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IP-UDP-RTP Computer Networking (In Chap 3, 4, 7) 건국대학교 인터넷미디어공학부 임 창 훈.

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Presentation on theme: "IP-UDP-RTP Computer Networking (In Chap 3, 4, 7) 건국대학교 인터넷미디어공학부 임 창 훈."— Presentation transcript:

1 IP-UDP-RTP Computer Networking (In Chap 3, 4, 7) 건국대학교 인터넷미디어공학부 임 창 훈

2 IP-UDP-RTP Packet IP header UDP header RTP header Application message
UDP packet (segment) IP packet (datagram)

3 Network layer transport segment from sending to receiving host
on sending side encapsulates segments into datagrams on receiving side, delivers segments to transport layer network layer protocols in every host, router Router examines header fields in all IP datagrams passing through it application transport network data link physical network data link physical

4 Key Network-Layer Functions
forwarding: move packets from router’s input to appropriate router output routing: determine route taken by packets from source to destination Routing algorithms analogy: routing: process of planning trip from source to destination forwarding: process of getting through single interchange

5 Interplay between routing and forwarding
1 2 3 0111 value in arriving packet’s header routing algorithm local forwarding table header value output link 0100 0101 1001

6 Datagram networks no call setup at network layer
routers: no state about end-to-end connections no network-level concept of “connection” packets forwarded using destination host address packets between same source-dest pair may take different paths application transport network data link physical application transport network data link physical 1. Send data 2. Receive data

7 Forwarding table 4 billion possible entries
Destination Address Range Link Interface through through through otherwise

8 Longest prefix matching
Prefix Match Link Interface otherwise Examples DA: Which interface? DA: Which interface?

9 32 bit destination IP address
IP datagram format ver length 32 bits data (variable length, typically a TCP or UDP segment) 16-bit identifier Internet checksum time to live 32 bit source IP address IP protocol version number header length (bytes) max number remaining hops (decremented at each router) for fragmentation/ reassembly total datagram length (bytes) upper layer protocol to deliver payload to head. len type of service “type” of data flgs fragment offset upper layer 32 bit destination IP address Options (if any) E.g. timestamp, record route taken, specify list of routers to visit. how much overhead with TCP? 20 bytes of TCP 20 bytes of IP = 40 bytes + app layer overhead

10 IP addressing: CIDR CIDR: Classless InterDomain Routing
subnet portion of address of arbitrary length address format: a.b.c.d/x, where x is # bits in subnet portion of address subnet part host /23

11 Transport services and protocols
provide logical communication between app processes running on different hosts transport protocols run in end systems send side: breaks application messages into segments, passes to network layer receive side: reassembles segments into messages, passes to application layer more than one transport protocol available to apps Internet: TCP and UDP application transport network data link physical network data link physical network data link physical network data link physical logical end-end transport network data link physical network data link physical application transport network data link physical

12 Transport vs. network layer
network layer: logical communication between hosts transport layer: logical communication between processes relies on, enhances, network layer services

13 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 logical end-end transport network data link physical network data link physical application transport network data link physical

14 Multiplexing/demultiplexing
Multiplexing at send host: Demultiplexing at rcv host: delivering received segments to correct socket gathering data from multiple sockets, enveloping data with header (later used for demultiplexing) = socket = process application transport network link physical P1 P2 P3 P4 host 1 host 2 host 3

15 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 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

16 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

17 UDP: more often used for streaming multimedia apps loss tolerant
rate sensitive reliable transfer over UDP: add reliability at application layer application-specific error recovery! 32 bits source port # dest port # Length, in bytes of UDP segment, including header length checksum Application data (message) UDP segment format

18 RTP runs on top of UDP RTP libraries provide a transport-layer interface that extend UDP: port numbers, IP addresses payload type identification packet sequence numbering time-stamping


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