IP, Wireless The world is the network

From Ethernet up Ethernet uses 6 byte addresses Source, destination, data, and control stuff Local networks only Not all networks are IP Not all IP is ethernet

IP today Present networks are based on IPv4 Packets (called datagrams) –4 bytes describing IP version and other control, including TOS (type of service, often used to control speed and loss of packets) –4 bytes: Numbering system for splitting information into different fragments –4 bytes describing information and protocol used.

More on the IP packet –4 bytes source IP number –4 bytes destination IP number –Variable bytes describing other options –Data! Variable number of bytes

IP numbers and networks 4 bytes = 32 bits. Usually recorded as the 4 numbers corresponding to each byte: Part of the number is the number of the network, part the number of the host. Subnet mask tells us which bits are network number.

Subnets Mask = –top 3 bytes network, lower byte address –So, would be host number 2 in network Can have different sized networks: would have two bytes for the host.

Quick overview of routing and the Internet Internetworking is just moving packets from one network to another –When we transmit a packet, if it’s on our network, we just send it to a local machine –If it’s on another network, we send it to a gateway. Gateways are computers on our network and on another network Provide link between networks

Gateways and Bridges Gateway or router is a computer/box on a IP network, with two or more IP addresses –One IP on one side, one on another –Communicates at the IP level. Internetworking Protocol! Bridges connect two segments of the same IP or ethernet network –Act like one network, share IP range. –Can be purely ethernet.

Ethernet vs IP Ethernet is one kind of link-level network. IP is a more general form of network IP packets are payload of an ethernet packet in an IP over ethernet network (most modern nets) –Those nets have packets with both ethernet and IP addresses in packet. –Locally, communication uses ethernet addresses, send to other nets via IP addresses.

Ports Two main protocols: UDP and TCP Have a concept of ports: place a piece of information goes to on a given computer Ports: two bytes, 0 to Well-known ports: –Mail (SMTP): port 25 –Web: port 80 Packets come from a destination port to make sure they go to the right place.

UDP/IP vs. TCP/IP UDP is just ports on top of IP. Video and more. TCP is far more complex: –Provides mechanisms to adjust data speed –Automatically resends lost packets –Keeps data in order –Based on two-way handshake: packets flow back from destination to source to control everything. Slows things down. UDP fast, TCP reliable. Both are IP.

Wireless networking systems Transmit information over radio waves –Can be based on a constantly open link, like a radio version of a serial wire. Cellphones. –Can be based on transmitting packets: ethernet, IP, and more. Signals are transmitted over a band of frequencies centered at some frequency –Higher data rates = higher bandwidth = more power

Wireless Bridges Modern large wireless systems are ethernet bridges Work like ethernet transmitted over radio waves instead of wires Correct for errors: –Interference (spread-spectrum) –Noise (error detection and correction) –Multipathing: bouncing around and interfering with own signal (OFDM)

Radio waves Lower frequencies –Move over obstructions easily –Long range –Slow data rates Higher frequencies –Need line of sight, or even more! –Very high data rates –Need special antennae to get long range. Bouncing!

Range and data rate power fades as 1/distance^2 power needed goes as distance squared power needed proportional to data rate –Higher speed signals don’t go as far –More cells needed, or more power needed more range causes more problems with multipath, though

Antennae Concentrate the radio waves in one direction –more power in that direction –less or nearly no power in others Increases range and data speed possible “Effective Radiated Power” = real power * gain of antenna Increases signal received for a given local power level from a remote transmitter.

Antenna types Omni: spreads signal around evenly, but may reduce amount it goes up or down. Great for point to multipoint, but requires more power. Dish: gives a round, pencil-like, beam. Great for point to point connections. Sectoral: transmits in a pie-like area. Can handle height differences well, and is used for cellphone systems, or point to multipoint.

Urban areas Buildings block signals Buildings bounce signals around Lots of interferences from people on same frequencies Special transmission systems needed to fight problems. Big area, lots of cells. Lots of people though-can be cheap per person!

Remote areas Mountains, Trees, can block signals Rocks bounce signals around, even ground bounces signals if you go far enough Less interference Not many people-can’t afford many cells!