Lecture8
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X.25 is a connection-oriented packet switched network using virtual circuits to transfer data between identified end nodes over typical bandwidths of 2.4-9.6 kbps. Frame relay is a more efficient WAN technology than X.25 that uses virtual circuits without hop-by-hop error control. ATM uses fixed size 53 byte cells over virtual circuits to provide quality of service guarantees when transferring data over LANs and WANs with unlimited scalability.
Lecture8
- 1. X.25 WAN Technologies Packet switched Network consisting of X.25 switches. X.25 is a connection oriented protocol (Virtual Circuits). End nodes are identified by an X .25 address. Typical bandwidth offered is 2.4/9.6 kbps. IP networks interface with X .25 through IP- X.25 routers.
- 2. WAN Technologies X.25 and Virtual Circuits
- 3. Frame Relay WAN Technologies Designed to be more efficient than X.25 Developed before ATM Call control carried in separate logical connection No hop by hop error or flow control End to end flow and error control (if used) are done by higher layer Single user data frame sent from source to destination and ACK (from higher layer) sent back Two type of Virtual Circuits defined Permanent virtual circuits (PVCs) Switched virtual circuits (SVCs)
- 4. ATM WAN Technologies Small fixed size packets of 53 bytes, called cells, are used for transferring information. Each cell has 5 bytes of header and 48 bytes of payload for user information. Connection oriented protocol. A virtual Circuit is established between the communicating nodes before data transfer takes place. Can be seamlessly used in LANs and WANs. Almost unlimited scalability. Provides quality of service guaranties.
- 5. WAN Technologies Digital Subscriber Line (DSL) Digital Subscriber Line (DSL) uses the Ordinary Telephone line and is an always-on technology. This means there is no need to dial up each time to connect to the Internet. Because DSL is highly dependent upon noise levels, a subscriber cannot be any more than 5.5 kilometers (2-3 miles) from the DSL Exchange Service can be symmetric, in which downstream and upstream speeds are identical, or asymmetric in which downstream speed is faster than upstream speed. DSL comes in several varieties: Asymmetric DSL (ADSL) High Data Rate DSL (HDSL) Symmetric DSL (SDSL) Very High Data Rate DSL (VDSL)
- 7. Cable Modems WAN Technologies The cable modem connects a computer to the cable company network through the same coaxial cabling that feeds cable TV (CATV) signals to a television set. Uses Cable Modem at Home End and CMTS (Cable Modem Termination System) at Head End. Characteristics: Shared bandwidth technology 10 Mbps to 30 Mbps downstream 128Kbps-3 Mbps upstream Maximum Distance from provider to customer site: 30 miles
- 8. Cable Modems WAN Technologies
- 9. WAN Technologies Point-to-Point Microwave Link ISP Network RF Network Router Modem RF Modem Router MICROWAVE LINK ISP PREMISES CUSTOMER PREMISES
- 10. WAN Technologies Point-to-Point Microwave Link Typically 80-100 MHz Band or 5 GHz Radio Link band 2.4 GHz WiFi links are becoming popular Requires Line of Sight
- 11. VSAT WAN Technologies Very Small Aperture Terminal (VSAT) provide communication between two nodes through a powerful Earth station called a Hub. If two terminals want to communicate, they send their messages to the satellite, which sends it to the Hub and the Hub then broadcasts the message through the satellite. Typical Bandwidth offered is 9.6/19.2/32/64/128/256/512 Kbps. Operating modes are TDM/TDMA, SCPC PAMA & DAMA
- 12. VSAT WAN Technologies Each satellite sends and receives over two bands Uplink: From the earth to the satellite Downlink: From the satellite to the earth Satellite frequency bands Band Downlink Uplink C 3.7-4.2 GHz 5.925-6.425 GHz Ku 11.7-12.2 GHz 14-14.5 GHz Ku-band based networks, are used primarily in Europe and North America and utilize the smaller sizes of VSAT antennas. C-band, used extensively in Asia, Africa and Latin America, require larger antenna.