Internet Service Providers (ISPs) protocols:control the sending and receiving of information within the internet transmission control protocol(tcp) internet
protocol(ip) application programming interface(api): the rules that the sending program must follow so that the internet can deliver the data to the destination program
A protocol defines the format and the order of messages exchanged between two or more communicating entities, as well as the actions taken on the trans- mission
and/or receipt of a message or other event. The Internet’s end systems include desktop computers, servers, and mobile computers. digital subscriber line (DSL)
hybrid fiber-coaxial access network
Cable modems divide the HFC network into a downstream and an upstream channel,downstream channel typically allocated a higher transmission rate than the
upstream channel. cable Internet access is a shared broadcast medium. local area network(LAN) Ethernet is the most prevalent access technology in corporate,
university, and home networks. Wireless LAN access based on IEEE 802.11 technology:wifi Physical media fall into two categories: guided media and unguided
media. Two types of satellites are used in communications: geostationary satellites and low-earth orbiting (LEO) satellites.
each packet travels through communication links and packet switches (for which there are two predominant types, routers and link- layer switches). Most packet
switches use store-and-forward transmission: receive entire packet delay is 2L/R without router: L/R. dend-to-end = N(L/R) N links,N-1 routers
output buffer which stores packets that the router is about to send into that link， if link is busy, waiting in the queue--queue delay. buffer full:packet loss, either the
arriving packet or one of the already-queued packets will be dropped. two fundamental approaches to moving data through a network of links and switches:
circuit switching(need reserve):telephone networking. packet switching： does so while allowing for more than three times the number of users. frequencydivision multiplexing (FDM) or time-division multiplexing (TDM). bandwidth:the wid of the band, means the transmission capacity of a communication
channels. FDM:frequency domain is segmented into bands. TDM:time domain is segmented into frames
With FDM, each circuit continuously gets a fraction of the bandwidth. With TDM, each circuit gets all of the bandwidth periodically during brief intervals of time
(that is, during slots) Circuit switching pre-allocates use of the transmission link regard less of demand, with allocated but unneeded link time going unused. Packet
switching on the other hand allocates link use on demand. Link transmission capacity will be shared on a packet-by-packet basis only among those users who have
packets that need to be transmitted over the link. Internet Exchange Point (IXP)： meeting point where multiple ISPs can peer together
total nodal delay:nodal processing delay, queuing delay, transmission delay, and propagation delay（single router）
processing delay:the time required to examine the packet’s header and determine where to direct the packet.
queuing delay:waits to be transmitted onto the link.
transmission delay:first come first server L/R a function of the packet’s length and the transmission rate of the link
propagstion delay:propagate from the beginning of the link to router B,a function of the distance between the two routers. dnodal = dproc + dqueue + dtrans + dprop
traffic intensity： La/R need to less than 1 more close to 0, queuing delay more close to 0 The fraction of lost packets increases as the traffic intensity increases.
end to end delay: source to the destination dend-end = N (dproc + dtrans + dprop) n-1 routers between.
throughput is min{Rc, Rs}. protocol stack： five layers: the physical, link, network, transport, and application layers. application layer:message. transport layer:
TCP:connection-oriented service UDP:connectionless service segment. network layer:moving network-layer packets known as datagrams from one host to another.
including IP protocol,routing protocol. link layer(frame):move a packet from one node to the next nodein the router wifi ethernet,DOCSIS. physical layer:move the
individual bits within the frame from one node to the next. Open Systems Interconnection (OSI):application layer, presentation layer, session layer, transport layer,
network layer, data link layer, and physical layer. link-layer switch: link layer(2),physical layer(1);router switch:network layer,link layer, physical layer
1字=2字节(1 word = 2 byte) 1字节=8位(1 byte = 8bit) bps:bit for second Five generic tasks are error control, flow control, segmentation and reassembly,
multiplexing, and connection setup IP address is a 32-bit quantity that we can think of as uniquely identifying the host. port number:identify the receiving process
(more specifically, the receiving socket) running in the host. choosing transport layer protocol:reliable data transfer, throughput, timing, and security.
The TCP service model includes a connection-oriented service and a reliable data transfer service. handshaking. Secure Sockets Layer (SSL) . UDP is a no-frills,
lightweight transport protocol, providing minimal services. connectionless,unreliable data transfer service application layer protocol defines:
1.The types of messages exchanged, for example, request messages and response messages
2.The syntax of the various message types, such as the fields in the message and how the fields are delineated
3.The semantics of the fields, that is, the meaning of the information in the fields
4.Rules for determining when and how a process sends messages and responds to messages
An application-layer protocol is only one piece of a network application SMTP (Simple Mail Transfer Protocol). HyperText Transfer Protocol (HTTP)： a client
program and a server program HTTP defines how Web clients request Web pages from Web servers and how servers transfer Web pages to clients.HTTP uses TCP as
its underlying transport protocol HTTP is said to be a stateless protocol： an HTTP server maintains no informa- tion about the clients
non-presistent connection:each TCP connection transports exactly one request mes- sage and one response message.
round-trip time (RTT) 双程时间， includes packet-propagation delays, packet- queuing delays in intermediate routers and switches. persistent connection:multiple
Web pages residing on the same server can be sent from the server to the same client over a single persistent TCP connection. of http request message:request line.
three fileds:method,URL,HTTP version. great majority:GET. subsequent line:header lines. response message. an initial status line, six header lines, and then the
entity body.
cookies. it is often desirable for a Web site to identify users define:allow sites to keep track of users. 4components:
(1) a cookie header line in the HTTP response message;
(2) a cookie header line in the HTTP request message;
(3) a cookie file kept on the user’s end system and managed by the user’s browser;
(4) a back-end database at the Web site.
they can also be considered as an invasion of privacy. A Web cache—also called a proxy server—is a network entity
that satisfies HTTP requests on the behalf of an origin Web server. a cache is both a server and a client at the same
time.Typically a Web cache is purchased and installed by an ISP. advantage： a Web cache can substantially reduce
the response time for a client request, Web caches can substantially reduce traffic on an institution’s access link to the
Internet. The total response time—that is, the time from the browser’s request of an object until its receipt of the
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