June 20 overheads

Homework #1

Due June 26
Obtain an RFC from INTERNIC identified by the last four digits of your social security number. Email andrzej@cs.uoregon.edu with instructions on how to find the document in your directory.

Data communication

Distibutes data bases
Information interchange
Distributed computation

Internetworking

Connecting disparate physical networks through a set of communication conventions hiding the detail of network hardware.

Open System:

Specifications publicly available rather than proprietary allowing independent software developement.

Packet switching networks:

Assumed but the overall system indepenent of network characteristics.

Internet

Descendant of ARPA and NSF nets. Provides application and network level services:

Electronic mail
File transfer
Remote login
Packet delivery
Stream transport

Distinguishing features:

Independent of network technology
Universal addressing system
End_to_end acknowledgement
Application protocol standards

1970's ARPANET (Two dozen computers)

Packet switching through leased lines, forays into radio networks, satellite channels. 1979 Internet control and configuration board

ICCB

1983 Internet architecture board

IAB

socket as an abstraction of UNIX I/O mechanism

1986 NSFNET (20,000 computers)

1994 INTERNET (3,000,000 computers)

INTERNIC

June 21 overheads

Network technology

Circuit switched	Establish a circuit by reserving a path of physical links to be occupied throughout transmission
vs.
Packet switched	Subdivide the data into packets, each within a frame containing addressing and control info, and send these individually towards destination where it has to be assembled.

Wide area
WAN: over large distances/miles
Using long distance cables (lines), radio and satellites. Lower data rates (56Kbps -- 155Mbps)
Longer delays

vs.

Local area
LAN: buildings or city blocks (yards)
High speed cables (Gbps)
Small delays

Ethernet

Basics

Common medium network: "One transmits, everybody hears" (broadcast).
Carrier Sense Multiple Access / Collision Detect (CSMA/CD)
Collision: Interfering transmissions
Collision detection & correction: retransmission after random back off time

Ether wire

Thick coaxial cable with shield: Branching through transducers. Bulky, expensive, inflexible. Ranges up to 500m.
Thinwire: Coax cable, branching and communication circuitry integrated.
Twisted pair: Like telephone connections, hub box, up to 100m.
Extensions:
- Repeaters: Electrical connectors, up to 2 on any path.
- Bridges: Active interface, includes some communication intelligence.

Frame:	Length	Function
Preamble	8	Alternating 0's & 1's
Destination	6	Addresses: physically associated with the interface
Source	6
Frame type	2	self-identifying
Data	64-1500	Size depends on type
CRC	4	Error detection

June 22 overheads

Fiber distributed data interconnect (FDDI)

Basics:

Token ring structure: a frame passing continuously in a circular fashion among the sites.
The site with the token is allowed to send a packet of data along with the token.
In the dual counter rotating ring structure, a single site/line failure can be withstood by a loop-back.
Data rates up to 100 Mbps.
Fiber optics technology

Frames

Frame:	Length	Function
Preamble	32	Alternating 0's & 1's
Start delimiter	1
Frame control	1
Destination	2 or 6	Addresses
Source	2 or 6
Routing info	2
Data		Size depends on type
Frame check	4	Error detection
End delimiter
Frame status

Asynchronous transfer mode (ATM)

Data switching at great speeds by dedicated hardware & software.
53 octet cells (frames) with 5 octet headers.
Connection oriented service (circuit switching for individual packets).
Data rates: Gigabits per second.

ALOHA

U. Hawaii radio network

Store-and-Forward Networks

ARPAnet

A network of (a few dozen) interface message processors (IMPs) dedicated communication computers (now called packet switching nodes (PSNs) to which host computers were connected at specified (physical) ports.
PSN, linked through leased lines, hosts with PSN, through high speed dedicated cables (56Kbps vs. Mbps).
Network operation center at BBN (Boston)
Topology requirement: biconnectivity (no single failure disconnects the network).
Messages (packets) queued in buffers associated with ports of a PSN (size limitations).
Flow control via receipt acknowledgement.
Phased in acceptance of the international telecommunication standard protocol X.25
Addressing: <PSN ID, Port No>

NFSnet

Hierarchical view:

Backbone (supercomputers)
End users

ANSnet

The industry becomes a player: MCI

ser@cs.uoregon.edu