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计网

lecture 0

  • network edge:

  • host(sever, client), mobile network, home network, institutional network.

  • net work core:

  • interconnected routers, network of networks.

  • how to connect end systems to edge routers？

  • residential access nets.

  • institutional access networks.

  • mobile access networks.

  • access net:

  • DSL(digital subscriber line):

    • dedicated line

  • cable network:

    • frequency division multiplexing: different channels transmitted in different frequency bands. (shared access network). like HFC(hybrid fiber coax)

  • home network:

  • Enterprise access networks:

  • Wireless access networks:

    • 1.wireless LANs
    • 2.wide-area wireless access

  • Host:

  • send packets

  • transmition delay = L/R

  • pyhsical media:

  • bit:

    • propagates between transmitter/receiver pairs

  • physical link:

    • what lies between transmitter & receiver

  • guided media:

    • signals propagate in solid media: copper, fiber, coax

  • unguided media:

    • signals propagate freely,e.g., radio

lecture 1:

  • packet-switching:

  • hosts break application-layer messages into packets

  • store and forward: entire packet must arrive at router before it can be transmitted on next link

  • queuing and loss:

  • If arrival rate (in bits) to link exceeds transmission rate of link for a period of time:
    packets will queue, wait to be transmitted on link.
    packets can be dropped (lost) if memory (buffer) fills up

  • Alternative core: circuit switching:

  • dedicated resourse(no sharing)

  • Commonly used in traditional telephone networks.

  • FDM verse TDM:

  • Four sources of packet delay:

  • d = d(proce)+d(queue)+d(trans)+d(prop)

  • d(process): check bit errors, determine output link

  • d(queue): time waiting at output link for transmission. determined by congestion level.

  • d(transmition): d=L/R

  • d(propagation): d/s

  • Throughput:

  • rate (bits/time unit) at which bits transferred between sender/receiver

  • encapsulation:

  • switch : physical -- link --physical

  • router : Hn,Ht,M pyhsical --link(Hl,Hn,Ht,M) --network(Hn,Ht,M) -- link(Hl,Hn,Ht,M) --pyhsical

  • IP address and Subnets:

  • host part : low order bits

  • subnet part: high order bits

lecture 21

  • Application architectures:

  • peer-peer, client-sever

  • Who send/recv msg to/from network?

  • Processes

  • Where does process send/recv msg to/from?

  • socket

  • Processes within same host:

  • communicate using inter-process communication (defined by OS)

  • processes in different hosts:

  • communicate by exchanging messages

  • TCP service:

  • reliable data transfer

  • flow control

  • congestion control

  • connection-oriented

  • does not provide:

    • timing sensitive
    • Throughput guarantee
    • security
  • UDP service:
    • unreliable data transfer
    • does not provide:
      • reliablity
      • flow control
      • congestion control
      • timing
      • Throughput guarantee
      • security
      • connection setup.
  • HTTP :
    • response time:
      nonpersistent: 2RTT+filr transmition time
    • HTTP method:
      HTTP1.0: GET, POST , HEAD
      HTTP1.1: GET, POST, HEAD,PUT, DELETE
  • web cache:
    • goal: satisfy client request without involving origin server.
    • why web cache?
      • reduce response time for client request
      • reduce traffic on an institution’s access link
      • Internet dense with caches: enables “poor” content providers to effectively deliver content (so too does P2P file sharing)
  • conditional get:
    • goal:don't send object if cache has up-to-date cached version.

lecture 2_2

  • DNS :
    • iterated query
    • recursive query
    • dns record:
      • type = A: name is host name, value is ip
      • type = NS: name is domain, value is host name of authoritative name server for this domain
      • type = CNAME: name is alas name,value is canonical name
      • type = MX: value is name of mailsever associated with name.
  • p2p application:
    • flie transfer time:
      • client-sever: max(NF/Us,F/dmin)
      • p2p: max(F/Us,F/dmin,NF/(us+u+...+u))

lecture 2_3

  • DASH(dynamic adaptive streaming over HTTP): for client intelligence

  • Multimedia: video:

    • encoding:
      • spatial(within image)
      • temporal(from one to next image)

lecture 3_1

  • Multiplexing/demultiplexing:
    • handle data from multiple sockets, add transport header
    • use header info to deliver received segments to correct socket