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Copy path12. Connecting to the Internet
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12. Connecting to the Internet
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* Connecting to the Internet
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* Dial-up, Modems and Point-to-point protocols :
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-> Early primituve technologies - mostly focused on connecting devices in close proximity;
- PSTN (Public switch telephone network) and POTS (Plain old telephone service); - using phone lines to transmit data;
-> 2 Duke students - using PSTN - to transfer data - built USENET;
-> Dial-up connection - to exchange a series of messages with each other;
- It uses POTS for data-transfer, and the connection is established by dialing a phone number;
- Computer -> digital -> modem -> analog -> telephone exchange -> Analog -> modem -> digital -> computer;
-> Modem -> Modulator / Demodulator -> Take computer understandable data and turn them into audible wavelengths that can be transmitted over POTS; since the telephone lines where created to transmit voice from one place to another;
- Similar to line coding conceptually that turns ones and zeros into modulating electrical charges across the Ethernet cables;
- Early modem - very low baud rates;
* Baud rate -> A measurement of how many bits can be transmitted across a phone line in a second;
-> 1950s -> baud rate - 110 bps;
-> USENET -> 300 bps;
-> Dial-up access -> 14.4 kbps (1990);
Previously dial-up usage was wide-spread;
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* Broadband
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-> Any connectivity technology that is not dial-up Internet;
-> Very fast, long lasting connections that don't need to be established with each use;
-> T carrier technologies: Originally invented by AT&T in order to transmit multiple phone calls over a single link; Eventually able to transmit data faster than any dial-up connection;
- T-carriers require dedicates lines, hence expensive;
-> Common broad-band solutions
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1. T-carrier technology;
2. DSL - Digital subscriber lines;
3. Cable broadband;
4. Fiber connections;
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1. T-Carrier Technologies
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- Invented by AT&T - inorder to provision a system that allowed lots of phone calls to travel across a single cable;
- Every individual phone calls were made across individual pairs of copper wire before Transmission System 1 (First T-Carrier Specification / T1);
- AT&T invented a way to carry up to 24 simultaneous phone calls across a single piece of twisted pair copper;
- Later on the same technology was re-purposed for data-transfer;
- 24 phone channels - each capable of transmitting 64 kilobits per second;
- Single T1 line -> cable of transfering - 1.544 megabits per second;
-> With advancements -> T3 line -> 28 T1s all multiplexed -> 1.544 mbps x 28 = 44.736 mbps;
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2. Digital Subscriber lines :
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-> Twisted pair copper used by modern telephone lines was capable of transmitting way more data than that was needed for voice to voice calls;
-> By operating at a frequency range that did not interfer with normal phone calls, data transfer could occur - this technology - Digital subscriber line;
-> Voice calls and data transfers could occur at the same time in the same lines;
-> The manner similar to who Dail-ups used Modems, DSL technologies use their own modem - DSLAMs (Digital subscriber line acess multiplexers);
- DSLAMS - these devices establish data connections across phone lines, and long-running (its not torn-dom easily);
- Different kinds of DSL
1. ADSL - Asymmetric DSL - upload and download speeds are different; (outbound and incoming data);
2. SDSL - Symmetric DSL - upload and download speeds are same; - 1.544 Mbits/s
3. HDSL - High Bit-rate DSL - speeds > 1.544 Mbits/s;
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3. Cable Broadband :
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-> The coaxial cables used for the cable television into a person's home were capable of transmitting data more than required for TV viewing, by using frequencies that don't interfere with television broadcast;
-> Cable-based technologies were able to deliver high speed internet access across the same cables (for TV viewing);
-> This is "Cable broadband"/ "Shared bandwith technologies";
-> Technologies like DSL / Dial-up connection from home/ office -> goes to Central Office (CO);
-> CO's are offices stacked with telephone operators - who use switchboard to manually connect the caller with the callee;
-> With technological improvements - the CO's became smaller pieces of automated hardware that handled this functions for the telephone companies;
-> Cable Internet connections are managed by a cable modem.
-> Cable modem - sits at the edge of the consumer's network and connects it to the CMTS (Cable Modem Termination System);
-> CMTS - connects lots of different cable connections to an ISPs core network;
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4. Fiber Connections
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-> Internet core uses fiber for its connections
- higher speeds;
- without much signal degradation;
-> Expensive - therefore it was used only for the ISPs;
-> FTTX - Fiber to the X;
- FTTN - Fiber to the Neighbourhood - data delivered to a single physical cabinet - population, then on twisted pair copper / co-axial cables can be used for the last length of distance;
- FTTB - Fiber to business/building/basement - data-delivery to an individual building, twisted pait copper is used inside the building;
- FTTH - Fiber to the Home - Fiber runs to each individual homes;
- FTTP - Fiber to the premise - FTTB / FTTH;
-> Instead of modem the demarcation for fiber technolgy is - Optical Network Terminator (ONT);
- ONT - Converts data from protocols the fiber network can understand to those that more traditional, twisted-pair copper networks can understand;
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* Wide Area Network Technologies (WANs) :
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Consider:
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1. Few employees with few computers at a single office, therefore use non-routable address space for internal IPs since IP addresses are scarce and expensive;
2. Configure a router to perform NAT;
3. Configure a local DNS server and a DHCP server to make network configuration easier;
4. Sign a contract with ISP (Internet service provider) to deliver a link to Internet to this office so users can access the web;
5. In case sales people want to connect to the resource set-up on the LAN - configure a VPN server and ensure it is accessible via port forwarding;
6. Employees all over the world can connect via office LAN;
7. Another office is setup across the country and they need to use resources from the office - here WAN is required;
* WAN - Acts like a single network but spans across multiple physical locations;
- It requires a contract a link across the Internet with the ISP;
- The ISP handles sending data from one side to another;
* Typical WAN setup:
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Regional Office -> Demarcation point -> Local loop (LEC / ISP) -> WAN -> Local loop (LEC / ISP) -> Demarcation point -> Regional office;
-> Local loop - T-Carrier line, high-speed optical connection to the providers local regional office;
-> Connects to the ISPs core network and the Internet at Large;
-> WANS use a number of protocols at the data-link layer to transport data from one site to another;
----------------------------------------------------------------------------------------------------------------------------------------* Point-to-Point VPNs :
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- Popular alternative to WAN technology are Point-to-Point VPNs;
- Companies are moving more and more of their internal services into the cloud;
- the cloud lets companies outsource all or a part of different pieces of infrastructrure to other companies to manage;
- Example e-mails - pay another company to handle email services;
- VPN tunneling logic is handled by network devices at either sides so that users all don't have to establish their own connections;
Site 1 ----> Internet ( VPN tunnel ) --------->Site 2;
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