffic </li></ul><ul><ul><li>Minimize latency (delays) </li></ul></ul><ul><ul><li>Inherent reliability (low loss rate) </li></ul></ul><ul><ul><li>Etc. </li></ul></ul>
    45. 45. ATM <ul><li>Speeds are beyond most corporate needs today </li></ul><ul><li>High costs </li></ul><ul><li>Seen as the next generation </li></ul><ul><ul><li>But Frame Relay keeps increasing in speed in low Mbps range where market demand is highest </li></ul></ul>See ATM pricing in 97 Also Verizon project prices
    46. 46. Pricing Packet Switched Services <ul><li>Customer Premises Equipment </li></ul><ul><li>Access Line to Point of Presence </li></ul><ul><li>Port Speed </li></ul><ul><li>Per PVC Price </li></ul><ul><li>Distance and Traffic Volume </li></ul>
    47. 47. Customer Premises Equipment <ul><li>Access Device </li></ul><ul><ul><li>Has link to internal system (often a LAN) </li></ul></ul><ul><ul><li>Has CSU/DSU to put internal traffic into format for Frame Relay transmission </li></ul></ul><ul><ul><li>In Frame Relay, called Frame Relay Access Device (FRADS) </li></ul></ul>Access Device LAN Access Line to Network
    48. 48. Modular Routers <ul><li>CSU/DSUs are removable expansion boards </li></ul>Router Switching Circuitry Port 1 CSU/DSU (T1) Port 2 CSU/DSU (56 kbps) Port 3 CSU/DSU (T3) Port 4 CSU/DSU (56 kbps) Modular Router T1 Line 56 kbps Line T3 Line 56 kbps Line
    49. 49. Elements of a Packet Switched Network Customer Premises A LEC Switching Office POP at LEC Office Leased Access Line to POP Leased Access Line to POP You need a leased access line to the network’s POP. Sometimes the packet switched network vendor pays the cost of the access line for you and bundles it into your service charges.
    50. 50. Elements of a Packet Switched Network Switched Data Network Trunk Line Network Switching Office POP Customer Premises B Leased Access Line
    51. 51. Pricing of Frame Relay <ul><li>Speed of the Access Line from Site to Network </li></ul><ul><ul><li>Determines maximum transmission rate to the network </li></ul></ul><ul><ul><li>Often called the Port Speed (not in the book) </li></ul></ul><ul><ul><li>Often the most important price determinant </li></ul></ul><ul><ul><li>Must be fast enough for needs </li></ul></ul>See Frame Relay vs. DSL -- a price issue
    52. 52. Pricing of Frame Relay <ul><li>In Some Frame Relay networks, two speeds </li></ul><ul><ul><li>Committed Information Rate (pretty much guaranteed) </li></ul></ul><ul><ul><li>Available Bit Rate (like flying standby) for bursts. Not guaranteed. </li></ul></ul><ul><ul><li>Price depends both on CIR and ABR </li></ul></ul><ul><ul><li>Access line speed must be fast enough for ABR </li></ul></ul>
    53. 53. Pricing of Frame Relay <ul><li>Additional price per PVC </li></ul><ul><ul><li>Usually small compared to the access line charge </li></ul></ul><ul><ul><li>One access line can multiplex all PVCs to/from site </li></ul></ul><ul><ul><li>PVCs share access line speed </li></ul></ul>Site PVC1 PVC2
    54. 54. Calculations <ul><li>Situation </li></ul><ul><ul><li>You have four sites </li></ul></ul><ul><ul><li>You want any one to be able to reach any other </li></ul></ul><ul><li>Questions </li></ul><ul><ul><li>How many PVCs do you need? </li></ul></ul><ul><ul><li>How many access lines do you need? </li></ul></ul>
    55. 55. Calculations <ul><li>PVCs </li></ul><ul><ul><li>If you have N sites, there are N(N-1)/2 possible connections </li></ul></ul><ul><ul><li>In this case, you would have 4(3)/2 or 6 possible connections </li></ul></ul><ul><ul><li>Some vendors count this as 6 PVCs, others as 12 PVCs </li></ul></ul><ul><li>Access Lines </li></ul><ul><ul><li>You would need four access lines (one for each site) </li></ul></ul><ul><ul><li>Each will multiplex 3 PVCs </li></ul></ul><ul><ul><li>Must be fast enough for the needs of communication with the three other sites </li></ul></ul>
    56. 56. Pricing of Frame Relay <ul><li>May Depend on Distance </li></ul><ul><ul><li>But often a flat monthly rate throughout the carrier’s service area </li></ul></ul><ul><li>May Depend on Traffic </li></ul><ul><ul><li>But often a flat monthly rate based only on the speed of the access line </li></ul></ul>
    57. 57. Leased Lines vs. Packet-Switched Data Networks <ul><li>Leased Lines </li></ul><ul><ul><li>Point-to-point, inexpensive for thick routes </li></ul></ul><ul><ul><li>Inflexible: must be established ahead of time </li></ul></ul><ul><li>Packet Switched Networks </li></ul><ul><ul><li>Also must be established ahead of time for PVCs </li></ul></ul><ul><ul><li>Competitor for leased line networks </li></ul></ul><ul><ul><li>Priced aggressively </li></ul></ul><ul><ul><li>Carrier does all the management </li></ul></ul><ul><ul><li>Killing the leased line business </li></ul></ul>
    58. 58. Circuit-Switched vs. Packet-Switched Services <ul><li>Circuit Switched Networks (ISDN, Switched 56) </li></ul><ul><ul><li>Any-to-any connectivity by dialing number </li></ul></ul><ul><ul><li>Highest speed is ISDN: 64 kbps to 128 kbps </li></ul></ul><ul><li>Packet Switched Networks (X.25, Frame Relay, ATM) </li></ul><ul><ul><li>PVCs make them primarily competitors to leased lines </li></ul></ul><ul><ul><li>Megabit to gigabit speeds </li></ul></ul><ul><ul><li>SVCs may provide any-to-any flexibility in the future </li></ul></ul>
    59. 59. Virtual Private Network Corporate Site A VPN Server Corporate Site B Tunnel Internet Extranet Remote Access for Intranet 1. Site-to-Site VPN Server 2. Remote Customer PC (or site) 3. Remote Corporate PC
    60. 60. VPN advantage <ul><li>Virtual Private Network (VPN) </li></ul><ul><ul><li>Transmission over the Internet with added security </li></ul></ul><ul><ul><li>Some analysts include transmission over a PSDN with added security </li></ul></ul><ul><li>Why VPNs? </li></ul><ul><ul><li>PSDNs are not interconnected </li></ul></ul><ul><ul><ul><li>Only good for internal corporate communication </li></ul></ul></ul><ul><ul><li>But Internet reaches almost all sites in all firms </li></ul></ul><ul><ul><li>Low transmission cost per bit transmitted </li></ul></ul>
    61. 61. VPN issues <ul><li>VPN Problems </li></ul><ul><ul><li>Latency and Sound Quality </li></ul></ul><ul><ul><ul><li>Internet can be congested </li></ul></ul></ul><ul><ul><ul><li>Creates latency, reduces sound quality </li></ul></ul></ul><ul><ul><ul><li>Use a single ISP as for VoIP (voice over IP) </li></ul></ul></ul><ul><ul><li>Security </li></ul></ul><ul><ul><ul><li>PPTP for remote access is popular </li></ul></ul></ul><ul><ul><ul><li>IPsec for site-to-site transmission is popular </li></ul></ul></ul>
    62. 62. ISP-Based PPTP Remote Access VPN <ul><li>Remote Access VPNs </li></ul><ul><ul><li>User dials into a remote access server (RAS) </li></ul></ul><ul><ul><li>RAS often checks with RADIUS server for user identification information. Allows or rejects connection </li></ul></ul>Internet ISP PPTP Access Concentrator Local Access Corporate Site A Secure Tunnel Unsecure TCP Control Channel RADIUS Server PPTP RAS
    63. 63. VPN and PPTP <ul><li>Point-to-Point Tunneling Protocol </li></ul><ul><ul><li>Available in Windows since Windows 95 </li></ul></ul><ul><ul><ul><li>No need for added software on clients </li></ul></ul></ul><ul><ul><li>Provided by many ISPs </li></ul></ul><ul><ul><ul><li>PPTP access concentrator at ISP access point </li></ul></ul></ul><ul><ul><li>Some security limitations </li></ul></ul><ul><ul><ul><li>No security between user site and ISP </li></ul></ul></ul><ul><ul><ul><li>No message-by-message authentication of user </li></ul></ul></ul><ul><ul><ul><li>Uses unprotected TCP control channel </li></ul></ul></ul>
    64. 64. IPsec in Tunnel Mode Tunnel Only Between Sites Hosts Need No Extra Software Secure Tunnel Tunnel Mode IPsec Server IPsec Server Local Network Local Network No Security In Site Network No Security In Site Network
    65. 65. IPsec in Transfer Mode End-to-End (Host-to-Host) Tunnel Hosts Need IPsec Software Secure Tunnel Transfer Mode IPsec Server IPsec Server Local Network Local Network Security In Site Network Security In Site Network
    66. 66. IPsec alternatives <ul><li>IP Security (IPsec) </li></ul><ul><ul><li>Tunnel mode: sets up a secure tunnel between IPsec servers at two sites </li></ul></ul><ul><ul><ul><li>No security within sites </li></ul></ul></ul><ul><ul><ul><li>No need to install IPsec software on stations </li></ul></ul></ul><ul><ul><li>Transfer mode: set up secure connection between two end hosts </li></ul></ul><ul><ul><ul><li>Protected even on internal networks </li></ul></ul></ul><ul><ul><ul><li>Must install IPsec software on stations </li></ul></ul></ul>
    67. 67. Security at the internet layer <ul><li>IP Security (IPsec) </li></ul><ul><ul><li>At internet layer, so protects information at higher layers </li></ul></ul><ul><ul><li>Transparent: upper layer processes do not have to be modified </li></ul></ul>Internet Layer with IPsec Protection TCP UDP HTTP SMTP FTP SNMP Protected
    68. 68. Common IPsec configuration <ul><li>IP Security (IPsec) </li></ul><ul><ul><li>Security associations: </li></ul></ul><ul><ul><ul><li>Governed by corporate policies </li></ul></ul></ul>List of Allowable Security Associations List of Allowable Security Associations Party B Party A IPsec Policy Server

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