host/end system (ES)----communications link-----host
host: PC, server, printer, WAP, IP phone, "appliance"(printer,camera,NAS etc)
host can be client and/or server (often large and single-purpose: web, file, print,)
link: medium (wire,fiber,radio) and bandwidth (bps).
if hosts not directly connected by a link, go thru intermediate systems (IS)/routers.
| | | | | | host--------routerA--------routerB--------routerC-----host | / | | / | routerD--------------------/ |more routers
node/entity: ES or IS.
hosts and routers run protocols that control the sending and receiving of information.
protocol is rules of operation: format and order of messages, actions taken upon send or receive of message.
TCP/IP suite of protocols is Internet, or private intranet.
defined by IETF's RFCs.
Internet packet switching network edge (hosts) complex, core (routers) simple.
PSTN circuit switching network: edge (phone) simple, core (switches etc) complex.
network infrastructure enables applications
(web,email,IM,games,streaming, remote login,games, P2P file sharing, VoIP,
etc) on ESs to exchange data.
Provides message-passing services:
1. connection-oriented (TCP): ESs create a logical connection thru handshaking (exchange of packets that establishes connection). ISs oblivious. Data transfer is reliable (app can rely on data to be transferred).
2. connectionless (UDP): no handshaking. not reliable but simpler and faster.
Metcalfe's Law: the value of the network expands exponentially as the number of users increases.
* message switching: entire message sent from router to router which
are store and forward, thus sequential. packets pipelined/parallel.
bit error: packet vs message retransmittal.
but overhead of header per packet.