Switching and Teletraffic Theory Lecture 8

TCP/IP Concepts

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

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)

IPv4 Header

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

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

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

Options Security Source routing Route recording Stream identification Timestamping

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

IPv4 Address Formats

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

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

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

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

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

IPv6 Structure

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

IP v6 Header

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

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

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

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

Asynchronous Transfer Mode (ATM)

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 622.08Mbps

Protocol Architecture

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

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

ATM Connection Relationships

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

Call Establishment Using VPs

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

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

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

ATM Cell Format

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

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)

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

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

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

ATM Bit Rate Services

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

Wireless Systems

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

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

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)

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

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

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

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