1. Switching and Teletraffic Theory
Lecture 8

2. TCP/IP Concepts

3. Addressing Level Network-level address
Network Address
Used to route PDU through one network
IP address or internet address
Used to route packet through multiple networks
At destination data must routed to some process
Each process is assigned an identifier
TCP/UDP port

4. Addressing Mode Usually address refers to a single system or port
Individual or unicast address
Address can refer to more than one entity or port
Multiple simultaneous recipients for data (Multicast)
Broadcast for all entities within domain (Broadcast)
Multicast for specific subset of entities (e.g. Anycast)

5. IPv4 Header

6. Header Fields (1) Version Internet header length Type of service
Currently 4
IP v6 - see later
Internet header length
In 32 bit words
Including options
Type of service
Total length
Of datagram, in octets

7. Header Fields (2) Identification Flags Fragmentation offset
Sequence number
Used with addresses and user protocol to identify datagram uniquely
Flags
More bit
Don’t fragment
Fragmentation offset
Time to live
Protocol
Next higher layer to receive data field at destination

8. Header Fields (3) Header checksum Source address Destination address
Reverified and recomputed at each router
Set to zero during calculation
Source address
Destination address
Options
Padding
To fill to multiple of 32 bits long

9. Options Security Source routing Route recording Stream identification
Timestamping

10. Data Field Carries user data from next layer up
Integer multiple of 8 bits long (octet)
Max length of datagram (header plus data) 65,535 octets

11. IPv4 Address Formats

12. Subnets and Subnet Masks
Allow arbitrary complexity of internetworked LANs within organization
Insulate overall internet from growth of network numbers and routing complexity
Site looks to rest of internet like single network
Each LAN assigned subnet number
Host portion of address partitioned into subnet number and host number
Local routers route within subnetted network
Subnet mask indicates which bits are subnet number and which are host number

13. IP v6 - Version Number IP v 1-3 defined and replaced
IP v4 - current version
IP v5 - streams protocol
IP v6 - replacement for IP v4
During development it was called IPng

14. Why Change IP? Address space exhaustion
Two level addressing (network and host) wastes space
Network addresses used even if not connected to Internet
Growth of networks and the Internet
Extended use of TCP/IP
Single address per host
Requirements for new types of service

15. IPv6 Enhancements (1) Expanded address space Improved option mechanism
128 bit
Improved option mechanism
Separate optional headers between IPv6 header and transport layer header
Most are not examined by intermediate routes
Improved speed and simplified router processing
Easier to extend options

16. IPv6 Enhancements (2) Increased addressing flexibility
Anycast - delivered to one of a set of nodes
Improved scalability of multicast addresses
Support for resource allocation
Replaces type of service
Labeling of packets to particular traffic flow
Allows special handling
e.g. real time video

17. IPv6 Structure

18. Extension Headers Hop-by-Hop Options Routing Fragment Authentication
Require processing at each router
Routing
Similar to v4 source routing
Fragment
Authentication
Encapsulating security payload
Destination options
For destination node

19. IP v6 Header

20. IP v6 Header Fields (1) Version Traffic Class Flow Label
Classes or priorities of packet
Flow Label
Used by hosts requesting special handling
Payload length
Includes all extension headers plus user data

21. IP v6 Header Fields (2) Next Header Source Address Destination address
Identifies type of header
Extension or next layer up
Source Address
Destination address

22. IPv6 Addresses 128 bits long Assigned to interface
Single interface may have multiple unicast addresses
Three types of address

23. Types of address Unicast Anycast Multicast Single interface
Set of interfaces (typically different nodes)
Delivered to any one interface
the “nearest”
Multicast
Set of interfaces
Delivered to all interfaces identified

24. Asynchronous Transfer Mode (ATM)

25. Protocol Architecture
Similarities between ATM and packet switching
Transfer of data in discrete chunks
Multiple logical connections over single physical interface
In ATM, data flow on each logical connection is sent in fixed sized packets called cells
Minimal error and flow control
Reduced overhead
Data rates (physical layer) 25.6Mbps to Mbps

26. Protocol Architecture

27. Reference Model Planes
User plane
Provides for user information transfer
Control plane
Call and connection control
Management plane
Plane management
Whole system functions
Layer management
Resources and parameters in protocol entities

28. ATM Logical Connections
Virtual channel connections (VCC)
Basic unit of switching
Between two end users
Full duplex
Types
User-User (data)
User-network exchange (control)
Network-network exchange (network management and routing)
Virtual path connection (VPC)
Bundle of VCC with same end points

29. ATM Connection Relationships

30. Advantages of Virtual Paths
Simplified network architecture
Increased network performance and reliability
Reduced processing
Short connection setup time
Enhanced network services

31. Call Establishment Using VPs

32. Virtual Channel Connection Uses
Between end users
End to end user data
Control signals
VPC provides overall capacity (e.g. to connect branch with main office)
VCC organization done by users
Between end user and network
Control signaling
Between network entities
Network traffic management
Routing

33. Control Signaling - VCC
Signaling sent on a separate connection
Semi-permanent VCC
User to network signaling virtual channel
For control signaling
Used to set up VCCs to carry user data
User to user signaling virtual channel
Within pre-established VPC
Used by two end users without network intervention to establish and release user to user VCC

34. ATM Cells Fixed size 5-octets header 48-octets information field
Small cells reduce queuing delay for high priority cells
Small cells can be switched more efficiently
Easier to implement switching of small cells in hardware

35. ATM Cell Format

36. Header Format Generic flow control Virtual path identifier
Only at user to network interface
Controls flow only at this point
Virtual path identifier
Virtual channel identifier
Payload type
e.g. user info or network management
Cell loss priority
Header error control

37. ATM Service Categories
Real time
Constant bit rate (CBR)
Real time variable bit rate (rt-VBR)
Non-real time
Non-real time variable bit rate (nrt-VBR)
Available bit rate (ABR)
Unspecified bit rate (UBR)
Guaranteed frame rate (GFR)

38. UBR
May be additional capacity over and above that used by CBR and VBR traffic
Not all resources dedicated
Bursty nature of VBR
For application that can tolerate some cell loss or variable delays
e.g. TCP based traffic
Cells forwarded on FIFO basis
Best effort service

39. ABR
Application specifies peak cell rate (PCR) and minimum cell rate (MCR)
Resources allocated to give at least MCR
Spare capacity shared among all ABR sources
e.g. LAN interconnection

40. Guaranteed Frame Rate (GFR)
Designed to support IP backbone subnetworks
Better service than UBR for frame based traffic
Including IP and Ethernet
Optimized handling of frame based traffic passing from LAN through router to ATM backbone
ABR difficult to implement between routers over ATM network
GFR better alternative for traffic originating on Ethernet
Network aware of frame/packet boundaries
When congested, all cells from frame discarded
Guaranteed minimum capacity
Additional frames carried if not congested

41. ATM Bit Rate Services

42. Adaptation Layer Services
Handle transmission errors
Segmentation and re-assembly
Handle lost and misinserted cells
Flow control and timing

43. Wireless Systems

44. Wireless Systems
In wired systems, there is a permanent link between the subscriber and the network
Such a link does not exist in wireless systems
Subscribers must compete to get a link
Subscribers can lose the link during the connection (mobility)
This user-network link/channel is the main issue in wireless systems
Other stuff is similar to wired networks

45. User-Network Channels
All data must travel through the air
More than one transmitter will cause interference and hence no data will be received
Access to the air (spectrum) must be organized
Between operators-> government
Between users-> operator

46. Spectrum Organization
Operator must rent part of the spectrum for his sole use (license)
The allocated spectrum is expensive and limited
It is divided into 2 parts
Uplink (mobile-> basestation)
Downlink (basestation-> mobile)
Each part is further divided into two (unequal) parts
Control (signaling)
Voice (data)

47. Wireless Channels Control (and voice) channels are organized in pairs
One channel in the uplink (reverse channel) has a corresponding channel in the downlink (forward channel)
Channels are assigned to terminals/basestations in pairs
Terminals always listen to the basestation control channel (forward control channel)
If they want to call, they send in basestation reverse control channel

48. Mobile Switching Center
A large central office
Connected to other operators networks
All basestations are connected to the MSC via permanent links
All calls are relayed by the switching center
Basestations forward data from the terminal to the switching center

49. Call Setup-Landline to Mobile
MSC
Receive call request from PSTN, forward to all BSs
Verify MS info
Request BS to move MS to VC
Connect call to PSTN
Basestation
FCC
TX MIN
Instruct MS to move to VC
RCC
RX Ack, forward to MSC
FVC
Begin TX
RVC
Begin RX
Mobile
RX MIN, compare with own
RX Instruction
Ack, send MS info

50. Call Setup-Mobile to Landline
MSC
Verify MS info
Request BS to move MS to VC
Connect call to PSTN
Basestation
FCC
Instruct MS to move to VC
RCC
RX info, forward to MSC
FVC
Begin TX
RVC
Begin RX
Mobile
RX Instruction
Send call request with number and MS info