Communication Networks A Second Course Jean Walrand Department of EECS University of California at Berkeley

Review of TCP/IP Networks History Key Ideas Protocols Technology

Networks WAN MAN

Networks WAN MAN LAN

WAN LAN Networks

History 1962 – L. Kleinrock proposes Packet SwitchingL. Kleinrock 1966 – L. Roberts proposes architecture to DarpaL. Roberts 1969 – First demonstration of packet switching: 4-node Arpanet 1969 – S. Croker introduces RFCs (managed by J. Postel) 1972 – R. Kahn proposes an open architecture: Inter-networking with stateless routers, best effort, no control planeR. Kahn 1973 – Kahn and V. Cerf propose early ideas of IP (32-bit address) and TCP (end-to-end ACKs with a window scheme)V. Cerf 1973 – R. Metcalfe invents EthernetR. Metcalfe 1982 – IGP and EGPIGP and EGP Late 1970s, early 1980s – Berkeley develops BSD, a modified implementation of UNIX that includes TCP/IP 1983 – Arpanet switches to TCP/IP 1983 – P. Mockapetris invents DNSP. Mockapetris 1988 – Van Jacobson fixes TCPVan Jacobson 1985 – 1995 – Internet supported by NSF and other agencies 1993? – T. Berners-Lee invents WWWT. Berners-Lee 1995 – Internet is privatized 2000… - WiFi,VoIP, P2P See

Key Ideas Packet Switching End-to-End error and flow control Internetworking Multiple Access DNS P2P VoIP

Packet Switching A B A | B | …. C A | C | ….

End-to-End Error and Flow Control A B A | B | n | … | EC A | B | m | … | EC B | A| k | m | … | EC ACKs all packets from A up to packet m Error control field A can have up to N packets for B that have not been acknowledged Selecting N adjusts the rate of transmissions: limit congestion If ACK is late, A retransmits packets

Internetworking Goal: Connect different networks 1.1 a 1.2 b 1.0 c 2.0 d 2.1 e 2.2 f a  c|1.1  2.2 | X d  f |1.1  2.2 | X a  b|1.1  1.2 | Y ROUTER Router looks at IP addresses (1.1, …) Each network uses local addresses (e.g., a, b, c, …)

Multiple Access Goal: Share one medium (e.g., WiFi) A B C time A | B | C | A | “Collision” Wait random time after collision C | A | “Busy” A | B | Wait until idle

DNS: Domain Name Service Translate Name into IP address (e.g., google.com into ) Directory of DNS is distributed:.com,.edu, ….edu: berkeley.edu, stanford.edu, … Mapping can depend on source address Mapping can be done to multiple addresses

P2P: Peer-to-peer Goal: All peers become servers Example: Each peer knows the addresses of a set of peers: his “friends” To find a file, peer A asks his friends who in turn ask their friends, and so on, until someone, B, says he has the file… (can limit search); A then asks B for the file. Many variations are possible. The key idea is that there is no specialized server; every client becomes a server.

VoIP: Voice over IP Goal: Place phone calls over Internet (Should be cheaper because the Internet infrastructure is much lighter than that of the phone network.) Steps: Gateway converts phone signal into IP packets and vice- versa Protocol to convert phone number into gateway IP address Gateway converts usual control signals (dial tone, ringing, busy, …) into IP packets and vice-versa

Protocols: IP: Internet Protocol TCP: Transmission Control Protocol UDP: User Datagram Protocol HTTP: Hypertext Transfer Protocol FTP: File Transfer Protocol ARP: Address Resolution Protocol TCPUDP IP HTTPFTP

Protocols: Fiber, Wires, WL Eth. HTTP, FTP, … IP UDP - TCP Physical Interface Synchronous unreliable bit pipe Data Link Control Data Link Control Asynchronous reliable bit pipe Physical Link Network Asynchronous routed path FHData Physical Interface Synchronous unreliable bit pipe Data Link Control Asynchronous reliable bit pipe Physical Link Network Asynchronous routed path FHData Transport PHDataPHData THData End NodeRouterEnd Node Application Data

IP: Internet Protocol Delivers packets between any two hosts Organizes address, manages routing tables Addresses: 32 bits, arranged so that prefix determines next router toward destination Routing algorithm: Essentially shortest path. Done in two levels: nodes are grouped; shortest path inside each group and across groups. Tables updated periodically to adjust to changes

TCP: Transmission Control Protocol Implements reliable delivery of byte stream between hosts Multiplexes multiple connections to and from a host: adds a “port” number End-to-end retransmissions Regulates flow to avoid congesting Destination (flow control) Routers (congestion control) Method: ACKs, control number of unacknowledged packets

TCP Service: IP Transport ABC [A | B | p1 | p2 | …] p1p2p1p2p3p1p2 ports Application HTTP DNS ftp TCP: Byte Stream  Ordered, reliable, well-paced

Congestion Control: Flows share links: How to share the links bandwidth?

TCP AlgorithmTCP Algorithm: AIMD AB x C DE y Limit rates: x = y TOC TOC – Congestion Control - TCP Algorithm – AIMDCongestion Control TCP Algorithm Try to be fair

TCP: Summary W 1 64KB X 0.5 TO 3DA X 0.5 3DA TO X 0.5 SSCA SS CA 3 3

Flow Control Objective: Avoid saturating destination Algorithm: Receiver avertizes window RAW RAW window = min{RAW – OUT, W} where OUT = Oustanding = Last sent – last ACKed W = Cong. Window from AIMD + refinements [ACK | RAW | …]

SYN k SYN n; ACK k+1 DATA k+1; ACK n+1 ACK k+n+1 data exchange FIN FIN ACK ½ close FIN FIN ACK ½ close TCP Phases: 3-way handshake

UDP: User Datagram Protocol Unreliable delivery of packets with error detection Multiplexes multiple connections to and from a host: adds a “port” number Adds error detection code for the packet No retransmission, no flow control

FTP: File Transfer Protocol Reliable delivery of file between hosts Converts file into byte stream for TCP

HTTP Transfer of html files Sets up TCP connections and FTP to transfer files Closes connections after transfer

ARP: Address Resolution Protocol Discovers local address from IP address Example: In “Internetworking” slide, host 1.1 uses ARP to discover local address b of 1.2 Protocol: Host 1.1 broadcasts request on local network: Who is 1.2? Host 1.2 replies to 1.1; local address of source (b) is in the packet.

Technology Communication Links Switches

Communication Links Fibers Cat5 Unshielded Twisted Pairs Coaxial Cable Wireless

Communication Links Convert bits string into signals that propagate as electromagnetic waves Optical: Typically ON/OFF  pulses of light; encoding makes sure there are enough transitions for the receiver to remain in sync Fibers: up to 10Gbps over 100 km per wavelength; up to 128 wavelengths per fiber Wired and wireless: Typically pulses of sine waves at different frequencies or phases to encode groups of bits Wires: 100 Mbps over 100 m Wireless: 100 Mbps over 30 m with multiple antennas (802.11n) Error control codes: typically to detect errors

Telephone SwitchTelephone Switch RouterRouter

Switches Various links: optical, cable, wires Looks up destination address and sends packet to corresponding output port May perform some traffic policing (limit rate) and some differentiated service (e.g., priority to VoIP packets) Fast router: total throughput of 500 Gbps From a few to 128 ports