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

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

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.

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

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

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

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: 802.11a, 802.11b, 802.11.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?

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

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

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

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

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

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

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)

Data link layer

☺ 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?

☺ 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?

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?

Network layer

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?

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

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?

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

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?

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

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

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.

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

Application layer

Summary of duties [ ]

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, …

OSI model