Lecture 7 - Foundations of the Internet

FDMA, TDMA, AND CDMA ALL…

Use circuit switching by dedicating / assigning network resources. Not all resources are used constantly.

Paradigm Shift

Packet switched: let everyone share the resources

Session

Application level; Unicast: one source, one destination

ARPA

Created plan for large packet-switched computer network

BBN Technologies

Received contract to build first computers for network.

ARPANET

Combined form of ARPA and BBN. Founding locations were UCLA, Stanford< UCSB, and the University of Utah

TCP/IP

Protocol: “language” for devices

Scalable way to connect hosts

became part of Internet in 1983

NSFNET

Academic research network. Not for commercial activities until 1990s. Three tiered structure

The Internet

Early 1990s used ISPs, 1994 WWW and web browser were used

1995

NSFNET decomissioned, superseded by commercial Internet.

What is better, circuit switching or packet switching?

Packet Switching won because of scalability and quality control

Circuit Switching

Each session has a dedicated circuit, throughput and delay performance do not change.

Packet Switching Advantages

Ease of connectivity, scalable (large # of diverse sessions), statistical mulitplexing and resource pooling

Tier 1 Examples

AT & T, Verizon, Level 3

Tier 1

Global footprint, full mesh peering, form the Internet backbone.

Tier 2 Examples

Vodafone, Comcast

Tier 2

May also peer, customer-provider with tier-1

Tier 3 Examples

Campus, corporateT

ier-3

take traffic only to and from customers. Customer-provider with tier-2

Layered Protocol Stack

5 - layer internet model, each layer provides service to the layer above and uses service from the layer below.

ayer 5

Physical Layer: Network medium (fiber, wireless)L

ayer 4

Link layer: Managing device access to the network medium; random access protocols (CSMA)

Layer 3

Network Layer: Handles routing (IP)

Layer 2

Transport Layer: End to end managment (TCP)

Layer 1

Application layer: what we interact with (HTTP)

No clear-cut division in the protocol because…

It ensures robustness and greater error control

Transport Layer

End to end, connection oriented in TCP

Network Layer

Hop by hop, connectionless in IP

Packet Headers

Encapsulate: augment data with them

Header Payload

Actual content

The Header Itself

Identification and control information, creates OVERHEAD (ability to distinguish messages)

End Hosts

Server, computer, process all 5 layers

Routers

Processes up to 3 layers, has IP addresses

Switches

Process up to 2 layers, do not have or process IP