More on TCP/IP and Networking

1
More on TCP/IPandNetworking

• CS-328
• Dick Steflik

2
Open Systems Interconnection Model

• 7 Layer model
• 7 Application
• 6 Presentation
• 5 Session
• 4 Transport
• 3 Network
• 2 Data Link
• 1 Physical Hardware Connection

3
X.25 and the ISO Model

• International Standard
• Fully compliant with the OSI 7 layer model
• X.25 is the set of protocols recommended by
  Telecommunications Section of the International
  Telecommunications Union (ITU-TS)

4
Physical Layer

• X.25 specifies a standard for physical
  interconnection
• electrical specs (voltages, current)
• connectors

5
Data Link Layer

• specifies how data travels between a host and the
  packet switch it is connected to
• frame - unit of data
• specs for framing of data
• what defines start of frame and end of frame
• frame checksuming and acknowledgement and receipt
• HDLC - High level data Link Control

6
Network Layer

• also called the network or communication subnet
  layer
• defines the basic Unit of Transfer
• includes destination addressing and routing
• assembles a packet and uses layer to transfer it
  to the packet switch

7
Transport Layer

• provides end-to-end reliability
• double checks what what was done at the lower
  layers

8
Session Layer

• Remote Terminal Access
• so important that it occupies its own layer

9
Presentation Layer

• services used by applications
• text compression/decompression
• graphic object serialization

10
Application Layer

• applications that use the network
• e-mail - x.400
• file transfer

11
X.25 vs TCP/IP

• Main difference is approach to reliability
• X.25 - reliability is at link level and insurance
  is provided at all layers
• causes possible retries many times
• TCP/IP - reliability is an end-to-end problem
• done almost exclusively at Transport layer
• retries only done at transport layer rather than
  every layer

12
Another Difference

• X.25 - idea of a network is a utility that
  provides transport service
• network vendor provides billing, handling routing
  problems, flow control
• network is complex with simple hosts at the end
  points

13
Another Difference (more)

• TCP/IP
• hosts actively participate in reliability,
  routing and network control (ICMP)
• the network is a simple packet delivery system
  with complex hosts at end points