1 / 16

Cell Networking

Cell Networking. Carey Williamson. Department of Computer Science University of Calgary. Definition. The term “cell networking” means packet switching, but with fixed size packets (called cells) Contrast with “frame relay” which uses variable size packets

elam
Download Presentation

Cell Networking

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. Cell Networking Carey Williamson Department of Computer Science University of Calgary

  2. Definition • The term “cell networking” means packet switching, but with fixed size packets (called cells) • Contrast with “frame relay” which uses variable size packets • ATM is an example of cell networking with 53-byte cells

  3. Rationale for Cell Networks • Simpler interfaces • Simpler buffering • Simpler switches • slotted system • synchronous stages • Better control of delay • Better control of delay jitter

  4. Delay Example

  5. Delay Example (Cont’d) Job 1, Size 10, arrives at time 0 + Job 2, Size 2, arrives at time 3 Server = Depart Job 1 departs at time 10 Job 2 departs at time 12

  6. Delay Example (Cont’d) • In the Internet, for example, a small packet (e.g., a telnet packet) that happens to get stuck behind a large packet (e.g., an ftp packet) can experience a large delay • FIFO service, non-preemptive

  7. Delay Example (Cont’d) Job 1, Size 10, arrives at time 0 + Job 2, Size 2, arrives at time 3 Server = Depart Job 1 departs at time 12 Job 2 departs at time 7 (assumes jobs are equal priority)

  8. Delay Example (Cont’d) Job 1, Size 10, arrives at time 0 + Job 2, Size 2, arrives at time 3 Server = Depart Job 1 departs at time 12 Job 2 departs at time 5 (assumes job 2 is higher priority)

  9. Advantages of Cells • High priority or delay-sensitive traffic will likely spend less time “stuck behind” other traffic • The smaller the cell, the better • Lower mean delay, and lower variation of delay • Easier to provide performance guarantees to integrated traffic

  10. Summary • In addition to the ease of implementation considerations, cell based networks offer a better framework for providing delay guarantees on integrated traffic flows (e.g., data, voice, video) • That is why ATM uses cells

  11. Why 53 bytes? • The smaller the cell, the better (in terms of delay guarantees) • Need to design for traffic with the most stringent delay requirements • Considerations for voice traffic were an overriding concern

  12. Why 53 bytes? (Cont’d) • The ATM cell size was chosen by the CCITT international standards committee (now called ITU) • Influenced by voice traffic requirements and existing telco equipment in place at the time (e.g., echo cancellation)

  13. Why 53 bytes? (Cont’d) • European community wanted 32 bytes of data per ATM cell • American community wanted 64 • Result: compromise! • (32 + 64) / 2 = 48 • thus, 48 bytes of data per ATM cell • Both sides equally (un)happy

  14. Why 53 bytes? (Cont’d) • European community wanted 4 bytes of header per ATM cell • American community wanted 6 • Result: compromise! • (4 + 6) / 2 = 5 • thus, 5 bytes of header per ATM cell • 48 + 5 = 53 bytes per ATM cell

  15. Why 53 bytes? (Cont’d) • Equally inefficient for all types of traffic (data, voice, video) • data networks want big packets • ATM overhead is 5/53 = 10% (too high!) • voice networks want small(er) packets • 48 bytes @ 64 kbps = 6 msec • video probably wants big(ger) packets

  16. Summary • 53 bytes is now the international standard for ATM cell size • “Only a standards committee could come up with a packet size that is a prime!’’ (Raj Jain, 1993) • Live with it; everyone else is!!

More Related