Standards are needed at all Layers

warmersafternoonΔίκτυα και Επικοινωνίες

23 Οκτ 2013 (πριν από 3 χρόνια και 11 μήνες)

66 εμφανίσεις

1

Basic Communications Model

Standards are needed at all Layers

User Layer

Application Layer

Computer (Transport) Layer

Transmission Layer

2

Subnet Layer

1

2

3

Station A

Station B

Transmission of Messages

1. Within a Single Subnet, or

2. in Point
-
to
-
Point Links Between Subnets

4

1

2

3

Internet Layer

Station A

Station B

Routing of Messages

Across multiple subnets in an internet

1

2

3

4

4

Internetting

Station A

Station B

internet: c
ollection of subnets

such that
any station
on any subnet can communicate with any other
station on any other subnet simply by giving the
internet address of the other station
.

1

2

3

4

5

Layering in Major Architectures

Basic Model

Application

Computer

(Transport)

Internet

TCP/IP

Internet

IPX/SPX

Internet

Subnet

(OSI)

OSI

Application (7)

Presentation (6)

Session (5)

Transport (4)

Network (3):

Internet &

Subnet

Data Link (2)

Application

Application

Transport:

TCP, etc.

Complex:

SPX, etc.

Physical (1)

Subnet

(OSI)

Subnet

(OSI)

6

OSI Architecture


Reference Model for Open Systems
Interconnection (OSI)


Standards Agencies


ISO (computers)


Don’t confuse OSI and ISO!


ITU
-
T (telecommunications)


De jure standards (official/open)

7

OSI Architecture


Standards are sophisticated


Sophistication brings complexity


Slow standards development


Products are late to market and expensive


The result: low acceptance of OSI standards
in general


But OSI dominates at the single network
(subnet) transmission layer

8

Physical Layer (OSI Layer 1)


Physical transmission standards


Physical


Connector


Transmission media


Electrical


Voltage levels


Meanings of various voltage levels

9

The Data Link Layer (OSI Layer 2)

10

Data Link Layer (OSI Layer 2)


Organize data for transmission over a data link


Data packages at various layers are called protocol
data units (PDUs)


The Data Link Layer PDU is called a frame


Organization allows addressing on shared data links


Organization allows error checking and other meta
delivery processes


Media Access Control


Controls when stations may transmit in shared media
LANs and other shared data links

11

TCP/IP Architecture


Internet Engineering Task Force (IETF)


Of the Internet Society


De jure

(official/open)

12

TCP/IP Architecture


Standards are simple


Often have “Simple” in the name


Standards and products are fast to market


Products are inexpensive and fast to market


Widely Used


On the Internet


In many corporate networks


Dominates at internet and transport
layers

13

IPX/SPX


Novell Corporation


De facto (proprietary/closed)


Used only in Novell NetWare PC networks


But NetWare dominates PC networking


Second most widely used architecture at
transport layer

14

SNA


Systems Network Architecture


IBM Corporation


De facto (proprietary/closed)


Dominates in mainframe communication


On IBM mainframe systems


On mainframe systems of other vendors

15

Transport
-
Layer Traffic


TCP/IP

38%

Rising


IPX/SPX (NetWare)

34%

Falling



SNA (Mainframes)

18%


Other (including OSI)


10%


Total

100%

Source: Molloy (1994), 1993 data

16

Transmission Speeds


Bit: single 1 or 0


Transmission speed is measured in bits
per second (bps)


Duration of a single bit


Not velocity of propagation

101101000011101010100101111010101

17

Notations for Transmission Speed

Prefix

Use

Metric Meaning

Example

Interpretation

kilo

kbps

1,000

64 kbps

64,000 bps

Mega

Mbps

1 million

1.544 Mbps

1,544,000 bps

Giga

Gbps

1billion

2.4 Gbps

2,400,000,000 bps

Tera

Tbps

1 trillion

2 Tbps

2,000,000,000,000

Note upper case T

18

LANs, MANs, & WANs


LAN


Local area network


Single office, building, campus


10 Mbps to 100 Mbps to the desktop common


1 Gbps coming


Will carry most traffic, because most traffic
is local

19

PC Networking on a small LAN

Network Interface

Card (NIC)

In each PC

Each client and server needs a NIC
rather than a modem

20

PC Networking on a small LAN

Wiring Hub

15 to 50 cm (6 to 19 inches)

Usually, a wiring hub
connects the computers
together

Telephone wiring

and RJ
-
45 plugs

21

LANs, MANs, & WANs


WAN


Wide area network


Intercity, international


9,600 bps to 1 Mbps common to the desktop


Links with higher speed are usually shared
(multiplexed) by several desktops


Emerged before LANs, due to high cost of
long
-
distance telephone charges