CS 4390 Exam 1

Multiplexing/Demultiplexing

- A Host receives a datagram IP, - Each datagram has a source IP address - Destionaion IP address - Each datagram carries one transport layer segment - Each segment has a source destination port number - Host IP addresses and port numbers to direct segment to appropriate socket

Hyper Text Transfer Protocol (HTTP)

- Adopts the application layers protocol client/server model - Client: browser that requests receives and displays web objects - Server: Web server that sends (using HTTP protocol) objets in response to requests

Server (Client Server Paradigm)

- Always on host - Permanent IP address - Often in data centers, for scaling

Client (Client Server Paradigm)

- Contact, communicate with server - May be intermittently connected - May have dynamic IP address - Do not communicate directly with each other

web cache

- Goal: Satisfy Client Requests without involving origin server - User configures browsers to point to a local web cache - Browsers send all HTTP Requests to the cache - If the object is in the cache it is returned - Else cache requests objects from origin server, caches received object then returns object to the client - Acts as a server to client requesting - And a client to the origin server.

HTTP3

- Internet draft yet not fully standardized - Formally referred to as HTTP2 over QUIC - Implemented in application layer over UDP - Adds security, per object error and congestion control, over UDP.

HTTP/2 increased flexibility (at server in sending objects to client)

- Key goal is decreased delay in multi-object HTTP requests - Transmission order of requested objects are based on client-specified object priority - Divide objects into frames, schedule frames to mitigate HOL blocking

peer to peer architecture

- No always on server - Arbitrary end systems directly communicate - Peers request service from other peers, service in return to other peers - Peers are intermittently connected and change IP address - Example: P2P file sharing

peer to peer architecture

- No sever - Peers are intermittently connected - IP address may change - Highly scalable - Difficult to manage - Example: bit torrent - Everything is everywhere

socket

- Process sends/recieves message to/from its socket - is similar to a door - Sending processes shoves messages out the door - Sending process relies on transport infrastructure on either side of the door tod eliver messages to socket at receiving process - Two of these are involved one on either side - To receives messages a process must have an identifier - Identifier includes both and IP address and port numbers associated with process on host

TCP (Transmission Control Protocol)

- Reliable - Congestion control - Flow control - Connection setup

non persistent HTTP

- TCP connection opened - At most one object can be sent over TCP connection TCP connection then closed - Downloading multiple objects required multiple connections - Two RTTs per objects want to cut

persistent HTTP

- TCP connection opened to a server - Multiple objects can be sent over a single TCp connection between client and that server - TCP connection closed - Server leaves connection open after sending response - Cuts response time in half to on RTTS

Multiplexing/Demultiplexing

- TCP has a welcoming socket that waits for connection establishment - TCP client creates sockets and sends request to Welcoming Socket - Newly created connection socket is identifies by 4 values

Application Layer Protocol

- Type of messages exchanged: request, or response - Message syntax 1. What fields i messages & how fields are delineated 2. Message semantics: Meaning of information in fields - Rules for when and how processes send and respond to messages 1. Open protocols 2. Defined in RFCs, everyone has access to protocol definition

UDP (User Datagram Protocol)

- Unreliable - Un order delivery - No frills extension of best effort IP

cookies

- Web sites and client browsers use cookies to maintain somes tate between transactions four components: 1. Cookie header line of HTTP response message being sent to a client. 2. Cookie header line in next HTTP request message 3. Cookie file kept on user's host, managed by user's browser 4. Back-end database at Website history of interactions with that user. - Using cookies and the data collected cookies use to store state of a user, to take cookie related actions.

Local Area Network (LAN)

- connects to a base station that is operated by the cellular provider, if its an iphone or android. - Finally, Wireless or LAN used to connect the system to the edge router. - Seen on laptops, phones, laptops, the user transmits/receives packers to/from an access point that is connected into the enterprise's network. - Wireless users must be typically in distance of the connection point and satellite Based

Digital Subscriber Line (DSL)

- gets the internet access from the same company that provides it wired local phone access. - goes to the DSLAM located in the central office. - The splitter splits telephone signals and internet data allowing for the data to either go to the customer or the internet. - Hundreds or even thousands connect to a single modem

cable based

- makes use of the telvsions companies existing tv infrastructure. Requires special modems called cable modems. - Typically an external device and connects via ethernet port. - IMPORT Quirck of a Cable Based access is that is is a shared broadcast medium. - In particular every packet sent by the head and the end travels downstream on every link to every home and. Because of this if several people are downloading a video file on a downstream channel, the actual rate which the file is received is significantly lower\

sockets

- sits on the transport layer, it may be TCP, and then it goes through the hallway which is the internet - is like a door open one door go through the hallway which is the transport layer and then exit the other door to the other endpoint which is the process

application layer

- supporting network applications - Implemented in software, application layer packet: is the message

2005 - present

18bil devices attached to internet, 2007 Iphone, aggressive development of broadband access, services providers like google fb miscrosft create their own networks,

HTTP uses TCP

= Client initiates TCP connection to server on PORT 80 - Server accepts TCP connection from client - HTTP messages are exchanged between a browser and a webserver - TCP Connection is closed - HTTP is also stateless - Server maintains no information about past client requests - HTTP Connection Two Types

1967

ARPAnet concieved

1970

AlohaNet satellite network in Hawaii

1972

Arapa Net public demo

1990s

Arpanet decommissioned

1979

Arpanet has 200 Nodes

Packets Queueing Delay

Arriving packets dropped if no free buffers, loss happens if the queue is full

1964

Baran Packetswithcing in military nets

1974

Cerf and Kahn Architecture for networks

1983

DNS defined for name to ip address translation

link layer

Data transfer between neighbooring elements, link layer packet frame

1976

Ethernet at Xeroax PARC

Physical Media

Examples include twisted-pair copper wire, coaxial cable, multimode fiber-optic cable, terrestrial radio spectrum, and satellite radio spectrum

1969

First Arapa Net node Operational

packet loss

If the buffer, storage space for packets that are waiting to be sent, the packets have to be dropped and are lost, lost packet may be retransmitted by a node or a original source, or not at all.

packet switching

Is not suitable for real-time services because of its variable and unpredictable end-to-end delays. However it offers better sharing of transmission capacity than circuit switching. Its simpler more efficient and less costly to implement than circuit switching. allocates link use on demand.

1961

Kleinrock theory shows packetswitching

1990s-2000s

More exciting apps, instant messaging, P2P file sharing, network security to forefront, Est 50 Million, 100 Million Users:

1991

NSF lifts restrictions for commercial use of NSFnet

Network Core

Packet Switching Vs Circuit Switching

circuit switching

Pre allocates the use of transmission link regardless of demand, with allocated but unneeded link time going unused.

4 sources of packet delay

Processing, Queuing, Transmission, Propogation

1988

TCP congenital control

TCP demultiplexing

TCP socket identified by 4-tuple

Server (HTTP)

Web server that sends (using HTTP protocol) objets in response to requests

protocol stack

application, transport, network, link, physical

rate / time

average

physical layer

bits on the wire different physical media different protocol

Client (HTTP)

browser that requests receives and displays web objects

protocil

defines the format and the order of messages exchanged between two or more communicating entities, as well as the actions taken on the transmission and/or receipt of a message

TCP (Transmission Control Protocol)

demultiplexing using 4 tuple: source and destination IP addresses, and port numbers

UDP (User Datagram Protocol)

demultiplexing using destination port number only

1983

deployment of first TCP/IP

1985

ftp protocol defined

Client Server Paradigm

has clients and servers

diagrams

network application layer packet

transmission delay

packet being transmitted

server process

process that waits to be contacted

client process

process the initiates communication

transport layer

process-process data transfer, transport application-layer message to application endpoints

Instantaneous throughput

rate at a given time.

Demux

receiver uses all four values to direct segment to appropriate socket

network application layer

routing of datagram from source to destination, IP routing protocols implemented with hardware and software

throughput

the rate at which bits are transferred between sender/receiever.

Guided Media

the waves are guided along a solid medium such as a fiber optical cable or a twisted pair of copper wire.

Unguided Media

the waves propagate in outer space, such as wireless LAN or digital satellite channel

processing

thinks the processor has to do, checking bit error, figuring out output link, based on the address in the packet.

propagation

time it takes for the signal to move across the medium, typically a short amount of time

segment

transport layer

early 1990s

web