Chapter 9: WAN Technology Ad Protocols Switching Networks

Chapter 9:

WAN Technology ad Protocols

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Switching Networks • Switching nodes - provide a switching facility that move data between nodes • Stations – devices attached to the network • Nodes – switching devices that provide communication • Communications network – collection of nodes • Switched communication network – data entering the network from a station are routed to the destination by being switched from node to node

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1 Switching Networks • Long distance transmission is typically done over a network of switched nodes • Nodes not concerned with content of data • End devices are stations —Computer, terminal, phone, etc. • A collection of nodes and connections is a communications network • Data is routed by being switched from node to node

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Nodes • Nodes may connect to other nodes only, or to stations and other nodes • Node to node links usually multiplexed • Network is usually partially connected —Some redundant connections are desirable for reliability • Two different switching technologies —Circuit switching —Packet switching

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2 Simple Switched Network

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Circuit Switching • Dedicated communication path between two stations • Three phases —Establish —Transfer —Disconnect • Must have switching capacity and channel capacity to establish connection • Must have intelligence to work out routing

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3 Public Circuit Switched Network

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b End office

c Trunk Intermediate exchange Trunk

End office d

Figure 9.3 Circuit Establishment

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4 Circuit-Switching Technology

• Driven by applications that handle voice traffic —Key requirement is no transmission delay and no variation in delay • Efficient for analog transmission of voice signals • Inefficient for digital transmission • Transparent —Once a circuit is established it appears as a direct connection; no special logic is needed

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Telecom Components • Subscriber — Devices attached to network • Subscriber line — Local Loop — Subscriber loop — Connection to network — Few km up to few tens of km • Exchange — Switching centers — End office - supports subscribers • Trunks — Branches between exchanges — Multiplexed

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5 Circuit Establishment

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Circuit Switch Elements

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6 Circuit-Switching Concepts

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Blocking or Non-blocking • Blocking —A network is unable to connect stations because all paths are in use —A blocking network allows this —Used on voice systems • Short duration calls • Non-blocking —Permits all stations to connect (in pairs) at once —Used for some data connections

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7 Space Division Switching • Developed for analog environment • Separate physical paths • Crossbar switch —Number of cross-points grows in n2 —Loss of cross-point prevents connection —Inefficient use of cross-points • All stations connected, only a few cross-points in use —Non-blocking

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Space Division Switch

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8 Multistage Switch • Reduced number of cross-points • More than one path through network —Increased reliability • More complex control • May be blocking

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Three Stage Space Division Switch

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9 Interconnection Networks

• Omega Network

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Interconnection Networks

• Butterflies — isomorphic to Omega (a composition of shuffle-exchange networks with programmable switches) and SW-Banyan switch — closely related to hypercube and shuffle-exchange network — number of nodes N = (k + 1)2k • this means k + 1 rows (or ranks) consisting of n = 2k nodes each — Let node(i,j) refer to the j-th node in the i-th row, where i is in [0,k] — Then node(i,j) in row i>0 is connected to two nodes in row i-1 • node(i-1,j) and node(i-1,m) where m is the integer found by inverting the i-th most significant bit in the binary representation of j. — Note that if node(i,j) is connected to node(i-1,m), then node(i,m) is connected to node(i-1,j). — Benes network is consisting of two butterflies back to back

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10 Interconnection Networks

• Butterflies

row 0

row 1

row 2

row 3

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Interconnection Networks

—Delta Switch Matrix • non-blocking/blocking • self routing

Hal96 fig.10.9

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11 Interconnection Networks

Two extremes

Hal96 fig.10.8

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Time Division Switching Ø Modern digital systems use intelligent control of space & time division elements Ø Use digital time division techniques to set up and maintain virtual circuits Ø Partition low speed bit stream into pieces that share higher speed stream Ø Individual pieces manipulated by control logic to flow from input to output

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12 1 a b b a 1 I J I J I I TSI J J N N

(a) TSI Operation

Data in Data out

Write address

I a Read J b address

Data store J I

Read address I J Time slot counter Address store

(b) TSI Mechanism Figure 9.7 Time-Slot Interchange

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SEL

SEL SEL

TSI

Figure 9.8 A Time-Multiplexed Switch

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13 Traditional Circuit Switching

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Softswitch

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14 Circuit Switching • Circuit switching designed for voice —Resources dedicated to a particular call —Much of the time a data connection is idle —Data rate is fixed • Both ends must operate at the same rate

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Packet Switching: • Packet switching was designed for data • Data transmitted in small packets —Typically 1000 octets —Longer messages split into series of packets —Each packet contains a portion of user data plus some control info • Control info —Routing (addressing) info • Packets are received, stored briefly (buffered) and past on to the next node —Store and forward

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15 Use of Packets

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Advantages • Line efficiency — Single node to node link can be shared by many packets over time — Packets queued and transmitted as fast as possible • Data rate conversion — Each station connects to the local node at its own speed — Nodes buffer data if required to equalize rates • Packets are accepted even when network is busy — Delivery may slow down • Priorities can be used

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16 Switching Techniques

• Station breaks long message into packets • Packets sent one at a time to the network • Packets can be handled in two ways:

Datagram Virtual circuit

• Each packet is treated • A preplanned route is independently with no established before any reference to previous packets are sent packets

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Datagram • Each packet treated independently • Packets can take any practical route • Packets may arrive out of order • Packets may go missing • Up to receiver to re-order packets and recover from missing packets

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17 Datagram Diagram

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Virtual Circuit • Preplanned route established before any packets sent • Call request and call accept packets establish connection (handshake) • Each packet contains a virtual circuit identifier instead of destination address • No routing decisions required for each packet • Clear request to drop circuit • Not a dedicated path

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18 Virtual Circuit Diagram

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Virtual Circuits vs. Datagram • Virtual circuits —Network can provide sequencing and error control —Packets are forwarded more quickly • No routing decisions to make —Less reliable • Loss of a node looses all circuits through that node • Datagram —No call setup phase • Better if few packets —More flexible • Routing can be used to avoid congested parts of the network

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19 Packet Size

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Circuit vs Packet Switching • Performance —Propagation delay —Transmission time —Node delay

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20 Mainframe

C Personal Server computer

Personal B computer

Personal computer Packet-Switching E Network Personal computer A Solid line = physical link Dashed line = virtual circuit F

Figure 9.14 The Use of Virtual Circuits CS420/520 Axel Krings Page 41 Sequence 9

(a) Circuit switching (b) Virtual circuit packet switching (c) Datagram packet switching

propagation processing Call delay delay Call request request signal packet Pkt1 Call Call accept accept Pkt2 signal packet Pkt1 Pkt3 Pkt2 Pkt1 Pkt3 Pkt2 User Pkt1 data Pkt3 Pkt2 Pkt1 Acknowledge- ment signal Pkt3 Pkt2 Pkt1 Pkt3 Pkt2

Pkt3 Acknowledge- ment packet

link link link

Nodes: 1 2 3 4 1 2 3 4 1 2 3 4

Figure 9.15 Event Timing for Circuit Switching and Packet Switching CS420/520 Axel Krings Page 42 Sequence 9

21 Circuit Switching Datagram Packet Switching Virtual Circuit Packet Switching Dedicated transmission path No dedicated path No dedicated path Table Continuous transmission of Transmission of packets Transmission of packets 9.1 data Fast enough for interactive Fast enough for interactive Fast enough for interactive Messages are not stored Packets may be stored until Packets stored until delivered delivered The path is established for Route established for each Route established for entire Comparison entire conversation packet conversation of Communication Call setup delay; negligible Packet transmission delay Call setup delay; packet transmission delay transmission delay Switching Techniques Busy signal if called party Sender may be notified if Sender notified of connection busy packet not delivered denial Overload may block call Overload increases packet Overload may block call setup; no delay for established delay setup; increases packet delay calls Electromechanical or Small switching nodes Small switching nodes computerized switching nodes User responsible for message Network may be responsible Network may be responsible loss protection for individual packets for packet sequences Usually no speed or code Speed and code conversion Speed and code conversion conversion (Table can be found Fixed bandwidth Dynamic use of bandwidth Dynamic use of bandwidth on page 291 in No overhead bits after call Overhead bits in each packet Overhead bits in each packet textbook) setupCS420/520 Axel Krings Page 43 Sequence 9

Asynchronous Transfer Mode (ATM)

• A switching and multiplexing technology that employs small, fixed-length packets called cells • A fixed-size packet ensures function could be carried out efficiently, with little delay variation • Small cell size supports delay-intolerant interactive voice service with a small packetization delay • Designed to provide the performance of a circuit- switching network and the flexibility and efficiency of a packet-switching network • Standardization effort was to provide a powerful set of tools for supporting a rich QoS capability and a powerful traffic management capability

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22 ATM • Commonly used by telecommunications providers to implement wide area networks • Used by many DSL implementations • Used as a backbone network technology in numerous IP networks • Multiprotocol Label Switching (MPLS) has reduced the role for ATM

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Protocol Architecture (diag)

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23 Virtual Channel Connection (VCC)

• Logical connection in ATM • Analogous to a virtual circuit • Basic unit of switching in an ATM network • Set up between two end users through the network, and a variable-rate, full duplex flow of fixed-size cells is exchanged over the connection • Also used for user-network exchange and network-network exchange

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Virtual Path Physical Transmission Path Virtual Channels

Figure 9.16 ATM Connection Relationships

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24 Virtual Path Advantages

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Virtual Channel Characteristics • ITU-T Recommendation I.150 lists the following characteristics of VCCs:

Quality of service (QoS) •Specified by parameters such as cell loss ratio and cell delay variation

Switched and semipermanent VCCs •A switched VCC is an on-demand connection which requires a call control signaling for setup and tearing down •A semipermanent VCC is one that is of long duration and is set up by configuration or network management action

Cell sequence integrity •The sequence of transmitted cells within a VCC is preserved

Traffic parameter negotiation and usage monitoring •Traffic parameters can be negotiated between a user and the network for each VCC •The network monitors the input of cells to ensure that the negotiated parameters are not violated

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25 ITU-T Recommendation I.150 lists the following characteristics of VPCs:

Quality of service (QoS)

Specified by parameters such as cell loss ratio and cell delay variation Characteristics Path Virtual Switched and semipermanent VPCs A switched VPC is an on-demand connection which A semipermanent VPC is one that is of long duration requires a call control signaling for setup and tearing and is set up by configuration or network management down action

Cell sequence integrity

The sequence of transmitted cells within a VPC is preserved

Traffic parameter negotiation and usage monitoring

Traffic parameters can be negotiated between a user The network monitors the input of cells to ensure that and the network for each VPC the negotiated parameters are not violated

Virtual channel identifier restriction within a VPC

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Control Signaling

VCCs VPCs

• Semipermanent VCCs may be used • Can be established on a for user-to-user exchange semipermanent basis by prior — No control signaling is required agreement • If there is no preestablished call — No control signaling is required control signaling channel, then one must be set up • VPC establishment/release may — Meta-signaling channel be customer controlled • The meta-signaling channel can be — The customer uses a signaling used to set up a VCC between the VCC to request the VPC from the user and the network for call control network signaling • VPC establishment/release may — User-to-network signaling virtual be network controlled channel — The network establishes a VPC for • The meta-signaling channel can also its own convenience be used to set up a user-to-user — The path may be network-to- signaling virtual channel network, user-to-network, or user- — Such a channel must be set up within a to-user preestablished VPC

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26 8 7 6 5 4 3 2 1 8 7 6 5 4 3 2 1 Virtual path identifier Generic flow control Virtual path identifier Virtual path identifier

Virtual channel identifier 5-octet Virtual channel identifier header Payload type CLP Payload type CLP

Header error control Header error control

53-octet cell Information field Information field (48 octets) (48 octets)

(a) User-Network Interface (b) Network-Network Interface

Figure 9.17 ATM Cell Format

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Table 9.2

Payload Type (PT) Field Coding PT Coding Interpretation 0 0 0 User data cell, congestion not experienced, SDU-type = 0 0 0 1 User data cell, congestion not experienced, SDU-type = 1 0 1 0 User data cell, congestion experienced, SDU-type = 0 0 1 1 User data cell, congestion experienced, SDU-type = 1 1 0 0 OAM segment associated cell 1 0 1 OAM end-to-end associated cell 1 1 0 Resource management cell 1 1 1 Reserved for future function

SDU = Service Data Unit OAM = Operations, Administration, and Maintenance

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27 Summary • Switched • Packet-switching communications principles networks —Switching technique • Circuit-switching —Packet size networks —External network • Circuit-switching interface concepts —Comparison of circuit switching and packet —Space division switching switching —Time-division switching • Asynchronous transfer • Softswitch architecture mode —ATM logical connections —ATM cells

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