1. Announcement Chapter 3, slide:
Info about Midterm is sent via class , please read it carefully.
100+(40 extra credit), 80 min
5-layer Internet Protocol, and describe the functionality and relations between some of these layers. You may refer to the slides, in class discussions and especially hand notes posted on this.
Comparison of TCP and UDP, their pros cons, and potential use-cases for them as discussed in the class.
 RTT Analysis for TCP with Exponential Weighted Moving Average (EWMA) expression. Write the basic expression, explain its two main components and objectives, and then write it in open form for n’th iteration as I have done in my hand notes in the class. Then, as I described in the class, explain the terms that are negligible (how related to negligible function), weighted, moving average and so on, over the equation.
One selected question from HW1
One selected question from HW2
Congestion Control Mechanisms. I described the main idea behind AIMD, slow start, Tahoe and Reno protocols.
I will ask these main ideas to be described with a few sentences only for each, and then show their relation with each other. For instance, slow start addresses a limitation of AIMD, and they both play a role in Reno, and so forth. These are available in slides, and I have talked about them in detail already in the class.
Reliable data transfer: Behaviors of stop-n-wait, go-back-n, and selective repeat. Compare and contrast them, as I have did in the class. Only main differences with a few sentences for each will suffice.
Basic network  layer concepts recently covered (e.g., routing, control/data plane etc..)
Extra Credits:
Huffman coding
Bloom filter (optional)
Questions from featured lecture
No electronic device, cheat sheet, etc.
Brief answers for “main idea” and, comparison and description questions: A few sentences, a small paragraph
Chapter 3, slide:

2. Chapter 4: Network Layer
Chapter goals:
understand principles behind network layer services:
network layer service models
forwarding versus routing
subnetting and IP addressing
Chapter 4, slide:

3. Network layer network layer protocols run at Sender side:
end systems &
routers
Sender side:
get segments from transport layer
encapsulates segments into IP datagrams
router examines header fields in all IP datagrams
Receiver side:
delivers segments to transport layer
application
transport
network
data link
physical
network
data link
physical
application
transport
network
data link
physical
Chapter 4, slide:

4. Interplay between routing and forwarding
local forwarding table
header value
0100
0101
0111
1001 3 2 1
output link
routing algorithm: constructs routing tables
routing algorithm
forwarding table: a lookup table for figuring out output port for each input pkt
forwarding process: move pkts from input to output
0111
value in arriving
packet’s header 1
Source 2 3
Destination
routing process: find route taken by packets from source to dest.
Chapter 4, slide:

5. Two Key Network-Layer Functions
forwarding: move packets from router’s input to appropriate router output
routing: determine route taken by packets from source to dest.
routing algorithms
Chapter 4, slide:

6. Network layer: data plane, control plane
local, per-router function
determines how datagram arriving on router input port is forwarded to router output port
forwarding function
Control plane
network-wide logic
determines how datagram is routed among routers along end-end path from source host to destination host
two control-plane approaches:
traditional routing algorithms: implemented in routers
software-defined networking (SDN): implemented in (remote) servers 1 2 3
0111
values in arriving
packet header
Chapter 4, slide:

7. Per router control plane
Individual routing algorithm components in each and every router interact in the control plane
Routing
Algorithm
data
plane
control
values in arriving
packet header
0111 1 2 3
Chapter 4, slide:

8. Logically centralized control plane
A distinct (typically remote) controller interacts with local control agents (CAs)
Remote Controller CA
data
plane
control
values in arriving
packet header 1 2
0111 3
Chapter 4, slide:

9. Datagram networks no call setup at network layer
no state about end-to-end connections is kept in routers
no network-level concept of “connection”
packets forwarded using dest. host address
packets (same source-dest pair) may take different paths
application
transport
network
data link
physical
application
transport
network
data link
physical
1. Send data
2. Receive data
Chapter 4, slide:

10. Forwarding table 4 billion possible entries
Destination Address Range Link Interface
through
through
through
otherwise
Chapter 4, slide:

11. Longest prefix matching
Prefix Match Link Interface
otherwise
Examples
DA:
Which interface?
DA:
Which interface?
Chapter 4, slide:

12. The Internet Network layer
Host, router network layer functions:
Transport layer: TCP, UDP
IP protocol
addressing conventions
datagram format
packet handling conventions
Routing protocols
path selection
RIP, OSPF, BGP
Network
layer
forwarding
table
ICMP protocol
error reporting
router “signaling”
Link layer
physical layer
Chapter 4, slide:

13. IP Fragmentation & Reassembly
network links have MTU (max.transfer size) - largest possible link-level frame.
different link types, different MTUs
large IP datagram divided (“fragmented”) within net
one datagram becomes several datagrams
“reassembled” only at final destination
IP header bits used to identify, order related fragments
fragmentation:
in: one large datagram
out: 3 smaller datagrams
reassembly
Chapter 4, slide:

14. IP Fragmentation & Reassembly (ctd)ID =x
offset =0
fragflag
length
=4000
One large datagram becomes
several smaller datagrams
Example
4000 byte datagram
= 20 (header) (data)
MTU = 1500 bytes
Chapter 4, slide:

15. IP Fragmentation & Reassembly (ctd)ID =x
offset =0
fragflag
length
=4000 =1
=1500
=185
=370
=1040
One large datagram becomes
several smaller datagrams
Example
4000 byte datagram
= 20 (header) (data)
MTU = 1500 bytes
1480 bytes in data field
offset =
1480/8
1040= 20 (header) (data)
1020 (data) =3980 –
Chapter 4, slide:

16. IP Addressing: introduction
IP address: 32-bit identifier for
host,
router interface
interface: connection between host/router and physical link
multiple interfaces per router
one interface per host
one IP address per interface =
223 1
Chapter 4, slide:

17. Subnets IP address: What’s a subnet ? subnet part (higher bits)
subnet
IP address:
subnet part (higher bits)
host part (lower bits)
What’s a subnet ?
device interfaces with same subnet part of IP address
can physically reach each other without intervening router
subnet
part
host
/23
network consisting of 3 subnets
Chapter 4, slide:

18. Subnets
/24
/24
/24
Recipe
To determine the subnets, detach each interface from its host or router, creating islands of isolated networks. Each isolated network is called a subnet.
Subnet mask: /24
Chapter 4, slide:

19. IP addressing: CIDR Classful addressing: A, B, C
(only 28 subnets, but 224 hosts per subnet)
(216 subnets, and 216 hosts per subnet)
(224 subnets, but only 28 hosts per subnet)
Classful addressing: A, B, C
A: /8
B: /16
C: /24
Problem: see which class is needed for 300 hosts? Issue?
CIDR: Classless InterDomain Routing
subnet portion of address of arbitrary length
address format: a.b.c.d/x, where x is # bits in subnet portion of address
subnet
part
host
/23
Chapter 4, slide:

20. IP addresses: how to get one?
Q: How does host get IP address?
hard-coded by system admin in a file
DHCP: Dynamic Host Configuration Protocol:
dynamically get IP address from as server when joining the network
IP address can be reused by other hosts if released
Can renew IP addresses if stayed connected
Chapter 4, slide:

21. DHCP: Dynamic Host Configuration Protocol
goal: allow host to dynamically obtain its IP address from network server when it joins network
can renew its lease on address in use
allows reuse of addresses (only hold address while connected/“on”)
support for mobile users who want to join network (more shortly)
DHCP overview:
host broadcasts “DHCP discover” msg [optional]
DHCP server responds with “DHCP offer” msg [optional]
host requests IP address: “DHCP request” msg
DHCP server sends address: “DHCP ack” msg
Network Layer: Data Plane

22. DHCP client-server scenario
DHCP server:
DHCP discover
src : , 68
dest.: ,67
yiaddr:
transaction ID: 654
arriving
client
Broadcast: is there a DHCP server out there?
DHCP offer
src: , 67
dest: , 68
yiaddrr:
transaction ID: 654
lifetime: 3600 secs
Broadcast: I’m a DHCP server! Here’s an IP address you can use
DHCP request
src: , 68
dest:: , 67
yiaddrr:
transaction ID: 655
lifetime: 3600 secs
Broadcast: OK. I’ll take that IP address!
DHCP ACK
src: , 67
dest: , 68
yiaddrr:
transaction ID: 655
lifetime: 3600 secs
Broadcast: OK. You’ve got that IP address!
Network Layer: Data Plane

23. DHCP client-server scenario
server B
arriving DHCP
client needs
address in this
network E
Chapter 4, slide:

24. IP addresses: how to get one?
Q: How does network get subnet part of IP addr?
A: gets allocated portion of its provider ISP’s address space
ISP's block /20
Organization /23
Organization /23
Organization /23
… … ….
Organization /23
Chapter 4, slide:

25. NAT: Network Address Translation
Motivation:
range of addresses not needed from ISP: just one IP address for all devices
can change addresses of devices in local network without notifying outside world
can change ISP without changing addresses of devices in local network
devices inside local net not explicitly addressable, visible by outside world (a security plus).
Chapter 4, slide:

26. NAT: Network Address Translation
rest of
Internet
local network
(e.g., home network)
10.0.0/24
All datagrams leaving local
network have same single source NAT IP address: ,
different source port numbers
Datagrams with source or
destination in this network
have /24 address for
source, destination (as usual)
Chapter 4, slide:

27. NAT: Network Address Translation
NAT translation table
WAN side addr LAN side addr
1: host
sends datagram to
, 80
2: NAT router
changes datagram
source addr from
, 3345 to
, 5001,
updates table
, , 3345
…… ……
S: , 3345
D: , 80 1
S: , 80
D: , 3345 4
S: , 5001
D: , 80 2
S: , 80
D: , 5001 3
4: NAT router
changes datagram
dest addr from
, 5001 to , 3345
3: Reply arrives
dest. address:
, 5001
Chapter 4, slide:

28. IPv6 Initial motivation: Additional motivation:
32-bit address space soon to be completely allocated (if not already!)
Additional motivation:
header changes to facilitate QoS
Major changes from IPv4:
Fragmentation: no longer allowed; drop packet if too big; send an ICMP msg back
Checksum: removed to reduce processing time; already done at transport and link layers
Chapter 4, slide:

29. Transition From IPv4 To IPv6
Can all routers be upgraded simultaneously ??
Answer: it can’t; no “flag days”
Analogy: (IP for Internet) ~ (foundation for House)
To change the foundation, you need to tear down the house!!
Solution
gradually incorporate IPv6 (may take few years)
How will the network operate with mixed IPv4 and IPv6 routers?
Tunneling??
Chapter 4, slide:

30. Tunneling What is the problem here?F
IPv6
tunnel
Logical view:
Physical view: A B E F
IPv6
IPv4 C D
Flow: X
Src: A
Dest: F
data
Be aware that:
IPv6 nodes have both IPv4 & IPv6 addresses
Nodes know which nodes are IPv4 and which ones are IPv6 (use for e.g. DNS)
What is the problem here?
Why can’t B just send an IPv4 packet to C ?
Problem: D won’t be able to send an IPv6 packet to E? Why?
A-to-B:
IPv6
Chapter 4, slide:

31. Tunneling Be aware that: A B E F Logical view: A B C D E F
IPv6
IPv6
IPv6
IPv6 A B C D E F
Physical view:
IPv6
IPv6
IPv4
IPv4
IPv6
IPv6
Flow: X
Src: A
Dest: F
data
Flow: X
Src: A
Dest: F
data
Src:B
Dest: E
B-to-C:
IPv6 inside
IPv4
Flow: X
Src: A
Dest: F
data
Src:B
Dest: E
B-to-C:
IPv6 inside
IPv4
Flow: X
Src: A
Dest: F
data
E-to-F:
IPv6
Be aware that:
IPv6 nodes have both IPv4 & IPv6 addresses
Nodes know which nodes are IPv4 and which one are IPv6 (use for e.g. DNS)
A-to-B:
IPv6
Chapter 4, slide: