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• 1 Network Architectures

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• Why can the internet be considered as a network of networks? 

  Because all the Tier-1 ISP's are connected to Tier-2 ISP's. These Tier-2 ISP's are connected w i t h T i e r - 3 I SP ' s . T h e r e a r e 3 T i e r - 1 I SP ' s i n t h e w o r l d , b u t m a n y T i e r - 2 I SP ' s a n d T i e r - 3 ISP'swhichareconnectedtoeachother inanetwork.

• What is the difference between a host and an end system?Is a Webserver endsystem? 

  
  
  
  There is no difference.  “host” and “end system” are used interchangeably. End systems include PCs, workstations, Web servers, mail servers, Internet-connected PDAs, WebTVs, etc. 
  Het zijn allebei computersystemen die verbonden zijn met het netwerk en netwerk applicaties.

• What is the difference between a host and an end system?List several different types of endsystems.IsaWebserver anendsystem? 

  
  
  
  There is no difference. Throughout this text, the words “host” and “end system” are used interchangeably. End systems include PCs, workstations, Web servers, mail servers, Internet-connected PDAs, WebTVs, etc. 

• List six access technologies. Classify each one as home access, enterprise access, or wide- area wireless access.

  1. Dial-up modem over telephone line: home;
  2. DSL over telephone line: home or small office;
  3.Cable to HFC:home;
  4.100Mbps switched Ethernet:enterprise;
  5.Wifi(802.11): home and enterprise 
  6.3G and 4G:wide-area wireless.

• Supposethereisexactlyonepacketswitchbetweenasendinghostandareceivinghost. The transmission rates between the sending host and the switch and between the switch and the receiving host are R1 and R2, respectively. Assuming that the switch uses store- and-forward packet switching, what is the total end-to-end delay to send a packet of length L?(Ignore queuing, propagation delay, and processing delay.) 

  
  
  
  
  At time t0 the sending host begins to transmit. At time t1 = L/ R1, the sending host completes transmission and the entire packet is received at the router (no propagation delay). Becausetherouter hastheentirepacket at timet1,it canbegintotransmit thepacket tothe receiving host at time t1. At time t2 = t1 + L/ R2, the router completes transmission and the entire packet is received at the receiving host (again, no propagation delay). Thus, the end- to-end delay is L/ R1 + L/ R2. 

• What advantage does a circuit-switched network have over a packet-switched network? What advantages does TDM have over FDM in a circuit-switched network? 

  
  
  
  
  A circuit-switched network can guarantee a certain amount of end-to-end bandwidth
  for theduration of acall.Most packet-switched networkstoday (includingthe
  Internet) cannot makeany end-to-end guaranteesfor bandwidth.In apacket switched network, the packets from different sources flowing on a link do not follow any fixed, pre- defined pattern. In TDM circuit switching, each host gets the same slot in a revolving TDM f r am e. 

• By what are End sytems together connected?

  Comunication links and Packet Switches

• 1.1 What does a Packet Switches?

  A packet switch take a packet arriving on one ofits incomming communication links and forwards that packeton one of its outgoing  comunnication links

• There a two types of switches. Whats the name of the two switches?

  Routers and link-layer switches

• Through what acces the End Systems the Internet?

  Though Internet Service Provides(ISPs)