Outline: Network Architecture
- Models
- OSI
- IEEE 802
- Internet
- Open Data Networks
- ATM
- End-to-End Services
- Physical models
Network Architecture:
OSI
Figure 2.11
Network Architecture:
IEEE 802
Figure 2.12
Network Architecture:
Internet
Figure 2.13
Network Architecture:
Open Data Network
Figure 2.14
Network Architecture:
ATM
Figure 2.15
What's the point of models?
- Enhance understanding, exchange of ideas
- Aid design of new protocols
- Perhaps aid protocol implementation
End-to-End Services
- compare intended application(s) to capabilities of network
- cost
- security
- delay
- error rate
- availability
Example Application:
Network Computer
- NC performs some operations, server other operations
- NC has higher bandwidth to user
- Server is easier to maintain, upgrade
- NC/NS combination may be cheaper (cost of operation and
maintenance) than full computer
Example Services
-
- Messages of M bytes (M <= 10^6$)
- Delay per message T <= 1s$
- Message error probability \epsilon <= 10^{-4}$
-
- Bit rate R >= 150Kb/s$
- Delay 0.01s <= T <= 1.2s$
- error probability \rho <= 10^{-8}$ errors per bit
Example Application
videophone
- Bit rate R >= 150Kb/s$
- Delay 0.01s <= T <= 1.2s$
- error probability \rho <= 10^{-8}$ errors per bit
maximum delay 1.2s$ means either:
- constant 1.2s$ delay in video stream, or
- very poor quality ("jumpy") video
therefore, the available service is inadequate for the proposed application.
Example Application
video on demand
- Bit rate R >= 150Kb/s$
- Delay 0.01s <= T <= 1.2s$
- error probability \rho <= 10^{-8}$ errors per bit
- not interactive, so maximum delay does not matter
- if video stream has a rate of less than 150Kb/s$, we can carry it
as long as we can buffer 1.2s worth of data, or 180Kb = 23KB$.
therefore, the available service may be adequate for the proposed application.
Physical Models
A network is made up of:
- links
- routers/switches/hubs
- end systems (host):
Links
- Bit Pipes
- Bit rate R$
- Delay T$:
- T = 5 u s / km$ in fiber
- T = 4 u s / km$ in coaxial cable
- T = 3.3 u s / km$ in free space
- Bit error rate BER$:
- If bit errors are independent, the probability PER$ of an error in
a packet with P bits is PER = 1 - ((1 - BER)^P)$
- If bit errors occur in bursts of size P, PER = BER$
Switches and Routers
- Input and output links
- Accept data on input links, forward it on output links
- Link rates
- Number of links
- Maximum switch rates
- Delay across switch
- Buffers in the switch