Where Are We? Basics: Network Classification Network Architecture Reliable Data Transfer Delay Models Implementation: Protocol Design
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1 Where Are We? Basics: Network Classification Network Architecture Reliable Data Transfer Delay Models Implementation: Protocol Design
2 Layered Architecture
3 Layered Architecture
4 Data Link Layer Functionality Reliable Delivery of Frames Flow Control Error Detection Error Correction
5 Multiaccess Media
6 Multiaccess Media
7 Multiaccess Media Rules Don t interrupt when someone else is speaking Raise your hand if you have a question Give everyone a chance to speak
8 Multiaccess Media Rules Don t interrupt when someone else is speaking Raise your hand if you have a question Give everyone a chance to speak
9 Multiaccess Media Rules Don t interrupt when someone else is speaking Raise your hand if you have a question Give everyone a chance to speak
10 Multiaccess Media Rules Don t interrupt when someone else is speaking Raise your hand if you have a question Give everyone a chance to speak
11 Multiaccess Protocols Channel Partitioning (Cellular Wireless Networks) Random Access (Ethernet, WiFi) Taking Turns (Token Ring)
12 Multiaccess Protocols Channel Partitioning (Cellular Wireless Networks) Random Access (Ethernet, WiFi) Taking Turns (Token Ring)
13 Multiaccess Protocols Channel Partitioning (Cellular Wireless Networks) Random Access (Ethernet, WiFi) Taking Turns (Token Ring)
14 Multiaccess Protocols Channel Partitioning (Cellular Wireless Networks) Random Access (Ethernet, WiFi) Taking Turns (Token Ring)
15 Protocols for Multiaccess Networks Hosts broadcast packets When a collision occurs, all transmitted packets are lost Lost packets have to be retransmitted
16 Protocols for Multiaccess Networks Hosts broadcast packets When a collision occurs, all transmitted packets are lost Lost packets have to be retransmitted
17 Protocols for Multiaccess Networks Hosts broadcast packets When a collision occurs, all transmitted packets are lost Lost packets have to be retransmitted
18 Protocols for Multiaccess Networks Hosts broadcast packets When a collision occurs, all transmitted packets are lost Lost packets have to be retransmitted
19 Protocols for Multiaccess Networks Hosts broadcast packets When a collision occurs, all transmitted packets are lost Lost packets have to be retransmitted => Need Multiaccess Protocol
20 Protocols for Multiaccess Networks Goal: Understand Multiaccess Protocols Understand Ethernet and IEEE Protocol Issues: How to deal with collisions? Maximal traffic load? ( > Protocol design) ( > Protocol performance)
21 Protocols for Multiaccess Networks Goal: Understand Multiaccess Protocols Understand Ethernet and IEEE Protocol Issues: How to deal with collisions? Maximal traffic load? ( > Protocol design) ( > Protocol performance)
22 Protocols for Multiaccess Networks Goal: Understand Multiaccess Protocols Understand Ethernet and IEEE Protocol Issues: How to deal with collisions? Maximal traffic load? ( > Protocol design) ( > Protocol performance)
23 Protocols for Multiaccess Networks Goal: Understand Multiaccess Protocols Understand Ethernet and IEEE Protocol Issues: How to deal with collisions? Maximal traffic load? ( > Protocol design) ( > Protocol performance)
24 Protocols for Multiaccess Networks Goal: Understand Multiaccess Protocols Understand Ethernet and IEEE Protocol Issues: How to deal with collisions? Maximal traffic load? ( > Protocol design) ( > Protocol performance)
25 Time is divided into slots: unit time = L C seconds Packet arrival rate (over all hosts) of λ packets/time unit Collision or Perfect Reception Immediate Feedback: 0, 1, e (Re-)transmission Probability: q r Infinite number of hosts (i.e. each node has at most one packet to transmit)
26 Time is divided into slots: unit time = L C seconds Packet arrival rate (over all hosts) of λ packets/time unit Collision or Perfect Reception Immediate Feedback: 0, 1, e (Re-)transmission Probability: q r Infinite number of hosts (i.e. each node has at most one packet to transmit)
27 Time is divided into slots: unit time = L C seconds Packet arrival rate (over all hosts) of λ packets/time unit Collision or Perfect Reception Immediate Feedback: 0, 1, e (Re-)transmission Probability: q r Infinite number of hosts (i.e. each node has at most one packet to transmit)
28 Time is divided into slots: unit time = L C seconds Packet arrival rate (over all hosts) of λ packets/time unit Collision or Perfect Reception Immediate Feedback: 0, 1, e (Re-)transmission Probability: q r Infinite number of hosts (i.e. each node has at most one packet to transmit)
29 Time is divided into slots: unit time = L C seconds Packet arrival rate (over all hosts) of λ packets/time unit Collision or Perfect Reception Immediate Feedback: 0, 1, e (Re-)transmission Probability: q r Infinite number of hosts (i.e. each node has at most one packet to transmit)
30 Questions Throughput? How to choose q r? Would q r = 1 work? Probability for (re-)transmission after k 1 slots: Average time until (re-)transmission:
31 Questions Throughput? How to choose q r? Would q r = 1 work? Probability for (re-)transmission after k 1 slots: Average time until (re-)transmission:
32 Questions Throughput? How to choose q r? Would q r = 1 work? Probability for (re-)transmission after k 1 slots: Average time until (re-)transmission:
33 Questions Throughput? How to choose q r? Would q r = 1 work? Probability for (re-)transmission after k 1 slots: Average time until (re-)transmission:
34 Questions Throughput? How to choose q r? Would q r = 1 work? Probability for (re-)transmission after k 1 slots: Average time until (re-)transmission:
35 Questions Throughput? How to choose q r? Would q r = 1 work? Probability for (re-)transmission after k 1 slots: Average time until (re-)transmission:
36 Notation λ: aggregated arrival rate n: number of backlogged packets G(n) = nq r : average number of transmissions per time slot Want to compute P succ : probability of successful transmission in a time slot (as a function of G(n)) Throughput = Psucc 1
37 Notation λ: aggregated arrival rate n: number of backlogged packets G(n) = nq r : average number of transmissions per time slot Want to compute P succ : probability of successful transmission in a time slot (as a function of G(n)) Throughput = Psucc 1
38 Notation λ: aggregated arrival rate n: number of backlogged packets G(n) = nq r : average number of transmissions per time slot Want to compute P succ : probability of successful transmission in a time slot (as a function of G(n)) Throughput = Psucc 1
39 Notation λ: aggregated arrival rate n: number of backlogged packets G(n) = nq r : average number of transmissions per time slot Want to compute P succ : probability of successful transmission in a time slot (as a function of G(n)) Throughput = Psucc 1
40 Notation λ: aggregated arrival rate n: number of backlogged packets G(n) = nq r : average number of transmissions per time slot Want to compute P succ : probability of successful transmission in a time slot (as a function of G(n)) Throughput = Psucc 1
41 Notation λ: aggregated arrival rate n: number of backlogged packets G(n) = nq r : average number of transmissions per time slot Want to compute P succ : probability of successful transmission in a time slot (as a function of G(n)) Throughput = Psucc 1
42 P succ = nq r ( 1 q r ) n 1 = nq r 1 q r ( 1 q r ) n
43 P succ = nq r ( 1 q r ) n 1 = nq r 1 q r ( 1 q r ) n For q r small, we have ( 1 q r ) n e nq r and nq r 1 q r nq r,
44 P succ = nq r ( 1 q r ) n 1 = nq r 1 q r ( 1 q r ) n For q r small, we have ( 1 q r ) n e nq r and nq r 1 q r nq r, and we obtain P succ nq r e nqr = G(n)e G(n) where G(n) = nq r
45 Throughput: G(n)e G(n) where G(n) = nq r
46 Throughput: G(n)e G(n) where G(n) = nq r Note: Arrivals according to a Poisson distribution with rate G: p k = Gk k! e G
47 If G(n)e G(n) > λ: If G(n)e G(n) < λ: Optimal G(n) = nq r = 1, or q r = 1 n
48 If G(n)e G(n) > λ: If G(n)e G(n) < λ: Optimal G(n) = nq r = 1, or q r = 1 n
49 If G(n)e G(n) > λ: If G(n)e G(n) < λ: Optimal G(n) = nq r = 1, or q r = 1 n
50 If G(n)e G(n) > λ: If G(n)e G(n) < λ: Optimal G(n) = nq r = 1, or q r = 1 n
51 What did we learn? λ max = e q r should dynamically change Binary Exponential Backoff q r = 2 k
52 What did we learn? λ max = e q r should dynamically change Binary Exponential Backoff q r = 2 k
53 What did we learn? λ max = e q r should dynamically change Binary Exponential Backoff q r = 2 k
54 What did we learn? λ max = e q r should dynamically change Binary Exponential Backoff q r = 2 k
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