Networks Ch. 2
What is meant by a handshake protocol?
-Exchange control packets before sending data to each other -used by SMTP at application layer
Why is it said that FTP sends control information "out-of-band?"
-FTP uses 2 parallel TCP connections. -one for sending control information -one for transferring file -Control info is not sent over the same TCP connection, so is considered 'put of band'
What information is used by process running on one host to identify a process on another host?
-IP address and port numbers -IP address gives destination host and port number gives port number of destination socket
Suppose Alice, with a web-base e-mail account, sends a message to Bob, who uses POP3 to get his mail from the servers. How does the message get from Alice to Bob?
-Message is first sent from Alice's host to the email server over HTTP -Alice's mail server then sends the message to Bob's mail server over SMTP -Bob then transfers the message from his mail server to his host over POP3
Network Architecture Vs. Application Architecture
-Network architecture can handle the communication process into layers in the network organizations (5 layer internet architecture) -An application developer is designing the application architecture (client-server, P2P)
What's an overlay network? Does it include routers? What are its edges?
-Overlay networks contains the node participating in the file sharing system and the logical link between the nodes in a P2P file sharing system -There is a logical link (an edge) from node A to node B if there is a semi-permanent TCP connection between A and B -Does not include routers
List the 4 classes of services that a transport protocol can provide. Indicate if UDP or TCP provides the service.
-Reliable data transfer: TCP -Guarantee that a certain throughput will be achieved: Neither -Guarantee that data will be delivered within a specific time frame: Neither -Security: Neither
Why do HTTP, FTP, SMTP, and POP3 run on top of TCP instead of UDP?
-TCP provides reliable file transfer, meaning data is received in correct order without gaps
List 5 non proprietary internet applications and the application layer protocols that they use.
-The web: HTTP -Remote login: Telnet -Network News: NNTP -e-mail: SMTP -File Transfer: FTP
Suppose you wanted to do a transaction from a remote client to a server as fast a possible. Would UDP or TCP be better?
-UDP: with UDP the transaction can be completed in one round trip time RTT -the client sends the transaction request into a UDP socket and the server sends the reply back to the client UDP -With TCP, a min of 2RTTs is required, one to set up the TCP connection and one for the client to request and the server to reply
Describe how web caching can reduce the delay in receiving a requested object. Will web caching reduce the delay for all objects requested?
-Web caching brings the desired content 'closer' to the user, possibly to the same LAN to which the users host connects -Web caching can reduce the delay for all objects, since caching reduces the traffic on the link.
Consider an e-commerce site wants to keep a purchase record for each of its customers. How is this done with cookies?
-When a user first visits the site, the server creates a UID number and an entry in its back-end database and returns the ID number as a cookie number -This cookie number is stored on the users host and is managed by the browser -During each subsequent visit, the browser sends the cookie number back to the site
From a user perspective, what is the difference between the download-and-delete mode and the download-and-keep mode in POP3
-in D&D, client receives messages from a POP, then deletes them -in D&K, client receives messages from a POP, and keeps them. Thereby being accessible on different devices
The UDP server needs only 1 socket while TCP needs 2. Why?
-in UDP, there's no greeting protocol -in TCP, one socket initializes the communication and one socket transfers the data
From a communication session between a pair of processes, which process is the client/server?
-the process which initiates the communication is typically the client and the process that waits to be contacted is the server
CDNs (content delivery networks) typically adopt one of two different server placement philosophies, name them.
Enter deep: -Deploys server clusters in access ISPs all over the world -goal is to get closer to end users and improve user perceived delay and throughput by decreasing the number of links -Routers between the end user and the CDN cluster from which it receives content. Because of this highly distributed design, maintaining and managing clusters is challenging. Bring Home: -Can be taken by LimeLight and other CDNs, brings the ISPs home by building large clusters at a smaller number of locations and connecting the clusters using a private high speed network -Instead of getting inside the access ISPs, these CDNs typically place each cluster at a location that is simultaneously near the point of presence(POP) of many tier-1 ISPs -Compared with enter deep, the bring home design typically results in lower maintenance and management overhead, possibly at the cost of higher delays and lower throughput to end users
Besides network related considerations such as delays, loss, and bandwidth performance, there are other important factors that go into designing a CDN server selection strategy. Name them
ISP Delivery Cost: -clusters may be chosen based on different cost structures, so that ISP delivery cost is minimized Load o on the Clusters: -we're bothered when a client is to be directed to a cluster, so that the client is not directed to an overloaded cluster
For a P2P file sharing application, is the statement "There is no notion of client and server sides of a communication session" true?
No -any communication session should have a server/client -Peer receiving the file is the client -Peer sending the file is the server
If a TCP server were to support n simultaneous connections, each from a different client host, how many sockets would be needed?
n+1 -n clients with 1 greeting socket
