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									Part 1: Common network/protocol functions
 Goals:                     Overview:
  identify, study           signaling: telephone net,
   common                     Internet, ATM net
   architectural             state mangement
   components, protocol       (signaling)
   mechanisms                randomization
  synthesis: big picture
                             indirection
  depth: important
                             multiplexing
   topics not covered in
                             virtualization
   an intro course
                             design for scale

                                                     Part 1   1-1
signaling: exchange of messages among network entities
       to enable (provide service) to connection/call

 before, during, after connection/call
    call setup and teardown (state)
    call maintenance (state)
    measurement, billing (state)
 between:
    end-user <-> network
    end-user <-> end-user
    network element <-> network element

                                                Part 1   1-2
 SS7 (Signaling System no. 7): telephone
 Q.2931: ATM
 RSVP (Resource Reservation Protocol), SIP
 (Session Initiation Protocol): Internet
     other Internet examples:
       • end-user <-> network
       • end-user <-> end-user
       • network element <-> network element

                                               Part 1   1-3
    Telephone Network
     created in 1876
     currently a global infrastructure
                            long haul
              central       Network              central
              office                             office
                                 voice “trunk”


subscriber access lines
    (twisted pair)        Toll switch
                                                           Part 1   1-4
Central Office and Local Loop
                  long haul
     central                    central
     office                     office


                Toll switch

 each phone user (subscriber) has   direct connection to
  switch in central office (local loop)
 local loop length 1 - 10 km
 central office switch: (local) exchange
 company providing local telephone service: local
  exchange carrier, LEC (e.g., Verizon)
                                                     Part 1   1-5
                                                  N/2 lines to CO
      central                           central
      office                            office

                                                        N users
                               N users, N lines to CO

 PBX (Private Branch Exchange)
    telephone system within enterprise: switches internal
     calls on local lines
    users share (multiplex) fixed # external lines to central
     office, saving per-user line cost to central office
                                                                  Part 1   1-6
Long-haul network
                   long haul
     central                    central
     office                     office


                toll switch

toll switches:
 long-distance connectivity over long distance
 ~500 toll switches in US
 toll switch runs 100,000+ phone calls
                                                    Part 1   1-7
How is voice transmitted ?
Two ways:
 analog voice transmission: voice channel
  allocated bandwidth of 3.5 kHz
 digital voice transmission: analog voice
  stream converted to digital stream
     standard scheme: 8000 8 bit samples

                                             Part 1   1-8
The digital phone network
Until 1960s:
      analog telephone network
      frequency-division multiplexing
      local loop analog (typically)
      rest of network digital (based on TDM)
When do we get all digital network?
      ISDN (Integrated services Digital Network): all digital
       circuit switching technology. available since the early-
       1990s (in Europe) or mid-1990s (US). No wide
       deployment in US
      ADSL – asymmetrical digital subscriber line
      IP telephony: digital, but not circuit-switched
                                                             Part 1   1-9
Analog local loop / digital network

 first telephone switch digitizes voice call (8000 8-bit
  samples per second)
      switching method is TDM.
 switch multiplexes calls, interleaving samples in time.
  call receives one 8-bit slot every 125 µs
                                                   Part 1   1-10
All digital network

 telephone   at subscriber digitizes voice,
 sends one 8-bit sample every 125 µs

                                               Part 1   1-11
Digital Multiplexing
 Digital Signaling (DS) transmission hierarchy
  used in US for multiplexing digital voice
                    Number of       Bandwidth
                   voice circuits
         DS0   1                    64 kbps
         DS1   24                   1.544 Mbps

         DS2   96                   6.312 Mbps

         DS3   672                  44.736
                                                 Part 1   1-12
Addressing and Routing
 each subscriber has address (telephone
   hierarchical addresses
   example: Antonio’s Pizza in downtown Amherst

         1      413      253        0808

      country   area   number of   subscriber
        code    code     local       number
 telephone address used for setting up
  route from caller to callee
                                                Part 1   1-13
Telephone network: services
 point-to-point POTS calls
 special telephone numbers:
    800 (888,877) number service: free call to customer
    900 number service: bill caller
    numbers for life
 caller ID
 calling card/third part charging
 call routing (to end user): prespecified, by time-of-day
 “follow me” service
 incoming/outgoing call restrictions
 support for cellular roaming: “home” number routed to
  current cell location

                                                   Part 1   1-14
 Telephone network: AIN
AIN: Advanced Intelligent (phone) Network: migration
from service-in-the-switch to service logic external to
(on top of) switching systems

 looks like Internet philosophy:
    e.g., DNS is at application layer; (RIP,OSPF, BGP
     above IP)
 AIN advantages:
    introduce new services rapidly
    open interfaces: vendor customization, vendor
     independence of services

                                                  Part 1   1-15
Telephone network: circuit-switched voice trunks
(data plane)

                                          Part 1   1-16
Telephone network: data and control planes

                                             Part 1   1-17
SS7: telephone signaling network

                   Note: redundancy in SS7 elements

                                                      Part 1   1-18
Signaling System 7: telephone network signaling

   out-of-band signaling: telephony signaling carried over
    separate network from telephone calls (data)
     allows for signaling between any switches (not just
      directly-connected )
    allows for signaling during call (not just before/after)
    allows for higher-than-voice-data-rate signaling
    security: in-band tone signaling helps phone phreaks; out
      of band signaling more secure
 SS7 network: packet-switched
    calls circuit-switched
 lots of redundancy (for reliability) in signaling network links,

                                                               Part 1   1-19
Signaling System 7: telephone network
  signaling   between telephone network elements:
                          signaling transfer point (STP):
                           packet-switches of SS7 network
                           send/receive/route signaling messages

signaling control point (SCP):
“services” go here
 e.g., database functions

 signaling switching
 point (SSP):
  attach directly to
 end user
  endpoints of SS7
 network                               Q: Internet analogies of
                                       SSP, SCP, STP?
                                                                  Part 1   1-20
Example: signaling a POTS call

                                            4. STP X forwards
                          3. STP W forwards    IAM SSP B
      2. SSP A formulates    IAM to STP X
         Initial Address
         Message (IAM),
         forwards to STP W            W
1. caller goes
    offhook, dials
    callee. SSP A                                  X
    decides to
    route call via
    SSP B. Assigns         A                                 B
  idle trunk A-B

                                                         Part 1   1-21
  Example: signaling a POTS call
                             5. B determines it serves callee, creates
                                address completion message
                                (ACM[A,B,trunk]), rings callee phone,
                                sends ringing sound on trunk to A

                         6. ACM routed to Z to Y to A

7. SSP A receives                           W              Z
   ACM, connects
   subscriber line to
   allocated A-B trunk
   (caller hears                            Y             X
                                A                                    B

                                                                 Part 1   1-22
  Example: signaling a POTS call
                                           8. Callee goes off hook, B
                                              creates, sends answer
                                              message to A
                          9. ANM routed to A

                                         W              Z

10. SSP A receives
   ANM, checks caller                     Y             X
   is connected in both
   directions to trunk.
                               A                                   B
  Call is connected!

                                                               Part 1   1-23
 Example: signaling a 800 ca11
  800 number: logical phone number
   translation to physical phone number needed, e.g.,
    1-800-CALL_ATT translates to 162-962-1943

               3. M performs lookup,
                  sends reply to A
       2. STP W forwards               W
          request to M

1. Caller dials 800
    number, A                          Y
    recognizes 800
    number, formulates
                              A                          B
    translation query,
    send to STP W

                                                     Part 1   1-24
  Example: signaling a 800 ca11
   800 number: logical phone number
    translation to physical phone number needed

                                   W          Z

1. A begins signaling to
   set up call to                             X
   number associated
   with 800 number
                           A                           B

                                                   Part 1   1-25
                              ISDN end-user
Example: SS7 protocol stack   signaling

TCAP: application
layer protocols:
800 service,
calling card, call
return, cellular

       to multiple
       upper layer

SS7-specific network, link,
physical layer protocols
 move to IP (RFC 2719)?
                                    Part 1   1-26
  Signaling: discussion
 800 logical-number-to-physical number translations: looks like DNS
 Differences?

 Where is state stored?

                                                              Part 1   1-27
Asynchronous Transfer Mode: ATM
 1990’s/00 standard for high-speed (155Mbps to
  622 Mbps and higher) Broadband Integrated
  Service Digital Network architecture
 Goal: integrated, end-end transport to carry voice,
  video, data
    meeting timing/QoS requirements of voice, video
     (versus Internet best-effort model)
    “next generation” telephony: technical roots in
     telephone world
    packet-switching (fixed length packets, called
     “cells”) using virtual circuits

                                                 Part 1   1-28
ATM networks

               Part 1   1-29
 ATM Layer: Virtual Channels
 VC transport: cells carried on VC from source to dest
    call setup, teardown for each call before data can flow
    each cell carries VC identifier (not destination ID)
    every switch on source-dest path maintain “state” for each
     passing connection
    link, switch resources (bandwidth, buffers) may be allocated to
     VC: to get circuit-like perf.
 Permanent VCs (PVCs)
    long lasting connections
    e.g., “permanent” route between two IP routers
 Switched VCs (SVC):
    dynamically set up on per-call basis

                                                           Part 1   1-30
ATM Signaling: Q.2931

                    (private network-
                   network interface)

                        ATM       ATM
                       network   network

                UNI          NNI           UNI
      (user-network       (network-        (user-network
          interface)       network         interface)

                                                           Part 1   1-31
ATM Signaling: Q.2931

 point to point and point-to-multipoint
 symmetric/asymmetric BW requirements
 QoS negotiation
 error recovery mechanism

                                           Part 1   1-32
  ATM Q.2931 Call Setup Signaling
                                      VCI=5; VPI=0 used
                 user           UNI   as signaling channel   UNI           user

call reference
traffic spec
                                                                              call reference
QoS                     setup
                         call                                                 traffic spec
call reference                                                     setup
                         proc                                                 QoS
VPI/VCI                                                            call       VPI/VCI

                        connect                                    conn
                                      user-user data

                                                                              Part 1   1-33
  ATM Q.2931 Call Release Signaling
                 user             UNI                    UNI         user


                                        user-user data
call reference

                         release                           release      call reference
call reference                                                          cause
cause                   complete

                                                                        Part 1   1-34
ATM UNI Connection control messages
SETUP: initiate call estab
CALL PROCEEDING: call estab begun
CONNECT: call accepted
CONNECT ACK: call accept ACK

RELEASE: initiate call clearing
RELEASE COMPLETE: call cleared

STATUS ENQUIRY: req. status
STATUS: requested status info

RESTART: restart all VC’s

ADD PARTY: add party to existing connection
DROP PARTY: drop party from existing connection
                                                  Part 1   1-35
ATM Q.2931 Call Setup: Timers
  timers used to recover from problems
     10 timers at user side, 10 timers at network side


start T303    setup
              call                                setup
                                     start T303
stop T303     proc
start T310
                                    stop T303      proc
                                    start T310    connect    start T313

             connect                stop T310
stop T310                                           ack      stop T313

                                                            Part 1   1-36
ATM Q.2931 Call Release Signaling
             user             UNI                         UNI         user


                                    user-user data

start T308          release

                     release                 start T308     release
stop T308           complete
                                            stop T308      complete

                                                                         Part 1   1-37
                          “ a specific link, one switching system plays
                          the role of the user side, and the other plays the
PNNI Signaling:           role of the network side, as defined in the UNI 3.1
                          Specification.” ATM Forum af-pnni-0026.000

     user                   PNNI                UNI            user

             call                                     setup
             proc             call
                              proc                    call
            connect                                   conn
                             conn                      ack
            conn              ack
                          user-user data
                                                                  Part 1   1-38
ATM Signaling: Discussion
 state?

 recovery?

                            Part 1   1-39
Components of cellular network architecture
                           connects cells to wide area net
                           manages call setup (more later!)
                           handles mobility (more later!)
 covers geographical
   base station (BS)               Mobile
analogous to 802.11                 Center
AP                                               Public telephone
                                                 network, and
 mobile users attach
to network through
BS                                 Mobile
   air-interface:                Switching
physical and link layer
protocol between
mobile and BS                                  wired network

                                                        Part 1   1-40
 Components of cellular network architecture

                                data                 Internet
                                                                SS7 signaling
             radio cell                                           (control)
   BSS                              Mobile
radio cell                          Center            MSC
   MS MS                                       VLR

     BTS           BSC                                             Operations
                                    Center                         Maintenance

   radio subsystem (RSS)            Network, Switching             Operation
                                    Subsystem (NSS)                    Part 1 1-41
                                                                subsystem (OSS)
Cellular networks: the first hop
Two techniques for sharing
  mobile-to-BS radio
 combined FDMA/TDMA:
  divide spectrum in                 time slots
  frequency channels, divide
  each channel into time
  slots                  frequency
 CDMA: code division

  multiple access

                                                  Part 1   1-42
GSM: TDMA, FDMA structure

                                            935-960 MHz
                                            124 channels (200 kHz) downlink

                            890-915 MHz
                            124 channels (200 kHz) uplink

     GSM TDMA frame

                                                  4.615 ms

                  user                       user
     guard tail   data       S Training S    data      tail guard
                  57 bits        26 bits     57 bits
                                                577 ms                        Part 1   1-43
Components of cellular network architecture

     recall:                               correspondent
                           wired public

                   MSC                          MSC


               different cellular networks,
               operated by different providers

                                                             Part 1   1-44
Handling mobility in cellular networks

   home network: network of cellular provider you
  subscribe to (e.g., Sprint PCS, Verizon)
    home location register (HLR): database in home
     network containing permanent cell phone #,
     profile information (services, preferences,
     billing), information about current location
     (could be in another network)
 visited network: network in which mobile currently
    visitor location register (VLR): database with
     entry for each user currently in network
    could be home network

                                                     Part 1   1-45
  GSM: calling to a mobile
                                        network                       correspondent
home MSC consults HLR,             Switching
gets roaming number of              Center
mobile in visited network
                                                               1               call routed
                                                                               to home network
                                                       3           Public
                                  VLR                              switched
                                                       home MSC sets up 2nd leg of call
                                                       to MSC in visited network
             user                                   MSC in visited network locates BSS
                                   visited          conntaining mobile via paging, completes
                                   network          call through base station to mobile
                                                                                      Part 1   1-46
  GSM: handoff with common MSC

                                          Handoff goal: route call via
                                           new base station (without
          VLR Mobile                      reasons for handoff:
               Switching                       stronger signal to/from new
                                                BSS (continuing connectivity,
                                                less battery drain)
          old           new
                                               load balance: free up channel
old BSS
                                                in current BSS
                               new BSS
                                               GSM doesn’t mandate why to
                                                perform handoff (policy), only
                                                how (mechanism)
                                          handoff initiated by old BSS

                                                                      Part 1   1-47
   GSM: handoff with common MSC
                                             1. old BSS informs MSC of impending
                                                handoff, provides list of 1+ new BSSs
                                             2. MSC sets up path (allocates resources)
                                                to new BSS
              VLR Mobile                     3. new BSS allocates radio channel for
                    Center 2                    use by mobile
                      4                      4. new BSS signals MSC, old BSS: ready
               8                             5. old BSS tells mobile: perform handoff to
old BSS   5                    6
                                                new BSS
                                   new BSS
                                             6. mobile, new BSS signal to activate new
                                             7. mobile signals via new BSS to MSC:
                                                handoff complete. MSC reroutes call
                                             8 MSC-old-BSS resources released

                                                                            Part 1   1-48
GSM: handoff between MSCs

                                          anchor MSC: first MSC
                                           visited during cal
home network
                       correspondent          call remains routed
 MSC                                           through anchor MSC
                                        new MSCs add on to end
anchor MSC
                    PSTN                 of MSC chain as mobile
                                         moves to new MSC

                                        IS-41 allows optional

                                         path minimization step
                                         to shorten multi-MSC
               (a) before handoff

                                                                Part 1   1-49
GSM: handoff between MSCs

                                          anchor MSC: first MSC
                                           visited during cal
home network
                       correspondent          call remains routed
 MSC                                           through anchor MSC
                                        new MSCs add on to end
anchor MSC
                    PSTN                 of MSC chain as mobile
                                         moves to new MSC

                                        IS-41 allows optional

                                         path minimization step
                                         to shorten multi-MSC
               (b) after handoff

                                                                Part 1   1-50
Signaling in the Internet
    connectionless                              no network
      (stateless)         best effort       signaling protocols
   forwarding by IP
                      +     service     =       in initial IP
        routers                                    design

 new requirement: reserve resources along end-to-end
  path (end system, routers) for QoS for multimedia
 RSVP: Resource Reservation Protocol [RFC 2205]
    “ … allow users to communicate requirements to
     network in robust and efficient way.” i.e., signaling !
 earlier Internet Signaling protocol: ST-II [RFC 1819]
 designed with multicast in mind
                                                              Part 1   1-51
(Brief) detour into Internet Multicast

 multicast group concept:
   hosts send IP datagram pkts to multicast group
   hosts that have “joined” that multicast group will
    receive pkts sent to that group

 group addressing: class D IP addresses

            1110 Multicast Group ID
                            28 bits
                                                         Part 1   1-52
Joining a mcast group: 2-step process
    local: host informs local mcast router of desire to
   join group: IGMP (more later)
  wide area: local router interacts with other
   routers to receive mcast packet flow
     many protocols (e.g., DVMRP, MOSPF, PIM)

                                                     Part 1   1-53
Multicast Routing: Problem Statement
 Goal: find a tree (or trees) connecting
  routers having local mcast group members
     tree: not all paths between routers used
     source-based: different tree from each sender to rcvrs
     shared-tree: same tree used by all group members

         Shared tree           Source-based trees
Example Mcast routing algorithm
 mcast forwarding tree: tree of shortest
 path routes from source to all receivers
     Dijkstra’s algorithm via link-state broadcast
  S: source                               LEGEND
              R1        2
               1            R4                 router with attached
                                               group member
        R2                       5
                                               router with no attached
         3         4
                                     R5        group member
   R3                        6             i   link used for forwarding,
                   R6       R7                 i indicates order link
                                               added by algorithm

 many other algorithms/protocols
RSVP Design Goals
1.   accommodate heterogeneous receivers (different
     bandwidths along paths)
2.   accommodate different applications with different
     resource requirements
3.   make multicast a first class service, with adaptation
     to multicast group membership
4.   leverage existing multicast/unicast routing, with
     adaptation to changes in underlying unicast,
     multicast routes
5.   control protocol overhead to grow (at worst) linear
     in # receivers

                                                   Part 1   1-56
RSVP: does not…
 specify how resources are to be reserved
     rather: a mechanism for communicating needs
 determine routes packets will take
     that’s the job of routing protocols
     signaling decoupled from routing
 interact with forwarding of packets
     separation of control (signaling) and data
      (forwarding) planes

                                                   Part 1   1-57
RSVP: overview of operation
 senders, receivers join a multicast group
    done outside of RSVP (IGMP, multicast routing)

 sender-to-network signaling
    path message: make sender presence known to routers
    path teardown: delete sender’s path state from routers

 receiver-to-network signaling
    reservation message: reserve resources from sender(s) to
    reservation teardown: remove receiver reservations

 network-to-end-system signaling
    path error
    reservation error

                                                         Part 1   1-58
Path msgs:      RSVP sender-to-network signaling

  path message contents:
     address: unicast destination, or multicast group
     flowspec: bandwidth requirements spec.
     filter flag: if yes, record identities of upstream
      senders (to allow packet filtering by source)
     previous hop: upstream router/host ID
     refresh time: time until this info times out
  path message: communicates sender info, and roting
   info about reverse-path-to-sender
     later upstream forwarding of receiver reservations

                                                    Part 1   1-59
RSVP: simple audio conference
 H1, H2, H3, H4, H5 both senders and receivers
 multicast group m1
 no filtering: packets from any sender forwarded
 audio rate:   b
 only one multicast routing tree possible

H2                                           H3

                R1         R2       R3        H4


                                               Part 1   1-60
RSVP: building up path state
 H1, …, H5 all send path messages on m1:
  (address=m1, Tspec=b, filter-spec=no-filter,refresh=100)
 suppose H1 sends first path message

                                                          in        L7
            in L1                                   m1:
            out   L2 L6                                   out L3 L4
                            m1: in     L6
                                out L5    L7

 H2                                                                      H3
             L2                                                  L3

                       R1   L6                 L7
                                      R2                  R3    L4       H4
                  L1                  L5


                                                                              Part 1   1-61
RSVP: building up path state
 next, H5 sends path message, creating more state
  in routers

                                                       in        L7
     m1: in
             L1    L6                            m1:
         out L1 L2 L6                                  out L3 L4
                                 L5 L6
                         m1: in
                             out L5 L6 L7

H2                                                                    H3
          L2                                                  L3

                    R1   L6                 L7
                                   R2                  R3    L4       H4
               L1                  L5


                                                                           Part 1   1-62
RSVP: building up path state
 H2, H3, H4 send path msgs, completing path state

                                                       in L3 L4 L7
     m1: in
             L1 L2 L6                            m1:
         out L1 L2 L6                                  out L3 L4 L7
                                 L5 L6 L7
                         m1: in
                             out L5 L6 L7

H2                                                                    H3
          L2                                                  L3

                    R1   L6                 L7
                                   R2                  R3    L4       H4
               L1                  L5


                                                                           Part 1   1-63
reservation msgs:             receiver-to-network signaling

  reservation message contents:
     desired bandwidth:
     filter type:
        • no filter: any packets addressed to multicast group can
          use reservation
        • fixed filter: only packets from specific set of senders can
          use reservation
        • dynamic filter: senders who’s packets can be forwarded
          across link will change (by receiver choice) over time.
       filter spec
  reservations flow upstream from receiver-to-senders,
   reserving resources, creating additional, receiver-
   related state at routers
                                                            Part 1   1-64
RSVP: receiver reservation example 1
H1 wants to receive audio from all other senders
 H1 reservation msg flows uptree to sources
 H1 only reserves enough bandwidth for 1 audio stream
 reservation is of type “no filter” – any sender can use
  reserved bandwidth

H2                                                  H3
          L2                                   L3

                    R1   L6         L7
                               R2        R3   L4    H4
               L1              L5


                                                         Part 1   1-65
RSVP: receiver reservation example 1
 H1 reservation msgs flows uptree to sources
 routers, hosts reserve bandwidth b needed on downstream links
  towards H1

                          L6                                     in L3        L4   L7
  m1: in L1 L2                                             m1:
      out L1(b) L2        L6                                     out L3       L4   L7(b)

                               m1: in L5        L6    L7
                                   out L5       L6(b) L7

 H2                                                                                  H3
                b                                                         b
           L2                                                               L3
                                   b                  b
                                  L6                  L7                   b
                    b     R1                    R2               R3       L4
                     L1                     b                                         H4


                                                                                           Part 1   1-66
RSVP: receiver reservation example 1 (more)

 next, H2 makes no-filter reservation for bandwidth                            b
 H2 forwards to R1, R1 forwards to H1 and R2
 R2 takes no action, since         b already reserved on L6

                      L6                                      in L3        L4   L7
  m1: in L1 L2                                          m1:
      out L1(b) L2(b) L6                                      out L3       L4   L7(b)

                            m1: in L5        L6    L7
                                out L5       L6(b) L7

 H2        b                                                                        H3
                b                                                      b
           L2                                                            L3
                                b                  b
                               L6                  L7                   b
                 b     R1                    R2               R3       L4
                                         b                                          H4
                b L1                         L5


                                                                                         Part 1   1-67
RSVP: example 2
 H1, H4 are only senders
   send path messages as before, indicating filtered reservation
   routers store upstream senders for each upstream link

 H2 will want to receive from H4 (only)

 H2                                                   H3
           L2                                  L3

                     R1   L6        L7
                               R2        R3   L4       H4

                                                           Part 1   1-68
     RSVP: example 2
      H1, H4 are only senders
           send path messages as before, indicating filtered
in  L1, L6                                         in   L4, L7
    L2(H1-via-H1     ; H4-via-R2   )                L3(H4-via-H4       ; H1-via-R3   )
out L6(H1-via-H1     )                          out L4(H1-via-R2       )
    L1(H4-via-R2     )                              L7(H4-via-H4       )

      H2                                                                         H3
                L2                            R2                         L3

                            R1         L6                L7
                                                                  R3   L4            H4
           H1                           in   L6, L7
                                            L6(H4-via-R3      )
                                        out L7(H1-via-R1      )
                                                                                         Part 1   1-69
     RSVP: example 2
      receiver H2 sends                reservation message for source H4
       at bandwidth b
           propagated upstream towards H4, reserving b
in  L1, L6                                          in   L4, L7
    L2(H1-via-H1      ;H4-via-R2 (b))                L3(H4-via-H4 ; H1-via-R2   )
out L6(H1-via-H1       )                         out L4(H1-via-62 )
    L1(H4-via-R2       )                             L7(H4-via-H4 (b))

      H2                                                                     H3
                 L2                      b
                                               R2         b             L3
                                                          L7             b
                               R1       L6
                                                                  R3   L4       H4
            H1                           in   L6, L7
                                             L6(H4-via-R3 (b))
                                         out L7(H1-via-R1 )
                                                                                    Part 1   1-70
RSVP: soft-state
 senders periodically resend path msgs to refresh (maintain) state
 receivers periodically resend resv msgs to refresh (maintain) state
 path and resv msgs have TTL field, specifying refresh interval

   in L1, L6                                         in   L4, L7
      L2(H1-via-H1     ;H4-via-R2 (b))                L3(H4-via-H4 ; H1-via-R3     )
  out L6(H1-via-H1      )                         out L4(H1-via-62 )
      L1(H4-via-R2      )                             L7(H4-via-H4 (b))

        H2                                                                      H3
                  L2                      b
                                                R2         b             L3
                                                           L7             b
                                R1       L6
                                                                   R3   L4       H4
             H1                           in   L6, L7
                                              L6(H4-via-R3 (b))
                                          out L7(H1-via-R1 )
                                                                              Part 1   1-71
     RSVP: soft-state
  suppose H4 (sender) leaves without performing teardown
  eventually state in routers will timeout and disappear!

in  L1, L6                                         in   L4, L7
    L2(H1-via-H1     ;H4-via-R2 (b))                L3(H4-via-H4 ; H1-via-R3      )
out L6(H1-via-H1      )                         out L4(H1-via-62 )
    L1(H4-via-R2      )                             L7(H4-via-H4 (b))

      H2                                                                        H3
                L2                      b
                                              R2         b             L3
                              R1       L6                L7
                                                                 R3   L4      gone
                         L1                                                 fishing!
           H1                           in   L6, L7
                                            L6(H4-via-R3 (b))
                                        out L7(H1-via-R1 )
                                                                                      Part 1   1-72
The many uses of reservation/path refresh

 recover from an earlier lost refresh message
    expected time until refresh received must be longer than
     timeout interval! (short timer interval desired)
 handle receiver/sender that goes away without
      sender/receiver state will timeout and disappear
 reservation refreshes will cause new reservations
  to be made from receiver to sender that has
  joined since receivers last reservation refresh
      e.g., in previous example, H1 only receiver, H3 only
       sender. Path/reservation messages complete, data flows
      H4 joins as sender, nothing happens until H3 refreshes
       reservation, causing R3 to forward reservation to H4,
       which allocates bandwidth
                                                          Part 1   1-73
RSVP: reflections
 multicast as a “first class” service
 receiver-oriented reservations
 use of soft-state

                                         Part 1   1-74
Signaling Discussion: SS7 vs Q.2931 vs

 similarities

 differences

                                         Part 1   1-75
SIP: Session Initiation Protocol
[RFC 3261]

SIP long-term vision:

 all telephone calls, video conference calls
  take place over Internet
 people are identified by names or e-mail
  addresses, rather than by phone numbers
 you can reach callee, no matter where
  callee roams, no matter what IP device
  callee is currently using
                                            Part 1   1-76
 SIP Services
 Setting up a call,
                          determine current IP
  SIP provides             address of callee:
  mechanisms ..                maps mnemonic
   for caller to let           identifier to current IP
    callee know she
                          call management:
    wants to establish       add new media streams
    a call                    during call
                             change encoding during
   so caller, callee
    can agree on             invite others
    media type,              transfer, hold calls
   to end call                                     Part 1   1-77
        Setting up a call to known IP
        address                 Alice’s SIP invite                                           
                                                                                             message indicates her

                                                                                             port number, IP address,                                    
                                                                                             encoding she prefers to
                     INVITE bob
                     c=IN IP4 16
                                                                                             receive (PCM ulaw)
                     m=audio 38              4
                                060 RTP/A
                                           VP 0
                                                               port 5060    Bob's             Bob’s 200 OK message
                                                                                             indicates his port number,
                                                                            terminal rings
                                         200 OK
                                                                                             IP address, preferred
                                         c=IN IP4 193.64
                                         m=audio 48 753 RTP/AVP 3
                 port 5060
                                                                                             encoding (GSM)
                                                               port 5060

                                                                                              SIP messages can be
                                              m Law audio
                port 38060                                                                   sent over TCP or UDP;
                                                                                             here sent over RTP/UDP.
                                                                                             default   SIP port number
                                                             port 48753

                                                                                             is 5060.
              time                                                       time
                                                                                                             Part 1   1-78
Setting up a call (more)
 codec negotiation:
                          rejecting a call
   suppose   Bob
                           Bob can reject
    doesn’t have PCM
                            with replies
    ulaw encoder.
                            “busy,” “gone,”
   Bob will instead        “payment
    reply with 606          required,”
    Not Acceptable          “forbidden”
    Reply, listing his
                        media can be sent
    encoders Alice can
                         over RTP or some
    then send new
                         other protocol
    INVITE message,
    different encoder                     Part 1   1-79
Example of SIP message
Via: SIP/2.0/UDP         Here we don’t know
From:            Bob’s IP address.
                                       Intermediate SIP
                                       servers needed.
Content-Type: application/sdp          Alice sends, receives
Content-Length: 885                    SIP messages using
                                       SIP default port 5060

c=IN IP4                 Alice specifies in
m=audio 38060 RTP/AVP 0                Via:
Notes:                                 header that SIP client
                                       sends, receives SIP
 HTTP message syntax
                                       messages over UDP
 sdp = session description protocol
 Call-ID is unique for every call.
                                                    Part 1   1-80
Name translation and user
                            result can be based on:
 caller wants to call         time of day (work, home)
  callee, but only has         caller (don’t want boss to

  callee’s name or e-           call you at home)
                               status of callee (calls sent
  mail address.                 to voicemail when callee is
 need to get IP                already talking to
  address of callee’s
                           Service provided by SIP
  current host:              servers:
   user moves around
                            SIP registrar server
   DHCP protocol
                            SIP proxy server
   user has different
    IP devices (PC, PDA,
    car device)                                      Part 1   1-81
SIP Registrar
 when Bob starts SIP client, client sends SIP
  REGISTER message to Bob’s registrar server
  (similar function needed by Instant
Register Message:

Via: SIP/2.0/UDP
Expires: 3600

                                          Part 1   1-82
SIP Proxy
 Alice sends invite message to her proxy server
    contains address

 proxy responsible for routing SIP messages to
      possibly through multiple proxies.
 callee sends response back through the same set
  of proxies.
 proxy returns SIP response message to Alice
      contains Bob’s IP address
 proxy analogous to local DNS server

                                                   Part 1   1-83
Caller                                SIP registrar

with places a

call to                                             SIP
                                            2                       registrar
(1) Jim sends INVITE
                              SIP proxy
message to umass SIP
proxy. (2) Proxy forwards         1                       7                5
request to upenn                      8
registrar server.

(3) upenn server returns                                      9

redirect response,          SIP client
                                                                       SIP client
indicating that it should

(4) umass proxy sends INVITE to eurecom registrar. (5) eurecom
registrar forwards INVITE to, which is running keith’s SIP
client. (6-8) SIP response sent back (9) media sent directly
between clients.
Note: also a SIP ack message, which is not shown.
                                                                     Part 1      1-84
Comparison with H.323
 H.323 is another signaling     H.323 comes from the
  protocol for real-time,         ITU (telephony).
 H.323 is a complete,
                                 SIP comes from IETF:
  vertically integrated suite     Borrows much of its
  of protocols for multimedia     concepts from HTTP
  conferencing: signaling,
                                    SIP has Web
  registration, admission
  control, transport, codecs         flavor, whereas
 SIP is a single component.
                                     H.323 has
  Works with RTP, but does           telephony flavor.
  not mandate it. Can be         SIP uses the KISS
  combined with other
                                  principle: Keep it
  protocols, services
                                  simple stupid.
                                                   Part 1   1-85

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