1. Part I. Overview of Data Communications and Networking
Chapter 2. Network Models
COMP 3270 Computer Networks
Computing Science
Thompson Rivers University

2. Chapter Contents Layered tasks Internet model
ISOC
OSI (Open Systems Interconnection) model
ISO

3. Learning Objectives
List the five layers in the Internet network model.
Relate the two adjacent layers in terms of service user, service provider, and interfaces.
Interpret encapsulation and decapsulation.
List the four address types in the Internet network model, with the corresponding layer in which each address types is mainly used.
Show the change of addresses in a packet that is delivered to a destination through three different physical networks, given an example of a network of networks.
Identify main roles and functions in each layer in the Internet network model.
Identify what kind of information is added in each layer.
State the purpose of framing.
List the three types of control.

4. 1. Layered Tasks Sender, Receiver, and Carrier Hierarchy: layers
Interface and Service: a layer uses the services of the next lower layer through interfaces

5. Example: sending a letter
House
House
Mail box
Mail box
Post office
Post office

6. 2. The Internet Model Layered Architecture Peer-to-Peer Processes
Encapsulation

7. Layered Architecture 5 layer model TCP/IP protocol suite
Only upper 3 layers are standardized by IETF.
Application
Transport
Network
Data link layer is standardized by mostly IEEE Project 802.
Ethernet: 802.3
WLAN: a, b, g, …
The concept of layered architecture: Layer n+1 uses the services provided by the layer n and the layer n provides the services for layer n+1, through the interface between the layers n and n+1.
An interface is usually implemented as a set of functions.
TCP/IP protocol suite
☺ How many protocols do you know?

9. IP, ARP, ICMP, IGMP, RIP, OSPF, …
Application
I.E., Eudora, iMash, MSN, …
FTP, HTTP, SMTP, …
Transport
TCP, UDP, …
Network
IP, ARP, ICMP, IGMP, RIP, OSPF, …
Data link
Ethernet, …
Link layer
Physical

10. Peer-to-peer processes
☺ Protocol?
Service?
Interface?
Encapsulation?
☺ No 5 layers?

11. ☺ What kind of information is included in headers?
Encapsulation and decapsulation
☺ What kind of information is included in headers?
Encapsulation
Decapsulation

12. Some questions ☺ A layer is software? ☺ A protocol is software?
☺ Can one protocol exist over two or more layers?
☺ Can several protocols exist in the same layer?
☺ What is an advantage of the layer model?
Easy to understand
Easy to standardize
Easy to implement
Less development cost

13. 3. Layers in the Internet Model
Application
Transport
Network
Data link
Physical
Bottom-up approach in our study from now on

14. Physical layer Bit stream
To handle mechanical and electrical specifications
of the hardware interface and transmission media

15. Physical
Main responsibility/role: Node-to-node delivery of bit streams
Specific topics/duties:
Physical characteristics of hardware interfaces and transmission media
Representation of bits – encoding/decoding
Data transmission rate
Synchronization of bits
Implemented on NICs (Network Interface Cards)

16. Data link layer

17. ☺ Does the data link layer decide the next hop?
Node-to-node delivery
☺ Does the data link layer decide the next hop?
At B, to C or E?

18. ☺ What type of line configuration? ☺ What type of physical topology?
☺ Is it node-to-node delivery?
☺ How can the frame find the host 87?
0x800
Protocol ID
☺ What other information does the header and the trailer contain?

19. Data link
Main responsibility/role: Node-to-node (or also called hop-to-hop) delivery of frames
Specific topics/duties:
Framing
In a frame,
Framing information
Source address
Destination address [passed from the upper layer]
Upper layer protocol id [passed from the upper layer] – IP, ARP, …
Error controlling code
Payload
Physical addressing
☺ Can a computer have several physical addresses?
Flow control
Error control
MAC (Medium Access Control) especially in multi-point line configuration
Implemented on NICs
☺ Which layer decides the next node?

20. Network layer

21. Host-to-host delivery
B decides the next hop E with f3. f2 f1 f3
Host-to-host delivery f1 f3
☺ Two data link
entities?

22. Example [Routing] Forwarding Routing Not F Forwarding
Packet: from A to P
Next hop: N
Address resolution: N => 33
Delivery
Framing
Encapsulation
Frame: from 99 to 33
Signal
[Routing]
Forwarding
Encapsulation: the payload
Packet: from A to P;
Protocol id (payload type)
Next hop: F
Address resolution: F => 20
Encapsulation: the packet
Frame: from 10 to 20;
Protocol id
Electromagnetic signal
Routing
Forwarding
Not F
☺ How many physical networks?
☺ What information is changed?
Routing
Forwarding

23. In the previous figure we want to send data from a node with network address A and physical address 10, located on one LAN, to a node with a logical (network) address P and physical address 95, located on another LAN. Because the two devices are located on different networks, we cannot use physical addresses only; the physical addresses only have local jurisdiction. What we need here are universal (globally unique) addresses that can pass through the LAN boundaries. The logical (network) addresses have this characteristic.
But Ethernet addresses are globally unique. ☺ Why can’t we use Ethernet addresses for routing in the network layer?

24. Network
Main responsibility/role: Host-to-host (or also called source-to-destination) delivery of packets
Specific topics/duties:
Logical (or also called network) addressing
☺ Can a computer have several logical addresses?
In a packet,
Source address
Destination address
Upper layer protocol id – TCP or UDP, …
Error control information …
Forwarding
☺ It decides the next hop using ? and how ?
Using route command; record of the forwarding (or called routing) table: destination, gateway, metric, interface, …
Then, it hands packets down to the data link layer.
☺ Data link layer knows only physical addresses, then who finds the physical address of the next node?
ARP (Address Resolution Protocol)
Using arp command;
Routing
Implemented in [system] software

25. Transport layer ☺ How can the network layer at the destination deliver
the message to a specific protocol, i.e., TCP or UDP,
in the transport layer?

26. Or also called end-to-end delivery
End-to-end delivery of a message [ ]
Or also called end-to-end delivery

27. It should know the destination port and address,
and the transport layer protocol that it uses.
Segmentation
Upper layer protocol id
included

28. The previous figure shows an example of transport layer communication
The previous figure shows an example of transport layer communication. Data coming from the upper layers have port numbers j and k (j is the address of the sending process, and k is the address of the receiving process). Since the data size is larger than the network layer can handle, the data are split into two packets, each packet retaining the port numbers (j and k). Then in the network layer, logical (network) addresses (A and P) are added to each packet.

29. Transport
Main responsibility/role: End-to-end (process-to-process) delivery of messages (or datagrams)
Specific topics/duties:
Port addressing
☺ What does a port number represent?
☺ Why don’t we use process ids instead?
From the upper layer, with the destination logical (network) address
Note: Connection association
Segmentation and reassembly
Connection control -> ordered delivery
Flow control
Error control
Congestion control

30. Application layer

31. Summary of duties [ ]

32. Blue color: given from the upper layer Green color: decided in the layer
Application
Destination IP addresses (or translated from domain name)
Source and destination port numbers (addresses) (service)
Protocol in the transport layer: TCP or UDP
Transport
Destination IP addresses
Source and destination port numbers (addresses)
Protocol in the network layer: IP
Network
Source and destination IP addresses
Protocol id in the transport layer: TCP or UDP
Physical addresses of the next nodes (hops)
Protocol in the data link layer: Ethernet, …
Data link
Physical addresses of the next nodes
Protocol id in the network layer: IP, …

33. OSI model