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Review Session I

EE 122: Intro to Communication Networks

Fall 2010 (Tuesday 7th December)

Sameer Agarwal

http://inst.eecs.berkeley.edu/~ee122/

Announcements

• 16th December 8-11 AM @ 105 Stanley

• Closed book, with single 8.5x11 (both sides) crib sheet

• Exam covers entire semester– Roughly 30% before midterm, 70% after midterm

• Following is not a part of Finals:o Socket Programmingo Designing in 90 minuteso Advanced routing (except what’s in final review)o P2P (except what’s in final review)o The Future of Networking

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TCP & Congestion Control

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Vanilla TCPsegment 1SS:cwnd = 1

ACK 2SS:cwnd = 2 segment 2

segment 3

ACK 4SS:cwnd = 4 segment 4

segment 5segment 6segment 7

ACK 4

ACK 4

ACK 3

ACK 4

segment 4

Timeout!Set SSthresh

SS:cwnd = 1ACK 8

SS:cwnd = 2 segment 8segment 9

ACK 10AIMD:cwnd = 3

ACK 9

segment 10segment 11segment 12

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TCP+ Fast Retransmissionsegment 1SS:cwnd = 1

ACK 2SS:cwnd = 2 segment 2

segment 3

ACK 4SS:cwnd = 4 segment 4

segment 5segment 6segment 7

ACK 4

ACK 4

ACK 3

ACK 4segment 4

3 Dup ACKs!Set SSthresh

SS:cwnd = 1

ACK 8SS:cwnd = 2 segment 8

segment 9

ACK 10AIMD:cwnd = 3

ACK 9

segment 10

segment 12

segment 11

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TCP+ Fast Retransmission & Fast Recovery

segment 1SS:cwnd = 1

ACK 2SS:cwnd = 2 segment 2

segment 3

ACK 4SS:cwnd = 4 segment 4

segment 5segment 6segment 7

ACK 4

ACK 4

ACK 3

ACK 4segment 4

3 Dup ACKs!Set SSthresh

AIMD:cwnd = 2

ACK 8AIMD:cwnd = 3 segment 8

segment 9

ACK 10AIMD:cwnd = 4

ACK 9 segment 10

segment 12

segment 11ACK 11

Question 1a (‘Vanilla’ TCP)

7Set SSthresh = 1; Enter directly into AIMD since SSthresh is already crossed.

Set SSthresh = 5;Enter Slow Start

SSthresh = 5 crossed. Enter AIMD

Note: Slightly modified from review session

Question 1b (TCP Retransmission + Fast Recovery)

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Set SSthresh = 1; Enter directly into AIMD since SSthresh is already crossed.

Set SSthresh = 5;However, enter AIMD direclty!

Interdomain Routing

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IGP, eBGP, iBGP,….

Border routerInternal router

1. Provide internal reachability (IGP)2. Learn routes to external destinations (eBGP)3. Distribute externally learned routes internally (iBGP)4. Select closest egress (IGP)

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4 9 2

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Routing Follows the Money!

• Peers provide transit between their customers

• Peers do not provide transit to each other11

traffic allowed traffic not allowed