1Review Test 2

EECS 563 Fall 2013

Review Test 2

2Review Test 2

Network traffic � Request for resources

� Rate of requests= λ � Average resource hold time = Th

� Common Assumptions– Time between arrivals ~ exponentially– Holding time ~ exponentially

� Voice� λ = call/sec� Th= average holding time sec/call� Load = λ*Th Erlangs

3Review Test 2

Network traffic � Packet Voice

�Constraint� limit on end-to-end delay� Packetization time (ms/packet)� Role of the Jitter buffer

– Too small � lose packets– Too large � increase delay

4Review Test 2

Network traffic � Packet Voice

�Components of end-to-end delay (delay budget) & trade-offs– Packetization time– Clocking time– Network delay (random)– Jitter buffer

�VoIP Rate calculation

5Review Test 2

Network traffic � Video

�MPEG� Frame types

� Data� Burstyness = (Peak rate)/(Average rate)� Large Burstyness leads to effective statistical multiplexing.

6Review Test 2

Performance Anaysis� Given

� Traffic

�QoS

� Design system

� Find C

� System size

� Find Number of Servers� Assumptions

� Service time ~ Exponentially distributed

� Interarrival time ~ Exponentially distributed

7Review Test 2

M/M/1

1[ ]

1

L

CE Tµ λ ρ

= =− −

Where Average Service Rate, Average Arrival Rate, C= Capacity, L = Average Packet Lengthµ λ= =

inrL

C C

λρ λ

µ= = =

[ ]

[ ] 1

P System Busy

P System Empty

ρ

ρ

=

= −

Given on Test

8Review Test 2

M/M/1/N and M/M/N/N

� M/M/1/N

� M/M/N/N � Erlang B

1

(1 )

1

N

B NP

ρ ρρ +

−=

− Given on Test

Table Given on Test

9Review Test 2

MAC

� Scaling & trade-offs WRT: rate (b/s), number of users, and size (km)

� Deterministic (Polling)

�Operation (why called deterministic)

�Calculate effective rate & efficiency'

' where

As Max

a Ring LatencyL

C

a S

ττ= =

↑ ↓

10Review Test 2

MAC

� Random Access

�Collision process

– Time vulnerable to collision

– Detecting Collisions

� Time

– Unslotted

– Slotted

� Role of backoff

11Review Test 2

MAC (Random Access-continued)

� Types (all can be slotted/unslotted)� ALOHA (for unslotted Smax=18%, for slotted Smax= 36%)

� CSMA

– p-persistent (1-persistent)

– Non-persistent

– CSMA/CD

� Leads to specification of Min/Max Packet size

where End-to-End Propagation TimeaL

C

ττ= =

As and as 1,Max Max

a S a S ALOHA↑ ↓ → →

12Review Test 2

MAC

� Collision Free Protocols

� Random Access and Reservation Systems

� In upstream send requests to transmit – Use part of frame (contention slots) to send requests

– Use random access to share contention slots

� Receive grants in the downstream

� No contention in downstream

� If no grant in downstream then assume collision for the request, backoff and resend request in upstream

13Review Test 2

MAC- Ethernet

� IEEE 802.3

� Evolution

– Bus

– Hub

– Switch

– 10 Mb/s � 100 Gb/s

� Role of CSMA/CD

14Review Test 2

Network Elements

� Repeater

� Bridge

� Switch

� Router� Layer 2 Switch

� Layer 3 Switch

� Layer 4 Switch

� Layer “Any” Switch

15Review Test 2

MAC- Wireless Networks

� Issues

�Noise

� Signal Fading

�Hidden terminal

� RTS/CTS

16Review Test 2

MAC- Cable Networks

� DOCSIS

� Access protocol

� CM, Headend, CMTS

17Review Test 2

DLC

� Goal� point-to-point error free link

� Functions

� Framing� Flags & bit stuffing

� Error recovery

� Flow control

18Review Test 2

DLC

� Sliding window flow control

� n bits/SN in packet header

� Max window �N= 2n-1

� N=1 � Stop and Wait

� When to retransmit?– Timeout

– RNR (NACK)

� What to retransmit?– SN

– Go-back-N

– Selective Repeat

19Review Test 2

DLC

� Piggybacking

� Frame structure

� HDLC

20Review Test 2

DLC

� Performance

� Stop&Wait*

� Sliding window*

#

Time to tx #

eff

eff

R

R

bitsR

bits

η =

=

&

1

21

stop wait

f

R

n

ητ

=+

21 if N 1

2 if 1

21

f

SlidingWindow

f

f

R

n

N RN

R n

n

τ

η ττ

≥ +

= < +

+

* Understand assumptions behind these equations

21Review Test 2

DLC

� Open Loop Control

�DE bit

�Methods

– CIR, Bc, Be

– Token bucket� Average rate

� Maximum burst size