1 / 14

Chapter 17 Homework

Chapter 17 Homework. 1,7,15,28, 35, 36. Chapter 17 X.25. X.25 Layers X.25 Operation. X.25. X.25 : A packet switching WAN developed by ITU in 1976 ITU recommends packet size of 128 bytes It can support larger packets up to 1024 bytes Normal speed is 64 Kbps .

aliya
Télécharger la présentation

Chapter 17 Homework

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter 17Homework • 1,7,15,28, 35, 36

  2. Chapter 17X.25 • X.25 Layers • X.25 Operation

  3. X.25 • X.25 : A packet switching WAN developed by ITU in 1976 • ITU recommends packet size of 128 bytes • It can support larger packets up to 1024 bytes • Normal speed is 64 Kbps. • European standards support 2.048 Mbps • It provides connection oriented service • Data transmission rate are fixed

  4. X.25 (continued) • User machines (terminal or computer) are called Data Terminal Equipment (DTE) • Packet switching nodes are called (Data Communications Equipment or Data Circuit-terminating Equipment (DCE)) • A device that establishes, maintains and terminates a session on a network. It may also convert signals for transmission.

  5. X.25 (continued) • All control packets and data are carried on the same channel. (inband signaling used) • Intermediate nodes must process control data as well. • X.25 functions are implemented at 3 layers. • Both layer 2 and layer 3 include error control and flow control functions. • Multiplexing of VCs takes place at layer 3.

  6. X.25 Implementation • X.25 is implemented at three layers. • Physical layer • Data link layer (Frame Layer) • Packet (network) layer

  7. Physical Layer • Standards (called X.21) provides for: • Electrical, mechanical, procedural interface between the host and the X.25 network. • It requires digital signaling

  8. Data Link Layer(Frame Layer (LAPB)) • Link layer standards called (link access procedure- balanced) provide: • Error and flow control functions for the connection between DTE and DCE.

  9. Packet (network) layer • Receives user data from the higher layers • Link setup between DTE and DCE • Transferring data • Disconnecting the Link • Establishing virtual connections between DTEs. (end-to-end connection)

  10. Virtual Circuits in X.25 Networks • Created at the network layer. • Identified by virtual circuit identifier (called logical channel number LCN) • Permanent virtual circuit (PVC) • No call setup is required • Analogous to leased line • Switched virtual circuit (SVC) • Call setup is required

  11. Addressing in X.25 networks • X.121 protocol defines global addressing in X.25 networks. • Address field is 14 digits. • The first 4 digits define the country (3 digits) and the network within that country (1 digits). • Next ten digits called (NTN, National Terminal Number) refer to DTEs in a particular network.

  12. Triple-X Protocols • X.3, X.28, and X.29 are called triple-X protocols. • X. 121 protocol defines global addressing in X.25 networks. • X.3 defines a PAD. • Used to set connection between a dumb terminal and an X.25 network • X.28 defines the comm. rules between dumb terminal and a PAD. • X.29 defines the communication terms between a PAD and a remote DTE.

  13. Flow and Error Control • X.25 uses sliding-window flow control. • Flow and error control are implemented at data link layer and network layer. • For error control: • For each packet, there must be an acknowledgment received. • Go-back-N (ARQ) is used.

More Related