1. Viet Nguyen Jianqing Liu Yaqin Tang
ECE 544 Project3
Viet Nguyen
Jianqing Liu
Yaqin Tang

2. Assumptions and Address Scheme
Each host can only connect to one router
Same content available at multiple end nodes
If two routers are connected, cost = 1
Naming scheme and eventual address scheme
Routers and end hosts: IP Address
Contents: ID from 0 to 255

3. Bootstrapping and Discovery
Algorithm
Routers boot up
- Neighbor router receive broadcast message,
send back their IP addresses
- Routers add its neighbors to routing table
Hosts boot up
- Broadcast DHCP requesting packet to
- Routers reply with info about default gateway

4. Bootstrapping and Discovery
Routers discover other routers
- Sending broadcast message
- Add neighbors info into routing table step by step
Hosts discover their default router
- Through DHCP request

5. Bootstrapping and Discovery
Packet Format
- Router boot up packet
Type
Packet Length
Cost
Source Router’s IP Address
Neighbor Router’s IP Address

6. Bootstrapping and Discovery
Packet Format
- Host boot up packet
Type
Packet Length
TTL
yiaddr (Default Router’s IP Address)
chaddr (16 bytes, Host’s Ethernet Address)

7. Contents Advertisement
A host periodically sends an advertisement message to tell its router about its contents
After receiving advertisement message, the router stores both the host’s IP address and its contents into its routing table
Destination
Cost
Next Hop
TTL H1 1 C1 C2 C1 C2 H1 R1

8. Content Advertisement packet
Packet type
Message Length
Number of Contents
Host’s IP Address
Content ID #1
Content ID #2 …. …

9. Link-state Advertisement packet
Packet type
Message Length
LS Age
Advertising router’s IP Address
LS sequence number
Number of neighbor routers
Neighbor node’s IP Address #1
Neighbor node’s IP Address #2 …
Neighbor node’s IP Address #n
Number of hosts
Host IP Address #1
Host IP Address #2
Host IP Address #3
NumOfContents
Content ID #1
Content ID #2

10. Information at each router
Link state table
Neighbors table
Routing table

11. Link state table (for each router)
Router’s IP
Number of neighbor routers
List of neighbor routers
Number of hosts
List of hosts
Number of contents
List of contents
TTL R5 1 R2 H2 C2 2
R1, R5 -
@R1 H2 C2
Each router store Link state of OTHER router! C1 R5 H1 R1 R2

12. Neighbor table (for each router)
Number of neighbor routers
List of neighbor routers
Number of hosts
List of hosts
Number of contents
List of contents 1 R2 H1 C1
@R1 H2 C2 C1 R5 H1 R1 R2

13. Routing table Each router maintains its own routing table
Calculated from Link state table and neighbor table
As each host can be either content requester or content provider, routing is based on both content identifiers and host addresses
Destination
Cost
Next Hop H1 1 C1 C2 C1 C2
@R1 H1 R1

14. Routing Protocol
We use link-state protocol with reduced message format (Link-state packet - LSP)
Routers flood LSPs to all other routers
Once a router has a copy of the LSP from every other router, it computes a complete map for the topology of the network, and from this map decide the best routes to each destination
Algorithm: Dijkstra’s shortest-path algorithm

15. Routing Protocol (2)
LSP also carries a time to live. A node always decrements the TTL of a newly received LSP before flooding it to its neighbors.
It also “ages” the LSP while it is stored in the node
When the TTL reaches 0, the node refloods the LSP with a TTL of 0, which is interpreted by all the nodes in the networks as a signal to delete that LSP

16. Routing protocol (3)
Each router sends “hello” packet to its immediate neighbors at defined intervals.
If a sufficiently long time passes without receipt of a “hello” from a neighbor, the link will be declared down, and a new LSP will be generated to reflect this fact.

17. Router - ‘Hello’ Packet
Send to neighbor routers to say “I am alive”
Packet type
HELLO
Message Length
Option
Router’s IP Address

18. Routing protocol (4) Only generate LSP if:
Timer expires
Change in topology (link dies, a neighbor router dies)
A change in LSP table or neighbor table causes a router to recalculate the routing table!

19. Host: REQUEST packet format
Packet type
(REQUEST)
Content ID
SeqNum
Option
Requester’s IP Address
Content provider’s IP Address (=0)
SeqNum: used for supporting resume download from different content provider

20. How to route a content-request packet (Content discovery)
@host_H1: get (content_C3)
H1 sends request to its router R1 C1 C2 C3 H1 R1 R2 R3 H3
get(C3)

21. How to route a content-request packet (Content discovery)
@host_H1: get (content_C3)
R1 looks up its routing table for next hop to send
Routing R1:
Destination
Cost
Next Hop … C3 3 R2 C1 C2 C3 H1 R1 R2 R3 H3
get(C3)

22. How to route a content-request packet (Content discovery)
@host_H1: get (content_C3)
Routing R2:
Destination
Cost
Next Hop … C3 2 R3 C1 C2 C3 H1 R1 R2 R3 H3
get(C3)

23. How to route a content-request packet (Content discovery)
@host_H1: get (content_C3)
Routing R3:
Destination
Cost
Next Hop … C3 1 H3 C1 C2 C3 H1 R1 R2 R3 H3
get(C3)

24. How to route a content-request packet (Content discovery)
@host_H1: get (content_C3)
Request packet arrived at H3 ! C1 C2 C3 H1
Arrived R1 R2 R3 H3
get(C3)

25. Delivering data
After request packet arrived, the host with the needed content start data transfer process. C1 C2 C3 H1 R1 R2 R3 H3
Data transfer

26. Delivering data: Error
If during transfer, the connection dies (router down, link dies, etc.), both the provider and the requester must be able to detect!
Proposed method: set limitation on how many times we send the same packets (same sequence number)
After detecting dead connection, discard this connection: requester does CONTENT DISCOVERY again, provider STOPS transferring data

27. Delivering data: Error (2)
After retrieving IP address of new content provider, the requester RESUME from the last sequence number
Append to the file received from the last provider

28. Data Transfer and Reliability
Message Forward
Unicast: ACK & Data transmission
Broadcast: boot up & update file ID info
DATA Packet Format
- TTL: time to live SeqNum: sequence #
- Offset: offset regard to fragmented file
Type
File ID
SeqNum
TTL
Source Address
Destination Address
Payload (file to be transmitted)

29. Data Transfer and Reliability
Message Forward
ACK Packet Format
Type
File ID
SeqNum
TTL
Source Address
(File receiver’s IP Address)
Destination Address
(File sender’s IP Address)

30. Data Transfer and Reliability
ARQ Scheme
End-to-end
Routers know the cost of the entire network
Selective-repeat
- Transmit continuously, no waiting
- Receiver ACKs all successfully received packets
- Sender only retransmits unACKed packets when
their timers expire
- buffer needed at both transmitter and receiver

31. Data Transfer and Reliability
Selective-
repeat

32. Advantages and Disadvantages
Aspects
Good or not
Scalability ✔
Latency
Bandwidth ✗
Reliability

33. Scenario 1: @host_H2: get (content_C3) H2 C1 C2 R5 C3 H1 R1 R2 R3 R4

34. Scenario 1: @host_H2: get (content_C3) @R1: Destination Cost Next Hop4 R2
@R1: H2 C1 C2 R5 C3 H1 R1 R2 R3 R4 H3
get(C3)

35. Scenario 1: @host_H2: get (content_C3) @R2: Destination Cost Next Hop

36. Scenario 1: @host_H2: get (content_C3) @R3: Destination Cost Next Hop

37. Scenario 1: @host_H2: get (content_C3) @R4: Destination Cost Next Hop

38. Scenario 1: @host_H2: get (content_C3) H2 C1 C2 R5 C3 H1 Arrived R1 R2

39. Scenario 1: @host_H2: get (content_C3) Data transfer H2 C1 C2 R5 C3 H1

40. Appendix: Network Architecture
Scenario get (content_C2) H1 H2 H3 C1 C2 C3 R1 R2 R3 R4 R5
H1 send request for C2 to default router R1
R1 choose shortest path, set DstAdrr as H2
When H2 receives request, ACK back
Connection between H1 & H2 established

41. Appendix: Network Architecture
Scenario get (content_C2) H1 H2 H3 C1 C2 C3 R1 R2 R3 R4 R5
H2 prepare fragmented file
Begin file transmission
Selective-repeat mechanism to ensure delivery

42. Appendix: Network Architecture
Scenario get (content_C1)
- Basic mechanism is the same as discussed H1 H2 H3 H4 C1 C2 C3 C1 C1

43. Appendix: Network Architecture
Scenario get (content_C1)
- Link to H2 die:
- H1 send 10 ACKs for the same packet
- H1 gives up and request for C1 again starting with
the smallest sequence number lost