11
1 Review Session I EE 122: Intro to Communication Networks Fall 2010 (Tuesday 7 th December) Sameer Agarwal http://inst.eecs.berkeley.edu/~ee122/
1
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
2
3
TCP & Congestion Control
4
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
5
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
6
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)
8
Set SSthresh = 1; Enter directly into AIMD since SSthresh is already crossed.
Set SSthresh = 5;However, enter AIMD direclty!
Interdomain Routing
9
10
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)
62
4 9 2
13
3
Routing Follows the Money!
• Peers provide transit between their customers
• Peers do not provide transit to each other11
traffic allowed traffic not allowed
