1. Protocols Plesiochronous digital hierarchy (PDH) Synchronous digital hierarchy (SDH/SONET) Medium access control (MAC)

2. Plesiochronous Digital Hierarchy Level 0 1 2 3 4 Rate(Mb/s) 0.064 2.048 8.448 34.368 139.264 Factor 1 32 4.125 4.06818 4.0521415

3. Synchronous Digital Hierarchy Also known as SONET in USA Designed to make multiplexing and de-multiplexing easy Global synchronisation Frame structure Includes management information – Section – Line – Path

4. SDH Streams Level STM-1 STM-4 STM-8 STM-16 STM-64 Rate(Mb/s) 155.52 622.08 1244.16 2488.32 ~10GHz In USA: STM-N=STS-3N Optical: STM-N=OC-3N C-suffix: indicates unmultiplexed

5. SDH Frames Voice calls use 8 bit sampling so sampling time is: 8/64000 = 125  s and this is the SDH frame size So an SDH frame from a stream of rate B carries So an STM-1 stream has 2430 bytes (octets) per frame

6. SDH Frame Structure STM-1 frame has 2430 bytes arranged in a 9x270 matrix STM-N consists of N of this blocks

7. SDH Frame Features Framing bytes – essential to enable the network equipment to locate the position of a frame boundary – scrambling is used to lower the probability of this occurring elsewhere in the frame Pointers – Reveal the location of specific payloads which have been multiplexed together – allows recursive multiplexing Management bytes

8. SDH Access Ring ADM

9. Shared Access Networks Common form of local area networking – sharing of network infrastructure – division of resources amongst users Optical implementations – Optical Ethernet – Fibre Distributed Data Interconnect (FDDI) Access Protocol – Static vs Dynamic – Collisions

10. Static Channels User 1User 2User 3..............User N How many users? Simple to manage Wasteful if slots unused Little gain over independent provision of physical access

11. Dynamic Allocation ALOHA – pure – slotted Carrier Sense – persistent – non-persistent Assumptions – independent arrival times (this may be bad) – Collisions destroy frames

12. Ethernet Listen to channel Only begin to transmit if quiet The transmission is a single frame which has a minimum and a maximum size Stop immediately a collision is detected If a collision occurs wait a random time before trying again – beware cheating There are constraints on the network size and bandwidth

13. Propagation Effects Propagation speed – limited to c, smaller in general = v LAN size – allowed size, L, specifies maximum time separation, T Time T2T collision Packet length (bit rate =B) – must be larger than 2T N=2LB/v

14. Randomisation Need randomness to avoid collision locking Following successful frames there is a collision – divide time up into contention slots – apply some algorithm until no contention occurs Successful frame(s)Contention slots X

15. O-E comparison LvBNLvBN ElectricalOptical 500m.9c 10MHz 70 10km.7c 1GHz 95238

16. 10Gbit/s Ethernet Pre-requisites – Preserve 802.3 Ethernet frame format – Preserve 802.3 min/max frame size Preserve 802.3 New specifications 802.3ae – Full Duplex operation – Fibre only – Support LAN up to 40km Define two families of Physical Layers – A LAN PHY, operating at a data rate of 10.000 Gb/s – A WAN PHY, data rate compatible with SONET OC-192

17. Token Networks Originally designed for railways to avoid crashes – access to a single line section governed by possession of a token In LANs the token is virtual – Token ring (IEEE 802.5), passed in one direction – Token bus (IEEE 802.4), passed around a logical ring MAC protocols are much more complex than for Ethernet

18. Next Lecture Optical LANs – FDDI – Reflective Star – TPON – RAINBOW