Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Wake-on-LAN wikipedia , lookup
Distributed firewall wikipedia , lookup
Asynchronous Transfer Mode wikipedia , lookup
Computer network wikipedia , lookup
Airborne Networking wikipedia , lookup
Deep packet inspection wikipedia , lookup
Zero-configuration networking wikipedia , lookup
Network tap wikipedia , lookup
Cracking of wireless networks wikipedia , lookup
Internet protocol suite wikipedia , lookup
Recursive InterNetwork Architecture (RINA) wikipedia , lookup
07- Transport Layer Transport Layer 3-1 Transport services and protocols provide logical communication between app processes running on different hosts transport protocols run in end systems send side: breaks app messages into segments, passes to network layer rcv side: reassembles segments into messages, passes to app layer more than one transport protocol available to apps Internet: TCP and UDP application transport network data link physical application transport network data link physical Transport Layer 3-2 Transport vs. network layer network layer: logical communication between hosts transport layer: logical communication between processes relies on, enhances, network layer services Transport Layer 3-3 Transport vs. network layer Demultiplexing Multiplexing Transport Layer 3-4 Transport vs. network layer network layer: logical communication between hosts transport layer: logical communication between processes relies on, enhances, network layer services Household analogy: 12 kids sending letters to 12 kids processes = kids app messages = letters in envelopes hosts = houses transport protocol = Ann and Bill who mux, demux to in-house siblings network-layer protocol = postal service Internet transport-layer protocols reliable, in-order delivery (TCP) congestion control flow control connection setup unreliable, unordered delivery: UDP no-frills extension of “best-effort” IP services not available: delay guarantees bandwidth guarantees application transport network data link physical network data link physical network data link physical network data link physical network data link physical network data link physical application transport network data link physical Transport Layer 3-6 Multiplexing/demultiplexing Multiplexing at send host: gathering data from multiple sockets, enveloping data with header (later used for demultiplexing) Demultiplexing at rcv host: delivering received segments to correct socket = socket application transport network link = process P3 P1 P1 application transport network P2 P4 application transport network link link physical host 1 physical host 2 physical host 3 Transport Layer 3-7 How demultiplexing works host receives IP datagrams each datagram has source IP address, destination IP address each datagram carries 1 transport-layer segment each segment has source, destination port number (recall: well-known port numbers for specific applications) host uses IP addresses & port numbers to direct segment to appropriate socket 32 bits source port # dest port # other header fields application data (message) TCP/UDP segment format Transport Layer 3-8 Connectionless demultiplexing Create sockets with port numbers: UDP socket identified by two-tuple: (dest IP address, dest port number) When host receives UDP segment: checks destination port number in segment directs UDP segment to socket with that port number IP datagrams with different source IP addresses and/or source port numbers directed to same socket Transport Layer 3-9 Connectionless demux (cont) DatagramSocket serverSocket = new DatagramSocket(6428); P2 SP: 6428 SP: 6428 DP: 9157 DP: 5775 SP: 9157 client IP: A P1 P1 P3 DP: 6428 SP: 5775 server IP: C DP: 6428 Client IP:B SP provides “return address” Transport Layer 3-10 Connection-oriented demux TCP socket identified by 4-tuple: source IP address source port number dest IP address dest port number recv host uses all four values to direct segment to appropriate socket server host may support many simultaneous TCP sockets: each socket identified by its own 4-tuple web servers have different sockets for each connecting client non-persistent HTTP will have different socket for each request Transport Layer 3-11 Connection-oriented demux (cont) P2 P3 SP: 80 SP: 80 DP: 9157 DP: 5775 SP: 9157 client IP: A DP: 80 P1 P1 P4 SP: 5775 server IP: C DP: 80 Client IP:B Transport Layer 3-12 Connection-oriented demux: Threaded Web Server P1 P2 P4 P1P3 SP: 5775 DP: 80 S-IP: B D-IP:C SP: 9157 client IP: A DP: 80 S-IP: A D-IP:C SP: 9157 server IP: C DP: 80 S-IP: B D-IP:C client IP:B Transport Layer 3-13 Is every protocol the same? Demultiplexing Multiplexing Transport Layer 3-14 Based on what we’ve talked about, why would anyone use UDP? Transport Layer 3-15 UDP: User Datagram Protocol [RFC 768] “no frills,” “bare bones” Internet transport protocol “best effort” service, UDP segments may be: lost delivered out of order to app connectionless: no handshaking between UDP sender, receiver each UDP segment handled independently of others Why is there a UDP? no connection establishment (which can add delay) simple: no connection state at sender, receiver small segment header no congestion control: UDP can blast away as fast as desired Transport Layer 3-16 UDP: more often used for streaming multimedia apps loss tolerant rate insensitive Length, in bytes of UDP segment, including header other UDP uses DNS SNMP reliable transfer over UDP: add reliability at application layer application-specific error recovery! 32 bits source port # dest port # length checksum Application data (message) UDP segment format Transport Layer 3-17 UDP checksum Goal: detect “errors” (e.g., flipped bits) in transmitted segment Sender: Receiver: treat segment contents compute checksum of as sequence of 16-bit integers checksum: addition (1’s complement sum) of segment contents sender puts checksum value into UDP checksum field received segment check if computed checksum equals checksum field value: NO - error detected YES - no error detected. But maybe errors nonetheless? More later …. Transport Layer 3-18 Internet Checksum Example Note: when adding numbers, a carryout from the most significant bit needs to be added to the result Example: add two 16-bit integers 1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 1 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 wraparound 1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1 sum 1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 0 checksum 1 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1 Transport Layer 3-19 Checksum calculation UDP uses 1’s complement for their checksums. Suppose you have the following 8-bit bytes: 01010011, 01010100, 01110100. What is the 1’s complement of the sum of these 8-bit bytes? How does the receiver detect errors? Transport Layer 3-20