CS138-lecture-20210316

Review for exam #

Example question set for Ch 1-2 #

What are the layers in TCP/IP protocol stack?

Application, transport, network, link, physical
What are layers in OSI reference model?

Extra 2 layers are presentation and
What is the major difference between packet switching and circuit switching?

Circuit reserves some resources, packet switchings allows sharing
What is the difference between routing and forwarding?

Router is global, forwarding is local
What is the relationship between routing and forwarding?

Interplay
How many types of packet delay does a network have?

4, nodal processing, packet transmission, propagation delay, queueing delay
Which tool/utility/program can be used to find out the IP address of the routers on the path from one source and destination?

traceroute
Which tool/utility/program can be used to intercept and analyze network packets?

Wireshark
On which layer is SSL/TLS implemented for network security?

Application layer
What does DDoS mean?

Distributed denial of service
Among HTTP, FTP, SMTP, DNS, which protocols use TCP?

HTTP, FTP, SMTP
What are the service port numbers for HTTP, FTP, SMTP, DNS respectively?

80, 21/20, 25, 53
What is the major difference between persistent and non-persistent modes of HTTP?

Persistent allows one connection to be shared by multiple object transmissions. Non-persistent must have a connectino for each object transmission.
What is the major difference between Client/Server model and P2P model?

Client/server has an always on server, P2P doesn’t have a server (everyone is a peer)
Where is URL specified in HTTP request format?

In the first line (the request line) of request format
Where is the status code specified in HTTP response format?

In the first line, the status line
Is web cache a client or server for the original browser who sent the request to get one object?

Server
What benefits come from the conditional get technology? (at least 2 examples)

No object transmission delay, lower link utilization
What is the major difference between SMTP and POP/IMAP?

Push versus pull
What is the format for DNS resource records? (RR)

Name, value, type, TTL
Among the socket library functions, what are used by TCP and what are used by UDP?

TCP: UDP:
What is the major difference between TCP and UDP?

TCP has a handshake, and is reliable. UDP is non-reliable

True or false questions #

Internet is a single network? (F)
DNS runs on routers as it’s a network core function. (F)
A network alyer does not need to rely on any service from its below layer. (F)
TCP is a protocol on Application layer. (F)
FDM/TDM is a pcket switching protocol (F)
It’s impossible to have packet loss as the network is supposed to guarantee reliability (F)
All the packet headers are added to data at application layer when the data leaves the application program (F)
Routers support all seven layers of the OSI reference model (F)
SMTP is a P2P protocol and there is no client in its communications (F)
SMTP is a pull protocol (F)

Long answer questions #

Cookie scenario in slides of ch. 1. How many components to make cookie system function? What are they respectively? What are their functionalities respectively? Especially, what cookie header lines in the first HTTP response message and next HTTP request messages?

There are four functions. Cookie on client, database on server, header line with cookie ID, header line from server. Database on server side contains all the info, cookie contains the ID, all future client/server messages have ID in headers.